FR2517270A1 - MODULATION VALVE ASSEMBLY DETECTING DECELERATION FOR VEHICLE BRAKING SYSTEMS - Google Patents

Abstract

INVENTION RELATING TO THE BRAKING OF VEHICLES. A DETECTION DETECTION BALL 17, IN A CAGE 18 IS SOLICITED TOWARDS A GRADIN 19 OF THE WRAPPED BODY 1 AND TOWARDS A SHOULDER 23 OF A CONTROL PISTON 9 BY A SPRING 20. A VALVE SEAT 15 IS PROVIDED ON ITS PISTON A THE END OF A PASSAGE 16, CONNECTING THE INPUT PORT 7 OF A MASTER CYLINDER AND THE OUTPUT 8 GOING TO THE REAR BRAKES. THE USEFUL AREA OF THE PISTON, SUBJECT TO THE INLET PRESSURE, IS LESS THAN THAT SUBJECT TO THE OUTLET PRESSURE. WHEN THE BALL 17 STUCKS AGAINST THE SEAT 15 AS A RESULT OF A DECELERATION, THE PRESSURE RISE MOVES THE PISTON AND THE BALL IS RELEASED FROM THE SEAT BY A LEVER 22 PRODUCING A BEND IN THE CHARACTERISTIC. APPLICATION TO THE REALIZATION OF SUCH COMPACT AND CHEAP UNITS.

Description

The present invention, concerning the braking of vehicles, is more

specifically relating to

  modulation valve assemblies detecting deceleration

  for a vehicle braking system of the kind comprising a casing body provided with a brake pressure input and a brake pressure output, a control piston moving in the casing body which governs the relationship between the inlet and outlet pressures and a deceleration detection element which is housed in the casing body and adapted to actuate a deceleration valve for decelerations of the casing body greater than a deceleration threshold, the operation of the valve of deceleration being arranged to influence the control exerted by the control piston will be designated later such a valve assembly by "valve of the

exposed genre ".

  There have been several proposals for making valve assemblies of this kind. Usually the brake pressure input of such a set is connected to a source of brake pressure which is also connected to the front wheel brakes, the output of brake pressure being connected to the rear wheel brakes, and the arrangement of the control piston is selected so that for input pressures greater than an input pressure threshold value, the rate of increase of the outlet pressure is reduced compared to the rate of increase of the inlet pressure, so

  to provide rear wheel brakes with

  proportionately reduced to take account of

  cations of the distribution of weights during the

vehicle's celeration.

  It is known to dispose of the death valve

  in various ways in order to modify the relationship between

  between the inlet and outlet pressures The deceleration valve is designed to take into account the

  that we need more brake pressure

  to produce a given deceleration in a vehicle.

  the loaded state for the unloaded state of the vehicle and therefore it has been proposed to modify the threshold value.

  input pressure by making this value dependent on

  the closing of the deceleration valve. eci avoids using a mechanical link that

  bends when the load of the vehicle is changed

  cule. In one such type of valve assembly, the closure of the deceleration valve is arranged to enclose, without escaping, a volume of fluid in a control chamber limited by a regulating piston, which control the solicitation by spring

  of the control piston Usually a spring

  the control piston acts between the two pistons.

  tones, but such an arrangement leads to a relatively long valve assembly and its characteristics of

  operation are not entirely satisfactory.

  British Patent No. 2,010,425 A illustrates an attempt to obtain better characteristics, but this has led to a composite assembly comprising

many pieces.

  It is an object of the present invention to provide a valve assembly of the type exposed, which is compact and relatively inexpensive to manufacture, yet can be arranged to have

  satisfactory operating characteristics.

  According to the invention, in a

  valve of the type exposed, the element detecting the

  3. aeration is housed in a cage that can slide inside a chamber subjected to the inlet pressure and is elastically urged to come into contact with a first stop provided in the casing body and with a second stop of the piston of control, the deceleration valve comprises a valve seat on the piston which is adapted to be closed, by cutting the communication with the inlet, by the deceleration detecting element, the cage comprises a detachment portion of the seat which can be engaging with the deceleration detecting element and arranged so that the valve seat is opened during a relative movement of separation of the piston and the cage from the relative position in which the cage is applied

  against the second stop and the piston has a pre-

  first pressure area exposed to the inlet pressure to produce a force acting on the piston

  in the direction away from the cage and one

  the second effective area of pressure, acting in the opposite direction, exposed to the outlet pressure, the second area being greater than the first area, the area of the valve seat being

  included in the calculation of the first area.

  With such a valve, a discontinuity

  of the characteristic of the outlet pressure as a function of the inlet pressure can be obtained, after closure of the valve seat by the deceleration detection means, as a result of the application of the cage against the first stop, this which thus releases the control piston from the spring force The removal of spring force on the control piston is an important factor which requires an appreciable increase in the inlet pressure before the outlet pressure This discontinuity is useful to rule out the characteristic of the theoretically ideal curve that would otherwise be cut off by a portion of

  subsequent measurement of the characteristic and which

  53 would lock the rear wheels.

  Also, with such a valve it is possible to have first and second areas

  virtually identical, so with a vehicle.

  loaded an amplification part of the characteristic,

  which begins when the valve seat is closed by

  deceleration detection and which has a slope corresponding to the ratio of the two areas, may be

  brought to a slope close to 450, which means

  that the theoretical curve can be closely

  followed at low inlet pressures.

  Preferably the first stop is provided by a step in the envelope body, against which

  applies one end of the cage.

  Preferably the detachment portion of the seat of the cage is provided by an annular lip of the cage, directed inwards in the direction

  radial, and said lip can be applied against the

  piston stop, so as to determine the size of the

  of the movement of the piston and the cage together.

  The resilient means biasing the cage preferably comprises a compression spring which bears against an end wall of the cage at its end

away from the piston.

  A direct hermetic connection contact can be obtained between the deceleration detection element and the valve seat, but according to another possibility a perforated end wall of the cage can be arranged in the vicinity of the piston, so as to form a seal around the opening by connecting the valve seat on the one hand and the deceleration sensing element on the other hand, all so as to provide an indirect seal between the deceleration sensing element and the seat

of valve.

  In one embodiment for use with a dual circuit braking system the control piston is in two parts normally in contact, a first piston portion provided with said valve seat and exposed at the far end of the valve. valve seat, at the outlet pressure of a circuit, and at its end opposite the inlet pressure of this circuit, and a second piston portion exposed, at the end remote from the first piston portion, to the unmodified master cylinder pressure in the other circuit In the case of a lack of fluid pressure of said other circuit, the portion of the first piston is rendered incapable of operation, so that the output pressure in said circuit is not reduced beyond the inlet pressure. The invention will now be described in more detail, by way of non-limiting example, with reference to the accompanying drawings in which: FIG. 1 is a longitudinal section of a valve assembly according to the invention, parts or parts being represented in the non-actuated state of the assembly;

  FIG. 2 is a graph explaining the function

  the whole of Figure 1; Figure 5 shows a modified sealing arrangement with respect to that used in Figure 1, but on a larger scale; FIG. 4 is a longitudinal section of a valve assembly suitable for use with a dual circuit braking system and according to the invention, the parts or parts being shown in the non-actuated state of the assembly and the Figure 5 is a graph explaining the

  operation of the whole of Figure 4.

  With reference to FIG. 1, it can be seen that the assembly comprises a casing body 1 provided with a stepped bore 2 comprising piercing parts.

  3, 4 and 5 having a smaller and smaller diameter.

  The bore 2 is closed at one end by a plug 6 provided with an inlet orifice 7, intended to be connected to an output of the master cylinder, and the opposite end

  piercing communicates with an outlet port 8,

  born to be connected to a rear wheel brake actuator.

  A stepped control piston 9 has its left-hand and larger diameter portion slidably connected in the piercing portion 5 by an O-ring-shaped seal 11 supported in an outer annular recess of the piston and its piston portion. right

  12 smaller diameter can slide in a ring -

  stationary 13 and is sealingly connected to the ring 13 by an adjacent O-ring 14 compressed radially between the wall of the piercing portion 4 and the radially outer surface of the piston portion 12. piercing 3

  from one end while providing the choke

  necessary, complementary to the part of

  piston 12 A ventilation opening 13 'going to the

  mosphere is provided behind the ring 13.

  The piston 9 is provided with a drilling hole

  axial discharge 16 which normally provides a communication

  direct cation between the inlet 7 and the outlet 8 At its right end, the piston portion 12 is shaped with a frustoconical valve seat 15 which surrounds the bore 16 and against which can be applied, with sealing, an element of deceleration detection

  having the shape of a ball 17 housed in a tubular cage

  The cage 18 can slide axially in the piercing portion 3 and is biased towards a step 19 of the shell body, located between the

  piercing parts 3 and 4 by a compressor spring

  pre-stressed coil assembly 20 which acts between the

  chon 6 and a closure plate 21 holding the ball 17 captive inside the cage 18 The cage 18 is

  provided, at its left end, with an annular lip

  22, directed radially inwards, which can come into contact with an annular shoulder 23 of the piston portion 12 by a reduction of the outer diameter of the end portion 24.

  end 24 adapts with appreciable play in the

  the interior of the central opening defined by the lip 22 and its length is chosen so that when the cage 18 is applied against the step 23, the ball 17

  can move to come into contact with

  with the seat 15 without being generated by the lip 22, but also so that only a slight relative movement of the spacing of the cage 18 and the piston 9 is necessary before the lip 22 comes into contact with the ball 17 to detach this ball from the seat 15. The cage 18 comprises at least one axial slot passing through the lip 22 so as to ensure that the inlet pressure is propagated in the chamber in

  which the ring ring 14 is housed.

  We will now describe the operation of

  the whole of Figure 1 with reference to Figure 2.

  The regular curves A and B represent the relationships

  theoretically ideal between the braking pressures of the rear and front wheels, respectively for the vehicle supporting only the driver or

in the fully charged state.

  We will first examine the operation of the whole if there is only the driver in the vehicle; when the initial application of the brakes the parts will be in the positions shown in Figure 1 The casing body 1 is mounted in a vehicle, with the left end pointing to

  the front of the vehicle and a small inclination

  Zontal, so that the right end is lower than the left end Because of this inclination the ball 17 rests against the plate 21 being well clear of the valve seat 15, so that the initial increases in the input pressure are directly transmitted to the outlet 8 by the bore 16 to provide the portion of the graph from C to D It is seen in Figure 2 that this part is located entirely below the theoretical curve A It is particularly important that for low braking pressures the output pressure does not exceed the theoretical curve, otherwise the rear wheels could lock at point D which is just below the curve A we arranged for the

  deceleration of the vehicle containing only the

  tor is just sufficient to cause the ball 17 to roll to the left in the cage 18, so that it is pressed against the valve seat 15, the piston 9 being held in the position shown in FIG. the force, directed to the right, which is generated by the input pressure (which is equal to that of the output) acting on the effective areas

  opposite pressure values A 1 and A 2, respectively

  Piston rings 12 and 10 The area A 1 corresponds to the piercing of the ring 13 and the area A 2 to the cross-sectional area of the piercing portion 5; as A 2 is greater than A, the net force acting on

the piston 9 acts to the right.

  It is expected that the net fluid pressure force, directed to the right, which acts on the piston 9 at the point D is just equal to the preload of the spring 20 This ensures that, in the loaded state of the vehicle, as it will be explained later, the cage 18 will be removed from the step 19 when the ball

17 rolls.

  When the inlet pressure, in the state where the vehicle only supports the driver, is

  increased from point D, the pressure of

  As the seat is closed, it will increase the fluid pressure force, directed to the left, on the piston 9, so that it will move in the same direction to absorb the pressure. interval between the ball 17 and the lip 22, so as to bring the ball 17 into contact with the lip 22 As the cage is supported by the casing body because of its abutment against the step 19, the application of the ball against lip 22 will result in an effective decrease in the area of the

  piston 9 on which the inlet pressure acts.

  This surface loss is equal to the area A delimited by the contact line of the ball 17 with the valve seat 15. As the inside of the valve seat 15 continues to communicate, via the bore 16, with At exit 8, there will also be an effective loss of the area A 2 on which the exit pressure acts, which gives an area of

work A 2-A 3.

  Also, during the movement to the left of the piston 9 from the position shown in Figure 1, the force of the spring 20 is lost to the piston 9, because it is fully supported by the casing body 1 by abutment of the cage 18 against step 19 This means that the inlet pressure must rise by an amount to compensate for the lack of

spring force.

  The result of the effective modification of the area A of the piston 9 and the fall of the force of the spring is therefore that the inlet pressure must rise by an appreciable amount, at the point E, before a new increase of the outlet pressure

not happen.

  At point E, the force generated by the

  input pressure which acts to the right on the piston 9, on an area A 1 -A 3, becomes equal to the force generated by the output pressure acting to the left on the piston 9 on the area A 2-A , so that

  in a subsequent increase of the pressure of

  The piston 9 moves to the left and the ball 17 is disengaged from the valve seat 15 by the stationary lip 22. There then follows a dosing effect.

  3 U when the piston 9 oscillates backwards and towards the

  while the valve opens and closes to give part F of FIG.

slope (A 1 -A 3) / (A 2 -A 3).

  Although part F of the curve will eventually cut the theoretical curve A, this will only happen for high input pressures,

  for which the wheels would in any case be blocked.

  1 UJ n will now consider the operation of the assembly of Figure 1 for the fully loaded state of the vehicle and, in this state, the inlet pressure will rise from C to G before sufficient deceleration of the vehicle is produced for the ball rolling 17 causes the seat to engage 15 At point D, the net force to the right, due to the inlet pressure acting to the right on the piston 9, on an area A 2-A 1 , has been provided equal to the prestressing of the spring 20, so that during the increase of the inlet pressure from D to G the piston

  9 and the cage 18 move to the right by

  to the body envelqpel under the effect of the force

  of the pressure of the fluid acting on the piston 9,

  thus increasing the force on the spring 20.

  After closing the valve seat 15 at point G by ball 17, a further increase

  of the inlet pressure acting on the area A 1 in

  a progressive movement will be made to the left of the piston 9 at the same time as that of the cage 18, so that the outlet pressure will rise at a rate determined by the ratio of the areas A 1 / A 2 = since the seat of Valve 15 is closed This gives the part of the graph from G to H The invention allows this ratio to be relatively close to the unit to provide a slope slightly less than 450, so that a maximum amplification is obtained at the point G Therefore the curve

  Theoretical approach is closely followed

entry.

  At point H, which is located just

  below the theoretical curve B, the cage 18 comes into contact with the step 19 and practically at the same time the area A 3 of the piston 9 is made ineffective, by the movement towards the left of the piston 9, to succeed

  contacting the lip 15 with the ball 17.

  As in the unloaded state, this causes a delay in the continuation of the increase of the outlet pressure, while the inlet pressure rises to take account of the actual loss of the area A and the fall of the force of the spring acting on the piston 9 when the cage 18 comes into contact with the step 19 of the body envelope At point K the force directed to the left on the piston 9, which is due to the action the inlet pressure on the area A 1 A 5 is sufficient to overcome

  the force to the right due to the output pressure acting

  in the area A 2 to 3, so that once again the dosing starts with the same relation between the outlet pressure and the inlet pressure as for the part a, so as to produce the part J of graph which we will see that it is actually the continuation of the line P. Therefore the whole of Figure 1 produces the significant offsets of D in E and H in K characteristics, so as to ensure that the actual characteristics of the valve does not traverse the theoretical curves except at high inlet pressures, and nevertheless the actual characteristics closely follow the theoretical curves at low pressures in the region from C to D and from C to H,

  respectively in the condition that the vehicle

  only wears the driver or is totally

charge.

  The closure plate 21 is provided with a series of orifices 26, so that during rapid application of the master cylinder resulting from a sudden braking in an emergency, the ball 17 is projected against the seat of valve 15 by fluid pressure forces for

  move the point D towards the low pressures.

  The disposition of the ball 17 in the direct path of the

  fluid between inlet 7 and outlet 8 facilitates the

  this characteristic arrangement.

  It will be understood that the arrangement of all the pieces in a single piercing 3 rather than in

  Separate holes help reduce manufacturing costs.

  FIG. 3 shows a modified sealing arrangement with respect to that of FIG. 1, which uses direct metal-to-metal contact between the ball 17 and the seat. The parts or parts corresponding to those of FIG. 1 have been designated by FIG. the same benchmarks as in Figure 3 In the provision of the

  3, the cage 18 is provided with an end wall.

  Means 27, adjacent the piston portion 12, which has a central hole 28 surrounded on the opposite sides of the wall 27 by respective seat rings 29, 30 of elastomer, which are glued to it The seat ring 29 is adapted to receive the bevel 15 of the part of

  piston 12 for making a joint between the end wall and

  In the initial elevation of the inlet pressure, the piston 9 will move to the right to bring the bevel 15 to the seal 17 and the piston portion 12 and the ring 30 can be sealingly connected to the ball 17. apply against the seat ring 29 So when the ball 17 rolls to apply against the ring 30,

  an indirect seal is obtained between ball 17 and the ex-

  piston end 15 through the wall 27.

  The radially inner edge of the bevel 15 defines the area A which is made inactive when the ball 17 is in contact with the ring 30 and the bevel

  15 is applied against the ring 29.

  The valve assembly of Fig. 4 is intended to be used with a dual circuit braking system. Parts or parts corresponding to those of

  Figures 1 and 3 have been designated by the same references.

  In this embodiment, the control piston assembly comprises two separable portions 31, 32 bearing one against the other. A dosing assembly similar to that of FIG. 3 is used, except that the seat ring 29 is carried by the right end of the piston portion 32 The bore 16 of the piston opens into a

  intermediate chamber 33 of the envelope body, through

  In the middle of radial recesses 34 formed in the left end face of the piston portion 52, the primary outlet orifice 8, which is a transverse orifice in the present case, communicating directly with the chamber 33. 7 is connected to an outlet 35 of a tandem master cylinder 36 and the second outlet 37 is connected to an orifice 38 arriving in a chamber 39 located at the left end of the piston portion

  31, this room communicating directly with one

  16 x outlet port 40 Primary port 8 is connected

  a rear wheel brake actuator, not shown

  felt, and the secondary outlet port 40 is connected to a front wheel brake actuator, which is not

no longer represented.

  The piston portion 32 is a conventional piston

  at its right end at the inlet pressure and at its left end, at the primary outlet pressure in the chamber 33, while the piston portion 31 has a stepped shape whose left end , larger, is exposed to the secondary inlet pressure (which is equal to the outlet pressure) and its lower right end is exposed to the pressure of the chamber 33 The area of the left end of the piston portion 31 and that of its right end will be designated respectively by A 1 and A 2 The cross-sectional area of the chamber 33 and that of the piston portion 32 will be designated A 3 and the area of the cross section of the seat 29, by A 4 (These designation marks do not

  do not correspond to those used for Figure 1).

  When both circuits are capable of

  function, we can arrange for the characteristics

  of the valve assembly are identical to those of FIG. 1, as can be seen in FIG. 5 in which the corresponding parts of the

  characteristics have been designated by the same letters.

  The effective pressure area of the piston assembly

  31, 32, exposed to the inlet pressure and

  in the direction away from the cage, is (A 3 A 1) because the inlet pressure acts on the right end of the piston portion 52 and on the left portion of the portion The effective area of counter pressure of the piston assembly

  command is exposed to the output pressure is (A 3 A 2).

  Thus the slope of the characteristic part G to H is (A 3 A 1) / (A 3 A 2) and that of the dosing parts Y and J is (A 3-A 1 -A 4) / (A) - A 2-A 4) By making sure that A 1 is smaller than A 3 and choosing suitably

  areas, it is possible to obtain

to those in Figure 2.

  In the case of a pressure drop in the secondary circuit connected to the chamber 39, the area A 1 turned to the left will be lost for the inlet pressure, so that the control piston assembly 31, 32 will be held completely to the left by the primary inlet pressure acting to the left on the area A 3 at the right end of the piston portion 32, to prevent the seat 29 from sealingly joining the wall of the cage 27 So even when the

  ball 17 is applied against the seat 30, the chamber

  33 will continue to communicate with the primary entrance

  mayor 7 beyond the open seat 29 and maximum braking

  will be applied to the rear wheels as indicated

  by line L in broken line of Figure 5.

  According to a variant, not shown, of the valve assembly of Fig. 4, the piston portion 31 is provided as an ordinary piston, and the piston portion 32, a stepped piston;

Claims (5)

  A deceleration-sensing modulation valve assembly for a vehicle braking system comprising a casing body having a brake pressure input and a brake pressure output, a control piston moving in the casing body which regulates the relationship between the inlet and outlet pressures and a deceleration sensing element housed in the casing body and adapted to operate a deceleration valve for decelerations of the body   envelope above a deceleration threshold, the.   operation of the deceleration valve being arranged to influence the control exerted by the control piston, said assembly being characterized in that the deceleration sensing element (17) is housed in a cage (18) which can slide in a chamber exposed to the inlet pressure and is resiliently biased to meet a first abutment (19) provided in the casing body (1) and a second abutment (23) on the control piston (9), in that the deceleration valve comprises a valve seat (15) on the piston which is adapted to be closed, by opposing communication with the inlet (7), by the deceleration detection element, in that the cage includes   a part (22) detaching the seat that can be   interacting with the deceleration detection element and arranged so that the valve seat is open during a relative movement of separation of the piston and the cage from the relative position in which the cage is in contact with the second stop and in that the piston has a first effective pressure area (A 1) exposed to the inlet pressure to produce on the piston a force acting in the direction away from the cage and a second effective area (A 2) pressure, acting in the opposite direction, which is exposed to the outlet pressure, the second area (A 2) being larger than the first area (A 1),   the area (A 5) of the valve seat being included in the cal-   estimate of the first area.   Valve according to claim 1, characterized   in that the first stop comprises in the body a step (19) which is in contact with one end of the cage.   Valve according to claim 1 or 2, characterized in that the detachment part of the seat, in the cage comprises on the cage an annular lip (22) directed radially inwards, and in that said lip can come into contact with the second   piston stop to determine the size of the displacement.   joint cement of the piston and the cage.   Valve according to one of the preceding claims   cedeentes, characterized in that the elastic means of   stressing the cage comprises a compression spring   projection (20) which bears against an end wall (21)   of the cage, at its end remote from the piston.   Valve according to one of the preceding claims   cedeentes, characterized in that a perforated end wall (27) of the cage adjacent the piston is arranged to connect hermetically around the opening with the valve seat on the one hand and with   the deceleration element on the other hand, so as to   to establish an indirect joint between the sensing element   deceleration and valve seat.   Valve according to one of the preceding claims   cedeentes, and intended to be used with a dual circuit braking system, characterized in that the control piston is formed of two parts (31, 32) normally bearing one against the other, a first piston portion ( 32) being formed with said seat of   valve and arranged, to be exposed at the far end.   of the valve seat at the outlet pressure of a circuit and, at its opposite end, at the inlet pressure of that circuit and that a second part   of this piston (31) is arranged to be exposed to the ex-   tremite removed from the first piston part, at the pressure dou maltre-cylinder, unmodified, in the other circuit.