METHOD FOR OPERATING A MOTOR VEHICLE, DEVICE, AND MOTOR VEHICLE

Abstract

A method for operating a motor vehicle. The motor vehicle includes a first actuating element, an actuatable second actuating element, and a braking system including an activatable braking force generator and a master brake cylinder, at least one hydraulic piston displaceably mounted in the master brake cylinder and is steplessly displaceable between first and second end positions. A first deceleration value is predefined for the motor vehicle when the instantaneous position of the piston falls short of a change position between the first and second ends. The braking force generator, when the first deceleration value is predefined, is activated in such a way that the hydraulic piston is displaced as a function of a level of the first deceleration value. The first deceleration value is decreased upon detection of the actuation of the second actuating element by the driver.

Claims

1-9. (canceled)

10. A method for operating a motor vehicle, the motor vehicle including a first actuating element, an actuatable second actuating element, and a braking system including an activatable braking force generator and a master brake cylinder, at least one hydraulic piston being displaceably mounted in the master brake cylinder, the first actuating element being steplessly displaceable between a first end position and a second end position, a change position being predefined between the end positions, an acceleration value for the motor vehicle being predefined when an instantaneous position of the first actuating element exceeds the change position, the method comprising: predefining a first deceleration value for the motor vehicle when the instantaneous position of the first actuating element falls short of the change position; activating the braking force generator, when the first deceleration value is predefined, in such a way that the hydraulic piston is displaced as a function of a level of the first deceleration value; displacing the hydraulic piston during an actuation of the second actuating element by a driver of the motor vehicle; and decreasing the first deceleration value upon detection of the actuation of the second actuating element by the driver.

11. The method as recited in claim 10, wherein a second deceleration value is predefined during the actuation of the second actuating element, the braking force generator, when the second deceleration value is predefined, is activated in such a way that the hydraulic piston is displaced as a function of a level of the second deceleration value.

12. The method as recited in claim 10, wherein the first deceleration value is continuously changed as a function of an extent of the actuation of the second actuating element.

13. The method as recited in claim 10, wherein the first deceleration value is decreased immediately upon detection of the actuation of the second actuating element.

14. The method as recited in claim 10, wherein the first deceleration value is decreased independently of a displacement of the first actuating element.

15. The method as recited in claim 10, wherein the braking system includes at least one friction braking unit, the master brake cylinder being fluidically connected to a slave cylinder of the friction braking unit so that the friction braking unit is actuated during the displacement of the hydraulic piston.

16. The method as recited in claim 10, wherein the motor vehicle includes at least one electric machine, the electric machine being operated as a generator as a function of an extent of the displacement of the hydraulic piston.

17. A device for operating a motor vehicle, the motor vehicle including a first actuating element which is steplessly displaceable between a first end position and a second end position, an actuatable second actuating element, and a braking system including a braking force generator and a master brake cylinder, at least one hydraulic piston being displaceably mounted in the master brake cylinder, the device comprising: a control unit configured to: predefine a first deceleration value for the motor vehicle when the instantaneous position of the first actuating element falls short of the change position, wherein the braking force generator is configured to be activated, when the first deceleration value is predefined, in such a way that the hydraulic piston is displaced as a function of a level of the first deceleration value, and the hydraulic piston is configured to be displaced during an actuation of the second actuating element by a driver of the motor vehicle; and decrease the first deceleration value upon detection of the actuation of the second actuating element by the driver.

18. A motor vehicle, comprising: a first actuating element which is steplessly displaceable between a first end position and a second end position; an actuatable second actuating element; a braking system including an activatable braking force generator and a master brake cylinder in which at least one hydraulic piston is displaceably mounted; and a device configured to operate the motor vehicle, the device including: a control unit configured to: predefine a first deceleration value for the motor vehicle when the instantaneous position of the first actuating element falls short of the change position, wherein the braking force generator is configured to be activated, when the first deceleration value is predefined, in such a way that the hydraulic piston is displaced as a function of a level of the first deceleration value, and wherein the hydraulic piston is configured to be displaced during an actuation of the second actuating element by a driver of the motor vehicle, and decrease the first deceleration value upon detection of the actuation of the second actuating element by the driver.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 shows a motor vehicle in a simplified illustration, according to an example embodiment of the present invention.

[0020] FIG. 2 shows a method for operating the motor vehicle, according to an example embodiment of the present invention.

[0021] FIG. 3 shows a deceleration-counter force characteristic curve, according to an example embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0022] FIG. 1 shows a motor vehicle 1 in a simplified illustration. In the present example, motor vehicle 1 includes four wheels 2 and 3, wheels 2 being assigned to a front axle 4 and wheels 3 being assigned to a rear axle 5. Motor vehicle 1 furthermore includes a drive system 6 including a driving machine 7, which in the present example is an electrical driving machine 7 operable as a generator. Driving machine 7 is connected by a differential gear 8 and shafts 9, 10 and 11 to wheels 2 of front axle 4, so that wheels 2 are drivable by driving machine 7.

[0023] Motor vehicle 1 furthermore includes a braking system 12. Braking system 12 includes four friction braking units 13, each of wheels 2 and 3 being assigned a different one of friction braking units 13. For actuating friction braking units 13, braking system 12 includes a master brake cylinder 14, which in the present example is designed as a tandem master brake cylinder 14 so that two hydraulic pistons, which are not shown, are displaceably mounted in master brake cylinder 14. Master brake cylinder 14 is fluidically connected to slave cylinders of friction braking units 13.

[0024] A braking force generator 15 is assigned to master brake cylinder 14. Braking force generator 15 includes an activatable electric motor. The electric motor is coupled to the hydraulic pistons in such a way that the hydraulic pistons are displaced during an activation of the electric motor.

[0025] Motor vehicle 1 furthermore includes a device 16 including a control unit 17. Control unit 17 is communicatively connected to driving machine 7 and designed to activate driving machine 7. Moreover, control unit 17 is communicatively connected to braking force generator 15 and configured to activate braking force generator 15 or the electric motor of braking force generator 15.

[0026] Motor vehicle 1 furthermore includes a first actuating element 18. First actuating element 18 is designed as a pedal and is steplessly displaceable between a first end position and a second end position. The position of first actuating element 18 in the first end position corresponds to a percentage value of 0% based on the actuating travel from the first end position to the second end position. In the second end position, the position of first actuating element 18 corresponds to a percentage value of 100%. First actuating element 18 is communicatively connected to control unit 17 so that the instantaneous position of first actuating element 18 is provided to control unit 17. Control unit 17 predefines a virtual change position situated between the end position of first actuating element 18.

[0027] If the position of first actuating element 18 exceeds the change position, control unit 17 predefines an acceleration value for motor vehicle 1. The instantaneous position of first actuating element 18 is then in an acceleration range situated between the change position and the second end position. When the acceleration value is predefined, control unit 17 activates driving machine 7 in such a way that motor vehicle 1 is accelerated.

[0028] If the position of first actuating element 18 falls short of the change position, control unit 17 predefines a first deceleration value for motor vehicle 1. The instantaneous position is then in a deceleration range situated between the first end position and the change position. When the first deceleration value for motor vehicle 1 is predefined, control unit 17 activates braking force generator 15 in such a way that the hydraulic pistons are displaced as a function of a level of the first deceleration value. When the first deceleration value increases, an extent of the displacement of the hydraulic pistons also increases.

[0029] When the hydraulic pistons are displaced, motor vehicle 1 is decelerated, an extent of the deceleration of motor vehicle 1 corresponding to the extent of the displacement of the hydraulic pistons. A hydraulic fluid is transported out of master brake cylinder 14 as a result of the displacement of the hydraulic pistons. Motor vehicle 1 is preferably decelerated by an actuation of friction braking units 13. For this purpose, the hydraulic fluid is transported into the slave cylinders. As an alternative, motor vehicle 1 is preferably decelerated by driving machine 7 being operated as a generator. In this case, the hydraulic fluid is transported into at least one low-pressure fluid reservoir, which is not shown, to prevent the actuation of friction braking units 13.

[0030] Motor vehicle 1 furthermore includes a second actuating element 19, which is a brake pedal 19. Brake pedal 19 is steplessly displaceable between a third end position and a fourth end position. The position of brake pedal 19 in the third end position corresponds to a percentage value of 0% based on the actuating travel from the third end position to the fourth end position. In the fourth end position, the position of brake pedal 19 corresponds to a percentage value of 100%.

[0031] A spring unit 20 is assigned to brake pedal 19, which urges brake pedal 19 in the direction of the third end position and, in particular, into the third end position. Brake pedal 19 is accordingly displaceable against a spring force of spring unit 20 in the direction of the fourth end position, so that the spring force represents a counter force which has to be overcome to displace brake pedal 19 in the direction of the fourth end position. Spring unit 20 is held preloaded between brake pedal 19 on the one hand and a housing, which is not shown, in particular, a housing of braking force generator 15, on the other hand. Spring unit 20 is accordingly supported, directly or indirectly, at brake pedal 19 on the one hand and, directly or indirectly, at the housing on the other hand.

[0032] Brake pedal 19 is actuatable by a driver of motor vehicle 1. An actuation of brake pedal 19 shall be understood to mean that the driver applies an actuating force on the brake pedal 19 in such a way that brake pedal 19 is displaced in the direction of the fourth end position, compared to the position which brake pedal 19 assumes in the unactuated state.

[0033] In the present example, brake pedal 19 is mechanically coupled to the hydraulic pistons in such a way that the hydraulic pistons are displaced as a result of the mechanical coupling when brake pedal 19 is actuated. According to one further exemplary embodiment, such a mechanical coupling between brake pedal 19 and the hydraulic pistons is dispensed with.

[0034] In the present example, brake pedal 19 is coupled to a displaceably mounted actuating element of braking force generator 15 in such a way that brake pedal 19 is displaced in the direction of the fourth end position when braking force generator 15 is activated in such a way that the hydraulic pistons are displaced. Accordingly, the position of brake pedal 19 is variable in the unactuated state and is influenced by the level of the first deceleration value, and thus the activation of braking force generator 19 or the extent of the displacement of the hydraulic pistons.

[0035] Brake pedal 19 is communicatively connected to control unit 17 so that the extent of the actuation of brake pedal 19 or the instantaneous position of brake pedal 19 is provided to control unit 17. When brake pedal 19 is actuated, control unit 17 predefines a second deceleration value for motor vehicle 1. When the second deceleration value for motor vehicle 1 is predefined, control unit 17 activates braking force generator 15 in such a way that the hydraulic pistons are displaced as a function of a level of the second deceleration value. When the second deceleration value increases, an extent of the displacement of the hydraulic pistons also increases.

[0036] An advantageous method for operating motor vehicle 1 is described hereafter with reference to FIG. 2. In this regard, FIG. 2 shows a first diagram A, a second diagram B, and a third diagram C.

[0037] First diagram A shows the percentage value of the position of first actuating element 18 as a function of time t. Second diagram B shows first deceleration value VW as a function of time t. Third diagram C shows the percentage value of the position of brake pedal 19.

[0038] The position of first actuating element 18 is in the acceleration range between first point in time T1 and a second point in time T2. Accordingly, no first deceleration value VW is predefined between points in time T1 and T2. The position of brake pedal 19 corresponds to the third end position.

[0039] Proceeding from change position WS, first actuating element 18 is displaced into the first end position between second point in time T2 and a third point in time T3 so that, at third point in time T3, the position of first actuating element 18 corresponds to the first end position. The position of first actuating element 18 is kept constant hereafter. Since the position of first actuating element 18 between points in time T2 and T3 is in the deceleration range, control unit 17 predefines first deceleration value VW. Due to the displacement of first actuating element 18 into the first end position, the level of first deceleration value VW is continuously increased between points in time T2 and T3 until the level of the first deceleration value has reached a maximum value MW. Due to first deceleration value VW being predefined, control unit 17, starting at second point in time T2, controls braking force generator 15 in such a way that braking force generator 15 displaces the hydraulic pistons. In the process, the extent of the displacement of the hydraulic pistons corresponds to the level of first deceleration value VW. When first deceleration value VW is increased, the extent of the displacement of the hydraulic pistons also increases. Due to brake pedal 19 being coupled to the hydraulic pistons and/or the actuating element of braking force generator 15, brake pedal 19 is displaced in the direction of the fourth end position. In the process, no actuating force is provided by the driver. In this respect, brake pedal 19 is in the unactuated state between points in time T2 and T3.

[0040] Starting at a fourth point in time T4, brake pedal 19 is actuated by the driver. The driver thus provides an actuating force which exceeds the counter force so that brake pedal 19 is displaced by the driver in the direction of the fourth end position. Between fourth point in time T4 and a fifth point in time T5, brake pedal 19 is continuously displaced in the direction of the fourth end position so that the percentage value of the position of brake pedal 19 increases continuously. The actuation of brake pedal 19 is detected by control unit 17. As a result, control unit 17 continuously decreases the level of first deceleration value VW between points in time T4 and T5.

[0041] Starting at a sixth point in time T6, the extent of the actuation of brake pedal 19 is decreased. Brake pedal 19 is thus displaced in the direction of the third end position again by the counter force until brake pedal 19, at a seventh point in time T7, is in the unactuated state again. The decrease of the actuation of brake pedal 19 is detected by control unit 17. As a result, control unit 17 continuously increases the level of first deceleration value VW between points in time T6 and T7.

[0042] Since brake pedal 19 is actuated between points in time T4 and T7, control unit 17 also predefines the second deceleration value between these points in time. The profile of the second deceleration value, however, is not shown in FIG. 2 for the sake of clarity.

[0043] FIG. 3 shows a fourth diagram D in which different deceleration-counter force characteristic curves are shown. A deceleration-counter force characteristic curve is a characteristic curve which describes deceleration V of motor vehicle 1 as a function of counter force F provided by spring unit 20.

[0044] A first deceleration-counter force characteristic curve L1 describes the deceleration of motor vehicle 1 as a function of counter force F provided by spring unit 20 in the case of inactivity of the single-pedal function of first actuating element 18 or in the absence of a first actuating element including a single-pedal function. When the single-pedal function is inactive, an acceleration value is always predefined during the actuation of first actuating element 18, as is the case with conventional gas pedals. As is apparent from FIG. 3, the driver, proceeding from the previously unactuated second actuating element 19, has to overcome a counter force having a certain first value W1 to increase the deceleration of motor vehicle 1.

[0045] A second deceleration-counter force characteristic curve L2 describes deceleration V of motor vehicle 1 as a function of counter force F provided by spring unit 20 in the case of activity of the single-pedal function of first actuating element 18. The position of first actuating element 18 is in the deceleration range. In this respect, first deceleration value VW is predefined, and motor vehicle 1 is decelerated. If first deceleration value VW is not decreased during the actuation of brake pedal 19, the driver has to overcome a counter force having a certain second value W2 to increase deceleration V of motor vehicle 1, as is apparent from characteristic curve L2. Value W2 is considerably higher than value W1. For the driver, it is unusual to have to overcome such a high counter force F to increase deceleration V of motor vehicle 1.

[0046] A third deceleration-counter force characteristic curve L3 also describes deceleration V of motor vehicle 1 as a function of the provided counter force F in the case of activity of the single-pedal function of first actuating element 18. In the case of third deceleration-counter force characteristic curve L3 as well, the position of first actuating element 18 is in the deceleration range, so that first deceleration value VW is predefined, and motor vehicle 1 is decelerated. However, if the driver overcomes counter force F, and thus actuates brake pedal 19, first deceleration value VW is decreased, as is described above with reference to FIG. 2. As a result, deceleration V of motor vehicle 1 is also temporarily decreased. The driver therefore only has to overcome a counter force having a certain third value W3, which is between first value W1 and second value W2, to increase deceleration V of motor vehicle 1. When the driver overcomes the counter force having value W2, the increase of the second deceleration value outweighs the decrease of the first deceleration value VW, so that deceleration V of the vehicle overall increases. Since third value W3 is lower than second value W2, the driver perceives the actuation of brake pedal 19 according to third characteristic curve L3 to be more pleasant than the actuation of brake pedal 19 according to second characteristic curve L2.