DE102016215759A1 - Hydraulic brake system in a vehicle for generating a hydraulic parking brake pressure - Google Patents

Abstract

A hydraulic brake system in a vehicle for generating a hydraulic parking brake pressure in a brake circuit at standstill of the vehicle has a pressure switch in the brake circuit, which switches pressure-dependent and activated when falling below a brake pressure, a control unit for increasing the current parking brake pressure.

Description

The invention relates to a hydraulic brake system in a vehicle for generating a hydraulic parking brake pressure according to the preamble of claim 1.

State of the art

From the WO 2006/032417 A2 a hydraulic vehicle brake is known in a vehicle, comprising two brake circuits, each with two hydraulically actuated wheel brake on the wheels of the vehicle. In each brake circuit, a switching valve is integrated, which is adjustable between a first position in which the brake system is used as a regular vehicle brake, and a second switching position, in which the brake system can be used as a parking brake for locking the vehicle at a standstill. Each switching valve can be adjusted by means of an actuating cylinder, which is acted upon by further adjustable valves with fluid from a pressure fluid tank. For the implementation of the regular braking function for braking the vehicle while driving, the actuating cylinder is acted upon by the hydraulic pressure from the pressure fluid tank. If, on the other hand, the vehicle brake is to be used as a parking brake, the pressure is discharged from the actuating cylinder, as a result of which the switching valve is displaced and the currently prevailing hydraulic parking brake pressure is enclosed in the brake circuit.

Disclosure of the invention

The parking brake system according to the invention can be used in vehicles for generating a hydraulic parking brake pressure in order to generate in a brake circuit of the brake system at a standstill parkfest the vehicle parking brake. In this case, the hydraulic parking brake pressure acts in a hydraulically actuable wheel brake device on at least one vehicle wheel, preferably in wheel brake devices on two vehicle wheels, for example on the two vehicle wheels on the rear axle of the vehicle. The parking brake preferably works exclusively hydraulically without electromechanical assistance.

According to a preferred embodiment, the braking system is the regular vehicle brake that is used to decelerate when the vehicle is moving. When the vehicle is stationary, the braking system can be used as a parking brake system.

To realize the parking brake function, an adjustable switching valve is adjusted in the brake circuit of the brake system in a locking or blocking position in which the current brake pressure is included in the brake circuit and acts as a hydraulic parking brake pressure in the at least one wheel brake.

In the hydraulic brake system according to the invention, a pressure switch is arranged in the brake circuit, the pressure-dependent between two switching positions is adjustable. The change between the switching positions in the pressure switch takes place when the limit pressure in the brake circuit is undershot or exceeded. The pressure switch is acted upon by the current parking brake pressure in the brake circuit, so that the switching position of the pressure switch depends on the current parking brake pressure. If the current hydraulic parking brake pressure falls below the limit pressure, the pressure switch changes its switching position and activates a control unit, whereupon the current parking brake pressure is raised. Advantageously, the pressure switch changes its switching position solely due to a pressure change, so that the pressure switch does not have to be connected to a further energy source.

This embodiment has the advantage that the activation of the control unit via the pressure switch in dependence on the current hydraulic pressure in the brake circuit, whereby it is possible that the controller remains inactive, as long as the hydraulic pressure is above the limit pressure. The limit pressure is sufficiently high to ensure sufficient parking brake power and to secure the vehicle with sufficient safety. Since the switching position of the pressure switch depends on the current pressure in the brake circuit, the pressure switch serves as a monitoring unit, with no additional energy required for the monitoring function in the pressure switch. The change of the switching position in the pressure switch is exclusively pressure-dependent.

This allows the controller to remain inactive and to consume no energy as long as the pressure in the brake circuit is above the limit pressure. If, on the other hand, the pressure drops below the limiting pressure, for example due to leakage or thermally induced changes in length, the switching position in the pressure switch is automatically changed and the control unit activated, which then transmits actuating signals to an actuating unit in order to control the pressure in the brake circuit via the same limiting pressure or raise higher limit pressure. As soon as this is done, the pressure switch again changes its switching position, whereupon the control unit is switched back to inactive and consumes no further energy.

Advantageously, the pressure switch is below the limit pressure in an electrically conductive position and above the same or higher Limit pressure in an electrically non-conductive position. In the non-conducting position, the current flow through the pressure switch, which is preferably in a circuit with the control unit, interrupted, so that also according to the control unit is inactive. In the electrically conductive position, however, the circuit is closed and the control unit active.

According to yet another expedient embodiment, the control unit, which is actuated by the control unit to increase the current parking brake pressure, a control valve via which a hydraulic additional accumulator is fluidly connected in the brake system with the brake circuit. The control valve is adjustable between a blocking position and a connecting position, being decoupled in the blocking position of the additional hydraulic accumulator and the pressure in the additional memory does not work in the brake circuit. In the connecting position of the additional memory is connected to the brake circuit, so that the hydraulic pressure of the additional memory is also effective in the brake circuit.

The control valve is designed for example as a solenoid valve. If the pressure is above the limit pressure, the control valve remains in its blocking position. In the case of using the hydraulic brake system as a vehicle brake, the control valve is advantageously also adjusted in its blocking position, so that the vehicle brake operates independently of the additional hydraulic accumulator. To increase the hydraulic pressure when functioning as a parking brake, the control valve is opened and then, after the hydraulic pressure in the brake circuit has risen to a value above the same or a higher limit pressure, adjusted by the control unit back to the locked position.

According to another expedient embodiment, the actuating unit, which is actuated by the hydraulic pressure raising control unit, is a hydraulic pump. The hydraulic pump is for example part of an ESP system (Electronic Stability Program) in the brake system or an ABS system (Anti-lock Braking System). But it is also, for example, an embodiment of the hydraulic pump as a so-called iBooster into consideration, in which an electric motor actuates the master cylinder via a transmission. With the activation of the hydraulic pump, the pressure in the brake system rises to a value above the brake pressure, whereupon the pressure switch is moved back into its other switching position and the control unit is deactivated.

It may be expedient to realize a hysteresis function with a lower and an upper limit pressure when activating and deactivating the control unit. The control unit is activated when the hydraulic pressure in the brake circuit drops below the lower limit pressure. The control unit is deactivated again only when the hydraulic pressure in the brake circuit has risen to a value above the upper limit pressure. In this way it is avoided that the control unit is permanently switched on and off.

According to a further expedient embodiment, which relates to the actuation of a hydraulic pump for raising the hydraulic pressure, the switching valve in the brake circuit, which is usually in a blocking position to implement the parking brake function to include the hydraulic parking brake pressure in the brake circuit, adjusted to an open position to promote hydraulic fluid from a hydraulic reservoir upon actuation of the hydraulic pump. After completion of the promotion, the switching valve is moved back to the locked position. In an alternative embodiment, the switching valve remains in the blocking position and, to raise the hydraulic pressure, a high-pressure switching valve is opened, via which hydraulic fluid is conveyed into the brake circuit upon actuation of the hydraulic pump.

The switching valve is, according to a further expedient embodiment, designed as a bistable switching valve which is in a stable position both in its open position and in its closed position. This embodiment has the advantage that energy is required only for the transfer of the switching valve from one to the other position, but both the open and the closed position can be permanently maintained without power supply.

According to yet another expedient embodiment, the pressure switch is connected to a brake fluid line between the switching valve and an inlet valve of a wheel brake. However, it is also possible to arrange the pressure switch in the brake fluid line between the inlet valve and the wheel brake.

According to yet another advantageous embodiment, the limit pressure is set to a value that is less than the target parking brake pressure. As a result, a safety distance is ensured, the limit pressure is chosen in particular high enough that a setting of the vehicle is still guaranteed at the limit pressure.

Further advantages and expedient embodiments can be taken from the further claims, the description of the figures and the drawing which shows a hydraulic circuit diagram of a vehicle brake system which can also be used as a parking brake.

The in the hydraulic circuit diagram according to 1 illustrated hydraulic brake system 1 , which is the vehicle brake of a vehicle, has a Vorderachsbremskreis 2 and a rear axle brake circuit 3 for the supply of wheel brake devices 8th and 9 on the front wheels or 10 and 11 on the rear wheels with hydraulic brake fluid on. In principle, brake systems are also considered in which the brake circuit distribution is diagonal, so that one wheel brake device is provided on each of the front wheel and the rear wheel per brake circuit.

The two brake circuits 2 . 3 are on a common master cylinder 4 Connected via a brake fluid reservoir 5 supplied with brake fluid. The master cylinder 4 is from the driver via the brake pedal 6 operated, the pedal travel exerted by the driver can be measured via a pedal travel sensor. Between the brake pedal 6 and the master cylinder 4 may be a brake booster, which includes, for example, an electric motor, which preferably via a transmission, the master cylinder 4 pressed (iBooster). The adjusting movement of the brake pedal 6 is transmitted, for example, as a sensor signal to a control unit of the brake booster, in which control signals are generated for controlling the brake booster.

In every brake circuit 2 . 3 is a switching valve 12 arranged in the flow path between the master cylinder 4 and the respective wheel brake devices 8th and 9 respectively. 10 and 11 lies. The changeover valves 12 stand in their currentless basic position in a connection position in which a flow through the valve is possible. Each changeover valve 12 is associated with a parallel check valve, which can be flowed through in the direction of the respective wheel brake devices.

Between the switching valves 12 and the respective wheel brake devices 8th . 9 respectively. 10 . 11 are inlet valves 13 , which are also currentless in the connecting position and which are associated with check valves, which in the opposite direction, so can be flowed through by the wheel brake in the direction of the master cylinder.

Every wheel brake device 8th . 9 respectively. 10 . 11 is each an exhaust valve 14 assigned, which is normally in a disconnected position in which the flow is interrupted. The exhaust valves 14 are each with the suction side of a pump unit 15 connected in each brake circuit 2 . 3 a delivery pump 18 respectively. 19 having. The pump unit is an electric drive or pump motor 20 assigned to a wave 21 both feed pumps 18 and 19 actuated. The pressure side of the feed pump 18 respectively. 19 is at a line section between the switching valve 12 and the two intake valves 13 connected per brake circuit.

The suction sides of the feed pumps 18 and 19 each with a high pressure switching valve 22 connected to the master cylinder 4 hydraulically connected. In a dynamic driving control intervention can stand for a fast brake pressure build-up in the de-energized state in disconnected high-pressure switching valves 22 be opened so that the feed pumps 18 and 19 directly from the master cylinder 4 Aspirate hydraulic fluid. This brake pressure build-up can be performed independently of an actuation of the brake system by the driver. The pump unit 15 with the two feed pumps 18 and 19 , the electric pump motor 20 and the wave 21 belongs to a driver assistance system and is part of an Electronic Stability Program (ESP). The electric pump motor 20 is made by actuating signals of a control unit 25 set.

Between the exhaust valves 14 and the suction side of the feed pumps 18 and 19 is located per brake circuit 2 . 3 a storage chamber 23 , which serves for the intermediate storage of brake fluid, which during a dynamic driving engagement by the exhaust valves 14 from the wheel brake devices 8th . 9 respectively. 10 . 11 is omitted. Every storage chamber 23 is associated with a check valve, which is in the direction of the suction side of the feed pumps 18 . 19 opens.

For pressure measurement is a pressure sensor 24 in the brake circuit 3 adjacent to the master cylinder 4 arranged.

In the rear axle brake circuit 3 is in the brake fluid line between the switching valve 12 and the intake valves 13 On-off valve 26 arranged in a use of the hydraulic brake system as a parking brake for locking the vehicle at a standstill in a closed or separating position, in which the flow rate between the switching valve 12 and the inlet valve 13 Is blocked. As a result, the current hydraulic brake pressure as a parking brake pressure in the rear axle brake circuit 3 locked in. The switching valve 26 is the changeover valve 12 in the rear axle brake circuit 3 immediately downstream.

To compensate for a drop in the brake pressure when parking the vehicle, but at the same time to realize the monitoring of the parking brake pressure without energy consumption, is in the brake fluid line between the switching valve 26 and the intake valves 13 a pressure switch 27 integrated with the parking brake pressure in the rear axle brake circuit 3 is charged. The pressure switch is below a limit pressure in an electrically conductive Position and above the limit pressure in an electrically non-conductive position.

The switching valve 26 is designed as a bistable switching valve, which is in a stable position both in its open position, in which a free flow through the switching valve is given, as well as in its closed position. As long as the brake system is used as a regular vehicle brake to brake the vehicle while driving, is the switching valve 26 in its open position and allows the flow of brake fluid.

Advantageously, a hysteresis function is realized in the pressure switch by the lowering of the parking brake pressure below a lower limit pressure of the pressure switch is placed in an electrically conductive position, but the pressure switch is only offset with the exceeding of an upper limit pressure of the electrically conductive into an electrically non-conductive position. The lower limit pressure and the upper limit pressure differ by a defined minimum differential pressure, which is for example 5 bar.

The pressure switch 27 is electrically connected to the control unit 25 connected and enabled or disabled the controller 25 , The pressure switch 27 is for example in a circuit of the control unit 25 and activates the deactivated control unit as soon as the hydraulic parking brake pressure drops below the limit pressure. Accordingly, the controller 25 deactivated as soon as the hydraulic parking brake pressure exceeds the limit pressure. Because the pressure switch 27 exclusively from the currently prevailing hydraulic pressure in the rear axle brake circuit 3 is switched, it is a passive component that does not require a separate power supply. At the same time, the pressure switch takes over 27 a safety and monitoring function and monitors the hydraulic parking brake pressure in the rear axle brake circuit 3 ,

The controller can be activated by activating 25 an actuating unit for increasing the currently prevailing parking brake pressure in the rear axle brake circuit 3 drive. The actuator is in particular the electric pump motor 20 for driving the feed pump 19 in the rear axle brake circuit 3 , At the same time, the switching valve 26 adjusted from the closed position to the open position to a promotion of brake fluid from the brake fluid reservoir 5 to enable. After a desired parking brake pressure is reached, for example, the upper limit pressure, the switching valve 26 moved back to the closed position, whereupon the control of the electric pump motor 20 through the control unit 25 is ended. The termination of the control is preferably carried out directly via the pressure switch 27 , which is offset from the pressure increase from the electrically conductive to the electrically non-conductive position.

This results in two functions for the pressure switch or for its connection to the control unit: Firstly, the control unit is awakened from the inactive state, on the other hand informs the pressure switch the activated control unit, if a sufficiently high pressure prevails and the pressure generation are switched inactive can.

The pressure switch 27 is located in the section of the brake fluid line between the switching valve 26 and the intake valves 13 , As shown by the dashed line, it is also possible to use the pressure switch 27 between an inlet valve 13 and a wheel brake to arrange.

The current parking brake pressure in the rear axle brake circuit 3 may optionally be alternative to a control of the electric pump motor 20 also via an additional memory 28 be increased, in which brake fluid is received with a desired parking brake pressure. The additional memory 28 is via a control valve 29 , For example, a solenoid valve, with the brake fluid line downstream of the feed pump 19 in the rear axle brake circuit 3 connected. During operation of the brake system 1 as a regular vehicle brake is the control valve 29 in its locked position, in which the auxiliary storage 28 from the rear axle brake circuit 3 is decoupled, as well as a function of the braking system as a parking brake, as long as the parking brake pressure is above the limit pressure. With the parking brake pressure falling below the limit pressure and the change in the switching state of the pressure switch 27 from the electrically non-conductive position to the electrically conductive position, the state of the controller 25 transferred from the inactive state to an active state and may be the control valve 29 from the control unit 25 be adjusted in its open position. Then brake fluid flows from the additional storage 28 in the rear axle brake circuit 3 and increases the prevailing brake fluid pressure to the desired parking brake pressure. Subsequently, the control valve 29 again transferred to its closed position to the additional memory 28 from the rear axle brake circuit 3 to decouple.

Filling the additional memory 28 with brake fluid with setpoint parking brake pressure can with open control valve 29 and simultaneous control of the feed pump 19 in the rear axle brake circuit 3 be performed.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2006/032417 A2 [0002]

Claims (10)

Hydraulic brake system in a vehicle for generating a hydraulic parking brake pressure in a brake circuit ( 2 ) at standstill of the vehicle, with at least one hydraulically actuable wheel brake device ( 8th . 9 ) in the brake circuit ( 2 ), which is to be supplied with brake fluid, with at least one switching valve ( 12 ) for enclosing the hydraulic parking brake pressure in the brake circuit ( 2 ) at standstill of the vehicle, characterized in that a pressure switch ( 27 ) in the brake circuit ( 2 ) is arranged, the pressure-dependent between two switching positions is adjustable and when falling below a limit pressure in the brake circuit ( 2 ) a control device ( 25 ) to increase the current parking brake pressure activated. Brake system according to claim 1, characterized in that the pressure switch ( 27 ) is below the limit pressure in an electrically conductive position and above the limit pressure in an electrically non-conductive position. Brake system according to claim 1 or 2, characterized in that a hydraulic additional storage ( 28 ) via a control valve ( 29 ) to at least one brake circuit ( 2 ) is connected, wherein the control valve ( 29 ) is in a blocking position, as long as the current parking brake pressure exceeds the limit pressure, and the control unit ( 25 ) when the limit pressure falls below the control valve ( 29 ) into an auxiliary memory ( 28 ) with the brake circuit ( 2 ) connecting position adjusted. Brake system according to one of claims 1 to 3, characterized in that the control unit ( 25 ) activated when the pressure falls below the limit pressure, a hydraulic pump. Brake system according to claim 4, characterized in that the hydraulic pump is part of an ESP system (Electronic Stability Program). Brake system according to one of claims 1 to 5, characterized in that the switching valve ( 26 ) in the brake circuit ( 2 ) is designed as a bistable switching valve which is in a stable position both in the open position and in the closed position. Brake system according to one of claims 1 to 6, characterized in that the pressure switch ( 27 ) with a brake fluid line between the switching valve ( 26 ) and an inlet valve ( 13 ) is connected to a wheel brake. Brake system according to one of claims 1 to 6, characterized in that the pressure switch ( 27 ) with a brake fluid line between the inlet valve ( 13 ) and the wheel brake device is connected. Brake system according to one of claims 1 to 8, characterized in that the limit pressure is less than the desired parking brake pressure. Method for generating a parking brake force in a vehicle with a hydraulic braking system ( 1 ) according to one of claims 1 to 9, wherein the control device ( 25 ) is inactive, as long as the current parking brake pressure is the limit pressure in the brake circuit ( 2 ), and the control unit ( 25 ) is activated when the current parking brake pressure falls below the limit pressure.

Images