Apparatus and method for controlling brake torque and at least partially electrically powered vehicle

Abstract

The present invention relates to regenerative deceleration of at least partially electrically powered vehicles. To this end, it is intended to determine the minimum number of revolutions of the wheel at which regenerative deceleration should take place from parameters such as the vehicle speed and the friction value between the tire and the roadway, so that the regenerative deceleration of the vehicle can be adjusted based on this minimum number of revolutions.

Description

[Technical Field]

[0001] The present invention relates to a device and a method for controlling braking torque, in particular for regenerative deceleration, and further to an at least partly electrically driven vehicle having such a device. [Background technology]

[0002] Fully or at least partially electrically powered vehicles are becoming increasingly important. These types of vehicles are equipped with an electric drive system that can drive the vehicle using the electrical energy of a traction battery. In addition, such electric drive systems can also be operated in generator mode. In this case, the kinetic energy of the vehicle is converted by an electric machine into electrical energy. This electrical energy can be used to charge the vehicle's traction battery.

[0003] A typical braking strategy for electric vehicles aims to limit the braking torque generated by the electric machine. For example, US Pat. No. 5,623,999 proposes limiting the braking torque generated by the electric machine applied to the rear axle of the vehicle so that the slip applied at the wheels of the rear axle does not exceed a predetermined limit value. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] German Patent Application Publication No. 102012217679 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides a device for controlling the braking torque and an at least partly electrically driven vehicle having the features of the independent claims. Further preferred embodiments are the subject of the dependent claims. [Means for solving the problem]

[0006] It contemplates the following:

[0007] An apparatus for controlling the brake torque of an at least partially electrically driven vehicle has at least one first processing module and a second processing module, and a control device. The first processing module is designed to determine an actual speed of the vehicle. The second processing module is designed to determine a friction value between the roadway and the vehicle's tires. The control device is designed to determine a minimum number of revolutions for the wheels of an axle of the vehicle. In particular, the control device can determine the minimum number of revolutions for the wheels of the axle using the determined actual speed and the determined friction value. Furthermore, the control device is designed to output a request for regenerative deceleration of the vehicle. The request can then be output using the determined minimum number of revolutions for the wheels of the axle.

[0008] Additionally, the following is contemplated:

[0009] An at least partly electrically driven vehicle having an electric drive system and a device according to the invention for controlling the brake torque.

[0010] Finally, it is contemplated that:

[0011] A method for controlling regenerative braking torque of an at least partially electrically powered vehicle, comprising determining an actual vehicle speed and determining a friction value between a roadway and the vehicle's tires. The method further includes determining a minimum number of revolutions for the wheels of an axle of the vehicle. In particular, the minimum number of revolutions for the wheels of the axle can be determined using the determined actual speed and the friction value. The method further includes regeneratively decelerating the vehicle, the deceleration of the vehicle being performed using the determined minimum number of revolutions for the wheels of the axle. [Effects of the Invention]

[0012] The present invention is based on the finding that the electric drive system of an at least partially electrically driven vehicle can also be used to decelerate the vehicle. However, conventional operating strategies for decelerating the vehicle limit the maximum regenerative braking torque to ensure vehicle stability during the braking process. This means that, precisely when the braking demand becomes stronger, a large portion of the braking torque must continue to be embodied through mechanical, especially hydraulic, brake components.

[0013] The idea of ​​the present invention is therefore to provide a concept that allows as much of the required braking torque as possible to be realized by regenerative deceleration of the electric drive system. To this end, the present invention aims to determine a stability-related parameter, such as the friction value between the tires and the roadway, and from this determine an appropriate value for slip, i.e., the difference between the wheel speed and the vehicle speed. In this way, the maximum braking torque for regenerative deceleration of the vehicle can be increased without jeopardizing driving stability during the braking process.

[0014] For example, the current actual speed of the vehicle can be determined using sensors present in the vehicle or using information from control components of the vehicle. Furthermore, for example, the friction value between the vehicle's tires and the roadway can be determined based on slip monitoring. Such a determination of the friction value can be derived, for example, from a comparison of the vehicle's actual speed and the current wheel rotation speed while the vehicle is driving. However, in principle, any other approach for determining the slip or friction value is also possible.

[0015] Subsequently, the maximum allowable wheel slip and, therefore, the minimum wheel rotation speed permitted during braking can be determined from the current friction value between the roadway and the vehicle's tires and from the current vehicle speed. Subsequently, the deceleration of the vehicle can be controlled by regenerative braking on the drive axle so that the minimum rotation speed is not exceeded. In this way, vehicle stability can be ensured even during regenerative braking.

[0016] If the required or desired braking torque is greater than the maximum braking torque that can be achieved by such a regenerative braking process, the remaining required braking torque can be realized on another axle, for example, by a mechanical or hydraulic brake system, thereby enabling a reliable and stable deceleration of the vehicle with maximum regenerative braking power.

[0017] In one embodiment, the device for controlling the brake torque includes a third processing module. This third processing module is designed to determine the slip angle of the vehicle. In this case, the control device can also be designed to use the determined slip angle to determine the minimum number of rotations for the wheels of the vehicle axle. This method can also take into account disturbances due to vehicle drift, i.e., disturbances due to the vehicle's motion vector that are different from the direction of travel of the wheels. In this way, stability during the braking process can be further improved.

[0018] In one embodiment, the control device is designed to receive a request for a brake torque to be adjusted. The control device may further be designed to adjust the distribution of the brake torque to each axle of the vehicle using the determined friction value. For example, the brake torque at each axle of the vehicle can be adjusted so that a minimum wheel rotation speed condition is met during regenerative braking depending on the determined friction value.

[0019] In one embodiment, the control device is designed to determine the maximum braking torque for one of the vehicle's axles using the determined friction value. This maximum braking torque can be determined specifically for the drive axle that is to be decelerated by regenerative braking depending on the determined minimum rotational speed of the wheels of the axle. Furthermore, in this case, the control device can be designed to determine the distribution of the braking torque to each axle of the vehicle using the maximum braking torque for these axles of the vehicle. In other words, the distribution of the braking power to the individual axles is performed so that the determined maximum braking torque for regenerative braking at the corresponding axle is not exceeded.

[0020] In one embodiment, the control device is designed to determine the maximum braking torque for one of the vehicle's axles using the maximum possible regenerative braking power. The maximum possible regenerative braking power may be limited, for example, by the maximum power output of the electric machine at that axle. Furthermore, for example, a high state of charge or operating temperature of the traction battery may also limit the maximum charging power of the traction battery and thus the maximum electric braking power. Accordingly, these types of basic conditions can also be taken into account when distributing the braking power.

[0021] In one embodiment, the control device adjusts the braking torque at one axle of the vehicle for which a maximum braking torque has been determined so as not to exceed this maximum braking torque. The control device can then adjust the remaining percentage of the required braking torque at other axles of the vehicle. For example, the percentage of the required braking torque that cannot be achieved by regenerative braking at the axle can be implemented at the other axle by mechanical or hydraulic braking.

[0022] In one embodiment, the second processing module is designed to determine the slip between the vehicle's wheels and the roadway. The second processing module can then use this slip to determine a friction value. The slip can be determined, for example, from the difference between the vehicle's current actual speed and the current wheel speed.

[0023] The above-described embodiments and developments can be combined with one another in any way that is meaningful. Further embodiments, developments and realizations of the invention also include combinations of the inventive features described above or below with reference to the examples, but not explicitly mentioned. In particular, those skilled in the art will also add individual aspects as improvements or supplements to the respective basic aspects of the invention.

[0024] Further features and advantages of the present invention will be explained below with reference to the drawings, in which: [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a principle diagram illustrating a vehicle having a device for controlling brake torque according to one embodiment; [Figure 2] FIG. 1 is a schematic diagram showing a block diagram of an apparatus for controlling braking torque, according to one embodiment. [Figure 3] 1 is a flowchart underlying a method for controlling brake torque according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0026] 1 shows a schematic diagram of a vehicle according to one embodiment, in particular an at least partially electrically driven vehicle 1. The vehicle 1 includes four wheels R1 to R4. Here, two wheels R1, R2 are arranged on a first axle A1, and two other wheels R3, R4 are arranged on a second axle A2. For example, the first axle A1 can be the front axle of the vehicle 1, and the second axle can be the rear axle of the vehicle 1. However, the reverse arrangement is also possible in principle.

[0027] Each wheel R1, R2, R3, R4 is provided with a braking device B1, B2, B3, B4, which may be, for example, a hydraulic or electromechanical braking device.

[0028] Furthermore, the vehicle 1 includes an electric drive system 20. The electric drive system 20 may include, for example, an electric machine, a power converter, and an electric energy source, for example, a traction battery. To drive the vehicle 1, the electric DC voltage of the traction battery may be converted by the power converter into a single-phase or multi-phase AC voltage and provided to the electric machine.

[0029] Furthermore, the electric machine can convert the vehicle's kinetic energy into electrical energy, which can be converted by a power converter into a DC voltage to charge the traction battery, a process known as regenerative braking.

[0030] Furthermore, the vehicle 1 includes a device 10 for controlling the brake torque, in particular for controlling the regenerative braking of the vehicle. As will be explained in more detail below, the device 10 for controlling the brake torque processes a number of parameters for this purpose and is able to control the regenerative braking on the basis of these parameters. In this way, it is possible, on the one hand, to maintain vehicle stability during regenerative braking and, on the other hand, to convert as high a proportion as possible of the vehicle's kinetic energy into electrical energy.

[0031] 2 shows a principle diagram of an apparatus 10 for controlling a braking torque according to one embodiment. The apparatus 10 may include a first processing module 11, which is designed for example to determine the current actual speed of the vehicle 1. To this end, the first processing module 11 may receive, for example, sensor values ​​of sensors of the vehicle 1 and / or may receive information from one or more control modules of the vehicle.

[0032] Furthermore, the device 10 for controlling the brake torque can include a second processing module 12 designed to determine a friction value between the vehicle's tires and the underlying roadway. For this purpose, the current slip of the vehicle's wheels can be evaluated. For example, the current wheel speed, i.e., the speed of the tire's outer surface in contact with the roadway, can be compared with the current actual speed of the vehicle 1. If necessary, the current drive torque at the corresponding wheel can also be taken into account for determining the current friction value. In addition to this, any other suitable parameters can, of course, also be taken into account for determining the friction value.

[0033] Furthermore, the device 10 for controlling the braking torque may include a third processing module 13 for determining the slip angle of the vehicle. Any suitable vehicle parameters, sensor values, control data, etc. may be evaluated for this purpose. The slip angle may be considered to be the difference between the motion vector of the vehicle 1 and the alignment or direction of travel of the vehicle 1 depending on the wheel position.

[0034] The data determined by the processing modules 11, 12, 13 regarding the actual speed, friction value, and slip angle can be provided to the control device 14, which can use this data to determine the maximum permissible slip for the wheels or the corresponding minimum wheel rotation speed during braking. For each of the above-mentioned parameters, such as the actual speed, friction value, slip angle, and possibly other parameters, a tabular or functional relationship can be specified, from which the maximum permissible slip or the minimum wheel rotation speed can be derived during braking. The corresponding data can be stored in the memory of the respective processing modules 11, 12, 13 or of the control device 14 in the form of a look-up table, parameters of a formula, or any other suitable form.

[0035] Subsequently, based on this minimum wheel speed, the regenerative braking / deceleration of the vehicle 1 can be controlled, whereby a maximum braking torque can be adjusted at the vehicle axle A2 linked to the electric drive system 10 that does not violate the minimum wheel speed requirement.

[0036] In some cases, further basic conditions may also be taken into consideration. For example, the maximum braking torque of the electric drive system may be limited by characteristics such as the maximum power output of the electric machine and / or the electric current converter. In addition, the characteristics of the traction battery, which is charged during regenerative braking, may also limit the maximum regenerative braking power. For example, a high traction battery state of charge or a very high or very low operating temperature of the traction battery may limit the maximum charging power of the traction battery. Naturally, other operating conditions that limit the maximum regenerative charging power may also be taken into consideration.

[0037] If the vehicle 1 is to be decelerated with a braking torque greater than the maximum braking power that can be achieved by regenerative braking based on the basic conditions described above, the vehicle 1 can also be braked additionally by the braking elements B1, B2, B3, B4. In addition, the braking elements B1, B2, B3, B4 can also be used to ensure that driving stability can continue to be maintained during deceleration of the vehicle 1. For this purpose, conventional stability systems such as ABS, ESP, etc. can be used.

[0038] If the regenerative braking based on the settings described above does not allow the required braking torque to be fully applied on axle A2, the braking torque on each of the other axles A1 can be adjusted, for example, so that the required braking torque is fully achieved in total.

[0039] In some cases, the user can be informed about the distribution of the braking torque between regenerative braking and mechanical braking during the braking of the vehicle. For example, the user can be notified if the required braking torque cannot be fully achieved by regenerative braking. In this way, the user can optionally adapt his / her driving behavior in response to this, thereby increasing efficiency by using as high a proportion of regenerative braking as possible.

[0040] 3 shows a flow chart underlying a method for controlling a regenerative braking torque according to one embodiment, which method can in principle include any of the steps already described above in connection with the device 10 for controlling a braking torque. Similarly, the device 10 for controlling a braking torque described above can also include any of the components required for the implementation of the method described below.

[0041] In step S11, the actual speed of the vehicle 1 can be determined.

[0042] In step S12, the friction value between the roadway and the tires of the vehicle 1 can be determined.

[0043] In step S13, the slip angle of the vehicle 1 can optionally be determined.

[0044] In step S20, a determination is made of the minimum rotational speed for the wheels R3, R4 of the axle A2 of the vehicle 1. The minimum rotational speed can be determined in particular using the determined actual speed and friction values, and possibly also using the slip angle of the vehicle 1.

[0045] Finally, in step S30, the vehicle 1 is regeneratively decelerated using the determined minimum rotational speed of the wheels R3, R4 of the axle A2.

[0046] If the required braking torque cannot be achieved entirely by regenerative deceleration of the vehicle 1, the remaining proportion of the required braking torque can be achieved by braking the wheels R1, R2 of the vehicle's other axle A1.

[0047] In summary, the present invention relates to regenerative deceleration of an at least partially electrically driven vehicle, for which it is intended to determine, from parameters such as the vehicle speed and the friction value between the tire and the roadway, a minimum number of revolutions for the wheels at which regenerative deceleration should occur, and then the regenerative deceleration of the vehicle can be adjusted based on this minimum number of revolutions. [Explanation of symbols]

[0048] 1 vehicle 10 equipment 11 First Processing Module 12 Second Processing Module 13 Third Processing Module 14 Control Devices 20 Electric Drive System A1, A2, A3, A4 axles R1, R2, R3, R4 wheels S11 Actual speed determination S12 Friction value determination S13 Slip angle determination S20 Determining the minimum rotation speed S30 Regenerative Deceleration

Claims

1. A device (10) for controlling the brake torque of an at least partially electrically driven vehicle (1), comprising: a first processing module (11) designed to determine the actual speed of the vehicle (1); a second processing module (12) designed to determine the friction value between the roadway and the tires of said vehicle (1); a control device (14) designed to determine a minimum number of revolutions for the wheels (R3, R4) of the axle (A2) of the vehicle (1) using the determined actual speed and the determined friction value, and to output a request for regenerative deceleration of the vehicle (1) using the determined minimum number of revolutions for the wheels (R3, R4) of the axle (A2).

2. a third processing module (13) designed to determine the slip angle of the vehicle (1), 2. The apparatus (10) according to claim 1, wherein the control device (14) is designed to determine a minimum number of rotations for the wheels (R3, R4) of the axle (A2) of the vehicle (1) by further utilizing the determined slip angle.

3. 3. The apparatus (10) according to claim 1 or 2, wherein the control device (14) is designed to receive a request for a brake torque to be adjusted and to adjust the distribution of the brake torque to a plurality of axles (A1, A2) of the vehicle (1) using the determined friction value.

4. 4. The apparatus (10) of claim 3, wherein the control device (14) is designed to use the determined friction value to determine a maximum braking torque for one of the axles (A2) of the vehicle (1) and to use the maximum braking torque at the axle (A2) of the vehicle (1) to determine a distribution of the braking torque to the multiple axles (A1, A2) of the vehicle.

5. 5. The apparatus (10) according to claim 4, wherein the control device (14) is designed to determine a maximum braking torque for one of the axles (A2) of the vehicle (1) using a maximum possible regenerative braking power.

6. 6. The device (10) according to claim 3, wherein a braking torque not exceeding the maximum braking torque is adjusted at the axle (A2) of the vehicle (1) for which a maximum braking torque has been determined, and the remaining proportion of the required braking torque is adjusted at the other axle (A1) of the vehicle (1).

7. 7. The device (10) according to any one of claims 1 to 6, wherein the second processing module (12) is designed to determine a slip between the wheels of the vehicle (1) and the roadway and to use the slip to determine a friction value.

8. In an electrically driven vehicle (1), an electric drive system (20); A device (10) for controlling a braking torque according to any one of claims 1 to 7, and an electrically driven vehicle having the same.

9. A method for controlling regenerative braking torque for an at least partially electrically driven vehicle (1), comprising the steps of: The actual speed of the vehicle (1) is determined (S11), The friction value between the roadway and the tires of the vehicle (1) is determined (S12), Using the determined actual speed and friction value, a minimum rotation speed is determined (S20) for the wheels (R3, R4) of the axle (A2) of the vehicle (1); The vehicle (1) is regeneratively decelerated (S30) using the determined minimum number of rotations of the wheels (R3, R4) of the axle (A2).

10. A step (S13) of determining a slip angle of the vehicle (1), 10. The method of claim 9, further utilizing the determined slip angle to determine a minimum number of revolutions for the wheels (R3, R4).

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