DE102012212012A1 - Actuator for performing pressure-increase in electro-hydraulic brake-by-wire braking system for motor vehicle, has switching device and pump device designed such that direction of volume flow without reversing pump motor is reversed - Google Patents

Abstract

The actuator (2) has a pump device (8) with a pump motor by which volume flow of fluid is pumped to a user circuit (14). A switching device (56) and the pump device are designed such that direction of volume flow without reversing the pump motor is reversed if needed. The switching device comprises switching valves (26, 68). A low-pressure battery (86) is hydraulically connected to the pumping device by a storage conduit (80). A pilot valve (92) or a differential pressure valve is connected to the storage conduit. An independent claim is also included for a method for building up and reducing brake pressure in an electro-hydraulic brake-by-wire braking system.

Description

The invention relates to an actuator for pressure build-up and pressure reduction in an electro-hydraulic brake-by-wire brake system, with a pump device with a pump motor through which a volume flow of brake fluid is pumped into at least one consumer circuit. It further relates to an associated brake system. It further relates to a corresponding method.

In automotive brake-by-wire systems, precise operation requires that the actuators can both open and close the pressures in the brake circuits with high positioning accuracy. Previous approaches to this use piston-pressing spindle systems or linear drives with a motor, optionally a gear and a spindle drive, or pump drives. While in linear drives the system pressure in the brake system or in the corresponding brake circuits is reduced by reversing the motor, in pump systems the pressure reduction is controlled or regulated via outlet valves.

While the spindle-based solutions are relatively complex and large, pump drives can be formed with inexpensive and established components. Known pump-based approaches, however, suffer from the fact that the pressure buildup is volumetrically well controlled via the piston movement of the pump, the pressure reduction via an outlet valve comparatively uncontrolled and therefore possibly takes place with too high dynamics, so that in particular control operations of the brake pressure is not executed precisely enough can be.

It is therefore the object of the invention to provide an actuator of the abovementioned type, by means of which a volumetrically defined pressure reduction is made possible. In addition, an associated brake system should be specified. Furthermore, a method for operating such an actuator should be specified.

With respect to the actuator, this object is achieved according to the invention with a switching device, wherein the pumping device and the switching device are configured such that, if necessary, the direction of the volume flow can be reversed without reversing the pump motor.

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

The invention is based on the consideration that for the precise and, if necessary, fast and repeated carrying out of control processes during braking, the phase of the pressure reduction should be as precisely and volumetrically metered as possible by a corresponding actuator as the pressure build-up phase. Only then can the brake pressure be adjusted to the desired value at every moment of the control process, and inaccuracies with regard to the quantity of brake fluid removed during the pressure reduction can be avoided.

The known embodiments with pumping devices for pressure build-up, in which the pressure reduction takes place by removal of the brake fluid via exhaust valves, do not meet these requirements.

As has now been recognized, these requirements can be met by the fact that the volume flow, which is promoted to the pressure build-up of the pumping device to the load circuit, in the pressure reduction phase in its direction with precise timing and thus reversed vice versa. That is, the brake fluid flows during pressure reduction back from the consumer circuit back towards the pumping device. This allows a volumetrically accurate return promotion can be achieved. This, if necessary, purposeful and precise reversal of the conveying direction of the brake fluid, which in particular is made possible by the fact that the pump motor does not have to be reversed, can now be achieved with a switching device, depending on the switched state, either a flow in the load circuit to build up pressure or a drain in the reverse direction allows for pressure reduction.

By such a switching device, the volume flow can be promoted not only volumetrically precise in both directions. The actuator is thereby also trained to perform a precise timing control of the volume flow, so that it can be synchronized, for example, with the operation of the corresponding pumping device.

Advantageously, the switching device has a number of switching valves. These can, depending on requirements, as self-switching valves (eg check valves) or electrically controllable switching valves can be formed. Switching valves can be switched by simple and robust control and thus allow a timely and precise reversal of the volumetric flow.

In a preferred embodiment of the actuator extends from the pumping device at least one supply line with a supply valve of the switching device, which is opened in the supply of brake fluid in the load circuit to the load circuit and at least one discharge line with a discharge switching valve Switching device which opens when the removal of brake fluid in the consumer circuit, from the consumer circuit to the pumping device.

Separate lines are available for the inflow of brake fluid into the consumer circuit and for the return flow, which can also be blocked or blocked or released by the corresponding valves as required. The supply valve may be formed as a check valve, which prevents the return flow of brake fluid from the consumer circuit through the supply line.

Preferably, a low-pressure accumulator is provided for demand-fast removal of brake fluid from the pumping device or from the consumer circuit, which is hydraulically connected by at least one storage line with the pumping device, and wherein in the storage line as a supply valve, a switching valve is connected or a differential pressure valve which opens, when the pressure in the pumping device exceeds the pressure in the consumer circuit is switched. The respective valve thus opens (switched or due to the pressure conditions) when the pump delivers brake fluid into the low pressure accumulator.

In the case of a switching valve, this can be opened as soon as the pressure medium or the brake fluid to be introduced into the low-pressure accumulator. In the case of a said differential pressure valve, this opens automatically when the pressure in the pumping device exceeds the pressure in the consumer circuit, so that then brake fluid flows into the low-pressure accumulator or the storage line is so long, until the pressure in the pumping device is less than or equal to the Pressure in the consumer circuit is.

Advantageously, a bypass line bridging the bypass valve is provided, in which a check valve is connected, which blocks the flow of brake fluid from the pump device into the low-pressure accumulator and allows in the reverse direction. Through this bypass line, the pressure medium can be sucked as the low-pressure accumulator by the pumping device, without the valve in the storage line must change its position. The check valve prevents the undesired or uncontrolled flow of pressure medium from the pumping device through the bypass line into the low-pressure accumulator.

In a preferred embodiment, the pump device has an electric motor with a motor axis, which moves via a driving element at least one piston in an associated cylinder, wherein the driving element is configured such that the respective piston can be moved in two opposite directions without the direction of rotation the motor axis must be reversed. By this embodiment of the pumping device reversals of the engine and the associated strong forces and high electrical system currents are avoided.

Advantageously, each cylinder is associated with a supply and a discharge line and a storage line, wherein the discharge lines each have a common second switching valve. That is, the outflow of brake fluid through the respective discharge lines can be controlled by switching a common valve. Depending on the application or dimensioning of the actuator advantageously two or three or more cylinders are provided.

The driving element is preferably designed as an eccentric or as a connecting rod mounted eccentrically to the motor axis.

With respect to the brake system, the above object is achieved according to the invention with an actuator specified above.

With regard to the method for constructing and reducing brake pressure in a hydraulic brake-by-wire brake system, the abovementioned object is achieved according to the invention by boosting a volume flow of brake fluid from a pump device with a pump motor into the consumer circuit to build up pressure in at least one consumer circuit is, and wherein the pressure reduction by a switching device, the direction of the flow rate at the same direction of rotation of the engine, d. H. is reversed without reversing the pump motor, so that the volume flow from the consumer circuit flows back into the pumping device.

For pressure reduction is advantageously removed in a first step brake fluid from the consumer circuit in the pumping device and pumped in a second step brake fluid from the pumping device into a low-pressure accumulator.

Advantageously, brake fluid is discharged during the pressure reduction by establishing a direct hydraulic connection between the load circuit and the low-pressure accumulator directly and without the involvement of the pump motor in a low-pressure accumulator when an extremely rapid pressure reduction is necessary. This is preferably done by opening valves in the hydraulic connection between the load circuit and the low-pressure accumulator.

The advantages of the invention are in particular that in the described actuator can be made of known and inexpensive components and compared to alternative solutions comparatively small space is required. By a volumetrically defined pressure reduction coupled to the engine speed, a better control function for comfort and control functions can be provided - compared to conventional pump drives.

If the engine for pressure reduction does not have to be reversed is especially in control operations such. B. ABS or TSC reduces the electrical system load due to the elimination of the engine reversing or it can also be used in contrast to systems with necessary engine reversal carrier and cheaper engine types that z. B. were optimized for one direction and / or use cheaper magnetic materials.

The actuator knows no limitation of its working capacity and can therefore continuously and without interruption brake fluid in the brake system and remove. Interruptions in pressure build-up phases - z. B. because of the retraction of a piston - are therefore not necessary.

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 actuator having a pump device with a cylinder and a piston movable therein, a supply line, a discharge line, in each case in the line switching valves and a low-pressure accumulator in a first preferred embodiment during a first phase of the pressure build-up,

2 the actuator off 1 during a second phase of pressure build-up,

3 the actuator off 1 and 2 during a first phase of pressure reduction,

4 the actuator from the 1 to 3 during a second phase of pressure reduction,

5 an actuator in a second preferred embodiment with a differential pressure valve between the pumping device and low-pressure accumulator,

6 an actuator in a third preferred embodiment with two cylinders and pistons and two differential pressure valves, and

7 an actuator in a fourth preferred embodiment with three cylinders and pistons and three differential pressure valves.

Identical parts are provided with the same reference numerals in all figures.

An in 1 illustrated actuator 2 includes a pumping device 8th , By the need to pressurize brake fluid in a consumer circuit 14 through a supply line 20 can be pumped. Furthermore, a discharge line 30 for the removal of brake fluid from the consumer circuit 14 intended.

The pumping device 8th comprises an electric motor (not shown), on whose axis an eccentric 32 is attached, the rotation of the motor axis in the direction of rotation 38 Pressure in the consumer circuit 14 build up or dismantled. This is a piston 44 in a cylinder 50 emotional. The piston 44 is doing so on the eccentric 32 attached so that the piston can be moved in two opposite directions without the electric motor must change the direction of rotation of its axis.

The actuator has a switching device 56 on, by which the volume flow of the brake fluid in its direction from the pumping device 8th to the consumer circle 14 and back can be changed purposefully. The switching device 56 has to do this in the supply line 20 as a supply valve switched check valve 26 on, by which a return flow of a volume flow of brake fluid from the consumer circuit 14 into the pumping device 8th is prevented, and a second switching valve 68 which is in the discharge line 30 is switched.

The supply line 20 and the discharge line 30 lead to a common leadership 74 from which a storage line 80 to a low-pressure accumulator 86 leads. In the storage line 80 is a switching valve 92 switched, that, if necessary, the memory line 80 releases or makes permeable to brake fluid. The switching valve 92 is from a bypass line 96 bridged into which a check valve 102 which switches the flow of brake fluid from the pumping device 8th in the direction of the low pressure accumulator 86 locks.

A first pressure building phase will now be based on the 1 explained. The discharge switching valve 68 and the switching valve 92 are locked. The piston 44 moves in a Ausschubrichtung 108 , causing brake fluid from the cylinder 50 over the check valve 26 , which with the first switching valve 62 connected in series, in the consumer circuit 14 , For example, a wheel brake, is passed.

In 2 is a second phase of the pressure buildup shown. The piston 44 moves in the suction direction 114 and sucks in this way through the bypass line 96 , which acts as a kind of suction line, and through the check valve 102 Brake fluid from the low-pressure accumulator 86 or low pressure reservoir. The check valve 26 prevents during this phase brake fluid from the supply line 20 is sucked. This can be reflected in the 1 connect the phase shown, and the two phases together can be repeated until enough brake fluid in the consumer circuit 14 was promoted.

A first phase of pressure reduction is in 3 shown. The switching device 56 allowed by a fast switching of the valve 68 a reversal of the volume flow of the brake fluid for pressure reduction. For this purpose, the somewhat self-closing non-return valve blocks 26 while the second switching valve 68 switched to passage. The switching valve 92 is locked. The piston 44 moves in the suction direction 114 , As a result, brake fluid flows out of the consumer circuit 14 back to the pumping device 8th or the cylinder 50 trained pump room.

Between the second switching valve 68 and the pumping device 8th can in the discharge line 30 a check valve to be switched.

A second phase of pressure reduction is in 4 which are usually related to the first, in connection with 3 discussed pressure reduction phase connects. The switchable valve 68 has been switched to blocking position.

The switching valve 92 is switched to passage. The piston 44 moves in the extension direction 108 and delivers brake fluid from the piston 50 through the switching valve 92 in the low pressure area (brake fluid reservoir) or low pressure accumulator 86 , The first ( 3 ) and second ( 4 ) Phase of the pressure reduction can be repeated one after the other until the desired amount of brake fluid reaches the consumer circuit 14 has left and the brake pressure has been reduced to the desired value. Reversing the electric motor of the pumping device 8th is not necessary.

A quick, immediate introduction of the brake fluid into the low-pressure accumulator can, if necessary, be carried out by the valves 68 . 92 be opened at the same time. At the same time, the pipes function 74 . 80 as emptying line. This means that the brake fluid flows out of the consumer circuit 14 through the pipe 74 and the line 80 directly into the low pressure accumulator 86 , Such emptying is advantageous in braking situations, as they are typical of a μ-jump, for example, in a sudden or immediate change of surface of grippy asphalt on ice. In such situations, a maximum pressure reduction dynamics is required and the return of brake fluid exclusively via the motor-driven pumping device would be too slow.

A second preferred embodiment of an actuator 2 is in 5 shown. The bypass line 96 with the check valve 102 is also provided here, but not shown. In the discharge line 30 is between pumping device 8th and second switching valve 68 a check valve 120 Connected in series, that is a flow of brake fluid from the pump device 8th in the direction of the consumer circle 14 locks. In line with the check valve 26 is an additional supply switching valve 62 connected.

Unlike the actuator 2 from the 1 to 4 is at the actuator 2 according to 5 instead of a switching valve 92 in the storage line 80 now a differential pressure valve 126 provided, continue the check valve 120 The differential pressure valve 126 opens or gives the memory line 80 free when moving the piston 44 in the extension direction 108 a pressure p2 in the pumping device 8th is greater than a pressure p1 in the consumer circuit 14 , So as soon as p2> p1 applies, brake fluid flows from the cylinder 50 in the low-pressure accumulator 86 , In this way, an additional switching operation is avoided, and it must only the two switching valves 62 . 68 be actively switched by a control current. The differential pressure valve 126 is a control element, which depends on the pressure conditions in the pumping device 8th and the consumer circle 14 the memory line blocks or releases. The actuator 2 according to the 1 to 4 has as a control element, the switching valve 92 on.

An actuator 2 in a third preferred embodiment is in 6 shown. This actuator 2 has a pumping device 8th on, next to the cylinder 50 and pistons 44 another piston 140 and cylinders 146 having, wherein the piston 140 also with the eccentric 32 connected is. A 180 ° arrangement as shown is not mandatory, but favorable in terms of a more uniform engine torque.

From the cylinder 146 leads a hydraulic discharge line 152 through a check valve 158 to the discharge line 30 or flows into this at the mouth point 164 between the second switching valve 68 and check valve 120 , In addition, a supply line leads 172 through a check valve 178 to the supply line 20 or flows into this at a confluence point 184 , That is, both supply lines 172 . 20 run through the first switching valve 62 . and both discharge lines 30 . 152 run through the second switching valve 68 , So it is also in this arrangement with two cylinders 50 . 146 no more switching operations to reverse the volume flow of the brake fluid necessary. A multi-piston design has several advantages over a single piston design. The more pistons, the less pulsating the pump will be at the same delivery rate (equivalent to the situation with an internal combustion engine). In addition, the engine torque with increasing number of cylinders is becoming more uniform. In a symmetrical arrangement, the bending load is on the eccentric of the pump device 8th minimized because the forces almost balance each other.

For on-demand discharge of brake fluid from the respective cylinder 50 . 146 in the low-pressure accumulator 86 is next to the memory line 80 another storage line 190 intended. In the respective storage line 80 . 190 is in each case acting as a control element differential pressure valve 196 . 202 whose operation is similar to that of the 1 to 4 discussed differential pressure valve 126 equivalent. In an alternative embodiment of the actuator instead of the differential pressure valves 196 . 202 as control members and switching valves are used as in the actuator 2 according to 1 ,

The differential pressure valve 196 allows a controlled flow of brake fluid from the piston 50 in the low-pressure accumulator 86 , and the differential pressure valve 202 analogously allows a controlled flow of brake fluid from the piston 146 in the low-pressure accumulator 86 ,

The storage lines 80 . 190 are, as with the actuator 2 out 1 advantageously provided with bypass lines, in each of which a check valve is connected and bridge the respective control member.

An actuator 2 in a fourth preferred embodiment is finally in 7 shown. He has three cylinders 50 . 210 . 222 and three pistons each movable therein 44 . 216 . 228 on. From the cylinder 50 leads the storage line 80 as in the previous embodiments to the low pressure accumulator 86 , The design of the cylinder 50 with the connected supply line 20 and discharge line 30 is carried out as in the above examples. From the cylinder 210 leads a line 234 through a check valve 240 and flows into the discharge line 30 , Another hydraulic line 246 leads from the cylinder 210 through a check valve 294 in the consumer circle 14 ,

From the line 246 branches a memory line 258 off, via a differential pressure valve 264 to the low pressure accumulator 86 leads.

From the cylinder 222 similarly performs a memory line 270 into which a differential pressure valve 276 is switched to low pressure storage 86 , For all three storage lines 80 . 258 . 270 As in the previous examples, in each case a bypass line with a check valve is provided, so that, if necessary, via this line from the low-pressure accumulator 86 Brake fluid in the corresponding cylinder 50 . 210 . 222 can be sucked. From the cylinder 222 leads another line 282 through a check valve 288 to the consumer circle 14 and a hydraulic line 302 into which a check valve 308 is switched, flows into the discharge line 30 ,

The wires 20 . 246 . 282 act as supply lines while the lines 30 . 234 and 302 act as discharge lines.

The differential pressure valves 126 . 264 . 276 act here again as control members. These can be switched in an alternative embodiment via a mechanical or electrical control chain, which switches in direct or indirect connection with the motor or Exzenterposition. That is, the control members are opened and closed depending on the engine or Exzenterposition via the mechanical or electrical timing chain.

LIST OF REFERENCE NUMBERS

2

 actuator

8th

 pumping device

14

 consumer circuit

20

 supply line

26

 check valve

30

 discharge line

32

 eccentric

38

 direction of rotation

44

 piston

50

 cylinder

56

 switching

62

 Supply switching valve

68

 Discharge switching valve

74

 management

80

 storage line

86

 Low-pressure accumulator

92

 switching valve

96

 bypass line

102

 check valve

108

 out direction

114

 suction direction

120

 check valve

126

 Differential pressure valve

140

 piston

146

 cylinder

152

 discharge line

158

 check valve

164

 mouth point

172

 supply line

178

 check valve

184

 mouth point

190

 storage line

196

 Differential pressure valve

202

 Differential pressure valve

210

 cylinder

216

 piston

222

 cylinder

228

 piston

234

 management

240

 check valve

246

 management

252

 check valve

258

 storage line

264

 Differential pressure valve

270

 storage line

276

 Differential pressure valve

282

 management

288

 check valve

294

 check valve

302

management

308

 check valve

p1

 print

p2

 print

Claims (13)

Actuator ( 2 ) for an electrohydraulic brake-by-wire brake system, in particular for motor vehicles, having a pump device ( 8th ) with a pump motor through which a volume flow of brake fluid into at least one consumer circuit ( 14 ) is pumped, wherein a switching device ( 56 ) is provided, and wherein the pumping device ( 8th ) and the switching device ( 56 ) are configured such that, if necessary, the direction of the volume flow can be reversed without reversing the pump motor. Actuator ( 2 ) according to claim 1, wherein the switching device ( 56 ) a number of switching valves ( 68 . 62 . 26 ) having. Actuator ( 2 ) according to claim 2, wherein the pump device ( 8th ) at least one supply line ( 20 ) with a supply valve ( 26 . 62 ) of the switching device ( 56 ), which in the supply of brake fluid in the consumer circuit ( 14 ) is opened, to the consumer circuit ( 14 ) and at least one discharge line ( 30 ) with a discharge switching valve ( 68 ) of the switching device ( 56 ), which in the removal of brake fluid from the consumer circuit ( 14 ) opens, from the consumer group ( 14 ) to the pumping device ( 8th ) runs. Actuator ( 2 ) according to claim 3, wherein a low-pressure accumulator ( 86 ) provided by at least one memory line ( 80 ) hydraulically with the pumping device ( 8th ), and wherein in the memory line ( 80 ) On-off valve ( 92 ) or a differential pressure valve ( 126 ), which opens when the pressure (p2) in the pumping device exceeds the pressure (p1) in the consumer circuit ( 14 ), is switched. Actuator ( 2 ) according to claim 4, wherein one of the switching valve ( 92 ) or pressure differential valve ( 126 ) bridging bypass line ( 96 ) is provided in which a check valve ( 102 ), which is the flow of brake fluid from the pump device ( 8th ) in the low-pressure accumulator ( 86 ) locks and allows in the opposite direction. Actuator ( 2 ) according to one of claims 1 to 5, wherein the pumping device ( 8th ) has an electric motor with a motor axis, which via a driving element ( 32 ) at least one piston ( 44 ) in an associated cylinder ( 50 ), wherein the driving element ( 32 ) is configured such that the respective piston ( 44 ) can be moved in two opposite directions, without the direction of rotation of the motor axis must be reversed. Actuator ( 2 ) according to claim 6, wherein each cylinder ( 50 . 146 ) each have a feed ( 20 . 172 ) and a discharge line ( 30 . 152 ) and a memory line ( 80 . 190 ) and the discharge lines ( 20 . 172 ) each have a common discharge valve ( 68 ) exhibit. Actuator ( 2 ) according to claim 7, wherein two cylinders or three cylinders ( 50 . 210 . 222 ) are provided. Actuator ( 2 ) according to one of claims 6 to 8, wherein the driving element as an eccentric ( 32 ) or designed as an eccentric mounted to the motor shaft connecting rod. Brake system with an actuator ( 2 ) according to one of claims 1 to 9. Method for building up and reducing brake pressure in a hydraulic brake-by-wire brake system, wherein the pressure build-up in at least one consumer circuit ( 14 ) a volume flow of brake fluid from a pumping device ( 8th ) with a pump motor in the consumer circuit ( 14 ), and wherein for pressure reduction by a switching device ( 56 ) is reversed without reversing the pump motor, the direction of the flow, so that the flow from the consumer circuit ( 14 ) in the low-pressure accumulator ( 86 ) flows back. The method of claim 11, wherein for pressure reduction in a first step brake fluid from the consumer circuit ( 14 ) into the pumping device ( 8th ) is discharged, and wherein in a second step brake fluid from the pumping device ( 8th ) into a low pressure accumulator ( 86 ) is pumped. Method according to one of the preceding claims, wherein during the pressure reduction brake fluid by establishing a direct hydraulic connection between the consumer circuit ( 14 ) and the low pressure accumulator ( 86 ) directly and without the involvement of the pump motor in a low-pressure accumulator ( 86 ) is discharged.

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