GB1590208A

GB1590208A - Fluid brake system

Info

Publication number: GB1590208A
Application number: GB658378A
Authority: GB
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1977-03-31
Filing date: 1978-02-20
Publication date: 1981-05-28
Also published as: FR2385567B1; JPS5753721Y2; DE2811005C2; DE2811005A1; FR2385567A1; JPS53133976U

Description

(54) FLUID BRAKE SYSTEM (71) We, NISSAN MOTOR COMPANY, LIMITED, a corporation organized under the laws of Japan, of No. 2, Takaramachi, Kanagawa-ku, Yokohama City, 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: This invention relates to a fluid brake system.

Many up-to-date cars and vehicles employ a fluid brake system of the split type in which a master cylinder is connected to wheel cylinders by way of two independent fluid transmission lines for fail-proof braking operation. In this type of brake system, two separate pressure control valves have been installed in the respective fluid transmission lines. A fairly large space and working time has been required by separately mounting these valves.

In the past, it has been known to unitize two control valves, one for each transmission line, in one housing. The two valves are arranged parallely and are loaded by a common spring which is borne by one spring seat supported on a fixed guide shaft. The spring seat has an annular flange on which the spring bears. The side opposite to the spring carrying side of the spring seat is pressed against the near ends of valve plungers of both control valves by the action of the valve spring.

It is ordinary that a machining and mounting tolerance results in a difference in total length between two valve assemblies. Even such a small difference entails that the timings at which the valves open and close is different between the two control valves under the equal fluid pressure delivered from the master cylinder. Thus, there is produced a difference in the output braking fluid pressure between two wheel cylinders; the two rear wheels of the vehicle are subject to different braking efforts. Machining and mounting accuracy must be uneconomically raised to avoid this dangerous condition.

It is therefore a general object of the invention to provide a unitary control valve assembly having two valves of the aforementioned type, one for each fluid transmission line of the split brake system, which properly control the braking fluid pressure to be applied to the wheel cylinder compensating for the machining and mounting tolerance of the two control valves.

Another more specific object of the invention is to so arrange and construct the unitary valve assembly of the aforementioned type that a spring seat for a plunger spring common to the two control valves has a hollow cylindrical portion slidably carried on a fixed guide shaft, which defines with the outer periphery of the guide shaft an annular space tapering by a predetermined taper angle toward the end of the guide shaft adjacent the control valves.

A further object of the invention is to provide a control valve assembly of the aforementioned type in which, upon failure in one of the fluid transmission lines, the control valve in the other fluid transmission line operates to compensate for the failure by applying enough braking effort to one wheel cylinder.

According to the invention, there is provided a fluid brake system for an automobile comprising a tandem master cylinder having two outlets, front wheel brake cylinders, rear wheel brake cylinders, two fluid transmission means including a first line connecting one outlet of the master cylinder to at least one of the front wheel cylinders and to at least one of the rear wheel cylinders, and a second line connecting the other outlet of the master cyliner to at least one of the front wheel cylinders and to at least one of the rear wheel cylinders, two control valves, accommodated in one housing in parallel relationship with each other, each the control valve being disposed in one of the first and second fluid lines at a portion between the master cylinder and the one of the rear wheel brake cylinders to control the fluid pressure directed to the rear wheel brake cylinder and having an elongate piston-plunger, a spring common to the two valves to load the piston-plungers in the valve open position, and a spring seat supporting the spring and engaging the piston-plungers to apply the action of the spring thereon, the spring seat being tiltable toward one of the piston-plunger and away from the other piston-plunger through a predetermined angle, whereby the difference in size between the two control valves due to manufacturing and mounting tolerance is compensated for, while in failure of one fluid transmission line, the spring act only upon the valve piston-plunger of the other failed fluid line.

In the drawing, the fluid brake system comprises a tandem master cylinder 10 of any conventional type which is loaded by depression of a brake pedal 12. The two fluid outlets (no numeral) are respectively directly connected to front wheel cylinders 14, 16 for the right and left front wheels (not shown). The master cylinder is further connected to the rear wheel cylinders 18, 20 for the right and left rear wheels (not shown) through a control valve assembly according to the invention to be hereinafter described. Located between the master cylinder and the rear wheel cylinders 18, 20 is a valve housing 30 defining two parallel-extending valve bores 32, 33. The valve bore 32 communicates with one outlet of the master cyllinder through an inlet 34 and with the rear, left wheel cylinder 20 through an outlet 35, forming a first fluid transmission line.Likewise, a second fluid transmission line is formed by the other outlet of the master cylinder, an inlet 36, bore 33, outlet 37 and rear, right wheel cylinder 18. Thus, the tubing connection for the brake system is of a diagonal type for failure-proof purpose. It would be apparent that any other type of split brake system is available, if desired.

Both control valves 38 and 39 accommodated in the bores 32, 33, respectively, are of the identical structure so that only one of them 38 will be explained below for brevity. A piston-plunger 40 is slidably received in the bore 32 nearly throughout the length of the bore. The plunger consists of a larger diameter portion 40a fitted within the bore 32 and a reduced diameter portion 40b forming an annular shoulder 40c with the larger diameter portion. The plunger 40 defines therein a blind bore 41 extending substantially the length of the larger diameter portion. An annular valve seat 43 is fixed to the plunger at the open end of the blind bore 41. The blind bore accommodates therein a poppet valve with a head 42 and with a stem 45 extending through a small bore (no numeral) in the valve seat 43 to abut against the inner wall surface of the housing 30.The valve head 42 is loaded by a spring 44 toward the valve seat 43. When the plunger is moved rightwardly in the drawing, the valve head 42 is seated against the valve seat 43 by the action of the spring 44, the stem 45 being then protruded from the bore of the valve seat.

The valve seat 43 is formed with a radial orifice 46 for communication of the blind bore 41 with the valve bore 32. A sleeve 48 is fitted in the valve bore 32 surrounding the reduced diameter portion 40b at an annular space 50 from the reduced diameter portion. The sleeve 48 is also formed with a radial orifice 49. Another radial orifice 47 of the piston-plunger communicates the blind bore 41 with the annular space 50. Thus the fluid path from the master cylinder to the wheel cylinder 20 is formed by the inlet 34, orifice 49, annular space 50, orifice 47, blind bore 41, orifice 46 and outlet 35.

The end 40d of the plunger opposite to the valve seat 43 protrudes from the open end of valve bore 32 and is fluid-tightly supported by a valve retainer 51.

The two valve plungers 40, 40' are loaded by a common spring which will be described below. A guide shaft 63 is threadedly fixed to the body of the housing 30 intermediate the two valve bores and slidably carries a spring seat 62 thereon. The spring seat 62 essentially consists of a hollow cylindrical portion 64 and an annular flange portion 65 extending radially from the cylindrical portion. The annular flange portion 66 on one side abuts against the near ends of the plungers 40, 40'. A valve spring 67 is borne between the opposite side of the annular flange 66 and a spring support 65 fixed to the outer end of the guide shaft 63. Between the hollow surface of the cylindrical portion 64 and the guide shaft 63 is fittedly interposed a bushing 68 of resinous material to facilitate slide movement of the spring seat 62 on the guide shaft. Thus the spring 67 applies a load to the valve plungers in the leftward direction in the drawing via the spring seat 62 to keep the valve 42 unseated from the valve seat 43 in an inoperative condition shown in the drawing.

According to the invention, the resin bushing 68 defines a small clearance or annular space 69 with the outer periphery of the guide shaft. The resin bushing is tapered toward the end of the guide shaft near the control values; the annular space 69 is gradually reduced in diameter toward the annular flange 66. As a matter of course, if no bushing is used, the hollow of the cylindrical portion itself is tapered toward the end of the guide shaft near the control valves.

There might be a difference between the distance h and h' from the end face of the housing 30 to the protruded tip end of the respective plungers 40, 40'. The difference may be due to some mostly inevitable manufacturing and mounting tolerance, for instance, during working the plungers, installing the valve head, stem and seat in the plungers, etc.

Then, the spring seat 62 will be slightly tilted with respect to the central axis of the guide shaft in the rest condition of the valves as shown.

The tapering angle of the hollow of the bushing or cylindrical portion is so determined as to meet the following two requirements: (1) With the maximum tolerable difference between the distances h and h', the inner surface of the bushing or cylindrical portion should not contact the major part of the outer periphery of the guide shaft.

(2 Upon failure in one fluid transmission line with one control valve being kept inoperable, the inner surface of the bushing or cylindrical portion is brought into contact with the guide shaft before the other safe control valve is closed, to allow the force of the spring 67 to act only upon the plunger of the safe valve, while the valve plunger of the failed line is separated from the annular flange.

The fluid brake system as described above operates in a manner as will be hereinafter explained.

Each plunger has a larger pressure sensing area b1 and a smaller pressure sensing area b2.

When the brake pedal 12 is depressed to operate the master cylinder 10, the fluid under pressure PM1 and PM2 is delivered directly respectively to the front wheel cylinders 14, 16 for the right and left front wheels. At the same time, the fluid under pressure PM1 reaches the inlet 34 of the control valve 38 while the fluid under pressure PM2 reaches the inlet 36 of the other valve 39. Since the valves are yet open, the fluid passes through the valve bores 32, 33 and is delivered to the respective rear wheel cylinders 18, 20 through the outlets 35 and 37.Under the fluid pressure PM and the spring force F acting oppositely on each plunger, the following equation holds PM b2 = (1/2)F where PM1 = PM2 = PM .p ~ F PM 2b2 Thus, the fluid under pressure PR1, PR2 (PR1 = PR2 = PR) equal to the pressures PM1, PM2 and the fluid is respectively delivered to the rear wheel cylinders through the outlets 35, 37.

As the operator further depresses the brake pedal until PM b2 > (1/2F), is reached, each plunger moves rightwardly in the drawing. The valve seats 43, 43' then abut against the valve with heatd 42, 42', to interrupt communication between the inlet and outlet of the valve bores 32, 33. No fluid is thus admitted into the rear wheel cylinders 18, 20. Meanwhile, the fluid under pressure PM is applied to the annular shoulder 40c, namely the larger pressure sensing area b1. Thus, the equation holds, PM(bl - b2) + (1/2)F = PRb1 PR - b1 - + PM F .. (1) b1 +5b1 When the fluid pressure PM is further raised by depressing the brake pedal, the plunger resumes the initial position to open the valves 42, 42'.Consequently, the pressure PR to the rear wheel cylinders 18, 20 is allowed to rise gently by a degree with respect to the abrupt rise of the pressure PM, efficiently controlling skiding.

The difference between the distance h and h' as previously mentioned can be compensated for by the annular space between the bushing 69 and the guide shaft 63: If the bushing or cylindrical portion throughout its length were fitted around the guide shaft with no clearance, the spring would act on the plunger with the greater distance h or h' more strongly than on the plunger with the smaller one, accordingly the different output fluid pressure PR would be delivered to the respective wheel cylinders. According to the invention, the spring seat is permitted to slightly tilt without contacting the guide shaft by virtue of the tapering clearance between the bushing or cylindrical portion and the guide shaft. Hence, the spring action will equally act on the both plungers through the annular flange of the spring seat.

If one of the fluid transmission lines, for instance, to the front wheel cylinder 16, fails, the control valve 39 is held in the inoperative position shown in the drawing. As the fluid pressure in the other said fluid transmission line rises, the plunger 40 moves rightwardly in the drawing against the action of the spring 67 as already described. The spring seat 62 is then tilted until the inner surface of the bushing 69 is brought into contact with the outer surface of the guide shaft 63. The spring seat with the annular flange, disengaging the tip end of the plunger 40', is then slidingly moved on the guide shaft to close the valve 42. It is apparent that the spring force is then acting only upon the plunger 40.

Thus the equation holds PR = bi 2 PM + b1 Thus, only one control valve develops a large braking fluid pressure enough to compensate for the drop of the pressure in the other fluid transmission line. Upon further depressing the brake pedal to raise the pressure PM, the pressure PR rises by a degree as in the usual operation with two control valves.

WHAT WE CLAIM IS: 1. A fluid brake system for an automobile comprising a tandem master cylinder having two outlets, front wheel brake cylinders rear wheel brake cylinders, two fluid transmission means including a first line connecting one outlet of the master cylinder to at least one of said front wheel cylinders and to at least one of said rear wheel cylinders, and a second line connecting the other outlet of the master cylinder to at least one of said front wheel cylinders and to at least one of said rear wheel cylinders, two control valves accommodated in one housing in parallel relationship with each other, each said control valve being disposed in one of said first and second fluid lines at a portion between the master cylinder and said one of the rear wheel brake cylinders to control the fluid pressure directed to the rear wheel brake cylinder and having an elongate piston-plunger, a spring common to the two valves to load the piston-plungers in the valve open position, and a spring seat supporting said spring and engaging said piston-plungers to apply the action of the spring thereon, said spring seat being tiltable toward one of the piston-plunger and away from the other piston-plunger through a predetermined angle, whereby the difference in size between the two control valves due to manufacturing and mounting tolerance is compensated for, while in failure of one fluid transmission line, the spring act only upon the valve piston-plunger of the other failed fluid line.

2. A fluid brake system for an automobile comprising a tandem master cylinder having two outlets, front wheel brake cylinders rear wheel brake cylinders, two fluid transmission means including a first line connecting one outlet of the master cylinder to at least one of said rear wheel cylinders, and a second line connecting the other outlet of the master cylinder to at least one of said front wheel cylinders and to at least one of said rear wheel cylinders, two control valves accommodated in one housing in parallel relationship with each other, each said control valve being disposed in one of said first and second fluid lines at a portion between the master cylinder and said one of the rear wheel brake cylinders to control the fluid pressure directed to the corresponding rear wheel brake cylinder and having an elongate piston-plunger, a spring assembly common to the two valves to load the valves in the valve opening

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. strongly than on the plunger with the smaller one, accordingly the different output fluid pressure PR would be delivered to the respective wheel cylinders. According to the invention, the spring seat is permitted to slightly tilt without contacting the guide shaft by virtue of the tapering clearance between the bushing or cylindrical portion and the guide shaft. Hence, the spring action will equally act on the both plungers through the annular flange of the spring seat. If one of the fluid transmission lines, for instance, to the front wheel cylinder 16, fails, the control valve 39 is held in the inoperative position shown in the drawing. As the fluid pressure in the other said fluid transmission line rises, the plunger 40 moves rightwardly in the drawing against the action of the spring 67 as already described. The spring seat 62 is then tilted until the inner surface of the bushing 69 is brought into contact with the outer surface of the guide shaft 63. The spring seat with the annular flange, disengaging the tip end of the plunger 40', is then slidingly moved on the guide shaft to close the valve 42. It is apparent that the spring force is then acting only upon the plunger 40. Thus the equation holds PR = bi 2 PM + b1 Thus, only one control valve develops a large braking fluid pressure enough to compensate for the drop of the pressure in the other fluid transmission line. Upon further depressing the brake pedal to raise the pressure PM, the pressure PR rises by a degree as in the usual operation with two control valves. WHAT WE CLAIM IS:

1. A fluid brake system for an automobile comprising a tandem master cylinder having two outlets, front wheel brake cylinders rear wheel brake cylinders, two fluid transmission means including a first line connecting one outlet of the master cylinder to at least one of said front wheel cylinders and to at least one of said rear wheel cylinders, and a second line connecting the other outlet of the master cylinder to at least one of said front wheel cylinders and to at least one of said rear wheel cylinders, two control valves accommodated in one housing in parallel relationship with each other, each said control valve being disposed in one of said first and second fluid lines at a portion between the master cylinder and said one of the rear wheel brake cylinders to control the fluid pressure directed to the rear wheel brake cylinder and having an elongate piston-plunger, a spring common to the two valves to load the piston-plungers in the valve open position, and a spring seat supporting said spring and engaging said piston-plungers to apply the action of the spring thereon, said spring seat being tiltable toward one of the piston-plunger and away from the other piston-plunger through a predetermined angle, whereby the difference in size between the two control valves due to manufacturing and mounting tolerance is compensated for, while in failure of one fluid transmission line, the spring act only upon the valve piston-plunger of the other failed fluid line.

position comprising a guide shaft fixed to said housing, a spring seat slidably mounted on said guide shaft; a spring supported on said spring seat to load the spring seat into engagement with the two control valves, said spring seat being arranged in a manner to provide around the guide shaft an annular space tapering by a predetermined taper angle toward an end of the guide shaft adjacent the control valves.

3. A fluid brake system as defined in Claim 2, in which said taper angle of the annular space is so determined that said spring seat will tilt without contacting substantially the outer surface of the guide shaft with the maximum tolerable difference in size between the two control valves, and that upon failure in one of the fluid transmission lines to render the control valve in said one fluid line inoperative, the inner surface of the hollow cylindrical portion can be brought into contact with the outer circumference of the guide shaft before the control valve in the other fluid transmission line is closed, thereby preventing further tilting of the spring seat with respect to the guide shaft.

4. A fluid brake system as defined in Claim 2, in which said spring seat further comprises a bushing fitted thereto and defining said annular space with the outer surface of the guide shaft.

5. A fluid brake system as defined in Claim 2, in which each said control valve comprises an elongate plunger within an axial bore and having differential pressure sensing areas, a valve head of a valve housed in a blind bore within the plunger, a valve seat fixed to and movable together with the plunger, and means defining a plurality of orifices for fluid communication of the inlet of the valve with the outlet via the valve when open, said plunger at its tip end engaging said annular flange on the side thereof opposite to the side supporting said valve spring.

6. A fluid brake system substantially described herein with reference to the accompanying drawing.