WO1996015015A1 - Method and device for control of a fluid-return pump - Google Patents

Abstract

Described are a method and device for controlling a fluid-return pump in a brake system, the fluid-return pump being controllable as a function of the correcting variable and/or control deviation of an anti-slip controller and/or a controller governing the speed of a vehicle.

Description

Method and device for controlling a return conveyance.

State of the art

The invention relates to a method and a device for controlling a return pump of a brake system according to the preambles of the independent claims. Such a method and such a device for controlling a return pump of a brake system is known from WO 94/07717. There, a method and a device for regulating the delivery rate of an electromotive hydraulic pump, which is controlled with a variable pulse / pulse pause sequence, are described. The hydraulic pump, which is also referred to as a return pump, serves to generate an auxiliary pressure in a brake system with a traction control system and / or an anti-lock control system.

During the pulse pauses, the generator voltage generated by the pump motor is evaluated as a measure of the pump speed. In a control loop, a pump speed setpoint is compared with an actual value of the pump speed and the new manipulated variable for pump control is derived from the difference. The disadvantage of this known arrangement is that a very complicated controller is required which generates a pulse-width-modulated signal based on the difference between the setpoint and actual value.

Object of the invention

The object of the invention is to provide a method and a simple device which is as simple as possible in a method and a device for controlling a return pump of the type mentioned at the beginning. This object is achieved by the features characterized in the independent claims.

A slip controller is also known from WO 89/02382, in which the difference between an allowable and an actual slip is determined. This difference is carried out via a control amplifier and implemented in control times for a brake pressure control unit.

Furthermore, a hydraulic brake system is known from DE-OS 40 35 527 (US 52 05 623).

Advantages of the invention

The device according to the invention and the method according to the invention are designed much simpler than the device according to the prior art.

Advantageous and expedient refinements and developments of the invention are characterized in the subclaims. drawing

The invention is explained below with reference to the embodiments shown in the drawing. 1 shows the essential elements in the form of a block diagram of a brake system with an anti-lock control system (ABS) and a traction control system (ASR), in FIG. 2 the essential elements of a slip controller, and in FIG. 3 the essential elements of the control circuit for controlling the Rückför¬ derpumpen motor and in Figure 4, the essential elements of the control for the return pump motor shown.

Description of the embodiments

1 shows the essential elements in the form of a block diagram of a brake system with an anti-lock control system (ABS) and a traction control system (ASR). The wheel brake cylinders 10 of the drive wheels 11, 12 together with the wheel brake cylinders 10 of the non-driven wheels 13 and 14 are divided between the two brake circuits, so that in each case one wheel brake cylinder 10 of a drive wheel 11 or 12 and one wheel brake cylinder 10 of a non-driven wheel 13 or 14 belong to a brake circuit.

In general, the drive wheels 11, 12 are the front wheels of the motor vehicle. The dual-circuit brake system includes, in a manner known per se, a master brake cylinder 15 which has two separate brake circuit outputs 16 and 17 for connecting one of the two brake circuits in each case and is connected to a brake fluid reservoir 18. When a brake pedal 19 is actuated, an equal brake pressure at the two brake circuit outputs 16, 17 is controlled.

The dual-circuit brake system also includes a four-channel hydraulic unit 20 which has four outlet channels 21 to 24 and four Has inlet channels 25 to 28. The two inlet channels 25, 26 belonging to a brake circuit are each connected via a connecting line 29a and 29b to the brake circuit outlet 17 of the master brake cylinder 15 and the two inlet channels 27, 28 belonging to the other brake circuit via connecting lines 30a and 30b to the brake circuit outlet 16 of the master brake cylinder 15 connected.

A wheel brake cylinder 10 of the wheels 11 to 14 is connected to each outlet channel 21 to 24 of the four-channel hydraulic unit 20.

A control valve 31 to 34 is assigned to each outlet channel 21 to 24. The control valves 31 to 34 are controlled by control electronics (not shown) and build up a wheel pressure-dependent brake pressure in the associated wheel brake cylinders 10.

A return pump 35, which is part of the four-channel hydraulic unit 20, has two self-priming trained pump elements 36, 37, which are driven jointly by an electric motor 38 and serve to reclaim brake fluid when the pressure in the brakes is reduced.

In each case one pump element 36 or 37 is effective in a brake circuit and is connected on the input side to the control valves 31, 32 and 33, 34 belonging to the brake circuit, in this connection a check valve 39 with a flow direction pointing to the pump element 36 or 37 is arranged.

In addition, the pump elements 36, 37 are each connected to a low-pressure accumulator 40 on the input side. The low-pressure accumulators 40 serve to temporarily hold brake fluid flowing out of the wheel brake cylinders 10. On the output side, the two pump elements 36, 37 with the Inlet duct 26 and the inlet duct 27 of the hydraulic unit 20 are connected, that is to say those inlet ducts 26, 27 which correspond via the control valves 32, 33 to the outlet ducts 22, 23 to which the wheel brake cylinders 10 of the drive wheels 11, 12 are connected.

In each connection between pump element 36, 37 and inlet duct 26, 27, a damper chamber 41 and a throttle position 42 are switched on. Each pump element 36, 37 has a pump inlet valve 55 and a pump outlet valve 56. Each control valve 31 to 34 is formed by a valve unit comprising an inlet valve 43 and an outlet valve 44. In their non-energized basic position, the inlet valves 43 allow unimpeded passage from the inlet channels 25 to 28 to the respectively assigned outlet channels 21 to 24 and thus to the wheel brake cylinders 10 of the wheels 11 to 14. In the working position which can be brought about by magnetic excitation, they block Inlet valves 43 let this pass.

In their working position which can be brought about by magnetic excitation, the outlet valves 44 connect the outlet channels 21 to 24 and thus the wheel brake cylinders 10 of the wheels 11 to 14 to the input of the associated pump element 36 or 37 and block this connection in their unexcited basic position. The check valves 39 already mentioned are contained in the connection of the outlet valves 44 to the pump elements 36 and 37. A check valve 45 with a flow direction pointing to the inlet channels 25 to 28 is connected in parallel to the inlet valves 43.

A valve arrangement 46 or 46 'assigned to a brake circuit in each case serves to provide a brake supply pressure in the case of traction control (ASR operation). Both valve arrangements 46, 46 'are constructed identically, the same components being provided with the same reference symbols and are distinguished by a comma to distinguish them. The valve arrangement 46 or 46 'has a loading valve 47 or 47' and a Umsehal valve 48 or 48 '. All valves are designed as 2/2-way solenoid valves with spring return, the changeover valves 48, 48 'being open in their unenergized basic position and the loading valves 47, 47' blocking in their unenergized basic position. Each loading valve 47, 47 'is arranged in a suction line 49 or 49', which leads from a brake fluid container 50 to the inlet of a pump element 36 or 37. The brake fluid reservoir 50 is connected to the brake fluid reservoir 18. The brake fluid container 50 only serves as additional protection to avoid air being sucked in by the pump elements 36, 37 in the event of a fault if the connecting hose to the brake fluid container 18 is not properly connected. The level switch 51 switches off the return pump 35 as soon as the fluid level in the brake fluid reservoir 50 has reached a lower level, below which there is a risk of air intake.

The changeover valve 48 is connected in the connecting line 29b between the brake circuit outlet 17 and the inlet channel 26 of the hydraulic unit 20 and the changeover valve 28 'in the connecting line 30b between the brake circuit outlet 16 of the master brake cylinder 15 and the inlet channel 27 of the hydraulic unit 20. A check valve 53, 53 'with the flow direction pointing to the inlet channels 26, 27 is connected in parallel with the switching valve 48, 48'. In addition, a pressure limiting valve 54, 54 'can be arranged in a bypass 52, 52' to the changeover valve 48 or 48 'and thus parallel to the check valve 43 or 53'.

The pressure limiting valve 54, 54 'only has a protective function for the pump element 36 or 37. The two valve arrangements 46, 46 ', like the control valves 31 to 34 and the activation of the return pump 35, are controlled by control electronics.

The operation of this arrangement is described in DE-OS 40 35 527 (US-A 5 205 623).

In FIG. 2, an example of a brake slip regulator, which can also be called a blocking protection regulator, is shown using a block diagram. 100 denotes a wheel brake, which acts on a controlled system 120, which comprises the wheel, tire and road systems. The controlled system has the input variables braking torque M _B and vehicle speed Vp and the output variables wheel speed V _R. The measured wheel speed signal V _R is fed to a slip generator 130, to which a reference variable V _Re f of a block 150 is also fed. The reference variable is additionally fed to a target slip generator 140, which specifies a permissible slip value, for example 5%. The target slip generator 140 can be controlled via a terminal 160 and switched to an externally predeterminable value, for example a curve.

The slip λ formed in the slip generator 130 according to the relationship λ = 1 - v _{R /} v _Ref is compared in a comparator 170 with the desired slip λ * and the deviation Δλ is fed to a control amplifier 180. This control amplifier 180 essentially has a proportional and / or a differential transmission behavior between the control deviation Δλ and its output variable U.

Furthermore, it can be provided that the transmission behavior of the controller 180 is dependent on the reference variable V _e f and the output variable of a correction element 110. The output signal U of the controller amplifier 180 arrives via a Switching means 190 to the correction element 110. The switching means 190 can also be controlled by the block 150. In addition, the correction in the correction element 110 takes place as a function of a signal B 1 of the block 150. The deviation Δλ and the slip number λ are supplied to the block 150 as input variables. Block 111 converts output variable U ₂ of correction element 110 into control signals ΔT for intake and exhaust valves 33 and 34. The exact functioning of the controller arrangement is described, for example, in the application WO 89/02382.

FIG. 3 shows the essential elements of the circuit arrangement for controlling the return pump motor 38. A connection of the return pump motor 38 is connected to supply voltage U___. The second connection of the return pump motor 38 is connected to ground via a switching means 305 and possibly via a current measuring means 310.

The switching means 305 is preferably acted upon by control signals from a controller 320. The controller 320 processes the output signal of a node 325, at the first input of which the output signal of a setpoint specification 330 is present. At the second input there is optionally the output signal I of a current evaluation 334, which provides a signal relating to the current flowing through the motor 38. As an alternative to this, it can also be provided that the voltage applied to the motor is sensed and used as the actual value UI. When the switching means 305 is open, the voltage applied to the motor 38 corresponds to the speed or the output of the return pump driven by the motor 38.

Based on the comparison between the setpoint value, which is provided by the setpoint value specification 330, and an actual value with respect to the speed of the return pump, which is at the Return pump applied voltage, and / or the current flowing through the return pump, the controller 329 determines the control signal to act upon the switching means 305.

When the switching means 305, which is preferably implemented as a field effect transistor, is closed, the pump motor 38 is supplied with current.

In a preferred embodiment, the return conveyor motor 38 is operated in such a way that only the delivery capacity required for the pressure reduction is provided in order to convey the hydraulic fluid drained off from the outlet valves 44 back again. The output signal U of the controller 180 and the output signal U _{2 of} the correction element 110 of the slip controller described in FIG. 2 represent a measure of the required delivery rate. One of these variables is supplied to the setpoint generator 330. Depending on this variable, the setpoint generator determines a setpoint for the pump speed or the voltage UI dropping at the pump, which corresponds to the pump speed.

The invention is not only applicable to controllers according to FIG. 2. It can also be used with other controllers, in which case a size corresponding to size U is evaluated.

In a particularly advantageous embodiment, the return pump is only controlled in that the setpoint value 330, based on the signal U or U ₂ , specifies a pulse-pause ratio for a control signal modulated by the width of the pus. In this case, controller 320, node 325 and the feedback of voltage or current can be omitted. The return pump is activated depending on the requirement when the pressure is reduced. In ABS operation, the pressure on the wheel brake cylinders is reduced by actuating the exhaust valves. The hydraulic fluid drained from the outlet valves is conveyed back into the master brake cylinder by the return pump. According to the invention, the return pump is energized so that the delivery rate is just sufficient to reclaim the drained hydraulic fluid.

This reduces unnecessary energization of the return pump and the noise emissions that occur as a result. There is a need-based control during pressure reduction in ABS operation.

External braking intervention is often carried out in such ABS / ASR systems. If the vehicle in which this system is used is equipped, for example, with a vehicle speed control and / or a vehicle speed limit, it can occur, particularly when driving downhill, that the injection quantity or the throttle valve position is reduced not enough to set the vehicle to the desired speed. In this case, the vehicle speed controller or the vehicle speed limiter sends a signal to the ABS / ASR system which indicates a desired braking intervention and / or a desired braking torque. A corresponding signal, which indicates a braking intervention, can also be supplied by other systems, for example a driving dynamics control.

According to the invention, it is now provided that the pressure build-up is determined via the pump motor in such systems in the case of a desired active brake intervention. In the exemplary embodiment shown, the return pump is controlled according to the invention as a function of the control deviation of a controller which influences the wheel speed. Such controllers which influence the wheel speed are, for example, driving speed controllers, vehicle speed limiters, driving dynamics controllers. - left

ier. In this embodiment, the return pump is controlled depending on the need for pressure build-up.

It is advantageous in this embodiment that no switching of solenoid valves takes place during the pressure build-up phase. This can prevent the switching noise of the solenoid valves. Furthermore, a needs-based pump control is possible. No pump noise occurs, especially in the pressure maintenance and pressure reduction phases. The pressure reduction is possible directly via the outlet valve when the return pump is switched off. Different degradation gradients can thereby be set. The procedure described can also be used with other external brake interventions, for example with a distance control or a vehicle dynamics control.

FIG. 4 shows a block diagram of the device according to the invention for regulating the return pump. With 38 the return pump motor is again designated. With 44 the outlet valve, with 48 the changeover valve, with 43 the inlet valve is marked. The return pump 38 is controlled by the controller 320. The voltage applied to the return pump 38 is fed to one input of the controller. The output signal U _{§ of} a selection device 420 is present at the second input of the controller. The selection device also applies control signals to the outlet valve 48.

The selection device 420 processes the output signal of a controller 430 as an input variable. On the one hand, the controller 430 is supplied with a setpoint value of a higher-level control device 440 and an actual value with a signal conditioning unit 450. The higher-level control device is preferably a vehicle speed controller, a vehicle speed limit, a vehicle dynamics controller, a distance controller and / or another device that can specify a deceleration value. The signal conditioning 450 processes the speeds V of the individual wheels 460. A brake 470 acts on the wheels, which applies a braking torque Mg. This braking torque essentially depends on the pressure in the brake hydraulic system.

This device now works as follows: The higher-level control device 440 specifies a setpoint AS for the desired deceleration of the vehicle. This setpoint AS is compared with an actual value AI, which the signal conditioning 450 specifies.

The comparison between the setpoint AS and the actual value IS takes place in the controller 430. Based on the comparison, the controller 430 determines a manipulated variable. The controller 430 preferably has PID behavior, the control behavior being dependent on various operating parameters. Based on the manipulated variable, the selection device 420 decides whether a pressure build-up or a pressure decrease is required.

If the actual deceleration is greater than the desired deceleration, pressure is reduced by activating the drain valve for a predetermined time ΔT. If, on the other hand, the setpoint AS for the deceleration is greater than the actual value AI, the selection unit 420 transmits a corresponding setpoint US to the controller 310. The setpoint US corresponds to the delivery rate to be applied by the return pump in order to ensure the desired pressure build-up.

The selection device 420 preferably comprises a characteristic diagram or an arithmetic unit which, based on the manipulated variable of the controller 430 and thus dependent on the control deviation between the signals AS and AI, the desired delivery capacity of the return pump. During the switch-off process, the return pump 38 continues to run for a certain time and thereby generates the voltage UI, which is essentially proportional to the speed and thus the delivery rate. Starting from the manipulated variable of the controller 430, the selection device 420 specifies a desired value US for the voltage that drops at the return pump 38.

In one embodiment of the device, it can be provided that the higher-level control device 440 specifies a desired braking torque and / or a desired delivery rate of the return pump depending on the control deviation between a target and an actual value. In these cases, the device must be modified accordingly. This means that, for example, controller 430 can be changed or omitted entirely. The selection device 420 then takes over the corresponding tasks.

Controller 310 is preferably a so-called two-point controller. This works as follows: If the voltage UI applied to the return pump exceeds the setpoint US, the controller 310 interrupts the power supply for the return pump by opening the switching means 305. If the actual value UI falls below the setpoint US, the controller closes the switch.

Claims

Expectations 1. A method for controlling a Rückfδrderpump a brake system, characterized in that the return pump can be controlled as required depending on the value of a manipulated variable and / or a control deviation of a controller that influences the braking torque and / or the wheel speed. 2. The method according to claim 1, characterized in that when the pressure is reduced, the return pump can be controlled as required depending on the value of the manipulated variable of a slip controller. 3. The method according to any one of the preceding claims, characterized in that when the pressure builds up, the return pump can be controlled as required depending on the value of the control deviation of a controller influencing the wheel speed. 4. The method according to any one of the preceding claims, characterized in that the voltage at the return pump and / or the current flowing through the return pump can be regulated to a predefinable setpoint. 5. The method according to claim 4, characterized in that starting from the manipulated variable and / or the control deviation of a slip controller and / or a controller influencing the wheel speed and / or the control deviation, the setpoint can be predetermined. 6. The method according to any one of claims 4 or 5, characterized ge indicates that the setpoint is a two-point controller feedbar, which provides a signal for acting on the return pump. 7. The method according to any one of claims 4 to 6, characterized in that starting from the target value, a duty ratio for controlling the return pump can be predetermined. 8. Device for controlling a return pump of a brake system, characterized in that means are provided which control the return pump as required depending on the value of a manipulated variable and / or a control deviation of a controller which influences the braking torque and / or the wheel speed.