DE4034839C1 - - Google Patents

Abstract

Device for operating an anti-lock hydraulic braking system for a motor vehicle with control electronics (42) to assess the signals from the rotation speed sensor (17) allocated to a vehicle wheel (18) dependently upon the deceleration or acceleration state of the vehicle wheel (18), whereby the control electronics (42) emit a control signal to the proportional magnet (26) of the valve device (14) to affect the brake pressure in the appropriate brake circuit, whereby the proportional magnet (26) in the starting range (54) of its power-travel characteristic diagram takes the control slide (20) of the proportional pressure valve (13) to a first position in which the passage from the first connecting line (12) to the wheel brake cylinder (16) is blocked and the proportional magnet (26) on the way following the first position operates in the range (55) in which the blocking of the first connecting line (12) remains and the control edges of the control slide (20) form a pressure modulator co-operating with the auxiliary pressure source (59) and the low-pressure chamber (34), a brake pressure adapted to the momentary acceleration conditions at the vehicle wheel concerned (18) is generated in the second connecting line (15) and in the wheel brake cylinder (16), whereby the brake pressure generated, reacting on the front (37) of the control slide (20) produces a force which is in equilibrium with the operating force of the proportional magnet (26).

Description

The invention relates to a device for operating an anti-lock hydraulic brake system for a Motor vehicle according to the preamble of claim 1. With such a braking system will block the Vehicle wheels prevented when braking. The motor vehicle remains therefore steerable at all times even during full braking directionally stable.

DE 39 42 683 A1 describes a generic type anti-lock hydraulic brake system known. Master cylinder and auxiliary pressure source are here via one common line connected to the valve device so that repercussions of the anti-lock mode Auxiliary pressure pump on the brake pedal can result.

To avoid such repercussions, DE 38 34 539 A1 known, through the master cylinder - and thus the brake pedal Switching on separate isolating valves in the event of a blockage protection shut off hydraulically, but with an increase in the number the solenoid valves are connected.

It is therefore an object of the invention a generic Device for operating an anti-lock hydraulic Brake system for a motor vehicle to improve that separation without increased effort on hydraulic components of the master cylinder in the event of an anti-lock condition.  

This object is achieved with the characteristic Features of claim 1 solved. The further one Embodiment of the invention results from the features of Claims 2 to 7.

The advantages achieved with the invention also exist in that the formation of the spool a economic production of the proportional pressure valve allowed, that by the low cost of components Anti-lock device for the hydraulic brake system low investment costs for a vehicle to be equipped with it revealed that the uncomplicated training of Anti-lock device of the hydraulic brake system makes dynamic functional processes manageable, that a relatively simple retrofit for existing ones Vehicle braking systems yields that so far without Anti-lock function work as per anti-lock Brake circuit only the valve device in the connecting line between the master cylinder and the brake circuit is that the braking system has the functions for anti-lock protection and Traction control combined in a simple manner and that the modular structure of the control electronics the optional equipment a vehicle only with anti-lock protection, only with Traction control or with anti-lock protection and Traction control system allowed.

From DE-36 44 304 A1 it is still known in one anti-lock hydraulic vehicle brake system one of a proportional solenoid controlled proportional valve to be arranged, one from the master cylinder to the valve device extending control line is provided so that the Master cylinder pressure the one face of the spool Valve device acted on. After controlling the Valve device remains by excitation of the proportional magnet the master cylinder pressure is constantly on the face of the  Control spool effective. In this way the outlet pressure the valve device depending on the Master cylinder pressure controlled.

An embodiment of the invention is in the drawing shown and will be described in more detail below. It shows

Figure 1 schematically shows an anti-lock hydraulic brake system on a vehicle wheel of a vehicle with front-wheel drive and in a position of the control slide in the proportional pressure valve with the non-energized proportional magnet.

Fig. 2 force-displacement map of the proportional magnet.

An anti-lock hydraulic brake system of a motor vehicle has a master brake cylinder 11 which can be actuated by a brake pedal and is connected to the wheel brake cylinder 16 of a driven front vehicle wheel 18 via a first connecting line 12 and a second connecting line 15 with the interposition of a valve device 14 .

Because of the better clarity, the interaction of all parts of the brake system is only fully shown and described for the vehicle wheel 18 in the example. Indicatively, 1, the line branches that lead to non-illustrated parts of the braking system are illustrated in Fig..

The controllable valve device 14 consists of a proportional pressure valve 13 and a proportional magnet 26 . The term proportional in connection with the magnet refers to the course of the characteristic in the force-current characteristic field of the magnet. In this representation of the characteristic curve, there is an approximately linear relationship between a change in the excitation current and the resulting change in the magnetic force, ie there is proportionality. However, the illustration in FIG. 2 does not show the force-current characteristic diagram, but rather a section of the force-displacement characteristic diagram of the proportional magnet. The proportionality of current and force cannot be seen in this graph. In FIG. 2, the course of the magnetic force P for constant excitation currents A 1, A 2, A plotted 3 for the armature stroke S, wherein the characteristic curve from the constructive interference of the magnetic flux is dependent by non-magnetic internals in the coil portion.

The housing 25 of the proportional pressure valve 13 has a control slide 20 guided in a bore 21 and four control openings 19 , 22 , 23 , 24 opening radially into the bore 21 . The proportional magnet 26 is flanged to the housing 25 and has a coil 27 and an armature 28 which can move axially and cooperate with the control slide 20 . A return spring 40 holding the control slide 20 and the armature 28 in the rest position is arranged in a spring chamber 39 of the housing 25 .

The first connecting line 12 is connected to the first control opening 19 of the housing 25 , while the second connecting line 15 starts from a connection which is connected to the bore 21 of the housing 25 . A high-pressure source 59, which is connected to a reservoir 34 for brake fluid and consists of a pump 29 and a pressure accumulator 30 , is connected to the second control opening 22 via a line 31 . The pump 29 is used to automatically maintain the pressure in the pressure accumulator 30 . Between pump 29 and accumulator 30 a check valve 32 and between the pressure accumulator 30 and the housing 25 is arranged a controllable shutoff valve 33 in the conduit 31st

The third control opening 23 is connected by a line 36 to the second connecting line 15 and the fourth control opening 24 by means of line 35 to the storage container 34 below the liquid level. The storage container 34 is open to the atmosphere and thus corresponds to a space of low pressure.

The control slide 20 , which is axially displaceable in the housing 25, has an end control surface 37 and a circumferential groove 38 , between which a cylindrical guide section 58 is formed. The length of the guide section 58 is greater than the axial distance between the first and second control openings 19 , 22 . The axial width of the circumferential groove 38 corresponds to the distance between the adjacent edges of the second and fourth control openings 22 , 24 . The spring chamber 39 is connected to the control opening 24 by a relief channel 56 .

The brake system is controlled by control electronics 42, which are programmable to the conditions to be taken into account for the vehicle in question, as a function of the signals from the speed sensors 17 arranged on the anti-lock vehicle wheels 18 and the signal from a brake signal transmitter 51 arranged on the master brake cylinder 11 .

The control electronics 42 consists of a first evaluation module 43 for controlling the anti-lock function, which has signal inputs 41 , 41 a, 41 b for all speed sensors, a second evaluation module 44 for controlling the traction control system, which only has signal inputs 41 and 41 a for Has speed sensors of driven vehicle wheels and a plurality of control modules 47 , 47 a, 47 b for the proportional magnets of the brake system. The signal outputs 45 , 45 a, 45 b, 46 , 46 a of the evaluation modules 43 , 44 are connected to the signal inputs of the control modules 47 , 47 a, 47 b, the signal outputs 45 , 46 and 45 a, 46 a for driven vehicle wheels are connected to the control modules 47 , 47 a and the control module 47 b assigned to a non-driven vehicle wheel is only connected to the signal output 45 b of the evaluation module 43 . According to the example in FIG. 1, the output signal lines 45 , 46 lead to a control module 47 , the output of which is connected via a signal line 48 to the coil 27 of the proportional magnet 26 .

The brake signal generator 51 is connected by a signal line 50 to all of the control modules 47 , 47 a, 47 b arranged in the control electronics 42 . The evaluation modules 43 , 44 of the control electronics 42 each have a further signal output 52 , 53 , which are connected to the shut-off valve 33 via a signal line 49 .

The functional sequence of an anti-lock braking with the brake system according to the invention is as follows: When a braking operation is initiated by actuating the master brake cylinder 11 , a brake pressure builds up, which via the first connecting line 12 , the first control opening 19 , the bore 21 , the second connecting line 15, the wheel brake cylinder 16 reached and triggers the wheel brake. Until then, the process corresponds to normal braking without an anti-lock function.

The actuation of the master brake cylinder 11 causes the immediate signal from the brake signal generator 51 to the connected control modules 47 , 47 a, 47 b in the control electronics 42 . As a result, the output signal line 45 of the evaluation module 43 for the anti-lock function is switched through from the control module 47 to the signal line 48 leading to the proportional magnet 26 . The signals continuously arriving in the control electronics 42 from the speed sensor 17 during driving operation are checked in the evaluation module 43 to determine whether the braking of the vehicle wheel 18 due to the braking approaches a critical deceleration value that would mean that the vehicle wheel 18 would lock. The evaluation module 43 has a map memory that is matched to the vehicle and contains the programmed association between the determined critical speed values and the corresponding excitation current for the coil 27 of the proportional magnet 26 .

If such a speed value is determined by the evaluation module 43 , the coil 27 of the proportional magnet 26 is excited with a specific current strength by the control module 47 via the signal line 48 . At the same time, the shut-off valve 33 is switched to passage by a signal from the signal output 52 , so that the pressure of the pressure accumulator 30 is present in the second control opening 22 of the proportional pressure valve 13 . The excitation of the coil 27 results in an axial movement of the armature 28, as a result of which the control slide 20 is displaced from the rest position shown in FIG. 1. During the initial stroke of the armature 28 , the proportional magnet 26 operates in the first start-up area 54 of its force-displacement characteristic diagram ( FIG. 2). Until the working area 55 of his force-displacement characteristic field required for the anti-lock function is reached, the control slide 20 is displaced by the armature 28 of the proportional magnet 26 to such an extent that the front control surface 37 slides over the first control opening 19 and the connection between the first and second connecting line 12 , 15 interrupts. The pressure in the master brake cylinder 11 is ineffective for the further course of the braking process.

At the end of the initial stroke, the control slide 20 with its circumferential groove 38 is approximately opposite the third control opening 23 , but has not yet passed the fourth control opening 24 with the right control edge of the circumferential groove 38 . The excessive brake pressure in the wheel brake cylinder 16 , which would cause the vehicle wheel 18 to lock, can then be reduced via the connecting line 15 , line 36 , third control opening 23 , circumferential groove 38 , fourth control opening 24 and line 35 into the reservoir 34 . The reduction in brake pressure leads to a weakening of the braking effect and to an increase in the speed of the vehicle wheel 18 , which causes a signal change in the speed sensor 17 . If the braking process is ongoing, ie if the master brake cylinder 11 is still actuated, this results in a corresponding change in the signaling of the control electronics 42 to the proportional magnet 26 .

As the pressure in the wheel brake cylinder 16 drops, the pressure present on the front control surface 37 of the control slide 20 also drops. The force on the control slide 20 which counteracts the instantaneous actuating force of the proportional magnet 26 thus becomes smaller. The resulting excess of actuating force on the armature 28 while the coil 27 remains energized causes a further displacement of the control slide 20 until the left control edge of the circumferential groove 38 opens the second control opening 22 . With the pressure of the high-pressure source 59 present there , the brake pressure value in the wheel brake cylinder 16 is now raised again via the circumferential groove 38 , the third control opening 23 , line 36 and connecting line 15 to the extent that the actuating force of the armature 28 caused by the control signal of the evaluation module 43 and the force balance resulting from the brake pressure, effective on the end face 37 of the control slide 20 .

In the state of equilibrium of the forces, the control slide 20 assumes a position in which the control edges of the circumferential groove 38 are just congruent with the adjacent edges of the control openings 22 and 24 . This position arises when the anti-lock vehicle wheel is decelerated with optimum braking effect. The circumferential groove 38 and control openings 22 , 24 have the function of a pressure modulator in this position of the control slide 20 . By small control movements of the armature 28 or the control slide 20 , a braking pressure value is temporarily formed in the circumferential groove 38 or in the wheel brake cylinder 16 by alternately briefly opening the second control opening 22 and fourth control opening 24 . This temporary brake pressure value is in each case proportional to the current strength controlled by the evaluation module 43 or the excitation of the coil 28 of the proportional magnet 26 caused thereby, and is suitable for preventing the vehicle wheel 18 from blocking.

As soon as the actuation of the master brake cylinder 11 stops, the brake signal generator 51 becomes inactive. The control module 47 thereby falls back into its rest position, as a result of which the connection between the evaluation module 43 and the control module 47 is disconnected and the excitation of the proportional magnet 26 is ended. Armature 28 and control slide 20 are returned to their rest position by the return spring 40 . The passage from the first connecting line 12 to the second connecting line 15 is thus released again by the control slide 20 . The shut-off valve 33 is also deactivated by the control electronics 42 , so that the line 31 is blocked again.

When the master brake cylinder 11 is not actuated, the control module 47 is always in the position in which the signal output 46 of the evaluation module 44 is effective for the traction control on the control module 47 . If necessary, the coil 27 of the proportional magnet 26 can be excited at any time via the signal line 48 .

The traction control system is automatically activated by the control electronics 42 if, for example, during an acceleration process of the vehicle. B. when starting, in an overtaking or on slippery roads, the evaluation of the signals of the speed sensor 17 in the evaluation module 44 results in an acceleration value that indicates a slipping of the driven vehicle wheel 18 . The evaluation module 44 has a map memory that is matched to the vehicle and contains the programmed assignment between the determined critical acceleration values and the corresponding excitation current for the coil 27 of the proportional magnet 26 .

The control module 47 then generates, on the basis of a command sent by the evaluation module 44 , a control signal of a specific current strength with which the coil 27 of the proportional magnet 26 is excited. At the same time, the shut-off valve 33 is switched to passage by a signal via the signal output 53 and the signal line 49 , so that the pressure of the high-pressure source 59 is present in the second control opening 22 of the proportional pressure valve 13 .

The excitation of the coil 27 results in an axial movement of the armature 28, as a result of which the control slide 20 is displaced from the rest position shown in FIG. 1. During the initial stroke of the armature 28 , the proportional magnet 26 operates in the start-up area 54 of its force-displacement characteristic diagram. Until the working area 55 of the force-displacement characteristic map required for traction control is reached, the control slide 20 is displaced by the armature 28 of the proportional magnet 26 to such an extent that the front control surface 37 slides over the first control opening 19 and the connection between the first and second connecting line 12 , 15 interrupts.

Since there is initially no brake pressure when the traction control system begins in the wheel brake cylinder 16 , the force opposed to the actuating force of the armature 28 is also missing on the end control surface 37 of the control slide 20 . The control slide 20 is therefore moved by the armature 28 to the extent that the left control edge of the circumferential groove 38 opens the second control opening 22 . As a result, the pending pressure of the high-pressure source 59 reaches the wheel brake cylinder 16 via the circumferential groove 38 , third control opening 23 , line 36 and second connecting line 15 . The response of the wheel brake prevents the vehicle wheel 18 from slipping or uncontrolled slipping.

With the buildup of the brake pressure value in the wheel brake cylinder 16 , the brake pressure value is also present on the front control surface 37 of the control slide 20 via the second connecting line 15 , so that there is a counterforce to the actuating force of the armature 28 . In the state of equilibrium of the forces, the control slide 20 assumes a position in which the control edges of the circumferential groove 38 are just congruent with the adjacent edges of the control openings 22 and 24 . The circumferential groove 38 and control openings 22 , 24 have the function of a pressure modulator in this position of the control slide 20 . By small control movements of the armature 28 or the control slide 20 , a braking pressure value is temporarily formed in the circumferential groove 38 or in the wheel brake cylinder 16 by alternately briefly opening the second control opening 22 and fourth control opening 24 . This temporary brake pressure value is in each case proportional to the current strength controlled by the evaluation module 43 or the excitation of the coil 28 of the proportional magnet 26 caused thereby, and is suitable for preventing uncontrolled slippage or the spinning of the driven vehicle wheel 18 . The adhesion limit between the tire and the road surface is not exceeded. As a result, the vehicle wheel can support lateral forces at all times and always remains steerable.

When the evaluation of the signals of the speed sensor 17 no longer causes any fear of spinning, the proportional magnet 26 and the shut-off valve 33 are deactivated. The control slide 20 then returns to its rest position, whereby the passage from the first connecting line 12 to the second connecting line 15 in the proportional pressure valve 13 is free again. This completes a traction control cycle. The evaluation module 44 can optionally also have an additional signal output (not shown), from which a signal for influencing operating variables of the vehicle drive system can be tapped during a traction control cycle.

The actuating movements in the wheel brake cylinder 16 and in the proportional pressure valve 13 are very small. The hysteresis of the hydraulic brake system is therefore negligible. It follows from this that the excitation current for the coil 27 of the proportional magnet 26, which is respectively predetermined by the control electronics 42, is actually actually proportional to the brake pressure value modulated in the proportional pressure valve 13 . This application of the proportional technique for influencing the brake pressure value in the wheel brake cylinder with anti-lock or traction control function results in an analog brake pressure build-up or reduction. The known arrangement of anti-lock devices with digital brake pressure build-up induced vibrations in the chassis of the vehicle are completely avoided with the proposed arrangement. The prevention of this undesirable vibration stress has a positive effect on the service life of vehicle components.

In FIG. 2, the course of the force P that can be developed by the armature 28 for various excitation currents A 1 , A 2 , A 3 of the coil 27 is plotted over the stroke S of the armature 28 or the control slide 20 .

The spring chamber 39 can be connected to the first connecting line 12 via a channel 57 (indicated by dash-dotted lines in FIG. 1) instead of the relief channel 56 leading to the room pressure. In this case, the pressure generated in the master brake cylinder 11 prevails in the spring chamber and the gap surrounding the armature 28 . When the anti-lock function is activated, this means that the force resulting from the brake pressure on the front control surface 37 is partially compensated for by the pressure prevailing in the spring chamber 39 .

A commercially available pressure relief valve 60 can be inserted into the first connecting line 12 and automatically limits the maximum brake pressure that can be generated in the master brake cylinder 11 .

The pressure compensation by means of relief channel 57 and the maximum pressure limitation by the pressure relief valve 60 opens up the possibility of working with a lower excitation current for the coil 27 of the proportional magnet 26 , which reduces the size of the proportional magnet 26 and lowers the cost of the anti-lock hydraulic brake system.

Claims (7)

1. Device for operating an anti-lock hydraulic brake system for a motor vehicle with a master brake cylinder actuated by a brake pedal, with an auxiliary pressure source and a low pressure space, with one valve device for each anti-lock brake circuit, each brake circuit being assigned at least one vehicle wheel, a first connecting line between the master brake cylinder and the valve device, a second connecting line between the valve device and the wheel brake cylinder, the valve device being a proportional pressure valve controlled by a proportional magnet with a control slide, with a speed sensor on each anti-lock vehicle wheel, with control electronics for evaluating the signals of the speed sensor assigned to a vehicle wheel as a function of the situation from the deceleration or acceleration state of the vehicle wheel, the control electronics sending a control signal to the proportional magnet n of the valve device for influencing the brake pressure in the associated brake circuit, characterized in that the proportional magnet ( 26 ) brings the control slide ( 20 ) of the proportional pressure valve ( 13 ) into a first position in the start-up area ( 54 ) of its force-displacement map the passage from the first connecting line ( 12 ) to the wheel brake cylinder ( 16 ) is blocked, and that the proportional magnet ( 26 ) works on the path following the first position in the working area ( 55 ), in which the first connecting line ( 12 ) is shut off remains and the control edges of the control spool ( 20 ) form a pressure modulator that cooperates with the auxiliary pressure source ( 59 ) and the low pressure space in such a way that a brake pressure value in the second connecting line ( 15 ) and in the wheel brake cylinder ( 18 ) that is adapted to the instantaneous acceleration conditions on the assigned vehicle wheel ( 18 ) 16 ) is generated, the brake generated sdruckwert on the end face ( 37 ) of the control slide ( 20 ) results in a force that is in equilibrium with the actuating force of the proportional magnet ( 26 ). 2. Device for operating an anti-lock hydraulic brake system for a motor vehicle according to claim 1, characterized in that the proportional pressure valve ( 13 ) in a housing ( 25 ) axially displaceable control slide ( 20 ) with an end face control surface ( 37 ) and a circumferential groove ( 38 ) has that the housing ( 25 ) of the proportional pressure valve ( 13 ) has a connection for the second connection line ( 15 ) and four connections, each opening into a radial control opening ( 19 , 22 , 23 , 24 ), for the first connection line ( 12 ) and three further lines ( 31 , 35 , 36 ) has a cylindrical guide section ( 58 ) formed between the front control surface ( 37 ) and the circumferential groove ( 38 ) of the control slide ( 20 ), the length of which is greater than the distance between the first and second Control opening ( 19 , 22 ) plus at least one control opening width that the first radial control opening ( 19 ) na ch an initial stroke of the control slide ( 20 ) is closed by the guide section ( 58 ) that after the initial stroke ( 54 ) of the control slide ( 20 ) the circumferential groove ( 38 ) faces approximately the third radial control opening ( 23 ) and the control edges of the circumferential groove ( 38 ) interact with the adjacent edges of the second and fourth control openings ( 22 , 24 ) and that the second control opening ( 22 ) via a line ( 31 ) with an auxiliary pressure source ( 59 ), the third control opening ( 23 ) via a line ( 36 ) is connected to the second connecting line ( 15 ) and the fourth control opening ( 24 ) through a line ( 35 ) with a space of low pressure. 3. Apparatus according to claim 2, characterized in that in the line ( 31 ) between the auxiliary pressure source ( 59 ) and proportional pressure valve ( 13 ) one of the control electronics ( 42 ) controllable shut-off device ( 33 ) is arranged. 4. The device according to claim 2, characterized in that the signal lines of all speed sensors ( 17 ) are simultaneously connected to a first and second evaluation module ( 43 , 44 ) of the control electronics ( 42 ). 5. The device according to claim 4, characterized in that the control electronics ( 42 ) for each proportional magnet ( 26 ) of the brake system has a control module ( 47 , 47 a, 47 b), which together via a signal line ( 50 ) with one on the master brake cylinder ( 11 ) arranged brake signal transmitter ( 51 ) are connected. 6. The device according to claim 2, characterized in that a return spring ( 40 ) for control spool ( 20 ) and armature ( 28 ) receiving spring chamber ( 39 ) with the low pressure space ( 24 ) is connected via a relief channel ( 56 ). 7. The device according to claim 2, characterized in that the spring chamber ( 39 ) with the first connecting line ( 12 ) via a channel ( 57 ) is connected.