DE19632130A1 - Hydraulic brake system - Google Patents

Abstract

The invention proposes a hydraulic braking system, the brake pressure generator (1) of which has a compensating chamber (77) connected to the pressure chamber (7, 79) via a central valve. The compression rod piston (82) in the compensating chamber (77) has an effective area which is loaded with pressure from the compensating chamber (77) to apply extra force on the compression rod piston (82). The preloading pumps (19) can therefore be used multifunctionally: on the one hand, they can provide the necessary amount of pressure in cases when brake pressure must be built-up in the braking circuits (1, 11) without a pedal being activated. On the other hand they can provide pressure in the compensating chamber (77) when a pedal is activated so as to increase the force of the pedal. This can be uncontrolled, namely in all cases when specific signals establish that the driver would like to brake quickly. It can also be controlled, however, when, for example, pressure at the exit to the preloading pump (19) is adjusted in line with or just below the level of pressure in the main brake cylinder.

Description

The invention relates to a hydraulic brake system according to the preamble of claim 1.

Such a brake system is known from DE 41 10 851 A1. The brake circuits connected to the master cylinder are, contain means (return pumps, valves), which means of an electronic controller can be controlled. Depending on, which control algorithm implements in the electronic controller is tiert, with such a system z. B. blocking the wheels during a brake initiated by the driver can be prevented. In the aforementioned disclosure Scripture is also proposed the hydraulic brake system to prevent the driven wheels from spinning to prevent using a corresponding traction controller other.

In order to be able to carry out such a regulation, the system must be provided with resources that are capable of at least least with the brake circuit that contains the driven wheels To fill pressure medium. A precharge pump is provided for this purpose, from the reservoir of the master cylinder in one Follows the master cylinder that promotes a Central valve with the working chamber and thus with a brake circuit of the system is connected.

To carry out traction control, first of all by means of the pre-charge pump in the connected brake circuits a brake pressure builds up, causing the wheel to spin tends to slow down.  

Similar braking systems are also used to work on all four Wheels of a vehicle to build up braking forces, each can be set individually for the wheel, so that targeted moments around the vertical axis of the vehicle can be built, which the Keep the vehicle stable in critical driving situations.

In GB 21 47 963 A1 there is also a braking system with a Pre-charge pump described with both an anti-lock rain tion as well as traction control can. The hydraulic circuit is constructed so that the Pump does not feed directly into the brake circuits, but instead Pressure medium is available on the suction side of the return pump puts these further in the brake circuits, so there a brake pressure can be built up.

In both cases described, the master cylinder is on Brake booster upstream, which on the main brake pedal force exerted on the cylinder is increased. Such amplifiers are necessary as not assumed in all cases can be that the driver alone the need can apply agile actuation forces for braking. In general, either so-called pneumati are used cal or hydraulic booster. The pneumatic amplifier use the pressure difference between the At atmosphere and the pressure in the intake area of a combustion engine tors. Since the pressure difference is very small, the effective one Area of the amplifier can be chosen very large, which results has that it occupies a relatively large space in the engine compartment men.

This problem does not occur with hydraulic amplifiers, because they are equipped with a hydraulic high-pressure accumulator are. However, these amplifiers are quite complex to build because special security requirements have to be met  sen. In addition, the control valve of the amplifier must be very fine lig work, so that it is generally very expensive to construct is.

The invention is therefore based on the task for a pedalbe actuated brake pressure transmitter in a hydraulic brake system effective pedal force amplification according to the generic term to provide. To this end, the invention proposes that the precharge pump pe to increase the pedal force at the latest at the beginning of a Pedal actuation is switched on. By the invention it is thus possible to use the master brake cylinder as a hydraulic brake let assistants take effect.

The pre-charge pump serves two purposes. Systems are known with which one tries, based on the behavior of the driver (quick release of the accelerator pedal, quick movement of the right one Foot on the brake pedal) before the actual pedal actuation to conclude an intended brake actuation. If this is possible, the preliminary be switched on so that the brake circuits are already so can be filled to such an extent that empty runs are balanced, before the driver depresses the pedal. This has the advantage that a brake pressure builds up immediately when the pedal is pressed can be made without first having to travel through empty paths have to.

In a second step, the pre-charge pump fulfills a real one Amplifier function. It creates a brake in the trailing area pressure on an effective surface of the push rod piston Master cylinder is directed. The effective area arises because the diameter of the push rod piston is larger than that Shaft of the push rod piston, through the end seal of the master cylinder is guided. This will also be a Force exerted on the push rod piston, which results from the  Size of the effective area and that of the precharge pump built pressure results. This in turn means that the usual Upstream pneumatic amplifiers usually do not needs to have a large effective area, and thus smaller builds. It may even be possible to add an additional one Amplifiers are dispensed with. To avoid that in the Ver stronger phase pressure medium, which is pumped by the pump in reaches the brake circuit, a pressure relief valve can be installed can be seen, the opening pressure of the master cylinder pressure is determined. The pressure in the wake room is therefore always low ner than the pressure in the working chamber of the master cylinder, so that about the non-return sleeves on the push rod piston no Flow pressure medium from the trailing chamber into the working chamber can. The pressure build-up in the trailing chamber can be proportional to the applied foot force. In this case there is one Amplifier function before. The structure can also be disproportionate tional up to full control. In this case lies a braking assistance function with which it is possible To exceed the vehicle in certain situations hesitate, given by the driver by pedaling is.

The peculiarity of the proposed brake system thus exists in that the pre-charge pump is used both to pressure to provide funds in cases where none Pedal actuation is available as well as pressure medium to an amplifier function or braking assistance function to realize.

The pre-charge pump can, such as. B. in GB 21 47 963 A1 in the single connection path between the reservoir and Ar beitskammer switched. But this presupposes that the Pump switched off in both directions when switched off can be streamed. The pump can also run parallel to one  Check valve (precharge valve) that are switched in a Connect the trailing space to the storage container in parallel det. This check valve closes as soon as the pump is switched on. This valve can also be clocked used to regulate the pressure of the precharge pump lieren.

In the following, the invention is described in several embodiments games explained. The shows

Fig. 1 shows the hydraulic circuit diagram of a hydraulic brake system according to the invention.

Fig. 2 also shows a schematic representation of the connection of a precharge pump to a Hauptbremszy cylinder.

Fig. 3 shows the execution of a suitable master brake cylinder.

Fig. 4-7 Features for controlling a hydraulic brake system with hydraulic brake assistants.

The first embodiment of the brake system according to the invention shown in the drawing has two brake circuits I and II, the structure of which is completely identical, so that the following description of one brake circuit also applies to the other. The brake system shown consists essentially of a brake pressure sensor 1 , to the unspecified hy metallic lines wheel brake cylinders 17 , 18 can be connected, a switched between the brake pressure sensor 1 and the wheel brakes hydraulic unit 2 , and an electronic controller, not shown, with associated sensors . The assignment of the wheel brake cylinders 17, 18 to the individual brake circuits I, II is such that one wheel brake cylinder 17 is assigned either a wheel of a vehicle axle and the other wheel brake cylinder 18 is the diagonally opposite wheel of the other vehicle axle (diagonal division of the brake circuits) or else both wheel brake cylinders 17 , 18 are assigned to the same vehicle axle, as shown (black and white division of the brake circuits).

The actuatable by the driver of the motor vehicle by means of a brake pedal 33 pressure sensor 1 consists of a pneumatic brake booster 5 , which is connected to a master brake cylinder, preferably a tandem master cylinder 3 , the pressure spaces 7, 8 with a pressure medium reservoir 4 are connect bar. An actuating rod 34 is coupled to the brake pedal 33 , which enables the vehicle driver to actuate a control valve, not shown, which controls the build-up of a pneumatic differential pressure in the housing of the vacuum brake booster 5 .

The hydraulic unit 2 has a motor-pump unit 20 which consists of a hydraulic return pump 14 driven by an electric motor (not shown), the suction side of which is connected via a first check valve 24 and an electromagnetically actuated switching valve 9 to the first pressure chamber 7 of the master brake cylinder 3 is. The pressure medium flows from the pressure side of the return pump 14 via a second check valve 25 and a damping chamber (not shown) to a hydraulic node 21 . Connected to these are both a line section 31 leading to the first wheel brake cylinder 17 and a line section 32 leading to the second wheel brake cylinder 18 . A hydraulic line 23 ver binds the pressure side of the return pump 14 with the tandem master cylinder 3rd In addition, a preferably electromagnetically operable isolating valve 10 is connected between the node 21 and the master brake cylinder 3 , and both a third check valve 29 and a pressure limiting valve 28 are connected in parallel. To modulate the pressure in the first wheel brake cylinder 17 serve a parallel connection of an inlet ( 11 ) with a fourth check valve 26 and an outlet valve 12 , wherein the parallel connection mentioned is inserted in the line section 31 and the outlet valve 12 for the purpose of a wheel brake pressure reduction a connection between the first wheel brake cylinder 17 and a low pressure accumulator 13 , which is connected via a fifth check valve 30 to the suction side of the return pump 14 .

In order to be able to regulate the hydraulic pressure entered in the second wheel brake cylinder 18 belonging to the brake circuit under consideration, analogously to the wheel brake cylinder 17 already considered, a second parallel connection of a second inlet valve ( 15 ) with a sixth check valve 27 and a second outlet valve 16 are provided, wherein the aforementioned parallel circuit is inserted in the line section 32 and the exhaust valve 16 for the purpose of a wheel brake pressure reduction a connection between the second wheel brake cylinder 18 and the never derdruckspeicher 13 produces.

In order to achieve, if necessary, for example at very low temperatures, the return pump 14 the pressure medium under a higher pressure, or a pre-filling of the wheel brakes 17, 18 , an auxiliary pressure source is provided, which is effective between the pressure medium reservoir 4 and the master cylinder 3 is arranged. The auxiliary pressure source is formed in the exemplary embodiment shown by a precharging pump 19 driven by an electric motor 22 , the suction side of which is connected to the pressure medium reservoir 4 and the pressure side of which is connected to the master brake cylinder pressure chamber 7 (pressure rod circuit). The precharge pump 19 generates a pressure medium flow, which is fed via the master cylinder outputs, depending on the switching position of the valves 9, 10 , either the suction side of the return pump 14 or directly to the wheel brakes 17, 18 . The precharge pump supplied by the precharge pressure should be so high that it can move the two th pressure chamber 8 limiting master cylinder piston against the resistance of a biasing him against the direction of actuation return spring to generate a precharge pressure in the second brake circuit II. This arrangement has the advantage, among other things, that only the pressure medium volume which corresponds to the stroke of the piston delimiting the second pressure chamber 8 is fed into the second pressure chamber 8 . This results in a better or more pleasant pedal feel.

If only one axle with high system dynamics is required in the vehicle the precharge pump mentioned can be designed in this way that the pressure it applies is just high enough that no displacement of the secondary piston and therefore no supply The pressure build-up takes place in the second brake circuit.

The precharge pump can be designed as a centrifugal, vane, gear or piston pumps and can be arranged in the pressure medium reservoir 4 , in the master cylinder 3 or between the pressure medium reservoir 4 and master cylinder 3 . In addition to the already mentioned electric motor 22 , both hydraulic and pneumatic drive cylinders can be considered as drives.

As can be seen from FIG. 2, the master brake cylinder 3 has two working chambers 79, 80 which are separated from one another by a floating piston 83 . The push rod piston 82 , which is driven un indirectly by the vacuum brake booster 5 or the pedal 33 , is designed stepwise, so that a running space 77 is formed. The push rod piston 82 adjoins a working chamber 79 with a surface with the diameter D, while the surface of the push rod piston 82 which faces away from the working chamber 79 has a diameter d. The trailing space 77 thus has an effective area which results from the subtraction of the two areas just mentioned. The pressure in the trailing space 77 acts on this effective area and drives the push rod piston in the direction of the working chamber 79 .

The trailing space 77 is connected via a line 100 to the reservoir 4 . There is also a connection between the trailing chamber and the one working chamber 79 both via a central valve 85 and via a check valve 87 . The central valve 85 is arranged such that it closes in the actuating direction when the push rod piston 82 is moved.

The already mentioned admission pressure pump 19 also connects to the trailing space 77 , the suction line 101 of which is directly connected to the reservoir 4 . In order to prevent pressure medium, which is conveyed by the pump 19 , back into the reservoir 4 , a check valve or Vorladeven valve 90 is provided between the reservoir 4 and the trailing chamber 77 . The pressure at the outlet of the follow-up pump 19 can be limited in various ways, either via a throttle 102 or a pressure limiting valve 103 . This Druckbegren supply valve 103 can either have a fixed switchover point, that is, set a fixed pressure at the outlet of the pump or, which is not shown here, can be controlled by the main cylinder pressure, in such a way that the pressure at the outlet of the precharge pump is not greater can be called the master cylinder pressure.

Fig. 3 shows the execution of a suitable Hauptzylin ders. The push rod piston is designed stepped, and has a head 110 which is guided in the bore 111 of the master cylinder housing. A shaft 112 led out of the master cylinder housing 111 has a smaller diameter than the head of the push rod piston. At the end of the main cylinder housing, a ring closure part 113 is provided with a device 114 in which the shaft 112 is sealingly guided. Between the rear end of the head 110 and the closure member 113 , the annular space 77 is formed, which is connected via a channel 115 , which corresponds to the line 100 , with the connection spigot 116 for the reservoir 4 . The Vorla deventil 90 is inserted into this line in the housing of the master brake cylinder. The precharge pump 19 connects to the channel 115 via a transverse bore.

The central valve 85 is formed by a plunger in the pressure rod piston, which rests against a valve seat and is held in the open position by a cross member in the basic position of the piston. The check valve 87 is designed as a sealing sleeve 120 .

The system works as follows. In all the cases in which a brake pressure has to be built up in the brake circuits without the pedal 33 being actuated, the precharge pump 19 is switched on and the precharge valve 90 is closed. At the same time, the isolating valve 10 is blocked in the brake lines and the electronic changeover valve 9 is opened, so that Druckmit tel, which is conveyed into the brake circuit by the precharging pump 19 , reaches the suction side of the return pump 14 . This promotes the pressure medium to the connected wheel brakes, in which a pressure can be built up, which is adjusted by means of the inlet and outlet valves to the respective control algorithms.

When the driver applies the brakes, the brake circuits can be preloaded as well as an exclusive brake boost. A pre-charge can also be provided in particular if it is possible to determine the driver's intention to initiate braking before the driver presses the brake pedal. If such an intention is determined, the precharge pump 19 is switched on and the precharge valve 90 is blocked. Now brake fluid penetrates into the brake circuits via the open central valve 85 and the check valve 87 . This leads to an overcoming of the system-inherent free travel. By pressing the pedal, the pressure piston rod 82 is moved, whereby the central valve 85 is closed ge. As a result, a pressure is built up in the pressure rod brake circuit 79 which is generally greater than the pressure which is made available by the precharge pump 19 . The pressure of the precharge pump is still effective in the trailing space 77 , so that this exerts an additional actuating force on the pressure rod piston based on the effective area, which leads to an increase in pressure in the brake circuits. In order to ensure that no additional Druckmit tel gets into the brake circuits in this phase, means can be provided to limit the pressure of the precharge pump to the pressure in the brake circuits. This can be achieved by means of a pressure relief valve controlled by the master cylinder pressure, which ensures at the outlet of the precharge pump that the pre-charge pressure does not exceed the master cylinder pressure.

The pre-charge pump can therefore be used in a multifunctional way: On the one hand, it can be used in cases where a brake pressure in the brake circuits must be built without a pedal the necessary pressure medium volume is available supply. On the other hand, it can with a pedal actuation provide a pressure in the wake room, which increases the pedal force. This can be unhappy  rules take place, namely in all cases in which due special signals can be found that the driver want to brake quickly. But this can also regulated take place by z. B. the pressure at the outlet of the precharge pump on the master cylinder pressure or just a little below is posed.

Important aspects of the invention are to be seen in the fact that, if required, an additional brake force support for the pneumatic brake booster 5, the precharge pump 19 is switched on and the precharge valve in the wake area is closed. By building up pressure in the wake area and taking into account the area ratio, a hydraulic support force on the push rod piston 110 is effective. This enables a hydraulic brake assistant to be implemented. The pressure regulation can take place via clocked pump control or clocking of the precharge valve 90 . In addition, in systems with traction control and vehicle dynamics control, a further increase in pressure in combination with the precharge pump 19 can be made possible by opening the switching valve 9 and building up pressure via the return pump 14 in the wheel brakes 17 , 18 .

In general, in the presence of a precharge pump 19, the brake booster 5 can be made smaller and the preload pump 19 can be controlled for servo assistance if necessary. In addition, the combination of panic brake assistance in combination with a standard brake pressure booster 5 is possible.

On the basis of the following figures as shown in FIGS. 4 to 7 different control options are explained tenfunktion for operation of the hy draulic brake system with a hydraulic brake Assisten.

Fig. 4 shows a combination of the elements from the previously described in Figs. 1 and 2 and thus known elements. Likewise, with reference to the preceding Be parts of the description of the hydraulic brake assist function, as summarized on the description page 12, 2nd paragraph has been carried out, the necessary sensors for the actuation method of the hydraulic brake assist system are now dealt with specifically on the basis of games.

This requires the detection of the movement characteristics of the brake pedal 33 , preferably by means of a displacement sensor 333 and determination of the pressure in each case in the hydraulic circuit, preferably by means of pressure sensors 444 arranged on the working chamber 80 and the pump pressure line 21 . The resulting sensor signals, depending on the driving speed of the vehicle, also detected in a computer, preferably in the ABS control unit, upon detection of panic braking by the computer, to the closed position of the pre-charge valve 90 and to an activation of the pre-charge pump 19 , which results in a builds up actuation pressure to the pedal force in the master cylinder 3 . This is illustrated graphically, inter alia, in FIG. 7. This increased actuation supply pressure ensures that the brake pressure level in the wheel brake cylinders 17 , 18 can be listed as close as possible to the blocking pressure. This leads to the shortest possible braking distance without the need for additional pedal force.

An expedient embodiment of the mode of operation explained in relation to FIG. 4 can be seen from the illustration in FIG. 5. This provides, for the purpose of reacting as quickly as possible to the hydraulic brake assistant function described in FIG. 4, a high-pressure accumulator 555 on the pressure side of the precharging pump 19 , namely between the return check valve 666 and a isolating valve 888 connected to the charging line 777 , to be connected. The isolating valve 888 is preferably designed as an electromagnetically operable, in the basic setting, closed 2/2-way valve which, according to the preceding explanations for FIG. 4, is additionally opened electromagnetically in the event of an activation, by the volume in the preloaded high-pressure accumulator 555 in the at the trailing space 77 connected charging line 888 to let sen. The other end portion of the charge line 888 is separated from the pressure medium reservoir 4 by the electromagnetically blocked precharge valve 90 .

Fig. 6 shows on the basis of the brake system construction already described in detail, an embodiment variant which differs from the brake systems according to FIGS. 4 and 5 in that, instead of a displacement sensor, a force sensor 999 detects the pedal force exerted on the brake pedal 33 and does not more kor relative pressure increase in the brake circuit under further force increases each foot force in a computer, preferably in the ABS control unit, is compared to determine the modulation point of the pneumatic brake booster 5 . When reaching the modulation point, the precharge pump 19 is activated gently to achieve a comfortable pedal feel. The pressure reduction in the trailing space 77 can be accomplished, as in all of the previously described exemplary embodiments, by deactivating the precharge valve 90 . It can also take over the function of the pressure limiter valve 103 if necessary.

This embodiment is mainly used for particularly small-sized pneumatic brake booster 5 , either to effect an additional hydraulic amplification by means of the precharge pump 19 and / or a high-pressure accumulator 555 for pneumatic amplification or to cause a pneumatic gain deficit caused by a vacuum deficit by means of a hydraulic boosting effect of the precharge pump 19 and / or a high pressure accumulator 555 .

Fig. 7 shows with reference to the representation of FIG. 6, a force diagram in which the characteristic curve a of the pneumatic brake booster 5 as well as the hydraulic characteristic curve b expanded representation of the characteristic curve a is drawn. The force increase dFa of the modulation force Fa plotted over the ordinate and the force increase dFe of the modulation force Fe applied via the abscissa, which is generated by the foot force, can be determined by means of the pressure sensors 444 described above and with the values of the force sensor 999 on the pedal Compare, so that the desired Aussteu erpunkt I of the pneumatic brake booster 5 is reached at a relatively small force increase ratio dFa / dFe, in which the additional hydraulic gain (characteristic curve b) is set by the precharge pump 19 . The same applies if the vacuum fails. As long as the force increase ratio dFa / dFe corresponds to the desired setpoint, however, there is no additional hydraulic amplification by means of the preload pump 19 . The complete failure of the pneumatic brake booster 5 is also shown in the diagram based on the characteristic line c.

Insofar as no details have been given regarding all of the elements shown in FIGS. 4 to 6, these correspond to the explanations according to FIGS. 1 to 3.

Claims (9)

1. Hydraulic brake system with a pedal-operated master brake cylinder ( 3 ) which has a working space ( 7 ) which is delimited by a push rod piston ( 82 ), an effective surface of the push rod piston ( 82 ) facing a trailing space ( 77 ), a precharging pump ( 19 ), which conveys into the trailing space ( 77 ), with at least one brake circuit with at least one wheel brake, characterized in that the precharging pump ( 19 ) can be switched on for pedal force amplification at the latest when a pedal is started. 2. Hydraulic brake system according to claim 1, characterized in that the brake circuit is provided with a return pump ( 14 ) and valves ( 11 , 12 , 15 , 16 ) for regulating the wheel brake pressure and an electronic controller, which in the cases where a brake pressure in the brake circuits is to be built up independently of a pedal actuation, at least the precharge pump ( 19 ) switches on. 3. Hydraulic brake system according to claim 1 or 2, characterized in that a pre-loading valve ( 90 ) is connected in parallel to the precharging pump ( 19 ). 4. Hydraulic brake system according to claim 1, characterized in that a pressure relief valve ( 103 ) is provided that limits the pressure at the outlet of the precharge pump. 5. Brake system according to claim 1, characterized in that the pressure of the precharging pump ( 19 ) is carried out by actuating the pre-loading valve ( 90 ). 6. Brake system according to claim 1, characterized in that for detecting the pedal actuation, a sensor, preferably a displacement sensor ( 333 ) and / or a force sensor ( 999 ) is hen vorgese. 7. Brake system according to claim 1, characterized in that at least one pressure sensor ( 444 ) is provided for detecting the pressure in the brake circuit. 8. A method of operating a hydraulic brake system with a pedal-operated master brake cylinder (3) having a working chamber (7) which is delimited by a push rod piston (82), wherein an effective area of the pressure bars is the piston (82) facing a supply chamber (77) , A precharge pump ( 19 ), which conveys into the trailing chamber ( 77 ), with at least one brake circuit, with at least one wheel brake, in particular according to claim 1, characterized in that the movement characteristics of the brake pedal ( 33 ), preferably by means of a displacement sensor ( 333 ) or a force sensor ( 999 ), and the hydraulic pressure in the brake system by means of pressure sensors ( 444 ) is detected, that the distance with the pressure characteristic in a computer, preferably an ABS control unit, is compared with signals of the vehicle driving speed, whereby upon detection of panic braking from the aforementioned signals, a hydraulic brake assistant function, preferably by Ak tivieren the pre-charge pump ( 19 ) and a precharge valve ( 90 ) is used. 9. The method according to claim 7, characterized in that the foot force exerted on the brake pedal ( 33 ) is detected by means of the force sensor ( 999 ) and does not correlate the pressure increase in the brake circuit with a further increase in the foot force in a computer, preferably in ABS control device, for determining the modulation point of the pneumatic brake booster ( 5 ) is compared, the precharge pump ( 19 ) being activated when the modulation point is reached.