NL2037251B1

NL2037251B1 - Crank for a vehicle, and method of manufacturing a crank.

Info

Publication number: NL2037251B1
Application number: NL2037251A
Authority: NL
Inventors: Joan Clement Tomas; Stöpler Bob
Original assignee: Stoepler Speedworks B V
Priority date: 2024-03-14
Filing date: 2024-03-14
Publication date: 2025-09-26
Also published as: WO2025193094A1

Abstract

A crank for a vehicle is described comprising a ﬁrst connection part (2;61;81;91) arranged to connect the crank to a vehicle component. The crank further comprises an elongated body (8) fixed to the first connection part, and comprising a first rod (9) and a second rod (10). The rods are positioned and oriented in such a way that they can be used to sense strain which can be input to a torque measurement system (190). The system is arranged to calculate torque on the crank which can be used to determine the power, a user applies to the crank. [Figure 14]

Description

Crank for a vehicle, and method of manufacturing a crank.

Field of the invention

The present invention relates to a crank for a vehicle, and to a method of manufacturing a crank for a vehicle.

Background art

In order to measure cycling performance of a cyclist, modern bicycles come with an integrated power meter. Power measurement is the most accurate way to measure the effort of a cyclist. A power meter is an electronic device that is built into the bicycle’s drivetrain and measures the power, or more specifically the torque, generated by the cyclist. Power meters are usually built into cranks, crank arms or pedals. Measured power values may be wirelessly transmitted to a remote computer on the handlebar for real-time monitoring, or to a remote computer for data analysis after a training session or sports event.

When cycling, a rider forces the pedals down creating both a torque and a torsion on the crank arm. The torsion is depending not just on the applied force by the rider but also the offset this force has from the crank arm axis. This makes it such that when trying to measure applied torque around the bracket axis by measuring strain in the material of the crank arm, it is rather difficult to determine what is the exact cause of the strain. As a result, it is not possible to accurately translate measured strain to applied force or torque. If the offset on the pedal changes, with the same applied torque, the strain will also change. Modern power meters combat this by using three or more strain gauges each measuring strain just in one axis, wherein the strain gauges are oriented in different directions to be able to determine the direction of the strain and thus account and compensate for the torsional component around the length axis of the crank arm, and bending moment components in the direction of the rotation axis.

However, compensating for strain originating from non-relevant input force components has disadvantages. Mainly the stack up of measurement errors from three or more strain gauges compromises the torque measuring accuracy. The torsional strain component is larger than the longitudinal strain in the arm that results from the actually applied torque that is of interest.

For this reason, some power meters currently measure power in the drive side crank’s spider. Here the bracket axle and drive side crank come together, and the bracket axle cancels out the strain caused by the non-relevant input force components originating from the pedal force offset and direction.

This method has two main disadvantages though. The chain line from the front (drive side) chainring changes based on the gear chosen on the rear wheel cassette, size of the front chainring and the load case changes continuously over a rotation of the crank set. This requires measurements on multiple locations in the spider and thus again getting tolerance stack up issues.

Summary of the invention

The aim of the present invention is to provide a crank for a vehicle that enables more precise power measurement as compared to the known techniques.

According to a first aspect of the present invention, there is provided a crank for a vehicle, the vehicle comprising a frame and a vehicle component rotationally mounted to the frame around a rotation axis. The crank comprises a first connection part arranged to connect the crank to the vehicle component, and an elongated body fixed to the first connection part, and comprising a first rod and a second rod, each of which extending in a direction that, at least in use, has no component parallel to the rotation axis, wherein the first rod and the second rod are arranged on opposing sides of a first virtual plane, wherein the first virtual plane incorporates a central axis of the elongated body and is orientated parallel to the rotation axis.

The crank also comprises a torque measurement system comprising a first strain sensor arranged to measure strain in the first rod, and a second strain sensor arranged to measure strain in the second rod.

Due to the fact that the first and second rod are only stiff in the longitudinal direction of the rods, they are not stiff to other then compressive or tensile loads The two rods only receive forces in the direction of the longitudinal direction of the rods.

In an embodiment, the elongated body comprises multiple enforcement members arranged in the same region of the elongated body. It is noted that the forces on the crank are distributed over the different members and the two rods which forces are proportional to the relative stiffness of the members/rods and depending on the direction of those forces/loads. So, if the enforcement members of the elongated body are stiff in these other directions, these forces are guided relative to the stiffness in resisting the applied loads. The rods only offer resistance to forces in the relevant directions and are not resisting the torsional component and thus not receiving such forces.

As a consequence, the two strain sensors only measure strain in those locations on the crank where the loading doesn’t change as a function of the crank’s rotation, and where the torsional component of the strain is insignificant relative to the applied torque resulting strain along the longitudinal axis of a crank. Thus purely measuring the desired strain that scales proportional to the applied input torque. Normally even when using common mode rejection on a crank that is mirror symmetric around the center of the crank with the gauges perfectly placed on opposing sides of the crank the torsion causes a very complex strain distribution causing the gauge location to be crucial to the result of the measurement. Also important is the fact that under torsion you do not get a perfectly mirrored strain pattern. By simplifying the situation by distributing the forces over several isolated members they get a more pure tensile or compressive loading situation causing more linear material behavior. Using signals from the two strain sensors, the torque measurement system can provide for accurate torque measurements.

In an embodiment, the first rod and the second rod cross a common cross section of the elongated body, the cross section being perpendicular to the central axis of the elongated body.

By arranging the rods in the same zone/section of the elongated body, sensors arranged on the rods will generate useful data for the torque measurement system.

In an embodiment, the elongated body comprises at least one enforcement member extending in a direction that has a vector component parallel to the rotation axis, the enforcement also crossing the common cross section. The enforcement member(s) provide for a construction that is stiff in resisting non-relevant torsional forces, whereas the two rods are stiff in the longitudinal direction of the elongated body and mainly receive strain in that direction relevant for the torque calculations.

In an embodiment, the enforcement member comprises two intersecting rectangular shaped elements. This results in a simple construction. Preferably, the enforcement member is mirror symmetric to a central plane of the body and not resisting a moment perpendicular to a central (longitudinal) axis of the body. Due to this symmetry the central moment bending axis is centred between the first and the second rod.

In an embodiment, a longitudinal axis of the first rod and a longitudinal axis the second rod lie in second virtual plane that incorporates the central axis of the elongated body and is orientated perpendicular to the rotation axis. By cleverly orienting and shaping the two rods with their center longitudinal axis in a plane perpendicular to the torque transmission plane (i.e. second virtual plane), and making sure there are no other members in that plane and in the same direction, causes the rods to have strain directly proportional to some applied torque.

In an embodiment, the two rods are opposing each other (relative to the first virtual plane) and are located in the second virtual plane, wherein no other members are oriented in the first plane. This guarantees that the two opposing rods receive strain that is scaled proportional to the torque in that plane around the torque/rotational axis.

In an embodiment, the first and second rod are arranged at a circumference of the crank.

By arranging the rods near or at the circumference of the crank, the distance between the rods is maximized. The has the advantage that the deformation in the two load sensing rods is as large as possible. This improves the measurement accuracy.

In an embodiment, the first rod and the second rod each have a straight centre line.

Having straight centre lines, and preferably a constant cross section over their length, the rods provide sensing location where strain gauges can be mounted. Furthermore, the strain on the rod is as homogenous as can be. For example: a cross section with halve the sectional area of another has double the strain. The larger the strain the easier it is to get a high resolution and low noise signal out of the measuring system connected to the gauges.

In an embodiment, the first rod and the second rod are arranged in parallel. This configuration is most simple and gave good results. The rods can be angled relative to each other, but in that case they both need to mirrored relative to the centre line of the crank.

In an embodiment, the first and second rod are arranged to resist any torsional load around a longitudinal axis of the elongated body with less than 5% of the combined torsional resistance of all elements in the common cross section.

Such a low contribution by the first and second rods to the overall torsional stiffness at the cross common section, is preferred to make the sensors less sensitive to torsional loads. This contribution can be determined by applying a purely torsional load on the crank around its longitudinal axis and in the cross-section plane measure for each member the force component in the plane and its resulting moment around the central axis. The sum of all moments of all members combined is preferably much bigger that the moment of just the first and second rod. In this application the less significant the contribution of the rods is, the better.

It should not be longer or stronger then strictly necessarily. It being too long is disadvantageous if this puts the element at risk of failing due to buckling. It should not be so short that it would be hard to mount the strain sensor.

In an embodiment, the elongated body comprises an organically shaped structure. The organically shaped structure could be the result of a design process using a generative design program that optimizes a structure given one or more criteria and/or restrictions. For example, the program can be asked to use as little material as possible given a required strength (measured as deformation in each given load case) and stiffness of the crank. The inventors have found that using such a generative design program can produce a strong crank that is also relatively light weight.

In an embodiment, the crank is a bike handle or part of a bike handle, also referred to as clip-on. In this case, the first connection part may be arranged to connect the clip-on to a front fork of a motor bike. At present, there are no clip-ons available that are equipped with torque measurement systems. But by adding such a system to a clip-on, useful measurements can be made. For example, this adding helps bikers to improve their performance and skills and can be used to assess chassis geometry performance.

In another embodiment, the crank comprises a second connection part arranged to connect to a pedal. The pedal may be a pedal of a bicycle, also referred to as a push bike. The second part may comprise an opening, that is used to couple a pedal. The opening may be a cylindrical opening having an axis which, at least in use, runs parallel to the rotation axis.

Alternatively, the second part may comprise an extension for connecting a pedal to.

In an embodiment, the crank comprises a number of connection members for connecting a chainring. The number of connection members may be three. Using only three connection members for connecting the chainring provides for a light weight yet strong structure of the whole crank set.

In an embodiment, each of the connection members is coupled to the rest of the crank by means of at least two rods. By using more than one rod for connecting of the chainring, the rods can be designed in an optimized unconventional manner. For example, some of the rods may be connected to the elongated body instead of to the first connection part which is normally the place to connect a spider of a crank set to.

According to a further aspect, there is provided a method of manufacturing a crank for a vehicle, the vehicle comprising a frame and a vehicle component rotationally mounted to the frame around a rotation axis. The method comprises:

- providing of a model of the crank wherein the model comprises a first connection part designed to connect the crank to the vehicle component, and an elongated body fixed to the first connection part, and comprising a first rod and a second rod, each of which extending in a direction that, at least in use, has no component parallel to the rotation axis, wherein the first rod 5 and the second rod are designed on opposing sides of a first virtual plane, wherein the first virtual plane incorporates a central axis of the elongated body and is orientated parallel to the rotation axis; - manufacturing of the crank using the designed model and a manufacturing technique, and - adding a first strain sensor to the first rod, and a second strain sensor to the second rod.

In an embodiment, the providing of a model comprises: - virtually positioning the first part in a design space using a computer aided design software program; - virtually adding the elongated body part to the first part.

In an embodiment, the providing of a model further comprises: - virtually positioning design limitation elements relative to the first connection part, the position and shape of the design limitation elements being defined by a crank design; - virtually positioning the first and the second rod; - virtually placing a blocking element around each of the first and second rod; - creating an organically shaped structure coupled to the first part, using a generative software program, wherein the organically shaped structure comprises the first rod and the second rod.

An advantage of creating an organically shaped structure produced by suitable software is that such a structure will with minimal amount of material given a required strength and stiffness.

In an embodiment, the manufacturing technique comprises an additive manufacturing technique, such as Selective Laser Melting (SLM) or Selective Laser Sintering (SLS). The crank may alternatively or additionally be manufactured with a CNC machine using subtractive manufacturing techniques.

According to a further aspect of the invention, the invention relates to a crank for a vehicle, wherein the crank comprises: - a first connection part with a first opening for connection to a drive axle, the first opening having a first axis; - a second connection part for connection to a pedal; - a socket fixed to the second connection part, wherein the socket has an ellipse shaped or wing-shaped cross section with its major axis directed under an attack angle (a) with a plane that runs perpendicular to the first axis, wherein the socket comprises two opposing elongated openings.

In this case, the vehicle may be a bicycle driven by a user by way of pushing the pedals down. In an embodiment, the crank comprises an organically shaped rod structure coupling the first connection part to the socket. The socket can be optimized for aerodynamics while the organic-shaped rod structure can be optimized for strength and minimizing weight.

Optionally, the cross section of the socket increases with distance to the second connection part. This will provide for an improved design of the crank.

In an embodiment, the organically shaped rod structure is arranged to reinforce at least part of the socket. In this way, the wall of the socket can be made very thin.

In an embodiment, the attack angle lies in a range of 0-20 degrees, more preferably in a range of 7-15 degrees. Using these angles resulted in low air flow resistance during software simulations, which are expected to approach the real-world performance of the crank.

Brief description of the drawings

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter. In the drawings,

Figure 1 is a perspective view of a crank according to an embodiment of the invention;

Figure 2 is a bottom view of the of Figure 1;

Figure 3 shows a cutaway side of the crank at the plane III-I shown in Figure 2 and looking in the direction of the arrows shown in Figure 2;

Figure 4 shows a top view of part of a motor bike comprising an upper triple clamp and two cranks according to an embodiment;

Figure 5 shows a side view of the construction of Figure 4 with an upper triple clamp, a part of the front forks, and one crank;

Figure 6 schematically shows a side view of a crank for a bike according to a further embodiment of the invention;

Figure 7 shows a cross section of the part of the elongated body where the two rods are located;

Figure 8 schematically shows a top view of the crank of Figure 6;

Figure 9 is a perspective view of a crank according to an embodiment;

Figure 10 is a perspective view of a crank according to another embodiment;

Figure 11 is a side view of the crank of Figure 10;

Figure 12 is a perspective view of an assembly of two cranks showing their relative location when mounted to a bike;

Figure 13 is a top view of the assembly of Figure 12;

Figure 14 shows a side view of crank wherein two edges of the air foil are indicated;

Figure 15 is a bottom view of the crank of Figure 14 showing one of the openings 110 for passage of air flow;

Figure 16 shows a cutaway side view at the cross section XVI in Figure 14;

Figure 17 shows the view of Figure 16 together with a location of the rider’s leg when the crank is down in the pedal stroke;

Figure 18 shows the view of Figure 16 together with a location of the rider’s leg when the crank is up in the pedal stroke;

Figure 19 schematically shows a torque measurement system according to an embodiment of the invention;

Figure 20 is a flow chart of a method of manufacturing a crank for a vehicle according to an embodiment of the invention;

Figure 21 shows an example crank model in a design space of a computer aided design software program;

Figure 22 shows a side view of the model of Figure 21;

Figure 23A shows a side view of a disk shape region together with a block shaped region;

Figure 23B shows a front view of the disk shaped region;

Figure 23C shows a cross section at the plane indicated by the arrows A-A in Figure 23B;

Figure 23D is an exploded view of the right design of the crank accompanied by several exclusion regions.

It should be noted that items which have the same reference numbers in different Figures, have the same structural features and the same functions, or are the same signals. Where the function and/or structure of such an item has been explained, there is no necessity for repeated explanation thereof in the detailed description.

Detailed description of embodiments

Figure 1 is a perspective view of a crank 1 according to an embodiment of the invention.

In this embodiment, the crank 1 is part of a handle of a motor bike (not shown). The crank 1 is also referred to as clip-on handlebar 1, or simply as clip-on 1. The inventors have realized that torque measurement in motor bike handles can be as useful as torque measurement in crank of bicycles. The latter will be discussed below as well. By measuring torque applied to the clip-on 1 by the rider, the rider can get useful training data which can be used to improve steering techniques and analyse chassis/geometric performance.

The crank 1 comprises a connection part 2 and an elongated body. The connection part 2 is a cylindrical shaped clamp arranged to connect with a front fork of the bike. In this example, the elongated body comprises a tube 3, a socket 4 and an enforcement structure 5. The enforcement structure 5 is made out of two intersecting plates, and an end plate 6 connecting the intersecting plates to the socket 4. The enforcement structure 5 also comprises a first rod 8 and a second rod 8, see also Figure 2. Figure 2 is a bottom view of the of Figure 1.

In Figure 1 and 2 a centre line 10 is shown which follows the centre of the crank 1. The centre line 10 is a straight line when seen from the bottom or top but may have a curve or turn when seen from the side. In Figure 2 two arrows F indicate possible forces, wherein e.g. in case of a force directed in the downward direction, the crank 1 experiences compression in the bottom part and tension in the top part. The points along the crank 1 where the bending moment is zero is called the (force) neutral axis. So, in this case, the centre line 10 can be regarded as the (force)

neutral line. The two load sensing elements if made appropriately thin relative to its length component cannot receive (because it cannot resist for it is not stiff) a bending moment (these forces are already guided through other members that are stiff in the same cross section perpendicular to the elongated body. The situation below is not wat we want in these two elements. We want an even distribution of tension stresses in the beam and these need to scale proportionally to the torque applied at the force receiving end of the crank. It is when drawing this neutral axis important that this is looking at the crank as a whole centred between the two-load sensing rods.

Figure 3 shows a cutaway side view of the crank 1 at the plane lll-lll shown in Figure 2 and looking in the direction of the arrows shown in Figure 2. A mirror plane 20 is shown which coincides with the centre line 10 and extends perpendicular to the plane of view (i.e. paper plane).

In this example, the enforcement structure 5 is symmetrical relative to the mirror plane 20. The mirror plane 20 is also referred to as the first virtual plane. Figure 3 also shows two load sensing elements 21,22. The load sensing elements 21,22 are also referred to as the strain sensors 21,22. The strain sensors 21,22 are arranged on opposite sides of the virtual plane 20. In this embodiment, the strain sensors 21,22 are mirrored relative to each other.

The virtual plane 20 is the plane around which a bending moment is measured which bending moment is proportional to the applied torque around the steering axis (see 54 in Figure 5) of the bike.

Figure 4 shows a top view of part of a motor bike comprising an upper triple clamp 41 and two cranks according to an embodiment, one of which is shown in the figure. The crank 1 is mounted to the upper triple clamp 41 in such a manner that an offset 42 between the centre line 10 and the rotation axis 54 of the steering bar 51. In this example, the offset 42 has a typical value of 61.6 mm.

Figure 5 shows a side view of the construction of Figure 4 with the upper triple clamp 41, a part of the steering bar 51, a part of the front forks 52, 53 and one crank 1. In this example, the tube 3 of the crank 1 makes an angle of 84.68 degrees in this example, while the centre line 10 of the enforcement structure 5 makes an angle of 90 degrees. As a result, the first and second rods 8, 9 having the strain sensors on them, also make a right angle with the axis 54. Since in this example, the strain sensors are exactly centred, they do not receive strain from a bending moment that is not around the steering axis of the front fork. By knowing the offset from the steering axis, it is possible to use the difference in strain between the two gauges to compensate for this offset. Without this offset just the common mode rejected signals of both gauges combined (together being a single measurement) are sufficient. When having the common mode rejected signal and the signal of one of the two strain gauge elements measured separately, we can even determine the applied torque/moment around a rotational axis which is offset from the centre/mirror line 10. This provides for an optimal accuracy of the common mode rejection measurements wherein signals of both strain sensors combined are processed to obtain the wanted torque values.

Figure 6 schematically shows a side view of a crank 60 for a vehicle according to a further embodiment of the invention. In this embodiment, the vehicle may be a push bike, like a bicycle.

The crank 60 comprises a first connection part 61 arranged to connect the crank to a crank axle of a push bike. The crank 60 comprises a second connection part 62 arranged to connect the crank to a pedal of a bike. Furthermore, the crank 60 comprises an elongated body 63 fixed to the first connection part 61 and to the second connection part 62. The elongated body 63 comprises a first bar 64 and a second bar 85. The two bars 64,65 are coupled by way of an open rod structure comprising two intersecting plates 66,67. At both sides of the rod structure, a rod 68, 69 is arranged. On both the rod 68 and the rod 69 a strain sensor 74,75, such as a strain gauge is arranged to measure strain in the longitudinal direction of the rods 68,69.

It is noted that the bars, the plates and the rods may be solid pieces of metal or other material that is generally used to support loads or transmit forces. The bars 64,65 may have a cross-section that is round, oval, square, hexagonal or any other suitable shape. The bars 64,65 may be hollow from the inside. Preferably, the rods 68,69 and the plates 66,67 are solid pieces so as to optimize the compressive and tensile strength while lowering the stiffness and strength to a bending moment to reduce to torsion around the centre of the elongated body.

Figure 7 shows a cross section of the part of the elongated body 63 where the two rods 68,69 are located. The cross-sectional view is chosen through the intersection of the two plates 66,67. It is noted that in this example the rods 68,69 have square cross-sections, but they may have other cross sections like round, oval, square, hexagonal or any other suitable shape.

Figure 8 schematically shows a top view of the crank 60. Now the first rod, i.e. rod 69 is visible and not the second rod 68 (see also Figure 8). It is noted that each of the rods extend in a direction that, at least in use, has no component parallel to the rotation axis 71 of the drive axle.

Furthermore, the first rod 68 and the second rod 69 are arranged on opposing sides of a first virtual plane which, in this example, coincides with the rotation axis 71 and a central axis 72 of the second connection part 62. In embodiments where the second connection part 62 is absent or where a central axis of the connection part cannot be defined, the first virtual plane can be defined as the plane that incorporates a central axis of the elongated body and is orientated parallel to the rotation axis 71.

The crank 60 may comprise at least part of a torque measurement system. The measurement system may be arranged to measure the torque forces on the crank 60 in order to be able to calculate the power put on the crank 60 by a person during use of the bike.

In an embodiment, the torque measurement system at least comprises the first strain sensor 74 arranged to measure strain in the first rod 68, and a second strain sensor 75 (see also

Figure 6) arranged to measure strain in the second rod 69. The measurement system may comprise further modules which will be described below with reference to Figure 19.

It is noted that the two rods 68,69 only resist pure tensile and compressive loads and since they cannot receive forces that they do not resist to. Any torsional forces in the elongated body will result in pure tensile loads in the rods 68,69, even though insignificant in magnitude.

Since the two rods experience the same tensile force resulting from a torsional load of the elongated body, the strain sensors, will give a signal including a torsion component that can be removed by subtracting the two signals. This will result in a measurement of the torque on the crank, which can be used to accurately determine the relevant power applied by the biker.

It is also noted that the two sensors 74,75 do not need to be located at a central location on the rods 68,68, nor do they need to be located at the same location on the rods. As long as the sensors are able to sense the strain in the respective rods, the measurement system will be allowed to calculate accurate torque values. Normally the distance from the rotational axis is inverse proportional to the bending moment in the cross section, and this distance is a major influence on the strain measured relative to the applied torque.

Figure 9 is a perspective view of a crank 80 according to an embodiment. The crank 80 comprises a first connection part 81 and a second connection part 82 with the same function as described with reference to Figure 6. The first connection part 81 has an opening for receiving part of a drive axle, and the second connection part 82 has an opening for receiving a part of a pedal axle or coupling part of a pedal. The first connection part 81 is coupled with the second connection part by means of an elongated body with organically shaped elements. The organically shaped elements are a result of a design process using strength optimization software programs, such as Autodesk Fusion 360 Generative Design Extension.

The elongated body of Figure 9 comprises a first rod 85 and a second rod 86 which are connected to a socket 87. The socket 87 is also referred to as air foil 87 or tube 87. Socket 87 comprises several openings, one of which is called the top opening 88. A bottom opening is also present but not visible in Figure 9. While the two rods 85,86 extend in a plane perpendicular to the rotation axis 71, other rods in the same region, like rod 89, are oriented in such a direction that they have a component parallel to the rotation axis 71. As a result, the first rod 85 and the second rod 86 predominantly experience pure compressive or tensile forces as a consequence of torque applied around the rotational axis 71, see F1, while the other rods, like rod 89, also experience strain as a consequence of torsional and other forces that do not translate to a torque around the rotational axis 71, see F2.

Figure 10 is a perspective view of a crank 90 according to another embodiment. The crank 90 is quite similar to the crank 80, but now also comprises a number of chainring connection members 93,94,95 for connecting a chainring (not shown).

Figure 11 is a side view of the crank 80, wherein the first connection part 81 and the second connection part 92 are shown together with the elongated body in between. Figure 11 also shows the chainring connection members 93,94,95. Each of the connection members is connected to the rest of the crank 90 by means of two or more rods, see e.g. rod 101 and rod 102 connecting the connection member 95 to the rest of the crank 80. The connection members 83 and 94 are connected to the rest of the crank 90 by way of three rods, two of which are coupled directly to the elongated body. It has been shown during tests and in simulations that the design shown in Figures 9, 10 and 11 provide for a lightweight crank with improved strength and stiffness.

Looking closely at the crank 90, it can be divided in three main sections or zones, see zone 1, zone 2 and zone 3. In zone 1, the crank 80 is mainly made out of a socket, which may be designed in such a way that the crank is optimized for having little airflow resistance, as will be discussed in more detail below.

In zone 2 the crank 90 is mainly made out of organically shaped rods, some of which are provided with strain sensors as was described above. Zone 2 could be regarded as the measurement zone. Zone 3 is that part of the crank wherein the design is focussed on a strong connection to the first connection part 91, and a good connection to the chainring coupling members 93,94,95.

Figure 12 is a perspective view of the crank 80 and the crank 90 showing their relative location when mounted to a bike (not shown). Figure 12 is a rendered view of the cranks showing more details of the organic structures in 3 dimensions. A distance d1 in Figure 12 indicates the distance between the cranks 80,90 at the driving axle. A distance d2 indicates the distance between the outer sides of the cranks, which distance is also referred to as the Q-factor. The skilled person will appreciate a relatively small Q-factor to decrease the torsional and bending forces on the cranks and the frame of the bike. In Figure 12 two lines 104 are shown indicating typical dimensions between the connection parts 82 and 92.

Figure 13 is a top view of the assembly of Figure 12. Due to the extremely stiff construction designed using a narrow form factor, and using strong and stiff materials, such as titanium or steel, a narrow Q-factor could be achieved equal to 130 mm with a distance d1 equal to 81.5 mm.

Figure 14 shows a side view of crank 90 wherein two edges 105,106 of the air foil 97 are indicated. The edges 105,106 are both a leading and trailing edge due to the crank rotating during the pedal stroke. In order to improve aerodynamics of the cranks 80,90 both the trailing and leading edge 105,106 have openings to feed the leading edge’s high pressure air stream to the low-pressure side at the trailing edge. Figure 15 is a bottom view of the crank 90 of Figure 14 showing one of the openings 110 for passage of air flow.

To further improve the air foils 87,97 and generate a large amount of lift relative to drag, in an embodiment, a symmetric air foil (trailing and leading sides are mirrored) with a relatively low cord width to thickness ratio is used. In an embodiment, the manufacturing method used to manufacture the cranks, comprises designing a crank with an air foil profile wherein the profile is based on the wing aerodynamic profile named SIKORSKY DBLN-526 AIRFOIL (dbln526-il).

Figure 16 shows a cutaway side view at the cross section XVI in Figure 14. By selecting an initial air foil design, and then letting the optimization program produce on optimal design, the air foil is partly deformed and enhanced with rod structures organized in an organic way. Figure 16 shows an outer wall 161 of the air foil and an inner wall 162 of the air foil. The inner wall 161 is, at least in use, facing the frame of the bike. At the opening of the air foil some enforcements are arranged to improve strength of the air foil 87,97, see rods 163 at the top and 164 at the bottom.

The inventors have realized that due to the force that is exerted on the cranks 80,90, typically having an offset of about 65 mm, the material strain in the cranks is caused by the torsion in its length axis. Since a wing aerodynamic profile, like the SIKORSKY DBLN-526 AIRFOIL, is not ideal for torsion stiffness and strength, in an embodiment of the method, a very thin outer aerodynamic shell is used with internal rods generated in a generative manner within this outer shell such that the inner structure is ideal for transmitting this torsion force. The internal rods generated form a more circular load path for torsion strength/rigidity, while at the same time allowing for air to pass through. This results in air being able to blead from the high-pressure leading edge to the trailing edge. Due to the fact that at high speed the air foil does not have laminar flow at the trailing edge, it is possible to reduce drag by directing high pressure air from the leading edge to the otherwise more turbulent air at the trailing edge. Again, which of the two edges is leading or trailing depends on the orientation of the crank (arm) in the pedal cycle.

Figure 17 shows the view of Figure 16 together with a location 170 of the rider's leg when the crank is down in the pedal stroke. The arrows in the drawing indicate air flow which is present both at the outer surface of the air foil and also internally in the air foil due to the openings arranged in the air foil. In an embodiment, the air foil has a main axis directed under an attack angle a relative to a direction of travel indicated by number 175.

Preferred values of the attack angle a lie not above the air foils stall angle and preferable as close as possible to the angle with the ideal lift to drag ratio to gain as much authority over the airflow as is possible in guiding the air past the rider’s leg or the frame with a minimal drag penalty. It is noted that the frame already causes air flow to be angled relative to the direction of travel. Due to a combination with the open leading and trailing edge, it is possible to keep good airflow characteristics (focussing on lift to drag ratio) at a 13 degree angle of attack, which is extreme compared to ordinary wing profiles that cannot blead leading edge air to the trailing edge.

During the pedal stroke, the crank arm passes by the rider's leg and frame. Both the leg and frame having different shapes and proximity to the air foil and both influencing the air differently call for the need to have an air profile which can cope with a wide range of attack angles without causing excessive drag due to the airflow detaching early because of the attack angle being too steep. The open leading and trailing edge construction combined with an internal load path facilitated by the internal organic beam structure 163,164, offer an improvement in both stiffness, strength and aerodynamics performance at extreme attack angles. This is true especially when the air profile has a low aspect ratio between the profile's cord and thickness.

By not just optimising the aerodynamics of the crank (arm) as such, but also its effect on the objects around it during the pedal stroke, the air foil 87,97 in this embodiment does not only the outer shell have a symmetric wing profile, but this profile also has a certain attack angle a relative to the direction of travel 175. This results in a crank that has good characteristics at the relevant air speeds and a favourable range of attack angles where it still has good drag to lift characteristics. When combined with a relatively open structure like the organically shaped rod structure described, it results in a lightweight crank having a super wide range of possible attack angles and the ability to go for an extremely low cord to thickness ratio (which is normally not beneficial). By suitable orienting the wing profile (i.e. the air foil) and arranging openings at the top and the bottom, and then also adding suitable enforcements, cranks can be made that are both aerodynamic, strong and light weight.

Figure 18 shows the view of Figure 16 together with a location of the rider’s leg when the crank is up in the pedal stroke, see 180. Now a similar situation is created as the one in Figure 17, but with the aero profile cross section shown in the situation wherein the crank is in its most upward orientation with the air flow now coming at it from the opposite side of the crank arm.

In Figure 18, the rider's leg 180 is out of the way but the bike’s frame (not shown) is right next to the crank and the air is being trapped between the crank arm and frame. Here, the direction of travel 175 point downwards. Due to the attack angle q, see 171, of the wing profile the air pressure around the frame (not shown) is lowered.

The above-described embodiments for connecting pedals to a bicycle are advantageous for multiple reasons. First of all, using a lattice structure locally that deconstructs compound forces into separate members. Having two of these members on opposing sides of the torque transmitting beam within a plane perpendicular to the rotational axis (in case of a bicycle a bottom bracket) in the centre of the crank. The other elements in zone 2 of the elongated body are not in the same plane or angled relative to these two rods. This concept also works but is less accurate if the plane with the two load/strain sensing elements is not centred in the crank. Because the two members at the opposite end receive strain that is proportional to the applied load in the plane of interest (offset causing torsion would be directed through the other members).

Secondly, the design prevents a buckling failure mode by avoiding very thin walls by lumping material together into the separate members. This allows for the use of other higher density, stronger and stiffer materials per unit of mass. This means that a very stiff object can be created, even with low profile members. Third, the crank has an aero profile that connects the leading and trailing edge through an opening with internal open structure for force transmission and airflow through the profile.

Furthermore, the organically shaped structure internally transmits forces in ideally shaped structure, so the load path is not solely through the outer shell. Also, the air foil reroutes air from the leading edge (high pressure) to the trailing edge (low pressure) significantly reducing drag.

And finally, a virtual shape of the air foil is created that is much rounder as compared to the aero shape of the outer wall. This is realized by placing a rod structure inside the air foil that connects the two wall sections of the air foil, which wall sections were created by the opening in the leading and trailing edges. This virtual shape has a more ideal shape for creating torsional rigidity which is the main cause of pedal end effector deflection.

In an embodiment, the cranks described above comprise a metal such as steel, aluminium or titanium. Such material provides for sufficient strength and can be machined relatively easily. Also, 3D printing may be used to produce (part of) the cranks. Alternatively, or additionally other materials may be used such as reinforced plastics. Such materials are lighter but sometimes sacrifices are made to the strength or stiffness.

Figure 19 schematically shows a torque measurement system 190 according to an embodiment of the invention. The system 190 comprises a first strain sensor 191 arranged to measure strain in the first rod 8;68;85, and a second strain sensor 192 arranged to measure strain in the second rod 9;69;86. In this embodiment, the system 190 comprises an A/D converter 193, a processing unit 184 and a sender 195. The sender is arranged to wirelessly communicate data from the processing unit 194 to a remote computer device by means of an antenna 196. The processing unit 194 may be arranged to forward measurements real time via the sender 195 to the remote computer device. Alternatively, the processing unit 194 may be arranged to store measurement data in a local memory (not shown). Data may comprise measurements from the strain gauges such as resistances of the gauges combined with time stamps. Additionally, or alternatively, the processing unit 194 may be arranged to calculate torque values, of power values in order to send the calculated torque and/or power to the remote computing device.

During tests, the system 190 achieved at least a 99.9% measurement accuracy, meaning that the combination of system error and random error in its readings is less than or equal to 0.1%. This accuracy is higher than current industry standards. In an embodiment, measurement signals of the strain sensors 191 and 192 are fed into a Wheatstone bridge in the A/D converter 193. As change in resistance of the strain sensors is inverted with respect to each other when a bending force is applied, whereas a torsional force does not change their resistance relative to each other, their presence in a Wheatstone bridge results in a low-noise differential signal that gets fed into a high-precision A/D converter. System error can be mitigated by factory calibration of measurement offset and scale.

The processing unit, the A/D converter, the sender and the antenna may be manufactured on a single printed circuit board (PCB) 197 or they may be arranged in different modules, which are arranged in or on the cranks. The PCB 197 may be sealed by a seal in order to prevent malfunctioning due to a hostile environment. The remote computing device receiving the measurement data from the system 190 may be a watch, a bike computer or a remote laptop. As will be clear to the skilled person, the data may also be stored and communicated to another device after a ride or race.

Figure 20 is a flow chart of a method 200 of manufacturing a crank for a vehicle according to an embodiment of the invention. The crank is manufactured to be used with a vehicle comprising a frame and a vehicle component that is rotationally mounted to the frame around a rotation axis.

The method 200 comprises providing 201 of a model of the crank wherein the model comprises a first connection part designed to connect the crank to the vehicle component, and an elongated body fixed to the first connection part, and comprising a first rod and a second rod, each of which extending in a direction that, at least in use, has no component parallel to the rotation axis 71. The first rod and the second rod are designed on opposing sides of a first virtual plane 20, wherein the first virtual plane 20 incorporates a central axis of the elongated body and is orientated parallel to the rotation axis 71.

The method 200 also comprises manufacturing 202 of the crank using the designed model and a manufacturing technique and adding 203 a first strain sensor to the first rod, and a second strain sensor to the second rod. Optionally, a further step comprises virtually positioning design limitation elements relative to the first connection part 212, the position and shape of the design limitation elements being defined by a crank design.

Figure 21 shows an example crank model in a design space of a computer aided design software program. An example of such a program is Autodesk Fusion 360 Generative Design

Extension. The virtual 3D model 210 is the model for manufacturing the crank 80 of Figure 9. The model 210 comprises a first part 212 having an axis 213. The model further comprises a second part 214 at the other outer end of the model. A socket 215 is added to the second part 214. Next, the first and the second rod are virtually positioned so as to start from the socket 215, see elements 216,217. Two blocking elements 301 and 302 are placed through the second part 214 which are to be machined features in the latter stages of production. These are machined in one of the last steps such that the finish machining operation can be customised to the desired length of the crank.

Two ring-shaped blocking element 303,304 are placed around each of the first and second rod. The blocking elements (i.e. negative objects) are used to avoid that the generative software program creates enforcement elements, such as rods, at unwanted places. In the proximity of the sensors, the first and second rod should be free of any connection to other members in order to be able to mainly or only experience tensile or compressive forces. A further blocking element 305 is positioned at the location where the PCB 197 is planned.

After having placed all positive and negative objects, having fed the model all relevant/determined load cases and set the right weight, stiffness goals and priorities between those goals, the inventors instructed the generative software program to create an organically shaped structure, wherein the organically shaped structure comprises the first rod and the second rod.

Figure 22 shows a side view of the model of Figure 21. Reference 215 shows the aerodynamic wing profile 215 described above. When using 3D printing techniques to manufacture the crank, it is preferred to design the socket 215 (i.e. the profile) at a minimum thickness that is still printable so as to minimize the weight of this part.

Figure 23A shows a side view of a disk shape region 231 where during the crank's orientation at some point in the rotation either the rider's foot/leg or the drive chain are present thus to prevent interference somewhere in the pedal stroke limiting where the model is allowed to put material. Furthermore, a block shaped region 232 is modelled which limits the generative model to not allow it to add extra material to the outside of the aerodynamic profile. Figure 23B shows a front view of the disk-shaped region 231. Figure 23C shows a cross section at the plane indicated by the arrows A-A in Figure 23B.

Figure 23D is a detailed view of the right design of the crank accompanied by several exclusion regions. The exclusion region 241 (231 in the previous images) is a revolved exclusion region for the rider's foot, chain and chainring. An exclusion region 232 is defined as an exclusion block for outside the aerodynamic profile. This forbids the modelling program to add material to the outside of the air foil.

The step of providing 201 a model may comprise several iterations so that multiple conflicting properties can be taken into account. For example, for the generative design model a number of aspects can be taken integrated in the modelling: 1. Load cases: based on mostly ISO norms and information the inventors gathered by 3D scanning available cranks to be able to determine the stiffness, weight and aerodynamics of their parts. Using that information a goal was set. 2. Space claim limitations: where is the chain, chainring and rider's foot during the rotation; for those objects clearance is wanted. For this a circular space limitation can be introduced in the model and also for the interfaces to the axle and pedal. 3. Airflow simulations simulating air flow around a bike frame in order to determine which air foils and their attack angle to use where, and where to decide on whether to select an open or a closed structure so as to control the air flow, or in case of an open structure, to ‘provide the air as much freedom to equalise as possible’. To limit drag the best part is no part and thus no drag by the part. So, a choice is to be made. Use the part to guide air using an aero profile and potentially by doing this positively guide the air around other parts in its proximity. If though this is not possible having an open structure which does not alter the airflow as much or trap air between parts is best.

In an embodiment, nearly optimal shape for the air foil 87,97 was drawn. This shape was then given a minimum thickness still possible to manufacture. In order to make sure the outside of the foil model is respected by the Al program, on the outside of the foil model an exclusion region may be added that follows the air foil’s outer surface, see also 232. In this way, the modelling program is only allowed to add material to the inside of the air foil.

Following the above-described method an organically shaped elongated body can be produced by an Al program which design requires only a minimal amount of material given a required strength and stiffness.

The above-described cranks can be manufactured using several different manufacturing techniques. The cranks or parts of it may be manufactured using components that are connected by way of welding. The crank, or parts of it, can be manufactured by using a CNC machine. In an embodiment, the manufacturing technique comprises an additive manufacturing technique, such as SLM or SLS. Such additive manufacturing techniques are advantages in case the crank has a complex structure, such as an organically shape rod structure that was designed to using optimization software programs.

In the above-described embodiments, the torque measurement is performed on a crank of a push or motor bike. It is however conceivable to implement the measurement system in a crank of another type of vehicle, such as a car, a boat, a scooter, a water scooter or a jet ski.

Furthermore, it is conceivable to implement the invention in other structural components (i.e. not being cranks) of a vehicle such as measuring torque in a fork boot holding a brake caliper of a motor bike or a car. Such a fork boot may comprise the sensing rods as described above.

The present invention has been described above with reference to a number of exemplary embodiments as shown in the drawings.

Modifications and alternative implementations of some parts or elements are possible as long as they are included in the scope of protection as defined in the appended claims.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments within the scope of protection as defined in the appended claims.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

Use of the verb “comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim.

The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements.

The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CONCLUSIONS

1. A crank (1;60;80;90) for a vehicle, the vehicle comprising a frame and a vehicle component pivotally mounted to the frame about an axis of rotation (4;84), the crank comprising: - a first connecting portion (2;61;81;91) adapted to connect the crankshaft to the vehicle component; - an elongate body (8) attached to the first connecting portion and comprising a first rod (9) and a second rod (10), each extending in a direction which, at least in use, does not have a component parallel to the axis of rotation (4;84), the first rod (9) and the second rod (10) being disposed on opposite sides of a first virtual plane (20), the first virtual plane comprising a central axis of the elongate body and being oriented parallel to the axis of rotation (4); - a torque measuring system (190), the system comprising a first strain sensor (21,22;74,75) adapted to measure tension in the first rod, and a second strain sensor adapted to measure tension in the second rod.

2. The crank of claim 1, wherein the first rod and the second rod intersect a common cross-section of the elongate body, the cross-section being perpendicular to the central axis of the elongate body.

3. The crank of claim 2, wherein the elongate body comprises at least one reinforcement member extending in a direction having a vector component parallel to the axis of rotation, the reinforcement member also crossing the common cross-section.

4. A stool as claimed in claim 3, wherein the reinforcing member comprises two intersecting rectangular-shaped elements.

5. A crank according to any preceding claim, wherein a longitudinal axis of the first rod and a longitudinal axis of the second rod lie in a second virtual plane comprising the central axis of the elongated body and oriented perpendicular to the axis of rotation (4).

6. A crank according to any preceding claim, wherein the first and second rods are arranged on a circumference of the crank.

7. A crank according to any preceding claim, wherein the first rod and the second rod each have a straight centre line.

8. A crank according to claim 7, wherein the first rod and the second rod are arranged parallel.

9. The crank of any one of claims 2 to 8, wherein the first and second rods resist each torsional load about a longitudinal axis of the elongate body with less than 5% of the combined torsional resistance of all elements in the common cross-section.

10. A stool according to any preceding claim, wherein the elongated body comprises an organically shaped structure (8).

11. Crank according to any of the preceding claims, wherein the crank (1) is a bicycle handlebar or part of a bicycle handlebar.

The crank according to any of claims 1 to 10, wherein the crank (100) comprises a second connecting part (62;82;92) adapted to connect to a pedal.

13. A crank according to claim 12, wherein the second connecting part comprises a cylindrical opening having an axis which, at least in use, is parallel to the axis of rotation.

14. Crank according to any of claims 12 to 13, wherein the crank comprises a plurality of connecting members (21,22,23) for connecting a chainring.

15. A crank according to claim 14, wherein the number of connecting members (21,22,23) is three.

16. Crank according to claim 14 or 15, wherein each of the connecting parts (21,22,23) is coupled to the remainder of the crank by means of at least two rods.

17. A method (200) of manufacturing a crankshaft for a vehicle, the vehicle comprising a frame and a vehicle part rotatably mounted to the frame about an axis of rotation, the method comprising: - providing (201) a model of the crank, the model comprising a first connecting portion designed to connect the crank to the vehicle part, and an elongate body attached to the first connecting portion and comprising a first rod and a second rod, each extending in a direction which, at least in use, does not have a component parallel to the axis of rotation, the first rod and the second rod being designed on opposite sides of a first virtual plane, the first virtual plane comprising a central plane axis of the elongate body and being oriented parallel to the axis of rotation; - manufacturing (202) the crank using the designed model and a manufacturing technique, and - adding (203) a first strain sensor to the first rod, and a second strain sensor to the second rod.

A method of manufacturing according to claim 17, wherein providing a model comprises: - virtually positioning the first part in a design space using a computer-aided design software program; - virtually adding the elongated body part to the first part.

19. A method of manufacturing according to claim 18, wherein providing a model further comprises: - virtually positioning design boundary elements relative to the first connection portion, the position and shape of the design boundary elements being defined by a crank design; - virtually positioning the first and second rods; - virtually placing a blocking element about each of the first and second rods; - creating an organically shaped structure associated with the first portion, using a generative software program, the organically shaped structure comprising the first rod and the second rod.

20. A method of manufacturing according to any one of claims 17 to 19, wherein the manufacturing technique comprises an additive manufacturing technique, such as SLM or SLS.

21. A crank (80) for a vehicle, the crank comprising: - a first connecting portion (81) having a first opening (83) for connection to a drive shaft, the first opening having a first axis (71); - a second connecting portion (82) for connection to a pedal; - a sleeve (87) attached to the second connecting portion (82), the sleeve having an elliptical or wing-shaped cross-section with its major axis oriented at an angle of attack (α) with a plane perpendicular to the first axis (71), and the sleeve comprising two opposed elongated openings (88).

22. A crank (80) as claimed in claim 21, wherein the crank comprises an organically shaped rod structure coupling the first connecting member (81) to the sleeve (87).

The crank (80) of claim 22, wherein the organically shaped rod structure is configured to reinforce at least a portion of the sleeve (87).

24. Crank (80) according to any of claims 21 to 23, wherein the angle of attack is in a range of 0-20 degrees, and preferably in a range of 7-15 degrees.