JPS6153564B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method in which a pressure chamber is formed in a bore of a body in front of a piston operating within the bore, the body having an outlet port leading from the pressure chamber, a recovery port that communicates the pressure chamber with the fluid tank when in the operating retracted position;
The first movement of the piston in the actuating direction within the bore closes the recovery port, isolating the pressure chamber from the tank, and the subsequent movement of the piston in the same direction adds fluid to the pressure chamber. The present invention relates to a hydraulic master cylinder for a vehicle clutch or brake system of the type that supplies pressure to the outlet port.

In known master cylinders of the above type, the recovery port is an opening in the wall of the body, the inner end of which is countersunk.
When the piston moves in the actuating direction, a seal carried on the piston closes the recovery port and isolates the pressure chamber from the tank. In theory, when the piston is actuated, the seal should move to occlude the recovery port before the fluid in the pressure chamber is pressurized. However, in reality, the movement of the piston in the actuation direction is so fast that pressure can build up in the pressure chamber before the recovery port is completely closed. The seal then has no radial support at the recovery port and is susceptible to rupture under such pressure. The axial spacing between the seal and the recovery port must be very carefully controlled during manufacturing to limit loss of stroke within acceptable limits.
This requires precise and costly control of not only the machining of the body, but also the machining of the piston and the seal carried by the piston. Usually, to provide a collection port whose inner end is countersunk,
Form an opening through the wall of the body from the inside using a tool that forms the required amount of countersinks. This work must be done as a precision operation at a very slow stage in the processing of the main body, and scrapping at this stage results in a considerable economic loss since the cost of processing is added to the cost of the main body itself. Furthermore, in such known master cylinders, in order to avoid hydraulic locking, a second flow port of a considerably larger diameter is provided in the body, so that at all positions of the piston in the bore, the tank is closed to the bore seal. It communicates with the part located on the rear side.

In most master cylinders of the known type mentioned above, the recovery port provides direct, unrestricted communication between the tank and the pressure chamber. However, in the master cylinder described in US Pat. No. 3,199,299, a plug of porous material is placed between the recovery port in the body wall and the tank. The material of this plug allows fluid to pass through at a low outlet pressure, but limits pressure loss during this flow, and when high pressure is present in the master cylinder, a pressure increase occurs on the master cylinder side. This causes a rapid build-up of pressure in the master cylinder, which also acts on the seal carried by the piston, which now has no radial support at the withdrawal port as described above. After all, this will cause the seal to break.

The present invention provides a hydraulic master cylinder of the type described above, in which the recovery port comprises a plug of porous material housed in an opening in the wall of the body, and the periphery of the inner end of the plug extends into the hole at the inner end of the opening. It conforms to the curved surface and brings the outer end of the plug into direct contact with the hydraulic fluid in the tank.

The porous plug allows fluid to pass through at low pressure, but limits the pressure loss during this flow, and when the master cylinder is actuated, the leading edge of the seal carried by the piston is located in front of the retracted position of the piston. quickly increases the fluid pressure within the pressure chamber even before traversing part of the area.

By filling the collection port with a plug,
The plug radially supports the seal at all locations where the seal is located on the inner end of the plug, reducing wear on the seal carried by the piston. Since the inner end surface of the plug is aligned with the inner surface of the hole, the seal can pass smoothly through the recovery port, and as described above, the seal receives the pressure of the pressure chamber before the leading edge of the seal crosses the plug. damage is prevented.

Supporting the seals by porous plugs prevents seal wear, especially when the piston is pushed back into the retracted position during operation due to the pressure increase in the pressure chamber that occurs, for example, when the master cylinder is installed in an anti-skid brake system. Helps reduce wear in case.

Because the porous plug replaces the conventional retrieval port, the precision machining that forms the conventional retrieval port is replaced by a simple, less rigorous machining that forms the opening that receives the plug.

The dimensions of the plug are preferably large enough to provide communication between opposing portions of the bore seal and the tank when the piston is in its inactive retracted position.

This eliminates the need for a second communication port in the wall of the body, as the plug provides communication between the tank and the rear portion of the seal in the bore. As a result, manufacturing is simplified as the second communication port is omitted and the length of the piston is reduced as the seal passes at least partially over the plug.

Conveniently, the plug is constructed from a sintered material (sintered metal being suitable).

Preferably the porosity of the sintered material is approximately 20%.

Preferably, the central portion of the inner end of the plug is concave with a radius of curvature smaller than the radius of curvature of the hole in the body, and the peripheral edge of the inner end matches the edge surrounding the opening receiving the plug in the inner wall of the hole in the body.

The plug is press-fit into an opening in the wall of the body hole so that its peripheral edge projects slightly from the opening into the blank hole in the body. During the subsequent hole finishing, only the periphery is affected, so that almost all the pores remain open.

Preferably, the plug is of circular cross-section, but includes a screwdriver slot at the outer end of the plug to enable correct orientation of the plug within the aperture. . For example, align the screwdriver slot with the longitudinal axis of the hole.

The slot may be provided in an enlarged head at the outer end of the plug. In such a construction, the enlarged head acts as a filter, allowing maximum surface area of the material to be in contact with the fluid in the tank.

If the master cylinder has a tandem structure having a first piston that operates within a hole and a second piston that operates between the first piston of the hole and the closed end of the main body, the first pressure between both pistons At least both recovery ports between the chamber and the tank and between the second piston-closed end and the second pressure chamber and the tank are formed by respective plugs of porous material.

Two embodiments of the invention implemented in conventional master cylinders are shown in the accompanying drawings.

The master cylinder shown in FIG. 1 comprises a body 1 having a longitudinally extending bore 2, which is closed at one end by a closing wall 3, in which a pedal operating piston 4 operates. The pedal acts on the piston 4 via a piston rod 5 passing through a pair of axially spaced seals 6 for the open end of the bore 2.

A return compression spring 7 acts on the inner end of the piston 4 to normally hold the piston 4 in the inoperative retracted position in engagement with the stop ring 8.

A seal 9 in the form of a lip seal is arranged on the small diameter part of the inner end of the piston 4, the spring 7 abuts a holder 10 on the inner end of the piston 4, and a finger 11 directed towards the rear of the holder 10 Seal 9
acts as a stopper that restricts the movement of the piston 4 from trying to separate from the piston 4.

A pressure chamber 12 is formed in the bore 2 between the seal 9 and the closing wall 3. Normally, the pressure chamber 12 communicates through a withdrawal port 13 with an enlarged outlet 14 projecting radially from the wall of the body 1, with which a fluid reservoir (not shown) communicates. Pressure chamber 12 is constantly connected through an outlet port (not shown) to
Connected to clutch or brake.

The above configuration and its operation are conventionally well known.

The recovery port 13 of the present invention has a plug 15 of porous material, suitably a sintered metal, which is received in an opening 16 extending radially through the wall of the body 1. Plug 15 allows fluid and air to pass through at low flow rates without significant pressure drops. For example, the return flow to the tank caused by the volumetric expansion of the heated brake fluid takes place over a long period of time, for example up to one minute. However, piston 4
If moving at a suitable speed, the plug 15 restricts the flow so that during the very short time it takes for the seal 9 to completely traverse the plug 15,
Outflow into the tank through the plug 15 is almost completely prevented. Therefore, the entire stroke of the piston is available to move fluid to the brake.

A plug of sintered material with 20% porosity was tested with good results.

Plug 15 has the outer shape shown in FIGS. 2 and 3, with a stem 17 of circular cross section carried by an enlarged head 18 passing through opening 16.

The inner end of the stem 17 has a concave spherical surface 19 with a radius of curvature r smaller than the radius R of the hole 2, and when the hole 2 is finished by grinding or rolling, etc., the stem 1
The inner edge of 7 (which closely matches the contour of the inner edge of opening 16) is affected by only a small area of its periphery. Therefore, almost all pores are kept open.

The head 18 has a screwdriver slot 20;
When the direction of this slot coincides with the major longitudinal axis of the hole 2, the plug 15 in the opening 16 is correctly oriented.

Head 18 acts as a fluid filter.

In the inoperative retracted position shown, the seal 9 is located behind the plug 15 and the flow port 21 provided in the wall of the body 1 is always unrestricted between the tank and the part of the bore 2 located behind the seal 9. This provides good communication and prevents the formation of pressure locks as the piston 4 advances within the bore.

In operation, movement of the piston in the direction of operation pressurizes the fluid in the pressure chamber 12 and supplies it to the clutch or brake. Pressurization begins before seal 9 completely covers plug 15 and completely isolates the tank from the pressure chamber. During this movement, the seal 9 passes smoothly over the inner end of the stem 17, since at least the peripheral region of the inner end of the stem 17 has the same cylindrical surface as the cylindrical wall of the bore 2.

By increasing the size of the plug 15, both sides of the seal can be placed in communication with the tank when the piston 4 is in the retracted position. This has the advantage that the communication port 21 can be omitted and the overall length of the master cylinder can therefore be reduced.

A tandem master cylinder is shown in FIG. In this master cylinder, a second piston 30 is provided between the piston 4 and the closure 3, one of the seals 6 is carried by the rear end of the piston 4, and a spring 7 engages the piston 4 and the second piston 30. A second spring 32 is accommodated in a second pressure chamber 33 between the second piston 30 and the closure body 3, and the second pressure chamber 33 acts between the second piston 30 and the closure body 3.
Connects with 4. The spring 32 presses the holding body 35,
The retaining body 35 has a rearwardly directed finger 36 which limits the relative movement of the second piston 30 and a seal 37 arranged on the extension 38 of the front end of the second piston 30 .

The basic structure and operation of the tandem master cylinder shown in FIG. At some point, the seal 9 in front of the piston 4
It extends both in front and behind the position. This makes the diameter of the plug larger than the axial length of the seal 9,
In the retracted position shown, this is achieved by placing the portions of the hole 2 on both sides of the seal 9 in communication with the tank.
Similarly, a similar plug 41 of porous material forming a recovery port between the second pressure chamber 33 and the outlet 42 to the tank is of sufficient diameter so that the second piston 30
provides communication between the tank and both sides of the seal when in the retracted position shown.

By increasing the relative size of plugs 15 (and 41), a second communication port corresponding to communication port 21 of the master cylinder of FIG. 1 is not required, thereby simplifying processing.

Upon actuation of the pedal, both pistons 4, 30 advance through bore 2 and pressurize the fluid in pressure chambers 12, 33, respectively, as described above in connection with piston 4 of FIG.

The structure and operation of the master cylinder of FIG. 4 is otherwise the same as that of FIG. 1, and corresponding numbers have been given to corresponding parts.

[Brief explanation of the drawing]

Figure 1 is a longitudinal cross-sectional view of the hydraulic master cylinder, Figure 2 is an enlarged view of a plug suitable for use in the master cylinder of Figure 1, as seen from the front and back of the main body, and Figure 3 is a view of the plug suitable for use in the master cylinder of Figure 1. FIG. 2 is a view of the plug seen from the side of the main body, and FIG. 4 is a longitudinal sectional view of the tandem master cylinder. 1: Body, 2: Hole, 4: Piston, 9: Seal, 12: Pressure chamber, 13: Recovery port, 15: Plug, 16: Opening.

Claims (1)

Claims: 1. A pressure chamber is formed in a bore of the body in front of a piston operating in the bore, the body having an outlet port leading from the pressure chamber and a position in which the piston is at least in an inoperative retracted position. a recovery port communicating the pressure chamber with a fluid tank, and an initial movement of the piston in the bore in the actuating direction closes the recovery port to isolate the pressure chamber from the tank; In a hydraulic master cylinder for a vehicle clutch or brake system of the type in which a subsequent movement of the piston in the same direction pressurizes the fluid in the pressure chamber and supplies it to the outlet port, the recovery port 13 is connected to the main body 1. It consists of a plug 15 of porous material housed in an opening 16 in the wall, the circumference of the inner end of the plug matching the curved surface of the hole 2 at the inner end of the opening 16, and the outer end of the plug 15 A hydraulic master cylinder characterized by direct contact with the hydraulic fluid therein. 2. In the master cylinder according to claim 1, the plug 15 is sufficiently large and at least when the piston 4 is in its inoperative retracted position,
A master cylinder characterized in that communication is provided between the portions of the hole 2 on both sides of the seal 9 carried by the piston and the tank. 3. The master cylinder according to claim 1 or 2, wherein the plug 15 is made of a sintered material. 4. In the master cylinder according to any one of claims 1 to 3, the central portion 19 of the inner end of the plug 15 has a concave spherical surface, and its radius of curvature r is equal to that of the hole 2 of the main body 1. A master cylinder characterized in that it is smaller than the radius R, and that the circumferential edge of the inner end of the plug matches the shape of the edge of the wall of the main body 1 surrounding the opening 16 that accommodates the plug 15. 5. A master cylinder according to any one of claims 1 to 4, in which the plug 15 has a circular cross section and is provided with a screwdriver slot 20 at the outer end of the plug 15, so that the plug 15 A master cylinder characterized in that the cylinder is correctly oriented within the opening 16.