DE102013210563A1 - Method for controlling and regulating an electrohydraulic brake system and brake system - Google Patents

Abstract

A method for controlling and regulating an electrohydraulic brake system (2) for motor vehicles, comprising an electrically controllable pressure supply device (8), which comprises a cylinder-piston arrangement (40) with at least one in a hydraulic pressure chamber (38) by an electromechanical actuator (14) by an electric motor movable pressure piston (32) which is displaced in a pressure build-up direction (44) for pressure build-up and in the opposite pressure build-up direction (44) for pressure build-up, a number of hydraulically actuated wheel brakes (100) being provided, each of which has an associated electrically actuated inlet valve (88) can be connected to the hydraulic pressure chamber (38) and via an associated electrically actuated outlet valve (106) to a brake fluid reservoir (118), a pre-pressure being determined and set by the movement of the pressure piston (32) in the pressure chamber (38), should be reliable and precisely the respective deliver the ordered pressure. For this purpose, it is provided that the pressure piston (32) is not moved during a control process, in particular ABS, or is only moved in the direction of pressure build-up (44).

Description

The invention relates to a method for controlling and regulating an electrohydraulic brake system for motor vehicles comprising an electrically controllable pressure supply device, which comprises a cylinder-piston arrangement with at least one electromotive actuator movable in a hydraulic pressure chamber by an electromechanical pressure piston, which for pressure build-up in a pressure build-up direction and pressure reduction is displaced in the opposite pressure reduction direction, wherein a number of hydraulically actuated wheel brakes is provided, which are each connected via an electrically actuated inlet valve to the hydraulic pressure chamber and an electrically actuated outlet valve with a brake fluid reservoir, and wherein a pre-pressure is determined and by the method of the pressure piston is set in the pressure chamber. It further relates to a corresponding brake system.

Automatic control systems such as ABS, ESP, TCS have become indispensable in modern motor vehicles and greatly increase the safety of vehicle occupants. They usually intervene when an unstable dynamic driving situation is detected (spinning the wheels, skidding, etc.) and transfer the vehicle by deliberately braking and releasing individual wheels back into a stable driving dynamic state. While in conventional hydraulic braking systems, where all brake pressure has to be applied by the driver through muscle power, these control systems can only selectively reduce brake pressure and independently generate no higher than the driver pressure, active, especially electro-hydraulic, braking systems are designed to be system-wise Even pressure independently or actively generated or can be built.

During control processes, a form is created. Form here refers to the pressure in the hydraulic pressure chamber in which the pressure piston is moved.

From the DE 10 2011 076 675 A1 a method for controlling an active brake system is known, which determines a suitable form for a variety of conceivable situations that result from an ongoing driver braking or active control functions in the comfort and safety area.

In the DE 10 2011 077 329 A1 It also describes how a significant improvement in comfort can be achieved, especially in the case of current ABS control, by limiting the pre-pressure to the absolute minimum, which is determined by the highest pressure requirement of all ABS-controlled wheel circuits. The pressure in the pre-compression chamber is driven exactly to the highest required pressure level. The advantage of this strategy is that now the wheel with the highest pressure is connected directly to the admission pressure chamber, its pressure is thus regulated without actuation of the corresponding intake valve. This is directly connected to the mechanically rigid admission pressure chamber at least one wheel. This "soft" or hydraulically elastic consumer means that the pressure in the pre-pressure chamber can be adjusted well. This is because the piston movement around a small piston stroke in this configuration also causes only a small pressure modulation.

If, on the other hand, the inlet valves of all wheel circuits are closed, it is difficult to set a desired pressure in the stiff admission pressure chamber. A slight return of the piston then causes the pressure to drop immediately to zero. An ancestor of the piston in the direction of pressure build-up in turn causes a large pressure gradient: a few millimeters of travel can be sufficient to vary the form between 0 bar and a maximum pressure of for example 200 bar. When setting a too high loop gain for the pressure regulator can lead to instabilities of the entire controlled system and thus to strong vibrations in the form.

It is therefore an object of the invention to provide a method which reliably and precisely delivers the respectively required requirement pressure. In addition, a corresponding device should be provided.

With regard to the method, this object is achieved in that the pressure piston is not moved during a control process, in particular ABS, or only moved in the pressure build-up direction.

Advantageous embodiments of the invention are the subject of the dependent claims.

The invention is based on the consideration that it is immensely important for the reliable performance of a control process that always the required, in particular the highest, pressure requirement can be served. Only then can be ensured in a control process such as an ABS braking process that the wheels are braked precisely and purposefully in the vehicle and a stable and safe driving dynamic situation is realized. In control operations in which the pressure piston is moved to reduce pressure, due to its inertia, the corresponding pressures can not be fast enough and / or not adjusted precisely enough due to unwanted fluctuations.

As has now been recognized, this pressure requirement can be met by the pressure piston either exclusively holding its position during a control operation, while maintaining the pressure in the pressure chamber, or moving to build up the pressure. The pressure piston is therefore not moved or moved in the opposite direction and thus used for pressure reduction. This prevents the pressure in the pressure chamber from dropping sharply as a result of such a retraction, and then the requisite pressure can not be built up quickly enough for a renewed pressure requirement, or unwanted pressure fluctuations occur, so that the control process can not be carried out precisely enough.

It is for the reasons mentioned above for the quality of the form control conducive to connect at any time at least one open Radkreis or brake circuit with the pre-pressure chamber or pressure chamber. To realize this completely, the front pressure would have to be set as required by the ABS of the high-pressure wheel, ie the wheel for which the highest brake pressure is required. In particular, when Raddruckabbau in the case of a recognized Radblockierneigung but must be as fast and accurate pressure reduction modulation done that the pressure piston can not implement quickly and accurately enough due to the high inertial masses of the entire engine drive. In order to achieve the dynamics required for precise pressure reduction, an extremely complex motor technology would have to be used, which would not be expedient for cost reasons and the lack of robustness.

Advantageously, therefore, takes place during a control process, the pressure reduction in a wheel only by closing the associated inlet valve and opening the associated exhaust valve. The closing of the inlet valve prevents pressure medium from flowing out of the pressure chamber, while the pressure medium flows out of the wheel brake through the opened outlet valve into the brake fluid reservoir or the pressure medium reservoir. As soon as enough pressure medium has flowed off, the outlet valve is closed again.

The actuator advantageously comprises an electric motor which converts a rotational movement of a motor shaft into a translational movement of the pressure piston, wherein in a first direction of rotation the pressure piston is displaced to build up pressure in the pressure buildup direction and in a second direction of rotation to reduce pressure opposite to the pressure buildup direction. In this case, the first direction of rotation, for example, positive speeds and the second direction of rotation can be assigned to negative speeds of the motor shaft, d. h., rotations in the first direction always have positive speeds. The condition that the pressure piston should not be pushed or moved at all or only in pressure build-up direction, can be formulated in this case so that only speeds greater than or equal to zero are allowed.

In a preferred embodiment, the pre-pressure set in the pressure chamber is always selected during a control process such that it corresponds in each case to the largest wheel setpoint pressure of the wheel brakes. This ensures that this pressure is available, as it were, instantaneously for one or more brakes and that there are no delays caused by pressure build-up.

The pressure piston is opposite to the pressure build-up direction for sucking pressure medium advantageously only proceed when a suction condition is met. The reason why a suction process may be necessary in the described method, is that the pressure medium supply always decreases in the process of the invention, the pressure medium supply during the control process in comparison with processes in which also during a control process for pressure reduction of the pressure piston is moved and therefore can be exhausted faster. If no more pressure medium in the pressure chamber available, no pressure can be built more in one or more Radkreisen more. To make this possible again, the pressure chamber must be refilled. The suction condition is advantageously met when the pressure medium volume of the pressure medium in the pressure chamber falls below a predetermined minimum setpoint. This means that if this minimum setpoint is undershot, a suction process is performed in each case, so that again enough pressure medium for subsequent pressure buildup is available.

The suction condition can preferably also be met when the pressure medium volume of the pressure medium in the pressure chamber falls below a predetermined minimum limit value and within a predetermined period no pressure build-up exceeding a predetermined pressure value is expected. That is, the hard limit given by the minimum setpoint has not yet been reached. But the pressure medium supply is already so low, so that already at this time the stock is filled as a precaution, unless large pressure build-up is expected. This can for example be realized so that it is tried to recognize the driving dynamics phase of the braking maneuver and based on experience or predetermined values to carry out a prognosis or extrapolation. Suction lasts about 200-300 ms, so this also roughly corresponds to the period over which a prognosis must be made. If, unexpectedly, a high pressure buildup is necessary, the direction of rotation of the motor and thus the travel direction of the piston are reversed again and pressure is built up.

The condition that a minimum volume is undershot corresponds to the condition or can also be formulated as a condition that a given piston travel is exceeded in the pressure build-up direction.

With respect to the brake system, the above object is achieved by providing an electronic control unit (ECU) which carries out a method according to any one of the preceding claims. The method can advantageously be present as an executable on the control unit and computer program. That is, the program contains instructions for performing the described method.

The advantages of the invention are, in particular, that a control process can run reliably and very close to the required pressure curve by limiting the piston movement to the holding of the pressure in the pressure chamber or the pressure build-up, whereby a particularly safe control of the vehicle is made possible in these situations.

The fact that the pressure reduction is performed exclusively by the control of valves, the wear of the components of the actuator is kept low because the engine does not have to perform a quick reversal or reversing of the motor axis. Also, the wear of the components of the cylinder-piston assembly is kept low because rapid reversal movements of the piston during a control process are not necessary.

By carrying out a suction cycle, when the exhaustion of the pressure medium reservoir threatens in the pressure chamber, it is ensured that in future pressure requirements again pressure can be built up in at least one of the wheel brake circuits.

An embodiment of the invention will be explained in more detail with reference to a drawing. In it show in a highly schematic representation:

1 an electro-hydraulic brake system with a control and regulating unit for carrying out the method in a preferred embodiment, and

2 a diagram with time curves of brake pressures and engine speeds.

An in 1 shown active or electro-hydraulic brake system 2 includes a pressure supply device 8th which is an electromechanical actuator 14 includes. This includes an electric motor 20 and a gearbox 26 and shifts a pressure piston to build up pressure 32 in a hydraulic pressure chamber 38 in pressure build-up direction 44 , Through the pressure piston 32 and the pressure room 38 is a cylinder-piston assembly 40 realized. The pressure piston 32 moves from a rest position 50 in a printing position 56 , whereby a defined volume of pressure medium from the pressure chamber 38 over a line 62 , an open isolation valve 68 and another line 74 in a wheel circle 80 is pushed where it passes through an initially opened inlet valve 88 in a brake line 94 and continue in a wheel brake 100 is moved. This will be in the wheel brake 100 generates a brake pressure. In the 1 is just a wheel circle 80 shown. In a motor vehicle are usually four wheel circles 80 provided, in each case via a separating valve 68 with the pressure room 38 are connectable. An electronic control unit 142 serves to control the components described above.

A brake pressure reduction, as it is carried out in known systems, can be done by the pressure piston 32 again in the direction of his resting position 50 , ie opposite to the pressure buildup direction 44 , moved or retracted. A quick brake pressure reduction, as required in the case of ABS control, but also, as proposed here, via the operation of the intake valve 88 and an exhaust valve 106 possible, which in a discharge line 112 is switched, through which the wheel brake 80 or the brake 100 with a brake fluid reservoir 118 or reservoir is connected. To reduce the brake pressure, the inlet valve 88 closed and the exhaust valve 106 open for a certain time. As a result, brake fluid or pressure fluid flows out of the wheel brake 100 over the brake line 94 through the outlet valve 106 and via the discharge line 112 in the brake fluid reservoir 118 , This measure of pressure reduction is useful if the pressure chamber or the pressure chamber 38 several wheel circles operated in parallel. So that the pressure in a wheel circuit in normal operation is never higher than the pressure in the admission pressure chamber or the pressure chamber 38 , is a check valve 124 to the inlet valve 88 connected in parallel. In one of the line 62 branching line 130 is a check valve 136 connected.

In an alternative embodiment of the brake system 2 can the pressure room 38 for safety reasons more, especially zweikreisig executed be with multiple pressure chambers, the pressure chambers the wheel circuits or brake circuits can be assigned diagonally or axle wise (black and white). In this case, would have multiple isolation valves 68 be used (one for each brake circuit).

The inventive method is on the control unit 142 executed and is in a preferred embodiment with reference to the in 2 illustrated waveforms explained. It is on an x-axis 150 the time t and on a y-axis 152 the pressure P applied.

The driver generates during a braking operation by his brake operation (for example, by pressing a brake pedal) a pressure request, which by a pressure request signal 200 is represented. The highest pressure requirement of all wheels is a maximum pressure request signal 206 shown. Since no higher than this pressure in the overall system is needed, exactly this pressure in the pressure chamber 38 be set. The wheel brake 100 , which requires exactly this pressure (this brakes the wheel with the highest pressure requirement) can directly and without activating the associated inlet valve 88 with the pressure room 38 stay connected. As the pressure contour of the maximum pressure request signal 206 is very sharp (this is due to the fact that the ABS must react very quickly with pressure reduction for precise control), it is almost impossible to modulate with an electric motor drive so accurately.

In real braking systems, the course of a modulation signal would be roughly the same 212 result. This has a time delay compared to the desired maximum pressure request signal 206 on. In addition, it is characterized by a transient response, which leads after a strong pressure reduction to undershoot (eg shortly after a time 218 ), so that too much pressure is reduced and is braked too weak. In the event of a severe undershoot, brake fluid may be drawn from the brake circuits, their intake valves 88 are closed by the respective check valve 124 opens. However, if the pressure then returns to the desired value, the pressure build-up but can not get into these brake circuits, as their intake valves 88 are closed and the check valves 124 lock in this direction. Thus, the undershoot in Vordruckverlauf the pressure level in actually separated and not to be modulated Radkreisen 80 unintentionally reduced, which would lead to an unwanted and sometimes dangerous loss of braking effect.

In the modulation of the pressure in the pressure chamber 38 applies in principle that a pressure build-up is achieved by the pressure piston 32 in pressure build-up direction 44 (in 1 to the left). This is in the present embodiment with positive speeds N of the electric motor 20 reached. For pressure reduction with the help of the electric motor 20 this must run in the opposite direction, ie with negative speeds N, so that the pressure piston 32 opposite to the pressure buildup direction 44 will proceed (in 1 to the right). Such a pressure reduction operation by means of the electric motor is also in the 2 shown. It is on an x-axis 156 the time and on a y-axis 158 the engine speed N is plotted.

An engine speed signal 224 represents the engine speed of the electric motor 20 as a function of time. To the pressure according to the ABS request after a time 218 To reduce, negative rotational speeds N are required, which by a dashed signal section 236 are shown. The switching or reversing the direction of rotation of the electric motor 20 but requires a certain finite reversing time, through which, inter alia, the undesirable undershoots discussed above arise in the course of the pressure.

With the method according to the invention, which is a control strategy for the brake system 2 includes, these disadvantages are eliminated. It is therefore provided, during a control, in particular an ABS control, never to allow the pressure piston 32 opposite to the pressure buildup direction 44 emotional. With regard to the electric motor 20 This means that during the control process no negative speeds are allowed or set, ie, the electric motor 20 rotates exclusively in the positive direction (pressure build-up) or stands still (holding pressure). In the pressure room 38 Thus, only an active pressure build-up or a holding of the pressure by the electric motor takes place 20 , This is achieved by adjusting the requested pressure in the pressure chamber 38 a limitation of the setpoint speed of the electric motor 20 is provided. In the specific case, only _nominal speeds N _{setpoint are} permitted that are greater than or equal to zero rpm (revolutions per minute). The in the brake circuits or Radkreisen 80 required pressure drops in the case of detected Radblockierneigungen are then about the wheel associated valve pair 88 / 106 causes. When the electric motor 20 during this time no negative speeds can proceed (as in the signal section 236 ), the form now remains at a constant level, previously at the time 218 was achieved. This results in a pressure curve 242 ,

It is still to be noted what happens when the respective wheel brake 100 after valve-controlled pressure reduction again with the pressure chamber 38 is connected. This is then on one higher or too high level, so that an unintentional pressure jump in the wheel circle 80 at a time 248 would be expected. However, such a pressure jump occurs due to the hydraulic characteristics of the brake system 2 not a. The pressure room 38 namely has a hydrodynamically stiff behavior: even the removal of a very small volume of liquid causes a collapse of the primary pressure or a lowering to a lower level before. Due to this fact, the wheel circle 80 despite the pressure difference to the pressure chamber 38 without hesitation by opening the inlet valve 88 be hydraulically connected or shorted with this. In fact, there is an automatic pressure equalization of the pressure in the pressure chamber 38 to the pressure of the activated wheel circle 80 , Around the wheel circle 80 desired pressure build-up between the time 248 and one time 254 To achieve, even a method of the pressure piston is again 32 in pressure build-up direction 44 and thus turning the electric motor 20 needed with positive speeds, so still some pressure medium volume from the pressure chamber 38 in the now open cycle circle 80 can be postponed.

By the described control strategy, in which a method of the pressure piston 32 opposite to the pressure buildup direction 44 and thus negative speeds can be avoided in the respective wheel circle 80 Achieve a pressure curve that is actually very close to the desired maximum pressure request signal 206 lies and has no significant undershoot.

The loads for the electric motor 20 and the gearbox 26 will be significantly reduced. The fast reversal of the direction of rotation of the entire drive leads in known systems to a large wear and high power consumption with very high current peaks. These disadvantages are avoided with the illustrated concept of continuous volume shifting in only one direction.

The fact that the pressure piston 32 either not at all or only in pressure build-up direction 44 is moved, that causes the system or the pressure medium supply in the pressure chamber 38 faster exhaustible than known systems. In other words, the printing position 56 approaches an end position at a certain time 58 , Once this is done, no further pressure build-up is possible. To make this possible again, it is necessary to fill the pressure chamber 38 With pressure medium a suction cycle can be inserted by the separating valve 68 closed and the pressure piston 32 as quickly as possible opposite to the pressure buildup direction 44 in the resting position 50 or start position is moved, which is achieved by negative engine speeds. About the check valve 136 will then be over the line 130 Pressure fluid or brake fluid from the brake fluid reservoir 118 sucked and the control process can then continue to run normally again. In the present case, therefore, negative speeds or a method of the pressure piston are opposite to the pressure build-up direction 44 only allowed during such a suction cycle.

LIST OF REFERENCE NUMBERS

2

 braking system

8th

 Pressure supply device

14

 actuator

20

 electric motor

26

 transmission

32

 pressure piston

38

 pressure chamber

40

 Cylinder-piston arrangement

44

 Pressure build-up direction

50

 rest position

56

 print position

58

 end position

62

 management

68

 isolation valve

74

 management

80

 wheel circuit

88

 intake valve

94

 brake line

100

 wheel brake

106

 outlet valve

112

 discharge line

118

 Brake fluid reservoir

124

 check valve

130

 management

136

 check valve

142

 Control unit

150

 X axis

152

 y-axis

156

 X axis

158

 y-axis

200

 Pressure request signal

206

 Maximum pressure request signal

212

 modulation signal

218

 time

224

 Engine speed signal

236

 signal section

242

 pressure curve

248

 time

254

 time

T

 Time

P

 print

N

 Engine speed

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

• DE 102011076675 A1 [0004]
• DE 102011077329 A1 [0005]

Claims (8)

Method for controlling and regulating an electrohydraulic brake system ( 2 ) for motor vehicles comprising an electrically controllable pressure supply device ( 8th ), which comprises a cylinder-piston arrangement ( 40 ) with at least one in a hydraulic pressure chamber ( 38 ) by an electromechanical actuator ( 14 ) electromotively movable pressure piston ( 32 ), which for pressure build-up in a pressure build-up direction ( 44 ) and for pressure reduction in opposite pressure reduction direction ( 44 ) is shifted, wherein a number of hydraulically actuated wheel brakes ( 100 ) is provided, which in each case via an associated electrically actuated inlet valve ( 88 ) with the hydraulic pressure chamber ( 38 ) and via an associated electrically actuatable outlet valve ( 106 ) with a brake fluid reservoir ( 118 ), wherein a pre-pressure is determined and by the method of the pressure piston ( 32 ) in the pressure chamber ( 38 ), characterized in that the pressure piston ( 32 ) during a control process, in particular ABS, not proceed or only in pressure build-up direction ( 44 ). Method according to claim 1, wherein during a control process the pressure reduction in a wheel brake ( 100 ) exclusively by closing the associated inlet valve ( 88 ) and opening the associated exhaust valve ( 106 ) he follows. Method according to claim 1 or 2, wherein the actuator ( 14 ) an electric motor ( 20 ), a rotational movement of a motor shaft in a translational movement of the pressure piston ( 32 ), wherein in a first direction of rotation of the motor shaft of the pressure piston ( 32 ) for pressure build-up in pressure build-up direction ( 44 ) and in a second direction of rotation for pressure reduction opposite to the pressure build-up direction ( 44 ). Method according to one of claims 1 to 3, wherein during a control process in the pressure chamber ( 38 ) preset pressure always the respective largest wheel set pressure of the wheel brakes ( 100 ) corresponds. Method according to one of claims 1 to 4, wherein the pressure piston ( 32 ) opposite to the pressure buildup direction ( 44 ) is moved to the suction of pressure medium only when a suction condition is met. A method according to claim 5, wherein the suction condition is met when the pressure medium volume of the pressure medium in the pressure chamber ( 38 ) falls below a predetermined minimum setpoint. The method of claim 5 or 6, wherein the suction condition is satisfied when the pressure medium volume of the pressure medium in the pressure chamber ( 38 ) is below a predetermined minimum limit and within a predetermined period no pressure build-up exceeding a predetermined pressure value is expected. Electrohydraulic braking system ( 2 ) comprising an electrically controllable pressure supply device ( 8th ), which comprises a cylinder-piston arrangement ( 40 ) with at least one in a hydraulic pressure chamber ( 38 ) by an electromechanical actuator ( 14 ) electromotively movable pressure piston ( 32 ), which for pressure build-up in a pressure build-up direction ( 44 ) and for pressure reduction in opposite pressure reduction direction ( 44 ) is shifted, wherein a number of hydraulically actuated wheel brakes ( 100 ) is provided, which in each case via an electrically actuated inlet valve ( 88 ) with the hydraulic pressure chamber ( 38 ) and via an electrically operated outlet valve ( 106 ) with a brake fluid reservoir ( 118 ), characterized in that an electronic control unit ( 142 ) is provided, which carries out a method according to one of the preceding claims.

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