WO1997017240A1

WO1997017240A1 - Process for operating a pneumatic brake servo

Info

Publication number: WO1997017240A1
Application number: PCT/EP1996/004859
Authority: WO
Inventors: Alfred Eckert
Original assignee: Itt Automotive Europe Gmbh
Priority date: 1995-11-08
Filing date: 1996-11-07
Publication date: 1997-05-15
Also published as: EP0857129A1; JPH11514607A; AU7566796A; DE19541535A1

Abstract

A process for the operation of an electromagnetically driven pneumatic brake servo characterised in that a sealing seat (15) of its control valve (12), actuatable by an electromagnet (20), is moved at maximum speed in a first time interval (T0-T1), in the direction of actuation of the electromagnet (20), until a maximum opening between the sealing seat (15) and the valve body (10) of the control valve (12) occurs, thus causing a rapid intake of the atmosphere into the working chamber (3) of the brake servo. In a second time interval, (T1-T2), the established position of the sealing seat (15) is held constant, while in a third time interval (T2-T3), the sealing seat (15) is moved at maximum speed in the direction opposite to that of actuation of the electromagnet (20) to reduce the opening, and the position of the first sealing seat (15), established in the third time interval, is held constant until completion of the braking operation independently of the actuating rod (7).

Description

Method for operating a pneumatic brake booster

The invention relates to a method for operating a pneumatic brake booster for motor vehicles with an amplifier housing, the interior of which is divided by a movable wall into a first chamber (vacuum chamber) and a second chamber (working chamber), and with a control housing in which a on the movable wall acting pneumatic pressure difference controlling control valve is arranged, which has a first sealing seat, the opening of which allows ventilation of the working chamber, a second sealing seat, the opening of which enables a connection between the two chambers, and an elastic valve body which interacts with the two sealing seats The first sealing seat can be actuated on the one hand by an actuating rod and on the other hand independently of the actuating rod by an electromagnet.

A pneumatic brake booster with electromagnetic auxiliary control is known from DE 44 05 092 Cl, in which the first sealing seat is formed on a cylindrical sleeve which is connected to the armature of an electromagnet arranged in the control housing. In order for the driver to actuate the known brake booster

ORIGINAL DOCUMENTS

enable, a valve piston, which is in force-transmitting connection with the actuating rod, is provided, on which the armature is supported axially and can thus be carried along by the valve piston during driver actuation. When operated externally or when the electromagnet is energized, the first sealing seat lifts off the valve body, so that the atmosphere can flow into the working chamber.

From DE 42 38 333 AI a vacuum brake booster is known, the control valve has a third sealing seat, which can be actuated by means of an electromagnet and which functionally replaces the second sealing seat when operated externally. The control valve is actuated by the electromagnet against the direction of actuation by the driver, so that the valve body is moved away from the first sealing seat formed on the valve piston by moving the third sealing seat.

Numerous possible uses of such externally controllable power amplifiers are currently known. One of the known uses is to support the driver in the event of panic braking, in which the maximum available braking force is applied by rapid external control of the control valve. External control takes place by applying an electrical voltage to the coil of the electromagnet, which results in a sudden opening of the control valve and thus rapid ventilation of the working chamber of the brake booster. After a certain time, a current value is set using pulse width modulation (PWM) of this voltage

between the atmospheric sealing seat of the control valve and its valve body through the external actuation opening gap just keeps open.

When determining this current value, however, all design tolerances of the brake booster and temperature influences must be taken into account, so that the current value must be considerably larger than the optimal value.

It is therefore the object of the present invention to propose a method for operating pneumatic power amplifiers of the type mentioned at the outset which enables the aforementioned influences to be eliminated while at the same time ensuring the rapid switching function of the external actuation.

A first solution to the problem on which the invention is based is that the first sealing seat is moved at maximum speed in a first time interval in the actuating direction of the electromagnet until a maximum opening gap is created between the first sealing seat and the valve body, in a second Time interval the controlled position of the first sealing seat is kept constant, after which the first sealing seat is moved in a third time interval at maximum speed against the direction of actuation of the electromagnet in the sense of reducing the opening gap and the position of the first sealing seat controlled in the third time interval at the end of the braking initiated independently of the actuating rod is kept constant.

A second solution, which is particularly suitable for pneumatic brake boosters, the control valves of which have an electromagnetically displaceable third sealing seat, which is actuated against the direction of actuation by the driver, consists in the fact that the third sealing seat coincides with the actuating direction of the electromagnet in a first time interval maximum speed is moved until an opening gap is formed between the first sealing seat and the valve body, the controlled position of the third sealing seat is kept constant in a second time interval, after which the third sealing seat in a third time interval at maximum speed against the actuation direction of the electromagnet in the Moving in order to reduce the opening gap and the position of the third sealing seat which was activated in the third time interval until the end of the braking independent of the actuating rod tant is kept.

The invention therefore consists in the use of position control of active, analog controllable brake boosters for the targeted representation of the on / off function. This ensures that the set position of the sealing seat is set to a pressure build-up position with a maximum gradient at the start of the function. After a certain time, which the brake system needs to build up the maximum pressure, a target position is specified which corresponds to a functional range lying between the pressure maintenance and the pressure build-up phase. The manner in which the position control (sliding mode control) is described the required current value is very small (optimal), whereby no pressure build-up due to interference is possible.

Further advantageous features of the subject matter of the invention are listed in subclaims 2 and 4 to 8.

The invention is explained in more detail in the following description using two exemplary embodiments in conjunction with the accompanying drawing, wherein corresponding parts are provided with the same reference numerals.

The drawing shows:

1 shows a first embodiment of an externally actuated brake force booster in longitudinal section; partially broken away, in the inactive standby position;

2 shows a second embodiment of an externally actuated brake booster in the externally actuated position; and

3 shows a diagrammatic representation of an external actuation of the brake booster shown in FIGS. 1 and 2, in particular the time profiles of the actuation path s _{h of} the first and third sealing seats - FIG. 3a, of the pressure build-up in a master brake cylinder downstream of the brake boosters (FIG. 3b) and of the current supplied to the electromagnets of the brake booster (FIG. 3c).

The vacuum amplifier housing 1 of the vacuum brake booster shown in FIG. 1, which is only indicated schematically, is divided by an axially movable wall 2 into a working chamber 3 and a vacuum chamber 4. The axially movable wall 2 consists of a sheet metal membrane plate 8 and an attached flexible membrane 18, which, not shown, forms a rolling membrane as a seal between the outer circumference of the membrane plate 8 and the booster housing 1.

An actuable by an actuating rod ^'7 control valve 12 iεt in a sealed in the booster housing 1 out, the movable wall 2 supporting the control housing 5 housed and consists of a first sealing seat 15, one formed in Steuergehäuβe 5 second sealing seat 16, and a with the two sealing seats 15,16 interacting, arranged in the control housing 5 sealed elastic valve body 10, which is pressed by means of a valve spring 22 against the valve seats 15, 16. The working chamber 3 can be connected to the vacuum chamber 4 via a channel 21 extending laterally in the control housing 5.

The braking force is transmitted via a rubber-elastic reaction disk 6, which rests on the end face to a front part 17 of the control housing 5, and a pressure rod 14 having a head flange 23, to an actuating piston of a master brake cylinder (not shown) of the brake system, which is attached to the vacuum-side booster half.

In order to be able to connect the working chamber 3 to the atmosphere when the control valve 12 is actuated, an approximately radially extending channel 24 is finally formed in the control housing 5.

As can also be seen in FIG. 1, the first sealing seat 15 is formed at the end of a cylindrical sleeve 32 which is in force-transmitting connection with the armature 27 of an electromagnet 20, the coil 26 of which is arranged immovably in the control housing 5. In order to be able to actuate the control valve 12 by means of the actuating rod 7, a valve piston 9 is provided which bears against the armature 31 under the pretension of a compression spring 13 which is supported on the sleeve 32. The return movement of the valve piston 9 at the end of a braking operation is limited by a cross member 11, that in the release position of the vacuum brake booster shown in the drawing rests against a stop 19 formed in the booster housing 1.

As can be seen from the diagrammatic representation in FIG. 3, the electromagnet 20 of the brake booster shown in FIG. 1 is acted upon by maximum current at the start of an external actuation (time T ₀ ) and is thus actuated such that the first sealing seat 15 is in a first time interval T _Q -TL at maximum speed away from the valve body 10 until there is an opening gap between it and the valve body 10 which, when the second sealing seat 16 is closed, causes the atmosphere to flow rapidly into the working chamber 3 and thus a sudden increase in the hydraulic pressure

in the master brake cylinder mentioned above to the maximum value.

In a second time interval T _x -T ₂ subsequent to the first time interval To-Tl, the current supplied to the electromagnet 20 is kept constant at the maximum level (T-max), so that the input in the first time interval T _Q -T _J The position of the first sealing seat 15 and thus the size of the opening or the distance of the sealing seat 15 from the valve body 10 cannot be changed and the pressure in the master brake cylinder is kept at a constant level. In a third time interval T ₂ -T ₃ , the current supplied to the electromagnet 20 is reduced to a value I _h , so that the first sealing seat 15 moves in the direction of the valve body 10 at maximum speed, ie in the sense of a reduction the distance between the sealing seat 15 and valve body 10 takes place.

The third time interval T2-T _{3 is} followed by a fourth time interval T ₃ -T ₄ , in which there is no movement of the first sealing seat 15 with respect to the valve body 10, so that the opening gap set in the third time interval T ₂ -T ₃ remains unchanged. The hydraulic pressure controlled in the master brake cylinder remains constant during the third and fourth time interval until the actuating force applied by the driver is removed or the external braking process is terminated at time T ₄ . In a fifth time interval T ₄ -T ₅ , the current supplied to the electromagnet 20 is reduced to zero, so that the first sealing seat 15 moves under the action of the compression spring 13 towards the valve body 10 at maximum speed or into its rest position , which is determined by the mechanical stop of the armature 27 on the valve piston 9. In the event of a pneumatic pressure equalization between the two chambers 3, 4 initiated by opening the second sealing seat 16 or the return movement of the movable wall 2, the hydraulic pressure in the master brake cylinder 2 is reduced to zero.

The control valve 12 of the brake booster shown in FIG. 2 consists of a first sealing seat 28 formed on the valve piston 9 connected to the actuating rod 7, a second sealing seat 29 formed in the control housing 5, and a third sealing seat 30 arranged radially between the two sealing seats 28, 29 and an annular valve body 31, which cooperates with the sealing seats 28, 29 and 30 and is guided in a guide part 32 arranged in a sealed manner in the control housing 5, which valve valve 33 supports the sealing seats 28, 29, 30 by means of a valve spring 33 which is supported on the guide part 32 is biased.

In order to initiate external actuation of the brake booster shown in FIG. 2 independently of the actuating rod 7, an electromagnet 34 is provided, which is preferably arranged in a housing 35 which is fixedly connected to the valve piston 9 and accordingly together with the valve piston 9 in the control housing 5 is displaceable. The electrical

Magnet 34 consists of a coil 36 arranged inside the housing 35 and an axially displaceable cylindrical armature 37 which is partially guided in a closure part 38 closing the housing 35 and on which a force transmission sleeve 39 is supported which supports the third sealing seat mentioned above 30 wears. A compression spring 40 is arranged between the valve piston 9 and the force transmission sleeve 39, which holds the armature 37 in its starting position, in which the third sealing seat 30 is arranged axially offset with respect to the first sealing seat 28 formed on the valve piston 9. The closing part 38, which is guided in the control housing 5, bears against the previously mentioned reaction disk 6 with the interposition of a transmission disk 41 and enables the input force introduced on the actuating rod 7 to be transmitted to the reaction disk 6.

As can be seen from the diagrammatic representation in FIG. 3, the electromagnet 34 of the brake force booster shown in FIG. 2 is acted upon by maximum current at the start of external actuation (time T ₀ ) and is thus actuated in such a way that the third sealing seat 30 in the first time interval T _Q -TL is moved at maximum speed towards the valve body 31 until it comes to rest on it and bridges the function of the second sealing seat 29 mentioned above. When the third sealing seat 30 moves further, it is first pressed into the material of the valve body 31 in the direction of actuation of the electromagnet 34, ie against the direction of actuation of the brake booster, and then displaces it away from the first sealing seat 28, so that between the valve body 31 and the

first sealing seat 28, a gap is created which allows the atmosphere to flow rapidly into the working chamber 3. In the process described above, there is an abrupt increase in pressure in the master brake cylinder connected downstream of the brake booster, the second sealing seat 29 being functionally replaced by the third sealing seat 30. The external actuation state described is shown in FIG. 2.

In one at the first time interval T ₀ -T **. Subsequent second time interval T _x -T ₂ , the current supplied to the electromagnet 34 is kept constant at the maximum level (Imax), so that the position of the third sealing seat 30 controlled in the first time interval T _Q -T _X and thus the size of the opening gap or the distance of the first sealing seat 28 from the valve body 31 cannot be changed and the pressure in the master brake cylinder is kept at a constant level.

In a third time interval T ₂ -T ₃ , the current supplied to the electromagnet 34 is reduced to a value I _h , so that a movement of the third sealing seat 30 at maximum speed against the direction of actuation of the electromagnet 34, ie in the sense of a reduction of the opening gap between the valve body 31 and the first sealing seat 28 takes place.

The third time interval T ₂ -T _{3 is} followed by a fourth time interval T ₃ -T4, in which there is no movement of the third sealing seat 31 with respect to the first sealing seat 28, so that the

third time interval T ₂ -T ₃ set opening gap remains unchanged. The hydraulic pressure applied in the master brake cylinder remains constant during the third and the fourth time interval until the actuating force applied by the driver is removed or the external braking process is terminated at time T ₄ .

In a fifth time interval T ₄ -T ₅ , the current supplied to the electromagnet 34 is reduced to zero so that the third sealing seat 30 moves under the action of the compression spring 40 into its rest position at maximum speed, which is achieved by the mechanical stop of the Anchor 37 is determined on the closure part 38. When the pneumatic pressure compensation between the two chambers 3, 4 or the return movement of the movable wall 2 is initiated by opening the second sealing seat 29, the hydraulic pressure in the master brake cylinder 2 is reduced to zero.

The times T _Q to T ₅ delimiting the individual time intervals can be determined as a function of threshold values of a displacement sensor (not shown) that detects the movement of the movable wall 2 or a pressure sensor (also not shown) with which the hydraulic pressure prevailing in or behind the master brake cylinder is sensed.

Claims

claims

1. A method for operating a pneumatic brake booster for motor vehicles with an amplifier housing, the interior of which is divided by a movable wall into a first chamber (vacuum chamber) and a second chamber (working chamber), and with a control housing in which a On the movable wall, a pneumatic pressure difference controlling control valve is arranged, which has a first sealing seat, the opening of which enables ventilation of the working chamber, a second sealing seat, the opening of which enables a connection between the two chambers, and one which cooperates with the two sealing seats has elastic valve body, the first sealing seat being operable on the one hand by an actuating rod and on the other hand independently of the actuating rod by an electromagnet, characterized in that the first sealing seat (15) is in a first time interval (To-T -iJ in the direction of actuation of the electromagnet (20) is moved at maximum speed until a maximum opening gap is created between the first sealing seat (15) and the valve body (10), and in a second time interval (T ₁ -T ₂ ) the activated position of the first sealing seat (15) is kept constant, after which the first sealing seat (15) in a third time interval (T ₂ -T ₃ ) at maximum speed ent moves against the actuation direction of the electromagnet (20) in the sense of reducing the opening gap

and the position of the first sealing seat (15) which has been activated in the third time interval (T ₂ -T ₃ ) is kept constant until the end of the braking which is initiated independently of the actuating rod (7).

2. The method according to claim 1, characterized in that the reduction of the opening step is carried out in the third time interval (T2-T ₃ ) until the first sealing seat (15) bears against the valve body (10).

3. Method for operating a pneumatic brake booster for motor vehicles with an amplifier housing, the interior of which is divided by a movable wall into a first chamber (vacuum chamber) and a second chamber (working chamber), as well as with a control housing, in which one on the movable wall acting pneumatic pressure difference is controlled by an actuating rod control valve is arranged that a first sealing seat, the opening of which allows ventilation of the working chamber, a second sealing seat, the opening of which enables a connection between the two chambers, a third sealing seat which can be actuated by an electromagnet and which functionally replaces the second sealing seat when actuated by the electromagnet, characterized in that the third sealing seat (30) in a first time interval (T ₀ -T _x ) in the actuating direction of the electromagnet (34) with maximum speed is moved until between

first sealing seat (28) and the valve body (31) an opening gap arises, and in a second time interval (^ -1 ₂ ) the controlled position of the third sealing seat (30) is kept constant, after which the third sealing seat (30) in a third time interval (T2-T ₃ ) is moved at maximum speed against the direction of actuation of the electromagnet (34) in the sense of reducing the opening gap and the position of the third sealing seat (30) activated in the third time interval (T ₂ -T ₃ ) until the end of the independently braking initiated by the actuating rod is kept constant.

4. The method according to claim 3, characterized in that the reduction of the opening gap in the third time interval (T ₂ -T ₃ ) until the valve body (31) abuts the first sealing seat (28).

5. The method according to claim 1 or 3, wherein the control valve can be actuated by the driver by means of an actuation pedal, characterized in that the size of the opening gap is determined as a function of the actuation pedal-Anschlagεgeεch speed.

6. The method according to claim 1 or 3, wherein the control valve can be actuated by the driver by means of an actuating pedal, characterized in that the actuating force acting on the actuating pedal is determined

and the size of the opening gap is determined depending on the actuation force gradient.

7. The method according to any one of claims 1 to 6, characterized ge indicates that the time intervals determining the time intervals (TQ to T ₅ ) are determined as a function of threshold values of a displacement sensor detecting the movement of the movable wall (2) of the brake booster.

8. The method according to any one of claims 1 to 6, characterized ge indicates that the time intervals determining the time intervals (T ₀ to T ₅ ) are determined as a function of threshold values of a pressure sensor that the hydraulic pressure in or behind the one

Brake booster downstream master cylinder detected.