WO1994010016A1

WO1994010016A1 - Braking system with antilock system and/or drive slip control

Info

Publication number: WO1994010016A1
Application number: PCT/EP1993/002746
Authority: WO
Inventors: Erhard Beck; Georg Sonnenschein
Original assignee: Itt Automotive Europe Gmbh
Priority date: 1992-10-24
Filing date: 1993-10-07
Publication date: 1994-05-11
Also published as: DE4236047A1

Abstract

A hydraulic system with an antilock system and/or a drive slip control has a master cylinder (2), electromagnetically controlled inlet and outlet valves (5, 6) for pressure modulation and a hydraulic pump (8) for returning the hydraulic fluid diverted during the diminishing phase of the braking pressure or for supplying an auxiliary pressure. The hydraulic valves (5, 6), in particular the inlet valve (5), are designed in such a way that when the valves are controlled by an alternative signal or by a pulse sequence whose frequency or whose pulse duration/pulse pause ratio is set to the valve characteristics, the valve armature (9) takes a dosing position. This dosing position, and therefore the opening of the valve, depends on the alternative or pulse control signal and on the pressure differential acting on the valve armature (9). The noises caused in particular during regulation by means of the inlet valve (5) are thus considerably reduced.

Description

Brake system with anti-lock and / or traction control

The invention relates to a hydraulic brake system with anti-lock and / or traction control, with a brake pressure transmitter, with electromagnetically actuable hydraulic valves which serve as inlet and outlet valves for modulating the brake pressure in the individual wheel brakes a hydraulic pump for returning the pressure medium derived from the wheel brakes in the brake pressure reduction phase or for auxiliary pressure supply, with sensors for obtaining the controlled variables and with an electronic circuit for processing the sensor signals and for generating brake pressure and pump control signals

It is already known to use electrically actuated inlet and outlet valves for modulating the pressure in the individual wheel brakes of a vehicle which is equipped with an anti-lock or traction control system. Suitable for this purpose are 2/2 way valves, that is hydraulic valves which only know two switching positions (open or closed). The desired pressure build-up or reduction gradient is achieved by activating the valves with pulse sequences and varying the pulse Permanent / pulse pause ratio reached. The inlet valve, which is inserted in the brake line between the brake pressure sensor or master cylinder and the wheel brake, is generally switched to passage in its rest position, while the outlet valve, which serves to reduce pressure, in the rest position, the pressure medium path to the return feed pump or to the surge tank locks.

Instead of the inlet / outlet valve pairs, valve arrangements with three switching positions (pressure build-up, pressure constant maintenance and pressure reduction) can of course also be used.

Of course, so-called proportional valves are also known which release a passage opening which is proportional to the control signal. The manufacturing effort for such valves is quite high.

A disadvantage of the known control with the aid of the fast switching valves is that the rapid armature movements, local deceleration and acceleration of the hydraulic fluid, transmission of the pulsation to components (structure-borne noise) etc. give rise to considerable noises which occur when a blockage occurs ¬ protection or traction control are perceived as disturbing. The noise level is significantly influenced by the pressure difference at the valve. Since this pressure difference across the inlet valve can become particularly high in certain situations, for example when the foot is strong and the road is smooth, the inlet valve in particular is a source of disturbing noises. The invention is based on the object of overcoming this disadvantage and reducing the noise resulting from the regulation of the pressure with the aid of the rapidly switching valves to a level which is no longer disruptive.

It has been shown that this object can be achieved with a brake system of the type mentioned at the outset, the special feature of which is that the inlet valve and / or the outlet valve are designed such that when the valve is actuated with an alternating signal or a pulse sequence, whose frequency or pulse duration / pulse pause ratio is matched to the characteristics of the valves (5, 6), the valve armature under the influence of the alternating signal or the pulse sequence and the hydraulic pressure or the pressure difference for the valve armature The duration of the control signal opens and assumes a dosing position that is dependent on the control signal.

According to an advantageous embodiment of the invention, the passage cross section of the valve is regulated by variation of the frequency or the pulse width and / or the pulse duration / pause ratio of the control signal.

By controlling the hydraulic valves, in particular the inlet valve, with a relatively high-frequency alternating signal or a high-frequency one During the pressure build-up phase, the valve armature is held in a middle position in a pulse sequence, in which a specific flow cross-section is released as a function of the control signal. Striking the valve armature in its end positions "open" and "closed" is avoided during the duration of the brake pressure modulation.

Another embodiment of the invention is that the coil, armature, magnetic core and air gap of the valve are designed such that the armature force in the working area is approximately proportional to the drive current or excitation current of the coil.

Further features, advantages and possible uses of the invention will become apparent from the following illustration of an exemplary embodiment with reference to the attached figure.

Show it:

1 shows a schematic simplification and partial representation of the most important hydraulic components of a brake system according to the invention and their hydraulic interconnection, and

2 shows in detail an exemplary embodiment of an inlet valve of the brake system according to FIG. 1.

To illustrate the invention, FIG. 1 shows only those components of an anti-lock device Played brake system that are required to explain the invention. The connection of a wheel brake 1 to a brake circuit I of a tandem master cylinder 2 of a hydraulic brake system is shown. The master cylinder 2 is actuated via an upstream vacuum booster 3 with the aid of a brake pedal 4. In the pressure medium path, which leads from the master cylinder 2 to the wheel brake 1, there is an inlet valve 5. Although this valve per se is a 2/2-way valve, it is operated according to the invention as a metering valve, as will be described below. In the rest position, this valve is switched to passage, with permanent excitation - in certain control phases - it assumes its blocking position.

The invention is illustrated here on the basis of a so-called “closed” hydraulic system. The pressure medium derived from the wheel brake 1 in the pressure reduction phase via an outlet valve 6 is fed back via a return pump 8 into the brake circuit I or into the master cylinder 2 and into the wheel brake 1. In an "open" hydraulic system, as is known, the pressure medium derived from the wheel brake 1 in the pressure reduction phase would first reach a pressure compensation tank to which the suction side of a hydraulic pump, which in such a case serves to supply auxiliary pressure, would also be connected.

In the closed system shown, there is a low-pressure accumulator 7 at the outlet of the outlet valve 6 Connected, which initially receives the pressure medium discharged via the outlet valve 6 at the beginning of an anti-lock control process or a pressure reduction phase before the pressure medium is then returned by means of the return pump 8. The low-pressure accumulator 7 is used in particular to increase the pressure reduction rate in the start-up rabbit of the hydraulic pump 8.

The construction of a hydraulic valve serving as inlet valve 5 is shown in FIG. 2. A longitudinal section through the valve is shown. It essentially consists of a valve armature 9, which is arranged axially displaceably in a valve housing 10. A valve tappet 11 is part of this armature 9. The armature 9 with the valve tappet 11 is held in the position shown, which is its rest position, by the force of a coil spring 12. In this rest position there is a hydraulic connection from a hydraulic connection or input 13 to an output _. 14; the connection 13 leads to the master cylinder 2, the output to the wheel brake 1 (see FIG

The valve shown has a valve actuation coil 15 and a magnetic core 16. The valve armature 9 and the magnetic core 16 are separated by an air gap 17, the design of which is essential for the valve characteristics. Due to the indicated, partly axial, partly radial course of the air gap 17, an approximately linear dependence of the force exerted on the armature when the coil 15 was excited was dependent on the exciter. - 1 -

Current reached. Construction measures for valves of this type are known. The electrical valve connections are designated 15a and 15b.

When the valve or the valve coil 15 is actuated, a force is exerted on the valve armature 9, which leads to the axial displacement of the valve tappet and thus to a reduction in the cross-sectional area of the valve 18. In the end position 17, the valve tappet sits on and thereby closes the pressure medium path from the inlet 13 to the outlet 14. The valve seat geometry indicated in FIG. 2 is designed such that the released flow cross-sectional area is largely proportional to the stroke of the tappet 11. By varying the frequency of the control signal or the pulse duration / pulse pause ratio of the control pulse sequence, a specific armature force and thus a specific position of the plunger 11, which gives the desired flow cross section from input 13 to output 14, is set according to the invention. In this way, the speed of the pressure rise or the gradient of the pressure build-up in the wheel brake 1 can be regulated quasi-continuously.

The brake system according to FIG. 1 with the valve according to FIG. 2 works in principle as follows:

As long as no blocking tendency is sensed, the valves are in the rest position shown. If the vehicle wheel shown is unstable, the inlet valve 5 closes and the brake pressure is reduced by actuating the Discharge valves 6 and simultaneous activation of the return pump 8 dismantled. For the dosed rebuilding of the brake pressure in the wheel brake 1, the inlet valve 5 is now switched back to passage and controlled with a relatively high-frequency alternating signal or with a pulse train, by means of which modulation the desired pressure build-up gradient is set in the manner described becomes. Instead of the rapid opening and closing of the valve, which previously led to the annoying noise, the illustrated inlet valve is operated to a certain extent like a proportional valve, although it has the simple structure of a switching valve which only knows two switching positions.

In principle, the pressure reduction valve 6 can be actuated in the same way in order to also reduce the noise caused by the switching back and forth of this valve. In practice, however, the quasi-continuous regulation of the pressure rise leads to a higher noise reduction, because in many situations the pressure difference across the inlet valve is higher in comparison to the pressure difference across the outlet valve; the level of the pressure difference has a strong influence on the noise when switching the solenoid valves from one end position to the other.

According to the invention, a very simple measure, which is at most associated with minimal additional effort in the manufacture of the valves, therefore achieves a considerable improvement in comfort.

Claims

Hydraulic brake system with anti-lock and / or traction control, with a brake pressure transmitter, with electromagnetically actuable hydraulic valves, which serve as inlet and outlet valves for modulating the brake pressure in the individual wheel brakes, with a hydraulic pump for returning the pressure medium derived from the wheel brakes in the brake pressure reduction phase or for auxiliary pressure supply, with sensors for obtaining the controlled variables and with an electronic circuit for processing the sensor signals and for generating brake pressure and pump control signals, characterized in that the inlet valve (5) and / or the outlet valve ( 6) are designed such that when the valve is actuated with an alternating signal or a pulse sequence, the frequency or the pulse duration / pulse pause ratio of which is matched to the characteristics of the valves (5, 6), the valve armature (9) under the influence of the alternating signal or the pulse sequence un d of the hydraulic pressure or the pressure difference acting on the valve armature (9) opens for the duration of the control signal and assumes a dosing position dependent on the control signal.

2. Brake system according to claim 1 characterized in that the passage cross section of the valve (5, 6) can be varied by varying the frequency or the pulse width and / or the pulse duration / pulse pause ratio.

3. Brake system according to claim 1 or 2, characterized ge ¬ indicates that the coil (15), the armature (9), the magnetic core (16) and the air gap (17) between the magnetic core and armature are formed such that the armature force in Working range is approximately proportional to the control current or the excitation current of the coil.