Method for braking a vehicle comprising an electric drive motor and a mechanical brake, computing unit and computer program

Abstract

The invention relates to a method for braking a vehicle (10) comprising an electric drive motor (14) and a mechanical brake (16, 17) until the vehicle is stationary and subsequently ensuring the vehicle remains stationary, wherein the electric drive motor (14) and an actuator for operating the mechanical brake (16, 17) are actuated such that a braking torque is generated by means of the electric drive motor (14) in a first braking phase, a braking torque is generated by means of the mechanical brake (16, 17) in a second braking phase, a start of the first braking phase takes place before a start (t2) of the second braking phase, an end (t1) of the first braking phase takes place after the start (t2) of the second braking phase, the end (t1) of the first braking phase takes place after the stationary state is achieved (t0), and the start (t2) of the second braking phase takes place before, during or after the stationary state is achieved (t0), depending on a tripping condition.

Description

[0001] Description

[0002] title

[0003] Method for braking a vehicle with an electric drive motor and a mechanical brake, computing unit and computer program

[0004] The present invention relates to a method for braking a vehicle with an electric drive motor and a mechanical brake as well as a computing unit and a computer program for carrying out the method.

[0005] Background of the invention

[0006] Various technical devices are available for braking a vehicle, for example wheel brakes or electric motors, which are either operated as generators so that a braking magnetic field is induced in the coil of the electric motor, or which are specifically energized so that the electric motor is subjected to a torque that decelerates the vehicle.

[0007] The control of electric motors in vehicles is usually based on a target torque as a reference variable. Since electric motors can provide both a positive and a negative torque regardless of the direction of rotation, the problem arises in the low speed range of precisely setting a specific position or speed of the electric motor. In this case, it must be ensured that at no time is a torque generated that would accelerate the vehicle in the opposite direction to the desired direction of movement. If, for example, it is desired to brake the vehicle to a standstill using the electric motor, it must be ensured that reversing does not occur immediately after coming to a standstill, which would be initiated by a corresponding torque from the electric motor.Vehicle standstill is typically detected based on an evaluation of the vehicle speed, while the vehicle speed, in turn, is derived from the wheel speed. Incremental encoders are typically used for this purpose, so the vehicle speed signal is only available as a discontinuous function. Due to this measurement inaccuracy and the fact that latencies exist during signal processing, using the wheel speed as an input variable for controlling the vehicle speed is unsuitable at low speeds, especially at speeds close to zero.

[0008] To improve this, DE 10 2019 205 180 A1 presents a method for braking a vehicle comprising an electric drive motor, wherein the vehicle is brought to a standstill using a speed control of the electric drive motor.

[0009] Disclosure of the invention

[0010] According to the invention, a method for braking a vehicle with an electric drive motor and a mechanical brake, as well as a computing unit and a computer program for implementing the method, are proposed, having the features of the independent patent claims. Advantageous embodiments are the subject of the dependent claims and the following description.

[0011] The invention specifically relates to a method for braking a vehicle with an electric drive motor and a mechanical brake to a standstill and then holding it at a standstill. In a first braking phase, a braking torque is generated by the electric drive motor, and in a second braking phase, a braking torque is generated by the mechanical brake.

[0012] The invention particularly relates to the interaction between the electric drive motor and the mechanical brake when the vehicle is stopped and at a standstill. The invention allows for the reduction of unintended vehicle movements during braking and / or when the vehicle is at a standstill, the reduction or prevention of wear and damage to the electric drive motor, and the improvement of comfort during braking maneuvers near or to a standstill.

[0013] If a vehicle is braked by an electric drive motor and held stationary, the motor must be continuously powered and support the existing torque, e.g., when driving downhill. This consumes energy and wears the components involved. Within the scope of the invention, a mechanical brake takes over this task at a specific point during a braking process, reducing wear and preventing damage to the drive motor components.

[0014] For this purpose, the electric drive motor and an actuator for actuating the mechanical brake are controlled in such a way that the start of the first braking phase is before the start of the second braking phase, the end of the first braking phase is after the start of the second braking phase, and the end of the first braking phase is after the standstill is reached.

[0015] Furthermore, the electric drive motor and the actuator for actuating the mechanical brake are controlled in such a way that the start of the second braking phase occurs before, during, or after the vehicle has reached a standstill, depending on a trigger condition. In other words, depending on the trigger condition, there are three ways the brakes can be actuated to ensure a comfortable yet safe stopping and holding process.

[0016] The invention thus allows, in particular, the vehicle to be safely braked and held in place even in the event of a malfunction or overload of the electric drive motor. For example, if the electric drive motor is unable to provide the required torque to decelerate or hold the vehicle, the mechanical brake can take over. The invention can be used in any vehicle with an electric drive motor with a separate braking system.

[0017] A computing unit according to the invention, e.g. a control unit of a vehicle, is configured, in particular in terms of programming, to carry out a method according to the invention.

[0018] The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, since this entails particularly low costs, in particular if an executing control unit is also used for other tasks and is therefore already present. Finally, a machine-readable storage medium is provided with a computer program stored thereon, as described above. Suitable storage media or data carriers for providing the computer program are, in particular, magnetic, optical, and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs, and others. Downloading a program via computer networks (Internet, intranet, etc.) is also possible. Such a download can be wired or cable-based or wireless (e.g., via a WLAN network, a 3G, 4G, 5G, or 6G connection, etc.).

[0019] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0020] The invention is illustrated schematically in the drawing using exemplary embodiments and is described below with reference to the drawing.

[0021] Short description of the drawings

[0022] Figure 1 shows a schematic representation of a vehicle configured to implement an embodiment of the method according to the invention; Figures 2 to 4 show different curves of vehicle speed and the operating state of the engine brake and the mechanical brake during exemplary stopping processes according to embodiments of the invention.

[0023] Embodiment(s) of the invention

[0024] Figure 1 shows a schematic representation of a vehicle 10 that is configured to carry out an embodiment of the method according to the invention. The vehicle 10 comprises a control unit 12, which can in particular be the control unit of a power electronics system. The vehicle 10 further comprises an electric drive motor 14 that is configured to drive at least one wheel 11 of the vehicle 10. A sensor device 15 is arranged on the electric drive motor 14 such that the sensor device 15 detects an angular position and / or a rotational speed of the electric drive motor 14 and transmits it to the control unit 12. The control unit 12 is connected to the electric drive motor 14 via a signal line, so that the electric drive motor 14 can be regulated and / or controlled by the control unit 12.The system can also be extended to include multiple drive motors, so that in addition to the drive motor, 14 additional ones can be controlled and used for deceleration.

[0025] The vehicle 10 further comprises mechanical brakes 16, 17, here for example in the form of a hydraulic service brake 16 and a mechanical parking brake 17. In the example shown, both have actuators that can be controlled by the control unit 12, so that they can be activated without intervention by the driver and can, for example, provide a so-called hill hold or auto hold function.

[0026] For example, if a driver wants to bring the vehicle to a standstill, they typically press the brake pedal. Alternatively, braking can also be initiated by an assistance system. Within the scope of one embodiment, the braking process is initially carried out using only the drive motor 14, i.e., using an electric engine brake, as described below, coherently and comprehensively, by way of example, with reference to the figures.

[0027] Figures 2 to 4 show exemplary stopping processes, each in the form of a graph, in which vehicle speed v, activation state 201, 301, 401 of the electric engine brake and activation state 202, 302, 402 of the mechanical brake are plotted against time t. If the electric engine brake is active, this means that a braking torque is generated by the electric drive motor 14. If the mechanical brake is active, this means that a braking torque is generated by the mechanical brake. Both are initiated by appropriate control by the computing unit 12, i.e. the electric drive motor and an actuator for actuating the mechanical brake 16, 17 are controlled by the computing unit 12 in such a way that the curves shown in Figures 2 to 4 result.

[0028] It can be seen that braking occurs in a deceleration phase until time to, and then the speed is zero, ie the vehicle is stationary.

[0029] Furthermore, it can be seen that in a first braking phase up to time h the electric motor brake is active, and that in a second braking phase from time t2 the mechanical brake is active, and that the mutual position of times t1 and t2 varies in Figures 2 to 4.

[0030] All figures show that the second braking phase begins (t2) before the first braking phase ends (ti). This ensures that a braking torque is applied at all times, allowing the vehicle to be safely decelerated and held in place.

[0031] Figure 2 shows an embodiment in which the second braking phase begins before standstill (at t0) is reached. This variant can be selected in the event that a malfunction of the electric drive motor 12 is detected, or it is detected that the required braking torque cannot be provided by the electric drive motor (e.g., because in both cases the deceleration is not as expected). This variant can also be used to blend the braking torques regardless of a malfunction of the drive motor.

[0032] This variant can be selected as an alternative or in addition to the speed-dependent mode, meaning the second braking phase begins when a speed threshold, e.g., 1-2 km / h, is reached or undercut. This allows for better control of the approach to a standstill, ie, the low-speed range.

[0033] Figure 3 shows an embodiment in which the second braking phase begins immediately upon reaching a standstill (at t0). This allows the vehicle to be held with the mechanical brake right from the start, reducing wear and strain on the electric motor brake. This variant can be selected if electrical holding of the vehicle is not desired, for example, if the thermal load on the drive motor is excessive.

[0034] Figures 2 and 3 show variants in which the vehicle 10 is held at a standstill by the mechanical brake, so that the electric drive motor in particular does not have to support any (significant) torque and is therefore not or hardly loaded. Figure 4, on the other hand, shows an embodiment in which the second braking phase only begins after the standstill has already lasted a time 403. This variant is selected if the electric drive motor is initially intended to hold the vehicle at a standstill before the mechanical brake takes over. This is expedient in order to achieve the greatest possible comfort during the stopping process, since, in contrast to friction brakes, there is no change from sliding friction to static friction when transitioning from deceleration to standstill. Electrical stopping thus reduces the change in acceleration, the jerk, until a standstill.The duration 403 of the electrical stop can depend on the limitation of the component protection, i.e. it is ended in particular before thermal overload, etc. occurs. The absence of the driver can also cause the electrical stop to end, since permanent standstill protection is not possible with the drive motor and, in the absence of the driver, this can only be ensured with a mechanical brake. Should a fault occur in the drive motor which impairs or makes electrical holding impossible, the mechanical brake can be used as a fallback system and thus standstill can be ensured. Malfunctions of the drive motor and the primarily controlled mechanical brake can only be intercepted by the intervention of an additional braking device such as the parking brake, or the driver must actively ensure standstill through their intervention.

[0035] If, in the meantime, the driver requests torque again while the vehicle is at a standstill before the second braking phase is started, it is advisable not to start the second braking phase again, but to take the driver's request into account.

Claims

Claims 1. A method for braking a vehicle (10) having an electric drive motor (14) and a mechanical brake (16, 17) to a standstill and holding it at a standstill, wherein the electric drive motor (14) and an actuator for actuating the mechanical brake (16, 17) are controlled such that in a first braking phase a braking torque is generated by means of the electric drive motor (14), in a second braking phase a braking torque is generated by means of the mechanical brake (16, 17), a start of the first braking phase is before a start (t2) of the second braking phase, an end (h) of the first braking phase is after the start (t2) of the second braking phase, the end (h) of the first braking phase is after the standstill is reached (t0), and the start (t2) of the second braking phase is before, at or after the standstill is reached (t0), depending on a triggering condition.

2. Method according to claim 1, wherein the electric drive motor (14) and the actuator for actuating the mechanical brake (16, 17) are controlled such that the start (t2) of the second braking phase for a triggering condition that the electric drive motor (14) does not generate sufficient braking torque is before the standstill is reached (to).

3. Method according to claim 1 or 2, wherein the electric drive motor (14) and the actuator for actuating the mechanical brake (16, 17) are controlled such that the start (t2) of the second braking phase for a triggering condition that the vehicle (10) reaches a certain speed threshold is before the standstill is reached (to).

4. Method according to one of the preceding claims, wherein the electric drive motor (14) and the actuator for actuating the mechanical brake (16, 17) are controlled such that the start (t2) of the second braking phase for a triggering condition that the electric drive motor (14) generates a sufficient braking torque is when the standstill is reached (to).

5. Method according to one of the preceding claims, wherein the electric drive motor (14) and the actuator for actuating the mechanical brake (16, 17) are controlled such that the start (t2) of the second braking phase for a triggering condition that a permanent standstill is required to avoid thermal stress is after the standstill has been reached (to).

6. Method according to one of the preceding claims, wherein the electric drive motor (14) and the actuator for actuating the mechanical brake (16, 17) are controlled such that the start (t2) of the second braking phase for a triggering condition that a permanent secured standstill is required in the absence of the driver is after the standstill has been reached (to).

7. Method according to one of the preceding claims, wherein the electric drive motor (14) and the actuator for actuating the mechanical brake (16, 17) are controlled such that the start (t2) of the second braking phase for a triggering condition that a fault in the drive motor impairs or makes impossible the electrical holding of the vehicle is after the standstill has been reached (to).

8. Method according to one of the preceding claims, wherein the electric drive motor (14) and the actuator for actuating the mechanical brake (16, 17) are controlled such that the start (t2) of the second braking phase for a triggering condition that a fault of the drive motor and the brake cannot ensure standstill and the driver is not absent, after reaching (to) standstill.

9. A computing unit (12) which is designed to carry out all the process steps of a To carry out the method according to one of the preceding claims.

10. Vehicle (10) with an electric drive motor (14), a mechanical brake (16, 17) and a computing unit (12) according to claim 9.

11. Computer program which causes a computing unit to carry out all method steps of a method according to one of claims 1 to 8 when it is executed on the computing unit.

12. A machine-readable storage medium having a computer program according to claim 11 stored thereon.

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