GB2202290A - Master cylinder assembly - Google Patents

Abstract

A master cylinder assembly for an agricultural tractor has a body (1) having a plurality of generally axial working bores (2, 3) each containing a pressure piston (4, 5). Generally radial valve bores (10, 11) communicate respectively with the working bores and with a cavity (9) bridging the valve bores to form a transfer passage, fluid flow through which is controlled by valve members (12, 13) in the valve bores (10, 11). The cavity is created by forming a bore in a boss (14) above the location of the valve bores and the valve bores are formed through the bore in the boss, prior to closing off the latter by insertion of a screw plug (16). In Fig 3 the cavity (9) comprises two intersecting boxes with respective caps (23, 24). <IMAGE>

Description

MASTER CYLINDER ASSEMBLY.

This invention relates to a master cylinder assembly, primarily for a vehicle hydraulic braking system, and of the general kind having a body defining therein a plurality of pressure cylinders between which extends a transfer passage controlled by valve means to permit communication between respective pressure chambers of the cylinders when the cylinders are actuated simultaneously and to prevent such communication when one of the cylinders is operated individually. Such an assembly is of particular use in an agricultural tractor, for example, in which normal straight-line braking is accomplished by the simultaneous actuation of a pair of cylinders and steering assistance can be provided by actuating one or other of the cylinders individually.

The invention is particularly concerned with the formation in such an assembly of the transfer passage and has for an object to provide a master cylinder assembly of the aforesaid general kind in which said passage is provided in a simple, convenient and cost-effective manner and in which said valve means may be readily and conveniently accommodated.

According to one aspect of the invention, a method of forming a master cylinder assembly of the aforesaid general kind comprises forming a body having a plurality of generally axial working bores therein for the reception of respective pressure pistons, forming a generally radial bore overlapping both cylinders and having its base spaced from said axial bores, forming generally radial valve bores extending between the respective axial bores and said radial bore, and inserting closure means in said radial bore such as to close the radially outer end thereof whilst providing a space between its radially inner end and the radially outer ends of said valve bores, said space and valve bores constituting a fluid transfer passage between said working bores, through which passage fluid flow between the working bores will be controlled in use by valve means operating in response to movement of said pistons.

According to another aspect of the invention, a master cylinder assembly of the aforesaid general kind comprises a body having a plurality of generally axial working bores each containing a pressure piston, generally radial valve bores communicating respectively wiSh said working bores and with at least one generally radially extending cavity bridging the adjacent radially outer ends of the valve bores, closure means closing the radially outermost end of the cavity whilst providing a space between the radially innermost end of the closure means and the radially outer ends of said valve bores, said valve bores and space constituting a transfer passage between said axial working bores, and valve means operable in response to working movement of said pistons to control fluid flow through the transfer passage between the working bores.

In one convenient arrangement, the body includes a generally radially projecting boss over the location of the valve bores, the boss having a bore forming said cavity communicating with both valve bores and being closed by a plug inserted, preferably by screwing, into its open end, the inner end of the plug being inset from the adjacent ends of the valve bores to form said space forming part of the transfer passage.

Alternatively, the boss may contain a plurality of mutually angled bores which intersect to form said cavity, each of said bores containing a respective closure member. Preferably, each of said angled bores is aligned with a respective one of said valve bores.

Conveniently, each valve bore has a surrounding valve seat for co-operation with a corresponding valve element which is conveniently actuated in response to working movement of the corresponding one of said pistons, typically by actuating means within the bore engaging a surface of said corresponding piston.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a transverse cross-section of one form of the master cylinder of the invention; Figure 2 is a view similar to Figure 1 illustrating an alternative form of the master cylinder of the invention, and Figure 3 is a view similar to Figure 2 illustrating a further alternative form of the master cylinder of the invention.

Referring to Figure 1, this illustrates a master cylinder having a body 1 containing a pair of parallel working bores 2, 3 containing respective working pistons 4, 5. The body 1 is enclosed by a reservoir element 6 which is spaced from the external surface 1A of the body such that the cavity thereby formed constitutes a reservoir for containing hydraulic fluid to be supplied to the cylinders 2 and 3 through recuperation ports controlled by suitable conventional valve means. Neither the ports nor the valve means are illustrated in the drawing. The reservoir element is closed by a cap 7 screwed on to a neck 8 of the element.

The cylinders 2 and 3 are interconnected by a transfer passage, indicated generally at 9 and it is with the formation of this transfer passage that the invention is particularly concerned. The body contains a pair of radial valve bores 10, 11 leading respectively from the cylinders 2 and 3 and, in this particular embodiment, converging in a direction towards the centre line A.

Each bore 10, 11 is stepped to form a respective valve seat 10A, 11A and each bore contains a valve element 12, 13 of which relatively small diameter stems 12A, 13A extend respectively into engagement with the adjacent outer surface of the associated piston, which surface is shaped in a suitable manner to enable the piston to actuate the valve member during working movement of the piston, in conventional manner. Each valve member is also provided with an enlarged head 12B, 13B, the underside of which is appropriately shaped to co-operate with the adjacent valve seat 10A, 11A.

The body 1 is provided with an upstanding boss 14 which lies over both of the radial bores 10 and 11 and is bored out so as to produce a cavity bridging between the bores 10 and 11. The bore of the boss is internally threaded over part of its length to receive a plug 16 which is screwed into the boss to close off its open end. With the plug fully inserted, a transfer passage comprising the bores 10 and 11 and a portion 15 of the cavity is formed between the cylinders and fluid flow therethrough is controlled by the valve members 12, 13, in response to working movement of the pistons 4, 5, in conventional manner.

It will be seen that the arrangement of the invention enables the transfer passage to be formed in a very simple and convenient manner by simply boring out the boss 14, drilling the bores 10 and 11 through the opening thus formed in the boss and, after insertion of the valve elements 12 and 13, closing off the boss by means of the screw plug 16 in such a manner as to leave the bores 10 and 11 in communication by way of the space 15 which remains after insertion of the plug.

Such an arrangement lends itself very well to manufacture by automatic machine tools and enables the master cylinder to be made in a considerably more cost-effective manner than some existing arrangements.

The master cylinder illustrated in Figure 2 is similar to that of Figure 1, with the reservoir element 6 illustrated in broken outline only. This embodiment differs in that the valve bores 10 and 11 extend parallel to the centre line A and each valve element is constituted by a large ball 12' 13' acting as the valve proper controlling fluid flow by engagement with the adjacent valve seat l0A, llA and smaller ball 12'', 13'' engaging the outer surface of the respective piston 4, 5 and acting to transmit thrust to the adjacent larger ball 12', 13' when it is required to dislodge the larger balls from the valve seats. This embodiment has the same advantages in terms of ease of manufacture as those described in connection with Figure 1.

Figure 3 illustrates another alternative embodiment in which the reservoir element 6 is again illustrated in broken outline. The valve bores 10 and 11 are arranged to converge towards the centre line A and the boss 14' is formed with a pair of bores 21, 22 which converge towards the centre line A from the opposite direction to the bores 10 and 11 and intersect at a sufficient distance from the upper ends of the bores 10 and 11 to form a cavity 15'. Each of the bores 21, 22 is closed by a corresponding plug 23, 24, leaving the cavity 15' in communication with the bores 10 and 11 so as to form a transfer passage 9 between the working bores 2 and 3.In this embodiment, a single relatively large diameter ball 25 is able to co-operate with valve seats formed respectively at the outer ends of the bores 10 and 11 and smaller diameter balls 26, 27 respectively engage the outer working surfaces of the pistons 4 and 5 and act as thrust members in relation to the ball 25 in order to control the action of the latter in opening and closing the bores 10 and 11 in response to working movement of the pistons 4 and 5. It will be seen that by first forming the bores 21 and 24, it is a relatively simple matter subsequently to form the valve bores 10 and 11 and this embodiment largely retains the manufacturing advantages described in relation to Figures 1 and 2.

Although the valve members illustrated in the various embodiments are urged towards their closed positions by the action of gravity only, it would be possible to subject the valve members to the action of light return springs sufficiently strong to retain the valve members in position on their seats. However, the valve members preferably should not be allowed to seal during normal operation of the cylinders, so that any expansion of fluid occurring in the cavity portion 15' of the transfer passage may be accommodated by reverse flow of fluid into the cylinders. The valve elements may conveniently be of compressible material so that each may be deformed into sealing engagement with its valve seat by the action of pressure in the other cylinder.

Claims (12)

CLAIMS.

1. A method of making a master cylinder assembly comprising forming a body having a plurality of generally axial working bores therein for the reception of respective pressure pistons, forming a generally radial bore overlapping both cylinders and having its base spaced from said axial bores, forming generally radial valve bores extending between the respective axial bores and said radial bore, and inserting closure means in said radial bore such as to close the radially outer end thereof whilst providing a space between its radially inner end and the radially outer ends of said valve bores, said space and valve bores constituting a fluid transfer passage between said working bores, through which passage fluid flow between the working bores will be controlled in use by valve means operating in response to movement of said pistons.

2. A method according to Claim 1, including the step of forming a screw thread in each said generally radial cavity-forming bore and inserting said closure means, which is correspondingly threaded, by screwing it into the threaded bore.

3. A method according to Claim 1 or Claim 2 wherein a pair of cavity-forming bores are formed, each being closed by the insertion of a respective closure means therein.

4. A method of making a master cylinder assembly, substantially as hereinbefore described, with reference to Figure 1, Figure 2 or Figure 3 of the accompanying drawings.

5. A master cylinder assembly comprising a body having a plurality of generally axial working bores each containing a pressure piston, generally radial valve bores communicating respectively with said working bores and with at least one generally radially extending cavity bridging the adjacent radially outer ends of the valve bores, closure means closing the radially outermost end of the cavity whilst providing a space between the radially innermost end of the closure means and the radially outer ends of said valve bores, said valve bores and space constituting a transfer passage between said axial working bores, and valve means operable in response to working movement of said pistons to control fluid flow through the transfer passage between the working bores.

6. A master cylinder according to Claim 5 wherein the body includes a generally radially projecting boss over the location of the valve bores, the boss having a bore forming said cavity communicating with both valve bores and being closed by a plug inserted into its open end, the inner end of the plug being inset from the adjacent ends of the valve bores to form said space forming part of the transfer passage.

7. A master cylinder according to Claim 7 wherein the bore of said boss and an external part of the plug are complementarily threaded and the plug is screwed into the bore.

8. A master cylinder according to Claim 5 wherein the body includes a generally radially projecting boss over the location of the valve bores, the boss containing a plurality of mutually angled bores which intersect to form said cavity, each of said bores containing a respective closure member.

9. A master cylinder according to Claim 8 wherein each of the angled bores is aligned with a respective one of said valve bores.

10. A master cylinder according to any one of Claims 5 to 9 wherein each valve bore has a surrounding valve seat for co-operation with a corresponding valve element constituting said valve means.

11. A master cylinder according to Claim 10 wherein each valve element extends through the wall of its associated cylinder for engagement by a piston in that cylinder.

12. A master cylinder substantially as hereinbefore described with reference to Figure 1, Figure 2 or Figure 3 of the accompanying drawings.