EP3924232A1

EP3924232A1 - Electronically slip-controllable external power brake system

Info

Publication number: EP3924232A1
Application number: EP19817275.1A
Authority: EP
Inventors: Michael Bunk; Verena BARSKE; Dirk Foerch; Andreas Krautter; Peter Ziegler; Ulrike Schaefer
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2019-02-14
Filing date: 2019-12-07
Publication date: 2021-12-22
Also published as: JP7256884B2; US11926306B2; CN113396089A; DE102019201907A1; KR20210125068A; CN113396089B; WO2020164775A1; JP2022520336A; US20220153247A1

Abstract

The invention relates to an electronically slip-controllable external power brake system (10) for a motor vehicle. A controllably drivable pressure generator (50) is provided in order to supply multiple brake circuits (16; 18), connected in parallel, with a pressure medium under brake pressure. Furthermore, each of the brake circuits (16; 18) can be separated from the pressure generator (50) by existing first directional valves (60), and the brake circuits have second directional valves (62) connected downstream of the first directional valves (60) in order to control the brake pressure in the wheel brakes (14) connected to the brake circuits (16; 18). An electronic controller (34) is proposed which is designed to control the pressure in the brake circuits (16; 18) and comprises three devices (90, 92, 94), the third device (94) being designed to bring the respective first directional valve (60) of a brake circuit (16; 18) into the through-flow position if a leakage (80) is ascertained downstream of the second directional valve (62) in the brake circuit (16a) by means of the first device (90) and if the second device (92) has ascertained that the pressure generated by the pressure generator (50) has at least approximately reached, or exceeded a threshold pressure (86) of the first directional valve (60).

Description

title

Electronically slip-controlled external power brake system

epiphany

The invention relates to an electronically slip-controllable external power brake system according to the features of the preamble of claim 1.

State of the art

Electronically slip-controlled braking systems are state-of-the-art in vehicle construction and are now required by law for new vehicles in many countries.

Such brake systems prevent the wheels from locking during braking, keep the vehicle in a stable driving state within the physical limits and ultimately contribute to increasing driving safety. In addition, such brake systems are able to build up a brake pressure independently in dangerous situations, that is, without the involvement of a driver, and thus counteract accidents. Such brake systems are often also used as brake systems with anti-block protection (ABS),

Drive slip (ASR) or driving stability control (ESP) called.

Brake systems with slip control are increasingly being designed as external power brake systems. External power brake systems are characterized by the fact that a driver's braking request is electronically recorded and converted into braking pressure by a controllably drivable pressure generator. The wheel brakes to which this brake pressure is applied ultimately bring about the desired vehicle deceleration.

It is also known as a pressure generator in slip-controllable

Brake systems to use cyclic piston pumps, continuously conveying gear pumps or plunger devices. That of the invention underlying slip-controllable external power brake system according to FIG. 1

comprises two brake circuits connected in parallel to one another, which are jointly supplied with pressure medium under brake pressure from a plunger pressure generator

become.

Since it is not with certainty under operating conditions of braking systems

it can be ruled out that mechanical damage or a leak causing a leak can occur in one of the brake circuits and because in this case due to the common

Pressure generator of the brake circuits the functionality of the entire

Brake system would be at risk, DE 10 2018 212 016 proposes a method for testing the brake system for leaks. Based on this

Procedure can be determined which of the brake circuits from the damage

is affected. This leaky brake circuit can then possibly be used by the others

Decouple the brake circuits so that the vehicle is still intact

Brake circuit can be safely braked to a standstill and pressure medium is not lost via the leak in the defective brake circuit.

To decouple it from the pressure generator, each brake circuit has a

electronically controllable directional valve. This directional control valve is also referred to as a plunger control valve, for example, and can be switched from a normally closed locking division to an open position. For this purpose, a plunger control valve has a valve cross section which is controlled by a closing element. The pressure forces on the plunger control valve have an opening effect on this closing element. Therefore, if the pressure acting on the closing element is higher than a limit pressure that can be set via the valve design, this opens

Plunger control valve and releases the valve cross-section. Pressure medium can consequently penetrate to a possibly existing leak and escape from the brake system. With a pressure medium leak, the functionality of the still intact brake circuit is reduced; In addition, escaping pressure medium may cause environmental pollution. Furthermore, the pressure in the intact brake circuit can no longer be maintained, since the pressure generating unit pushes volume into the defective circuit.

Advantages of the invention

The invention according to the features of claim 1 has the advantage that this volume emerging from a defective brake circuit is reduced to a minimum volume and that consequently the intact brake circuit for an extended period is available. In addition, undesirable environmental pollution is largely avoided.

Further advantages or advantageous developments of the proposal emerge from the subclaims or from the following description.

The invention is based on a modified electronic control unit for

Control of the brake system implemented and thereby has an advantageous effect in no increase in installation space or in an additional effort for parts or for the assembly of a hydraulic unit of such a brake system.

The invention is based i.a. on a device in an electronic control unit of the brake system, which is designed to move the plunger control valve of a leaked brake circuit into the open position when the pressure generated by the pressure generator has at least approximately reached or exceeded a limit pressure of the respective plunger control valve.

Surprisingly, the invention reduces the pressure medium leakage of a leakage-prone brake circuit in that this brake circuit is coupled to the pressure generator under given conditions and applied with brake pressure. The decoupling or coupling of the leaking brake circuit takes place by means of a corresponding electronic control of the leaking one

Plunger control valve assigned to the brake circuit.

drawing

An exemplary embodiment of the invention is illustrated with the aid of the figures and is explained in detail in the following description.

In this context, FIG. 1 shows the hydraulic circuit diagram of one of the

Invention underlying electronically slip-controllable

Power brake system. This hydraulic circuit diagram is disclosed in the earlier patent application DE 10 2018 212 016 together with a method on which the following invention is also based for testing the brake system for leaks.

FIG. 2a shows a section of a brake circuit according to this brake system

1 with a first brake circuit branch exhibiting a leak and an intact second brake circuit branch connected in parallel to it. The diagrams in FIG. 2b illustrate the leakage behavior of the individual components in the damaged brake circuit branch;

Figure 2c illustrates the total leakage of the brake circuit.

FIGS. 3a and 3b illustrate the invention with the aid of a representation of the first brake circuit branch, which is subject to leakage, with its two in series

switched directional control valves. The latter take place in Figures 3a and 3b

different valve positions.

Figures 4a and 4b are assigned to Figures 3a and 3b and

illustrate the total leakage of the brake circuit during

Pressure build-up or the pressure decrease phase by the pressure generator.

Description of an embodiment of the invention

The brake system 10 shown in Figure 1 is divided into a hydraulic unit 12 with wheel brakes 14 connected to it and a pressure medium reservoir 15 also connected to it. A total of four wheel brakes 14 are available, each of which is supplied with pressure medium in pairs via two existing brake circuits 16 and 18. In each case one of the two brake circuits 16; 18 of the brake system 10 is connected to one of a total of two pressure medium chambers 20; 22 one

Master cylinder 24 connected. The latter is also an example in

Hydraulic unit 12 housed. Each of the pressure medium chambers 20; 22 is in turn connected to the pressure medium reservoir 15. The master brake cylinder 24 can be actuated by the driver by means of an actuating device 26, exemplarily designed in the form of a pedal. For this purpose, the pedal is connected to a so-called rod piston 30 of the master brake cylinder 24 via a coupling rod 28.

The driver specifies a braking requirement by pressing the pedal. This braking request manifests itself in an actuation path of the coupling rod 28, which is determined by a first sensor device 32, which detects the actuation path of the coupling rod 28, and an electronic control unit 34 of the

Brake system 10 is supplied. The displacement of the rod piston 30 is transmitted to the floating piston 38 by a rod piston spring 36 with which the rod piston 30 is supported on a floating piston 38 of the master brake cylinder 24. The pressure medium chamber 20 of the master brake cylinder 24 assigned to the rod piston 30 is coupled to a simulator device 42 via a pressure medium connection controllable by a simulator control valve 40, in which the pressure medium displaced from the pressure medium chamber 20 of the master brake cylinder 24 is buffered when the pedal is actuated. When the simulator control valve 40 is open, an actuation path of the pedal can be displayed by means of the simulator device 42.

The two pressure medium chambers 20 and 22 of the master cylinder 24 are each connected to one of the brake circuits 16; 18 controllably connected. Electronically controllable circuit isolation valves 44 are provided to control the two pressure medium connections. In the normal operating state of the brake system 10 (not shown), the connection of the pressure medium chambers 20 and 22 to the brake circuits 16; 18 interrupted by the circuit separation valves 44 and the pressure medium connection of the pressure chamber 20 with the simulator device 42 is open.

A braking pressure proportional to the braking request or the pedal travel issued in the brake circuits 16; 18 is in the normal operating state of the brake system 10 by a pressure generator 50 and others. provided as a function of the signal of the sensor device 32. To this end, the pressure generator 50 is parallel to the master brake cylinder 24 with the brake circuits 16; 18 contacted. According to FIG. 1, a plunger device serves as a pressure generator 50, in which a plunger piston 52 is driven to a linear movement by a controllable motor 54 via a gear 56 connected downstream. This pressure generator 50 displaces pressure medium from a plunger working space 58 into the two brake circuits 16; 18 inside. Electronically controllable

Plunger control valves 60 are provided to clear existing connections between the brake circuits 16; 18 and the pressure generator 50 to control. With these

Plunger control valves 60 are electronically controllable, normally blocking switching valves which each control two pressure medium connections.

Downstream of the plunger control valves 60 and the circuit isolation valves 44, the brake system 10 has what is known as a pressure modulation device. For each connected wheel brake 14, this consists of an associated electronically controllable pressure build-up valve 62 and a similar one

Pressure relief valve 64. The pressure build-up valves 62 are controllable, normally open directional control valves for controlling two pressure medium connections each, which can be brought into a blocking division by electronic control, while the pressure relief valves 64, on the other hand, act as directional control valves for controlling two Pressure medium connections are formed which can be switched from a blocking division into an open position by electronic control. Pressure build-up valves 62 and pressure reduction valves 64 enable appropriate electronic

Activation of an adaptation of the wheel brake pressure prevailing in the individual wheel brakes 14 to the slip conditions on the respectively assigned wheel.

Pressure-controlled check valves 78 are connected in parallel to the pressure build-up valves 62. These check valves 78 control a bypass, which creates a direction-dependent flow around the pressure reduction valves 64. If a higher pressure is applied to the pressure medium connection of a check valve 78 facing the pressure generator 50 than to that facing a wheel brake 14

Pressure medium connection, the check valves 78 assume their blocking divisions. Conversely, the check valves 78 allow a flow around the

Pressure build-up valve 62 when the pressure level on the wheel brake side

Pressure medium connection 14 is higher than the pressure medium connection on the pressure generator side. The task of the check valves 78 is to enable a pressure reduction in the wheel brakes 14 as quickly as possible at the end of a braking process.

When the braking process is in progress, slip occurring on one of the wheels is detected by assigned wheel speed sensors 70 on the basis of a decreasing wheel speed. If a wheel threatens to lock, the brake pressure is reduced by opening the relevant pressure reduction valve 64 and, as a result, a

Pressure medium outflow from the wheel brake 14 into a return 46 leading to the pressure medium reservoir 15.

To regulate the brake pressure in the wheel brakes 14, the brake system 10 is equipped with further sensor devices. A sensor device 72 detects the brake pressure of the brake circuits 16; 18, additional sensor devices 74; 76 evaluate the drive of the pressure generator 50 or the actuation path of the plunger 52. The signals of the sensor devices 70-76 are the electronic

Control unit 34 is supplied, which sends a variable control signal to the motor 54 of the pressure generator 50 and to the explained valves 40; 44; 60; 62; 64 calculated.

In the first branch 16a of the first brake circuit 16 shown in FIG. 2a, the plunger control valve 60 or the first directional valve is located downstream of the pressure generator 50 in the non-actuated basic position and thus blocks the pressure medium connection from pressure generator 50 to wheel brake 14. The pressure build-up valve 62 or the second directional control valve of this branch 16a placed downstream of this plunger control valve 60 is electronically actuated and thereby also assumes its blocking division. The pressure medium connection from the pressure generator 50 to the wheel brake 14 is thus blocked twice and thus pressure medium cannot flow through it. As a result of a leak 80 in this first branch 16a between the second directional or pressure build-up valve 62 and the wheel brake 14, no pressure medium escapes in principle.

In contrast, in the illustrated second branch 16b of this brake circuit 16, the first directional or plunger control valve 60 facing the pressure generator 50 is electronically controlled and assumes its open position, while the second directional or pressure build-up valve 62 facing the wheel brake 14 is in the basic position and is thus also flowed through. There is no leak in the second branch 16b, so that a brake pressure build-up in the associated wheel brake 14 can be carried out by the pressure generator 50 by displacing pressure medium into this second branch 16b.

The two diagrams in FIG. 2b are assigned to the first branch 16a of the first brake circuit 16, which has the leak 80, and provide that

Leakage behavior of the two directional control valves in their positions shown in Figure 2a. The leakage characteristic curves 96a and 96b show the

Pressure medium leakage 82 at the corresponding directional control valve via the pressure 84 applied in each case to the directional control valve. A vertical line in the diagram

illustrates a so-called limit pressure 86. This limit pressure 86 can be specified by the dimensioning and structural design of the respective first directional or plunger control valve 60, in particular its closing element, its valve cross-section and its resetting device. The

Leakage characteristic curve 96a of plunger control valve 60 rises with a relatively high gradient as soon as the pressure applied to this plunger control valve 60 increases compared to the limit pressure 86 shown. Reason this

Valve behavior is that the hydraulic forces acting on the closing body have an opening effect and exceed counteracting, closing mechanical forces as soon as this limit pressure 86 is exceeded.

In contrast to this, the second directional or pressure build-up valve 62 shows a leakage characteristic curve 96b, which is below the limit pressure 86 in its course resembles a parabola open at the bottom in the diagram. This leakage characteristic is due to the check valve 78, which is connected in parallel to the second directional control valve and which is activated when there is a contact and from

Pressure generator 50 blocks pressure gradient acting in the direction of the wheel brake 14. However, a reliable blocking effect of this check valve 78 presupposes that a minimum force acts on a closing element of the check valve 78 in the blocking direction. This minimum force is achieved, for example, when a pressure equal to the limit pressure 86 of the plunger control valve 60 is applied to the check valve 78. At a pressure that is lower than this limit pressure 86, the blocking effect of the check valve 78 is accordingly imperfect and pressure medium can consequently flow around the second directional control valve 62 via the check valve 78.

The total leakage 96c in the brake circuit 16 resulting from the two leakage characteristic curves 96a and 96b according to FIG. 2b shows the diagram according to FIG. 2c. If the pressure in the brake circuit 16 is below the limit pressure 86, no leakage occurs since the plunger control valve 60 reliably blocks in this pressure range, as explained. Above the limit pressure 86 this is

Plunger control valve 60, however, overflows for the reasons explained and allows pressure medium to pass. Due to the initially low open

Control cross-section and the thus high throttling effect of the plunger control valve 60, the pressure loading the check valve 78 in the closing direction is so low that its blocking effect is not sufficient for a reliable blocking of the pressure medium connection to the wheel brake 14. Consequently, the flow around the second directional or pressure build-up valve 62. As a result, at pressures above the limit pressure 86, pressure medium can nevertheless advance to the leak 80 and exit the brake system 10. According to FIG. 2c, this pressure medium leakage assumes its maximum volume when the pressure in the brake circuit 16 is beyond the limit pressure 86. If the circuit pressure increases further, this pressure medium leakage goes back to zero, because then the forces acting on the check valve 78 closing are large enough to ensure its blocking effect.

These relationships change when the defective brake circuit 16 having the leak 80 is controlled in such a way that its two directional control valves connected in series with one another are those shown in FIGS. 3a and 3b

Take valve positions. The positions according to FIG. 3a are taken by the directional control valves during a pressure build-up phase by the pressure generator 50, if the pressure in the defective brake circuit 16; 18 is between 0 and a lower range limit of a hysteresis range 88 around the limit pressure 86 of the plunger control valve 60 facing the pressure generator 50 or if the pressure in the brake circuit 16 is between 0 and an upper range limit of the pressure generator 50 during a pressure reduction phase

Hysteresis range 88 is around the limit pressure 86 of the plunger control valve 60.

In contrast, FIG. 3b shows the position of the directional control valves during a pressure build-up phase by the pressure generator 50 when the pressure in the brake circuit 16 is between the lower limit of the hysteresis area 88 around the limit pressure 86 of the plunger control valve 60 and a maximum pressure that can be represented by the pressure generator 50 or during a pressure reduction phase the pressure generator 50 when the brake pressure in the brake circuit 16 is between an upper range limit of the hysteresis range 88 around the limit pressure 86 of the plunger control valve 60 and that deliverable by the pressure generator 50

Maximum pressure is.

According to Figure 3a, the directional control valves are initially controlled as in

Explained in connection with the description of FIG. This

Valve positions are maintained until the pressure in the brake circuit 16 approaches a lower range limit 88a of a hysteresis range 88 around the limit pressure 86. In this area, the first directional or plunger control valve 60 reliably seals the brake circuit 16 from the wheel brake 14. Reached or

If the pressure of the pressure generator 50 exceeds the lower range limit 88a of the hysteresis range 88 by the limit pressure 86 of the plunger control valve 60, according to the invention, the plunger control valve 60 is activated by the electronic one

Control device 34 activated and brought into its open position (Figure 3b).

The now open plunger control valve 60 reduces its throttling effect, so that the pressure of the pressure generator 50 acts almost unreduced on the check valve 78 connected parallel to the pressure build-up valve 62 and the effective pressure thereby ensures its blocking effect.

When the pressure is reduced by the pressure generator 50, the plunger control valve 60 according to FIG. 3b is electronically controlled and thus held in its open position until the pressure of the pressure generator 50 has reached an upper range limit 88b of the hysteresis range 88 around the limit pressure 86 of the plunger control valve 60. Now the control is this Plunger control valve 60 is withdrawn so that it returns to the blocking division shown in FIG. 3a.

A hysteresis range 88 with the lower and upper range limits 88a and 88b around the limit pressure 86 of the first directional or plunger control valve 60 is advantageously provided in order to avoid that at pressure values close to the specified limit pressure 86 of the plunger control valve 60 due to alternating electronic control between its blocking division and its open position switches back and forth with high frequency and thereby undesirably causes disturbing noises or is exposed to thermal or mechanical overload.

Figure 4a shows in connection with the above explanations

Leakage characteristic 96d of the brake circuit 16; 18 during a pressure build-up by the pressure generator 50 and FIG. 4b represents the leakage characteristic 96e of this brake circuit 16; 18 during a pressure reduction by the pressure generator 50.

According to Figure 4a occurs when pressure builds up in the brake circuit 16; 18 to

Reaching the lower range limit 88a of the hysteresis range 88 by the

Limit pressure 86 of the plunger control valve 60 no pressure medium leakage in a damaged brake circuit 16; 18 on. The pressure medium leakage then increases

suddenly to a low maximum value when the pressure in the brake circuit 16; 18 the lower range limit 88a of the hysteresis range 88 around the

Limit pressure 86 of the plunger control valve 60 has reached and goes on

subsequently, that is to say with a further increasing pressure in the brake circuit 16; 18, steadily back to 0.

In contrast, when the pressure is reduced by the pressure generator 50, a slight leakage of pressure medium occurs only when the pressure in the brake circuit 16;

18 lies between the limit pressure 86 of the plunger control valve 60 and the upper range limit 88b of the hysteresis range 88 around this limit pressure 86.

The maximum pressure medium leakage is reached when the pressure in the brake circuit 16;

18 corresponds to the pressure of the upper range limit 88b. With falling pressure in brake circuit 16; 18 the pressure medium leakage then goes as shown in one

steady curve back to 0.

The explained control of the plunger control valves 60 takes place when required by the electronic control device 34 of the brake system 10. This electronic control device 34 is equipped with a first device 90 (Figure 1), which the Brake circuits 16, 18 checked for leaks and thus any leakage that may occur in one of the brake circuits 16; 18 notices. The brake circuit 16 having a leak; 18 is decoupled from the first device 90 from the pressure generator 50 in that the brake circuit 16; 18 associated plunger control valve 60 is controlled in such a way that it assumes its blocking division. With regard to the further functioning of this first device 90, reference is again made at this point to the disclosure in the earlier patent application DE 10 2018 212 016.

In addition, the electronic control unit 34 is equipped with a second device 92 (FIG. 1) which is designed to compare the level of the pressure generated by the pressure generator 50 with electronically stored pressures. This

To this end, device 92 evaluates the values present in the brake system 10

Pressure sensor 72 delivered signals and compares these signals with im

Signals stored in control unit 34, which represent the limit pressure 86 of the first paths or plunger control valves 60. The aim is to determine whether the pressure of the pressure generator 50 exceeds the predetermined limit pressure 86 of the

Plunger control valve 60 exceeds. Furthermore, in this second device 92 of the electronic control device 34, the lower and upper

Range limit 88a; 88b of the explained hysteresis range 88 around this limit pressure 86 of the first directional or plunger control valve 60 can be stored.

A third device 94 (FIG. 1) also present in the electronic control unit 34 is designed to move the first directional or plunger control valve 60 closest to the pressure generator 50 at least indirectly into its open position if there is a leak from the first device 90 of the electronic control unit 34 is established in a brake circuit 16, 18 and the pressure generated by the pressure generator 50 has at least approximately reached or exceeded the limit pressure 86 of the plunger control valve 60.

As a result, the explained devices 90 - 94 of the electronic control unit 34 significantly reduce the pressure medium leakage that occurs in a damaged brake circuit 16, 18 compared to the prior art.

Of course, further changes or additions to the

described embodiment conceivable without departing from the basic idea of

Invention deviate.

Claims

Expectations:

1. Electronically slip-regulated external power brake system for a motor vehicle with a controllably driven pressure generator (50), several parallel to one another connected to the pressure generator (50)

Brake circuits (16, 18) per brake circuit (16; 18) each have an electronically controllable first

Directional control valve (60) for separating the brake circuit (16; 18) from the pressure generator (50) and an electronically controllable second directional control valve (62) arranged downstream of the first directional control valve (60) for controlling the brake pressure in one with the brake circuit (16; 18) coupled wheel brake (14) and with an electronic control device (34) controlling the pressure generator (50) and the directional control valves (60; 62), characterized in that the electronic control device (34) is equipped with a first device (90), which is designed to check the brake circuits (16; 18) for leaks and, if a leak is detected, at least indirectly to decouple it from the pressure generator (50), a second device (92) which is designed to compare signal variables representing pressures with one another and with a third device (94), which is designed to bring the first directional control valve (60) of a brake circuit (16; 18) into an open position when a Leak in this brake circuit (16; 18) is established and a pressure built up by the pressure generator (50) has at least approximately reached or exceeded a limit pressure (86) of the first directional control valve (60) of this brake circuit (16; 18).

2. Electronically slip-controlled external power brake system according to claim 1, characterized in that

that the first directional valve (60) by the application of pressure medium under an actuation pressure which is higher than a definable limit pressure (86) of this first directional valve (60) or by electronic control by the electronic control unit (34) from a normally closed basic position into a Position can be moved in which the first directional valve (60) can be flown through by pressure medium.

3. Electronically slip-controlled external power brake system according to claim 1 or 2, characterized in that

that a pressure-actuated check valve (78) is connected in parallel to the second directional valve (62), which has a locking pitch in the direction from the pressure generator (50) to the wheel brake (14) and that in the direction from the wheel brake (14) to the pressure generator (50) for Pressure medium is permeable.

4. Electronically slip-controlled external power brake system according to one of the

Claims 1 to 3, characterized in that

that a hysteresis range (88) around the limit pressure (86) of the first directional control valve (60) is stored in the electronic control unit (34) and

that the third device (94) of the electronic control unit (34) is designed to bring the first directional control valve (60) of the brake circuit (16; 18), which has a leak, at least indirectly into the open position when pressure builds up through the Pressure generator (50) a lower range limit (88a) of the hysteresis range (88) around the limit pressure (86) of the first directional control valve (60) has been reached or exceeded.

5. Electronically slip-controllable external power brake system according to claim 4, characterized in that

that the third device (94) of the electronic control unit (34) is designed to bring the first directional control valve (60) of the brake circuit (16; 18), which has a leak, at least indirectly into the blocking division when the pressure generator drops the pressure (50) an upper range limit (88b) of the hysteresis range (88) around the limit pressure (86) of the first directional control valve (60) has been reached or fallen below.