VEHICLE BRAKING SYSTEM AND PROCEDURES FOR ITS OPERATION

Abstract

Vehicle braking system (10) comprising the following: a wheel cylinder (20); a master cylinder (14) containing a master cylinder piston which, in a first operating mode, can be operated to move between an uncontrolled position and a controlled position; a valve (62) located between the main cylinder (14) and the wheel cylinder (20), wherein the valve (62) is in a closed position in a second operating mode; a brake pedal (18) that can be operated to switch between an extended position, corresponding to the unactuated position of the master cylinder (14), and a retracted position, corresponding to the actuated position of the master cylinder (14); and an amplifier (30) located between the master cylinder (14) and the brake pedal (18), wherein the main cylinder (14) can be operated in the first operating mode to selectively transmit a braking force from the brake pedal (18) to the wheel cylinder (20); wherein the amplifier (30) can be operated in the second operating mode to hold the brake pedal (18) in the retracted position without user input and without linked braking.

Description

BACKGROUND

[0001] The present disclosure relates to vehicle braking systems. In particular, the invention relates to a vehicle braking system for use in highly autonomous driving modes.

[0002] The publication DE 10 2014 214 786 A1 describes a method for adjusting at least one pedal of a motor vehicle pedal assembly and a corresponding device for this purpose.

[0003] The publication DE 10 2012 202 006 A1 describes a control device and corresponding method for transferring brake fluid into at least one wheel brake cylinder of a vehicle's brake system. SUMMARY

[0004] In one aspect, a vehicle braking system comprises a wheel cylinder, a master cylinder containing a master cylinder piston that, in a first operating mode, can be operated to move between an unactuated position and an actuated position, a valve located between the master cylinder and the wheel cylinder, the valve being in a closed position in the second operating mode, a brake pedal that can be operated to switch between an extended position corresponding to the unactuated position of the master cylinder and a retracted position corresponding to the actuated position of the master cylinder, and a booster located between the master cylinder and the brake pedal. In a first operating mode, the master cylinder can be operated to selectively transmit a braking force from the brake pedal to the wheel cylinder.In the second operating mode, the amplifier can be used to hold the brake pedal in the retracted position without user input and without linked braking.

[0005] In another aspect, a method of operating a vehicle braking system involves providing a brake pedal coupled to a master cylinder, with the brake pedal in an extended position ready for use, moving the brake pedal to a retracted position without braking to define an offset state, holding the brake pedal in the offset state without associated braking, automatically identifying a brake release with a controller and generating a signal from the controller in response to the identification of the brake release, separating a brake fluid flow path between a master cylinder and a wheel cylinder, and generating pressure at a wheel cylinder based on the signal, the magnitude of the pressure being independent of the position of the brake pedal and being generated without use of the brake pedal.

[0006] In yet another aspect, a vehicle braking system comprises a wheel cylinder, a master cylinder, and a valve located between the master cylinder and the wheel cylinder. In a second operating mode, the valve separates a brake fluid flow path between the master cylinder and the wheel cylinder. The system also includes a brake pedal that can be operated to switch between an extended position, in which the brake pedal is ready for use, and a retracted position, in which the brake pedal is offset. Finally, a pedal depressor can be operated to hold the brake pedal in the retracted position. In a first operating mode, the brake pedal can be actuated from the extended position to the retracted position, and the vehicle braking system can be operated to provide a variable braking force linked to the position of the brake pedal.In the second operating mode, the pedal depressor holds the brake pedal in the retracted position without an associated braking force, and the vehicle braking system can be operated to provide a variable braking force independently of the position of the brake pedal. BRIEF DESCRIPTION OF THE DRAWINGS The Fig. Figure 1 is a schematic view of a vehicle braking system, which includes a brake pedal and a brake unit. The Fig. 2A is a side view of the brake pedal of the vehicle's braking system. Fig. 1 in an extended position. The Fig. 2B is a side view of the brake pedal in a retracted position. DETAILED DESCRIPTION

[0007] Before any embodiments of the disclosure are explained in detail, it should be understood that the disclosure is not limited in its application to the design details and component arrangement set forth in the following description or illustrated in the following drawings. The disclosure is suitable for other embodiments and for operation or execution in various ways.

[0008] The Fig. Figure 1 illustrates a vehicle braking system 10. The braking system 10 comprises a brake unit 12, a fluid reservoir 16, an input device, such as a brake pedal 18, and several wheel cylinders 20 (as shown, the vehicle braking system 10 comprises four wheel cylinders 20, each wheel cylinder 20 being associated with a wheel of the vehicle) connected to the brake unit 12. The brake unit 12 pressurizes hydraulic fluid to achieve a braking force at the wheel cylinders 20 and comprises a master cylinder 14, an electromechanical brake booster 30, and an electronically controlled pressure generation unit 24 separate from the master cylinder 14 and the booster 30. The master cylinder 14 (alone or amplified by the booster 30) and the electronically controlled pressure generation unit 24 are two distinct fluid suppliers for applying braking force to the wheel cylinders 20 via fluid pressure.

[0009] The master cylinder 14 is a tandem master cylinder containing two master cylinder pistons 14A, 14B, which are biased towards one front of the master cylinder 14 by the master cylinder return springs 14C, 14D. The pistons 14A, 14B define the interior of the master cylinder 14 into a first chamber 14E and a second chamber 14F. Each chamber 14E, 14F of the master cylinder 14 is in selective fluid communication with a circuit 36A, 36B for one or more of the wheel cylinders 20. An input linkage 34 connects the master cylinder 14 to the brake pedal 18, with the brake booster 30 mounted nearby to modify the force applied to the brake pedal 18.

[0010] As in the Fig. 2A and Fig. As shown in Figure 2B, the brake pedal 18 is mounted within a footwell 38 of an operator's cabin 40. A partition 44 separates the pedal 18 from the master cylinder 14 and the booster 30 with the input linkage 34, which runs through the partition 44 to connect the pedal 18 to the master cylinder 14. The pedal 18 is used to change from an extended position ( Fig. 2A) to a retracted position ( Fig. 2B) can be operated by a force applied by the user (e.g., by the user's foot), indicated by arrow A1. The pedal 18 is biased into the extended position by the spring force of the master cylinder return springs 14C, 14D. To actuate the brake pedal 18, a user pushes the brake pedal 18 down from the extended position toward the partition 44 and toward the retracted position. This movement corresponds to and produces a displacement of the master cylinder pistons 14A, 14B against the return springs 14C, 14D. The movement of the brake pedal 18 between the extended and retracted positions is rotational about a pivot point 42, although the movement may also include a displacement aspect. The retracted position is an actuated position and not merely a setting for the driver's convenience.The extended position corresponds to a position in which pedal 18 is ready for intervention by the driver.

[0011] Again with reference to the Fig. 1: The electromechanical brake booster 30 is a vacuum-independent brake booster 30 (i.e., the booster 30 is not a vacuum booster). The input linkage 34 moves relative to a booster body 46. A differential travel sensor 48 measures this relative movement and transmits it to a controller 50. The controller 50 calculates the control signals for an electric motor 52. A transmission unit 54 converts the torque into a force that assists the driver during braking by amplifying the force applied by the user to the brake pedal 18. The power supplied by the booster 30 is converted into hydraulic pressure by the master cylinder 14. With adaptive cruise control, the presence of a motor 52 and a transmission unit 54 in the booster 30 allows the booster 30 to build up brake pressure without the application of the brake pedal 18 (i.e., without user input).The electromechanical brake booster 30 can, for example, be Bosch's iBooster (available from Robert Bosch GmbH, Stuttgart, Germany). In other designs, the electromechanical brake booster 30 can be a different booster capable of actuating the brake pedal 18.

[0012] The pressure generating unit 24 is operated in an electronic braking operating mode to generate a braking force at the wheel cylinders 20, in which the master cylinder 14 does not provide any braking force to the wheel cylinders 20. As shown, the electronically controlled pressure generating unit 24 includes a valve tappet 26, which is actuated by an electric motor 28 to displace fluid throughout the brake unit 12. Alternatively, the electronically controlled pressure generating unit 24 can be any of a range of electrically controlled pressure generating units that can be operated with electronic braking systems.

[0013] The brake unit 12 also contains several valves, in particular the inlet valves 58 and the exhaust valves 60. The in the Fig. The brake unit 12 shown contains four inlet valves 58 and four outlet valves 60, one for each of the 58 and 60, which are linked to each of the wheel cylinders 20. The inlet valves 58 are located between the respective wheel cylinder 20 and the fluid suppliers 14 and 24. The outlet valves 60 are located between the wheel cylinder 20 and the reservoir 16. The inlet valves 58 are closing valves, and the outlet valves 60 are opening valves. The valves 58 and 60 are selectively controlled (opened or closed to varying degrees via feedback from sensors, etc.) to control aspects of braking, such as an anti-lock braking system (ABS), traction control, or electronic stability control (ESP).

[0014] The brake unit 12 further includes a closing isolating valve 62 in each brake circuit 36A, 36B (i.e., corresponding to each master cylinder chamber 14E, 14F) to selectively connect or disconnect a brake fluid flow path between the master cylinder 14 and the respective wheel cylinders 20. Furthermore, the opening control valves 64 are located between the pressure generation unit 24 and the wheel cylinders 20 to likewise selectively connect or disconnect a fluid flow path between the pressure generation unit 24 and the wheel cylinders 20. Alternatively, the isolating valves 62 and the control valves 64 can be combined into a single valve per circuit 36A, 36B, which switches the input to the wheel cylinders 20 between the master cylinder 14 and the pressure generation unit 24.

[0015] The vehicle braking system 10 also includes a control unit 50. Various individual components (e.g., the pressure generating unit 24, etc.) of the braking system 10 may each contain their own control unit. These control units function together via interconnections and are described below as the control unit 50. The control unit 50 receives signals measured or detected by various sensors 66A, 66B, 66C, which indicate braking triggers, such as environmental conditions or inputs from the driver in and around the vehicle. Some of these environmental conditions may include the road surface condition (wet, icy, gravel), weather conditions (rain, snow, temperature, humidity), proximity to nearby objects (other vehicles, road markings), the pressure in the brake unit before brake application (e.g., measured by the pressure sensor 74), and tire conditions (tire pressure, tread depth).Driver inputs can include physical inputs to vehicle components (at the brake pedal 18, the accelerator pedal, the steering wheel) and mode selection (comfort mode, sport mode, performance mode, autonomous mode). This information allows the control unit 50 to modify the braking characteristics of the braking system 10, as described below.

[0016] Under normal operation, the vehicle braking system 10 can be operated in three ways to provide braking force to the wheel cylinders 20: non-amplified, amplified, and electronic braking. In non-amplified braking, the operator applies force to the brake pedal 18, which pivots the pedal 18 from the extended position towards the retracted position. This movement moves the input linkage 34 and the master cylinder pistons 14A, 14B against the force of the master cylinder return springs 14C, 14D. Brake fluid in the master cylinder chambers 14E, 14F is expelled from the master cylinder 14 and into the respective circuits 36A, 36B. With the separating valves 62 open, the pressure generated in the master cylinder 14 produces a braking force at the wheel cylinders 20 via the open inlet valves 58.

[0017] During aggravated braking, the operator applies force to the brake pedal 18, which pivots the pedal 18 from the extended position towards the retracted position. This movement displaces the input linkage 34. The displacement of the input linkage 34 is registered by the differential travel sensor 48, and the electric motor 52 and the gear unit 54 generate a torque to increase the force applied to the master cylinder pistons 14A, 14B. The amplification force generated by the amplifier 30 can be modified by the control unit 50 based on operating or environmental conditions or driver input. The master cylinder pistons 14A, 14B are displaced against the master cylinder return springs 14C, 14D. Brake fluid in the master cylinder chambers 14E, 14F is expelled from the master cylinder 14 and into the respective circuits 36A, 36B.When the separating valves 62 are in an open position, the pressure generated in the main cylinder 14 produces a braking force at the wheel cylinders 20 via the open inlet valves 58.

[0018] During electronic braking, the operator applies a force to the brake pedal 18, which pivots the pedal 18 from the extended position towards the retracted position. This movement displaces the input linkage 34. The amplifier 30 can be actuated to prevent the actuation of the master cylinder pistons 14A, 14B. Alternatively, with minor modifications to the valves between the master cylinder 14 and the reservoir 16, the pressure generated in the master cylinder 14 by the operator's input force can be released into the reservoir 16. A sensor (e.g., the differential travel sensor 48 of the amplifier 30, a standalone pressure or displacement sensor, etc.) measures the input and sends a signal to the control unit 50. The control unit 50 activates the motor 28 of the electronically controlled pressure generating unit 24, thereby displacing the valve tappet 26.When the control valves 64 are open, the pressure generated in the electronically controlled pressure generation unit 24 produces a braking force at the wheel cylinders 20 via the open inlet valves 58. The control valves 64 can be opened to varying degrees in order to adjust and control the circular pressures at the wheel cylinders.

[0019] During autonomous braking, such as in adaptive cruise control, collision avoidance, or vehicle dynamics control, the vehicle braking system 10 can be operated to use the amplifier 30 or the pressure generating unit 24 as described above, but without user input at the brake pedal 18. Instead, a sensor reading indicating an environmental condition or driver input can be analyzed by the controller 50 to provide an input for the amplifier 30 (amplification mode) or the pressure generating unit 24 (electronic braking mode) without the driver operating the brake pedal 18.

[0020] In highly or fully automated vehicles (i.e., with SAE autonomy levels 4 and 5), where the vehicle does not require input from a driver while traveling to a destination, it may be desirable to retract the brake pedal 18 to prevent accidental depressing of the pedal 18 and to provide additional foot space for the driver.

[0021] To move the brake pedal 18 to the retracted position during operation, the vehicle is placed in an autonomous driving mode in which the operator is not required to use the brake pedal 18. The operator can initiate the autonomous driving mode by setting a destination or by activating an input 70 in the vehicle cabin 40. As shown, the input 70 is a push button or switch mounted on the underside of an instrument panel 72, although the actuator can be mounted elsewhere in the cabin 40 (e.g., on a door panel, a vehicle seat, the center console, integrated with the vehicle's computer / entertainment center / climate control system, etc.). Alternatively, the vehicle can be preset to an autonomous driving mode.Once autonomous driving mode is selected, the controller 50 operates the booster 30 as a pedal depressor to hold the pedal in the retracted position and offset against or near the bulkhead 44 and out of the way of the vehicle operator. The controller 50 actuates the motor 52 and the gear unit 54 of the brake booster 30 to retract the brake pedal 18 from the pre-tensioned extended position to the retracted position, where the pedal 18 is offset and held. Actuating the amplifier 30 to retract the pedal 18 displaces the pistons 14A, 14B in the master cylinder 14. To prevent a pressure build-up (and the associated braking force) at the brake cylinders 20, which is generated by the displaced pistons 14A, 14B, the separating valves 62 and the outlet valves 60 are in open positions while the pedal 18 is retracted to direct the fluid to the reservoir 16.Alternatively, a fluid return line can be located between the master cylinder 14 and the separating valves 62. When the separating valves 62 are closed, this also directs the fluid expelled from the master cylinder 14 to the reservoir 16. To keep the pedal 18 in the retracted position, the booster 30 remains engaged to overcome the spring force produced by the master cylinder return springs 14C, 14D. Alternatively, frictional forces in the transmission unit 54 and the motor 52 can prevent the pedal 18 from returning without additionally engaging the motor 52. As a further alternative, a separate locking or hold-down mechanism can be used to physically retain the brake pedal 18 in the retracted position, allowing the motor 52 to be switched off while the brake pedal 18 remains in the retracted position.

[0022] The brake pedal 18 remains in the offset and retracted position during the vehicle's travel in autonomous driving mode, regardless of any braking force applied to the wheel cylinders 20. If a braking action is required based on an input from sensors 66A, 66B, 66C to the controller 50, the electronically controlled pressure generation unit 24 functions similarly to the electronic braking mode described above. Based on the sensor readings and according to the desired braking characteristics (e.g., time to stop, deceleration rate, etc.), the controller 50 opens the control valves 64 and actuates the motor 28 of the pressure generation unit 24 to displace the valve tappet 26 by a certain amount, thereby producing a braking force at the wheel cylinders 20.In some designs, the amplifier 30 can simultaneously function as a hold-down device and respond to brake commands from the control unit 50 to provide the requested braking force to the wheel cylinders 30. In such a design, the brake pedal 18 would start in the offset position upon a braking request and move within a range of retracted or offset positions when the amplifier is activated to provide the requested braking.

[0023] When the autonomous driving mode is deactivated, whether by completion of the requested route, by a scenario detected by the vehicle sensors 66A, 66B, 66C in which autonomous driving is no longer acceptable (e.g., pressure loss in the pressure generating unit), or by manual input from the operator, the brake pedal 18 is released by the amplifier 30, so that it returns to the pre-tensioned position, thus making the brake pedal 18 ready for use by the driver again in the extended position. If the master cylinder pistons 14A, 14B are displaced when the brake pedal 18 is in the offset position, in some designs these pistons 14A, 14B also return to the pre-tensioned position upon detection or manual input to end the autonomous driving mode, as described above.

[0024] Various features of the disclosure are set forth in the claims below.

Claims

[1] Vehicle braking system (10) comprising the following: a wheel cylinder (20); a master cylinder (14) containing a master cylinder piston which, in a first operating mode, can be operated to move between an uncontrolled position and a controlled position; a valve (62) located between the main cylinder (14) and the wheel cylinder (20), wherein the valve (62) is in a closed position in a second operating mode; a brake pedal (18) that can be operated to switch between an extended position, corresponding to the unactuated position of the master cylinder (14), and a retracted position, corresponding to the actuated position of the master cylinder (14); and an amplifier (30) located between the master cylinder (14) and the brake pedal (18), wherein the main cylinder (14) can be operated in the first operating mode to selectively transmit a braking force from the brake pedal (18) to the wheel cylinder (20); wherein the amplifier (30) can be operated in the second operating mode to hold the brake pedal (18) in the retracted position without user input and without linked braking. [2] Vehicle braking system (10) according to claim 1, wherein the amplifier (30) can be operated in the first operating mode to amplify the braking force generated by the master cylinder (14). [3] Vehicle braking system (10) according to claim 1, which further comprises an electronically controlled pressure generating unit (24) separate from the master cylinder (14), which in the second operating mode can be operated to generate a braking force at the wheel cylinder (20). [4] Vehicle braking system (10) according to claim 1, wherein the second operating mode is an autonomous driving mode, wherein the vehicle braking system (10) can be operated in autonomous driving mode to generate a braking force without input from the user and the brake pedal (18) cannot be operated to provide the braking force to the wheel cylinders (20). [5] Vehicle braking system (10) according to claim 4, which further comprises a controller (50) programmed to switch the vehicle braking system (10) from the first operating mode to the autonomous driving mode in response to an input from the user. [6] Vehicle braking system (10) according to claim 5, which further comprises one or more sensors (66A, 66B, 66C) that can be operated to detect a brake release, wherein the controller (50) is programmed to switch the vehicle braking system (10) from the second mode to the first mode in response to an input from the one or more sensors (66A, 66B, 66C). [7] Vehicle braking system (10) according to claim 5, wherein the control (50) is programmed to switch the vehicle braking system from the second mode to the first mode in response to an input from the user or upon detection that a desired brake pressure is not reached. [8] Method for operating a vehicle braking system (10) wherein the method comprises: to provide a brake pedal (18) coupled to a master cylinder (14), wherein the brake pedal (18) is in an extended position ready for use; to move the brake pedal (18) into a retracted position without braking, in order to define an offset state; to hold the brake pedal (18) in the offset state without linked braking; to automatically identify a brake trigger with a controller (50) and to generate a signal from the controller (50) in response to the identification of the brake trigger; to separate a brake fluid flow path between a master cylinder (14) and a wheel cylinder (20); and to generate pressure on a wheel cylinder (20) based on the signal, wherein the strength of the pressure is independent of the position of the brake pedal (18) and is generated without using the brake pedal (18). [9] Method according to claim 8, which further comprises switching on an electromechanical amplifier (30) to move the brake pedal (18) from the extended position to the offset position. [10] Method according to claim 9, further comprising entering a command into the control unit (50) to retract the brake pedal (18) prior to switching on the electromechanical amplifier (30), wherein entering the command into the control unit (50) includes bringing the vehicle into an autonomous driving mode. [11] Method according to claim 8, further comprising entering a command into the control unit (50) to release the brake pedal (18) into the extended position, wherein entering the command into the control unit (50) includes exiting an autonomous driving mode. [12] Vehicle braking system (10) comprising the following: a wheel cylinder (20); a master cylinder (14) and a valve (62) located between the master cylinder (14) and the wheel cylinder (20), wherein the valve (62) in a second operating mode separates a brake fluid flow path between the master cylinder (14) and the wheel cylinder (20); a brake pedal (18) that can be operated to switch between an extended position, in which the brake pedal (18) is ready for use, and a retracted position, in which the brake pedal (18) is offset; and a pedal holding device which can be operated to hold the brake pedal (18) in the retracted position, wherein the brake pedal (18) can be controlled in a first operating mode from the extended position to the retracted position and the vehicle braking system (10) can be operated to provide a variable braking force linked to the position of the brake pedal (18) and wherein in the second operating mode the pedal holding device holds the brake pedal (18) in the retracted position without an associated braking force and the vehicle braking system (10) can be operated to provide a variable braking force independently of the position of the brake pedal (18). [13] Vehicle braking system according to claim 12, wherein the second operating mode is an autonomous driving mode, wherein the vehicle braking system (10) can be operated in autonomous driving mode to generate the variable braking force without user input. [14] Vehicle braking system according to claim 12, wherein the pedal holding device is an electromechanical amplifier (30) which can be operated in the first operating mode to amplify the linked braking force and which can further be operated to retract the brake pedal (18) into the retracted position so that the system switches to the second operating mode. [15] Vehicle braking system according to claim 14, which further comprises an electrically controlled pressure generating unit (24) separate from the master cylinder (14) and the electromechanical amplifier (30), which in the second operating mode can be operated to generate a braking force at the wheel cylinder (20). [16] Vehicle braking system according to claim 12, which further comprises a master cylinder (14) and an electrically controlled pressure generating unit (24) separately from the master cylinder (14), wherein the electrically controlled pressure generating unit (24) can be operated in the first operating mode to generate a braking force at the wheel cylinder (20) in response to the actuation of the brake pedal (18). [17] Vehicle braking system according to claim 16, which further comprises one or more sensors (66A, 66B, 66C) that can be operated to detect a brake release, wherein the electronically controlled pressure generating unit (24) in the second operating mode can further be operated to generate a braking force at the wheel cylinder (20) in response to an input from the one or more sensors (66A, 66B, 66C).

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