GB2076916A

GB2076916A - Hydraulic power booster

Info

Publication number: GB2076916A
Application number: GB8114083A
Authority: GB
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1980-05-19
Filing date: 1981-05-08
Publication date: 1981-12-09
Also published as: DE3119502A1; JPS56163943A; FR2484564A1

Abstract

A hydraulic power booster for use with a brake system of an automotive vehicle includes a hollow booster body 10 with inlet 63 and outlet 64 ports. The booster body has therein a slideable power piston 11 and a slidable operating rod 13, which form a boost chamber 50. The power piston contains therein a spool valve 35 operated by the operating rod. When operated, the spool valve chokes the pressurized fluid flow from the inlet port to the outlet port and introduces the pressurized fluid into the boost chamber to force the power piston. An output rod 21 engages the power piston in such a manner as to be able to pivot about the engaged end thereof. The end of the booster body is closed by a closure member 12 with an aperture 27 through which the output rod passes. A sealing member 28 is arranged in the aperture in such a manner as to engage throughout the surface of the output rod and the inner surface of the closure member. The sealing member is designed to permit the output rod to move axially and radially while prevent fluid leakage along the output rod and inner surface of the closure member. <IMAGE>

Description

SPECIFICATION Hydraulic power booster 1. Field of the invention This invention relates generally to a hydraulic power booster for use with, for example, a braking system of an automotive vehicle, and more specifically to an hydraulic power booster having a radially movable power take-off rod improving the power take-off characteristics thereof.

2. Description of the prior art In a typical hydraulic power booster for use with a pedal-operated braking system on an automotive, a spool-type control valve chokes the flow from a fluid pump to a power steering system, so as to utilize the fluid pressure developed upstream of the control valve to actuate a tandem master cylinder of the braking system and thereby operate the braking system with boosted power. The power booster is arranged coaxially with and operatively connected to the brake master cylinder by a coaxial, slideably arranged power take-off rod to transmit the boosted power to the brake master cylinder.

If the axes of the power booster and the brake master cylinder are eccentric owing to a slightly erroneous connection thereof within tolerances, such a conventional power booster often produces an input'output power characteristic with great dispersion, since the power take-off rod is scarcely permitted to move radially and consequently the friction force from the sliding of the power take-off rod becomes relatively large when the power booster is operated. Moreover, the power booster sometimes produces an input'output power characteristic with step form variations since the power take-off rod frequently slips in its housing when the power booster is operated.

Summary of the invention It is an object of the present invention to provide a hydraulic power booster for use with, for example, a braking system of an automotive vehicle, which produces an inputloutput power characteristic with a relatively small dispersion and without step-form variations, even in the event that the axes of the power booster and the master cylinder of the braking system do not coincide.

This and other objects have been attained by the hydraulic power booster of the present invention, which includes a hollow booster body with an inlet port supplied with a pressurized fluid and an outlet port. The booster body has therein a slideable power piston and a slideable operating rod, which form a boost chamber within the booster body. The power piston contains a slideable spool valve operated by the operating rod. When operated, the spool valve chokes the pressurized fluid flow from the inlet to outlet ports and introduces pressurized fluid into the boost chamber and to force the power piston. An output rod engages the power piston in such a manner as to be permitted to rotate aboutthe engaged end thereof. A closure member closes one end of the booster body and has an aperture through which the output rod passes.Additionally, a sealing member is arranged in the aperture in such a manner as to engage throughout the surface of the output rod and the inner surface of the closure member to prevent fluid leakage along the output rod and the inner surface of the closure member.

The sealing member is designed to permit the output rod to move axially and radially while preventing fluid leakage along the output rod and the inner surface of the closure member.

The above and further objects, features and advantages of the present invention will becomes more obvious from the following description of a preferred embodiment thereof, taken in conjunction with the drawings.

Brief description ofthe drawings Figure 1 is a diagrammatic, transverse sectional view of a hydraulic power booster according to the present invention; Figure2 is a diagrammatic section of the hydraulic power booster of Figure 1 taken along the bent line A-A of Figure 1; Figure 3 is a graph of fluid pressure developed in a one-inch brake master cylinder versus thrust applied to an operating rod with multi-scanning; and Figure 4 is a graph of fluid pressure developed in the one-inch brake master cylinder versus thrust applied to the operating rod with single-scanning.

Detailed description of the preferred embodiment Referring to Figures 1 and 2, there is shown a hydraulic power booster of an automotive vehicle having a hollow booster body or housing 10 of an approximately cylindricai shape, and a power piston 11 arranged coaxially within the body 10 in such a way as to be free to slide in the axial direction but not to rotate, and as to divide the inside of the booster body 10 into hereinafter described drain and boost chambers. The booster body 10 is closed at one end by a plug 12 and at its other end by an operating rod 13. An O-ring 14 is attached to the inner surface of the booster body 10 to preventfluid leakage along the operating rod 13. The plug 12 is bolted to the booster body 10.

A tandem brake master cylinder body 15 is attached coaxially to the plug 12 and the booster body 10 by bolts 16. The booster body 10 can be secured at its end away from the plug 12 to the automobile body by bolts (not shown) to mount the hydraulic power booster.

Inside the booster body 10, a drain chamber 17 is formed between the plug 12 and the power piston 11, and is in communication with a drain port (not shown) to discharge a fluid. Inside the drain chamber 17, a return spring 18 is seated at one end on the inner wall of the plug 12 and at its other end on an annular ridge 19 on the power piston 11 to bias the power piston 11 rightwards to an rest position thereof. The booster body 10 has an annular shoulder 20 on its inner surface near the right-hand end to receive the end of the power piston 11 and thus to limit the axial movement or travel of the power piston 11.

The plug 12 has a coaxial center aperture 27 through which an output rod 21 passes. The output rod 21 engages at its opposite ends with the left-hand end of the power piston 11 and the right-hand end of a piston 22 disposed coaxially within the brake master cylinder body 15, so as to transmit force therebetween. The end of the power piston 11 has a coaxial cone-shaped recess 23 receiving the hemi-spherical end 24 of the rod 21 to form a self-centering engagement between the rod 21 and the power piston 11. Thus the axes of the rod 2-1 and the power piston 11 can be substantially connected continuously at the engaged ends thereof. The self centering engagement moreover permits the rod 21 to rotate about the engaged end thereof in any direction in a pivotal motion.The end of the piston 22 has a coaxial blind hole 25 of a slightly greater diameter than the rod 21 to receive the end 26 of the rod 21. The bottom of the hole 25 is of a hemi-spherical shape and the other end 26 of the rod 21 is of a corresponding hemi-spherical shape to establish a self centering engagement of the rod 21 and the piston 22. The the axes of the rod 21 and the piston 22 can be substantially connected continuously at the engaged portions thereof. The self centering engagement moreover permits the rod 21 to rotate slightly about the engaged end thereof in any direction in a pivotal motion.

In the center aperture 27 of the plug 12, an annular sealing member 28 is arranged around the output rod 21 in such a manner that the inner surface of the sealing member 28 contacts throughout the surface of the output rod 21 while the outer surface of the sealing member 28 contacts throughout the inner surface of the plug 12, so as to prevent fluid leakage along the output rod 21 and the inner surface of the plug 12. The sealing member 28 consists of a oil seal including an annular rubber or resilient member 29 with an annular groove 32 at one end of the member, a sleeve member 30, and a ring 31. The sleeve member 30 is placed within the groove 32 to press the outer portion of the rubber member 29 against the inner surface of the plug 12 and to reinforce the rubber member 29.The ring 31 is also placed within the groove 32 to press the inner portion of the rubber member 29 against the surface of the output rod 21.

The sealing member 28 is designed to allow the output rod 21 to move axially and radially while preventing fluid leakage along the output rod 21 and the aperture 27. In other words, the inner and outer portions of the sealing member 28 function to press against output rod 21 and the plug 12 respectively to preventfluid leakage, while the intermediate portion of the sealing member 28 functions to permit the output rod 21 to move radially.

The power piston 11 has a coaxial blind bore, in which a spool 35 is slideably disposed. Circumferential grooves 36 and 37 are provided on the inner surface of the power piston 11 in such a manner as to form a land 38 therebetween and a shoulder 39 at the left-hand end of the groove 36. Annular grooves 40 and 41 are provided on the outer surface of the spool 35 in such a manner that the right-hand end of the groove 40 faces the shoulder 39 while the groove 41 faces the land 38 and has a axial width corresponding to that of the land 38. The grooves 40 and 41 form lands 42,43 and 44. At the bottom of the power piston bore, a chamber 45 is defined by the power piston 11 and the left-hand end of the spool 35, the land 42.

The spool 35 has an axially extending stepped passage 46 which opens into the chamber 45. A return spring 47 is arranged within the chamber 45 and the passage 46 and seated at its ends on the inner end surface of the power piston 11 covered with a resilient member 1 la and on the step 48 of the inner surface of the spool 35 to bias the spool 35 rightwards to its rest position and to force the same againsttheoperating rod 13. The operating rod 13 is slideably inserted into the bore of the power piston 11 and is prevented from falling out of the power piston 11 by a snap ring 49 attached to the inner surface of the power piston 11. The snap ring 49 thus limits the axial movement of the operating rod 13 and the spool 35.

The operating rod 13 is formed with an annular groove thereon constructing a boost chamber 50 in conjunction with the end of the power piston 11. The chamber 50 communicates with the passage 46 through a passage 51 in the operating rod 13 and thus with the chamber 45. A radial through passage 52 is formed in the spool 35 in such a manner as to open at its opposite ends to the groove 41 and to the passage 46 in the spool 35.

The shoulder 39 of the power piston 11 and the land 43 of the spool 35 constitute a variable orifice 53, the land 38 of the power piston 11 and the land 43 of the spool 35 constitute a first control valve 54, and the land 38 and the land 44 of the spool constitute a second control valve 55. The variable orifice 53 and the control valves 54 and 55 constitute a spool valve system controlling pressurized fluid flow therethrough as described hereinafter. As best illustrated in Figure 1, the power piston 11 has on its outer surface axially extending grooves 56, 57, 58 and 59 spaced at 90 intervals. A stopper bolt 60 secured to the booster body 10 is inserted into the groove 59 to prevent rotation of the power piston 11 about its longitudinal axis without interfering with the axial movement of the power piston 11.The grooves 58 and 59 communicate with the annular groove 40 on the spool 35 through passages 61 and 62 respectively in the power piston 11. Inlet and outlet ports 63 and 64 are formed in the booster body 10 in such a manner as to keep open to the grooves 56 and 58 respectively throughout an entire stroke of the power piston 11.

The groove 56 communicates through a radially extending passage 65 with the annular groove 36, while the groove 58 communicates through a radially extending groove 66 with the annular groove 40.

The annular groove 37 communicates with the drain chamber 17 through a passage (not shown) in the wall of power piston 11. As illustrated in Figure 1, a branch passage 67 is provided in the booster body 10 to connect the outlet port 64 to the groove 57. A relief valve member 68 is slideably arranged at the end of the branch passage 67 near the outlet port 64.

Additionally, a passage 69 is provided in the booster body 10to connect the drain chamber 17to another axially extending groove 70 formed on the outer surface of the power piston 11.

The operating rod 13 has an axially extending hole 71 opening to the outside, whose base is of a conical shape to receive a hemi-spherical end of the input rod 72 for establishment of a self centering engagement therebetween. The rod 72 is connected in turn to a brake pedal 73 by a clevis to transmit force between the brake pedal 73 and the operating rod 13.

Afluid pump 80 usually driven by the automotive engine is connected to the inlet port 63 through a flow rate regulation valve 81 to supply pressurized working fluid to the booster body 10 from a fluid reservoir 82. The outlet port 64 is connected to the fluid reservoir82through a power steering apparatus 83 to return the working fluid from the booster body 10 to the fluid reservoir 82.

While the hydraulic pressure booster is at rest as shown in Figure 2, the pressurized working fluid supplied into the inlet port 63 flows via the groove 56, the passage 65, the groove 36, the variable orifice 53, the groove 58, and the outlet port 64 to the power steering apparatus 83 to actuate the same. At that time, the land 43 of the spool 35 partially overlaps the land 38 of the power piston 11 to close the first control valve 54 while the land 44 of the spool 35 is positioned away from the land 38 of the power piston 11 to open the second control valve 55, so that the boost chamber 50 is in communication with the drain chamber 17 via the passage 51, the passage 46, the passage 52, the groove 37, the radially extending passage (not shown), the groove 70, and the passage 69.

In this condition, when the brake pedal 73 is depressed, the input rod 72 pushes the operating rod 13, displacing the spool 35 leftwards, relative to the power piston 11, against the spring 47. Thus the land 43 moves toward the shoulder 39 to reduce the effective area of the variable orifice 53, and conse quentlythe amount of fluid flowing from the groove 36 to the groove 40, namely, the amount of the fluid flowing from the inlet port 63 to the outlet port 64 is decreased. At the same time, as a result of the leftward displacement of the spool 35, the second control valve 55 is closed whereas the first control valve 54 is opened. Therefore, the pressurized working fluid in the groove 36 is delivered into the boost chamber 50, via the first control valve 54, the groove 41, the passage 52, the passage 46, and the passage 51.

The pressure of the working fluid delivered to the boost chamber 50 is applied to the left-hand end surface of the power piston 11, displacing the power piston 11 leftwards against the spring 18 so as to cause the same to follow the spool 35. This leftward displacement of the power piston 11 makes the output rod 21 move leftwards, shifting the piston 22 leftwards to compress the brake fluid and thus actuate the brake system in the customary way. The boost ratio of the forces exerted on the input rod 72 to the output rod 21 depends on the ratio of the cross section areas of the operating rod 13 to the power piston 11. Simultaneously, a reaction force is applied to the brake pedal 73 as a braking "back force" in the customary way.

When the brake pedal 73 is returned to its rest position by removing the pressure on the brake pedal 73, the springs 18 and 47 retu-rn the power piston 11, the spool 35, the operating rod 13, and the input rod 72 rightwards to their respective rest positions as shown in Figure 2. Simultaneously the piston 22 of the brake master cylinder 15 is returned by a spring (not shown) to its rest position shown in Figure 2, removing the braking effect of the system in the customary way.

Even if the longitudinal axis of the piston 22 of the brake master cylinder 15 is not concentric with that of the power piston 11 owing to a slightly erroneous attachment of the brake master cylinder 15 to the booster body 10, the sealing member 28 allows the output rod 21 to rotate radially about the right-hand and left-hand ends thereof so as to off-set the eccentricity of the piston 22 with the power piston 11, while ccntinuing to prevent fluid leakage along the output rod 21 and the inner surface of the plug 12. Thus the longitudinal axes of the power piston 11, the output rod 21, and the piston 22 of the brake master cylinder 15 are substantially connected continuously with each other at the respective engaged portions thereof.The sealing member 28 also permits the inclined output rod 21 to move axially while continuing to prevent fluid leakage and maintain the continuous connection of the longitudinal axes. This causes stable transmission of force between the pistons 11 and 22, and therefore results in the reduction of dispersion and the prevention of step form variations of the input/output power characteristic.

Figure 3 illustrates an experimental characteristic diagram of fluid pressure generated in a brake master cylinder versus thrust applied to the operating rod with multi-scanning. With a one-inch brake master cylinder used and the theoretical output to input power ratio of the hydraulic power booster designed at 2.37, the experiment was performed under conditions where hydraulic fluid temperature : 45+5 C hydraulic fluid flow rate: limin thrust speed of the operating rod : 5 mm/sec.

This diagram corresponds to a input/output power characteristic of the hydraulic power booster of the present invention, since the fluid pressure developed in the brake master cylinder depends on the output power of the hydraulic power booster and the thrust on the operating rod depends on the power applied to the input rod. After arrangement, 99.9 percent of experimental values are positioned within the dotted region between the lines V and W (where the dots do not correspond to the experimental values), which indicates a dispersion of the inputs output power characteristic of the hydraulic power booster of the present invention.

For comparison, a similar experimental dispersion of an input/output power characteristic of a typical prior-art booster is also illustrated by the hatched region between the lines V and X. The experiment on the prior-art booster was performed under similar conditions to the experiment on the booster of the present invention. As shown in Figure 3, the dispersion on the booster of the present invention is remarkably reduced over that of the prior-art booster.

In Figure 4 are illustrated exemplary characteristic diagrams with single scanning picked up from the data of Figure 3, the line Y shows the characteristic of the booster of the present invention while the line Z shows that of the prior-art booster. As illustrated, the hydraulic fluid pressure developed in the brake master cylinder relative to the thrust applied to the operating rod, that is, the output power relative to the input power of the booster of the present invention usually varies smoothly, although that of the prior-art booster sometimes varies as a stepfunction.

It should be understood that further modifications and variations may be made in the present invention without departing from the spirit of the present invention as set forth in the appended claims.

Claims

1. A hydraulic power booster comprising: a) a hollow booster body having inlet and outlet ports, the inlet port supplied with pressurized fluid.

b) a power piston disposed slideably within the booster body, the power piston having therein a bore; c) a spool disposed slideably in the piston bore; d) an operating rod slideably disposed within the booster body, the operating rod and the power piston defining a boost chamber inside the booster body; e) a spool valve formed by the spool and the power piston, the spool engaging with the operating rod to be operated by the same, the spool valve choking the pressurized fluid flow from the inlet port to the outlet port and introducing pressurized fluid from the inlet port to the boost chamber when the spool is operated, the spool valve allowing the pressurized fluid to flow from the inlet to outlet ports when the spool is inoperative, whereby the power piston is forced by the fluid pressure in the boost chamber when the spool is operated;; f) a closure member closing one end of the booster body, the closure member having an aperture; g) an output rod engaging with the power piston so as to be moved axially by the same and also be permitted to rotate radially about the engaged end thereof, the output rod passing through the aperture of the closure member;; h) a sealing member arranged in the aperture of the closure member in such a manner as to engage at its inner surfaces with the outer surface of the output rod and at its outer surface with the inner surface of the aperture of the closure member to prevent fluid leakage along the outer surface of the output rod and the inner surface of the aperture, the sealing member permitting the output rod to rotate radially about its end engaged with the power piston while continuing to prevent fluid leakage, the sealing member also permitting the output rod to move axially while continuing to prevent fluid leakage.

2. A hydraulic power booster as defined by claim 1, wherein the sealing member comprises an annu lar rubber member, a sleeve member placed within the rubber member to press the outer portion of the rubber member against the inner surface of the aperture of the closure member, and a ring placed within the rubber member to press the inner portion of the rubber member against the outer surface of the output rod.

3. A hydraulic power booster as defined by claim 1, wherein the end of the output rod is of a hemi-spherical shape, the end of the power piston has a coaxial cone-shaped recess to receive the end of the output rod, whereby a self centering engage ment of the output rod and the power piston is constructed.

4. A hydraulic power booster as defined by claim 3, further comprising a brake master cylinder attached to the booster body, and a piston disposed slideably in the brake master cylinder, the piston having a blind hole whose bottom is of a hemi spherical shape, the other end of the output rod inserted into the hole and being of a hemi-spherical shape corresponding to the bottom of the hole, whereby a self centering engagement of the output rod and the piston in the brake master cylinder is I constructed.

5. A hydraulic power booster as defined by claim 2, wherein the sealing member has an annular groove in which the sleeve member and the ring are placed.