Method and control unit for operating a motor vehicle with a hydrodynamic starting element

Abstract

Method for operating a motor vehicle (10) with a hydrodynamic starting element (14), which has a pump side (15) and a turbine side (16) and is connected between a drive unit (11) and a transmission (13) such that the drive unit is coupled to the pump side (15) and the transmission to the turbine side (16), wherein, with the accelerator pedal (17) not depressed and a gear engaged for creeping, a torque is transmitted towards an output (12) depending on a differential speed between the pump side (15) and the turbine side (16), depending on which the motor vehicle rolls at a creeping speed, wherein, if a brake pedal (18) is depressed during creeping, the motor vehicle is decelerated from the creeping speed by applying a braking torque via a service brake (19), and wherein, during creeping, a target idle speed for the drive unit is maintained.An idle speed controller (23) regulates an actual idle speed based on the actuation of the brake pedal (18). Then, when the vehicle comes to a standstill while creeping and is automatically held stationary by the service brake (19) with the brake pedal not depressed, the setting of the target idle speed based on the actuation of the brake pedal (18) is discontinued, and a target idle speed dependent on an actual operating mode or a minimum target idle speed is set.

Description

[0001] The invention relates to a method for operating a motor vehicle with a hydrodynamic starting element. Furthermore, the invention relates to a control unit for operating a motor vehicle with a hydrodynamic starting element.

[0002] In practice, motor vehicles are known to have a drive unit, a transmission connected between the drive unit and an output shaft of the vehicle, and a hydrodynamic starting element connected between the drive unit and the transmission. A hydrodynamic starting element is also referred to as a torque converter, and it has a pump side and a turbine side. The drive unit is coupled to the pump side of the hydrodynamic starting element. The transmission is coupled to the turbine side of the hydrodynamic starting element.

[0003] In such a motor vehicle with a hydrodynamic starting element, when the accelerator pedal is not depressed and a gear is engaged in the transmission, a torque is transferred towards the output of the motor vehicle, depending on a differential speed between the pump side of the hydrodynamic starting element and the turbine side of the hydrodynamic starting element, so that the motor vehicle then rolls at a creeping speed.

[0004] If the motor vehicle is to be slowed down while creeping, the motor vehicle is slowed down from the creeping speed by applying a braking torque to the output via a service brake of the motor vehicle, depending on the activation of a brake pedal of the motor vehicle.

[0005] DE 102 21 835 A1 discloses a method for controlling a starting element of a motor vehicle during creeping. A creep torque setpoint is set for the starting element. The creep torque setpoint is adjusted depending on the current inclination of the motor vehicle and / or depending on the brake pedal pressure and / or depending on the distance of the motor vehicle to an obstacle and / or depending on the driver type.

[0006] DE 10 2015 110 800 A1 discloses a method for starting an internal combustion engine in a creeping motor vehicle. To start the internal combustion engine, the drive wheel speed of a torque converter is increased to the speed required for starting the internal combustion engine.

[0007] DE 10 2009 022 287 A1 discloses a method for controlling a starting element according to the preamble of claim 1.

[0008] DE 10 2006 003 714 A1 and DE 199 49 204 A1 reveal further state of the art.

[0009] As explained above, when a vehicle creeps, a torque is transmitted to the output shaft via the hydrodynamic starting element. In practice, a target idle speed for the drive unit is preset during creeping, and an idle speed controller regulates the actual idle speed to this speed. If the vehicle is to be brought to a standstill while creeping, a corresponding braking torque is applied to the output shaft via the service brake, which counteracts the torque transmitted by the hydrodynamic starting element. When the brake is subsequently released, the effective hydraulic forces can cause brake squeal, as well as noises and a jolt from the drivetrain. This is perceived as uncomfortable.

[0010] Therefore, there is a need for a method and a control unit for operating a motor vehicle with a hydrodynamic starting element, which can reduce or even completely avoid brake squealing when releasing a vehicle that has been slowed down while creeping, as well as a corresponding breakaway noise and a breakaway impact in the drivetrain.

[0011] The object of the invention is to create a novel method for operating a motor vehicle with a hydrodynamic starting element, as well as a control unit for operating a motor vehicle with a hydrodynamic starting element and a motor vehicle with such a control unit.

[0012] This problem is solved by a method according to claim 1, by a control unit according to claim 10 and by a motor vehicle according to claim 12.

[0013] According to the invention, during creeping, a target idle speed for the drive unit is specified, to which an idle speed controller regulates an actual idle speed for the drive unit, depending on the actuation of the brake pedal. This makes it possible to avoid brake squeal, a starting noise, and a starting jolt in the drivetrain when the vehicle is braked to a standstill during creeping and is subsequently to be accelerated.

[0014] According to the invention, when the motor vehicle comes to a standstill while creeping and is automatically held stationary by the service brake with the brake pedal not depressed, the setting of the target idle speed for the drive unit is terminated depending on the actuation of the brake pedal, and preferably a target idle speed dependent on an actual operating mode or a minimum target idle speed for the drive unit is set.

[0015] Preferably, during creeping, the target idle speed for the drive unit is predetermined depending on the brake pedal actuation such that the target idle speed for the drive unit decreases the more the brake pedal is depressed. This is particularly preferred to avoid brake squeal, as well as a start-up noise and a start-up jolt in the drivetrain when starting a vehicle that has been brought to a standstill during creeping.

[0016] When the brake pedal is not depressed during creeping, a maximum target idle speed is specified for the drive unit. When the brake pedal is fully depressed during creeping, a minimum target idle speed is specified for the drive unit. When the brake pedal is depressed less than fully during creeping, a target idle speed is specified for the drive unit that lies between the maximum and minimum target idle speeds, preferably based on a linear, progressive, or degressive relationship between brake pedal depressurization and the target idle speed. This is particularly preferred to avoid brake squeal, as well as a start-up noise and a start-up clunk in the drivetrain when a vehicle that has been brought to a standstill during creeping starts moving again.

[0017] It is also possible that, when the brake pedal is depressed less than maximum during creeping, the target idle speed for the drive unit can be adjusted based on a linear, progressive, or degressive relationship between the brake pedal deposition and the torque or tractive force transmitted by the hydrodynamic starting element, between the maximum and minimum target idle speeds. This also prevents brake squeal, a start-up noise, and a start-up clunk in the drivetrain when starting a vehicle that has been brought to a standstill during creeping.

[0018] Preferably, the target idle speed for the drive unit is set depending on the brake pedal actuation, furthermore depending on the current operating mode of the vehicle and / or depending on the current gear of the transmission and / or depending on the gear engaged in the transmission. This makes it possible to individually set the target idle speed for the drive unit during creeping for different operating modes of the vehicle, as well as for different gears and for different gears of the transmission. In particular, this allows the target idle speed to be increased during creeping in an off-road operating mode compared to a driving mode for on-road operation, thus making it possible to operate the vehicle by actuating the brake pedal without using the accelerator pedal. In this way, road irregularities, such as those caused by uneven surfaces, can be compensated for in off-road operation.obstacles caused by stones or rocks can be easily overcome.

[0019] Preferred embodiments of the invention are set forth in the dependent claims and the following description. Exemplary embodiments of the invention are explained in more detail with reference to the drawing, without being limited thereto. The drawing shows: Fig. 1. A block diagram of a motor vehicle, Fig. 2 a diagram to visualize a possible dependency between the actuation of the brake pedal and the target idle speed of the drive unit.

[0020] Fig. Figure 1 shows a highly schematic representation of a motor vehicle 10, which has a drive unit 11, an output 12, a transmission 13 connected between the drive unit 11 and the output 12, and a hydrodynamic starting element 14 connected between the drive unit 11 and the transmission 13. The hydrodynamic starting element 14 is also referred to as a torque converter. The hydrodynamic starting element 14 has a turbine side 15 and a pump side 16, with the drive unit 11 being coupled to the turbine side 15 and the transmission 13 to the pump side 16 of the hydrodynamic starting element 14.

[0021] When a motor vehicle equipped with a hydrodynamic starting element 14 has its accelerator pedal 17 disengaged and a gear, particularly a creeper gear, is engaged in the transmission 13, a torque is transmitted towards the output shaft 12, depending on the speed differential between the pump side 15 and the turbine side 16 of the hydrodynamic starting element 14. This torque is greater the greater the speed differential between the pump side 15 and the turbine side 16 of the hydrodynamic starting element. When the motor vehicle 10 is creeping and is to be decelerated from its creeping speed by actuating a brake pedal 18 of the motor vehicle 10, a braking torque is provided by a service brake 19 at the output shaft 12. This braking torque 19 counteracts the torque transmitted by the hydrodynamic starting element 14 in order to decelerate the motor vehicle 10 to a standstill.Then, when the motor vehicle 10 is operated on a slope, the braking torque provided by the service brake 19 at the output 12 must also brake away a torque acting on the output 12 as a result of the slope.

[0022] Fig. Figure 1 further shows control-side components of the motor vehicle 10, namely an engine control unit 20, a transmission control unit 21, and a brake control unit 22. The control units 20, 21, and 22 exchange data with each other as indicated by the dashed arrows. Furthermore, the engine control unit 20 exchanges data with the drive unit 11, the transmission control unit 21 with the transmission 13 and the hydrodynamic starting element 14, and the brake control unit 22 with the service brake 19. In the Fig. In the exemplary configuration of the motor vehicle shown in Figure 1, the accelerator pedal 17 exchanges data with the engine control unit 20 and the brake pedal 18 exchanges data with the brake control unit 22.

[0023] The in Fig. 1. Configuration of the motor vehicle shown, in particular the coupling of the control units 20, 21, 22 to each other and their coupling to the one shown in Fig. The assemblies shown in section 1 are, however, purely exemplary.

[0024] Fig. Figure 1 shows an idle speed controller 23 as part of the engine control unit 20. The idle speed controller 23 regulates the actual idle speed of the drive unit 11 to a target idle speed when stationary and when creeping.

[0025] The invention proposes to specify the target idle speed for the drive unit 11, and thus for the idle speed controller 23, depending on the actuation of the brake pedal 18 during creeping. During creeping, the target idle speed is then no longer a fixed or constant value, but rather depends on the actuation of the brake pedal 18. This makes it possible, in particular, to avoid brake squealing, start-up noises, and start-up shocks in the vehicle when, during creeping, the vehicle 10 has been decelerated from a creeping speed via the service brake 19 to a standstill and is subsequently to be accelerated.

[0026] During creeping, the target idle speed for the drive unit 11 is set according to the actuation of the brake pedal 18 such that the target idle speed for the drive unit 11, and thus also for the idle speed controller 23, decreases the more the brake pedal 18 is actuated. However, the reduction of the target idle speed is limited to a minimum target idle speed that prevents the drive unit 11 from stalling or shutting off.

[0027] Fig. Figure 2 shows an example of the determination of a target idle speed n-LEER-SOLL as a function of actuation S of the brake pedal 18. S0 corresponds to an unactuated or unactuated brake pedal 18, SMAX corresponds to a maximally actuated brake pedal 18.

[0028] According to Fig. 2. If the brake pedal 18 is not pressed during creeping, a maximum target idle speed nMAX is specified for the drive unit 11.

[0029] Then, when the brake pedal 18 is fully depressed during creeping, a minimum target idle speed nMIN is specified for the drive unit 11, which, however, prevents the drive unit 11 from stalling.

[0030] Then, when the brake pedal 18 is applied less than maximum during creeping, a target idle speed for the drive unit 11 is specified for creeping, which lies between the maximum target idle speed nMAX and the minimum target idle speed nMIN.

[0031] In accordance with Fig. 2 the target idle speed for the drive unit is adapted on the basis of a linear dependence between the actuation S of the brake pedal 18 and the target idle speed n-LEER-SOLL between the maximum target idle speed nMAX and the minimum target idle speed nMIN.

[0032] Although adjusting the target idle speed based on the actuation of the brake pedal 18 using a linear relationship is preferred, a non-linear relationship can also be used to adjust the target idle speed for the drive unit during creeping, depending on the actuation of the brake pedal 18. For example, the target idle speed can be adjusted in several discrete steps depending on the actuation of the brake pedal 18, or based on a progressive or degressive relationship.

[0033] Setting the target idle speed for the drive unit 11 during creeping, depending on the actuation of the brake pedal 18, can additionally depend on the current operating mode of the vehicle and / or on the current gear of the transmission 13 of the vehicle 10 and / or on a gear engaged in the transmission 13. Thus, it may be possible to allow setting the target idle speed for the drive unit 11 in all operating modes or only in certain selected operating modes, such as an off-road operating mode. If setting the target idle speed for the drive unit, depending on the actuation of the brake pedal 18, is permitted in several operating modes, the target idle speed can be individually adjusted for each operating mode depending on the actuation of the brake pedal 18.For example, a higher maximum target idle speed nMAX can be specified for an off-road operating mode with the brake pedal 18 not depressed than in a road operating mode of the vehicle 10. In this case, the minimum target idle speed nMIN for the drive unit 11 can be the same with the brake pedal 18 fully depressed, so that, when using linear dependencies, different slopes result for the linear dependencies for adjusting the target idle speed between the respective maximum target idle speed nMAX and the minimum target idle speed nMIN depending on the deactivation of the brake pedal 18.

[0034] Depending on the current gear position of the transmission 13, the adjustment of the target idle speed for the drive unit 11 based on the application of the service brake 18 may only be permitted if the current gear position is a forward gear position D or a reverse gear position R in the transmission 13. If, however, the gear position in the transmission 13 is neutral N or park P, the adjustment of the target idle speed for the drive unit 11 based on the application of the brake pedal 18 may be prevented.

[0035] If a forward gear D is engaged in transmission 13, the adjustment of the target idle speed for the drive unit 11, depending on the actuation of the brake pedal 18, can only be permitted if a creeper gear or starting gear is engaged in transmission 13 in the forward gear position, for example, first forward gear. In other forward gears, the adjustment of the target idle speed for the drive unit 11, depending on the actuation of the service brake 18, can then be prevented.

[0036] According to the invention, when the motor vehicle 10 comes to a standstill while creeping using the function according to the invention, i.e., by adjusting the target idle speed for the drive unit 11 depending on the actuation of the brake pedal 18, and when the motor vehicle is subsequently held stationary automatically by the service brake 19 with the brake pedal 18 not actuated, for example on a slope, the setting of the target idle speed for the drive unit 11 depending on the actuation of the brake pedal 18 is terminated, and a target idle speed dependent on an actual operating mode or a minimum target idle speed for the drive unit 11 is set. Thus, depending on an operating mode selected by the driver, a minimum target idle speed for the drive unit 11 can be set.

[0037] This prevents the target idle speed from being increased as a result of the unactuated brake pedal 18, particularly depending on the operating mode, when the motor vehicle 10 is automatically held at a standstill via the service brake 19 with the brake pedal 18 not depressed.

[0038] The invention allows for a particularly advantageous operation of a motor vehicle 10 with a hydrodynamic starting element 14 during creeping. Since, during creeping, the target idle speed for the drive unit 11 is adjusted depending on the actuation of the brake pedal 18, particularly depending on the actual operating mode of the motor vehicle 10 and / or depending on the actual gear of the transmission 13 and / or depending on a gear engaged in the transmission 13, brake noise, breakaway noise and breakaway impacts in the drive train of the motor vehicle 10 can be avoided, especially after the motor vehicle 10 has been braked and subsequently creeps forward.

[0039] Furthermore, the invention makes it possible to provide one-paddle operation when the motor vehicle 10 is creeping, for example off-road or when driving over a curb. By adjusting the target idle speed for the drive unit 11 depending on the actuation of the brake pedal 18, a target idle speed for the drive unit 11, and thus for the idle speed controller 23, can be specified, particularly when the brake pedal 18 is not actuated. As a result, the road surface irregularity to be overcome can be traversed solely by actuating the brake pedal 18 without using the accelerator pedal 17.

[0040] The invention further relates to a control unit configured to automatically execute the method according to the invention. This control unit is in particular the engine control unit 20, which includes the idle speed controller 23. The engine control unit 20 can receive a corresponding actuation of the brake pedal 18 either directly from the brake pedal 18, or as described in Fig. 1 shown, starting from the brake control unit 22 via the transmission control unit 21 or alternatively also directly from the brake control unit 22.

Claims

[1] Method for operating a motor vehicle (10) with a hydrodynamic starting element (14), wherein the hydrodynamic starting element (14), which has a pump side (15) and a turbine side (16), is connected between a drive unit (11) of the motor vehicle (10) and a transmission (13) of the motor vehicle (10) such that the drive unit (11) is coupled to the pump side (15) of the hydrodynamic starting element (14) and the transmission (13) is coupled to the turbine side (16) of the hydrodynamic starting element (14), wherein, with the accelerator pedal (17) of the motor vehicle (10) not depressed and with a gear engaged in the transmission (13), a torque is transmitted towards a drive (12) of the motor vehicle (10) for creeping, depending on a differential speed between the pump side (15) and the turbine side (16) of the hydrodynamic starting element (14), depending on which the motor vehicle (10) rolls at a creeping speed, wherein, when a brake pedal (18) of the motor vehicle is actuated during creeping, the motor vehicle (10) is decelerated from the creeping speed by applying a braking torque via a service brake (19) of the motor vehicle (10), characterized by , that During creeping, a target idle speed for the drive unit (11) is specified, to which an idle speed controller (23) regulates an actual idle speed for the drive unit (11), depending on the actuation of the brake pedal (18), then, when the motor vehicle (10) comes to a standstill while creeping and the motor vehicle (10) is automatically held at a standstill by the service brake (19) with the brake pedal (18) not depressed, the setting of the target idle speed for the drive unit (11) depending on the actuation of the brake pedal (18) is terminated and a target idle speed dependent on an actual operating mode or a minimum target idle speed for the drive unit (11) is set. [2] Method according to claim 1, characterized by , that during creeping the target idle speed for the drive unit (11) is specified depending on the actuation of the brake pedal (18) such that the target idle speed for the drive unit (11) is lower the more the brake pedal (18) is actuated. [3] Method according to claim 1 or 2, characterized by , that then, if the brake pedal (18) is not pressed during creeping, a maximum target idle speed for the drive unit (11) is specified for creeping, then, when the brake pedal (18) is fully depressed during creeping, a minimum target idle speed for the drive unit (11) is specified for creeping, Then, when the brake pedal (18) is applied less than maximum during creeping, a target idle speed for the drive unit (11) is specified for creeping, which lies between the maximum target idle speed and the minimum target idle speed. [4] Method according to claim 3, characterized by, that when the brake pedal (18) is applied less than maximum during creeping, the target idle speed for the drive unit (11) is adjusted based on a linear or progressive or degressive relationship between the application of the brake pedal (18) and the target idle speed between the maximum target idle speed and the minimum target idle speed. [5] Method according to claim 3, characterized by , that when the brake pedal (18) is applied less than maximum during creeping, the target idle speed for the drive unit (11) is adjusted based on a linear, progressive or degressive relationship between the application of the brake pedal (18) and a torque transmitted by the hydrodynamic starting element (14) between the maximum target idle speed and the minimum target idle speed. [6] Method according to any one of claims 1 to 5, characterized by , that the specification of the target idle speed for the drive unit (11) is dependent on the actuation of the brake pedal (18) and is further dependent on an actual operating mode of the motor vehicle (10). [7] Method according to any one of claims 1 to 6, characterized by , that the specification of the target idle speed for the drive unit (11) is dependent on the actuation of the brake pedal (18) and is further dependent on an actual driving stage of the transmission (13) of the motor vehicle. [8] Method according to any one of claims 1 to 7, characterized by , that the setting of the target idle speed for the drive unit (11) depends on the actuation of the brake pedal (18) and further depends on a gear engaged in the transmission (13). [9] Method according to claims 7 and 8, characterized by, that the specification of the target idle speed for the drive unit (11) when a forward gear stage is valid as the actual driving stage of the transmission (13) only takes place if a creeper gear is engaged in the transmission (13) in the forward gear stage. [10] Control unit for operating a motor vehicle (10) with a hydrodynamic starting element (14), characterized by, that the control unit is configured to specify a target idle speed for the drive unit (11) during creeping, to which an idle speed controller (23) regulates an actual idle speed for the drive unit (11), depending on the actuation of the brake pedal (18), and that the control unit is further configured to cease specifying the target idle speed for the drive unit (11) depending on the actuation of the brake pedal (18) when the vehicle (10) comes to a standstill during creeping and the vehicle (10) is automatically held at a standstill by the service brake (19) with the brake pedal (18) not actuated, and to specify a target idle speed dependent on an actual operating mode or a minimum target idle speed for the drive unit (11). [11] Control unit according to claim 10, characterized by that the same is set up to carry out the method according to any one of claims 1 to 9. [12] Motor vehicle (10) with a control unit according to claim 10 or 11.

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