DE3712273A1 - Hydraulic brake system for motor vehicles - Google Patents

Abstract

The brake system described comprises a tandem brake master cylinder (1) which, controlled by a brake pedal (3), can be actuated by a vacuum brake booster (2). Wheel brakes (20 to 23), the pressure actuation of which can be controlled by way of solenoid valves (17 to 29, 24 to 26) of a brake slip control device, are connected to the working chambers (5, 6) of the tandem brake master cylinder (1) by way of brake lines (15, 16). For supplying the pressure medium, a double pump (29, 30) is provided, which at the onset of control delivers pressure medium into the brake lines (15, 16). When the double pump (29, 30) is switched on, the pressure in the working chambers (5, 6) is regulated by hydraulically controlled control valves (8, 10) in the float piston (4) and in the master cylinder piston (7) of the tandem brake master cylinder (1) proportional to the actuating force. The control is thereby independent of the position of the float piston (4) and of the master cylinder piston (7) and does not lead to a return movement of the piston (4, 7) and hence of the brake pedal (3) into the original position. In order to maintain an adequate reserve stroke, the control valves (8, 10) can also be actuated mechanically if a maximum travel or a maximum pressure is exceeded. <IMAGE>

Description

The invention relates to a hydraulic brake system for Motor vehicles with one attached to an unpressurized container closed master cylinder, from the working chamber one Brake line to pressure control valves of a brake slip control device leads, which at least one wheel brake nachge is switched, and with a when switching on the brake slip Control device connectable pressure to the working chamber medium source, the outlet pressure by a in the main brake cylinder the arranged control valve is controllable by one Connection between the working chamber and the container and is controllable.

In such brake systems, the pressure medium source is used usually by an electric motor-driven pump Penaggregat is formed to promote the pressure medium amount that during a brake slip control for that again caught applying the wheel brakes after a brake release phase is needed. The pump set is at the beginning a brake slip control switched on and remains for the Duration of the control process in operation.

In German patent application P 36 01 914.3 is already a braking system of the type described, in which the  Control valve for regulating the outlet pressure of the pressure medium source through a central valve in the Master brake cylinder is formed, which is only in the brake release position of the master cylinder piston in its open position reaches. This has the disadvantage that during a brake activated pump unit initially with Höchst pressure starts up and into the working chamber of the main brake cylinder ders until the master cylinder piston and thus that Brake pedal has been pushed back to the starting position are. Only in this position can the control valve open and a pressure in the area proportional to the actuating force beitskammer and accordingly at the outlet of the pump set to adjust. With the onset of the brake slip control thus the brake pedal in the brake system described above against the driver's foot force in its starting position moved back. This leads to an undesirable in practice Pedal feeling.

The invention has for its object a brake system to create of the type mentioned, in which one of the Operating force proportional pressure at the outlet of the pressure medium source in the actuation position reached in each case of the master cylinder piston can be regulated and a Impairment of the pedal feeling by retreating the Brake pedal is avoided up to the starting position.

This object is achieved in that the Control valve is hydraulically actuated, one of which is off practiced actuating force proportional pressure in closing direction tion and the pressure prevailing in the working chamber in opening direction is effective. By hydrau invention  The control process continues to trigger the control valve immediately on if by switching on the pressure medium source the pressure in the working chamber of the master brake cylinder increases slightly. The position of the master cylinder piston has no influence on the control process, so that a Retraction of the master cylinder piston and thus the brake dals not in its starting position.

The control valve according to the invention can be designed that it is open in its normal position by a valve spring is held. As a result, the control valve also takes over the function of the central valve of the master brake cylinder, which simplifies the braking system.

According to an advantageous embodiment of the invention provided that the control valve one in the master cylinder piston arranged, pressurized in the working chamber and in the trailing space opening closing body and that the closing body in the closing direction by a rule piston is movable into one in the master cylinder piston arranged control chamber protrudes in which one of the exercised Operating force proportional pressure can be generated. The Control chamber can be advantageous by a tax be limited to the piston with the actuating force Actuation of the master cylinder piston can be acted upon. The In this way, the control chamber forms a master cylinder piston upstream cylinder through which the actuation transferred hydraulically to the master cylinder piston becomes. This ensures that the control valve at each Actuation of the master brake cylinder first in its closing position reached.  

According to the invention it can further be provided that at Er such a pressure range from a predetermined control pressure is displaceable from the control chamber that the Control piston in direct mechanical contact with the rule piston arrives. This ensures that at high Operating forces and a correspondingly small reserve stroke of the master cylinder piston, the control valve only by one prevailing operating pressure in the working chamber considerably exceeding pressure can be opened. When switching on the source of pressure medium is therefore clear Pressure increase in the working chamber, due to the same permanent operating force of the master cylinder piston pushed and its reserve stroke on a for security reasons required dimension is increased.

The pressure-dependent pressure medium displacement from the tax Chamber can be achieved according to the invention in that Control piston a gebil by a spring-loaded piston The volume storage is provided. In addition to their structural Simplicity, this solution has the advantage that with one Decrease in the operating force and a corresponding Lowering the control pressure again displaces the pressure volume is pushed back into the control chamber so that the control piston and control piston are separated from each other and that Control valve perform its hydraulic control function again can.

The invention can also be applied to braking systems which a tandem master cylinder with one through a float piston separated from a first working chamber second Have working chamber. Here, according to the invention can be seen that the floating piston is the second working  contains chamber with the container connecting control valve that the pressure in the first working chamber in the closing direction and from the pressure in the second working chamber in the opening direction is acted upon, its hydraulic active surfaces in both working chambers are essentially the same. By this further development according to the invention is also the pressure in the second working chamber when switching on the pressure medium swell without returning the floating piston to its end gear position adjustable.

The control valve in the floating piston can according to the invention one opening in the trailing space of the floating piston Closing body and the closing body in the closing direction stressing rule that protrudes into the first working chamber piston exist. Furthermore, the control valve can be a valve have spring, through which it is open in its basic position is held. This allows the control valve to function a central valve arranged in the floating piston men.

According to a further proposal of the invention can be provided be that in the first working chamber between the rule piston in the floating piston and the master cylinder piston one Compression spring is provided, which is pre-exceeded when a distance between the floating piston and the main zy the piston is compressible. This will increase the opening pressure of the control valve in the floating piston is sufficient if the specified safety distance between the The master cylinder piston and the floating piston is undershot, so that when switching on the pressure medium source one over the controlled actuation pressure lying pressure in the ar produced working chambers and master cylinder pistons and floating pistons are pushed back until their safety position is restored.  

To the hydraulic separation of the two to the first and the second working chamber to ensure connected brake circuits afford, can also be provided according to the invention that the two working chambers separately from each other a pump circuit of a double pump are connected.

The invention is illustrated below with the aid of an embodiment game described in more detail, which is shown in the drawing is.

The drawing shows in a single figure a circuit diagram of a hydraulic dual-circuit brake system for motor vehicles with a brake pressure transmitter formed by a tandem master cylinder 1 and a vacuum brake booster 2 , which can be actuated by a brake pedal 3 . The tandem master cylinder 1 shown in longitudinal section has two working chambers 5 , 6 which are separated from one another by a floating piston 4 and which piston 7 can be reduced in size by an actuation stroke of a master cylinder. In the floating piston 4 , a control valve 8 is provided, which is open in its basic position shown and connects the working chamber 5 with a run space 9 after. Likewise, a control valve 10 which is open in its basic position is provided in the master cylinder piston 7 and connects the working chamber 6 to a trailing chamber 11 . The two trailing spaces 9 , 11 are connected via lines 12 , 13 to an unpressurized container 14 .

Separate brake lines 15 , 16 lead from the working chambers 5 , 6 of the tandem master brake cylinder 1 to solenoid valves 17 , 18 , 19 of a brake slip control device which are open in their de-energized basic position. Wheel brakes 20 21 22 23 are connected to the solenoid valves 17 to 19 . The wheel brake 20 is assigned to the right front wheel and the wheel brake 21 to the left front wheel of a vehicle. The wheel brake 22 is assigned to the right rear wheel and the wheel brake 23 to the left rear wheel of the vehicle. It is thus in the embodiment of a dual-circuit brake system in which the wheel brakes 20 , 21 of the front wheels are connected to one brake circuit and the wheel brakes 22 , 23 of the rear wheels to the other brake circuit.

In parallel to the solenoid valves 17 to 19 , the wheel brakes 20 to 23 are connected to solenoid valves 24 , 25 , 26 , which can also be controlled by the brake slip control device and are closed in their de-energized basic position. Through the solenoid valves 24 to 26 , the wheel brakes 20 to 23 can be closed on a return line 34 leading to the container 14 .

A pressure line 27 , 28 branches off from each brake line 15 , 16 and leads to an independent pump circuit of a double pump driven by an electric motor 31 . On the suction side, the pump circuits 29 , 30 are connected to the loading container 14 via a common line 32 , in which a filter 33 is arranged.

The control valve 8 in the floating piston 4 consists of a spherical closing body 35 , which is provided at one end of a regulating piston 36 . The middle, larger diameter region of the control piston 36 serves to guide it in the bore of the floating piston 4 and forms a spring plate for a valve spring 37 which acts on the control piston 36 in the opening direction. The end 38 of the control piston 36 opposite the closing body 35 is reduced in diameter to such an extent that its cross section corresponds to the sealing cross section of the closing body 35 . The end 38 passes through a seal in the end wall of the floating piston 4 and carries a spring plate 39 on its outer end projecting into the working chamber 6 , on which a compression spring 40 bears. The compression spring 40 is arranged within a sleeve 41 and is at its other end to the bottom of a cup-shaped cap 42 , which is also located in the sleeve 41 . The interior of the cap 42 creates a free space for the axial movement of a stop head 43 at the end of a pin 44 connected to the master cylinder piston, which together with the sleeve 41 binds to the return spring 45 arranged between the floating piston 4 and the master cylinder piston 7 forms. If the axial movement of the stop head 43 exceeds the free space inside the cap 42 , the compression spring 40 is compressed and an additional closing force is transmitted to the closing body 35 .

The control valve 10 corresponds in its structure to Regelven valve 8 and it consists of a closing body 46 , a control piston 47 and a valve spring 48th The diameter tapered ver end 49 of the control piston 47 protrudes into a control chamber 50 formed in the interior of the master cylinder piston 7 , which is designed in the manner of a master cylinder and has an actuatable by the push rod 51 of the vacuum brake booster 2 control piston 52 . The control chamber 50 is connected to the trailing chamber 11 via a compensating bore 53 , which can be closed when actuated by the sealing collar of the control piston 52 . In the interior of the control piston 52 , a storage space 54 is formed with a storage piston 56 acted upon by a prestressed compression spring 55 .

The operation of the brake system is explained below tert:

To initiate a braking operation, the brake pedal 3 is actuated and the vacuum brake booster 2 is activated. The vacuum brake booster 2 first moves the control piston 52 into the control chamber 50 via the push rod 51 until the compensating bore 53 is closed. Now a pressure builds up in the control chamber 50 , which acts on the end 49 of the control piston 47 and thereby closes the control valve 10 . As soon as the control valve 10 is closed, the pressure medium enclosed in the control chamber 50 transmits the actuating force to the master cylinder piston 7 , the pressure in the control chamber 50 increasing in proportion to the actuating force. As a result, the master cylinder piston 7 is shifted together pressing the return spring 45 , whereby a pressure is built up in the working chamber 6 , which line 16 and the open solenoid valve 19 reaches the wheel brakes 22 , 23 via the brake. The pressure in the working chamber 6 continues to act on the end 38 of the control piston 36 , whereby the control valve 8 is also closed. With further Druckan increased in the working chamber 6 , the floating piston 4 is moved against the force of the return spring 57 , so that a pressure is also built up in the working chamber 5 , which via the brake line 15 and the open solenoid valves 17 , 18 to the wheel brakes 20 , 21 arrives. The double pump is not in operation during this actuation phase and its pump circuits 29 , 30 are secured in the usual way by check valves so that no pressure medium can escape from the brake lines 15 , 16 into the pump circuits.

If the braking slip control device registers a tendency to lock on one or more vehicle wheels during a braking operation, the electric motor 31 is immediately switched on and the double pump is driven. As a result, a pressure is generated in the pump circuits 29 , 30 , which continues to propagate via the pressure lines 27 , 28 into the brake lines 15 , 16 and the working chambers 5 , 6 . Due to the increasing pressure in the working chambers 5 , 6 , the control valves 8 , 10 open and thus maintain the pressure in the pump circuits 29 , 30 at the pressure level set in the working chambers 5 , 6 by the actuating force exerted on the brake pedal 3 . Since the control valves 8 , 10 are controlled hydraulically, the control process in the actuating position of the floating piston 4 and the main cylinder 7 uses a piston, so that the brake pedal 3 remains in this position and a favorable pedal feel is achieved.

Simultaneously with the switching on of the double pump, the solenoid valves 17 to 19 and 24 to 26 are controlled by the brake slip control device according to the predetermined control characteristic, in order to prevent the wheels of the vehicle from blocking by periodically building up and reducing the pressure in the wheel brakes 20 to 23 . The necessary for these control processes pressure medium volume is taken from the pump flow of the pump circuits 29 , 30 , while the floating piston 4 and the master cylinder piston 5 remain in their operating position.

Is the master cylinder piston 7 when starting the double pump due to the volume of the wheel brakes 22 , 23 at such a distance from the floating piston 4 that the stop head 43 abuts the cap 42 and the compression spring 40 is compressed by a certain amount, so that the Compression spring 40 additionally on the control valve 8 via transmitted closing force that the control function only starts at a higher pressure level. The pressure in the working chambers 5 , 6 thus rises above the pressure level predetermined by the actuating force exerted on the brake pedal 3 and thereby acts to push back the floating piston 4 and the master cylinder piston 7 in the brake release direction. The distance between the floating piston 4 and the master cylinder piston 7 is increased until the stop head 43 lifts off the cap 42 , so that the control valve 8 can again adjust the brake pressure in proportion to the actuating force. This process ensures that when the brake slip control of the floating piston 4 and the master cylinder piston 7 come into a safety position, which ensures that the braking process is maintained if the double pump fails.

In addition to the path-dependent influence on the control behavior of the control valve 8 , a pressure-dependent influence on the control behavior of the control valve 10 is provided. Overwriting tet the pressure in the control chamber 50 a predetermined by the compression spring 55 value, the accumulator piston 56 differs in the memory space 54 back and made possible by the so verbun dene volume receiving an approximation of the control piston 52 to the end 49 of the control piston 47th At a limit pressure that corresponds to a high actuation pressure in the working chambers 5 , 6 , the control piston 52 rests on the control piston 47 and thereby causes an increase in the closing force on the control valve 10 . Now uses the brake slip control, the air flowing into the working chamber 6 the pump pressure, the control valve 10 does not open, and it comes into the Arbeitskam chambers 5, 6 to a pressure increase over the existing pressure level addition, by the turn of the floating piston 4 and the master cylinder piston 7 be pushed back into a safety position in the direction of brake release. This pressure-dependent influence on the control behavior of the control valve 10 ensures that at high actuation pressures at which the reserve strokes of the floating piston 4 and the master cylinder piston 7 are small, an increase in the reserve strokes is achieved when the brake slip control is used.

• Reference list: 1 tandem master brake cylinder
  2 vacuum brake boosters
  3 brake pedal
  4 floating pistons
  5 working chamber
  6 working chamber
  7 master cylinder pistons
  8 control valve
  9 trailing space
  10 control valve
  11 trailing space
  12 line
  13 line
  14 containers
  15 brake line
  16 brake line
  17 solenoid valve
  18 solenoid valve
  19 solenoid valve
  20 wheel brake
  21 wheel brake
  22 wheel brake
  23 wheel brake
  24 solenoid valve
  25 solenoid valve
  26 solenoid valve
  27 pressure line
  28 pressure line
  29 pump circuit
  30 pump circuit
  31 electric motor
  32 line
  33 filters
  34 return line
  35 closing body
  36 control pistons
  37 valve spring
  38 end
  39 spring washer
  40 compression spring
  41 sleeve
  42 cap
  43 stop head
  44 pen
  45 return spring
  46 closing body
  47 control pistons
  48 valve spring
  49 end
  50 control room
  51 push rod
  52 control pistons
  53 Compensating hole
  54 storage space
  55 compression spring
  56 accumulator pistons
  57 return spring

Claims (11)

1.Hydraulic brake system for motor vehicles with a master brake cylinder connected to an unpressurized container, from the working chamber of which a brake line leads to pressure control valves of a brake slip control device, to which little least a wheel brake is connected, and with a pressure medium source which can be connected to the working chamber when the brake slip control device is switched on, the latter Outlet pressure can be regulated by a control valve arranged in the master brake cylinder, through which a connection between the working chamber and the container can be opened and closed, characterized in that the control valve ( 8 , 10 ) can be actuated hydraulically, with one of the actuating forces exerted in proportion tional pressure in the closing direction and the prevailing pressure in the working chamber ( 5 , 6 ) in the opening direction is effective. 2. Brake system according to claim 1, characterized in that the control valve ( 10 ) in the master cylinder piston ( 7 ) is arranged, acted upon by the pressure in the working chamber ( 6 ) and in the trailing chamber ( 11 ) opening closing body ( 46 ), and that the closing body ( 46 ) can be moved in the closing direction by a control piston 47, which projects into a control chamber ( 50 ) arranged in the master cylinder piston ( 7 ), in which a pressure proportional to the actuating force exerted can be generated. 3. Brake system according to claim 2, characterized in that the control chamber ( 50 ) is delimited by a control piston ( 52 ) which can be acted upon with the actuating force for actuating the main cylinder piston ( 7 ). 4. Brake system according to claim 3, characterized in that the control chamber ( 50 ) through a channel ( 53 ) which can be closed by an actuating stroke of the control piston ( 52 ) with the trailing chamber ( 11 ) of the master brake cylinder. 5. Brake system according to one of claims 2 to 4, characterized in that upon reaching a predetermined control pressure such a quantity of pressure medium from the control chamber ( 50 ) is displaceable that the control piston ( 52 ) in direct contact with the control piston ( 47 ) reached. 6. Brake system according to claim 5, characterized in that in the control piston ( 52 ) by a spring-loaded piston ( 56 ) formed volume memory ( 54 ) is provided. 7. Brake system according to a preceding claim with a tandem master cylinder with a floating piston ( 4 ) from a first working chamber ( 6 ) separate second working chamber ( 5 ), characterized in that the floating piston ( 4 ) with a second working chamber ( 5 ) contains the control valve ( 8 ) connecting the container ( 14 ), which is impacted by the pressure in the first working chamber ( 6 ) in the closing direction and by the pressure in the second working chamber ( 5 ) in the opening direction, its hydraulic active surfaces in both working chambers ( 5 , 6 ) are essentially the same. 8. Braking system according to claim 7, characterized in that the control valve ( 8 ) from a in the trailing space ( 9 ) of the floating piston ( 4 ) opening closing body ( 35 ) and one acting on the closing body ( 35 ) in the closing direction, in the first working chamber ( 6 ) protruding control piston ( 36 ) be. 9. Brake system according to one of claims 7 or 8, characterized in that both control valves ( 8 , 10 ) by valve springs ( 37 , 48 ) are kept open in their basic position. 10. Brake system according to one of claims 7 to 9, characterized in that a compression spring ( 40 ) is provided in the first working chamber ( 6 ) between the control piston ( 36 ) in the floating piston ( 4 ) and the main cylinder ( 7 ) when a predetermined distance between the floating piston ( 4 ) and the master cylinder piston ( 7 ) is pressed together. 11. Brake system according to one of claims 7 to 10, characterized in that the two working chambers ( 5 , 6 ) separately from each other to a circuit ( 29 , 30 ) of a double pump can be connected.