NL2005645C2

NL2005645C2 - Elastic sprocket.

Info

Publication number: NL2005645C2
Application number: NL2005645A
Authority: NL
Inventors: Colin Yip
Original assignee: Ebm Solutions Pty Ltd
Priority date: 2010-04-09
Filing date: 2010-11-08
Publication date: 2012-11-27
Also published as: NL2005645A; DE102010050048A1

Description

ELASTIC SPROCKET FIELD OF THE INVENTION

The field of the present invention relates to electromechanical devices, and particularly to electromechanical devices in power assisted vehicles such as bicycles.

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DESCRIPTION OF THE PRIOR ART

An electric power assisted bike is a bicycle that uses the power output provide by the rider in conjunction with a motor.

During riding, the motor works only when the rider exerts a certain force. If the rider 10 does not pedal then the motor does not provide any output that is usable by the rider to propel the bike. In this bike, the motor output power is related to the size of the applied force from the rider; the harder the rider pedals, the greater the power output from the motor, and vice versa. Here, the motor only plays the role of assistance, so it is called Power Assisted System (PAS) bike. In recent years, the PAS style of bike has become 15 very popular in Europe and America. However, the PAS system does have some noticeable drawbacks such as not being able to have reliable/accurate control over the output of the motor, which impinges on the performance of the system.

The way to achieve better control of the motor output power is an important objective to improve its performance.

20 In order to control the motor output power, first the force applied by the rider needs to be measured. In measuring the size of the force, what is measured is the amount of deformation of an object when subjected to an applied force. At present, there are several measuring methods.

For example, it is known to use strain gauges to measure the deformation of the bicycle 25 axle; or separating the outer rim of the sprocket and the sleeve into two components, and then connect them together by a spring, so that the force acting on the axle is transferred to the sprocket through the spring. Then by measuring the deformation of the spring, one can get the force acting on the sprocket connected to the bicycle axle. All these methods have drawbacks, such as, if the sprocket is re-connected by the 30 spring after separation, the sprockets axial stiffness and radial stiffness will be lost, as compared with the original rigid sprocket, the sprocket’s performance is greatly affected this way. In this invention, the sprocket is made to be elastic, and obtain the force acting on the sprocket by measuring the deformation amount directly.

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In comparing with the different existing measuring methods, this invention provides a method with advantages of simple structure and high accuracy of measurement.

OBJECT OF THE INVENTION

5 An object of the present invention is to provide a sprocket for a bicycle, wherein the sprocket is designed in part to flex under load.

Other objects and advantages of the present invention will become apparent from the following description, taking in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is 10 disclosed.

SUMMARY OF THE INVENTION

According to the present invention, although this should not be seen as limiting the invention in any way, there is provided a type of sprocket when used in an electrically 15 power assisted bikes, the sprocket generating a certain amount of elastic deformation. In preference, the sprocket if further characterised in that the outer rim of the sprocket and the sleeve of the sprocket centre are connected by a number of plate springs.

In preference, the deformation amount of the plate springs is proportional to the deformation amount of the sprocket due to the applied force.

20 In preference, the sprocket uses a deformation amplification lever to enlarge the deformation amount of the sprocket.

In preference, the sprocket further includes at least one stopper plates to limit the deformation of the sprocket.

In preference, the sprocket has an outer portion with an outer periphery having chain 25 engaging teeth positioned thereon, an inner axle sleeve shaped to engage a bottom bracket axle, a plurality of plate springs joining the inner axle sleeve to the outer portion, the plate springs being shaped to deform when a rider applies a predetermined load value, at least one stop member projecting from the axle sleeve towards an inner surface of the outer portion, such when a rider applies exceeds the predetermined load 30 value, the plate springs deflect until the at least one stop member projecting from the axle sleeve contacts the inner surface of the outer portion.

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In preference, the outer portion has an inwardly projecting ridge shaped to engage with the at least one stop member projecting from the axle sleeve when the rider exceeds a predetermined load value.

The term “plate spring” is interchangeable with the term “spider arms” or “joining 5 segment” and refers to portion that connects the outer section of the chaining that engages the chain of the bicycle to the inner axle sleeve that connects or mates with the bottom bracket.

BRIEF DESCRIPTION OF THE DRAWINGS 10 By way of example, an employment of the invention is described more fully the renown for with reference to the accompanying drawings, in which:

Figure 1 is a side view of the present invention;

Figure 2 shows a side view of the present invention when under load;

Figure 3 shows a close of Section A; 15 Figure 4 in a close up view of the invention showing the movement non-flexing portions of the device.

Figure 5 shows the invention with a deformation amplification device attached.

DETAILED DESCRIPTION OF THE INVENTION 20 As shown in Fig. 1, the outer rim (1) of sprocket, (2) has an axle sleeve of the sprocket, (5) is the plate spring or spider, which may have many pieces, are connected to the outer rim (1) of the sprocket with the axle sleeve (2) to form a new sprocket.

By varying the choice of spring stiffness and number of spring plates or arms of the spider, one can ensure that the sprocket has sufficient strength and rigidity, as well as 25 sufficient degree of flexibility so that sprocket has a certain amount of deformation under an applied force. The stopper plate (4) provides a limit to the amount of deformation of the sprocket.

Figure 2 shows an embodiment of the present invention in which there is a sprocket, or chain wheel (10) having an outer diameter (12) about which a plurality of teeth (14) are 30 positioned for engaging a bicycle chain. The outer diameter (12) is connected to an axle sleeve (22) by a number of joining segments (sometimes referred to as spokes or plate springs) (24). The axle sleeve has an inner circumference that has a plurality of splines shaped to mate with a suitably shaped bottom bracket axle such as ICIS®, Octalink® or 4 other suitably shaped system. The plate springs (24) project from the periphery of the axle sleeve (22) towards the inner surface (13), in a radial fashion. There is also at least one main arm (18) projecting from the axle sleeve (22) that extends substantially towards the inner surface (13) but is not directly joined thereto.

5 As can be seen in Figure 2 the stopper plate or non-flexing arm (18) has a projecting extension (28) with a contact face (29) located on one side. In this particular embodiment there are two projecting extensions (28) and (31) however the number of projecting extension may vary according to intended use.

The inner surface (13) has inwardly projecting stop members (35), each having a 10 contact face (36). The plate springs (24) are shaped to provide a certain degree of flex so as to first of all ensure that the chain wheel (10) has sufficient strength and rigidity as required to function properly when in use on a bicycle as well as to allow a sufficient degree of flexibility such that the chain wheel (10) has a certain degree of defamation under an applied force.

15 Section A of Figure 2 is enlarged as shown in Figure 3. As can be clearly seen the distance between the two projecting extensions (28) and (31) has reduced and they are almost in contact. As the user (39) continues to apply load that exceeds the predetermined load, the two surfaces would eventually meet but then stop at that point. Accordingly then, when in use, the chain wheel (10) is mated to a suitably shaped 20 bottom bracket and crank arm (not shown) are attached subsequently to the bottom bracket and a chain engages the teeth (14). As force is applied to the chain wheel (10) by the user (39) in a clockwise direction (40) force is transferred through the cranks to the axle sleeve (22), through the plate springs (24) to the outer diameter (12), the teeth (14) and the chain into the bicycles drive system.

25 As the user (39) begins to pedal, very little force is exerted through the chain wheel (10). However, as the user (39) applies more force through the cranks then the plate springs (24) begin to deflect or bend out of plane in a pre-determined manner. As this occurs the gap between the contact fact (29) of the projecting extension (28) and the contact face (36) of the stop member (35) reduces until such a time as the force exerted 30 by the user (39) exceeds that of the pre-determined deflection limit of the plate springs (24) and the two contact faces (29) and (36) come into contact.

At this time the plate springs (24) can deflect no further and any excess force applied by the user (39) does not result in any further deflection of the plate springs (24). In 5 this manner the stopper plate (18) prevents the chain wheel (10) from deflecting to such a point that might be considered dangerous. The number and shape of the projecting extensions (28) and stop members (35) may be varied according to use without necessarily departing from the scope of the invention. It is envisaged that the chain 5 wheel (10) of the present invention may have one or more main stopper plates (18).

In use, the sprocket system may be designed to withstand significant flex under, for example, a 20 kg load as applied by the user (39). When the user (39) exerts a load on the pedals and hence the crank arm attached to the bottom bracket, then the projecting extension (28) and the contact face (36) of the stop member (35) will be brought closer 10 together until such time as they contact one another, it is possible then to place a suitable measuring device across the gap between the projecting extension (28) and the contact face (36) of the stop member (35) and measures the torque as applied by the user (39).

This has great advantageous in bicycles that use an electric motor to assist a rider. Such 15 motors are only activated when the user applied a certain degree of force to the pedals. 20 kg is considered to be a nominal force for an ordinary user. When the force applied to the system employing the present invention exceeds 20 kg by the user then the measuring device detects that via the sprocket system flexing and then the electric motor is actuated to assist the rider.

20 Once the rider has finished pedaling, again the measuring device again detects that via the sprocket system returning back to its normal position and then the electric motor is deactivated.

As the person skilled in the art would readily understand the present invention is also suitable for use in a non powered bicycle where it were desirable to measure the force 25 being applied by the rider such is in a racing or training situation where such data relating to torque and power is often used to measure the performance of the rider.

In Figure 5 (3) is a deformation amplification lever, its role is to enlarge the amount of the sprocket deformation. When this lever is at its upper Point A, it is connected with the sprocket outer rim by hinge; when it is at Point B, it is hinge connected with the 30 stopper plate.

The relative circumferential displacement between Point A and B is the deformation amount of the sprocket. The measuring points of the displacement are at Point C of the deformation amplified lever (3) and Points D of the stopper plate (4).

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In the instance where the sleeve (2) is rotated clockwise, the outer sprocket rim (1) is driven by the plate spring and so also makes a clockwise rotation. At the same time, due to the deformation of the plate spring (5), the sleeve (2) and the stopper plate (4) rotate a very small angle more than the outer sprocket rim. Therefore, the amplified 5 lever rotates a small counter-clockwise angle. Thus, the distance between Point C and Point D is decreased. By measuring the distance change between Point C and Point D, one can obtain the circumferential deformation amount of the sprocket. The ratio of the length BC to the length AB is magnification of the circumferential deformation of the sprocket.

10 One of the advantages of this invention is only to change the existing rigid structure of the sprocket into flexible structure. It preserves the original nature of the rigid sprocket, which has sufficient strength and rigidity, as well as providing a certain degree of flexibility, with a simple structure; the plate spring is slender in shape, it has a good linear relationship between the deformation and the applied force, with high precision.

15 These advantages are not currently available in other existing methods.

Although the invention has been herein shown and described in what is conceived to be the most practical and preferred embodiment, it is recognized that departures can be made within the scope of the invention, which is not to be limited to the details described herein but it is to be accorded the full scope of the appended claims so as to 20 embrace any and all equivalent devices and apparatus.

Claims

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A chain wheel assembly for a bicycle, including a. An outer edge portion with a plurality of teeth for engaging the chain; 5 b. an internal axle sleeve for engaging a bicycle pedal axle; c. a plurality of connecting segments connecting the outer edge portion with the inner shaft sleeve; d. at least one non-flexing arm that extends radially from the shaft sleeve to an inner surface of the outer edge portion that is not connected to that portion; 10 e. characterized in that the connecting segments bend / deform as a user exerts a predetermined load whereby at least one non-bending arm moves closer to the inner surface of the outer edge portion.

2. The sprocket assembly according to Claim 1, further characterized in that the inner surface of the outer edge portion has an inwardly directed ridge positioned so that it comes to rest against at least one non-bending arm if the load exerted by the cyclist is equal to the predetermined tax.

3. The sprocket assembly according to Claim 2, further characterized in that there is a space of approximately 0.3 mm between the inwardly directed ridge of the outer edge portion and at least one non-bending arm.

The sprocket assembly according to Claim 2, further characterized in that there is a measuring instrument on the non-bending arm. 25

The sprocket assembly according to Claim 4, further characterized in that the measuring instrument is located on the non-bending arm and the outer edge portion.

The sprocket assembly according to Claim 5, further characterized in that the measuring instrument measures the distance between the non-bending arm and the outer edge portion.

The sprocket assembly according to Claim 5, further characterized in that the measuring instrument measures the distance between the non-bending arm and the inwardly directed ridge of the outer edge portion.