DE19649010B4 - Hydraulic brake system with an external pressure source - Google Patents

Abstract

hydraulic Brake system with at least one brake circuit (I, II), which at least a wheel brake (53, 54, 55, 56) includes a pedal-operated master cylinder (1) who over a respective brake line (4, 5) to the at least one brake circuit (I, II) is connected to an external pressure source (13) over at least a pressure line (12) to the at least one brake circuit (I, II) is connected, each with a valve assembly (6, 7) per brake circuit (I, II) which depends from the master cylinder pressure in the brake line (4, 5) external pressure in the respective brake circuit (I, II) einsteuert, wherein the master cylinder (1) a pressure / volume simulator (34) is connected, which has a with the master cylinder connected simulator chamber (36) and one with an unpressurized pressure medium tank (2) connected control chamber (37), characterized on the one hand in the connection between the control chamber (37) and the pressure fluid container (2) one to the pressure fluid tank (2) closing check valve (38) is that and on the other hand the. Control chamber (37) with interposition a pressure relief valve (41, ...

Description

The The present invention is based on a hydraulic brake system according to the preamble of Claim 1.

Such a brake system is for example from the DE 32 47 497 A1 known. In the known brake system is a dual-circuit brake system with slip control, in which wheel brakes are connected to each other hydraulically separated brake circuits via electromagnetically actuated intake and exhaust valves, in which the brake circuits on the one hand by a tandem master cylinder pressurizable and on the other hand driven by an electric motor , two-circuit pump unit are connectable. Both outputs of the pump unit are connected to the master cylinder pressure controlled, normally locked brake valves, which are arranged in the connections between the tandem master cylinder and the wheel brakes from the Ausgengsdruck the brake valves lockable Zuschaltventile. The brake valves and the Zuschaltventile are designed as seat valves, each Zuschaltventil having an axially pierced valve piston. An end face of this valve piston defines a non-pressurized chamber, while on the other end face of the valve piston, a biased on a valve seat valve closure member is formed. By the valve closure member connected to a pump outlet annulus is closed. Coaxially with the valve piston, a piston which can be acted upon by the master cylinder pressure is arranged, which closes the axial bore of the same when it rests against the valve piston and lifts the valve closure member integrally formed on the valve piston from its seat upon further displacement. In this way, with open axial bore of the valve piston, the output of the Zuschaltventils connected to a non-pressurized container and closure of the axial bore and lifting the valve piston from its seat, the pressure side of the pump unit with the wheel brakes. Since the piston serving as a control piston second piston is acted upon by the master cylinder pressure, proportional to the pedal force of the brake pedal pressure from the external pressure source is controlled.

Indeed arises when the brake valves with the high output pressure the external pressure source, namely the pump unit that the brakes from the master cylinder to the wheel leading brake line suddenly is shut off and thus creates a hard pedal feel. This can cause irritation lead the driver.

Another such brake system is for example of the generic type DE 35 26 556 A1 known. In the known brake system is a dual-circuit brake system with slip control, with a brake pressure transducer and a hydraulic Bremskraftverstarkung in which are connected to each other hydraulically separate brake circuits via electromagnetically actuated intake and exhaust valves wheel brakes, and softer the brake circuits on the one hand by the brake pressure generator under pressure settable and on the other hand connectable to an auxiliary pressure supply system. The special feature of the known brake system consists in the fact that the pedal travel simulator has a piston arranged in a cylinder, which is displaceable by the foot pressure proportional pressure resulting from brake actuation in the brake pressure generator against the force of a return spring and against the auxiliary pressure of the auxiliary pressure supply system.

From the DE 44 25 578 A1 is a motor vehicle brake system for driving stability and / or traction control known, in which as a brake pressure generator, an assembly. is used, which consists of a dual-circuit master cylinder or tandem master cylinder and a tandem master cylinder upstream pneumatic brake booster. The brake booster is controlled when entering the control regardless of the driver's will to achieve a pre-filling of the wheel brakes. After completion of the Vorfüllvorgangs the further pressure build-up in the wheel brakes with a return pump.

task The present invention is a hydraulic brake system to create the type mentioned, in which despite the buildup of external pressure without additional electronic measures a comfortable brake pedal feel persists.

These Task is solved in conjunction with the characterizing features of claim 1. By Recording a pressure / volume simulator in the brake line, so between master cylinder and valve assembly, the elasticity of the pedal feel is maintained. In the moment in which the valve assembly, which of the combination corresponds to connecting valve and brake valve, the brake line shuts off, the driver occurs at stronger activity the brake pedal against an elastic force which the elasticities of Brake system simulated.

advantageous Further developments of the brake system according to the invention are the dependent claims 2 to 10 removable.

The invention is by no means limited to slip-controlled brake systems. The external pressure source can just as well serve merely as a replacement for a hydraulic or pneumatic brake booster, which is normally connected between the brake pedal and the master cylinder is.

One the valve assembly in parallel check valve, which a Pressure medium flow from the master cylinder to the wheel brake allowed, however prevented in the opposite direction, guaranteed Braking at any time by a pedal operation, but prevents on the other side, that repercussions the external pressure source in the brake pedal are felt.

By an elastically preloaded piston, the one with the brake pipe connected simulator chamber separates from a control chamber, which via a pressure relief valve Connected to a reservoir, the control chamber can also with hydraulic fluid filled be so that there is no risk of leakage between hydraulic fluid and atmosphere results. The system is complete flooded. The reservoir with which the control chamber via the pressure relief valve is connected, can be both a non-pressurized reservoir as well as for example a low-pressure accumulator. The only important thing is that the container suitable for volume uptake.

In order to even after completion of the brake application of the piston of the simulator be reset can, we recommend a check valve of back to this reservoir to the control chamber, which allows a flow of pressure medium to the control chamber, when the piston returns to its preloaded initial position.

A Reduction in the number of parts is achieved by both pistons as well as the pressure relief valve are biased by one and the same spring.

Especially, but not only in brake systems without slip control, recommends It is to save on electronics, the valve assembly hydraulically to press.

If the brake system over Brake pressure modulation valves, so intake and exhaust valves or contains the same for slip control, so can the external pressure source at the same time use as an ABS pump, the exhaust valves of the wheel brakes to a low-pressure accumulator or can lead to a reservoir.

A additional provided with a switching valve line from the pressure side of External pressure source to the pressure modulation valves, bypassing the valve assembly and an electromagnetically lockable isolation valve in the connection between the valve assemblies and the pressure modulation valves allows it, the brake system in addition for active braking even without activation of the Use brake pedals.

to Realization of such active braking is recommended, at least a pressure switch or pressure sensor for detecting a driving brake request to arrange in the brake system. These pressure sensors allow then, for example, a so-called Springerfunktion, which at activity of the brake light switch immediately since electromagnetically operated switching valve opens and the electromagnetically operated Isolating valve closes and introduces a foreign pressure at least in a part of the wheel brakes. If the brake pressure applied by the driver is greater than a certain threshold, For example, 15 bar, this switching of the valves is again reversed, and it takes place in the further course of a fußkraftproportionale brake booster.

A Reduction of the control logic for The valves can be achieved by the fact that the electromagnetic isolation valve as normally open, the electromagnetic switching valve as normally closed valve are designed and the control these two valves take place together.

A details explanation of the inventive concept will now be based on the description of several embodiments of the invention with reference to five Characters. It shows:

1 a brake system according to the invention with hydraulic brake booster by a high-pressure pump,

2 the hydraulic brake system after 1 , where the in 1 structurally illustrated valves and simulators are now represented by equivalent circuit diagrams,

3 a brake system according to the invention, which is equipped with a device for slip control and is suitable for example for traction control,

4 a brake system according to the invention with slip control, a device for active braking and with Springer function,

5 a valve arrangement for a brake system according to the invention, which can be used as an alternative to the valve arrangement shown in the preceding figures,

6 an equivalent circuit diagram for the valve assembly according to 5 ,

The brake system after 1 has a tandem master cylinder 1 on, to which two brake circuits I and II are connected. The main cylinder 1 is from a storage container 2 fed and is by means of a brake pedal 3 pressurizable. About the brake lines 4 and 5 This pressure is applied to each valve assembly 6 respectively. 7 continued. Every valve arrangement 6 and 7 has four fluid ports, of which the first as mentioned with the brake line 4 respectively. 5 another is connected with wheel brakes 8th and 9 respectively. 10 and 11 , a third with the pressure line 12 a high pressure pump and the fourth with the reservoir 2 ,

Since both brake circuits I and II are constructed symmetrically, the following description of the brake circuit I also applies to the brake circuit II. In this case, all functional elements are duplicated except for the master cylinder 1 , the brake pedal 3 , the reservoir 2 and the high pressure pump 13 , which are only common for both brake circuits together.

The valve arrangement 6 essentially has a connection valve 14 and two check valves 15 and 16 on. The first check valve 15 is in the pressure branch line 17 installed, which of the pressure line 12 to an inlet chamber 18 of the connection valve 14 leads. In the inlet chamber 18 is a valve closure member 19 , a leader body 20 for the valve closing member and a valve body acting on this guide spring 21 arranged. The inlet chamber 18 is limited by a housing-fixed valve seat 22 leading to an outlet chamber 23 leads. On the valve closure member 19 lies a pestle 24 which has a thickened collar 25 having, in the illustrated system of the closing member 19 at the valve seat 22 on a housing-fixed stop 26 is applied. Beyond the collar 25 the plunger sits down 24 and carries at its opposite end another closing part 27 , which with a valve seat 28 interacts with a stepped control piston 29 is formed and the mouth of a bore forming the outlet chamber 23 with a pressure-free compensation chamber 30 combines. The connection between outlet chamber 23 and compensation chamber 30 is in the illustrated basic position of the Zuschaltventils 14 open. In the compensation chamber 30 is a compression spring 31 arranged, which the stepped control piston 29 from the inlet chamber 18 acted upon. That of the inlet chamber 18 facing the end of the control piston 29 takes that of the inlet chamber 18 opposite end of the plunger 14 as well as the closing part 27 and has a smaller cross-section which is sealed in a housing-fixed sleeve 33 is guided. With its inlet chamber 18 facing away from the end face, which has the largest cross-section of the control piston 29 has limited, this a control chamber 32 connected to the brake line 4 is connected and from which the brake line 4 over the check valve 16 with the wheel brakes 8th and 9 communicates. The two check valves 15 and 16 open at a form of the order of 2 bar.

The operation of this valve assembly 6 and the simulator described below 34 will be later based on 2 explained.

The simulator 34 has a stepped stimulator piston 35 on, with its face of largest cross section a simulator chamber 36 limited, which to the brake line 4 connected. With its smaller diameter portion, it is sealed axially guided, so that formed by the step formed by the two sections of an annular chamber 37 spanning, over a check valve 38 with the reservoir 2 connected is. The check valve 38 opens from the reservoir 2 to the annular chamber 37 and serves to supply pressure medium when the simulator piston 35 moved back from an operating position, not shown, in its dargestell te basic position. The home position is defined by loading the smaller diameter simulator piston with the force of a simulator spring 39 , which express their pressure via a spring plate 40 on the end of the simulator piston 35 transfers. At its other end, the simulator spring acts on a closing body 41 , which is coupled via a driver connection with the simulator piston and a simulator piston 35 opposite valve seat 42 closes. This forms the closing body 41 with the valve seat 42 a pressure relief valve, which communicates with the annular chamber 37 communicates. The closing body 41 , the simulator pen 39 as well as the spring plate 40 are like the smaller diameter simulator piston end in a pressureless equalization chamber 43 arranged, which with the reservoir 2 communicates. So if in the ring chamber 37 by pressing the brake pedal and moving the simulator piston 35 a high pressure occurs, so this planted up to the valve seat 42 continues and acts on the closing body 41 , The opening pressure of the valve seat 42 and the closing body 41 formed pressure relief valve is dependent on the position of the simulator piston 35 , It is lower in the illustrated home position and higher with the simulator piston shifted 35 , Initially, the opening pressure is about 2 bar. Exceeds the pressure in the annular chamber 37 the opening pressure of the pressure relief valve 41 / 42 , so the pressure medium builds up through the compensation chamber 43 in the reservoir 2 from.

Parallel to the pressure relief valve 41 / 42 is a check valve 38 with very low opening pressure, z. B. 0.2 bar, applied, which pressure medium in the annular chamber 37 from the reservoir 2 can flow when the simulator piston 35 upon completion of a pedal-operated brake returns to its illustrated home position.

The operation of the brake system is described below with reference to 2 described. Will the brake pedal 3 operated, so is in the brake lines 4 and 5 Pressure built up, which in the simulator chamber 36 of the simulator 34 arrives. In the further course of the brake line 4 also becomes the control chamber 32 of the connection valve 14 applied. Simultaneously with the operation of the brake pedal 3 the high pressure pump starts 13 to run, being a high-pressure accumulator 44 can be charged, which - not shown - may be provided with a shut-off valve to quickly provide a high pressure. The high pressure pump 13 However, it can also be directly via the pressure line 12 and the pressure branch line 17 Pressure medium via the admission pressure check valve 15 spend to Zuschaltventil.

At a master cylinder pressure from the order of 2 bar leaves the Zuschaltventil 14 proportional to the master cylinder pressure feed pressure of the high pressure pump to flow into the brake circuit by pushing the pressure branch line 17 with the wheel brakes 8th and 9 combines. That means that in 1 the stepped control piston 29 shifts to the right, causing the closing member 27 to the valve seat 28 applies and initially shuts off the connection from the reservoir to the wheel brakes and in the course of the displacement of the control piston 29 the closing member 19 from the valve seat 22 lifts and thus the pressure branch line 17 with the wheel brakes 8th and 9 combines. At this moment the pressure in the wheel brakes exceeds 8th and 9 the master cylinder pressure, so that on the admission pressure check valve 16 no pressure fluid from the master cylinder 1 more in the wheel brakes 8th and 9 arrives.

So that no hard pedal feeling results, is the simulator 34 to the brake line 4 connected. The simulator piston 35 shifts upward with further brake pedal operation in the figure, so that in the annular chamber 37 the pressure rises. The compression spring 39 gives the driver a natural pedal feel. Exceeds the pressure in the annular chamber 37 the opening pressure of the pressure relief valve 41 / 42 , then the pressure medium in the reservoir 2 drained.

The connection valve 32 and the pressure relief valve 41 / 42 are control valves that work in sniffing position and usually their end stop, so take full opening position, never take.

When a pedal-operated brake is stopped, the brake pedal becomes depressed 3 solved. The high pressure pump 13 will be switched off. Due to the decreasing master cylinder pressure, the sequence valve moves 14 to its illustrated basic position, and the pressure in the wheel brakes 8th and 9 becomes foot force proportional in the storage container 2 reduced. If in the simulator chamber 36 according to the pressure has dropped, is from the compression spring 39 the simulator piston 35 reset, taking over the check valve 38 Pressure fluid from the reservoir 2 in the ring chamber 37 can run after.

The brake system after 3 is different from the one after the 1 and 2 in that it is additionally equipped with a device for slip control and for active braking. In this embodiment, in which, for example, no pressure sensors are shown, can by the valve assembly within the hydraulic block 45 For example, an anti-lock control and a traction control can be performed.

In contrast to 1 has the high pressure pump 13 an active pressure line 46 on which of the pressure line 12 branches off and bypassing the valve assemblies 6 and 7 directly to the hydraulic block 45 leads. Electrically actuated, normally closed reversing valves 47 and 48 leads the active pressure line 46 directly to the intake valves 49 to 52 the wheel brakes 53 to 56 , About exhaust valves 57 to 60 are the wheel brakes 53 to 56 with the reservoir 2 connectable.

The brake system thus represents in a anti-lock control so-called open system, in which the high-pressure pump 13 both brake circuits supplied together and with its suction side directly to the reservoir 2 connected. Accordingly, this is for the purpose of a slip control of the wheel brakes 53 to 56 drained pressure medium also directly to the reservoir 2 fed.

Just as well, however, a slip-controlled brake system, which includes the invention, can also be realized as a so-called return flow principle when the exhaust valves 57 to 60 are connected to a low pressure accumulator, which to the suction side of the high pressure pump 13 leads. In this case, between the reservoir 2 on the one hand and the low pressure accumulator and the high pressure pump 13 on the other hand lie a valve which can block the connection to the reservoir.

In a traction control is also without pressing the brake pedal 3 the high pressure pump 13 turned on, being in such a case in the brake lines 4 and 5 isolation valves 61 and 62 be needed, that of the high pressure pump 13 constructed delivery pressure from the valve assemblies 6 and 7 and thus from the master cylinder and the reservoir 2 keep away.

At the beginning of a traction control so the changeover valves 47 and 48 and the isolation valves 61 and 62 switched from its illustrated basic position in their energized switching position, so that the active brake line 46 ge is open and the brake lines 4 and 5 are locked. In the event that all driven wheels are only in a brake circuit, for example in the brake circuit I, so is only the switching of the switching valve 47 and the isolation valve 61 This brake circuit required. The further course of traction control takes place in a known per se, the brake pressure by controlling the intake valves 49 to 52 and the exhaust valves 57 - 60 is regulated.

The brake system after 4 is similar in large parts of the after 3 , However, it is equipped with additional comfort and convenience through additional sensors and control logic. It offers the advantage of a so-called Springer function, which causes even with only slight actuation of the brake pedal 3 from the high pressure pump 13 a brake pressure is built up, which prevents the vehicle from rolling away at standstill.

In 4 is therefore on the brake pedal 3 a pedal sensor 63 located, which can be formed for example by the brake light switch, which is present in any brake system anyway. Furthermore, each of the two brake circuits I and II has a pressure sensor 64 respectively. 65 on, in this case immediately before the intake valves 49 to 52 is arranged. At least one of these pressure sensors 64 respectively. 65 is the driver request recognition, so the detection of whether a stronger pedal-operated braking is desired, as it corresponds to the Springerfunktion.

For the Springerfunktion it is sufficient, only one of the two brake circuits I and II with active brake pressure from the high pressure source 13 to supply. Therefore, for example, only switch the switching valve 47 and the isolation valve 61 around when the brake light switch 63 a pedal actuation detek benefits. At this moment is from the high pressure pump 13 a delivery pressure to the wheel brakes 53 and 54 spent, which causes a stationary vehicle even without strong operation of the brake pedal 3 is prevented from rolling away. In this case, then the pressure sensor is used 65 to determine if the driver intends to slow down the vehicle more. If in the brake line 5 a brake pressure of about 15 bar is reached, the valves 47 and 61 switched back and made a brake booster, as in connection with 1 is described.

By the pressure sensors and the driver request detection, it is also possible with this brake system, for example, to perform a yaw moment control by wheel-selective braking for the purpose of stabilizing the vehicle when cornering. The high-pressure pump is used 13 Similar to the traction control system as an active pressure source, wherein the individual wheel brakes are applied only by other criteria with brake pressure.

All described embodiments of inventive brake systems is common that the static, from the master cylinder 1 outgoing pressure circuits are separate, closed circuits, at least as long as the power supply of the high pressure source is intact. Without a high-pressure source, however, no higher brake pressure can be built up than that in the simulator chamber 36 to such a pressure increase in the annular chamber 37 causes the pressure relief valve 41 / 42 opens.

The dynamic pressure circuits, that is, those of the high pressure pump 13 are fed by the arrangement of the check valves 15 also separate pressure circuits. In the dynamic pressure circuits, however, are open circles, as the discharged from the wheel brakes pressure medium in the reservoir 2 passes and the high pressure pump 13 also draws pressure medium again from this open container.

The 5 and 6 Finally, show an alternative embodiment of the Zuschaltventils 14 , which provides a different spring loading of the individual functional elements. The connection valve 114 has a two-part control piston, which consists of a first part 129 larger diameter and a second part 129 ' smaller diameter. The second part 129 ' the control piston takes in its interior part of the plunger 124 and is like the smaller diameter section of the spool 29 out 1 sealed at its periphery axially guided in the housing. Between the two parts 129 and 129 ' the compression spring stretches 131 on, wherein they the second control piston part 129 ' over a spring pot 170 applied. The spring pot 170 causes the compression spring 131 is quasi fixed to the housing as the spring pot 170 is supported in the illustrated basic position on a housing stage. Accordingly, the equivalent circuit looks somewhat different than that of the connection valve 14 , The one from the master cylinder 1 resulting control pressure thus no longer acts directly, but only indirectly via the compression spring 131 on the connecting valve 114 one. Otherwise, the functionality is identical to that of the connection valve 14 , It is therefore against the Zuschaltventil 14 interchangeable.

Claims (10)

Hydraulic brake system with at least one brake circuit (I, II), which has at least one wheel brake ( 53 . 54 . 55 . 56 ), with a pedal-operated master cylinder ( 1 ), each of which has one brake line tion ( 4 . 5 ) is connected to the at least one brake circuit (I, II), with an external pressure source ( 13 ), which via at least one pressure line ( 12 ) is connected to the at least one brake circuit (I, II), each having a valve arrangement ( 6 . 7 ) per brake circuit (I, II) which depends on the master cylinder pressure in the brake line ( 4 . 5 ) External pressure in the respective brake circuit (I, II) einsteuert, wherein the master cylinder ( 1 ) a pressure / volume simulator ( 34 ) is connected to a simulator chamber connected to the master cylinder ( 36 ) and one with a pressure-free pressure medium container ( 2 ) associated control chamber ( 37 ), characterized in that on the one hand in the connection between the control chamber ( 37 ) and the pressure medium container ( 2 ) to the pressure medium container ( 2 ) closing check valve ( 38 ) and that, on the other hand, the. Control chamber ( 37 ) with the interposition of a pressure relief valve ( 41 . 42 ) with a compensation chamber ( 43 ) connected to the pressure medium container ( 2 ) connected. Brake system according to claim 1, characterized in that the simulator ( 34 ) an elastically biased piston ( 35 ) having the simulator chamber ( 36 ) from the control chamber ( 37 ) separates. Brake system according to claim 2, characterized in that the pressure relief valve ( 41 . 42 ) and the piston ( 35 ) of the same spring ( 39 ) are biased. Brake system according to one of the preceding claims, characterized in that the at least one brake circuit (I, II) additionally exhaust ( 57 to 60 ) and inlet valves ( 49 to 52 ) contains for slip control. Brake system according to one of the preceding claims, characterized in that the valve arrangement ( 6 . 7 ) is hydraulically operated. Brake system according to claim 5, characterized in that on the valve device ( 6 . 7 ) on the one hand, the pressure of the pedal-operated master cylinder ( 1 ) and on the other hand, the pressure of the external pressure source ( 23 ), wherein the compound ( 12 . 17 ) between the foreign pressure source ( 23 ) and the wheel brakes ( 8th . 9 ) by the pressure of the pedal-operated master cylinder ( 1 ), after which the hydraulic connection between the master cylinder ( 1 ) and the wheel brakes ( 8th . 9 ) is effectively separated by the pressure of the external pressure source. Brake system according to claim 5 or 6, characterized in that the external pressure source ( 13 ) via an electromagnetically actuated changeover valve ( 47 . 48 ) directly bypassing the valve assembly ( 6 . 7 ) is connectable to the one or more brake circuits (I, II) and that between each of the valve assemblies ( 6 . 7 ) and the associated intake valves ( 49 to 52 ) an electromagnetically lockable isolation valve ( 61 . 62 ) is arranged. Brake system according to claim 7, characterized in that at least one pressure switch or pressure sensor ( 64 . 65 ) is present for detecting a driver's braking request. Brake system according to claim 8 with a brake light switch ( 63 ), characterized in that upon actuation of the brake light switch ( 63 ) the changeover valve ( 47 ) at least one brake circuit (I) and the associated isolation valve ( 61 ) is closed and that when the driver's brake request corresponds to a brake pressure that is greater than a pressure threshold value, the switching valve ( 47 ) and the isolation valve ( 61 ) is opened. Brake system according to one of claims 7 to 9, characterized in that the switching valve ( 47 ) and the isolation valve ( 61 ) of a brake circuit are always controlled together.