GB2141498A

GB2141498A - An hydraulic piston and cylinder assembly

Info

Publication number: GB2141498A
Application number: GB08409172A
Authority: GB
Inventors: Wolfgang Dohrmann
Original assignee: Boge GmbH
Current assignee: ZF Boge GmbH
Priority date: 1983-06-14
Filing date: 1984-04-09
Publication date: 1984-12-19
Also published as: DE3321362C2; ES530986A0; DE3321362A1; GB8409172D0; ES8501497A1; GB2141498B

Abstract

A piston and cylinder assembly in which a compensation port 11 providing communication between a fluid reservoir and a working cylinder 2 is arranged clear of the axial working travel of a seal 4 so that damage to the grooved ring seal 4 due to poor de-burring of the compensation port 11 is avoided, and flow-generated noises caused by having a port of small diameter can also be eliminated. There is a second cylinder 8, coaxial with the first and of larger diameter, defining with the first cylinder 2 an annular space 9 into which the compensation port 11 opens, communication with the first cylinder being controlled by a pressure responsive valve 10 which is closed by excess pressure in the pressure chamber 7. <IMAGE>

Description

SPECIFICATION An hydraulic piston and cylinder assembly The invention relates to an hydraulic piston and cylinder assembly, particularly for use in motor vehicles, in which a piston is sealed with respect to a cylinder wall and is exposed on one side to hydraulic fluid, a fluid reservoir communicating with the cylinder via a compensation port.

Master cylinders are already known having a housing with an axial bore, a reservoir chamber and a corresponding fluid reservoir (DE-OS 30 21 893), in which the compensation port connects the working cylinder to the reservoir chamber. The pistons are provided with lip seals, with the drawback,that the compensation port lies within the travel of this seal, so that de-burring of the port is necessary. This is troublesome and expensive, and experience has shown that faulty de-burring is the most frequent cause of damage to the seal. A further disadvantage is that, because of the small diameter of the port, noise is generated by the flow of fluid.

An aim of the invention is to provide a piston and cylinder assembly in which the compensation port is displaced away from the region of axial travel of the piston and its seal, and which is therefore less liable to damage.

According to the invention, there is provided an hydraulic piston and cylinder assembly, in which a piston is sealed with respect to the wall of a first cylinder and is exposed on one side to hydraulic fluid, a fluid reservoir communicating with the first cylinder via a compensation port, and in which, coaxially with the first cylinder, there is provided a second cylinder of largeer diameter than the first, the first and second cylinders defining an annular space into which the compensation port connects, and being separated from one another by a pressure valve.

An advantage of this arrangement is that by having the compensation port open into an additional annular chamber, damage to the piston seal is less likely to occur. What is more, the troublesome and expensive de-burring by sizing, rolling or honing of the opening to the port is no longer necessary.

A further advantage is that the compensation port can have a larger diameter so that the noise problem can be eliminated compietely.

The compensation port may have a uniform inside diameter throughout its length. This does away with the troublesome and expensive manufacturing step of producing a stepped bore, as is otherwise generally employed. As there is a pressure valve interposed between the first and second cylinder, the diameter of the port can be made correspondingly larger so that overall a simpler and more economical manufacturing process is possible, particularly when one considers the idle times of the tools, e.g. of the borer needed to form the step.

Suitably, the pressure valve is of annular shape and has an inside diameter corresponding to the outside diameter of the first cylinder and an outside diameter corresponding to the inside diameter of the second cylinder. By this arrangement the pressure valve is also arranged to be coaxial with the first cylinder so that the piston together with its seal'can work over an unbroken smooth surface. This seal may suitably comprise a grooved ring sealing lip.

The pressure valve serves to allow a buildup of pressure in the working cylinder, so that apart from this the cylinder performs the normal functions required for an hydraulic clutch, an hydraulic brake installation or an hydraulic servo control or steering.

The pressure valve may comprise a pressure-tight abutment ring fixedly mounted between the two cylinders, and against which a spring acting on a valve plate abuts. Preferably, the spring, in the form of a compression spring, provides a clearance or passage between the reservoir and the working cylinder which is closed only during the build-up of pressure in the working cylinder due to the corresponding internal pressure. As long as there is a flow path, the corresponding amount of fluid required can pass from the reservoir into the working cylinder and subsequently, when the pressure in the inner cylinder exceeds the pressure of the spring, the valve is automatically closed.

The abutment ring may have a generally Ushaped cross-section, one limb of the 'U' forming a seal seating for the valve plate, and the two limbs being connected together by a web having at least one opening. The abutment ring is arranged to be pressure-tight between the two cylinders and the outside diameter of the valve plate is smaller than the inside diameter of the second cylinder, so that in the normal position there is a flow path past the valve plate and through the opening or openings in the abutment ring to the reservoir. On the build-up of pressure in the working cylinder the valve plate is urged axially against at least one limb of the abutment ring so that flow is no longer possible.

The valve plate may be located axially by means of a securing ring provided on the opposite side of the valve plate to the abutment ring. It is an advantage for this securing ring to serve also as means for limiting the axial movement of the valve plate.

In order to achieve a compact construction of the pressure valve, it is provided that in the closed position of the valve the spring is enclosed within the two limbs of the abutment ring. The length of at least one limb of the abutment ring is accordingly selected to correspond to the axial length of the compression spring such that when it is fully compressed the spring fits completely within the channel defined by the two limbs.

The invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a complete piston and cylinder assembly in section, and Figure 2 shows a section through a pressure valve to a larger scale.

The piston and cylinder assembly illustrated in Figure 1 substantially comprises a housing 1, inside which is arranged a first cylinder 2.

A piston 3 is axially movable within the first cylinder 2, which serves as the working cylinder, and sealing with respect to the first cylinder 2 is achieved by means of a grooved ring seal 4. The piston 3 is acted on by a compression spring 5 and is operated by a rod which extends outwards. Within an inner chamber 7 there is the hydraulic working fluid. Coaxially with respect to the first cylinder there is a second cylinder 8 which, together with the first cylinder 2, defines an annular space 9. The inner chamber 7 is in communication with a spigot 12, leading to a fluid reservoir (not shown) via a pressure valve 10, the annular space 9 and a compensation port 11.

The compensation port 11 is arranged so that no contact can take place between the port and the grooved ring seal 4. Likewise, the pressure valve 10 is disposed outside the working travel of the piston 3.

The housing 1 also has an outlet passage 1 3 communicating with an hydraulic clutch, an hydraulic brake installation or an hydraulic servo steering or control.

Figure 2 shows a detail of the pressure valve 10 illustrated in Figure 1. The valve 10 is arranged between the second cylinder 8 and the first cylinder 2 in the end portion of the annular space 9, the abutment ring 14 being sealed and fixed in a pressure-tight manner in the annular space 9 sealing it from the inner chamber 7. The abutment ring 14 has two limbs 1 5 and 1 6, between which is mounted a compression spring 17, and the two limbs are connected together by a web 18 having at least one opening 1 9.

A face 20 of the limb 1 5 forms a valve seating for a valve plate 21 and axial movement of the plate 21 is limited by a securing ring 22 mounted on the outside of the first cylinder 2. The pressure valve 10 illustrated here is shown in the open position and the hydraulic fluid can pass from the annular space 9 through the opening 19, past the spring 1 7 and through an annular gap 23 and into the inner chamber 7.

On the build-up of sufficient internal pressure in the inner chamber 7 the valve plate 21 is urged axially against the face 20 of the limb 1 5 of the abutment ring 14 and thereby closes the. valve 10.

Claims

1. An hydraulic piston and cylinder assembly, in which a piston is sealed with respect to a wall of a first cylinder and is exposed on one side to hydraulic fluid, a fluid reservoir communicating with the first cylinder via a compensation port, and in which, coaxially with the first cylinder, there is provided a second cylinder of larger diameter than the first, the first and second cylinders defining an annular space into which the compensation port connects, and being separated from one another by a pressure valve.

2. A piston and cylinder assembly as claimed in Claim 1, in which the compensation port has a uniform inside diameter throughout its length.

3. A piston and cylinder assembly as claimed Claim 1 or 2, in which the pressure valve is of annular shape and has an inside diameter corresponding to the outside diameter of the first cylinder and an outside diameter corresponding to the inside diameter of the second cylinder.

4. A piston and cylinder assembly as claimed in Claim 3, in which the pressure valve comprises a pressure-tight abutment ring fixedly mounted between the two cyiinders and against which a spring acting on a valve plate abuts.

5. A piston and cylinder assembly as claimed in Claim 4, in which the abutment ring has a generally U-shaped cross-section, one limb of the 'U' forming a seal seating for the valve plate, and the two limbs being connected together by a web having at least one opening.

6. A piston and cylinder assembly as claimed in Claim 4 or 5, in which the valve plate is located axially by means of a securing ring provided on the opposite side of the valve plate to the abutment ring.

7. A piston and cylinder assembly as claimed in Claim 5 or Claim 6 and Claim 5, in which when the pressure valve is in its closed position the spring is enclosed within the two limbs of the abutment ring.

8. A piston and cylinder assembly substantially as described with reference to the accompanying drawings.