Pressure control with pump

Abstract

The invention relates to a method for controlling a brake system having a plurality of wheel brakes, each having an inlet valve and an outlet valve, and a hydraulic pump for feeding brake fluid into the plurality of wheel brakes. In order to avoid high pressure peaks, the wheel brake having the highest pressure demand is determined as the largest wheel, a brake fluid volume is delivered by a hydraulic pump to adjust a set pressure, among the remaining wheel brakes, the inlet valves of the wheel brakes are opened and the outlet valves of the wheel brakes are closed until the set pressure is reached, in order to adjust the set pressure, the inlet valve is closed in the case of reaching the set pressure, and in the largest wheel in order to adjust the set pressure, the inlet valve of the largest wheel is opened and the outlet valve of the largest wheel is closed until reaching the set pressure, and in the case of reaching the set pressure, the inlet valve is kept open and the outlet valve is operated in a pulsed manner.

Description

[0001] The invention relates to a method for controlling a brake system having a plurality of wheel brakes, each with an inlet valve and an outlet valve, and a hydraulic pump for conveying brake fluid to the plurality of wheel brakes.

[0002] Such a braking system makes it possible to build up brake pressure by means of a pump and / or to return brake fluid expelled by a valve action, independently of the driver. This makes it possible to use such a braking system to perform anti-skid control and stability control.

[0003] If the pump is running at high speed, very high system pressures (> 250 bar) may occur with a closed inlet valve, since in this case the pump is operating in a hydraulically rigid space. Conventional brake systems therefore have burst protection elements to prevent such pressure peaks. Otherwise, the brake system may leak.

[0004] Such burst protection elements entail high costs, which must be avoided, in particular in the case of redundant brake systems. In the case of redundant brake systems, a plurality of pressure sources are available, so that the pump can be used as a backup stage if necessary.

[0005] The object of the present invention is to provide a method and a corresponding brake system which avoid the risk of bursting without expensive burst protection elements.

[0006] According to the invention, the object is achieved by a method for controlling a braking system, wherein the wheel brake with the highest pressure demand is determined. This is referred to as the largest wheel. In order to adjust the set pressure, the hydraulic pump is controlled to actively deliver the brake fluid volume. This can be based on the driver's braking request in a brake-by-wire braking system and / or based on the needs of an auxiliary system. Therefore, the pressure control according to the invention now provides that different controls are provided in the largest wheel and the remaining wheel brakes. In the remaining wheel brakes, the inlet valve of the wheel brake is opened and the outlet valve of the wheel brake is closed until the set pressure is reached. When the set pressure is reached, the inlet valve is closed so that the pressure does not rise further. In the largest wheel, in order to adjust the set pressure, the inlet valve is also opened and the outlet valve of the largest wheel is closed until the set pressure is reached. However, when the set pressure is reached, the inlet valve is kept open and the outlet valve is operated in a pulsed manner. This provides a pressure control in which the volume delivered by the pump can flow out via the outlet valve, thereby preventing a sharp increase in pressure. The inlet valve preferably includes a check valve connected in parallel accordingly.

[0007] In a preferred embodiment of the invention, the inlet valve of the largest wheel remains open in the case of power failure or partial power supply. When partially powered, the inlet valve moves to a position in which it provides a flow resistance greater than in the power failure state but less than in the closed state. In this state, the inlet valve can still prevent a sharp increase in pressure, in particular a pressure peak, and can also slow down the pump.

[0008] In another preferred embodiment of the invention, the inlet valve of the largest wheel is placed in a partially energized open state when two other inlet valves are already closed and the third inlet valve is closed at the same time, thereby building up an increased counterpressure at the pump outlet in advance, thereby slowing down the pump.

[0009] In a further preferred embodiment of the invention, the holding current at the inlet valve of the largest wheel is selected such that the inlet valve is pressed / opened at a predetermined pressure difference, for example at a pressure difference of 20 bar.

[0010] In another preferred embodiment of the invention, during pressure control, the pressure side of the pump is connected only to the inlet valve of the wheel brake and at least one closed isolating valve. This eliminates the need for expensive bursting elements.

[0011] In another preferred embodiment of the invention, the outlet valve is operated in a pulsed manner by pulse width control with a predetermined opening ratio, which is set so that the pressure of the largest wheel corresponds to the set pressure of the largest wheel. The current system pressure, the known pressure-volume characteristic, the target pressure and the known throttling coefficient of the outlet valve (flow coefficient of the throttling hole) make it possible to control the outflowing volume flow in terms of the switching time. For example, a period of 5 ms can be used in this case, with a resolution set to 1 ms. By setting the pulse width modulation, the pressure-dependent volume flow through the outlet valve, in particular into the pressureless brake fluid reservoir, is set. Therefore, the pressure in the largest wheel can be precisely controlled via pulse width modulation.

[0012] In another preferred embodiment of the invention, to release the pressure at the largest wheel, its outlet valve is opened while the inlet valve is still open. This also avoids hydraulic rigid spaces and thus avoids pressure peaks during pressure release.

[0013] In a particularly preferred embodiment of the invention, for the pressure relief, the pump speed is additionally reduced, thereby minimizing the volume of brake fluid flowing in the circuit and supporting the pressure relief. Alternatively or additionally, the inlet valve is partially energized, thereby also reducing the volume flow.

[0014] The object is also achieved by a hydraulic brake system for a motor vehicle, the hydraulic brake system having a control device which is configured to carry out one of the above methods.

[0015] The object is also achieved by a computer program product which is designed in such a way that one of the above methods is performed when the computer program product is executed in a control device.

[0016] Other features, advantages and possible applications of the invention are also derived from the following description of exemplary embodiments and the accompanying drawings. All features described and / or illustrated are associated with the subject matter of the invention individually and in any combination, independently of their combination in the claims or their reverse reference.

[0017] FIG. 1 schematically shows a braking system according to the present invention,

[0018] FIG. 2 shows an exemplary pressure curve without using the method according to the invention,

[0019] FIG. 3 shows an exemplary pressure control when using the method according to the invention.

[0020] FIG1 shows a redundant hydraulic brake system for a motor vehicle. According to the example, the brake system is designed for actuating four hydraulically actuable wheel brakes 8; it can be easily expanded to more wheel brakes. According to the example, wheel brakes (HL, HR) are associated with the rear axle and wheel brakes (VL, VR) are associated with the front axle of the vehicle.

[0021] The brake system includes: a first structural unit, which is configured as a first electronic hydraulic brake control unit having a valve block and a first electronic control device according to an example; and a second structural unit, which is configured as a second electronic hydraulic brake control unit having a valve block and a second electronic control device according to an example.

[0022] A pressure medium reservoir 4 having two chambers is arranged on the first structural unit, wherein a first reservoir port is associated with the first chamber and a second reservoir port is associated with the second chamber.

[0023] The first electrically actuatable pressure source 5 is arranged in the first structural unit.

[0024] Arranged in a second structural unit are second electrically actuatable pressure source 2 and wheel-specific brake pressure regulating valves which are designed as electrically actuatable inlet valve 6 and electrically actuatable outlet valve 7 respectively associated with each wheel brake 8 .

[0025] The first pressure source 5 and the second pressure source 2 are connected on the pressure side to a brake supply line to which four inlet valves 6 are connected. All four wheel brakes 8 can thus be actuated by means of the first pressure source 5 or by means of the second pressure source 2 .

[0026] An electrically actuatable circuit separation valve 40 is arranged in the brake supply line, so that when the circuit separation valve 40 is closed, the brake supply line is separated into a first line section, to which the inlet valve 6 and / or the wheel brake 8 of the rear axle is connected, and a second line section, to which the inlet valve 6 and / or the wheel brake 8 of the front axle is connected. The second pressure source 2 is hydraulically connected to the first line section, and the first pressure source 5 is hydraulically connected to the second line section. When the circuit separation valve 40 is closed, the brake system is thus separated or divided into two hydraulic brake circuits I and II. In this case, in the first brake circuit I, the pressure source 2 is still connected (via the first line section) only to the wheel brake 8 of the rear axle, and in the second brake circuit II, the first pressure source 5 is still connected (via the second line section) only to the wheel brake 8 of the front axle. The circuit separation valve 40 is advantageously configured to be open in the event of a power failure.

[0027] As described above, for each hydraulically actuatable wheel brake 8, the brake system comprises an inlet valve 6 and an outlet valve 7, which are hydraulically connected to each other in pairs via a central port and are each connected to a hydraulic wheel port of the second structural unit, to which the corresponding wheel brake 8 is connected. A check valve opening toward the brake supply line is connected in parallel to each of the inlet valves 6. The output port of the outlet valve 7 is connected to the pressure medium reservoir 4 or its second chamber via a common return line. The inlet ports of all inlet valves 6 can be supplied with the pressure provided by the first pressure source 5 by means of the brake supply line (i.e., with the circuit separation valve 40 open) or, for example, with the pressure provided by the second pressure source 2 in the event of a failure of the first pressure source 5.

[0028] The first electrically controllable pressure source 5 of the valve block is configured as a hydraulic cylinder-piston arrangement (or a single-circuit electrohydraulic actuator (linear actuator)), the piston of which can be actuated, in particular advanced and retracted, by a schematically indicated electric motor with an interposed rotary-translational transmission, also schematically shown, in order to build up and release pressure in a pressure chamber. The piston delimits the pressure chamber of the pressure source 5. A rotor position sensor is provided for actuating the electric motor, which detects the rotor position of the electric motor and is indicated only schematically.

[0029] A system pressure line section is connected to the pressure chamber of the first electrically controllable pressure source 5. By means of this line section, the pressure source 5 or its pressure chamber is connected to a hydraulic port of the first component unit, which is connected to a hydraulic port of the second component unit via a hydraulic connection element. This connection represents a single hydraulic pressure connection, in particular a single hydraulic connection, between the first component unit and the second component unit. The hydraulic connection is a hydraulic connection for transmitting a brake pressure for actuating the wheel brakes 8.

[0030] Regardless of the actuation state of the piston, the pressure chamber is connected to the pressure medium reservoir 4 via a (replenishing) line. A non-return valve 53 is arranged in this line, which is closed toward the pressure medium reservoir 4 and is connected to the second chamber. The electrically switchable valve 23 forms a further connection to this line, which is connected to the output port of the linear actuator 5. According to the example, the cylinder-piston arrangement 5 does not have any compensation bores.

[0031] According to the example, the second electrically controllable pressure source 2 of the second structural unit is configured as a double-piston pump, the two pressure sides of which are connected to each other. The suction side is connected to the return line and thus to the pressure medium reservoir 4. The pressure side is connected to the first line section of the brake supply line.

[0032] According to the example, in addition to the pressure source 2 and the brake pressure regulating valves 6, 7, an electrically actuatable isolating valve 26 is arranged in the second structural unit, which is advantageously opened in the event of a power failure. The isolating valve 26 is hydraulically arranged between the port and the second line section of the brake supply line. Thus, the first pressure source 5 is detachably connected to the second line section or the brake supply line via the isolating valve 26.

[0033] According to the example, the brake system comprises a pressure sensor in brake circuit I, which is therefore associated with the second pressure source 2. This is advantageous in preventing bursting when the circuits are separated, that is to say when the circuit separation valve 40 is closed. However, the pressure sensor can also be arranged in brake circuit II, or a second pressure sensor can be provided, so that each of the two brake circuits I and II can be monitored directly by means of a pressure sensor.

[0034] According to the example, for the purpose of monitoring leakage, the brake system comprises a level measuring device for determining the pressure medium level in the pressure medium reservoir 4 .

[0035] Each valve block is assigned an electronic control device. Each electronic control device includes electrical and / or electronic components (e.g., microcontroller, power module, valve driver, other electronic components, etc.) for controlling the electrically actuatable components of the associated valve block and optionally the associated sensors. The valve block and the electronic control device are advantageously configured as an electrohydraulic unit in a known manner.

[0036] The first electronic control device controls the first pressure source 5. According to the example, the first pressure source 5 is supplied with energy (from a first electrical energy source) via the first electronic control device.

[0037] The second electronic control device controls the second pressure source 2. According to the example, the second pressure source 2 is supplied with energy (from a second electrical energy source) via the second electronic control device.

[0038] According to an example, the first pressure source 5 can be controlled by a first electronic control device or only by the first electronic control device, and the second pressure source 2 can be controlled by a second electronic control device or only by the second electronic control device.

[0039] The brake system has a primary pressure source 5 and a secondary pressure source 2, each of which is electrically operated by the ECU and has a suction port and a pressure port. Even in a power-off state, no brake fluid can flow into the pressure port of the secondary pressure source 2. The primary pressure source 5 is preferably a linear actuator with a supplementary check valve 53, while the secondary pressure source 2 is a piston pump. The secondary pressure source 2 can preferably generate a higher pressure than the primary pressure source 5.

[0040] The suction sides of the two pressure sources 2 , 5 are connected to a pressure medium reservoir 4 , preferably in each case to at least one of the two separate chambers.

[0041] The pressure side of the primary pressure source 5 is connected to the primary circuit node via a solenoid valve 26 (also called a pressure-activated valve or isolation valve).

[0042] The pressure side of the secondary pressure source 2 is directly connected (ie without an intermediate valve) to the secondary circuit node. The two circuit nodes are connected to each other via a solenoid valve 40 (also called a circuit diverter valve).

[0043] In normal operation, the pressure in the wheel brake is built up by the primary pressure source 5. The pressure is released into the primary pressure source 5. The pressure is regulated by the inlet valve and outlet valve as required specifically for the wheel. If necessary, the isolation valve 26 is closed so that the primary pressure source 5 can be supplemented with additional volume.

[0044] If a particularly high volume flow is required, both pressure sources 5 and 2 are operated in parallel. When a particularly high pressure is required, the isolation valve 26 is closed and the secondary pressure source 2 increases the pressure to exceed the pressure of the primary pressure source 5. Outside of the braking operation, pressure equalization with the atmosphere can be permanently ensured via the isolation valve 23 and the isolation valve 26.

[0045] In the event of a leak in the brake system, the circuit separation valve 40 is closed and the system is thus divided into two independent brake circuits I and II.

[0046] The isolation valve 26 is preferably operated by the secondary (ECU).Based on this valve interrelationship, the following description of the operation in the event of a fault is made.

[0047] If an electrical fault occurs in the primary system, in particular the primary (ECU) or its voltage supply, the secondary (ECU) closes the isolation valve 26 in order to build up pressure via the secondary pressure source 2. The pressure is released via the isolation valve 26 or via the outlet valve 7. The inlet and outlet valves are preferably actuated by the secondary ECU so that the pressure can be adjusted specifically for the wheels.

[0048] If a secondary system, in particular a secondary ECU or its power supply, fails electrically, pressure is built up and released via the primary pressure source 5, as in normal operation. Wheel-specific pressure control must be abandoned, but a joint regulation of the wheel pressures is still possible to prevent the vehicle from becoming unstable due to wheel locking.

[0049] In the above operating mode, the piston pump 2 is therefore the pressure source for at least two wheel brakes. In this case, in addition to the inlet valve 6 of the wheel brake 8, the pressure side of the pump 2 is only partially connected to the closed valve, that is, the circuit separation valve 40 or the activation valve 26.

[0050] The wheel pressure controller (WPC) can maintain a high front pressure facing away from the wheel by closing the inlet valve. In the case of a high front pressure, pressure can be built up at the wheel by opening the corresponding inlet valve. To relieve the pressure at the wheel, the outlet valve is opened while the inlet valve is closed. Simultaneous opening of the inlet and outlet valves (hydraulic short circuit) is not part of the WPC.

[0051] If all inlet valves are closed, the pump 2 works against the hydraulically rigid space, which can lead to high pressure peaks. FIG. 2 shows the system pressure curve when the pump builds up a pressure ramp at 150 bar and all inlet valves are closed. The resulting system pressure exceeds 380 bar. According to the invention, the pressure control of the wheel brakes 8 is therefore carried out at the highest set pressure, so that the inlet valves 6 remain at least partially open, while the outlet valves 7 of the wheel brakes are controlled by pulse width modulation in order to adjust the set pressure.

[0052] When pressure is built up via the pump 2 (referred to herein as pump operation), the activation valve PFV 26 is closed. In pump operation, a pressure release in the system pressure can only be carried out by opening the outlet valve 7. If, in order to keep the rigidity in the system pressure chamber low and to avoid pressure peaks, the inlet valve is simply kept open, then without the method according to the invention, the pressure at the wheel can only be set very imprecisely via the pump, resulting in poor braking distance performance. Alternatively, if, with all four inlet valves closed, the holding current of the pump is selected in pump operation so that a system pressure peak causes the inlet valve 6 to be pressed, the volume flow entering the corresponding wheel brake 8 can only be corrected via the detected wheel slip. This also leads to poor braking distance performance. The method according to the invention makes it possible to achieve precise pressure control and thus better braking distance performance despite avoiding pressure peaks.

[0053] FIG3 shows the pressure control principle at two wheels by way of example. The pressure demand of one wheel is shown by the short dashed line (initially the upper line) and the pressure demand of the other wheel is shown by the longer dashed line. Next to these dashed lines are the corresponding actual pressure curves. The upper part of the image shows the pressure curves and the lower part shows the associated inlet and outlet valve states over time. The individual time phases are designated by tx.

[0054] During the pressure control shown, the hydraulic pump 2 continuously delivers a brake fluid volume, while the activation valve 26 is closed.

[0055] The marked switching state of the inlet valve means that the inlet valve is activated (ie hydraulically closed), otherwise the inlet valve is open. The marked switching state of the outlet valve means that the outlet valve is activated (ie hydraulically opened), otherwise the outlet valve is closed.

[0056] In phase t1 , a common pressure build-up occurs.

[0057] Phase t2:

[0058] The demand for no further increased pressure at wheel 2 is met by closing the inlet valve 6 at wheel 2. As the pressure demand at wheel 1 continues to increase, its inlet valve 6 remains open and the pump flow causes the pressure at wheel 1 to increase.

[0059] Phase t3:

[0060] The pressure demand at wheel 1 does not increase further. This pressure demand is then met by pulsing the outlet valve of wheel 1 with the inlet valve open. Since pump 2 will continue to deliver, the pressure curve at this wheel is the result of the pressure build-up by pump 2 and the pressure release by opening the outlet valve. The outlet valve can be actuated by a number of short control pulses or by a few long control pulses.

[0061] Phase t4:

[0062] The required pressure relief at the wheel 1 is achieved by opening the outlet valve for a longer period. In addition, the pump voltage can be reduced during this phase.

[0063] Phase t5:

[0064] At this point, the pressure requirements of the two wheels intersect. The largest wheel changes, and accordingly one inlet valve 6 is closed and the other is open. In order to avoid system pressure peaks, the inlet valves are controlled so that the closed inlet valves 6 do not overlap.

[0065] The invention is also applicable if the circuit separation valve 40 is closed instead of the activation valve 26 and if conventional braking (all wheel pressure requests are equal) instead of just one ABS (different wheel pressure requests) is used during pump operation.

[0066] A preferred variant is described as follows. At the wheel with the greatest brake pressure (referred to as the largest wheel for short), the inlet valve 6 can be not de-energized but partially energized. This makes it possible to provide a small amount of hydraulic resistance and avoid cross-flow when the outlet valve at this wheel needs to release too much pressure. Therefore, at the largest wheel, a low holding current is applied to the inlet valve 6. Advantageously, this partial closing of the inlet valve 6 at the largest wheel occurs when two inlet valves 6 already have to be closed in order to maintain or release the pressure at the wheel and a third inlet valve is closed at the same time.

[0067] The holding current at the largest wheel can be selected, for example, so that the inlet valve is pressed at a pressure difference of 20 bar. As a result, the largest wheel inlet valve offers a higher hydraulic resistance to the pump, which in turn leads to a stronger pump braking behavior and improves the pressure control accuracy.

[0068] The pressure relief capacity of the outlet valve becomes larger at higher pressures. Therefore, when releasing pressure at the largest wheel, the wheel pressure may drop to a lower value than the pressure of the other wheels. This brings another advantage: the partially closed inlet valve at the largest wheel prevents cross-flow via the check valves of the other inlet valves.

[0069] The invention makes it possible to dispense with complex burst protection components while still achieving highly accurate pressure regulation.

Claims

1. A method for controlling a brake system having a plurality of wheel brakes (8) and a hydraulic pump (2) for conveying brake fluid to the plurality of wheel brakes, the wheel brakes each having their own inlet valve (6) and outlet valve (7), characterized in that: The wheel brake (8) with the highest pressure demand is determined as the largest wheel, the brake fluid volume is delivered by the hydraulic pump (2) to adjust the set pressure, and in the remaining wheel brakes (8), the inlet valve (6) of the wheel brake (8) is opened and the outlet valve (7) of the wheel brake (8) is closed until the set pressure is reached, wherein the inlet valve (6) is closed when the set pressure is reached, and in the largest wheel, in order to adjust the set pressure, the inlet valve (6) of the largest wheel is opened and the outlet valve (7) of the largest wheel is closed until the set pressure is reached, wherein when the set pressure is reached, the inlet valve (6) is kept open and the outlet valve (7) is operated in a pulsed manner.

2. The method for controlling a braking system according to claim 1, characterized in that The inlet valve (6) of the largest wheel is kept open when power is off or partially energized.

3. The method for controlling a braking system according to claim 2, characterized in that: With the other two inlet valves (6) already closed and the third inlet valve (6) closed at the same time, the inlet valve (6) of the largest wheel is placed in a partially energized open state.

4. The method for controlling a braking system according to claim 2 or 3, characterized in that: The holding current at the inlet valve (6) of the largest wheel is selected such that the inlet valve (6) is actuated at a predetermined differential pressure, for example at a differential pressure of 20 bar.

5. Method for controlling a brake system according to one of the preceding claims, characterized in that During pressure control, the pressure side of the pump (2) is connected only to the inlet valve (6) of the wheel brake (8) and to at least one closed isolating valve (26).

6. Method for controlling a brake system according to one of the preceding claims, characterized in that The outlet valve (7) is operated in a pulsed manner by pulse width control with a predetermined opening ratio, the predetermined opening ratio being set so that the pressure of the largest wheel corresponds to the set pressure of the largest wheel.

7. Method for controlling a brake system according to one of the preceding claims, characterized in that To release the pressure, open the outlet valve (7) and at the same time open the inlet valve (6).

8. The method for controlling a braking system according to claim 7, characterized in that: To relieve the pressure, the pump speed is additionally reduced and / or the inlet valve (6) is partially energized.

9. A hydraulic brake system for a motor vehicle, the hydraulic brake system having a control device configured to carry out one of the above methods. 10 . A computer program product, which is designed such that, when it is executed in a control device, it performs the method according to claim 1 .

11. A data carrier signal transmitting the computer program product according to claim 10.

Images