GB1600459A

GB1600459A - Parallel proportioning valve assembly

Info

Publication number: GB1600459A
Application number: GB2454978A
Authority: GB
Original assignee: Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Electric Industries Ltd
Priority date: 1977-06-07
Filing date: 1978-05-30
Publication date: 1981-10-14
Also published as: DE2825005C2; DE2825005A1

Description

(54) PARALLEL PROPORTIONING VALVE ASSEMBLY (71) We, SUMITOMO ELECTRIC INDUSTRIES, LTD., a Japanese Company, of No. 15, Kitahama-5-chome, Higashi-ku, Osaka, Japan, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement:- The present invention relates to a parallel proportioning valve assembly for use in the fluid circuits of. for example, a dual braking system for a motor vehicle.

The U.S. Patent No. 3,423.936 owned bv Kelsey-Hayes Company discloses a proportioning valve comprising a chamber having an inlet connected to a pressure source and an outlet connected to a rear brake cylinder supplied with a reduced pressure. a pressure responsive plunger accommodated within the chamber so as to open and close a fluid passage between the inlet and outlet, and a spring urging the plunger in the direction to open the fluid passage.

A pair of such valves are normally used in the fluid circuits of a dual braking system.

In order to save material and manufacturing cost, there has been developed a valve device incorporating a pair of proportioning valves in a single casing. However, the valve device is so constructed that each of the valves has its on n spring to urge the pressure responsive plunger. and it has the disadvantage in that it is difficult to change the cut-in point of pressure reducing action of a valve if the other valve fails.

Thus, when one of two braking circuits becomes inoperative due to, for example, fluid leakage, it is desirable to increase substantially the effective pressure to be supplied to the rear brake cylinder by the other valve which is in operation, thus appropriately distributing the pressurization of front and rear brakes.

However, since each of the valves has its own spring which biasses each of the plungers. u hen one of the two braking circuits becomes inoperative, the valve in the other circuit normally operates so that the pressure reducing action will occur at a predetermined normal pressure, without shifting the cut-in point to a higher value.

A first object of the present invention is, therefore, to provide a parallel proportioning valve assembly in which both of the proportioning valves have substantially the same cut-in point of pressure reducing action by absorbing a difference of strokes of the pressure responsive plungers.

Accordingly the present invention consists in a parallel proportioning valve assembly comprising a casing. a pair of parallel chambers provided within the casing, each of the chambers having a fluid inlet connected to a pressure source and a fluid pressure supply outlet, a fluid pressure responsive plunger accommodated in each of the chambers, a valve seat provided in a fluid passage between each inlet and the corresponding outlet, the valve seat being adapted to be closed and opened by the respective pressure responsive plunger, a single spring urging both of the plungers in the direction to open the valve seats through a single abutting plate each end of which abuts the end of a respective plunger, and a guide means for limiting the movement of the abutting plate to substantially in the axial direction of the plungers.

In order that the present invention may be more readily understood various embodiments thereof will now be described by way of example and with reference to the accompanying drawings. in which: Fig. 1 is a longitudinal sectional view showing one embodiment of a parallel proportioning valve assembly of the invention:: Figs. 2 and 3 are longitudinally sectioned fragmentary views showing slight modifications of a parallel proportioning valves of the invention; Fig. 4 is a longitudinally sectioned fragmentary view showing another embodiment of the present invention; Fig. 5 is a longitudinally sectioned fragmentary view illustrating still further embodiment of the invention; Fig. 6 is a longitudinally sectioned fragmentary view showing a further embodiment of the invention; Figs. 7 and 8 are schematic views showing the operation of a parallel proportioning valve assembly of the invention; Fig. 9 is a longitudinally sectioned fragmentary view illustrating a modification of a parallel proportioning valve assembly of the present invention: Fig. 10 is a longitudinally sectioned fragmentary view showing a further modification of a parallel proportioning valve assembly of the present invention:: Fig. 11 is a schematic view showing the operation of the same: Fig. 12 is a longitudinally sectioned fragmentary view showing a still further modification of a parallel proportioning valve of the present invention: Fig. 13 is a longitudinally sectioned fragmentary view for comparison to the above: Fig. 14 is a longitudinally sectioned fragmentary view showing another modification of a parallel proportioning valve assembly of the present invention: Figs. 15 and 16 are schematic views showing the operation of the same: Fig. 17 is a longitudinally sectioned fragmentary view showing still another modification of a parallel proportioning valve assembly of the present invention: Fig. 18 is a diagrammatical explanatory view for the operation of the same:: Fig. 19 is a longitudinalls sectioned fragmentary view showing a further modification of a parallel proportioning valve assembly of the present invention: and Fig. 20 is a diagrammatical view for explaining the operation of the same.

Throughout the drawings, similar parts and elements are designated by the similar reference numerals and letters.

Referring now to Fig. 1. a casing generally indicated at 10 has fluid pressure chambers 11, 11' parallel to one another.

The chambers have inlets 12. 12' connected to a pressure source M such as tandem master cylinder. first outlets 13. 13' for the direct output of the pressure supplied from the pressure source M to front brake cylinders F, F', and second outlets 14. 14' for transmitting a proportionally reduced pressure to rear brake cylinders R, R'.

respectively.

In the chambers 11, 11' are incorporated valve assemblies 20, 20', respectively. Valve assembly 20 comprises a pressure responsive plunger 21, a valve seat 22 which is opened and closed by the plunger 21, and a plunger guide 24 which guides a shaft 23 of the plunger 21. A cup type seal 25 and 0ring 26 fitted in the plunger guide 24 provide a liquid-tight seal of the chamber 11. A washer 57 which is fitted in the inner end of the guide 24 prevents the removal of the cup seal 25.

The other valve assembly 20' is of identical construction and its corresponding integer have reference numerals with pulses.

The plungers 21, 21' have blind holes 27, 27' at their outer ends which slightly project out of the guides 24, 24', respectively. In the blind holes 27, 27' are engaged projections 31, 31' provided on the ends of an abutting plate 30, respectively. At the center of the abutting plate 30 is fixed a guide pin 32 which is slidably inserted in a guide hole 33 provided in the middle between the plungers 21 and 21'. Preferably, a ventilation hole 34 is provided axially through the guide pin 32.

A cap 35 closes the end face of the casing 10. A flange 36 of the cap 35 is fixed to the casing by means of bolts and engages the outer ends of the guides 24, 24' to retain the same.

A single spring 37 is mounted between the inside of the cap 35 and the abutting plate 30, and applies a pressure to the plungers 71.

21' through the abutting plate 30.

As shown in Fig. 2, the sealing means between the chamber 11 and the plunger guide 24 may be a single cup type seal 28. or as shown in Fig. 3, may be an O-ring 29 in place of the cup type seal 25 of Fig. 1.

In operation of the parallel proportioning valve of Fig. 1, when the inlet 12 of the chamber 11 is applied xith a fluid pressure from the pressure source M in the normal condition wherein both braking systems are working, the pressure is directly transmitted to the front brake cylinder F through the outlet 13.

On the other hand, the fluid pressure acts on the effective area corresponding to the sectional area of the shaft 23 of the plunger 21 within the chamber 11 to force the plunger leftwardly. However, since the pressure of the spring 37 overcomes the leftwardly biasing force of the fluid on the plunger. it stays at its position shown by the solid lines in Fig. 1 and the valve seat 22 still remains open, thus directly transmitting the fluid pressure to the rear brake cylinder R through the outlet 14.

When the fluid pressure is further increased so that the leftwardly biasing force on the plunger 21 finally overcomes the force of the spring 37, then the plunger 21 is moved leftwardly to close the valve seat 22. After this, a pressure proportionally reduced by the vibration of the plunger 21 is supplied to the rear brake cylinder R through the outlet 14.

The other proportioning valve assembly 20' operates in the same manner as the assembly 20.

Meanwhile. when one of the braking systems becomes inoperative due to, for example, fluid leakage, the fluid pressure from the pressure source M will not act on the inoperative plunger 21'. As a result, the plunger 21' stays at its position shown in Fig. 1. That is, the stroke thereof is zero.

While, on the plunger 21 acts a normal fluid pressure to force it leftwardly. However, since the inoperative plunger 21' will not move and the abutting plate 30 can move only in the axial direction of plungers 21, 21 h owing to the limitation of the guide pin 32 inserted in the guide hole 33, all the force of the spring 37 counteracts against the leftwardly biasing force of the fluid pressure acting on the operative plunger 21.That is, twice as much the force as that of the normal condition is applied to the operative plunger 21. As a result, the plunger 21 will not move before a fluid pressure from the pressure source becomes far higher than that of normal condition. 'During the time, as will be understood, the pressure reducing action will not occur and the pressure supplied from the pressure source is directly transmitted to the rear brake cylinder R to compensate a shortage of a braking force during the breakdown of one of the braking circuits.

However. if there be no guide pin fixed to the abutting plate 30 and inserted into the guide hole 33. the abutting plate 30 will incline on the projection 31' as the fulcrum which engages the inoperative plunger 21', according to the stroke of the operative plunger 21. As a result, the force of the spring 37 is spread between both plungers 21, 21', and it is impossible to increase the effective spring force so as to be higher than that of the normal condition.

The chambers 11, 11' are conveniently formed by drilling bores having stepped diameters reduced towards the outlet 14.

Further, the construction of the proportioning valve of just described can be considerably simplified by the single spring 37, single abutting plate 30 and the cap 35 which closes the casing 10 and at the same time prevents the removal of the guides 24, 24'.

As appears from Fig. 4, the guide pin 32 may be fixed to the opposite side of the abutting plate 30, and is inserted in a guide 38 fixed to the inside of the cap 35. The arrangement has substantially the same effect as that of Fig. 1.

As shown in Fig. 5, a guide wall 39 integral with the abutting plate 30 may be fitted in the cap 35 so as to be slidable along the inner periphery of the cap.

Fig. 6 shows another embodiment of the present invention. As seen, a clearance may be provided between the guide pin 32 and the guide hole 33. The range of the clearance will be explained hereinafter.

Preferably, rounded or conical ends of the shafts 23, 23' of the plungers are pivotally engaged with spherical or conical recesses 58, 58' provided on the end portions of the abutting plate 30, respectively.

The operation of the proportioning valve is explained in reference to Figs. 7 and 8.

Assuming that a difference +Ax exists between the strokes of the plungers 21, 21' during the normal condition of both of the two braking systems due to the accumulation of errors upon machining and assembling the valve, when the plungers project from the guides 24, 24' at their cut-in points, the end of one of the plungers projects beyond the other by 2Ax in maximum as shown in Fig. 7. If the abutting plate 30 could incline to this extent, both of the plungers 21, 21' will equally receive the force of the spring 37 to permit the pressure reducing action to occur substantially simultaneouslv and equally.This equalization can be attained by designing the clearance in a range which permits the inclination of the abutting plate 30 caused by the difference of strokes between the plungers 21, 71' during the normal condition of the two braking systems.

When one of the two braking systems is inoperative due to fluid leakage or the like, the inoperative plunger stays at its position, i.e., the stroke thereof is zero. As a result the abutting plate 30 will incline according to the stroke of the operative plunger.

Before the inclination reaches to a value corresponding to the cut-in point, i.e., before the pressure reducing action is performed by the normal stroke of the operative plunger, if the guide pin 32 is adapted to contact at its end edge to the inner periphery of the guide hole 33, the further inclination of the abutting plate 30 is limited.

In the above state shown by Fig. 8, if the plunger 21 further pushes the abutting plate 30, the latter will move leftwardly while slipping at the contacting point of the pin 32 and the hole 33 when a friction force at the contacting point is sufficiently small. As a result, substantially all the force of the spring 37 counteracts on the plunger 21, and thus the pressure reducing action of the plunger 21 begins at a point of pressure far greater than that of the normal condition.

Between the pin 32 and the guide 38 in Fig. 4 can be provided a clearance, and also between the guide wall 39 and the inner periphery of the cap 35 in Fig. 5.

As seen from Fig. 9, a spherical or conical recess 40 is provided on the center of the abutting plate 30. A projection 41 on the center of a receiving plate 42 pivotally engages the recess 40, whereby the center of the load transmitted from the spring 37 to the abutting plate 30 will not move irrespective of the inclination of the abutting plate 30, permitting a uniform pressure to be applied to both of the plungers 21, 21'.

In the case of Fig. 6, the length of the pin 32 should be sufficiently great in relation to the distance between the axes of the plunger 21 and the pin 32, while the friction coefficient of the pin 32 and the guide hole 33 should be sufficiently small. By the arrangement, even if the abutting plate 30 inclines and the pin 32 contacts the guide hole 33, the pin 32 will slide along the inner periphery of the hole 33 while contacting thereto to advance to the position where the pressure reducing action occurs. During the time, all the force of the spring 37 is applied to the operative plungers 21'shown in 21.

Contrary to the above, as shown in Fig.

10, if the length of the pin 32 relative to the distance between the axes of the pin 32 and the plunger 21 is appropriately chosen when the abutting plate 30 is inclined by the stroke of the operative plunger 21 as shown in Fig. 11 the pin 32 will contact the guide hole 33 and the pin 32 will not slide along the hole 33 so as to keep the abutting plate 30 at the position shown in Fig. 11, thus limiting the axial advancement of the plunger 21. As a result, the pressure reducing action either starts at a far higher pressure than that of the normal condition.

or will not occur at all. During the while, the input pressure is directly transmitted to the rear brake cylinder R without an > reducing effect.

An annular ridge 43 can be provided about the free end of the pin 32.

As shown in Fig. 12, an annular notch 44 may be provided about the periphery adjacent the base portion of the pin 32 to form a shoulder 45 approximately square to the outer periphery of the pin. As appears, when the abutting plate 30 inclines by the stroke of the operative plunger 21 with the other plunger 21' inoperative, the pin 32 also inclines so that the end edge 46 and the shoulder 45 contact to the inner periphery of the guide hole 33 to limit the inclinatiori of the pin 32. In the situation if the abutting plate 30 is further pushed leftwardly, the shoulder 45 bites the inner periphery of the hole 33, whereby the pin will not slide to be kept at the position and to limit the advancement of the abutting plate 30.

If no shoulder is provided about the pin just as a pin 32' of Fig. 13, it is difficult to keep the position of the abutting plate 30 since there easily occurs a sliding at the contacting point of the pin 32' and the edge 47 of the mouth of the hole 33. Considering the relation between the edge 47 of the hole 33 and the pin 32' contacting thereto. it is thought that a force for moving the corner 47 in the direction of arrow is applied thereto. In the state, since an angle A formed by the inner periphery of the hole 33 and the outer periphery of the pin 32' is considerably small, the sliding at the contacting point will easily occur.On the other hand, since an angle a formed by the inner periphery of the hole 33 and the shoulder 45 which relatively corresponds to the corner 47 is much larger than the angle , the shoulder will more easily bite the inner periphery of the hole 33 and the pin 32 is more difficult to slide.

As mentioned above, when the pin 32 inclines to limit the inclination of the abutting plate 30, if the inclination of the plate is so adapted as not to allow the normal stroke of the operative plunger, the valve seat 22 will not be closed by the operative plunger to release the pressure reducing action, thus transmitting directly the pressure from the pressure source to the rear brake cylinder R during the time when one of the two braking systems is not operative.

As shown in Fig. 14, a head 47 is provided about the free end of the pin 32. The head may be of circular, rectangular or polygonal shape, but the maximum width or diameter thereof must be smaller than that of the hole 33 so as to permit the head to advance thereinto. as shown in Fig. 15. The head 47 is normally positioned in a larger diameter bore 48 at the inner end of the hole 33 before the plungers 21. 21' begin stroke.

In operation. during the normal condition of the two braking systems, assuming that there exists a difference +Ax between the strokes of the plungers 21, 21' due to the accumulation of errors in machining and assembling, when the plungers project out of the guide 24, 24' at their maximum, one of the plungers projects beyond the other by 2Ax. In the state, if the abutting plate 30 can incline accordingly, the force of the spring 37 uniformly and equally acts on both of the plungers. thus making it possible to equalize the pressure reducing actions in both of the valve assemblies 20, 20'.In order to attain the object, a clearance D between the pin 32 fixed to the plate 30 and the guide hole 33 is to be so designed as to permit the inclination of the plate 30 which is caused by the difference of strokes of plungers due to the accumulation of errors in machining and assembling the valve, as shown in Fig.

15.

On the other hand. when one of the two braking systems is not operative, due to, for example, fluid leakage, one of the plungers stays at its position. i.e.. the stroke thereof is zero. As a result, the abutting plate 30 will incline correspondingly to the stroke of the operative plunger.

At this time, as shown in Fig. 16, the pin 32 inclines so that the head 47 engages the shoulder of the larger diameter bore 48 of the guide hole 33, thus limiting the movement of the abutting plate 30 in the axial direction of the plungers. Therefore, if this marginal inclination is so designed as to be sufficiently smaller than the inclination which is to be caused by the normal stroke of the operative plunger and the stroke of zero of the other inoperative plunger. the operative plunger cannot close the valve seat by the engagement of the head 47 and the larger diameter bore 48, not to perform the pressure reducing action but to directly supply the fluid pressure from the pressure source.

Figs. 17 and 18 illustrate another embodiment of the present invention. As shown in Fig. 17, the abutting plate 30 has at its centre a hollow member 49 which surrounds a pin 50 which is fixed at the middle between the plungers 21 and 21'.

The pin 50 has a head 51 to provide a shoulder 52.

A clearance is provided between the inside of the member 49 and the head 51 so as not to cause the outer end of the member 49 to engage the shoulder 5 during the normal strokes of both of the plungers.

More particularly, the clearance is in a range to permit the inclination of the abutting plate 30 which is caused by the difference of strokes between the plungers 21, 21' during the operative condition of both braking systems.

On the other hand, when one of the braking systems is not operative, the abutting plate 30 inclines according to the stroke of the operative plunger, and the member 49 engages the shoulder 52 of the pin 50, as shown in Fig. 18, thus limiting the movement of the plate 30 in the axial direction of the plungers. As a result, the operative plunger 21 cannot advance any more to not attain a normal stroke, thus preventing the pressure reducing action.

As shown in Figs. 19 and 20, a stop 53 is fixed in the inside of the cap 35, and a pin 54 is fixed to the abutting plate 30 at the outer face thereof oppositely to the stop 53. The end of the pin 54 enters into or moves out of a hole 55 of the stop 53 according to the strokes of the plungers 21, 21' during the normal condition of both of the braking systems. At the time, a clearance between the pin 54 and the hole 55 is adapted to be in a range that the pin 54 can enter into the hole 55 even if the pin inclines due to the inclination of the abutting plate 30 which is caused by the difference of strokes between the . plungers 21, 21' owing to the accumulation of errors in machining and assembling.

On the other hand, as shown in Fig. 20, with one of the braking systems inoperative, the inclination of the abutting plate 30 or the inclination of the pin 54 becomes large enough to cause the pin 54 to engage the mouth of the hole 55 before the operative plunger 21 reaches a normal stroke necessary for performing the pressure reducing action, thus preventing a further stroke of the plunger 21. As a result, the pressure from the pressure source is directly transmitted to the rear brake cylinder without any reducing action.

WHAT WE CLAIM IS: 1. A parallel proportioning valve assembly comprising a casing, a pair of parallel chambers provided within the casing, each of the chambers having a fluid inlet connected to a pressure source and a fluid pressure supply outlet, a fluid pressure responsive plunger accommodated in each of the chambers, a valve seat provided in a fluid passage between each inlet and the corresponding outlet, the valve seat being adapted to be closed and opened by the respective pressure responsive plunger, a single spring urging both of the plungers in the direction to open the valve seats through a single abutting plate each end of which abuts the end of a respective plunger. and a guide means for emitting the movement of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. thereinto. as shown in Fig. 15. The head 47 is normally positioned in a larger diameter bore 48 at the inner end of the hole 33 before the plungers 21. 21' begin stroke. In operation. during the normal condition of the two braking systems, assuming that there exists a difference +Ax between the strokes of the plungers 21, 21' due to the accumulation of errors in machining and assembling, when the plungers project out of the guide 24, 24' at their maximum, one of the plungers projects beyond the other by 2Ax. In the state, if the abutting plate 30 can incline accordingly, the force of the spring 37 uniformly and equally acts on both of the plungers. thus making it possible to equalize the pressure reducing actions in both of the valve assemblies 20, 20'.In order to attain the object, a clearance D between the pin 32 fixed to the plate 30 and the guide hole 33 is to be so designed as to permit the inclination of the plate 30 which is caused by the difference of strokes of plungers due to the accumulation of errors in machining and assembling the valve, as shown in Fig. 15. On the other hand. when one of the two braking systems is not operative, due to, for example, fluid leakage, one of the plungers stays at its position. i.e.. the stroke thereof is zero. As a result, the abutting plate 30 will incline correspondingly to the stroke of the operative plunger. At this time, as shown in Fig. 16, the pin 32 inclines so that the head 47 engages the shoulder of the larger diameter bore 48 of the guide hole 33, thus limiting the movement of the abutting plate 30 in the axial direction of the plungers. Therefore, if this marginal inclination is so designed as to be sufficiently smaller than the inclination which is to be caused by the normal stroke of the operative plunger and the stroke of zero of the other inoperative plunger. the operative plunger cannot close the valve seat by the engagement of the head 47 and the larger diameter bore 48, not to perform the pressure reducing action but to directly supply the fluid pressure from the pressure source. Figs. 17 and 18 illustrate another embodiment of the present invention. As shown in Fig. 17, the abutting plate 30 has at its centre a hollow member 49 which surrounds a pin 50 which is fixed at the middle between the plungers 21 and 21'. The pin 50 has a head 51 to provide a shoulder 52. A clearance is provided between the inside of the member 49 and the head 51 so as not to cause the outer end of the member 49 to engage the shoulder 5 during the normal strokes of both of the plungers. More particularly, the clearance is in a range to permit the inclination of the abutting plate 30 which is caused by the difference of strokes between the plungers 21, 21' during the operative condition of both braking systems. On the other hand, when one of the braking systems is not operative, the abutting plate 30 inclines according to the stroke of the operative plunger, and the member 49 engages the shoulder 52 of the pin 50, as shown in Fig. 18, thus limiting the movement of the plate 30 in the axial direction of the plungers. As a result, the operative plunger 21 cannot advance any more to not attain a normal stroke, thus preventing the pressure reducing action. As shown in Figs. 19 and 20, a stop 53 is fixed in the inside of the cap 35, and a pin 54 is fixed to the abutting plate 30 at the outer face thereof oppositely to the stop 53. The end of the pin 54 enters into or moves out of a hole 55 of the stop 53 according to the strokes of the plungers 21, 21' during the normal condition of both of the braking systems. At the time, a clearance between the pin 54 and the hole 55 is adapted to be in a range that the pin 54 can enter into the hole 55 even if the pin inclines due to the inclination of the abutting plate 30 which is caused by the difference of strokes between the . plungers 21, 21' owing to the accumulation of errors in machining and assembling. On the other hand, as shown in Fig. 20, with one of the braking systems inoperative, the inclination of the abutting plate 30 or the inclination of the pin 54 becomes large enough to cause the pin 54 to engage the mouth of the hole 55 before the operative plunger 21 reaches a normal stroke necessary for performing the pressure reducing action, thus preventing a further stroke of the plunger 21. As a result, the pressure from the pressure source is directly transmitted to the rear brake cylinder without any reducing action. WHAT WE CLAIM IS:

1. A parallel proportioning valve assembly comprising a casing, a pair of parallel chambers provided within the casing, each of the chambers having a fluid inlet connected to a pressure source and a fluid pressure supply outlet, a fluid pressure responsive plunger accommodated in each of the chambers, a valve seat provided in a fluid passage between each inlet and the corresponding outlet, the valve seat being adapted to be closed and opened by the respective pressure responsive plunger, a single spring urging both of the plungers in the direction to open the valve seats through a single abutting plate each end of which abuts the end of a respective plunger. and a guide means for emitting the movement of

the abutting plate substantially in the axial direction of the plungers.

2. A parallel proportioning valve assembly as claimed in claim 1, wherein said guide means comprises a guide hole provided in the casing parallel to the chambers at the middle therebetween, and a guide pin fixed to the center of the abutting plate and slidably inserted in the guide hole.

3. A parallel proportioning valve assembly as claimed in claim 1, wherein said guide means comprises a hollow guide member fixed in the inside of a cap closing the end face of the casing, and a guide pin fixed to the abutting plate at the outer face thereof and slidably inserted in the guide member.

4. A parallel proportioning valve assembly as claimed in claim 1, wherein said guide means comprises a cap closing the end face of the casing, and a guide member integral with the abutting plate and slidable along the inner periphery of the cap.

5. A parallel proportioning valve assembly as claimed in claim 2, wherein a clearance is provided between the guide pin and the guide hole, the clearance being so adapted as to permit the inclination of the abutting plate which is caused by a difference of normal strokes of the plungers and not to permit the inclination of the abutting plate which is caused by a stroke of the operative plunger with the other plunger inoperative.

6. A parallel proportioning valve assembly as claimed in any of the preceding claims, wherein an end of each of the plungers pivotally engages each end portion of the abutting plate.

7. A parallel proportioning valve assembly as claimed in any of the preceding claims, further comprising a plunger guide fitted in the end of each of the chambers so as to pilot each of the plungers and to liquidtightly seal the chamber, the guide being retained in the casing by a flange of the cap which partially abuts the end of the guide.

8. A parallel proportioning valve assembly as claimed in any of the preceding claims, further comprising a spring receiving plate mounted between the spring and the abutting plate, the receiving plate receiving one end of the spring and pivotally engaging the abutting plate at the center thereof.

9. A parallel proportioning valve assembly as claimed in claim 5, wherein an annular ridge is provided about the free end of the guide pin.

10. A parallel proportioning valve assembly as claimed in claim 5, wherein an annular notch is provided about the outer periphery of the guide pin to define a shoulder.

11. A parallel proportioning valve assembly as claimed in claim 1, further comprising an engagement means for limiting the movement of the abutting plate, the means being adapted not to operate when the inclination of the abutting plate is below a predetermined value, but to operate when the inclination of the abutting plate exceeds the predetermined value thereby preventing a normal stroke necessary for the pressure reducing action of the operative plunger.

12. A parallel proportioning valve assembly as claimed in claim 11, wherein the engagement means comprises a pin having a head at the free end thereof and fixed to the abutting plate, and a guide hole having a larger diameter bore in which normally positions the head of the pin.

13. A parallel proportioning valve assembly as claimed in claim 11, wherein the engagement means comprises a pin fixed to the casing and having a head at the free end thereof, and a guide member fixed on the abutting plate so as to surround the pin, the guide member being adapted to engage the head of the pin at a predetermined inclination of the abutting plate.

14. A parallel proportioning valve assembly as claimed in claim 11, wherein the engagement means comprises a pin fixed to the abutting plate at the outer face thereof, and a hole provided oppositely to the pin, a mouth of the hole being adapted to engage the pin at a predetermined inclination of the abutting plate.

15. A parallel proportioning valve assembly substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings or as modified as shown in any one of Figures 2 to 5 or Figures 6 to 8.

16. A parallel proportioning valve assembly substantially. as hereinbefore described with reference to Figure 9 or Figures 10 and 11 or Figures 12 and 13 of the accompanying drawings.

17. A parallel proportioning valve assembly substantially as herein before described with reference to Figures 14 to 16 or Figures 17 and 18 or Figures 19 and 20 of the accompanying drawings.