DE102022205462A1 - Energy-saving operating mode - Google Patents

Abstract

The invention relates to a hydraulic motor vehicle brake system having an electrical pressure supply device with a normally closed switching valve, at least one wheel brake and a control unit, which is set up to work in a first brake-by-wire operating mode, in which the electrical pressure supply device with the switching valve energized to act on the at least a wheel brake is operated with hydraulic pressure. In order to reduce energy consumption, the control unit is set up to work in an energy-saving mode, which is a second brake-by-wire operating mode, in which the electrical pressure supply device is operated when the switching valve is de-energized to apply hydraulic pressure to the at least one wheel brake, the pressure supply device the connection valve presses open.

Description

The invention relates to a hydraulic motor vehicle brake system having an electrical pressure supply device with a normally closed switching valve, at least one wheel brake and a control unit, which is set up to work in a brake-by-wire operating mode, in which the electrical pressure supply device with the switching valve energized to act on the at least one Wheel brake is operated with hydraulic pressure.

Such brake systems can build up pressure and thus brake with great comfort for the driver. However, if part of the brake system fails due to an error, fallback levels are necessary, which usually only enable reduced performance of the brake system.

An important aspect here is the energy requirement of the braking system when braking. If this is too high, braking to a standstill can only be ensured by means of a very high pedal force if the brake system is not fully functional, especially if the vehicle electrical system fails.

It is therefore the object of the invention to provide a brake system with a reduced energy requirement.

The object is achieved in that the control unit of the hydraulic motor vehicle brake system is set up to work in an energy-saving mode, in particular in the event of a vehicle electrical system failure, which is a second brake-by-wire operating mode in which the electrical pressure supply device is used to act on the at least one valve when the switching valve is de-energized Wheel brake is operated with hydraulic pressure, with the pressure supply device pressing open the switching valve. The switching valve is arranged at the outlet opening, i.e. in particular between the pressure supply device and at least one inlet valve of the at least one wheel brake. By not energizing the switching valve, its energy requirement is directly saved. Particularly when the brake pressure and pressure dynamics are low, a significant proportion of the energy requirement is accounted for by this valve. The operational readiness of the motor vehicle brake system is thus improved.

In a preferred embodiment of the invention, the motor vehicle brake system comprises an emergency energy storage unit, which takes over the energy supply in the event of a vehicle electrical system failure. Especially in conjunction with the reduced energy consumption, the emergency energy storage can ensure increased braking to a standstill.

In a further preferred embodiment of the invention, in the first brake-by-wire operating mode without a pressure request, a flow-open connection is established between the master cylinder and the wheel brakes, which is closed when a pressure request is present. This improves the NVH behavior of the brake in standby mode and thus comfort for the driver.

In a further preferred embodiment of the invention, the emergency energy storage comprises an electrical double-layer capacitor. This is particularly suitable as an emergency energy storage device and has the required energy and power densities.

In a particularly preferred embodiment of the invention, the emergency energy storage contains 100 to 2000 joules. This size represents a good compromise between costs and sizes on the one hand and the availability of the braking system on the other.

In a further preferred embodiment of the invention, a simulator valve is provided between the master brake cylinder and a simulator and/or a master cylinder valve between the master brake cylinder and inlet valves of the wheel brakes.

In a further preferred embodiment of the invention, the control device is set up in the energy-saving mode to maintain a pressure built up in the wheel brakes, to de-energize the pressure supply device, so that the pressure is maintained by the de-energized and therefore closed switching valve. The energy requirement for maintaining pressure, i.e. within the framework of a normal leakage-related minimal pressure loss, is therefore greatly reduced.

In a further preferred embodiment of the invention, the control device is set up to keep the pressure supply device de-energized and to open the master cylinder valve in the energy saving mode to reduce pressure. This allows the pressure in the direction of the master cylinder to be reduced.

In a particularly preferred embodiment of the invention, the control device is set up so that in the energy saving mode the pressure is only reduced when the pressure requirement is smaller by a limit value than the current pressure. A value between 5 and 20 bar, particularly preferably 10 bar, can preferably be selected as the limit value. The pressure reduction therefore takes place in stages, so that the number of energy-consuming switching operations of the valves used is minimized.

In a particularly preferred embodiment of the invention, the control device is set up so that in the energy-saving mode the pressure build-up only occurs when the pressure requirement is greater than the current pressure by a limit value. The limit value can preferably be a value between 1 and 10 bar, particularly preferably 5 bar to get voted. The limit value for building up pressure is preferably smaller than the limit value for reducing pressure. The pressure is built up in stages, so that the number of energy-consuming switching operations of the valves used for this purpose and in particular the starting operations of the motor of the pressure supply device is minimized. This is particularly advantageous if the pressure provision device is a linear actuator.

In a particularly preferred embodiment of the invention, the control device is set up so that the simulator valve is de-energized in the energy saving mode. Although this leads to poor pedal feel, it can further increase the standby time of the brake system.

In a particularly preferred embodiment of the invention, the control device is set up so that in the first by-wire mode the master cylinder valve is closed and in the energy saving mode a circuit isolating valve is closed instead of the master cylinder valve. The circuit separation valve separates different groups of wheel brakes, in particular the wheel brakes of the front axle and the wheel brakes of the rear axle, into two partial circles. By closing the circuit isolating valve, part of the wheel brakes is connected to the pressure supply device and another part to the master brake cylinder.

Further features, advantages and possible applications of the invention can also be found in the following description of exemplary embodiments and the drawings. All features described and/or illustrated are part of the subject matter of the invention, both individually and in any combination, regardless of their summary in the claims or their references.

This in 1 The brake system shown for a motor vehicle includes four hydraulically actuated wheel brakes 8a-8d. The brake system comprises a master brake cylinder 2 that can be actuated by means of an actuating or brake pedal 1, a path simulator or a simulation device or simulator 3 that interacts with the master brake cylinder 2, a pressure medium reservoir 4 under atmospheric pressure, an electrically controllable pressure supply device 5, and wheel valves, i.e. wheel-specific ones Brake pressure modulation valves, which are designed, for example, as inlet valves 6a-6d and outlet valves 7a-7d.

Furthermore, the brake system includes at least one electronic control and regulation unit 12 for controlling the electrically actuated components of the brake system. The control and regulation unit 12 in particular has at least two separate subunits, each of which regulates part of the hydraulic units.

According to the example, the wheel brake 8a is assigned to the left front wheel (FL), the wheel brake 8b to the right front wheel (FR), the wheel brake 8c to the left rear wheel (RL) and the wheel brake 8d to the right rear wheel (RR).

The master brake cylinder 2 has a master brake cylinder piston 15 in a housing 16, which delimits a hydraulic pressure chamber 17, and represents a single-circuit master brake cylinder 2. The pressure chamber 17 accommodates a return spring 9, which positions the piston 15 in an initial position when the master brake cylinder 2 is unactuated. On the one hand, the pressure chamber 17 is connected to the pressure medium reservoir 4 via radial bores formed in the piston 15 and a corresponding pressure compensation line 41, which can be shut off in the housing 16 by a relative movement of the piston 15. The pressure chamber 17, on the other hand, is connected to a brake supply line 13 by means of a hydraulic line section (also referred to as a first supply line) 22, to which the input ports of the inlet valves 6a-6d are connected. The pressure chamber 17 of the master brake cylinder 2 is connected to all inlet valves 6a-6d.

For example, no hydraulic valve, in particular no electrically or hydraulically actuated valve and no check valve, is arranged in the pressure compensation line 41 or in the connection between the pressure chamber 17 and the pressure medium reservoir 4.

Alternatively, a diagnostic valve, in particular a normally open diagnostic valve, preferably a parallel connection of a normally open diagnostic valve with a check valve closing towards the pressure medium reservoir 4, can be contained in the pressure compensation line 41 or between the master brake cylinder 2 and the pressure medium reservoir 4.

A separating valve 23 is arranged between the supply line 22 connected to the pressure chamber 17 and the brake supply line 13 or pressure chamber 17 is connected to the brake supply line 13 via the first supply line 22 with a separating valve 23. The isolation valve 23 is designed as an electrically actuated, preferably normally open (SO), 2/2-way valve. The hydraulic connection between the pressure chamber 17 and the brake supply line 13 can be shut off by the isolating valve 23.

A piston rod 24 couples the pivoting movement of the brake pedal 1 as a result of pedal actuation with the translational movement of the master brake cylinder piston 15, the actuation path of which is detected by a preferably redundant displacement sensor 25. As a result, the corresponding piston travel signal is a measure of the brake pedal actuation angle. It represents a driver's request to brake.

A pressure sensor 20 connected to the first supply line 22 detects the pressure built up in the pressure chamber 17 by moving the piston 15. This pressure value can also be evaluated to characterize or determine the driver's braking request. As an alternative to a pressure sensor 20, a force sensor 20 can also be used to determine the driver's braking request.

The simulation device 3 is, for example, designed to be hydraulic and is hydraulically coupled to the master brake cylinder 2. The simulation device 3, for example, essentially has a simulator chamber 29, a simulator rear chamber 30 and a simulator piston 31 separating the two chambers 29, 30 from one another. The simulator piston 31 is supported on a housing by an elastic element 33 (e.g. simulator spring) arranged in the (for example dry) simulator rear chamber 30. The hydraulic simulator chamber 29 is, for example, connected to the pressure chamber 17 of the master brake cylinder 2 by means of a preferably electrically actuated, preferably normally closed, simulator release valve 32.

The brake system or brake system includes an inlet valve 6a-6d and an outlet valve 7a-7d for each hydraulically actuated wheel brake 8a-8d, which are hydraulically connected in pairs via center connections and connected to the wheel brake 8a-8d. The inlet valves 6a-6d are each connected in parallel with an unspecified check valve that opens towards the brake supply line 13. The output connections of the outlet valves 7a-7d are connected to the pressure medium reservoir 4 via a common return line 14.

The electrically controllable pressure supply device 5 is designed as a hydraulic cylinder-piston arrangement or a single-circuit, electro-hydraulic actuator or linear actuator, the piston 36 of which can be actuated by a schematically indicated electric motor 35 with the interposition of a rotation-translation gear 39, which is also shown schematically. The piston 36 delimits the single pressure chamber 37 of the pressure supply device 5. A rotor position sensor, which is only indicated schematically and is used to detect the rotor position of the electric motor 35, is designated by the reference number 44.

A line section (also referred to as a second supply line) 38 is connected to the pressure chamber 37 of the electrically controllable pressure supply device 5. The supply line 38 is connected to the brake supply line 13 via an electrically actuated, preferably normally closed, switching valve 26. By means of the switching valve 26, the hydraulic connection between the pressure chamber 37 of the electrically controllable pressure supply device 5 and the brake supply line 13 (and thus the input connections of the inlet valves 6a-6d) can be opened and shut off in a controlled manner.

The actuator pressure generated by the force of the piston 36 on the pressure medium enclosed in the pressure chamber 37 is fed into the second supply line 38. In a “brake-by-wire” operating mode, in particular when the brake system is in a fault-free state, the supply line 38 is connected to the brake supply line 13 via the switching valve 26. In this way, during normal braking, wheel brake pressure is built up and reduced for all wheel brakes 8a-8d by moving the pistons 36 back and forth.

When the pressure is reduced by retracting the piston 36, the pressure medium previously displaced from the pressure chamber 37 of the pressure supply device 5 into the wheel brakes 8a-8d flows back into the pressure chamber 37 in the same way.

Alternatively, different wheel brake pressures for each wheel can be easily adjusted using the inlet and outlet valves 6a-6d, 7a-7d. When there is a corresponding pressure reduction, the pressure medium portion released via the outlet valves 7a-7d flows via the return line 14 into the pressure medium storage container 4.

A suction (“refill”) of pressure medium into the pressure chamber 37 is possible by retracting the piston 36 with the switching valve 26 closed, by drawing pressure medium from the container 4 via the line 42 with a flow direction to the actuator 5 opening check valve 53 can flow into the Akuatordruckraum or pressure chamber 37.

According to the example, when the piston 36 is in an unactuated state, the pressure chamber 37 is also connected to the pressure medium reservoir 4 via one or more sniffer holes. This connection between the pressure chamber 37 and the pressure medium reservoir 4 is separated when the piston 36 is actuated (sufficiently) in the actuation direction 27.

An electrically actuated, normally open circuit isolation valve 40 is arranged in the brake supply line 13, through which the brake system is divided into two hydraulic partial circuits. The brake supply line 13 is divided into a first line section 13a, which is connected (via the isolating valve 23) to the master brake cylinder 2, and a second line section 13b in the second hydraulic partial circuit, which is connected (via the switching valve 26) to the pressure supply device 5. The first line section 13a is connected to the inlet valves 6a, 6b of the wheel brakes 8a, 8b and the second line section 13b is connected to the inlet valves 6c, 6d of the wheel brakes 8c, 8d.

When the circuit isolating valve 40 is open, the brake system is designed as a single circuit. By closing the circuit isolating valve 40, the brake system, in particular controlled according to the situation, can be separated or divided into two hydraulic partial circuits, the brake circuits I and II. In the first brake circuit I, the master brake cylinder 2 is connected (via the isolating valve 23) to only the inlet valves 6a, 6b of the wheel brakes 8a, 8b of the front axle VA, and in the second brake circuit II the pressure supply device 5 (with the switching valve 26 open) is only connected connected to the wheel brakes 8c and 8d of the rear axle HA.

When the circuit isolating valve 40 is open, the input connections of all inlet valves 6a-6d can be supplied with a pressure via the brake supply line 13, which in a first operating mode (e.g. "brake-by-wire" operating mode) corresponds to the brake pressure supplied by the pressure supply device 5 is provided. The brake supply line 13 can be subjected to the pressure of the pressure chamber 17 of the master brake cylinder 2 in a second operating mode (e.g. in a de-energized fallback operating mode).

The brake system advantageously comprises a level measuring device 50 for determining a pressure medium level/level in the pressure medium reservoir 4. Advantageously, situation detection for circuit separation takes place by means of the circuit separation valve 40 via the level measuring device 50.

According to the example, the hydraulic components and hydraulic units, namely the master brake cylinder 2, the simulation device 3, the pressure supply device 5, the valves 6a-6d, 7a-7d, 23, 26, 40 and 32 as well as the hydraulic connections including the brake supply line 13, are together in one hydraulic control and regulation unit 60 (HCU). The hydraulic control and regulation unit 60 is assigned the electronic control and regulation unit (control system) 12. Hydraulic and electronic control and regulation units 60, 12 are preferably designed as a single unit (HECU).

The brake system includes a pressure sensor 19 or system pressure sensor for detecting the pressure provided by the pressure supply device 5. The pressure sensor 19 is arranged behind the switching valve 26 as seen from the pressure chamber 37 of the pressure supply device 5.

In order to be able to provide a sufficient delay of 0.4g even in the event of a vehicle electrical system failure, an emergency energy storage device is provided, which is designed as an electrical double layer capacitor (EDLC) with 500 joules.

2 shows simulation data of a by-wire pressure control with a pedal force of 200N and 40 bar pressure (top left). At the top right, the current drawn by the engine from the on-board network and the corresponding electrical energy are shown. The currents drawn from the on-board electrical system by the valves are shown at the bottom right. The individual energy consumption levels are shown at the bottom left. The simulation shows a total energy consumption of 455.4J, which can therefore just be met by the emergency power supply of 500J.

3 shows simulation data of a by-wire pressure control with a previous 15 second by-wire stand-by phase. It turns out that the energy consumption of 571 J is too high, so that the energy capacity of the emergency energy supply is exceeded.

4 shows simulation data of a by-wire pressure control with modulated pedal pressure known from the prior art. The energy requirement is also higher than the 500J available.

5 shows simulation data of a by-wire standby phase without pressure control known from the prior art. With the existing quiescent current, even without pressure build-up After 40 seconds, almost the entire energy storage of the emergency energy supply is used up.

6 now shows the behavior of the hydraulic motor vehicle brake system according to the invention. The pedal force of 200N and the corresponding pressure requirement of 40 bar are shown at the top left. This is built up by the linear actuator, which, as a pressure supply device, provides the pressure through the de-energized switching valve by pressing it open. After the desired pressure has been reached, the linear actuator is de-energized again so that no energy is required. As soon as no more volume flows through the activated switching valve and the pressure is equal across the switching valve, the valve spring returns it to the closed state. The pressure is therefore maintained even without power to the linear actuator. The energy required by the linear actuator motor decreases by 77J from 102 to 25J. Since in this simulation the switching valve was not closed the entire time, the energy consumption drops from 40 to 15J (instead of 0J). However, if you completely forego its power supply, the entire 40J can be saved. The energy requirement for this braking then drops by 77J + 40J from the previous 455J. This corresponds to an energy saving of around 25%.

Most long braking occurs with long pressure hold phases. By means of the motor vehicle brake system according to the invention, the pressure maintenance phases in particular can be designed to be energy efficient. This effect can be increased if the pressure control is divided into coarser stages.

Claims (12)

Hydraulic motor vehicle brake system comprising an electrical pressure supply device (5) with a normally closed switching valve (26), at least one wheel brake (8) and a control unit (12), which is set up to work in a first brake-by-wire operating mode in which the electrical Pressure supply device (5) is operated when the switching valve (26) is energized to apply hydraulic pressure to the at least one wheel brake (8), characterized in that the control unit (12) is set up to work in an energy-saving mode, which is a second brake-by -wire operating mode is in which the electrical pressure supply device (5) is operated when the switching valve (26) is de-energized to apply hydraulic pressure to the at least one wheel brake (8), the pressure supply device (5) pressing open the switching valve (26). Hydraulic vehicle brake system Claim 1 , characterized in that the motor vehicle brake system includes an emergency energy storage unit, which takes over the energy supply in the event of a vehicle electrical system failure. Hydraulic motor vehicle brake system according to one of the preceding claims, characterized in that in the first brake-by-wire operating mode without a pressure request there is a flow-open connection between the master cylinder (2) and the wheel brakes (8), which is closed when a pressure request is present. Hydraulic motor vehicle brake system according to one of the preceding claims, characterized in that the emergency energy storage is an electrical double-layer capacitor. Hydraulic motor vehicle brake system according to one of the preceding claims, characterized in that the emergency energy storage comprises 100 to 2000 joules. Hydraulic motor vehicle brake system according to one of the preceding claims, characterized in that a simulator valve (32) between the master brake cylinder (2) and a simulator (3) and / or a master cylinder valve (23) between the master brake cylinder (2) and inlet valves (6) of the wheel brakes (8) is provided. Hydraulic motor vehicle brake system according to one of the preceding claims, characterized in that in the energy saving mode for maintaining a pressure built up in the wheel brakes (8), the pressure supply device (5) is de-energized, so that the pressure is maintained by the de-energized closed switching valve (26). Hydraulic motor vehicle brake system according to one of the preceding claims, characterized in that in the energy saving mode to reduce pressure, the pressure supply device (5) is de-energized and the master cylinder valve (23) is opened. Hydraulic vehicle brake system Claim 8 , characterized in that in the energy saving mode the pressure is only reduced when the pressure requirement is smaller by a limit value than the current pressure. Hydraulic motor vehicle brake system according to one of the preceding claims, characterized in that in the energy saving mode the pressure builds up only when the pressure requirement is greater than the current pressure by a limit value. Hydraulic motor vehicle brake system according to one of the preceding claims, characterized in that the simulator valve (32) is de-energized in the energy saving mode. Hydraulic motor vehicle brake system according to one of the preceding claims, characterized in that in the first by-wire mode the master cylinder valve (23) is closed and in the energy saving mode a circuit isolating valve (40) is closed instead of the master cylinder valve (23).

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