DE10044820A1 - Actuating unit for an electro-hydraulic brake system - Google Patents

Abstract

The invention relates to an actuating unit for an electrohydraulic braking system of the "brake-by-wire" type, which is configured as a dual master cylinder, whose first and second pistons are respectively tensioned against the direction of actuation by a return spring. The first pressure chamber of the dual master cylinder is connected to a hydraulic chamber which is delimited by a simulator element. On its other side, said simulator element delimits a simulator chamber which accommodates a simulator spring and is connected to a storage container for hydraulic fluid. A valve device that closes or releases the hydraulic connection between the simulator chamber and the hydraulic fluid storage container is also provided. To increase the operational safety of a braking system equipped with the inventive actuating unit, the invention is characterized in that means (50, 116) for testing the function of the valve device (123, 124; 217, 224; 140) are provided.

Description

The present invention relates to an actuation unit for an electrohydraulic brake system of the "brake-by wire" type with:
a first piston (DK piston) pretensioned by a first return spring and a second piston (SK piston) pretensioned by a second return spring, which are arranged one behind the other in a housing and limit pressure spaces connected to an unpressurized pressure medium reservoir , to which hydraulic lines which can be shut off are connected by means of a first and a second valve device, with a path simulator which is formed by a simulator element which delimits a simulator chamber and cooperates with a simulator spring and which can be acted upon by means of a hydraulic connection with the pressure entered in the first pressure chamber, wherein a second hydraulic connection is provided between the simulator chamber and the pressure medium reservoir, and with a third valve device which provides the hydraulic connection between the simulator chamber and the pressure medium reservoir shuts off or releases container and which can be actuated by a relative movement of the second piston relative to the housing.

Such an actuator is such. B. from the DE 198 22 411 A1 known. The special thing about the known Actuator is that the simulator element is formed by a metallic bellows, which the Simulator spring absorbs preload-free. The earlier mentioned third valve device in the connection between the interior of the bellows and the trailing space of the second pressure chamber is composed of a Seat valve, which is arranged on an axis of rotation mounted two-armed rocker arm by the movement of the second piston is mechanically actuated. As a disadvantage is in particular in the known actuator considered the fact that the poppet valve is not monitoring can be, since it is only in the event of a fault in the brake system is in function and not with the intact brake system can be activated. This condition is therefore known as to evaluate "sleeping bug", which in a Failure mode analysis is weighted accordingly.

It is therefore an object of the present invention Actuating unit of the type mentioned to propose, where the previously mentioned disadvantage is largely eliminated.

This object is achieved in that Means for checking the third valve device are provided. The solution according to the invention is  naturally also with an actuation unit used, in which the third valve device hydraulic connection from the first pressure chamber to Shuts off or releases the simulator element and none second hydraulic connection between the simulator chamber and the pressure medium reservoir is provided. By this measure will significantly increase the Operational safety of the brake system achieved.

An advantageous development of the invention exists in that the simulator element by a hydraulic Simulator piston is formed and that the third Valve device by a arranged on the second piston Seal and the mouth area of an in Movement range of the channel formed channel that forms the second hydraulic connection.

In a further advantageous embodiment of the Subject of the invention, in which the third Valve device is designed as a seat valve and has a valve body in its closing direction is biased by means of a valve spring, that the simulator element by a hydraulic Simulator piston is formed and that the valve body of the Seat valve by means of an axially on the second piston adjacent cross member is actuated.

Further advantageous designs are in the Sub-claims 5 to 9 listed.

Further details, features and advantages of the invention go from the description below of four Embodiments with reference to the accompanying Drawing. The drawing shows:

Fig. 1 is a diagram of an electro-hydraulic brake system of the 'brake-by-wire ",

Fig. 2 shows a first embodiment of the actuator according to the invention in axial section;

. Fig. 3 shows a second embodiment of the actuator according to the invention corresponding to FIGS 1 illustration;

. Fig. 4 shows a third embodiment of the actuating unit according to the invention corresponding to FIGS 1 illustration;

. Fig. 5 shows a fourth embodiment of the actuator according to the invention corresponding to FIGS 1 illustration; and

Fig. 6 is a diagrammatic representation of characteristics to explain the function of the invention.

The electrohydraulic brake system of the "brake-by-wire" type shown in FIG. 1 has an actuation unit 1 which can be actuated by means of an actuation pedal (not designated in more detail), which essentially consists of a dual-circuit pressure generator or tandem master cylinder 2 , a travel simulator 3 and a pressureless pressure medium reservoir 6 exists. The master brake cylinder 2 in turn has two separate pressure spaces 4 , 5 , which are connected to the pressure medium reservoir 6 . Wheel brakes 7 , 8 , for example associated with the rear axle, are connected to the first pressure chamber (primary pressure chamber) 4 by means of a lockable first hydraulic line 11 . The line 11 is shut off by means of a first isolating valve 9 , while in the line section 17 leading to the wheel brake 8 an electromagnetically actuated, preferably normally open (S0) pressure compensation valve 16 is inserted, which enables a wheel-specific brake pressure control if required.

The second pressure chamber 5 of the master brake cylinder 2 , to which a pressure sensor 13 is connected, can be connected to the other pair of wheel brakes 14 , 15 , which is assigned to the front axle, via a second hydraulic line 12 which can be shut off by means of a second separating valve 10 . In the line section 18 leading to the wheel brake 15 , an electromagnetically actuated, preferably normally open (S0) pressure compensation valve 19 is inserted again. Since the structure of the hydraulic circuit connected to the second pressure chamber 5 of the master brake cylinder 2 is identical to that of the brake circuit 11 explained in the above description, it need no longer be discussed in the text below.

As can also be seen in the drawing, a motor-pump unit 40 serving as an external pressure source is provided with a high-pressure accumulator 21 , which in turn consists of a pump 23 driven by an electric motor 22 and a pressure relief valve 24 connected in parallel with the pump 23 . The suction side of the pump 23 is connected to the previously mentioned pressure medium reservoir 6 via a non-specified check valve, while the hydraulic pressure applied by the pump 23 is monitored by a pressure sensor 25 . The filling state of the high-pressure accumulator 21 is monitored by means of a displacement sensor 36 , which is only indicated schematically.

A third hydraulic line 26 connects the pressure side of the pump 23 or the high-pressure accumulator 21 to the input connections of two electromagnetically actuated, preferably normally closed (SG) 2/2-way valves 27 , 28 , which are connected upstream of the wheel brakes 7 and 8 . In addition, a hydraulic line 29 , 30 is connected to the output connections of the 2/2-way valves 27 , 28 , which on the other hand is connected to the unpressurized pressure medium reservoir 6 and in which a second electromagnetically actuated, preferably normally closed (SG-) 2 / 2-way valve 31 , 32 is inserted. In addition, the wheel brakes 7 , 8 are assigned pressure sensors 33 , 34 , with the aid of which the hydraulic pressure prevailing in the wheel brakes 7 , 8 is determined. An electronic control unit 35 is used to control the motor-pump unit 40 and the valves 9 , 10 , 16 , 19 , 27 , 28 , 29 , 30 , 31 , 32 mentioned above, which in particular the output signals of the pressure sensors 13 , 25 , 33 , 34 , the displacement sensor 36 and a preferably redundant brake request detection device 37 , which is assigned to the master brake cylinder 2 .

As can be seen in particular from FIG. 2, the previously mentioned pressure chambers 4 , 5 are delimited in a bore of a master brake cylinder housing 120 by two hydraulic master cylinder pistons 20 , 30 . While the first (primary) pressure chamber 4, with the interposition of a first central valve 112 arranged in the first piston 20 , is connected to the pressure medium reservoir 6 by means of a pressure medium channel 116 , the second piston 30 delimits a follow-up chamber 111 in the master brake cylinder housing 120 , which, on the one hand, has an im second piston 30 arranged second central valve 113 with the associated pressure chamber 5 and on the other hand via a pressure medium channel, not shown, formed in the master cylinder housing 120 with the pressure medium reservoir 6 . In the pressure medium channel 116 , an electromagnetically actuated, preferably normally open (SO) shut-off valve 50 is inserted, the task of which is explained in more detail in the text below.

As can further be seen from FIG. 2, a first and a second return spring 114 , 115 are arranged in the pressure chambers 4 , 5 mentioned, which bias the pistons 20 , 30 against their direction of actuation or hold them in the starting position. A hydraulic chamber 119 , which is delimited by a hydraulic piston or simulator piston 118 , is connected to the first or the primary pressure chamber 4 by means of a hydraulic connection 117 . The simulator piston 118 , which on the other hand delimits a simulator chamber 121 , forms, together with a simulator spring 122 arranged in the simulator chamber 121 , the previously mentioned travel simulator 3 , which gives the driver of the vehicle the usual pedal feeling when the pressure chambers 4 , 5 are shut off. The simulator spring 122 determines the course of the pedal characteristic, ie the dependence of the pedal force on the actuation path.

In order to enable a relative movement of the first piston 2 with respect to the master cylinder housing 120 when the pressure chambers 4 , 5 are shut off, which results in the hydraulic chamber 119 being pressurized with the pressure medium volume displaced from the first pressure chamber 4 , between the simulator chamber 121 and the one mentioned above Follow-up space 111 or the pressure medium reservoir 6, a hydraulic connection 123 is provided, which must be interrupted or blocked in the event of an emergency braking. In the example shown in FIG. 2, the hydraulic connection 123 is designed as a bore or a channel, in the mouth region of which in the trailing space 111 a seal or sealing sleeve 124 is arranged on the second piston 30 . The mouth region of the channel 123 forms a third valve device together with the sealing sleeve 124 . The described arrangement is achieved that the pressure medium enclosed in the second pressure chamber 5 from the first pressure chamber 4 on the (stationary) sealing sleeve 124 can be moved to the passing pressure fluid reservoir. 6 On the other hand, in the event of emergency braking, in which the above-mentioned isolating valves 9 , 10 remain open, the two pistons 20 , 30 are displaced so that the sealing sleeve 124 arranged on the second piston 30 passes over the mouth of the channel 123 and the connection between the simulator chamber 121 and the pressure medium reservoir 6 interrupts, so that the path simulator 3 can no longer accommodate a pressure medium volume and a hydraulic pressure can be built up in the two pressure chambers 4 , 5 .

The aforementioned third valve device is preferably designed in such a way that the hydraulic connection 123 opens into an annular groove which is dimensioned such that the sealing sleeve 124 is installed in the shown state in a radially stress-free manner. In the "brake-by-wire" mode, this eliminates both the friction forces as a disturbance variable in the force-displacement characteristic and the wear of the sealing sleeve.

Finally, as is also evident from Fig. 2, the simulator piston 118 has a blind bore 126 which 127 receives an elastic member such as a rubber-elastic disc, and an axial fitting on the elastic part 127. Pressure piece 128th Opposed to the pressure piece 128 in the simulator chamber 121 is a cylindrical extension 129 of a closure part 131 closing the simulator chamber 121 , against which the pressure piece 128 comes to rest in the event of an excessive stroke of the simulator piston 118 . The measures described result in an elastic stop. In order to perform a damping function when actuating the actuating unit according to the invention, hydraulic resistances or throttling means (not shown) can be provided in the hydraulic connection 117 or the second hydraulic connection 123 .

The construction of the second embodiment of the actuation unit according to the invention shown in FIG. 3 essentially corresponds to that which was explained in connection with FIG. 2. The third valve device mentioned in the preceding text, which in its open position enables the pressure medium to be shifted from the first pressure chamber 4 into the hydraulic chamber 219 delimited by the simulator piston 218 , blocks the first hydraulic connection 217 between the first pressure chamber 4 and in the embodiment shown from room 219 or releases this connection. Although a second hydraulic connection 223 between the simulator chamber 221 and the after-run space 111 mentioned in connection with FIG. 1 is also shown in FIG. 3, a further embodiment is conceivable in which no connection is provided between the simulator chamber 221 and the after-run room 111 , so that the simulator chamber 221 remains "dry". In order to implement the aforementioned elastic stop of the simulator piston, the simulator piston 218 in the embodiment shown has an axial extension 232 which can be brought to bear on a pressure piece 233 which rests on an elastic part 234 . Both the pressure piece 233 and the elastic part 234 are arranged in a closure part 235 closing the simulator chamber 221 . The first hydraulic connection 217 is shut off, similarly to the embodiment according to FIG. 2, in that a sealing collar 224 arranged on the second piston 30 passes over the mouth area of the connection 217 .

The third embodiment of the invention shown in FIG. 4 corresponds functionally to the first embodiment according to FIG. 2, in which the third valve device shuts off or releases the hydraulic connection 123 between the simulator chamber 121 and the trailing space 111 . The third valve device is designed here as a seat valve 140 , which can be mechanically actuated by a relative movement of the second piston 30 relative to the main cylinder housing 120 ′. For this purpose, a force transmission element 142 is guided in a bore 141 of the master cylinder housing 120 , which runs parallel to the bore that receives the two pistons 20 , 30 , in which a cross member 143 is fastened, which is provided on a contact surface formed on the second piston 30 144 rests axially. A valve body 145 , which cooperates with a valve seat 147 , blocks or releases the hydraulic connection 123 between the simulator chamber 121 and the pressure medium reservoir 6 , which leads via the trailing space 111 , on the force transmission element 142 under pretension of a valve spring 146 . As can be seen in FIG. 4, the hydraulic connection 123 consists of a bore 148 starting from the simulator chamber 121 , part of the bore 141 mentioned above and a channel 149 which is connected to a container connection 150 assigned to the second pressure chamber 5 . The seat valve 140 is preferably designed such that the closing path of its valve body 145 is greater than the closing path of the central valve 113 arranged in the second piston 30 . The guide of the valve body 145 is a guide ring 151, an axial extension extending through the valve body to 152 of the 145th In order to ensure proper flow of the hydraulic pressure medium between the simulator chamber 121 and the pressure medium reservoir 6 , the axial extension 152 is provided with radial ribs 153 .

Finally, the fourth embodiment shown in FIG. 5 of the actuation unit according to the invention corresponds functionally to the second embodiment according to FIG. 3, the third valve device or the seat valve 140 explained in connection with FIG. 4 being the hydraulic connection 217 between the first pressure chamber 4 and the through shuts off or releases the simulator piston 218 limited hydraulic space 219 . The force transmission element 142, which is guided in a sealed manner in the bore 141 , forms with its sealing sleeve 154 a hydraulic active surface which, in the open position of the seat valve 140, is acted upon by the pressure medium flowing out of the first pressure chamber 4 . This creates a force that supports the force of the valve spring 146 and thus the closing of the seat valve 140 . Otherwise, the mode of operation of this embodiment corresponds to the mode of operation of the second embodiment, so that a further explanation is unnecessary.

As is evident from the preceding description, if the electronics controlling the electrohydraulic brake system fail, it must be ensured that the aforementioned connections are prevented. On the other hand, no brake pressure for the schematically indicated brake circuit could be built up in the first pressure chamber 4 . In a known manner will now be the operating unit according to the invention in particular in Fig. 4 and 5 is actuated by depression of the brake pedal, not shown, as are the two pistons 20, 30 moves in the drawing to the left, the cross member 143 under the bias of the valve spring 146 follows the second piston 30 until the valve body 145 comes into contact with the sealing seat 147 .

An important technical aspect of all "Brake-by-Wire" brake systems is the reliable detection of the driver's deceleration request. In the course of developments, it has been found to be advantageous that signals from the actuation path of the actuation unit-detecting systems or sensor arrangements can be used for this purpose. Therefore, it is proposed to provide a schematically indicated displacement measuring system 37 in the entry area of the housing 120 , 120 ', whose elements, not shown, which are responsible for signal generation are attached to the cylindrical surface of the first piston 20 , while the signal pick-up elements are integrated in the master cylinder housing 120 , 120 are.

The above-mentioned check of the third valve device 123 , 124 or 224 , 217 or 140 is carried out as follows: First, the fourth valve device 50 is closed so that the first pressure chamber 4 is separated from the pressure medium reservoir 6 and the pressure medium flows out via the open central valve 112 is prevented in the pressure medium reservoir 6 . While the SG valve 27 ( FIG. 1) assigned to the first pressure chamber 4 is opened at the same time, the isolation valves 9 , 10 mentioned in connection with FIGS . 1 and 2 remain open. A pressure build-up then takes place either by means of the pump 23 or by means of the high-pressure accumulator 21 , in which pressure medium reaches the first pressure chamber 4 via the open SG valve 27 . Due to the pressure prevailing in the first pressure chamber 4 , both the second piston 30 and the simulator piston 118 , 218 are displaced in accordance with a known relationship between the pressure and the pressure medium volume fed in. The pressure medium volume required for this results from standard mathematical models for the volume pushed out by the pump per revolution or directly from the information from the pressure sensor 25 or the displacement sensor 36 ( FIG. 1), which are connected to the high-pressure accumulator 21 . The pressure arising in the second pressure chamber 5 is determined by means of the pressure sensor 13 .

With the intact third valve device, the second piston 30 will activate it after a certain path (curve I, FIG. 6) or volume consumption, so that no further pressure medium volume can be introduced into the path simulator 3 . The diagrammatic representation of the relationship between the pressure value p measured by the pressure sensor 13 and the path V of the second piston 30 can be seen in FIG. 6, as indicated previously. As curve II shows, which represents the same relationship with the defective third valve device, the same pressure value p1 is reached after the second piston 30 has covered the path V2, which is considerably longer than the path V1 covered with the intact third valve device. An error of the third valve device can thus be concluded in accordance with the available information with regard to the introduced pressure medium volume and the pressure sensor signal. It is particularly advantageous that the first piston 20 is not moved during the check and thus there is no undesired pedal reaction due to a pedal being pulled away.

Claims (9)

1. Actuating unit for an electrohydraulic brake system of the "brake-by-wire" type with: a first piston (DK piston) which can be actuated by means of an actuating pedal and is biased by a first return spring, and a second piston (SK piston) which is biased by a second return spring , which are arranged one behind the other in a housing and delimit pressure spaces in connection with a pressure-free pressure medium reservoir, to which hydraulic lines that can be shut off by means of a first and a second valve device are connected, with a path simulator, which by means of a simulator element delimiting a simulator chamber and interacting with a simulator spring is formed, which can be acted upon by a hydraulic connection with the pressure entered in the first pressure chamber, a second hydraulic connection being provided between the simulator chamber and the pressure medium reservoir, and with a third valve device Attention, which blocks or releases the second hydraulic connection and which can be actuated by a relative movement of the second piston relative to the housing, characterized in that means ( 50 , 116 ) for checking the function of the third valve device ( 123 , 124 ; 217 , 224 ; 140 ) are provided. 2. Actuating unit according to claim 1, characterized in that the simulator element is formed by a hydraulic simulator piston ( 118 ) and that the third valve device by a on the second piston ( 30 ) arranged seal ( 124 ) and the mouth area of a in the range of movement of the seal ( 124 ) trained channel is formed, which forms the second hydraulic connection ( 123 ). 3. Actuating unit according to claim 1, wherein the third valve device is designed as a seat valve and has a valve body which is biased in its closing direction by means of a valve spring, characterized in that the simulator element is formed by a hydraulic simulator piston ( 118 ) and that the valve body ( 145 ) of the seat valve ( 140 ) can be actuated by means of a cross member ( 143 ) axially abutting the second piston ( 30 ). 4. Actuating unit for an electrohydraulic brake system of the "brake-by-wire" type with: a first piston (DK piston) which can be actuated by means of an actuating pedal and is biased by a first return spring, and a second piston (SK piston) which is biased by a second return spring , which are arranged one behind the other in a housing and delimit pressure spaces in connection with a pressure-free pressure medium reservoir, to which hydraulic lines that can be shut off by means of a first and a second valve device are connected, with a path simulator, which by means of a simulator element delimiting a simulator chamber and interacting with a simulator spring is formed, which can be acted upon by a hydraulic connection with the pressure entered in the first pressure chamber, a third valve device being provided which can be actuated by a relative movement of the second piston with respect to the housing, thereby characterized The third valve device ( 217 , 224 ; 140 ) shuts off or releases the hydraulic connection ( 217 ) and that means ( 50 , 116 ) for checking the third valve device ( 217 , 224 ; 140 ) are provided. 5. Actuating unit according to claim 4, characterized in that the third valve device is formed by a seal ( 224 ) arranged on the second piston ( 30 ) and the mouth region of a channel formed in the movement range of the seal ( 224 ) which connects the hydraulic connection ( 217 ). forms and which is connected on the one hand to the first pressure chamber ( 4 ) and on the other hand to a hydraulic chamber ( 219 ) separated from the simulator chamber ( 221 ) by the simulator piston ( 218 ). 6. Actuating unit according to claim 4, characterized in that the third valve device is designed as a seat valve ( 140 ) and has a valve body ( 145 ) which is biased in its closing direction by means of a valve spring ( 146 ) and by means of a on the second piston ( 30th ) axially adjacent cross member ( 143 ) can be actuated. 7. Actuating unit according to claim 4, 5 or 6, characterized in that a second hydraulic connection ( 223 ) is provided between the simulator chamber ( 221 ) and the pressure medium reservoir ( 6 ). 6. Actuating unit according to one of the preceding claims, characterized in that the means for checking the function of the third valve device ( 123 , 124 ; 217 , 224 ; 140 ) are formed by a fourth, electromechanically actuated valve device ( 50 ) which is in a hydraulic Connection ( 116 ) between the first pressure chamber ( 4 ) and the pressure medium reservoir ( 6 ) is provided. 9. Actuating unit according to claim 8, characterized in that the fourth valve device ( 50 ) is designed as a normally open 2/2-way valve.