Method, computing unit and computer program for braking vehicle having electric drive motor and mechanical brake

Abstract

The invention relates to a method for braking a vehicle (10) having an electric drive motor (14) and a mechanical brake (16, 17) to a stationary state and then ensuring the stationary state, in which the electric drive motor (14) and an actuator for actuating the mechanical brake (16, 17) are actuated such that, in a first braking phase, the electric drive motor (14) and the actuator are actuated by the mechanical brake (16, 17). Generating a braking torque 10 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); the first braking phase begins before the start (t2) of the second braking phase; the first braking phase ends (t1) after the start (t2) of the second braking phase; the first braking phase ends (t1) after reaching (t0) a rest state; furthermore, the second braking phase starts (t2) before reaching (t0) the rest state, when reaching the rest state or after reaching the rest state according to the triggering condition.

Description

Technical Field

[0001] The invention relates to a method for braking a vehicle having an electric drive motor and a mechanical brake, as well as to a computing unit for carrying out the method and to a computer program for carrying out the method. Background Art

[0002] Various technical devices are available for braking a vehicle, such as wheel brakes or electric motors which are either operated as generators so that a braking magnetic field is induced in the coils of the electric motor or which are energized in a targeted manner so that they are loaded with a torque which decelerates the vehicle.

[0003] The regulation of electric motors in vehicles is usually based on a target torque as a reference variable. Since electric motors can provide both positive and negative torques regardless of the direction of rotation, there is the problem of accurately setting a specific position or speed of the electric motor in the low speed range. In this case, it must be ensured that no torque is generated at any time that would accelerate the vehicle against the desired direction of movement. For example, if it is desired to brake the vehicle to a standstill with the aid of the electric motor, it must be ensured that reversing does not occur immediately after the standstill due to the corresponding torque of the electric motor.

[0004] The detection of a vehicle's stationary state is usually based on an evaluation of the vehicle speed, which in turn is derived from the wheel speed. For this purpose, an incremental encoder is usually used, so that the vehicle's speed signal is only available as a discontinuous function. Due to the fact that this measurement is inaccurate and there are time delays in signal processing, using the wheel speed as an input variable to control the vehicle's speed in the low speed range, especially at speeds close to zero, is not suitable.

[0005] For the purpose of improvement, DE 10 2019 205 180 A1 proposes a method for braking a vehicle comprising an electric drive motor, wherein the vehicle is brought to a standstill using speed control of the electric drive motor. Summary of the invention

[0006] According to the invention, a method for braking a vehicle having an electric drive motor and a mechanical brake, as well as a computing unit for carrying out the method and a computer program for carrying out the method are proposed, having the features of the independent patent claims. Advantageous embodiments are the subject matter of the dependent claims and the subsequent description.

[0007] The invention relates in particular to a method for braking a vehicle having an electric drive motor and a mechanical brake to a standstill and then holding it in the standstill, wherein in a first braking phase a braking torque is generated by means of the electric drive motor and in a second braking phase a braking torque is generated by means of the mechanical brake.

[0008] The invention relates in particular to the interaction between the electric drive motor and the mechanical brake when the vehicle is parked and when the vehicle is at a standstill. The invention allows: reducing unintended vehicle movements when braking the vehicle and / or when the vehicle is at a standstill; reducing or avoiding wear and damage to the electric drive motor; and improving comfort during braking maneuvers when approaching or reaching a standstill.

[0009] If the vehicle is braked and held stationary by means of an electric drive motor, it must be continuously energized and support the available torque, for example downhill traction. This consumes energy and causes wear on the associated equipment. Within the scope of the present invention, this is now taken over by a mechanical brake at a certain point during the braking process, which reduces wear and prevents damage to the drive motor components.

[0010] For this purpose, the electric drive motor and the actuator for actuating the machinery brake are controlled such that: the first braking phase begins before the second braking phase begins; the first braking phase ends after the second braking phase begins; and the first braking phase ends after reaching a standstill.

[0011] Furthermore, the electric drive motor and the actuator for actuating the mechanical brake are controlled so that, depending on the triggering condition, the second braking phase begins before, when or after reaching a standstill. In other words, depending on the triggering condition, there are options as to how the brakes can be actuated in order to bring about a comfortable but still safe parking and stopping process.

[0012] Thus, the present invention allows in particular: even in the case of a fault or overload of the electric drive motor, the vehicle can be safely braked and brought to a standstill. If the electric drive motor, for example, cannot provide the torque required for braking or stopping the vehicle, the mechanical brake can take over this.

[0013] The invention can be used in any vehicle having an electric drive motor with an independent braking system.

[0014] A computing unit according to the present invention, for example a control unit of a vehicle, is designed, in particular programmed, to carry out the method according to the present invention.

[0015] In particular, when the executed control device is also used for other tasks and thus always exists, the implementation scheme in the form of a computer program or computer program product with a program code for executing all method steps according to the method of the present invention is also advantageous, because this causes particularly low costs. Finally, a machine-readable storage medium is provided, on which a computer program as described above is stored. In particular, storage media or data carriers suitable for providing the computer program are magnetic storage, optical storage and electrical storage, such as hard disks, flash memories, EEPROMs, DVDs and others, etc. It is also feasible to download the program via a computer network (Internet, intranet, etc.). Here, this download can be implemented in a wired manner or in a cable manner or in a wireless manner (for example, via a WLAN network, 3G, 4G, 5G or 6G connection, etc.).

[0016] Further advantages and embodiments of the invention are apparent from the description and the accompanying drawings.

[0017] The invention is schematically illustrated in the drawings based on exemplary embodiments and is described below with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram of a vehicle which is set up to carry out an exemplary embodiment of the method according to the invention is shown;

[0019] Figures 2 to 4 Different curves are shown for the vehicle speed and the operating states of the engine brake and the mechanical brake during an exemplary parking process according to an embodiment of the present invention. DETAILED DESCRIPTION

[0020] Figure 1 A schematic diagram of a vehicle 10 configured to carry out an embodiment of the method according to the invention is shown. The vehicle 10 comprises a control unit 12, which can in particular be a control unit of a power electronics system. The vehicle 10 also comprises an electric drive motor 14, which 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, so that the sensor device 15 detects the angular position and / or the rotational speed of the electric drive motor 14 and transmits the angular position and / or the rotational speed 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 adjusted and / or controlled by the control unit 12. The system can also be expanded to multiple drive motors, so that in addition to the drive motor 14, further drive motors are controlled and these further drive motors are used for deceleration.

[0021] The vehicle 10 also includes 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 device 12, so that they can be activated without driver intervention and can provide, for example, a so-called hill-hold or auto-hold function.

[0022] For example, if the driver wants to bring the vehicle to a standstill, he or she usually actuates the brake pedal. Alternatively, the braking process can also be initiated by an auxiliary system. In the context of the specific embodiment, it is provided that initially the braking process is performed only using the drive motor 14, i.e. using the electric motor brake, which is described in detail below by way of example with reference to the drawings.

[0023] exist Figures 2 to 4 In each of the figures, an exemplary parking process is shown in the form of a diagram in which the vehicle speed v, the activation state 201, 301, 401 of the motor brake and the activation state 202, 302, 402 of the mechanical brake are plotted against the time t. If the motor brake is in the activated state, this means that the braking torque is generated by the electric drive motor 14. If the mechanical brake is in the activated state, this means that the braking torque is generated by the mechanical brake. Both are started by corresponding control of the calculation unit 12, that is, the electric drive motor and the actuator for operating the mechanical brakes 16, 17 are controlled by the calculation unit 12 so that the braking torque is generated. Figures 2 to 4 The curve shown in .

[0024] It can be seen that: until time point t 0 Braking is performed during the deceleration phase up to the end, and then the speed is zero, that is, the vehicle is stationary.

[0025] It can also be seen that: until time point t 1 In the first braking phase up to time t, the motor brake is activated; and 2 At the beginning of the second braking phase, the mechanical brake is activated; and at time t 1 and t 2 The mutual position of Figures 2 to 4 changes in the.

[0026] In all figures it is shown that the second braking phase ends at the end of the first braking phase (t 1 ) had already begun before (t 2 ). This ensures that the braking torque is always present and that the vehicle can therefore be safely decelerated on the one hand and safely brought to a standstill on the other hand.

[0027] exist Figure 2 An embodiment is shown in FIG. 1 , in which the second braking phase is performed after reaching a standstill (at t 0 ) had already begun.

[0028] This variant can be selected for situations where a fault in the electric drive motor 12 is detected or where the electric drive motor cannot provide the required braking torque (e.g. because the deceleration is not as expected in both cases). This variant can also be used to blend these braking torques regardless of whether the drive motor has a fault.

[0029] Alternatively or additionally, this variant can be selected according to speed, that is, the second braking phase starts when reaching or falling below a speed threshold, for example 1-2 km / h. Thus, the state close to rest, that is, the low speed range, can be better controlled.

[0030] exist Figure 3 An embodiment is shown in FIG. 1 , in which when a stationary state is reached (at t 0 ), the second braking phase begins immediately. As a result, the vehicle can be brought to a standstill using the mechanical brakes from the outset, which reduces wear and stress on the electric motor brakes. This variant can be selected if it is not desired to bring the vehicle to a standstill electrically, for example when the thermal load on the drive motor is too high.

[0031] exist Figure 2 and Figure 3 , variants are shown in which, in the stationary state, the vehicle 10 is held stationary by means of a mechanical brake, so that the electric drive motor in particular does not have to support any (significant) torque there and therefore also does not bear any load or bears almost no load. Figure 4, an embodiment is shown in which the second braking phase begins only after the stationary state has lasted for a period of time 403. This variant is selected if the electric drive motor is to first also keep the vehicle at a standstill and then the mechanical brake takes over this. This is useful for achieving the highest possible comfort during the parking process, because compared to friction brakes, there is no transition from sliding friction to static friction when transitioning from deceleration to a stationary state. Therefore, electrical parking reduces the change in acceleration, i.e., jerk, until the stationary state. The duration 403 of electrical parking can be determined by the limitations of component protection, i.e., the duration ends in particular before thermal overload occurs, etc. The absence of the driver may also cause the end of electrical parking, because a continuous stationary state cannot be guaranteed using the drive motor, and in the absence of the driver, this can only be ensured by the mechanical brake. If a fault occurs in the drive motor, which prevents electrical parking or makes it impossible to achieve electrical parking, the mechanical brake can be used as a backup system and thus ensure the stationary state. Only by intervening with an additional braking device such as the parking brake can a faulty behavior of the drive motor and the primarily actuated mechanical brake be prevented, or the driver must actively ensure a stationary state by his intervention.

[0032] If, before the start of the second braking phase, the driver has already requested torque again during the period of stationary state, then expediently the second braking phase is no longer started, but the driver's request is taken into account.

Claims

1. A method for braking a vehicle (10) having an electric drive motor (14) and mechanical brakes (16, 17) to a standstill and for keeping the vehicle at a standstill, in, The electric drive motor (14) and the actuator for operating the mechanical brake (16, 17) are controlled so that In a first braking phase, a braking torque is generated by means of the electric drive motor (14); In the second braking phase, a braking torque is generated by means of the mechanical brakes (16, 17); The first braking phase starts before the second braking phase starts (t2); The first braking phase ends (t1) after the second braking phase starts (t2); The first braking phase ends (t1) after reaching (t0) a stationary state; and Depending on the triggering condition, the second braking phase begins (t2) before reaching (t0) a stationary state, when reaching a stationary state or after reaching a stationary state.

2. The method according to claim 1, wherein: The electric drive motor (14) and the actuator for actuating the mechanical brake (16, 17) are controlled so that, for a triggering condition in which the electric drive motor (14) does not generate sufficient braking torque, the second braking phase begins (t2) before reaching a standstill (t0).

3. The method according to claim 1 or 2, wherein: The electric drive motor (14) and the actuator for actuating the mechanical brakes (16, 17) are controlled so that, for a trigger condition that the vehicle (10) reaches a certain speed threshold, the second braking phase begins (t2) before reaching a standstill (t0).

4. A method according to any one of the preceding claims, wherein: The electric drive motor (14) and the actuator for actuating the mechanical brake (16, 17) are controlled so that a triggering condition for a sufficient braking torque is generated for the electric drive motor (14), and the second braking phase begins (t2) when a standstill is reached (t0).

5. A method according to any one of the preceding claims, wherein: The electric drive motor (14) and the actuator for actuating the mechanical brakes (16, 17) are controlled so that, for a trigger condition requiring a continuous standstill to avoid thermal loads, the second braking phase begins (t2) after reaching (t0) a standstill.

6. A method according to any one of the preceding claims, wherein: The electric drive motor (14) and the actuator for actuating the mechanical brakes (16, 17) are controlled so that, for a trigger condition requiring a permanent guaranteed standstill in the absence of a driver, the second braking phase begins (t2) after reaching (t0) a standstill.

7. A method according to any one of the preceding claims, wherein: The electric drive motor (14) and the actuator for actuating the mechanical brakes (16, 17) are controlled so that the second braking phase begins (t2) after reaching a standstill (t0) if a fault in the drive motor prevents or makes impossible a triggering condition for electrically stopping the vehicle.

8. A method according to any one of the preceding claims, wherein: The electric drive motor (14) and the actuator for actuating the mechanical brakes (16, 17) are controlled so that the second braking phase begins (t2) after reaching (t0) a stationary state, for triggering conditions that the stationary state cannot be guaranteed due to a failure of the drive motor and the brakes and the driver is not absent.

9. A computing unit (12) which is configured to carry out all method steps of the method according to any of the preceding claims.

10. A vehicle (10) having an electric drive motor (14), a mechanical brake (16, 17) and a computing unit (12) according to claim 9. 11 . A computer program which, when executed on a computing unit, causes the computing unit to execute all method steps of the method according to claim 1 .

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

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