DE102011076423A1 - Electro-hydraulic brake system controlling method for motor car, involves calculating pressure reference value of pressure provision device, and stopping transfer of motor car at predetermined pressure maximum value - Google Patents

Abstract

The method involves forming a pressure provision device (2) using a cylinder piston arrangement (29), where a piston (31) of the pressure provision device is actuated by an electromechanical actuator (30). A pressure reference value of the pressure provision device is calculated. Transfer of a motor car is stopped at a predetermined pressure maximum value. Operation of brake pedals (9) are determined using sensor devices (19, 40). A rate of change of the pressure reference value is limited based on standstill state of the motor car.

Description

The invention relates to a method for controlling a brake system for motor vehicles according to the preamble of claim 1 and a corresponding control device.

In automotive engineering, brake-by-wire brake systems are becoming increasingly widespread. Such brake systems often include a pedal decoupling unit which precedes a master cylinder, whereby brake pedal operation by the driver in "brake-by-wire" mode does not result in direct driver actuation of the master cylinder. The master cylinder is instead operated in the "brake-by-wire" by an electrically controllable pressure supply device, ie "foreign" -activated. In order to give the driver a pleasant pedal feel in the "brake-by-wire" mode of operation, the brake systems typically include a brake pedal feel simulation device. In these brake systems, the brake can be operated without active intervention of the driver due to electronic signals. These electronic signals can be output, for example, from an electronic stability program ESC or a distance control system ACC.

From the international patent application WO 2008/025797 A1 Such a braking system is known. In order to be able to dispense with a complex and energetically unfavorable intermediate storage of hydraulic authority energy, it is proposed that the pressure required for the electrical control of the pressure used in a space used to actuate the master cylinder pressure in the pressure supply means and kept pressurized if required under a higher pressure. The pressure supply device is z. B. formed by a cylinder-piston assembly whose piston is actuated by an electromechanical actuator. A method for controlling the brake system, in particular the pressure supply device is not described.

It is the object of the present invention to provide a method for controlling an electrohydraulic brake-by-wire brake system having an electrically controllable pressure supply device, which comprises a cylinder-piston arrangement whose piston can be actuated by an electromechanical actuator, by means of which the pressure supply device is protected from damage.

This object is achieved by a method according to claim 1. Advantageous developments of the method according to the invention are specified in the dependent claims 2 to 5.

Advantageously, the method according to the invention is carried out in a braking system for motor vehicles, which can be activated in a so-called "brake-by-wire" mode both by the driver and independently of the driver, preferably operated in the "brake-by-wire" mode is and can be operated in at least one fallback mode in which only the operation by the driver is possible.

Further preferred embodiments of the invention will become apparent from the subclaims and the following description with reference to figures.

They show schematically:

1 a hydraulic circuit diagram of a brake system for carrying out the method according to the invention,

2 a block diagram of an exemplary driver request detection, and

3 a block diagram of an exemplary method for limiting a target pressure value.

The brake system shown in the drawing consists essentially of an actuator 1 , a pressure supply device 2 in which the actuating unit and the pressure supply device form a brake booster, as well as a master brake cylinder or tandem master cylinder operatively connected downstream of the brake booster 3 , whose pressure chambers, not shown, with the chambers under atmospheric pressure of a first pressure medium reservoir 18 are connectable. On the other hand, wheel brake circuits I, II are connected to the pressure chambers, with the interposition of a known ABS or ESP hydraulic unit or a controllable Radbremsdruckmodulationsmoduls the wheel brakes 5 - 8th supply a motor vehicle with hydraulic pressure medium. The wheel brake pressure modulation module 4 is an electronic control unit 41 assigned. The actuating device 1 in a housing 20 is arranged, on which the tandem master cylinder 3 is attached is via a brake pedal 9 controllable, that via an actuating rod 10 with a first piston 11 the actuator 1 is operatively connected. The actuating travel of the brake pedal 9 is by means of a preferably redundant displacement sensor 19 captures the path of the first piston 11 detected. However, for the same purpose, a rotation angle sensor can be used, the the angle of rotation of the brake pedal 9 detected. The first piston 11 is in a second piston 12 arranged in which he has a pressure chamber 14 limited, which is a compression spring 15 the brake pedal is de-energized 9 the first piston 11 to rest on the second piston 12 brings. Alternatively or additionally, in the area of the push rod 10 or the brake pedal 9 a pedal return spring may be provided. The pressure chamber 14 is in the unactuated state of the actuator 1 with a chamber 38 a second pressure medium reservoir 38 . 39 connected, that of the actuator 1 assigned. The second piston 13 acts with a third piston 13 Together, the primary piston of the tandem master cylinder 3 In the example shown, between the second ( 12 ) and the third piston 13 a pressure booster piston 16 is arranged. Between the second piston 12 and the pressure intensifier piston 16 is a gap 21 limited, by the application of a hydraulic pressure of the second piston 12 at one in the housing 20 trained stop 22 is held while the pressure intensifier piston 16 and thus the primary piston 12 of the tandem master cylinder in the sense of a pressure build-up in the tandem master cylinder 3 be charged. A resulting from this stress movement of the pressure booster piston 16 is by means of a second displacement sensor 23 detected. In addition, the second piston limits 12 in the case 20 a hydraulic chamber 17 whose function is explained in the following text. To the hydraulic chamber 17 is a first line 34 connected via a normally open (SO) check valve 33 with a second line 35 connected to the previously mentioned pressure chamber 14 connected.

Furthermore is 1 to see that the previously mentioned pressure chamber 14 via a lockable connection line 24 with a hydraulic simulator chamber 25 communicating from a simulator piston 26 is limited. The simulator piston acts 26 with a simulator pen 27 and one of the simulator spring 27 parallel elastomer spring 28 together. The simulator chamber forms 25 , the simulator piston 26 , the simulator pen 27 as well as the elastomer spring 28 a Pedalwegsimulator that gives the driver when operating the brake system the usual pedal feel, which corresponds to a common brake pedal characteristic. This means that with low brake pedal travel, the resistance increases slowly and increases disproportionately with a larger brake pedal travel. To dampen the movement of the simulator piston 26 not shown, for example pneumatic damping means may be provided. The hydraulic connection line 24 between the simulator chamber 25 and the pressure chamber 14 or the chamber 38 of the second pressure medium reservoir is caused by a movement of the second piston 12 in the direction of actuation of the master cylinder 3 locked, whereby the pedal travel simulator is effectively switched off. The first piston 11 , the feather 15 , the hydraulic chamber 14 , the hydraulic connection 24 , the simulator chamber 25 , the simulator piston 26 , the simulator springs 18 and 27 , As well as the damping means, not shown, together form the simulation device, which together with a chamber under atmospheric pressure 38 the second pressure medium reservoir is associated with a first brake booster pressure medium circuit which is completely separated from the wheel brake circuits I, II.

The aforementioned electrohydraulic pressure supply device 2 consists essentially of a hydraulic cylinder-piston arrangement 29 and an electromechanical actuator 30 , which is formed for example by an electric motor with a reduction gear, the translational movement of a hydraulic piston 31 guaranteed, so in a pressure room 36 the hydraulic cylinder-piston arrangement 29 a hydraulic pressure is built up. The electromechanical actuator 30 is powered by an electrical energy storage with energy, with the reference numeral 49 is provided. The movement of the piston 31 is detected by means of a displacement sensor indicated by the reference numeral 32 is provided. The pressure room 36 is on the one hand to the gap 21 connected and on the other hand by means of a normally open (SO-) 2/2-way valve 37 with a chamber under atmospheric pressure 39 connectable to the second pressure medium reservoir. Here are the pressure supply device 2 , The gap 21 as well as the chamber 39 the second pressure medium reservoir associated with a second brake booster pressure medium circuit which is completely separated from both the first brake booster pressure medium circuit and the wheel brake circuits I, II. A pressure sensor 40 serves to capture the from the pressure supply device 2 provided or in the space 21 prevailing pressure.

The previously mentioned check valve 33 allows shut off the chamber 17 opposite the pressure chamber 14 , causing a movement of the second piston 12 is prevented in the direction of actuation. The chamber 17 , the first pressure medium line 34 , the check valve 33 , the second pressure medium line 35 , the pressure chamber 14 , the connection line 24 , the simulator chamber 25 and the second pressure medium reservoir 38 form a second brake booster pressure medium circuit, which is completely separated from the first brake booster pressure medium circuit and the two wheel brake circuits I, II. The said elements is a separate electronic control unit 42 associated with the previously mentioned electronic control unit 41 cooperates and the collection of sensor data, the processing of this data, the exchange of data with other, present in the vehicle, not shown control units, the control of the electromechanical actuator 30 , as well as the brake lights of the vehicle is used.

The operation of the braking system described above is known, for example, from the Applicant's International Patent Application cited in the prior art and need not be further explained in the following text.

2 shows in the form of a block diagram an exemplary driver request detection. The functional unit "driver request acquisition" 100 determined from the pedal unit for realizing the required pedal characteristic associated sensors the driver's request and calculates a signal for the target _{amplifier pressure} P _{V, Soll, Drv of} the linear actuator. The driver request recording 100 will be described in more detail below.

Depending on the design of the brake system here are one or more sensor signals available, which represent the driver's request. By way of example, the pedal position becomes redundant (signals X _{Ped, S1} and X _{Ped, S2 )} as well as the pedal force generated by the driver by means of the aforementioned pressure sensor 48 (Signal P _Drv ). Thus, stand for the driver's request calculation 102 For example, two physically independent information (X _Ped , P _Drv ) for the, the driver's brake request representing driver operation for setpoint generation of the required brake booster by means of the actuator available. A third, optional driver's request calculation 102 supplied information represents a vehicle speed and is designated by the reference V _Kfz . The one in the functional unit 102 calculated pressure setpoint P _{V, Soll, Drv, PWE} can then be additionally modified depending on the vehicle _speed V _Kfz , z. By multiplying by a vehicle speed dependent scaling factor. The redundant pedal position signals X _{Ped, S1} and X _{Ped, S2} are in the radio module 101 "Determination / monitoring pedal travel" plausibility and processed to a pedal position X _Ped .

As 2 can be further seen, the invention improves the functional unit "driver request detection" 100 to the effect that additional measures are taken at the transition of vehicle speed from slow driving to vehicle standstill and vehicle standstill. For this purpose, on the one hand the vehicle speed V _{motor vehicle is} considered, but in addition the operating state of the parking brake ST _{Bet, PB} and / or the selected gear stage ST _Gear (in vehicles with automatic transmissions) processed. This information is usually available as signals on a data bus (eg CAN bus).

In the function module 103 a calculation / determination of pressure limiting values is carried out. Without the additional measures described in more detail below, the value for the maximum _setpoint boost pressure P _{V, setpoint, Max} represents the maximum _setpoint pressure to be applied by the pressure supply device. The measure taken on the basis of the vehicle speed V _Kfz relates, for example, to limiting the maximum target _{boost pressure} P _{V, Soll, Max} when the vehicle is _stationary to the value P _{V, Soll, Max, Vveh0} or the reduction of the maximum target _{boost pressure} at low vehicle _speeds and transition to vehicle _standstill (P _{V, Soll, Max} = P _{V, Soll, Max, Vveh0} ). The measures taken on the basis of the signals ST _{Bet, PB} ^{and / or} ST _Gear relate, for example, to a further limitation of the maximum _setpoint boost pressure P _{V, Soll, Max} . If the brake is actuated when the vehicle is stationary and if additionally the gear stage "P" is engaged or the parking brake is actuated, this further limitation of the _desired boost pressure is effected to the value P _{V, setpoint, Max, park} (P _{V, setpoint, Max} = P _{V, Soll, Max, Park} ), where P _{V, Soll, Max, Park} ≤ P _{V, Soll, Max, Vveh0} . This additional limitation to P _{V, Soll, Max, Park} or P _{V, Soll, Max, Vveh0} is also carried out when a braking of an initial speed> 0 km / h was made to a standstill and after a predefined waiting time, the brake system is still being pressed. The two limiting maximum pressures P _{V, Soll, Max, Park} and P _{V, Soll, Max, Vveh0} are set according to the design of the brake system so that a rolling operation on the slope is prevented in any case.

According to another embodiment, in addition to the maximum pressure setpoint in the cases described above, according to the example, in addition, the setpoint pressure gradient is also limited _{to .DELTA.P.sub.V, SollGrad, Max} . In normal operation of the brake system there is no limitation of the gradient for the nominal amplifier pressure. If the above conditions are such that a setpoint pressure limitation to the value P _{V, Soll, Max} = P _{V, Soll, Max, Vveh0} or P _{V, Soll, Max} = P _{V, Soll, Max, Park is} made, then the Gradient also limited. In a standstill braking, in addition to _{P.sub.V , Soll, Max} = _{P.sub.V, Soll, Max, V.sub.veh0, there is} only a slight limitation of the nominal _{amplifier pressure} DP _{V, SollGrad, Max, Vveh0} (first Sollverstärkerdruckgradientengrenzwert), while in the case that additionally still Gear stage "P" is engaged or the parking brake is actuated next P _{V, Soll, Max} = P _{V, Soll, Max, Park} a very strong limitation of the Sollverstärkerdruckgeschwindigkeit DP _{V, setpoint, max, park} (second target _{intensifier pressure gradient limit} ). DP_ACTIVE corresponds to a control signal indicating whether a gradient limitation should be performed or not.

In block 104 is determined based on the determined maximum values P _{V, Soll, Max} and .DELTA.P _{V, SollGrad, Max} from the calculated setpoint P _{V, setpoint, Drv, FWE,} the pressure setpoint P _{V, setpoint, Drv of} the actuator. These limiting functions of the block 104 are, for example, in 3 shown schematically.

As 3 can be seen, is in the implementation of the limiting functions of the calculated, desired by the driver pressure setpoint P _{V, setpoint, Drv, FWE} first to the maximum value P _{V, setpoint, Max} (see function _block 105 ) limited. The limited to the maximum value P _{V, Soll, Max} pressure setpoint (signal P _Max ) is fed to a selection circuit, acting as a switch 106 which is controlled by a control signal ΔP_ACTIVE. The control signal ΔP_ACTIVE can assume two discrete values, namely a "1" and a "0". The in 3 shown switching state of the selection circuit 106 corresponds to the value ΔP_AKTIV = 0, so that there is no limitation of the pressure gradient and only one pressure limitation (see function block 105 ), so that at the output of the selection circuit 106 appearing signal P _{V, target, Drv} the limited pressure setpoint P _Max corresponds.

A limitation of the target pressure gradient, the value of the control signal ΔP_AKTIV = 1 or the switching state of the selection circuit 106 = "1", is in the function block 107 performed, which represents a discrete-time block diagram of the increase limiting function. If it is assumed that the pressure value at the output of the selection circuit 106 represents the pressure value in the sampling step k, takes place in the schematically indicated function block 108 a shift by one sampling step (k-1) back so that at the output of the function block 108 the pressure setpoint P _{V, setpoint, Drv} (k - 1) appears. This value is stored in the sampling step k in a subtraction element 109 compared with the above-mentioned limited pressure setpoint P _Max to form a _desired pressure difference ΔP _Soll , the limiting function 110 is supplied. By applying the limiting function 110 , which is controlled by a further control parameter _.DELTA.P VSollGradMax corresponding to a change in the pressure setpoint per sampling step, there is a limitation of the _desired pressure difference .DELTA.P _Soll to a maximum value, wherein the limited value .DELTA.P _{Soll, B} in a summing element 111 is added together with the pressure setpoint P _{V, setpoint, Drv} (k-1) of the previous sampling step. The result of the mentioned addition corresponds to a second switching state of the selection circuit 106 (ΔP_ACTIVE = 1) in which the pressure value is subjected to both a (maximum) pressure limitation and a gradient limitation.

The improved driver request recording ( 2 ) serves on the one hand the protection of the actuator from a thermally high load by a possible permanent brake operation with large brake pressures and possibly rapid target pressure changes that are not required at standstill of the vehicle, especially if additionally the parking brake was pressed or the gear stage "P "Was inserted. Another advantage of the improved driver input detection is a reduction in the energy consumption of the brake system, combined with the reduction of the burden on the electrical system, since due to the mentioned limiting functions in the considered operating case, the need for the static and dynamic engine torques substantially lower.

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 2008/025797 A1 [0003]

Claims (6)

Method for controlling an electrohydraulic brake system for motor vehicles, which can preferably be activated in a "brake-by-wire" mode, with a pressure-providing device which can be controlled by means of an electronic control and regulation unit (US Pat. 2 ), which with at least one hydraulically actuated wheel brake ( 5 . 6 . 7 . 8th ) is connected or connectable and by means of which the wheel brake ( 5 . 6 . 7 . 8th ) is hydraulically actuated, wherein the pressure supply device ( 2 ) by a cylinder-piston arrangement ( 29 ) is formed whose piston ( 31 ) by an electromechanical actuator ( 30 ) is operable, and wherein a pressure setpoint for the pressure-providing device ( 2 ) is determined, characterized in that the pressure setpoint (P _{V, Soll, Drv} ) at a standstill of the motor vehicle or at a transition of the vehicle to a standstill to a predetermined maximum pressure value (P _{V, Soll, Max} , P _{V , Soll, Max, Vveh0,} P _{V, Soll, Max, Park} ) is limited ( 104 ). A method according to claim 1, characterized in that the maximum pressure value (P _{V, Soll, Max, Vveh0,} P _{V, Soll, Max, Park} ) as a function of an actuation state of a parking brake (ST _{Bet, PB} ) and / or from a switching state of a transmission (ST _Gear ), in particular an automatic transmission of the motor vehicle, and / or the Kraftfahrzeugge A method according to claim 1 or 2, characterized in that the pressure setpoint (P _{V, Soll, Drv} ) based on at least two independent information (X _{Ped, S1} , X _{Ped Ped, S2} , P _Drv ) of at least one sensor device ( 19 . 40 ), which is an actuation of a brake pedal ( 9 ) detected. Method according to at least one of claims 1 to 3, characterized in that the rate of change of the pressure setpoint is limited at a standstill of the motor vehicle or at a transition of the vehicle to a standstill to a predetermined pressure gradient maximum value (.DELTA.P _{V, SollGrad, Max} ) ( 104 ). A method according to claim 4, characterized in that a maximum value of the pressure gradient (DP _{V, SollGrand, Max, Vveh0} , DP _{V, SollGrad, Max, Park} ) in response to an actuation state of a parking brake (ST _{Bet, PB} ) and / or a switching state a transmission (ST _Gear ), in particular an automatic transmission of the motor vehicle is determined ( 103 ). Control device for controlling an electro-hydraulic brake system for motor vehicles for carrying out the method according to one or more of claims 1 to 5.

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