HYDRAULIC SYSTEM WITH AT LEAST ONE PRESSURE SUPPLY DEVICE AND A SAFETY GATE FOR THE CONNECTION OF THE HYDRAULIC CIRCUITS

Abstract

A hydraulic system includes at least two hydraulic circuits with hydraulic circuit lines and at least one hydraulic component connected to each hydraulic circuit or to a hydraulic circuit line thereof via a respective switch valve used for pressure build-up and release. At least one pressure supply device can build up pressure in both hydraulic circuits. At least one circuit separating valve blocks or releases a hydraulic connection line connecting the two hydraulic circuits. At least one outlet valve selectively connects an accumulator container to at least one hydraulic circuit. A hydraulic connection between a pump of the pressure supply device and a respective hydraulic circuit connects a return flow from the hydraulic circuit into the pressure supply device or its pump. A controlled feed valve or a non-return valve controls the hydraulic connection. A pressure supply device or outlet valve releases pressure in at least one hydraulic component.

Claims

1. A hydraulic system, comprising the following: at least two hydraulic circuits with hydraulic circuit lines, at least one hydraulic component per respective hydraulic circuit, wherein each hydraulic component is connectable via a respectively assigned switching valve to the respective hydraulic circuit or to the hydraulic circuit line of the respective hydraulic circuit, wherein pressure build-up and pressure reduction in a respective hydraulic component are performed via the respectively assigned switching valve, at least one pressure supply device, wherein a pressure build-up in both hydraulic circuits is enabled by means of at least one pressure supply device, at least one circuit isolation valve, which serves for selectively shutting off or opening up a hydraulic connecting line that connects the two hydraulic circuits, at least one outlet valve by means of which a reservoir is connectable to at least one hydraulic circuit for pressure reduction directly or via a circuit isolation valve, and a hydraulic connection of a pump of the pressure supply device to the respective hydraulic circuit, wherein either a controlled infeed valve is provided for selectively shutting off and opening up the hydraulic connection, or a check valve is provided for preventing a return flow from the respective hydraulic circuit via the hydraulic connection into the pressure supply device or the pump of the pressure supply device, wherein pressure reduction in at least one hydraulic component is performed either by means of the at least one pressure supply device or via an outlet valve in a manner dependent on a state of the hydraulic system and/or on closed-loop pressure control.

2.-28. (canceled)

Description

[0064] In the drawings:

[0065] FIG. 1 shows a hydraulic system with two hydraulic circuits K1 and K2 and four wheel brakes and one pressure supply device and one auxiliary pressure supply and one pressure transducer, wherein the two hydraulic circuits can be selectively connected to or isolated from one another by means of a circuit isolation valve;

[0066] FIG. 2 shows the hydraulic system as per FIG. 1 with a safety gate with two series-connected circuit isolation valves;

[0067] FIG. 3 shows the hydraulic system as per FIG. 2 with an additional isolation valve in the first hydraulic circuit;

[0068] FIG. 4 shows a hydraulic system with rotary pump;

[0069] FIG. 5 shows the hydraulic system with two pressure supply devices and one auxiliary pressure supply with a safety gate with two series-connected circuit isolation valves;

[0070] FIG. 6 shows the hydraulic system according to the 4th safety level with two pressure supply devices and one auxiliary pressure supply with a safety gate with two series-connected circuit isolation valves for the selective connection of the first and the second hydraulic circuit, wherein the second hydraulic circuit can be connected to or isolated from a third hydraulic circuit by means of a further circuit isolation valve.

[0071] FIG. 1 shows brake system of safety level 1. The individual components can be combined to form modules. The brake system has two hydraulic circuits K1 and K2 to which a supply is provided by a pressure supply device DV which is connected to the first hydraulic circuit K1 via the infeed valve PD1. The infeed valve PD1 is preferably a valve which is closed when electrically deenergized, such that, in the event of failure of the pressure supply device DV, no failure of the first hydraulic circuit K1 occurs. If the pressure supply device DV performs a pressure change in the form of a pressure build-up P.sub.build-up or pressure reduction P.sub.reduction, the infeed valve PD1 is open. As illustrated, the pressure supply device may have a plunger pump with a spindle drive, which is preferably driven by means of an EC motor. The electrical connection 12 may also be of redundant configuration with a 2×3 phase connection. Instead of the pump with a plunger piston, use may also be made of a rotary pump with a toothed gear or of a piston pump, see for example FIG. 4, wherein, then, instead of the infeed valve PD1, use is for example made of a check valve to prevent an undesired backflow of hydraulic medium out of the brake circuit into the rotary pump.

[0072] The plunger pump can preferably be used for the pressure build-up P.sub.build-up and the pressure reduction P.sub.reduction, wherein this then, using a pressure-volume characteristic curve, displaces a corresponding volume of hydraulic medium in order to achieve the desired pressure change. Here, the volume is proportional to the adjustment travel of the plunger piston. Optionally, a breather hole may be provided, which is arranged such that it is opened up by the plunger piston only in the initial position of said piston, such that a pressure reduction P.sub.reduction is possible by dissipation via the working chamber of the plunger pump to a reservoir VB, which has great advantages.

[0073] The plunger pump solution is relatively complex in relation to the use of a rotary pump or rotary piston pump, because additional valves must be provided for the pressure reduction P.sub.reduction and the shut-off of the return line to the reservoir VB. The volume of the pressure supply device DV passes directly into the first hydraulic circuit K1 and via the circuit isolation valve BP1 into the second hydraulic circuit K2. The wheel brake cylinders or wheel brakes RZ1-RZ4 are each connected by means of respectively assigned switching valves SV to the respective hydraulic circuit K1, K2. In any hydraulic system, any number of actuating cylinders may be arranged in place of the wheel cylinders RZ 1-4.

[0074] The valves SV have the following functions:

1. Identification of a Wheel Brake Cylinder Fault

[0075] If a failure is present at a wheel brake cylinder RZ1-4, this is identified by way of the additional volume intake/delivery of the pressure supply device DV in relation to the so-called p-v characteristic curve, which is read in as a vehicle characteristic curve during the end of line inspection or is measured at intervals in the vehicle. This method is known per se. In conventional brake systems, however, this fault can be localized only with difficulty.

[0076] If the above-mentioned deviation is identified in the hydraulic system according to the invention, the following method is started in order to localize the fault. Firstly, the circuit isolation valve BP1 is closed and the pressure or pressure progression in the second hydraulic circuit K2 is measured. A check of the wheel brake cylinders RZ3 and RZ4 is thus performed. If the pressure changes over time, the switching valve SV3 of the wheel brake cylinder RZ3, for example, is closed next. If the pressure now remains constant in the second hydraulic circuit K2, the failure lies in the wheel brake cylinder RZ3. If the pressure does not change, the circuit isolation valve BP1 is opened and the switching valves SV3 and SV4 of the two wheel brake cylinders RZ3 and RZ4 are closed. The switching valve SV1 of the wheel brake cylinder RZ1 is also closed. If the pressure measured by means of the pressure transducer DG now remains constant, then a failure of the wheel brake cylinder RZ1 is present. To shorten the time of the diagnostic process described above, the hydraulic circuits K1 and K2 may also be checked at the same time, wherein, then, the above-described method is performed by means of the pressure transducer in the second hydraulic circuit K2 with the circuit isolation valve BP1 closed. At the same time, the pressure can be measured in the first hydraulic circuit K1 by means of the pressure supply device DV. If the piston of the pump moves in the presence of a constant current when only one switching valve SV1 or SV2 is open, this means that the wheel brake cylinder RZ1 or RZ2 respectively is leaking.

2. Use for the ABS Function

[0077] The second function consists in the use of the ABS function for the 1st safety level during pressure build-up P.sub.build-up. If the closed-loop controller reports that a wheel is for example delivering the criterion of excessive pressure, the pressure build-up P.sub.build-up can be stopped for the purposes of observation of the wheel. If the closed-loop controller now sends the signal “excessive braking torque/pressure”, the pressure reduction P.sub.reduction is performed. In this case, the outlet valve ZAV is opened and the associated switching valve SV is preferably controlled with a pulse-width-modulated signal (PWM), whereby the rate of the pressure reduction P.sub.reduction can be controlled. The closed-loop controller stops the pressure reduction P.sub.reduction by closing the outlet valve ZAV again. It is self-evidently also possible that the pressure reduction is also performed in two, three or four wheel brake cylinders RZ at the same time, wherein the respective switching valves are then controlled in pulse-width-modulated fashion such that the pressure reduction can be controlled individually for each wheel brake cylinder. As an alternative to the pulse width control of the switching valves, the pressure reduction P.sub.reduction may also be performed in a temporally offset or temporally overlapping manner in multiple wheel brake cylinders by virtue of the switching valves being switched in an overlapping manner, taking into consideration the switching times, wherein, for example, one switching valve SV.sub.i closes and the other switching valve SV.sub.j is already activated.

[0078] The pressure reduction P.sub.reduction may also be performed in the first hydraulic circuit K1 via the outlet valve ZAV. Likewise, the pressure reduction P.sub.reduction may be performed by means of the pressure supply device DV, which may likewise act as a pressure sink.

3. Use in Normal Operation

[0079] The switching valves SV1-4 may also be used for the pressure reduction in normal operation. There are three possible uses here: [0080] a. The pressure reduction P.sub.reduction is performed via all four switching valves SV1-4 with a brief stoppage, for example in accordance with Δt or Δp, for pressure equalization in the hydraulic circuits K1 and K2, because the switching valves SV1-4 are subject to tolerances. [0081] b. The pressure reduction is performed via the outlet valve ZAV with the switching valve SV and outlet valve ZAV permanently open, wherein at least one of the circuit isolation valves BP1, BP2 is controlled with a pulse-width-modulated signal. Alternatively, it is possible that the switching valves or the outlet valve is/are controlled by means of a pulse-width-modulated signal, wherein the other valves in the hydraulic connection to the reservoir are then permanently open during the pressure reduction. [0082] c. The pressure reduction P.sub.reduction is performed by means of the switching valve FV and the auxiliary pressure supply HDV, which corresponds to the single master brake cylinder SHZ, wherein, in this case, too, the switching valve SV1-4 may be controlled by means of PWM in order to control the pressure reduction rate.

[0083] The system has the auxiliary pressure supply HDV, which supplies a relatively low pressure to one or both hydraulic circuits in emergency operation. This may for example be a master brake cylinder HZ, which is connectable directly to the second hydraulic circuit K2 via the valve FV, which is open when electrically deenergized, and to the first hydraulic circuit K1 via the circuit isolation valve BP1.

[0084] The pressure build-up P.sub.build-up and the pressure reduction P.sub.reduction are performed here in normal operation without a closed-loop control function in the wheel brake cylinders RZ 1-4 by means of the pressure supply device DV. The pressure reduction P.sub.reduction may optionally also be performed by dissipation via the above-described breather hole of the pressure supply device DV to the reservoir VB. In ABS operation, the pressure reduction is performed either via the outlet valve ZAV or by means of the pressure supply device DV as a pressure sink, wherein it is also possible for the pressure reduction gradient or the pressure reduction to be controlled in open-loop and/or closed-loop fashion by means of a pulse-width-modulated control signal of a switching valve. In the event of failure of the pressure supply device DV and/or of the infeed valve PD1, the pressure reduction P.sub.reduction can be performed via the outlet valve ZAV or, with the switching valve FV open, also into the auxiliary pressure supply HDV. The pressure P in the hydraulic circuits K1 and K2 is measured by means of the pressure transducer DG when the valve BP1 is open. During the pressure build-up P.sub.build-up and during the pressure reduction P.sub.reduction, the correlation of pressure P to motor current I is measured, such that acceptable control is still possible in the event of failure of the pressure transducer DG. With the circuit isolation valve BP1 closed, closed-loop pressure control for the hydraulic circuit K1 may also be performed without measurement of the pressure by means of the pressure transducer DG, which now only measures the pressure in the second hydraulic circuit K2.

[0085] The hydraulic system illustrated in FIG. 2 differs from the hydraulic system according to FIG. 1 in that two circuit isolation valves BP1 and BP2 connected or arranged in series are now provided, whereby the 2nd safety level is formed. In the event of a double fault of, for example, the wheel brake cylinder RZ3 or RZ4 and the switching valves SV3 and SV4, the circuit isolation valve BP2 is closed, after which the double faults no longer have any effect on the auxiliary pressure supply HDV or on the first hydraulic circuit K1. BP1 additionally acts here. The first hydraulic circuit K1 is therefore safe with respect to double faults.

[0086] The second circuit isolation valve BP2 offers additional safety in the event of failure of the valve FV, wherein a failure may be present for example owing to a leak or a fault in the electrical connection. In the event of this fault, the two circuit isolation valves BP1 and BP2 are closed, whereby the travel simulator function of the travel simulator WS is advantageously maintained. In this case, braking operation is performed by means of the pressure supply device DV in the first hydraulic circuit K1 with approximately 50% braking action in the case of a diagonal brake circuit distribution. In the event of an emergency braking operation with a higher braking action desired by the driver, the circuit isolation valve BP2 may optionally be opened, in which case an additional pressure can then be generated in the second hydraulic circuit or brake circuit K2 by way of the foot-imparted force, which can increase the braking action by over 75%. In this case, the change in the pedal characteristic in relation to the travel simulator is also no longer great. However, in the event of failure of the valve FV, no ABS function is possible. In this case, the wheels can lock, in particular in the presence of a low coefficient of friction. However, if the valve FV only has a low leakage rate, the ABS function is still possible by virtue of the valve FV being closed and the pressure reduction P.sub.reduction being performed via the respective switching valve SV and the outlet valve ZAV. In this case, the valve FV remains closed. For the pressure build-up P.sub.build-up, a smaller pressure difference is selected in relation to the pressure reduction P.sub.reduction in order to prevent renewed locking of the vehicle wheels. Both switching valves SV remain closed for the rest of the braking operation. Thus, in this special case, steerability is maintained.

[0087] For the abovementioned fault situations, a diagonal brake circuit distribution is more favorable owing to the greater braking action of 50% in relation to the front axle/rear axle brake circuit distribution. Here, in the event of failure of the front axle VA, only approximately 30% is available with the rear axle HA. In the case of the circuit with so-called emergency braking, approximately 50% applies independently of the VA/HA brake circuit distribution, and 75% applies in the case of the diagonal brake circuit distribution.

[0088] The use of a multi-piston and gear pump further reduces the probability of failure.

[0089] FIG. 3 shows an additional isolation valve TV in the first hydraulic circuit K1, whereby even double faults of wheel brake cylinders RZ 1/2 and switching valves SV 1/2 do not lead to failure of the hydraulic system, whereby the 3rd safety level 3, which also corresponds to level 3, is attained.

[0090] FIG. 4 shows an embodiment of the hydraulic system according to the invention which corresponds to that illustrated in FIG. 2, wherein the pressure supply device DV is designed as a piston pump or rotary pump, which cannot deliver any volume in the return line for the purposes of the pressure reduction P.sub.reduction. Therefore, a second outlet valve ZAV1 is provided here for the first hydraulic circuit K1, which second outlet valve acts redundantly for the pressure reduction P.sub.reduction and the ABS closed-loop control. The check valve RV2 prevents the unwanted backflow of hydraulic medium and also acts redundantly in relation to the at least one outlet valve of the pump. The check valve may also be a constituent part of the rotary pump, such that there is no need for an additional check valve RV2 to be arranged in the hydraulic line connected to the pump.

[0091] The embodiment illustrated in FIG. 5 corresponds substantially to the embodiment illustrated in FIG. 3, but has two pressure supply devices DV1 and DV2, wherein the pressure supply devices DV1, DV2 may also both operate as rotary pumps or piston pumps, which is why the second outlet valve ZAV2 must then be provided. Instead of a switchable infeed valve, a check valve RV2 is arranged between the second pressure supply device DV2 and the second hydraulic circuit K2. A second check valve RV2red connected in series with the check valve RV2 increases safety, such that this brake system is also usable for level 3 or level 4 vehicles. The pressure reduction P.sub.reduction for the hydraulic components of the second hydraulic circuit K2 is performed here via the outlet valve ZAV1.

[0092] The hydraulic system illustrated in FIG. 6 corresponds in turn to the hydraulic system illustrated in FIG. 5, but has an additional circuit isolation valve BP3 for a third hydraulic circuit K2a. The wheel brake cylinders RZ3 and RZ4 are assigned to the front axle. Thus, in the event of failure of one wheel brake cylinder RZ and of one switching valve SV, a three-circuit system with 75% braking action would still be available in the case of the double fault of wheel brake cylinder RZ and switching valve SV, whereby the brake system is suitable for a level 4 or level 5 vehicle.

[0093] The open-loop and closed-loop control unit ECU is connected in the conventional manner directly to the hydraulic control unit HCU, which includes all hydraulic functions such as valves and pressure supply device(s) DV, DV1, DV2. This means that all electrical connections to the sensors, for example pressure transducer DG, solenoid valves and motor 12, can be easily implemented.

LIST OF REFERENCE DESIGNATIONS

[0094] ECU Electrical control unit [0095] RV1 Check valve 1 [0096] RV2 Check valve 2 [0097] RV2 red. Check valve 2 redundant [0098] RF Resetting spring [0099] RZ 1-4 Wheel cylinders [0100] SV 1-4 Switching valves [0101] DV Electromotive pressure provision unit [0102] HDV Auxiliary pressure supply [0103] HL 1-3 Hydraulic line connections [0104] VB Reservoir [0105] ZAV1/2 Central outlet valve [0106] BP1/2 Circuit isolation valve [0107] FV Infeed valve from master brake cylinder SHZ into brake circuit BK [0108] SV 1-4 Switching valve to wheel cylinder RZ [0109] DG Pressure transducer p=f (v) [0110] PP1 Infeed valve [0111] TV Isolation valve [0112] 10 Redundant electrical connection, possibly with redundant coil [0113] 11 Redundant connection to motor for 2×3 phase winding [0114] 12 Redundant connection for 2×3 phase motor [0115] 13 Electrical plug connector for on-board electrical system connection [0116] 17 Magnet coils [0117] 18 Ball valve