DE4022481A1 - HYDRAULIC MULTI-CIRCUIT BRAKE SYSTEM - Google Patents

Abstract

The heavy vehicle has separate front and rear wheel brake circuits and an ABS control. The rear wheel brakes (13,14) are linked to the brake system by proportional control valves (31,32) which provide an increasing brake force with increasing rear axle loads. These valves are bridged by the ABS control valves (43,44) which prevent rear wheel locking. - For normal operation the increasing loading results in increasing brake effect from the rear wheels. This relieves the front wheel brakes from excessive braking effort. If the rear wheel brakes start to lock, the normal ABS system protects the vehicle. The load regulators are mounted near the rear suspension, as are the proportional valves.

Description

Such brake systems are particularly in connection with known large heavy commercial vehicles, where the adaptable of the brake force distribution to a current axle load distribution due to the strongly changing loading conditions of such vehicles is of particular importance. The same applies to Off-road vehicles, often used as commercial vehicles be, but also in the field due to the topographical ver ratios, - steeply rising or falling terrain - subject to significant changes in the axle load distribution are. In order to have a higher rear axle To be able to utilize the braking force component than when the vehicle is unladen are, as related ratio actuators brake force controller - braking force reducer or limiter - in use (Ate, brake manual, 9th edition, 1986, pages 222 to 259), which automatically depends on the load, e.g. B. on the deflection state of the rear axle suspension appealing, a switchover the braking system to different values of a permanently installed Allow braking force distribution, such that when difficult loaded vehicle a higher proportion of rear axle braking force is exploitable, the design of such braking force regulator is that the dynamic braking behavior of the vehicle remains stable in the entire braking range, d. H.  the rear axle braking force share, the same coefficient of adhesion provided on the rear and front axles, never is "above" the parabola of the ideal braking force distribution and at most with the critical vehicle deceleration of the ideal braking force distribution corresponds. In practice means this in the partial braking area to a high proportion of poss brake power delivery on the rear axle can be dispensed with must, which in turn leads to the fact that the front brakes are relative are more heavily loaded than the rear brakes and therefore essential must be trained more stable, in other words, that the front brakes could be spared if the Rear wheel brakes are more powerful for braking the vehicle in the part braking range could be used, this also applies if the vehicle is out with an anti-lock braking system (ABS) is equipped, as this, stable braking force distribution in the first assuming the meaning explained, only responds if lower adhesion coefficients on the rear wheels between the road and the braked vehicle wheels are available as on the front axle and thus normally, d. H. if the ABS does not respond or only responds to the more braked front wheels, an increased contribution of the rear wheel brakes to the braking force loss tion is not possible.

The object of the invention is therefore to provide a hydraulic multi-circuit Braking system of the type mentioned to verbes to that effect learn that even in the partial braking area increased contributions of the rear wheel brakes can be used to brake the vehicle.

This object is achieved by the characterizing Part of patent claim 1 mentioned features solved.

Advantages that are clearly achieved by these features are at least the following:
If the ABS is ready for operation, a significantly higher proportion of the rear axle braking force can be used in the partial braking area by using the brake force distribution provided for the heavy load of the vehicle, since if the rear axle were ever braked, an otherwise unstable dynamic state would result of the vehicle can be "adjusted" as it were by the ABS on the rear axle. For a given operating force, which the driver controls via a brake pedal, increased rear-axle braking force components can be used and a more even - situation-appropriate - distribution of the braking force components can be achieved, which reduces brake wear on the front axle and thus increases the overall stability of the brake system.

If, as provided according to claim 2, two the rear brakes individually assigned ratio actuators and bypass flows mungspaths are provided, this ratio-Stell be arranged in the immediate vicinity of the wheel brakes and with the vehicle spring via small levers or linkages tion be functionally coupled. This design is for vehicles Suitable with any brake circuit division.

This is compared according to the features of claim 3 in a vehicle in which the rear brakes to a Hin terachs brake circuit are summarized, a significant structural Simplification achieved because a ratio actuator as it were can be "saved".

In combination with this, alternative features of inserting the ratio actuator into the brake system are indicated by the features of claims 4 and 5:
If, as provided in accordance with claim 6, the basic position of the respective bypass control valve is the one in which the bypass flow path is blocked and thus the respective ratio actuator is effective in terms of reducing the rear axle braking force, the bypass control valve must with each braking - functional ABS provided - be controlled in its functional position bridging the ratio actuator, ie much more frequently than if the basic position of the bypass control valve were its bridging position. This frequent switching of the bypass control valve reduces the probability that this valve could get stuck in its basic position.

In combination with this is due to the features of claim 7 a simple way of generating a for controlling the bypass Control valve appropriate signal specified.

The features of claim 8 are simple, alternative Design options for blocking and releasing the bypass Flow path suitable solenoid valves specified, the Design of a 3/2-way solenoid valve has the advantage that the Ratio actuator has no effect on the brake circuit can unfold.

At least that or the bypass control valve (s) is / are without can also be integrated into the hydraulic unit of the ABS. This applies if there is a "remote control" of the ratio actuator is also provided for this.

One in combination with the different designs of the Multi-circuit braking system is provided switchability of the ABS particularly advantageous for off-road vehicles, so with a Braking the vehicle on a loose surface, e.g. B. on sand  or a gravel road, otherwise the anti-lock braking system subject vehicle wheels can be locked and as a result, seen in the direction of movement of the vehicle, in front of the blocked wheels, a brake pad, as it were pushed underground material can build up what in a such a braking situation is usually a much better one Vehicle deceleration results as if the vehicle wheels - with limited brake slip due to the anti-lock control can still roll the ground.

Further details and features of the invention emerge from the following description of specific embodiments play with the drawing. Show it:

Fig. 1 shows a first embodiment of a brake system according to the invention with two the rear wheel brakes, each individually associated actuators ratio and bypass Strö mung paths,

Fig. 2 and 3 alternative designs and circuitry suitable for controlling a bypass flow path and the solenoid valves

Fig. 4 shows another embodiment for a vehicle with front axle / rear axle brake circuit division and only one ratio actuator with lockable bypass flow path.

In Fig. 1, a road vehicle is represented by a total designated 10 hy metallic dual-circuit braking system, which is intended for use in which very different axle and / or wheel load distributions can occur, for. B. a commercial vehicle, in which due to different loading conditions correspondingly varying axle loads and axle load distributions can occur, or an off-road vehicle, which can also result in drastically different axle load distributions when driving uphill and downhill in steep terrain.

In the brake system 10 , which for a vehicle with uniaxial, for. B. rear axle drive as well as for a vehicle with all-wheel drive is equally suitable, the front brakes 11 and 12 are combined to form a front axle brake circuit I and the rear wheel brakes 13 and 14 to form a rear axle brake circuit II. The two brake circuits I and II are designed in the illustrated embodiment as static brake circuits, for the brake pressure supply of which is designed as a tandem master cylinder, generally designated 16 brake device, which can be actuated by means of a brake pedal 17 via a brake booster 18 . The front-axle brake circuit I is of the brake unit joined attached to the primary output pressure chamber 19 16, which is of the brake unit 16 to which the Hinerachs brake circuit is connected II, pressure-tight against the secondary output pressure chamber 21 by a floating piston 22 of the brake unit 16 movable demarcated , on the primary piston 23 , which engages - by means of the brake booster 18 - increased actuation force, which is controlled by the driver via the brake pedal 17 .

The vehicle is equipped with an overall designated 23 anti-lock system, which comprises a hydraulic unit 24 shown only schematically in FIG. 1 and an electronic control unit 26 , the processing of level and / or frequency, the information on the Dynamic behavior of the vehicle wheels containing electrical output signals to the vehicle wheels individually assigned wheel speed sensors 27 to 30 control signals for brake units provided as part of the hydraulic unit 24 of ABS 23 , not specifically shown, designed as solenoid valves, by means of which on the individual wheel brakes 11 to 14 in the control purpose corresponding sequence and combination of brake pressure reduction, brake pressure maintenance and brake pressure reduction phases of the anti-lock control can be controlled. The ABS 23 is, in terms of structure and function, assumed to be realized in a known manner and is therefore not considered to require further explanation. In order to enable stable dynamic braking behavior of the vehicle even when the axle load distributions are drastically different, even if the ABS 23 is not functional, or if the option provided for special braking situations exists, it should be switched off and, on the other hand, use with a stable one To enable dynamic braking behavior of the vehicle to be even more compatible with the maximum possible rear-axle braking force components, which are the higher, the larger - according to the load condition of the vehicle - the rear-axle load component, based on the vehicle weight G, are the rear-wheel brakes 13 in the exemplary embodiment shown in FIG. 1 and 14 of the vehicle individually assigned braking force regulators or limiters 31 and 32 are provided, which operate in a load-dependent manner, that is to say in dependence on the loading condition of the vehicle, as ratio actuators which operate the ratio B _VA / B _{H A} of the front axle braking force component B _VA / G related to the vehicle weight G to the rear axle braking force component B _HA / G also related to the vehicle weight G as a whole in such a way that for the various possible loading conditions of the vehicle when braking, a stable dyna mixing behavior of the vehicle. "Stable" in the sense used above means that the rear wheels of the vehicle may only be blocked if the front wheels have already reached the blocking state and if the critical value of the braking of the vehicle is exceeded, ie the braking force is increased above that value which corresponds to the ideal braking force distribution for a predetermined high value of the frictional connection between the roadway and the vehicle wheels (eg µ = 1).

"Ideal" in the sense used above means that the pair of values B _VA / G, B _HA / G corresponds to a point of the parabola of the ideal braking force distribution for the above-mentioned high adhesion coefficient, which is applied to the braked by the same adhesion utilization Front and rear wheels of the vehicle is determined.

As related B _VA / B _HA ratio actuators - known per se - brake force regulators or limiters are provided which, depending on the deflection state of the rear axle suspension, ie depending on the axle load or the individual wheel loads, reduce the braking force or Convey limitation in that at lower rear wheel or rear axle loads, the brake pressure with which the rear wheel brakes 13 and 14 can be acted upon is lower than with higher wheel or axle loads, such that stable dynamic behavior in each case with full braking of the vehicle is guaranteed.

Suitable brake force regulators or limiters are the "brake Manual ", Alfred Tewes GmbH, 9th edition, 1986, Bartsch-Verlag, Ottobrunn near Munich, pages 122 to 259, whereupon, to explain such braking force regulator or limiter For the sake of simplicity.

In the exemplary embodiment shown in FIG. 1, the two ratio actuators 31 and 32 are connected between the rear wheel brakes 13 and 14 and the pressure outputs 33 and 34 of the hydraulic unit 24 of the ABS 23 assigned to them . The ratio actuators 31 and 32 thus lie, as it were, in the brake line branches 36 and 37 leading from the hydraulic unit 24 to the wheel brakes 13 and 14, and the branching point 38 of the main brake line 39 shown in the exemplary embodiment shown as arranged in the hydraulic unit 24 of the ABS 23 of the rear axle brake circuit II and are guided within the hydraulic unit 24 via brake pressure control valves (not shown) assigned to the rear wheel brakes 13 and 14 .

In combination with the two ratio actuators 31 and 32 , a respective to the respective actuator 31 or 32 hydraulically connected in parallel bypass flow path 41 and 42 is easily seen, each by means of a solenoid valve designed as a control valve 43 and 44 , controlled by electrical Output signals of the electronic control unit 26 can be released individually or together and - alternatively - can be blocked.

The control of these solenoid valves 43 and 44 is such that the bypass flow paths 41 and 42 are released when the ABS 23 is ready for operation, in which case the ratio actuators 31 and 32 are bridged, ie ineffective, and that the bypass flow paths 41 and 42 are locked if the ABS 23 , be it due to a defect or if it has been switched off, is not ready for operation, in which case the stable dynamic braking behavior of the same mediating brake force distribution is effective when the vehicle is not loaded.

The solenoid valves 43 and 44 in the embodiment shown in FIG. 1 are designed as 2/2-way valves, for which it is assumed that they are in each case from their basic position 0 into their excited position I by a high-level output signal of the electronic control unit 26 are switchable.

For the right rear wheel brake 14 , a design of its bypass control valve 44 is shown, in which its basic setting 0 is the flow position in which the ratio actuator 32 is bridged by the bypass flow path 42 . This valve 44 must therefore be switched into its blocking position I when the ABS 23 has failed or is switched off.

A related control signal can be obtained in a simple manner, as shown in simplified form in the right part of FIG. 1, as the output signal of an AND gate 46 , which has a first, non-negated input 47 , at which the brake system 10 is actuated when High-level output signal emitted output signal of the brake light switch 48 is present, and a second, negated input 49 , to which an output signal from the electronic control unit 26 is supplied, which, as long as the ABS 23 is functional, is present as a high-level signal.

In the design and configuration of the 2/2-way solenoid valve 44 shown for the bypass flow path 42 of the right rear wheel brake 14 described type of its control, this solenoid valve 44 is only rarely activated in practice and is therefore only exposed to slight wear.

In the design of the bypass control valve 43 provided for the bypass flow path 41 of the left rear wheel brake 13 , its basic position 0 is the blocking position. This Magnetven valve 43 must therefore, if and as long as the output signal of the elec tronic control unit 26 is present, that the ABS 23 is functional, with each braking in its excited position I, its flow position are switched. The appropriate control signal for the solenoid valve 43 can therefore be obtained in a simple manner as the output signal of an AND gate 51 which has two non-negated inputs 52 and 53 , with the one input 53 the brake light switch output signal and the other input of this AND Links 51 the output signal from the electronic control unit 26 is supplied, which indicates that the ABS 23 is functional. With this design and type of control of the solenoid valve 43 , this is always in its excited position I, its flow position, switched when the brake system is actuated and the ABS 23 is functional. It is thereby switched much more frequently than the solenoid valve 44 shown for the right rear wheel brake 14 .

It is understood that of the two described design and control types for a real vehicle only one is realized.

These two types of control of the bypass control valves are also possible if instead of 2/2-way solenoid valves 43 and 44 3/3-way solenoid valves 44 'and 45 ' are used, as the detailed representations of Fig. 2 and 3 entnehm bar.

In the embodiment shown in FIG. 2, the 3/2-way solenoid valve 44 'between the pressure output 52 of the ratio actuator 31 or 32 and the wheel brake 13 and 14 connected to it. Its basic position 0 is the flow position, in which the ratio actuator 31 or 32 is bridged by the bypass flow path 41 or 42 , but the wheel brake 13 or 14 against the output 52 of the ratio actuator 31 or 32 is cordoned off. Its excited position I is an alternative flow position, in which the pressure output 52 of the ratio actuator 31 or 32 is connected to the connected wheel brake 13 or 14 , but this is blocked against the bypass flow path 41 or 42 .

The solenoid valve 44 'of FIG. 2 is controlled in the same way as the solenoid valve 44 of FIG. 1st

In the embodiment shown in FIG. 3, a 3/2-way solenoid valve 45 'is also provided as a bypass control valve, which, viewed in relation to the ratio actuator 31 or 32 , is arranged on its input side. Its basic position 0 is its flow position, in which the ratio actuator 31 or 32 is effective in terms of reducing the braking force and the bypass flow path 41 or 42 is blocked against the connected wheel brake 13 or 14 . His excited position I is a flow position, in which the ratio actuator bridges 31 and 32 and its input 53 is blocked against the supplying brake line branch 36 and 37, respectively. The 3/2-way solenoid valve 45 'shown in FIG. 3 is controlled in the same way as for the 2/2-way solenoid valve 43 explained with reference to FIG. 1.

It is understood that the solenoid valve 45 'with the type of control described with reference to FIG. 3, as described with reference to FIG. 2 for the solenoid valve 44 ', could be arranged on the output side of the ratio actuator 31 or 32 . Likewise, a 3/2-way solenoid valve 44 ', as explained with reference to FIG. 2 in terms of design and function, could also be arranged on the input side of the ratio actuator 31 or 32 , as for the solenoid valve 45 ' with reference to FIG. 3 explained.

If, as explained with reference to FIG. 1, two ratio actuators 31 and 32 are provided, it is expedient to arrange them in the immediate vicinity of the suspension suspension elements arranged in the vicinity of the rear wheels of the vehicle, in order to reduce the ratio -Actuators 31 and 32 einwir kende, for detecting the spring travel, ie the axle or wheel loads provided transmission elements - z. B. swivel levers, transmission linkage or the like - can be made as simple and small as possible.

If the ABS 23 works on the rear axle with common control of the brake pressure on both rear wheel brakes 13 and 14 , and accordingly the hydraulic unit 24 '( FIG. 4) has only one pressure output 54 , to which the branching point 56 to the rear wheel brakes 13th and 14 branching section 57 of the main brake line 39 of the rear axle brake circuit II is connected, in which, when the ABS 23 is working, the controlled brake pressure prevails, a ratio actuator 58 is sufficient, which between these pressure output 54 of the hydraulic unit 24 'of the ABS 23 and the branching point 56 is switched in order to influence the brake pressure jointly as a function of the axle load in the two rear wheel brakes 13 and 14 , if required. The bypass flow path 59 parallel to this ratio actuator 58 can be realized in one of the ways described with the aid of FIGS . 1 to 3 and, in the exemplary embodiment shown, can be released and blocked in a controlled manner by means of a 2/2-way solenoid valve 43 ', which is the according to FIG. 1 for the left rear wheel brake 13 of FIG. 1 and analog designed in the hydraulic system is inserted.

A in the case of failed or switched off ABS 23 influencing the brake pressure in the rear axle brake circuit II ratio actuator 58 ', as shown in dashed lines in Fig. 4, also between the rear axle brake circuit II assigned pressure output 61 of the braking device 16 and the hydraulic unit 24th 'Of the ABS 23 can be switched, the bypass flow path 59 ' parallel to the ratio actuator 58 ', which can be shut off by means of a 3/2-way valve 45 ' according to FIG. 3 which can be controlled analogously to the 3/2-way valve and can be released, can again be implemented in one of the ways explained above.

This insertion of the ratio actuator 58 'between the brake device and the hydraulic unit 24 ' of the ABS 23 is particularly advantageous if the vehicle is also provided with a traction control system (ASR) which acts on the rear wheels, which are assumed to be driven.

The variants explained with reference to FIG. 4 of the insertion of the ratio actuator 58 or 58 'in the brake system 10 inevitably require that the ratio actuator 58 or 58 ' are arranged away from the suspension elements of the rear axle suspension and therefore transmission elements are provided must, by means of which the axle load can be detected and used as a manipulated variable for the ratio actuator.

This is easy if the vehicle is provided with a hydraulic level control device, the pressure of which is a measure of the rear axle load of the vehicle. In this case, a pressure-controlled brake force regulator can be used as the ratio actuator 58 or 58 ', the pressure in the level control system being fed as the control pressure.

It is also possible to provide electrical position sensors that detect the - load-dependent - deflection state of the rear axle and to control an electromechanical actuator with their output signal (s), which acts on the ratio actuator 58 or 58 '. By means of hydraulic or electrical, optionally also mechanical, for. B. as Bowden cables realized transmission and control elements controllable ratio actuators, including those provided for the control of the release and shutoff of the bypass flow paths, magnetic valves, can be integrated into the hydraulic unit 24 'of the ABS 23 .

Claims (8)

1. Hydraulic multi-circuit brake system, in particular dual-circuit brake system for a road vehicle, which is provided with an at least least on the rear brakes of the vehicle anti-lock braking system (ABS) and with at least one ratio actuator comprising brake force distribution control device , which, depending on the load condition of the vehicle, increases the rear axle braking force proportion at least when a threshold value of the rear axle load proportion is exceeded, characterized in that in parallel hydraulic connection with the ratio actuator ( 31 , 32 ; 58 , 58 ′) a bypass flow path ( 41 , 42 ; 59 , 59 ') is provided which can be released and shut off by means of a solenoid valve ( 43 , 44 ; 43 ', 44 '; 45 '), and that this solenoid valve ( 43 , 44 ; 43 ', 44 '; 45 ') by a signal for functional ABS ( 23 ) characteristic in the bypass flow path ( 41 , 42 ; 59 , 59 ') released End function position is controllable or held in this and, in the event that the ABS ( 23 ) is not ready for operation or switched off, remains in the functional position blocking the bypass flow path ( 41 , 42 , 59 , 59 '). 2. Hydraulic multi-circuit brake system according to claim 1, characterized in that two the rear wheel brakes ( 13 and 14 ) each individually assigned ratio actuators ( 31 and 32 ) and bypass flow paths ( 41 and 42 ) are provided. 3. Hydraulic multi-circuit brake system, the rear wheel brakes are combined to form a rear axle brake circuit, characterized in that only one ratio actuator ( 58 , 58 ') is provided between the pressure output assigned to the rear axle brake circuit (II) ( 61 ) of the braking device ( 16 ) and the branching point ( 38 ; 56 ) from which the brake line branches ( 36 and 37 ) leading to the rear wheel brakes ( 13 and 14 ) are connected. 4. Hydraulic multi-circuit brake system according to claim 3, characterized in that the ratio actuator ( 58 ') between the braking device ( 16 ) and the hydraulic unit ( 24 ) of the ABS ( 23 ) is connected. 5. Hydraulic multi-circuit brake system according to claim 3, characterized in that the ratio actuator ( 58 ) between the hydraulic unit ( 24 ) of the ABS ( 23 ) and the branch point ( 56 ) is connected, from which to the rear brakes ( 13 and 14 ) outgoing brake line branches. 6. Hydraulic multi-circuit brake system according to one of claims 1 to 5, characterized in that the basic position ( 0 ) of the respective bypass control valve ( 43 , 43 '; 45 ') is the one in which the bypass flow path ( 41 and / or 42 ; 59 , 59 ′) is blocked. 7. Hydraulic multi-circuit brake system according to claim 6, characterized in that the bypass control valve ( 43 ; 43 '; 45 ') by a signal from an AND operation ( 51 ) of the functional ABS ( 23 ) with the at Brake actuation occurring brake light switch output signal obtained in its bypass flow path ( 41 and / or 42 ; 59 ; 59 ') opening excited position (I) is controllable. 8. Hydraulic multi-circuit brake system according to one of claims 1 to 7, characterized in that the bypass control valve is designed as a 2/2-way valve ( 43 , 44 , 43 '), by means of which the bypass flow path ( 41 , 42 , 59, ) can be shut off alone, or as a 3/2-way valve ( 44 ', 45 '), in the functional position of which opens the bypass flow path ( 41 and / or 42 ), the ratio actuator against the / the connected rear wheel brake (s) ( 13 and / or 14 ) continuing section of the main brake line of the rear axle brake circuit (II) or to the respective rear wheel brake ( 13 or 14 ) branching brake line branch ( Fig. 2) or against the Ratio actuator leading section of the main brake line or the respective brake line branch ( Fig. 3) is blocked.