GB2074271A

GB2074271A - Bleeding Hydraulic Pressure Cylinders

Info

Publication number: GB2074271A
Application number: GB8110922A
Authority: GB
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1980-04-19
Filing date: 1981-04-07
Publication date: 1981-10-28
Also published as: GB2074271B

Abstract

A hydraulic pressure cylinder (1) is provided with a channel-shaped insert (35) of which the sides (35A) engage the internal cylinder wall to define a flow path for air which has accumulated in an upper region of the cylinder to a point circumferentially remote from the upper region. Such a flow path facilitates bleeding of the cylinder. <IMAGE>

Description

SPECIFICATION Hydraulic Pressure Cylinder This invention relates to an hydraulic pressure cylinder for use in a hydraulic pressure system and primarily for use as a master cylinder in an hydraulic brake or clutch actuating system of a motor vehicle.

It is usual in modern pressure cylinders, such as those employed in the actuation of vehicle brakes and clutches, for the fluid outlet to be disposed at an end of the cylinder, or at a location in a normally upper region of the cylinder, the outlet extending either upwardly or tangentially from that region. Any air trapped in the cylinder tends to accumulate in said upper region and can readily be expelled by conventional bleeding techniques through outlets disposed in the aforesaid locations.

In general, the siting of a fluid outlet at the top of a pressure cylinder used as a master cylinder in a vehicle hydraulic system, although facilitating bleeding, is inconvenient for the connection of pipe runs from brake or clutch actuating equipment which are normally located beneath and remote from the master cylinder. Moreover, the present day trend towards the use of thinwalled deep-drawn steel tubes for the pressure cylinder portion of master cylinders requires the use of pre-formed bosses attached to the tube and since the major portion of the upper region of the cylinder is often taken up by a fluid reservoir, particularly in the widely used tandem type of master cylinder, it is often inconvenient to site outlets in said upper region.

It will thus be seen that manufacturing and installation convenience dictates the siting of the cylinder outlet so as to be directed either transversely or downwardly. However, since the outlet, when so sited is remote from the upper region of the cylinder in which air accumulates, satisfactory bleeding of a system incorporating such a cylinder can be extremely difficult, if not impossible. This can be particularly disadvantageous in the case of a vehicle braking system since trapped air results in the brake pedal having a soft or spongy feel leading, in turn, to a lack of driver confidence.

Various forms of insert have hitherto been used in hydraulic pressure cylinders to facilitate bleeding of accumulated air therefrom, but these have often been of limited application to particular types of cylinder or to particular locations within cylinders, and/or have often been of relatively complicated shapes and therefore difficult and expensive to produce.

An object of the present invention is to provide a hydraulic pressure cylinder, primarily for use as a master cylinder in an hydraulic brake or clutch actuating system of a motor vehicle, and having a fluid outlet which is peripherally remote from the upper air-collecting region of the cylinder, in which comparatively simple and adaptable means is provided for facilitating the bleeding of accumulated air from the system through said outlet.

According to the invention, a pressure cylinder has a fluid outlet remote from the upper aircollecting region of the cylinder and includes a collector which communicates with the interior of the cylinder at said upper region, the collector being in the form of a generally annular insert of channel-shaped cross-section disposed around the internal periphery of the cylinder with the base of the channel being radially inwardly spaced from said cylinder wall, the insert having a pair of axially spaced generally circular flanges forming the sides of the channel and projecting radia!ly outwardly relative to the base to engage the cylinder wall and define therewith a flow path from said upper region peripherally along the cylinder wall to the outlet, thereby permitting the bleeding of accumulated air from said region through the outlet.

Communication with the outlet may conveniently be by way of a discontinuity in the flanges of the insert in the upper region of the cylinder. This may be in the form of a radial gap in the flanges or a chordal flattening of the external periphery of the flanges.

The insert is preferably positively located circumferentially and/or axially of the cylinder. For this purpose, the insert may be provided with a radial projection which engages in an opening in said cylinder internal wall, such opening conveniently being the fluid outlet.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a longitudinal cross-section of one embodiment of the pressure cylinder of the invention in the form of a tandem master cylinder for a motor vehicle braking system; Figure 2 is an enlarged perspective view of one form of collector means used in the master cylinder of Figure 1; Figure 3 is a perspective view to an enlarged scale of another form of collector means as used in the master cylinder of Figure 1; Figure 4 is a transverse cross-sectional view of a pressure cylinder iliustrating an alternative form of collector means; Figure 5 is a cross-section along the line 5-5 of Figure 4; Figure 6 is a perspective view of a further alternative form of collector means;; Figure 7 is a transverse cross ectional view of a pressure cylinder iilustrating the collector means of Figure 6 in place therein, and Figure 8 is a cross-section along the line 8-8 of Figure 7.

Referring to Figure 1, the tandem master cylinder therein illustrated has a working cylinder 1 which may conveniently be a thin-walled metal tube, as of steel for example, formed by a conventional deep drawing process. The cylinder is provided with a pair of outlets in the form of respective hollow bosses 2 and 3 secured to the normally lowermost surface of the cylinder 1, as by welding for example, and communicating with respective holes 4 through the cylinder wall. A container 5 defining twin fluid reservoirs 6 and 7 is mounted on the normally uppermost surface of the cylinder 1 and sealed against that surface by resilient sealing rings 8 housed in respective recesses 9.Within the regions defined by the sealing rings 8, the cylinder wall is provided with respective pairs of holes 10 and 11 therethrough and the bases of the reservoirs are provided with respective through holes 12 providing communication between the interior of the reservoirs and that of the cylinder 1.

Slidably mounted within the cylinder 1 is a piston assembly including a pair of pistons 14 and 1 5 urged apart by a spring 16 acting between a cup 17 bearing against the piston 14 and a component 18 located within the piston 15. The cup 17 and component 18 are interconnected by a screw 19 which is passed through an opening in the bottom of the cup so that a head 20 of the screw bears against the internal end surface of the cup and a threaded end portion 21 of the screw is threadedly engaged within the component 18.

The piston 14 is also provided with a component 22 and the components 18 and 22 act as retainers for respective pressure seals 23 and 24 of the pistons 15 and 14. The component 22 has a shoulder 25 providing an abutment for one end of a spring 26, the other end of which reacts indirectly against the closed end 27 of the cylinder. The pistons 14 and 15 define respective pressure chambers 28 and 29 within the cylinder and these chambers communicate via respective openings 10 with the associated reservoirs 6, 7.

The piston 14 is provided with a further pressure seal 30 which faces the chamber 29 and receives pressure therefrom to actuate the piston 14. The holes 11 permit recuperative flow of fluid from the reservoirs to the regions behind the respective pistons 14 and 15. The piston 15 is provided with a back-up seal 31 to prevent leakage of fluid from the rear end of the cylinder. The piston assembly is retained within the cylinder by a circlip 32 engaged within a circumferential groove in the cylinder wall and an actuating rod 33, which would normally be connected to a driver-operated pedal, extends through the circlip and engages a cup 34 which bears against the piston 1 5 and also acts as an abutment for the seal 31.

Operation of the master cylinder illustrated is conventional and will be well understood by those versed in the art.

The outlets 2 and 3 of the master cylinder illustrated are located in a region which is circumferentially remote from the upper region of the cylinder in which any air entering the cylinder would normally accumulate and bleeding of the cylinder through outlets sited in this manner would conventionally be extremely difficult, if not impossible. In order to facilitate the bleeding of accumulated air from the cylinder, the cylinder is provided with collectors 34 and 35 disposed respectively in the regions of the outlets 2 and 3.

Each collector is in the form of a generally annulat insert, as of plastics material for example, and, as will be seen more clearly from the enlarged illustrations in Figures 2 and 3, each insert is provided respectively with parallel radially projecting circumferential flanges 34A and 35A providing the inserts with a channelshaped transverse cross-section. Each insert has a gap 36 and the inserts are arranged within the cylinder with their flanges 34A and 35A against the circumferential internal wall of the cylinder and the gaps 36 located in the upper region of the cylinder in which air would normally accumulate.

The insert 34 is trapped between the spring 26 and the cylinder end 27 and is thereby axially located and the spring force contributes a measure of resistance against circumferential movement of the insert. The insert 35 is disposed within a shallow circumferential groove in the cylinder wall to ensure its axial location. The inserts may conveniently have sufficient inherent resilience to expand outwardly against the cylinder wall and provide resistance against circumferential movement, in use. The gap in the inserts also enables the inserts to be radially inwardly compressed to some extent, thereby facilitating their assembly into the cylinder.

It will be seen that the channel of each insert provides a circumferential path between the gap 36 in communication with the upper region of the cylinder and the respective outlets 2 and 3. Thus, by pumping the pistons along the cylinder in the manner conventionally adopted for bleeding braking and clutch systems, fluid and entrained air enters the flow path provided by the insert and is driven around the path to be expelled through the outlet.

When used as a master cylinder in a motor vehicle, the pressure cylinder of the invention would normally be secured to a bulkhead, for example, within the engine compartment with its longitudinal axis extending generally horizontally as shown. For this purpose, the cylinder is provided with a separately made apertured flange 1A which is passed over the external surface of the cylinder and abuts against a shoulder formed by an enlarged portion 1 B of the cylinder. The flange may be retained on the external wall of the cylinder either by being a tight press fit thereon, or by providing sharp splines on the internal surface of the flange aperture or on the external surface of the cylinders When splines are provided, these bite into the opposed surface of the non-splined component, providing resistance against relative rotation of the flange and cylinder.

The provision of a separately made flange permits flexibility of installation to be achieved, since the flange may be attached to the cylinder in any desired orientation to suit particular installation requirements.

Figures 4 and 5 illustrate one manner of positively locking an insert against excess axial and circumferential movement. The form of cylinder 1 illustrated is provided with a transverse outlet 2 and the insert 341, similar to insert 34 of Figures 1 and 2, is provided with a radial projection 37 which engages within the opening 4 in the cylinder wall and precludes the insert 341 from excess circumferential or axial movement relative to the cylinder, whilst permitting fluid to flow freely through the outlet 2. As will be seen clearly from Figure 5, the insert 341 has only one flange 34A, the axially opposed side thereof terminating in a thickened tapered portion 38 which bears against the end 27 of the cylinder and may form an abutment for a spring in the same manner as the ring 34 shown in Figure 1.It will be understood that the locking arrangement described above may be used with the insert of Figure 3 or with any other convenient form thereof.

Figures 6 to 8 show an alternative form of insert 342 again provided with a projection 37 engaging the opening 4 in the cylinder wall for the purpose described above. As will be seen from Figure 7, the projection 37 is disposed centrally between the two flanges 35A and, in this embodiment, the gap 36 is formed solely in the region of the flanges 35A, the remainder of the insert forming a complete annulus.

It will be seen that, by using a collector in accordance with the invention, it is possible to place the outlet or outlets of a pressure cylinder at any convenient point around the circumference thereof remote from the upper region and be able to bleed from the cylinder any air which accumulates in said upper region. The inserts of the type illustrated may be formed by moulding from plastics material and the projection 37, when used, may thereby be conveniently integrally formed. It will be understood that a plurality of collectors disposed at different locations in the cylinder may be arranged to direct accumulated air to a single outlet.

Claims

1. A hydraulic pressure cylinder having a fluid outlet remote from the upper air-collecting region of the cylinder and including a collector which communicates with the interior of the cylinder at said upper region, the collector being in the form of a generally annular insert of channel-shaped cross-section disposed around the internal periphery of the cylinder with the base of the channel being radially inwardly spaced from said cylinder wall, the insert having a pair of axially spaced generally circular flanges forming the sides of the channel and projecting radially outwardly relative to the base to engage the cylinder wall and define therewith a flow path from said upper region peripherally along the cylinder wall to the outlet, thereby permitting the bleeding of a accumulated air from said region through the outlet.

2. A cylinder according to Claim 1 wherein a discontinuity is formed in the flanges of the insert in the upper region of the cylinder to provide communication between the flow path and the interior of the cylinder.

3. A cylinder according to Claim 2 wherein said discontinuity is in the form of a radial gap in the flanges.

4. A cylinder according to Claim 3 wherein the radial gap extends also through the base of the channel.

5. A cylinder according to Claim 1 wherein the external peripheries of the flanges are chordally flattened to provide communication between the flow path and the interior of the cylinder.

6. A cylinder according to any one of the preceding claims wherein the insert is positively located circumferentially and/or axially of the cylinder.

7. A cylinder according to Claim 6 wherein the insert is provided with a radial projection which engages in an opening in the cylinder wall to provide said positive location.

8. A cylinder according to Claim 7 wherein said opening is constituted by said fluid outlet.

9. A cylinder according to Claim 7 or Claim 8 wherein the projection extends radially outwardly from the base of the channel between the flanges.

10. A cylinder according to Claim 1 wherein the insert is retained against an end of the cylinder by a return spring associated with a piston slidable within the cylinder.

11. A hydraulic pressure cylinder substantially as hereinbefore described with refernece to Figures 1,2 and 3 or Figure 4 and 5 as modified by Figures 6 to 8.