FR2644417A1 - Hydraulic braking circuit provided with a master cylinder and with an anti-lock device for the wheels, for a motor vehicle - Google Patents

Abstract

The circuit comprises a master cylinder 1 which communicates, under normal braking, with lines 7, 7' for supplying the brakes of a wheel 5, 6 through solenoid valves 8, 8'. When locking of the wheels becomes imminent, a pressure generator 12 is started up to make a slide-valve distributor 10, which cuts off the direct communication of the master cylinder 1 with the brakes 5, 6. According to the invention, under normal braking, an abrupt action on the brake pedal does not give rise to an accidental movement of the slide valve 27 of the distributor 10, because the increase in pressure applies to two bearing surfaces of identical cross-section of this slide valve. Application to an anti-lock braking circuit with enhanced operational safety.

Description

 The present invention relates to a hydraulic braking circuit provided with a master cylinder and an anti-lock device for wheels for a motor vehicle and, more particularly, to such a circuit provided with means for isolating screw wheel brakes. -with respect to the master cylinder, during the period of operation of the anti-lock device.

 FR-A- 2.611.630 describes such a braking circuit comprising a master cylinder actuated by a brake servo controlled by a pedal, a brake associated with each wheel of the vehicle, a solenoid valve for normally closing the braking circuit and for, under the control of the anti-lock device, relieve the pressure in a wheel brake by putting it in communication with means for storing the circuit brake fluid. In addition to means making it possible to filter unpleasant reactions for the driver on the brake pedal during the operation of the anti-lock device, the circuit includes a piloted valve sensitive to the relaxation of the pressure in the wheel brake to trigger the closing of the circuit. supply of this brake by a restriction slowing the rise in pressure of the circuit fluid. Such slow pressure rise phases occur during the operation of the anti-lock device, as is well known.

 The piloted valve comprises a valve, the head of which delimits, in the closed position on its seat, first and second fluid compartments, one of these compartments being placed between the restriction and the "isolation" side of the solenoid valve, l other compartment being placed between a non-return valve used for filtering reactions on the pedal and the output of a supply pump to the brake circuit, in anti-lock sequence, the end of the valve opposite to the head being movable in a chamber where there is a spring which charges the valve towards its open position, this chamber communicating with a supply line of the wheel brake.

 The circuit described in the above-mentioned document satisfactorily meets the objectives set. However, it has been noted that the presence of a piloted valve in such a circuit posed certain constraints as to the tolerable pressure drops in the valve, the solenoid valve and the supply lines of a wheel brake. In normal braking, in fact, if the driver of the vehicle abruptly depresses the brake pedal, the sudden rise in pressure which follows in the compartment of the piloted valve which houses the valve head is not balanced by a rise in pressure. equivalent in the chamber of this valve which communicates with the brake supply line, due to pressure losses in particular in the solenoid valve which then ensures communication between this compartment and this chamber. then closes in its seat by forcing the brake fluid expelled from the master cylinder by the pressure on the pedal, to pass through a restriction which further slows the rise in pressure of said chamber and of the brake supply line with which this room is in communication. This slow rise in pressure of the brake fluid in the wheel brake obviously does not allow the driver to obtain the rapid stop which he expected following the abrupt depressing of the brake pedal. To avoid this drawback it is then necessary to use in the circuit an electrovalve specially designed to introduce only very low pressure drops, which increases the size and the short of the circuit.

 The object of the present invention is to provide a hydraulic braking circuit equipped with a master cylinder and an anti-lock device for wheels which does not have these drawbacks.

 This object of the invention is achieved, as well as others which will appear in the following of this description, with a hydraulic braking circuit provided with a master cylinder controlled by a brake pedal and an anti-lock device. wheels, for a motor vehicle, this device comprising a pressure generator started at the start of an anti-lock braking sequence to selectively supply at least one wheel brake, and a member for automatically isolating the wheel brake from the master-cylinder * the start-up of the pressure generator. According to the invention, this member is constituted by a distributor comprising a movable slide in a bore drilled in a sleeve, between first and second pressure chambers connected respectively to a supply line brake and pressure generator, the drawer comprising two spans of the same cross section which isolates these two chambers from a third intermediate chamber. re so that, in a first position, at rest, of the drawer, the master cylinder and the wheel brake communicate by this third chamber while, in a second position of the drawer, this communication is cut, the drawer being moved in this second position by a differential pressure established between the first and second pressure chambers when the pressure generator is started, consecutive to the excitation of the anti-lock device.

 Thus, during a sudden compression of the brake pedal, the rise in pressure which follows in the third chamber has no effect on the position of the drawer, because the sections of the spans of the drawer are equal. The drawer does not move and the communication between the master cylinder and the wheel brake is not disturbed, which allows the driver to obtain the short braking required by his sudden pressure on the brake pedal during normal braking, then that the anti-lock braking device is not in play.

 According to the invention, the master cylinder and the intermediate chamber are in permanent communication, the distributor sleeve being pierced with a transverse passage which establishes a communication between the intermediate chamber and the wheel brake when the drawer is in its first position. , while this communication is closed by a range of the drawer when the latter occupies its second position.

 Thus, the spool valve which equips the braking circuit according to the invention plays the real of the piloted valve of the aforementioned document without having the possible drawbacks mentioned in the preamble of this description.

In the accompanying drawing, given only by way of example
- Figure 1 is a diagram of an embodiment of the braking circuit according to the invention, equipped with a slide valve which allows to selectively isolate the master cylinder from a wheel brake, in period of operation the anti-lock device, and
- Figure 2 is a sectional view of part of the.

Figure 1 circuit, which shows in detail the structure of the drawer distributor that equips this circuit.

 In Figure I 'it appears that the circuit according to the invention conventionally comprises a "tandem" master cylinder 1 with two control chambers supplied by brake fluid reservoirs 2, 2' and controlled by a brake pedal 3 by possibly via a brake booster 4.

 According to a preferred embodiment of the invention, the complete braking circuit for a four-wheeled vehicle comprises two identical circuits each connected to one of the two control chambers of the "tandem" cylinder 1. The drawing shows only 'only one of these two circuits, suitable for controlling a wheel brake 5 associated with a front wheel and a wheel brake 6 associated with a rear wheel, in a crossed position relative to the front wheel, as it is classic.

 The wheel brake 5 is connected by a supply line 7 to a three-way and two-position solenoid valve 8 itself connected by a line 9 & a distributor & drawer 10 which will be described in detail below. The distributor * drawer is itself connected to the master cylinder by a line 11.

 Likewise, the rear wheel brake is connected by a supply line 7 'to a second three-way, two-position solenoid valve 8', itself connected to the drawer distributor 10 by a line 9 'which joins line 9.

 Thus, under normal braking, the wheel brakes 5 and 6 are controlled by the master cylinder & through the distributor 10, as will be seen below, and through the solenoid valves 8, 8 'respectively then placed in the position shown in the figure where these solenoid valves establish communication between lines 7 and 9 on the one hand and between lines 7 'and 9' on the other.

 The solenoid valves 8, 8 'form part of an anti-lock device for the wheels incorporated in the braking circuit according to the invention. This anti-blocking device further comprises a pressure generator 12 which includes a pump 13 optionally interposed between a low pressure tank 14 and a high pressure accumulator 15 placed at the outlet of the pump. The anti-blocking device selectively controls the excitation of the solenoid valves 8, 8 'so as to pass them into their "detent" position where they establish communication between lines 7 and 16 on the one hand, and 7' and 16 'on the other. part, so that the liquid contained in the wheel brakes can flow into the low-pressure reservoir b, thereby bringing down the pressure in the wheel brakes. The high-pressure outlet of the pump is connected to lines 9 and 9 'for supplying the solenoid valves 8 and 8' respectively, through a non-return valve 17, by lines 18 and 18 'into which restrictions 19 and 19' are introduced respectively. The non-return valve 17 protects the high pressure outlet of the pump from the return of fluid from the supply lines 9 and 9 'of the solenoid valves 8, 8' respectively. The junction of restrictions 19 and 19 ′ is connected by a line 20 * line 11 which connects the master cylinder 1 to the drawer distributor 10, line 20 further comprising a restriction 21 which serves to filter reactions on the pedal of brake 3, during the operating sequences of the anti-lock device.

 As shown in Figure 1, and in more detail in Figure 2, the distributor 10 comprises first and second pressure chambers 22, 23 respectively connected by lines 24, 25 to the line 7 supplying the wheel brake before 5 and at the high pressure outlet of generator 12, respectively. A drawer 27 is movable in the distributor between the chambers 22 and 23 under the action of the difference in pressures prevailing in these chambers.

 In Figure 2 it appears that the distributor 10 is formed in a body 28 hollowed out of a stepped bore 29 which opens on a face 30 of the body 28, a cylindrical sleeve 31 being introduced into this bore 29. This sleeve has a head 32 which comes to bear on the bottom of an enlarged part of the bore 29 close to the face 30. The sleeve 31 is held in this position by a plug 33 which closes the bore 29 while pressing on the head 32 of the sleeve 31. The latter is pierced with an axial bore in which the drawer 27 can move, between the pressure chambers 22 and 23. The drawer 27 comprises two end bearing surfaces 34, 35 of identical sections to that of the bore drilled in the sleeve 31. The bearing surface 34 is loaded to the right (from the point of view of FIG. 2) by a spring 36 placed in the pressure chamber 22. An axial shaft 37 connects the bearing surfaces 34 and 35, this shaft - having a smaller section than that of the bore drilled d in sleeve 31.

A transverse pin 38 secured to the sleeve 31, passes through a hollow buttonhole in the shaft 37 to limit the axial stroke of the drawer 27. Thus, in the position of the drawer shown & in Figure 2, a transverse passage 39 drilled in the sleeve 31 is it clear F left of the scope 35, to establish a fluid communication between a third chamber 40, intermediate between the chambers 22 and 23, and the line 9 connected to the solenoid valve 8. As shown schematically in Figure 2, the chamber 40 communicates by a passage 40 'with line 11 so as to be thus connected to the master cylinder 1. Similarly, the pressure chamber 23 is connected to line 25 to establish a connection between the high pressure generator 12 and this chamber 23 In addition, a conduit materializes the line 24 which connects the pressure chamber 22 to the line 7 for supplying the front wheel brake 5. Annular seals 41 and 42 are fixed on bearing surfaces of the sleeve 31 to isolate the chamber 22 of the chamber 40 on the one hand and to close off any communication between the chamber 40 and the line 9 on the other hand, other than by the passage 39 controlled by the bearing surface 35 of the drawer 27.

 It is understood in this regard that when the pressure generator 12 is started by the anti-lock device, the pressure developed1 always greater than that prevailing in the brake supply lines, pushes the drawer to the left (from the point of view of FIG. 2) so that this drawer is stopped by the pin 38 in a position where the bearing 35 of the drawer 27 closes the passage 39 to thereby prohibit any communication between the intermediate chamber 40 and the line 9.

 It is clear that the distributor 10 of the braking circuit according to the invention allows, under normal braking, while the pressure generator 12 is out of service, to establish communication between line 11 and line 9 through the passages 40 'and 39 to thus allow the transmission, in lines 7 and 7' of supply of the wheel brakes 5 and 6 respectively, of the liquid. brake pressurized in the master cylinder 1 by an action of the vehicle driver on the brake pedal 3.

 According to a particularly advantageous characteristic of the circuit according to the invention, it will be noted that a sudden action of the driver on this brake pedal, creating a sudden increase in pressure in the intermediate chamber 40 of the distributor, does not cause any displacement of this distributor because of the equality of the sections of the bearing surfaces 34 and 35 on which st exerts this increase in pressure. This eliminates the drawback observed possibly in braking circuits of the type described in the aforementioned document, where such a sudden increase in pressure can cause the piloted valve to close, assuming that the pressure losses caused by the flow of fluid through the solenoid valve located upstream of this valve can establish a transient pressure difference between the brake supply line and the chamber which surrounds the valve head of the valve, connected to the generator high pressure.

 In this regard, FIG. 2 shows the detail of the solenoid valve 8, shown integrated into the body 28 which supports the slide valve 10. In this figure it appears that the solenoid valve 8 conventionally comprises a movable ball 50, under the action of an electromagnet contained in a housing 51, between two seats 50 ′ and 50 ″ for the selective closure of fluid communications.

When the electromagnet 51 is not energized, the ball 50 is loaded on the seat 50 'in a position where it allows communication between lines 7 and 9.

When the electromagnet is excited, the ball is moved to the right (from the point of view of FIG. 2) against the seat 50 "to close a communication between these lines 7 and 9 and, on the contrary, open a communication between line 7 et la-line 16, which allows to return to the inlet of the pump 13 of the generator 12, in the low pressure tank 14, of the liquid contained in the wheel brake 5, so as to relieve the pressure in this wheel brake , as is conventional during an operating sequence of the wheel anti-lock device.

 Incidentally, it will be noted that the known solenoid valve structure shown in FIG. 2, which implies a very marked change in direction of the circulation of the brake fluid, from line 11 to line 7, generates appreciable pressure losses which are the origin of the accidental closing of the piloted valve, in certain braking circuits of the type described in the aforementioned patent document. The distributor with drawer of the circuit according to the invention perfectly withstands such pressure drops and is therefore not subject to accidental switching to normal braking, when the driver abruptly depresses the brake pedal. This advantageous result is obtained with a distributor which however perfectly ensures the cut-off function of the direct master cylinder / brake link in the event of an anti-blocking braking sequence, just like the valve piloted by the braking circuits of the prior art described in the preamble to this description.

 As seen above, the slide valve distributor of the circuit according to the invention is integrated into a monobloc structure which further comprises the solenoid valve 8 and the pressure generator 12. A part of the solenoid valve 8 is thus mounted in a complementary bore provided for this purpose in the body 28, the rest of the housing 51 of the solenoid valve projecting from this body on which it is fixed by means of a bolt 52 or other similar fixing means. Similarly, bolts 53, 54 make it possible to fix the pressure generator 12 on the body 28. Following an advantageous arrangement, in particular by its compactness, the restriction 19 is mounted in line with the solenoid valve 8, as shown in FIG. 2, a permanent fluid communication (not shown) being established between the line 9 and the restriction 19, at the level of the solenoid valve 8. The restriction 19 is constituted conventionally, in the embodiment shown, by a stack of perforated discs .

 There is also diagrammatically shown in FIG. 2 the non-return valve 17 located between lines 20 and 25 of the braking circuit according to the invention, shown more completely in FIG. 1. This non-return valve 17, slightly tared, prevents a back flow of brake fluid, in the direction of restriction 25 line 25, towards the pressure generator 12, a situation which could otherwise appear under normal braking.

 Although a single solenoid valve 8 is shown in Figure 2, it is clear that the body 28 includes two solenoid valves, 8, 8 'and that the operation of the solenoid valve 8' repeats that of the solenoid valve 8. The circuits d supply of the two wheel brakes are distinguished only by the line 24 which connects the line 7 of the wheel brake 5 to the chamber 22 of the distributor, then such a similar line does not exist in the supply circuit of the wheel brake 6 Thus, when the computer of the anti-lock device detects the impending condition of a wheel lock, the start-up of the generator 12 which immediately results therefrom causes the drawer of the distributor 10 to tip over, thereby cutting off any direct connection between the master cylinder 1 and the supply lines 7 and 7 'of the wheel brakes. It will be noted in this regard that the pressure of the brake fluid delivered by the generator 12 being, conventionally, always greater than the pressure prevailing in the lines 7 or 7 ′, the starting of the pump 13 of the generator always triggers the tilting of the drawer 27, whatever the pressure prevailing in line 7, the spring 36 introduced into the chamber 22 for loading to the right (from the point of view of FIG. 2) the drawer 27 having the sole purpose of de-maintaining this drawer in the position shown in FIG. 2 outside the anti-lock braking sequences, without the stiffness of this spring being sufficient to prevent the drawer from tilting when the pump 13 is started.

 We will now describe the operation of the braking circuit according to the invention. In normal braking, the slide 27 being at rest in abutment on the pin 38 in the position shown & in Figure 2 where it clears the passage 39 which communicates the intermediate chamber 40 and the line 9, the pressure established in the master cylinder by the action of the driver on the brake pedal 3 is exerted on the two ranges 34 and 35 of the drawer. These two scopes being of the same section as we saw above, the drawer remains in balance on its rest position. The pressure established in the chamber 40 is then transmitted through the solenoid valves and the wheel brakes 5 and 6 are inflated with brake fluid by the lines 7, 7 '.

 It is known that an anti-lock device for the wheels of a vehicle includes speed sensors for these wheels and a computer which compares the peripheral speeds of the wheels with the speed of the vehicle to deduce therefrom the imminence of a locking situation. at least one of the vehicle wheels. The computer then reacts by sending switching orders to the solenoid valves 8 and / or 8 'so as to modulate the pressure in the wheel brakes to avoid arriving at this blocking situation resulting from too strong action of the driver on the brake pedal, taking into account the coefficient of friction at the wheel / road interface, which depends very much on the road condition, as well as the degree of wear of the tire on the wheel.

 In such a situation of imminent locking of a vehicle wheel, the first pressure build-up takes place as in the case of normal braking. During this first pressure build-up, the computer controls at a predetermined instant the excitation of the solenoid valve associated with the impending locking wheel, which then passes into its "relaxation" position, in which the solenoid valve 8, for example , connects lines 7 and 16 while cutting the direct anterior communication between lines 7 and 9. The communication of lines 7 and 16 allows the brake fluid contained in the wheel brake 5 to flow into the line 16 to join the low pressure reservoir 14 located at the inlet of the pump 13. It then follows a relaxation of the pressure in the brake and, simultaneously, a starting of the pump 13, controlled by the computer. The pressure established by the pump in the supply line 25 of the chamber 23 of the distributor then being greater than the pressure in the line 7, communicated by line 24- to the chamber 22 of the distributor, the drawer moves to the left (from the point of view of FIG. 2) by closing the passage 39 which previously communicated the intermediate chamber 40 of the distributor and the line 9 to allow direct supply of the line 7 by the master cylinder 1. The pin 38 stops then the drawer 27 in the position where it closes the passage 39.

 An anti-lock braking sequence conventionally counts a series of detents alternating with slow pressure increases. At the end of an expansion, the computer cuts the excitation of the solenoid valve 8, 8 'to establish communication between lines 18 and 7 or 18' and 7 '. The wheel brakes are then again supplied with liquid pressurized by the generator 12 and passing through lines 7 or 7 'through lines 20, 18 and restriction 19 with regard to line 7, and through line 18 'and the restriction 19' for line 7 '.

 When, thanks to this succession of detents interspersed with slow pressure increases obtained thanks to restrictions 19 or 19 ', the anti-lock device computer detects that the slip between the vehicle wheel and the road has disappeared, the computer cuts off the excitation of the pump 13, the pressure in the line 25 and the chamber 23 falls and the drawer 27 of the distributor 10 returns to the right in the position where it clears the passage 39 to establish direct communication between the master cylinder and the lines of 'supply 7, 7' of the brakes 5, 6, and thus restore the circuit to its normal braking configuration. The spring 36 then maintains the slide 27 in this position, until * a possible new sequence of operation of the anti-lock circuit of the wheels.

 Of course, the invention is not limited to the embodiment described and shown which has been given only by way of example. In particular, the invention can also find application * a circuit which would have several slide distributors and several pressure generating circuits to ensure a completely independent control of the various wheels of the vehicle, at the cost, however, of increased complexity. circuit.

Claims (10)

 1. Hydraulic braking circuit provided with a master cylinder controlled by a brake pedal and an anti-lock device for wheels, for a motor vehicle, this device comprising a pressure generator (12) started at the start of a anti-lock braking sequence for selectively supplying at least one wheel brake (5, 6) and a member for automatically isolating the wheel brake (5, 6) from the master cylinder (I) when the pressure generator is started, characterized in that this member is constituted by a distributor (10) comprising a drawer (27) movable in a bore drilled in a sleeve (31), between first and second pressure chambers (22, 23) connected respectively to a line (7 ) supplying the brake (5) and to the pressure generator (12), the slide comprising two bearing surfaces (34, 35) of the same cross section which isolate these two chambers from a third intermediate chamber (40) so that, in a first p osition, of rest, of the drawer (27), the master cylinder (1) and the wheel brake (5) communicate by this third chamber (40) while, in a second position of the drawer (27), this communication is cut off, the slide (27) being moved into this second position by a differential pressure established between the first and second pressure chambers (22, 23) when the pressure generator (12) is started, following the excitation of the device d 'anti-lock.  2. Circuit according to claim 1, characterized in that the master cylinder (1) and the intermediate chamber (40) are in permanent communication, the distributor sleeve being pierced with a transverse passage (39) which establishes a communication between the intermediate chamber (40) and the wheel brake when the drawer (27) is in its first position, while this communication is closed by a bearing (35) of the drawer when the latter occupies its second position.  3. Circuit according to any one of claims 1 and 2, characterized in that the travel of the drawer (27) is limited by the two ends of a buttonhole pierced in a shaft (37) connecting the two spans (34, 35), a pin (38) integral with the sleeve (31) of the dispenser passing through this buttonhole to constitute a stop for one and the other of the two ends of the buttonhole.  4. Circuit according to any one of claims 1 to 3, characterized in that a spring (36) placed in the first pressure chamber (22) loads the slide (27) to its first position.  5. Circuit according to any one of claims 1 to 4, characterized in that a solenoid valve (8, 8 ') is interposed between the intermediate chamber (40) of the drawer (27) and the supply line (7 , 7 ') of the wheel brake (5, 6).  6. Circuit according to claim 5, characterized in that said solenoid valve (8, 8 ') is three-way and two positions, the solenoid valve establishing in a first position communication between the supply line (7, 7' ) of the brake and the master cylinder (1) when the drawer (27) is in its first position, or between this line (7, 7 ') and the pressure generator (12) when the drawer is in its second position, the solenoid valve establishing in its second position a communication between the line (7, 7 ') of the brake supply and a low pressure reservoir (14) in which the brake fluid from this line then flows.  7. Circuit according to claim 6, characterized in that the low pressure reservoir (14) supplies a pump (13) for recharging a high pressure accumulator (15), the assembly constituting the pressure generator (12) of the anti-lock device.  8. Circuit according to any one of claims 5, 6 and 7, characterized in that a restriction (19, 19 ') is interposed between the high pressure generator (12) and the solenoid valve (8, 8').  9. Circuit according to any one of the preceding claims, characterized in that a non-return valve (17) and a restriction line (20) (21) are connected between the output of the high pressure generator (12) and the master. -cylinder.  10. Circuit according to any one of the preceding claims, characterized in that the outlet of the distributor is connected to two identical supply circuits of two brakes associated with wheels in crossed positions.