SE0950545A1 - Method and system for controlling a vehicle - Google Patents

Abstract

The present invention relates to a method of propelling a vehicle at the start of said vehicle, said vehicle comprising at least one drive wheel propelling said vehicle and said vehicle comprising an electric motor, and wherein said electric motor is arranged to produce a propulsion wheel on said drive wheel. The method comprises the steps of: - a) using said electric motor applying a torque propelling on said drive wheel in a first direction, - b) determining a representation of a grip against the base of said drive wheel, and - c) reversing the direction of rotation of said electric motor to apply a on said drive wheel propelling torque in one direction opposite to said first direction when the name representation of the grip against the base of said drive wheel meets a first criterion. Fig. 2

Description

20 25 30 by increasing the force applied to the drive wheels, preferably with a relatively high gear engaged, until the drive wheels spin loose, whereupon the driver immediately releases the accelerator and, if applicable, depresses the clutch so that the vehicle rolls back, the procedure being repeated when the movement in the opposite direction has stopped. By rocking the vehicle in this way, sufficient force can eventually be obtained to get the vehicle out of the pit/sink.

The probability of success with such a rocking function varies from driver to driver and with the driver's experience. For this reason, systems have been developed where the rocking function is automated. An example of such a function is described in the document WO 2004/098940 Al (Volvo Lastvagnar AB). This document describes an automated control of a vehicle's driveline system for use when starting under unfavorable ground conditions. Via the vehicle's driveline system, driving force is applied to at least one drive wheel, whereby application of driving force continues until a condition is detected, for example wheel spin, whereupon said application of driving force is interrupted, and driving force is instead applied in the opposite direction.

The function shown in the above-mentioned document thus has the advantage that the application of driving force to the vehicle's drive wheels during rocking can be carried out not only in one direction, but in both directions in order to try to increase the chances of successfully driving away with the vehicle in this way. The solution shown, however, has the disadvantage that when changing the driving force direction, it is first necessary to disengage the vehicle's driveline, and then to shift to a gear for driving in the opposite direction. Although such a procedure can in principle function well, the disengagement of the driveline, the subsequent gear change, and the re-engagement of the driveline mean that a comparatively considerable time is spent on these steps, with the result that changing the direction of the applied driving force often occurs too late to be fully utilized.

Thus, there is, at least in certain situations, a need for an improved method for freeing a stuck vehicle.

Summary of the Invention It is an object of the present invention to provide a method for controlling a vehicle when starting said vehicle which solves the above problem. This object is achieved by a method according to claim 1.

The present invention relates to a method for propelling a vehicle upon starting said vehicle, said vehicle comprising at least one drive wheel for propelling said vehicle and said vehicle comprising an electric motor, and said electric motor being arranged to generate a propelling torque on said drive wheel. By means of said electric motor, a propelling torque is applied to said drive wheel in a first direction, a representation of said drive wheel grip on the ground is determined, and the direction of rotation of said electric motor is reversed to apply a propelling torque on said drive wheel in a direction opposite to said first direction when said representation of said drive wheel grip on the ground meets a first criterion.

The present invention has the advantage that by using an electric motor to generate the driving torque in, for example, a rocking function as described above, the direction of the torque acting on the drive wheel can be reversed very quickly compared to the prior art when at least one of the vehicle's drive wheels loses grip on the ground, which can be determined, for example, by detecting wheel spin/rapidly increasing the rotational speed of the drive wheel(s), whereby the spinning wheel(s) can be stopped quickly and a driving torque in the opposite direction applied to assist the vehicle movement in the opposite direction and thereby increase the rocking with an increased probability of the vehicle coming loose as a result. With the help of the present invention, the driver can thus manage to get away with a vehicle in a situation where it would otherwise have needed towing assistance, or other assistance such as, for example, trying to put something under the wheels. The invention further has the advantage that it does not require any new hardware in vehicles with existing electric motor systems.

The above-mentioned steps with reversed torque direction can be advantageously repeated until the method is interrupted by, for example, a vehicle driver, or until the vehicle's control system detects that the vehicle has become unstuck and has de facto started.

In one embodiment, the electric motor is connected to said drive wheel via a conventional gearbox. The present invention has the advantage that even if the electric motor is connected to the drive wheel via a gearbox, the gearbox can still be driven in both directions, whereby one and the same gear can be used when carrying out the method according to the present invention, whereby no time is spent for disengagement and engagement of a new gear.

The invention is applicable to parallel hybrid vehicles as well as to other types of vehicles where an electric motor can be used for propulsion. For example, the invention can be used in series hybrid vehicles and in vehicles where one or more electric motors directly drive the vehicle's drive wheels without an intermediate gear, as well as in pure electric vehicles.

Further features of the present invention and advantages thereof will become apparent from the following detailed description of exemplary embodiments and the accompanying drawings.

Brief description of the drawings Fig. 1 shows a driveline in a hybrid vehicle in which the present invention can be advantageously used.

Fig. 2 shows an exemplary method according to the present invention.

Fig. 3 shows an exemplary rocking method according to the present invention.

Detailed description of exemplary embodiments As mentioned above, it is difficult to get an automatic clutch to disengage at the right moment in an automated rocking function, that is, just when the wheels start to spin. When the vehicle's drive wheels start to spin, the grip on the ground is lost, whereby, if the drive wheels are on their way up from a pit/sag, the vehicle will start to move in the opposite direction, that is, back down into the pit. In this case, it is desirable to be able to quickly engage a gear for operation in the opposite direction, so that the gravitational effect that occurs when the drive wheels roll back down into the pit can be utilized and used to attempt to get out of the pit in the opposite direction. However, due to the necessary decoupling of the engine output shaft from the gearbox input shaft during the shift, a not inconsiderable 10 15 20 25 30 time consumption is inevitable with such a solution, which is why optimal function cannot be obtained either.

The present invention, however, does not suffer from the aforementioned problems.

The invention will first be described in connection with a parallel hybrid system, and in the rocking function according to the present invention the combustion engine can be disengaged, e.g. by means of a conventional clutch, from the input shaft of the gearbox, whereby only the electric motor is used to drive the drive wheels during the rocking process. The direction of rotation and the rotational speed of an electric motor are controlled by means of the frequency of the voltage used to supply the electric motor.

The use of an electric motor therefore has the advantage that since its direction of rotation, unlike an internal combustion engine, is arbitrary, according to the present invention any gear can in principle be engaged, whereby the drive wheels can then be driven in both directions with said gear engaged by allowing the electric motor to change direction of rotation. Thus, according to the present invention, no gear change is required, and thus no time is required for carrying out the gear change itself. The present invention thus allows the change from applied driving torque from forward to reverse (or vice versa) to take place, at least in principle, instantaneously.

Fig. 1 shows a powertrain in a hybrid vehicle 100 according to a first exemplary embodiment of the present invention. There are various types of hybrid vehicles, and the vehicle shown is a parallel hybrid vehicle.

The driveline of the parallel hybrid vehicle in Fig. 1 comprises an internal combustion engine 101. The internal combustion engine 101 is connected in a conventional manner, via a shaft 102 output from the internal combustion engine 101, to a gearbox 103 via a friction element (clutch) 106. The vehicle further comprises drive shafts 104, 105, which are connected to the vehicle's drive wheels 113, 114, and which, as in a conventional internal combustion engine system, are driven by a shaft 107 output from the gearbox via a shaft gear, which may, for example, consist of a conventional differential 108.

Unlike a conventional vehicle, the vehicle shown in Fig. 1 also includes an electric motor 110, which is connected to the input shaft 109 of the gearbox 103, "downstream" of the clutch 106. Parallel hybrid vehicles can thus simultaneously transmit power to the drive wheels 113, 114 from two separate power sources, i.e. both from the combustion engine 101 and the electric motor 110. Alternatively, the vehicle can be propelled by either power source separately, i.e. either by the combustion engine 101 or the electric motor 110.

As is known to those skilled in the art, there are a number of types of electric motors that are suitable for use in hybrid vehicles, so the electric motor 110 can be any suitable type of electric motor. In the example description below, however, the electric motor is a three-phase motor, with the power supply to the electric motor 110 being a three-phase power supply.

Three-phase motors can be of both the so-called asynchronous and synchronous type, where the synchronous motor has the advantage that an exact speed determination can be carried out. In vehicle applications, it is naturally desirable that the rotational speed of the drive wheels, and thus the electric motor, can be varied in addition to the variation that can be obtained through conventional gear shifting by means of the gearbox, which is why the electric motor must also usually be speed-controlled.

The rotational speed of an electric motor is generally controlled by the frequency of the supply voltage with which the motor is powered, where the speed of the electric motor is directly proportional to this frequency. Speed control of an electric motor thus requires that the voltage supplied to the motor can be varied. In the case of an alternating current motor, this meant that the frequency of the AC supply voltage must be varied.

The motor 110 shown in Fig. 1 is therefore powered by a three-phase power supply with variable frequency, which is generated by using a power electronics device III, which in hybrid vehicles on the edge can also be used for a number of other functions, which will not, however, be described in more detail here.

The power electronics device 111 operates against an energy storage device 112, such as one or more batteries, supercapacitors, etc. The energy storage device can be arranged to be charged in several different ways, e.g. by regenerative braking using the electric motor 110 and/or via "plug-in" to an external power source such as a conventional electrical grid.

The power electronics device 111 shown in the figure may be of a type commonly found in hybrid vehicles and is therefore not described in more detail here. In general, however, it can be said that the power electronics 111, in the case of an AC motor, converts the DC voltage of the energy storage 112 into an AC voltage.

The conversion is carried out using a converter device which, for example, may consist of a plurality of IGBT (Insulated Gate Bipolar Transistor) transistors, which, by means of appropriate switching, can provide a three-phase voltage of desired and variable amplitude and frequency for driving the electric motor 110 and thus the vehicle's drive wheels 113, 114. 10 15 20 25 30 In this way, the electric motor 110 can be used at vehicle speeds from zero to maximum speed by controlling the frequency supplied to the motor 106 from 0 Hz to a frequency that results in the vehicle's (or, when working with the combustion engine, its) top speed.

Fig. 1 also shows a control unit 115 which can be used to control the method according to the present invention. The control unit 115 forms part of the vehicle control system. Vehicle control systems in modern vehicles usually consist of a communication bus system consisting of one or more communication buses for interconnecting various electronic control units and components located on the vehicle. Thus, signals to/from e.g. an electric motor control unit/power electronics as well as other vehicle functions involved in the inventive method can e.g. be communicated to/from the control unit 115 using a suitable communication bus. The vehicle control unit 115 can e.g. constitute an already existing control unit, whereby the present invention can thus be integrated in a simple manner at low cost.

An exemplary embodiment of the present invention will now be described with reference to Fig. 2, in which a rocking method is generally indicated at 200. The method begins at step 201, where it is determined whether the rocking function is to be activated. This determination can be made in a number of ways.

For example, the driver, after having determined that the vehicle is stuck, can activate the function using a button, lever or in another way, such as via a function selectable via a display.

The function can also be arranged to be initiated automatically, e.g. if the vehicle's control system detects wheel spin, but for safety reasons it may be preferable that the function is activated manually. The invention will therefore be described below for the case of manual activation.

Once it has been determined that a rocking function is to be initiated, the process continues to step 202, where it is determined whether actual execution of the function is to be initiated. This determination is not necessary but may be preferable so that the vehicle does not "live its own life" immediately when the rocking function is activated.

For example, the actual execution may be dependent on the driver pressing the accelerator pedal or otherwise indicating, such as by means of a spring-loaded button or lever, that the rocking function may be actively performed. This may further be combined with the driver selecting a preferred direction (forward or reverse) in which the vehicle should preferably start to move in order to facilitate the intended continued journey.

This may, for example, be desirable in situations where continued operation is only possible in one direction, for example due to obstacles in front of or behind the vehicle.

For example, the driver can indicate the preferred direction of movement by using the gear selector to indicate a forward or reverse direction. Regardless of the driver's choice, the control system can then select an appropriate actual gear in the transmission which is then used throughout the rocking function.

When it is detected in step 202 that the rocking function is actually to be performed, the process continues to step 203 (for safety reasons, the rocking function can advantageously be arranged so that it is immediately interrupted if the driver releases the accelerator and/or presses the brake). In step 203, the appropriate gear is selected for use in the rocking function. This gear normally consists of one of the lower gears of the gearbox, whether the gear is a gear intended for driving the vehicle in a forward or reverse direction does not play a role in the method, but may be important for the vehicle's continued travel once the vehicle has come out of the pit/sag. For example, it may be advantageous that the gear selected by the rocking function can also be used for continued propulsion of the vehicle so that there is no risk of the vehicle getting stuck again due to the inevitable interruption of propulsion torque that occurs when shifting and which at low vehicle speed can result in the vehicle stopping again and thus getting stuck.

Thus, it may be advantageous to select a gear intended for vehicle propulsion in the propulsion direction specified by the driver. Another parameter to take into account when selecting a gear for use in the inventive method is that the gear selection should result in the desired control characteristic being achieved, i.e. the selected gear should, together with the electric motor, be able to result in the desired torque on the drive wheels (this selection can be controlled at least in part based on the torque of the electric motor in relation to the torque of the combustion engine, the larger the electric motor, the greater the freedom in selecting the gear).

When the appropriate gear has been selected in step 203, the process continues to step 204, where a torque resulting in movement in the desired direction of propulsion is generated by the electric motor. With the help of the power electronics (the regulation of voltage and frequency for the motor's power supply), the speed of the electric motor can be regulated from standstill in a controlled manner, while the torque delivered by the electric motor can be regulated from 0 Nm to the maximum torque of the electric motor. Thanks to the control capabilities of the electric motor, both the desired speed of the electric motor and its delivered torque can be increased steplessly or ramp-wise.

It should be understood that as long as the torque output is less than the torque required to set the vehicle's drive wheels in motion, the electric motor shaft will remain stationary regardless of the applied frequency. A possible control method therefore consists of first increasing the torque output by the electric motor at low speed until the electric motor shaft begins to move, whereby the electric motor's rotational speed is successively increased once the drive wheel(s) have been set in motion. This rotational speed increase can be arranged to continue until a representation of the drive wheel(s) grip on the ground meets a first criterion, e.g. that the grip is lost by detecting wheel spin, in which case the process continues to step 205, or alternatively until the rocking is complete, in which case the process continues to step 206. In parallel with the rotational speed being increased, the torque can also be successively increased, this is illustrated in Fig. 3.

Wheel spin can be detected, for example, by determining the rotational speed of the electric motor. If the rotational speed of the electric motor begins to increase rapidly, this means that the rotational speed of the drive wheel(s) is also increasing rapidly. The determination can also be performed by comparing the rotational speed of the drive wheels with the rotational speed of non-drive wheels. For example, it can be determined whether a rotational speed difference between said drive wheels and at least one non-drive wheel arranged on the vehicle exceeds a first value.

Alternatively, or in addition, wheel spin can be detected by determining that a rotational speed of said drive wheel has reached a first speed. 5 l0 l5 20 25 30 l3 In Fig. 3 a graph of torque and wheel rotation (electric motor rotation) speed during an example rocking process is shown. It should be understood that the process shown in Fig. 3 is very schematic and that the actual process may look very different, e.g. depending on the choice of control principle, and depending on how quickly the vehicle's drive wheels spin off. The rocking process begins at time T=O where the electric motor torque is increased until the electric motor shaft (and thus the vehicle's drive wheels) begins to rotate at T=Tl. Between time T=Tl and time T=T2 the rotational speed of the wheels increases at the same time as the torque is also increased for at least part of that time. The increase in torque is preferably torque limited, i.e. The torque is only increased to a predetermined level to avoid wheel spin occurring too quickly. The speed achieved at the current torque is then maintained until time T=T3 when a rapid increase in the rotational speed begins. By constantly monitoring the rotational speed of the electric motor and/or the drive wheels, which can be carried out in several different ways, some of which will be described below, it can in principle be directly determined that the rotational speed increase that began at time T=T3 involved wheel spin, whereby the direction of rotation of the electric motor at T=T4, step 205, can in principle be directly reversed with the help of the three-phase voltage generated by the power electronics (by, for example, changing the phase sequence of the three phases that feed the electric motor, the direction of rotation of the rotating flux generated in the electric motor, which in turn drives the rotor of the electric motor, can in principle be immediately reversed, whereby the spinning drive wheels will be braked very quickly so that at time T=T5 they will start to rotate in the opposite direction. This has the advantage that since the torque acting on the drive wheels can in principle be immediately reversed, the electric motor can drive the drive wheels in the opposite direction. direction and thereby help the vehicle accelerate in the opposite direction when it starts to slide down into the pit/sag again. The process therefore returns to step 204 when reversing the direction of rotation. When then wheelspin is again detected, step 204 in the opposite direction is reversed, at T=T6, the electric motor torque is again reversed whereby the drive wheels can be driven at all times in a manner that is advantageous for getting the vehicle out of the pit/sag.

As shown in the figure, the maximum torque applied to the vehicle's drive wheels can be arranged to increase as the rocking process progresses.

By determining the torque delivered by the electric motor at the same time as the rotational speed of the drive wheels (electric motor) is determined, the torque increase together with the rotational speed increase can be used to determine whether the vehicle has emerged from the pit and continued travel should therefore begin. This is exemplified at time T=T7, where the rotational speed of the drive wheels has exceeded a level N1 at the same time as the rotational speed increase is so slow despite the applied engine torque that propulsion is in progress. This can be determined, for example, by determining a derivative for the rotational speed. If the derivative exceeds a threshold value, this can be determined as wheel spin, while if the derivative falls below a certain threshold value, the vehicle's drive wheels are considered to be propelling the vehicle forward. Said threshold value does not have to be fixed throughout the entire process but can, for example, depend on the current torque delivered by the electric motor. The higher the torque, the higher the relative speed increase is possible without it being classified as wheel spin. 10 15 20 25 30 15 When the vehicle speed has reached a certain speed, such as the speed Nl as above, the control system can determine that the rocking function should be interrupted, step 206, and continued travel in the usual way begins. When this is the case and the vehicle can drive normally forward (if this direction has been selected by the driver, e.g. by setting the gear selector to position 'D', or backwards if the gear selector is set to position 'R') the clutch is closed and the vehicle continues forward, now driven by the diesel engine. The diesel engine is preferably running and idling during the entire rocking process in order to be quickly used for continued propulsion once the vehicle has been released.

As mentioned above, it may be disadvantageous to perform a gear change just when the vehicle has started, which is why the control system may be arranged to prevent gear changing until a certain speed has been reached in order to prevent a new stop due to the inevitable torque loss during gear changing. In one embodiment, the disengagement of the automatic gear changing can be controlled by the driver, for example by preventing gear changing as long as the driver presses the accelerator pedal, whereby gear changing is only performed when the driver considers that gear changing can be performed without risk of a new stop and therefore releases the accelerator pedal.

The present invention thus has the advantage that very fast control processes are made possible by a conventional gearbox being driven in both directions and no time-consuming gear changing is thereby required. Since the direction of the torque delivered by the electric motor can in principle be reversed immediately when wheel spin is detected, very accurate torque control is also made possible, and thus good rocking function. l0 l5 20 25 30 l6 In the control process shown in Fig. 3, the speed control has been combined with torque limitation.

The above regulation can also be carried out by only monitoring the rotational speed of the drive wheels (electric motor). However, the use of torque limitation can be used to ensure that the drive wheels do not spin out undesirably quickly. The above rocking function can also be advantageously combined with the automatic engagement of all other aids that are available when a vehicle is stuck. For example, existing differential locks can be automatically engaged (alternatively, a message to the driver can be generated with the request "engage differential lock").

As mentioned above, the automatic gearshift function can also be deactivated.

The detection of wheel spin can be done in several different ways. For example, a sensor can be arranged on the output shaft of the gearbox, where the signal emitted from the sensor represents the rotational speed of the output shaft. Alternatively, one or more wheel speed sensors can be used (e.g. all of the vehicle's wheel speed sensors can be used in the detection to obtain the most accurate detection possible). Furthermore, a speed sensor can be arranged on the shaft of the electric motor. However, it is also possible to detect the rotational speed of the electric motor by superimposing a high-frequency signal on the electric motor's supply voltage. This superimposed high-frequency signal can then be used not only to detect the speed of the electric motor but also the position, whereby it is thus possible to detect exactly when the drive wheels start to rotate, which also enables very good torque control to be carried out based on the rotational speed of the drive wheels. Furthermore, it can be advantageous to use signals from several or all of the above sensors/sensors/signals to obtain the most reliable determination possible. 10 15 20 25 17 Furthermore, it is of course possible that the vehicle will come loose from the pit/sag in the "wrong" direction. The software that controls the function may therefore have a lock that prevents the car from moving more than, for example, a maximum of 30 cm in the wrong direction. The function should also be combined with clear warnings and an audible/visual signal for reversing, since the car will move slightly backwards even during the rocking process regardless of the direction in which it finally comes loose.

So far, the invention has been described for a parallel hybrid vehicle. However, the invention is equally applicable to other types of vehicles where an electric motor can be used for propulsion. For example, the invention can be used in series hybrid vehicles where the combustion engine is only used to drive a generator, which in turn charges an energy storage that is used to drive a drive wheel electric motor. The electric motor in series hybrid solutions is driven in a similar manner as described above, which is why the above principle can also be used in this type of vehicle with the only difference that no gear needs to be selected as the electric motor in series hybrid vehicles is often connected directly to a final drive such as a differential.

The invention is also applicable to vehicles where one or more electric motors directly drive the vehicle's drive wheels without an intermediate gear, as well as to pure electric vehicles.

Claims (12)

10 15 20 25 30 18 Patent claims A method of propelling a vehicle at the start of said vehicle on a ground, said vehicle comprising at least one drive wheel for propelling said vehicle and said vehicle comprising an electric motor, and said electric motor being arranged to generate a on said drive wheel propulsion torque, characterized in that the method comprises the steps of: - a) applying by means of said electric motor a torque propulsion on said drive wheel in a first direction, - b) determining a representation of said drive wheel grip against said ground, and - c) reversing the direction of rotation of said electric motor to apply a torque propelling on said drive wheel in a direction opposite to said first direction when said representation of the grip against the base of said drive wheel meets a first criterion. A method according to claim 1, wherein said first criterion is a determination of whether said drive wheel has lost grip against said ground. A method according to claim 1 or 2, wherein said representation of the grip against the ground constitutes a rotational speed of said drive wheel. A method according to any one of claims 1-3, wherein said first criterion is a determination of whether a rotational speed of said drive wheel has reached a first speed. A method according to any one of claims 1-4, wherein said first criterion is a determination of whether a rotational speed difference between said drive wheels and at least one non-driving wheel arranged on the vehicle exceeds a first value. A method according to any one of claims 1-5, wherein said representation of a rotational speed of said drive wheels includes a plurality of parameter values representing rotational speeds of said drive wheels at different times. The method of claim 6, wherein said first criterion is a determination of a change in said rotational speed of said drive wheel between two consecutive times. A method according to any one of claims 1-7, wherein steps b) and c) are repeated until a second criterion is met. Method according to claim 8, wherein said second criterion consists of something from the group: - the method is interrupted by a vehicle driver; a control unit arranged in the vehicle detects that further repetition of steps b) and c) is not required for continued propulsion of the vehicle. A method according to any one of claims 1-9, wherein the electric motor is connected to said drive wheel via a conventional gearbox. A system for propelling a vehicle at the start of said vehicle, said vehicle comprising at least one drive wheel for propelling said vehicle and said vehicle comprising an electric motor, and said electric motor being arranged to generate a torque propelling on said drive wheel, characterized in that the system comprises means for: - by means of said electric motor applying a torque propelling on said drive wheel in a first direction, - determining a representation of a grip against the base of said drive wheel, and - reversing the direction of rotation of said electric motor for applying a torque propelling on said drive wheel in a direction opposite to said first direction when said grip against the base of said drive wheel meets a first criterion. Vehicle, characterized in that it comprises a system according to claim 11.