GB2186637A - Hydraulic apparatus - Google Patents

Abstract

The hydraulic apparatus comprises a master cylinder 12, a slave cylinder 36, and a fluid passageway 32 interconnecting the master and slave cylinders. The master cylinder has a piston 18 therein displaceable axially so that, in use, transfer of hydraulic working fluid between the cylinders takes place through the fluid passageway interconnecting the cylinders. The slave cylinder has a piston 38 therein displaceable axially as a result of said fluid transfer, each piston dividing its cylinder into first and second chambers. Each of said cylinders includes a piston-like member 28,44 which is displaceable axially in its cylinder towards the piston under the influence of bias means 30,49 so as to maintain the hydraulic working fluid in the first chambers 14,34 of the cylinders under pressure. The piston in each cylinder is associated with a piston rod 24,41 passing through said first chamber and extending through the associated piston-like member. <IMAGE>

Description

SPECIFICATION Hydraulic apparatus This invention relates to an improved hydraulic apparatus and especially, but not exclusively concerned with a hydraulic shift for a motor vehicle automatic transmission.

Modern automobile manufacture features considerable use of pre-manufactured sub-assemblies. These are generally manufactured at a point remote from the production line and then stored prior to fitting, without any major adjustments to the vehicle on the product line.

The use of such pre-manufactured sub-assemblies simplifies vehicle manufacture and reduces production costs. Master/slave cylinder hydraulic assemblies can be supplied in such a pre-manufactured form. In general they comprise master and slave cylinders interconnected hydraulically through small-bore piping, the cylinders being provided with respective pistons, piston rods of which are adapted to be mechanically linked e.g. to a control lever and mode selection arm pivotally mounted on a casing of the transmission during fitting.

Conventionally such master/slave cylinders are pre-filled with oil under pressure at the point of manufacture so that they can be fitted directly to the vehicle without the need for filling on the vehicle production line. Generally, such prefilled assemblies are stored for a time before fitting and, during this storage period, it has been known for oil to leak. Such leakage is usually through the seal between the piston rods and the ends of the cylinders through which they extend.

Furthermore gradual loss of hydraulic fluid also occurs as the connecting rods move axially backwards and forwards carrying a film of fluid on their surfaces past the seal. Over a period of time a significant oil-pressure drop caused by this leakage will have an adverse effect on operation.

It is an object of the invention to provide an improved master/slave cylinder assembly which is provided with means for maintaining a desired hydraulic working fluid pressure within the assembly.

According to the invention there is provided a hydraulic apparatus comprising a master cylinder and a slave cylinder, a fluid passageway interconnecting the master and slave cylinders, said master cylinder having a piston therein displaceable axially so that, in use, transfer of hydraulic working fluid between the cylinders takes place through the fluid passageway interconnecting the cylinders, said slave cylinder having a piston therein displaceable axially as a result of said fluid transfer, each piston dividing its cylinder into first and second chambers, and at least one of said cylinders including a piston-like member which is displaceable axially in its cylinder towards the piston under the influence of bias means so as to maintain the hydraulic working fluid in the first chambers of the cylinders under pressure, the piston in said one cylinder being associated with a piston rod passing through said first chamber and extending through said piston-like member.

The rod is preferably arranged to transmit load to or applied by said piston.

Preferably the piston-like member forms an end wall of its cylinder.

The piston-like member may be biased by a resiliently deformable element, e.g. a washer.

The washer may be located between the piston-like member and location means on its cylinder.

It is desirable-to provide a further said piston-like member in the other of the master and slave cylinders which is displaceable axially in said other cylinder towards the piston in that cylinder. In such a case a piston rod of the piston in the other cylinder preferably passes through the first chamber of the other cylinder and extends through the further piston-like member. The rod is preferably used to transmit load to or applied by its piston.

As with the first said cylinder, the further piston-like member may form an end wall of the other cylinder and may be biased in a similar manner to the first said piston-like member.

Additional maintenance of pressure can be achieved by providing a reservoir for working fluid which communicates with said first chamber, the fluid in said reservoir being maintained under pressure by a resilientiy loaded reservoir piston.

Preferably the first chambers of the cylinders are interconnected by conduct to permit fluid flow therebetween and the second chambers are interconnected to permit fluid flow therebetween.

Preferably the apparatus is supplied as a unit prefilled with the working fluid under pressure with the or each piston-like member urged against its bias by said working fluid.

The apparatus preferably comprises a hydraulic selector or shift for an automatic transmission of a motor vehicle.

A hydraulic assembly in accordance with the invention will now be illustrated by way of example with reference to the accompanying drawings in which: Figure 1 is a schematic longitudinal cross section of a master/slave cylinder assembly, Figure 2 is a view of part of the assembly in Fig. 1 showing a piston-like member in an axial position different from that shown in Fig 1, and Figure 3 is a view similar to Fig. 1 including a reservoir of hydraulic fluid.

The master/slave cylinder-assembly comprises a master cylinder 12 divided into right hand and left hand chambers 14, 16 as viewed in the drawing by piston 18. The piston is sealed against the internal wall of the master cylinder by a sealing ring 22. The piston 18 has a connecting rod 24 which extends through a seal 26 in a piston-like end closure 28. A Belleville washer 30 is located between an in-turned rim 20 of a sleeve 21 and the closure 28, the sleeve 21 being screwed to the master cylinder.

A conduit 32 interconnects the right hand chamber 14 of the master cylinder with the right hand chamber 34 of a slave cylinder 36.

The slave cylinder 36 is of similar construction to the master cylinder 12, having a piston 38 provided with a connecting rod 41, a left hand chamber 42 an end closure 44, piston rod seal 46, sleeve 48 screwed to the cylinder 36 and a Belleville washer 49. The piston 38 has a sealing ring 40. The left hand chambers 16, 42 are interconnected by a conduit 50.

The piston rod 24 is provided with a mechanical coupling 51 for connection to a gear shift control lever 52 and the piston rod 41 is connected to a mode selector 53 in a transmission casing, 54.

In use, the assembly is filled with hydraulic fluid to a suitable pressure, the fluid occupying both chambers of the respective cylinders 12, 36. The fluid pressure is such that it places the Belleville washers 30, 49 under compression as in Fig. 1. Movement of the master cylinder piston 18 in direction A will then cause piston 38 to move in the opposite direction, fluid being displaced from chamber 16 to chamber 42 and from chamber 34 to chamber 14. Reverse displacement of fluid occurs when piston 18 is moved in the direction opposite to direction A.

If fluid leaks through seals 26 or 46, pressure in the system will be maintained by the resiliently loaded and closures 28, 44 which will move fractionally in direction A to compensate for the leakage. Fig. 2 illustrates the total available movement M from the Fig. 1 position of the end closure 28 as a result of the resilience of the Belleville washer 30. The Belleville washer 49 will similarly move the end closure 44. Sealing rings 55, 56 are provided on the pistons 18, 38 for sealing against respective cylinders 12, 36.

The maintenance of fluid pressure in the chambers 14, 34 will also serve to inhibit leakage of fluid past the piston seals 22, 40 from the left hand chamber to the right hand chamber of each of the master and slave cylinders.

The Belleville washers 30, 49 may be formed with a plurality of slots (not shown) extending radially from the inner and/or outer periphery of the washer.

Although both the master cylinder 12 and the slave cylinder 36 are shown as having movable end closures 28, 44 respectively, adequate compensation for fluid loss may be possible with only one such end closure. The end closure in the other cylinder would then be fixed.

If additional compensation for loss of fluid is required, an external reservoir may be provided as in Fig. 3. A reservoir 60 has a cylinder 62 in which a piston 63 is axially slidable.

The piston divides the cylinder into a first chamber 64 for containing hydraulic fluid and a second chamber 65 which contains a compression spring 66 arranged to act between a lid 57 of the cylinder 60 and the adjacent end of piston 63. The cylinder is connected to the conduit 32. The spring 66 will be placed under compression when the apparatus is filled with fluid and will move the piston 63 fractionally in direction A to compensate for fluid loss.

Ideally, the apparatus is supplied to the vehicle manufacturer as a pre-filled hydraulic system. The end closures 28, 44 and, where provided, the piston 63 will compensate for any slight fluid loss which may take place during storage in addition to loss which may occur during use.

The bias of each of the washers 30, 49 divided by the area of its associated pistonlike member 28, 44 may be greater than the pressure required to move the mode selector 53.

Claims (12)

1. A hydraulic apparatus comprising a master cylinder and a slave cylinder, a fluid passageway interconnecting the master and slave cylinders, said master cylinder having a piston therein displaceable axially so that, in use, transfer of hydraulic working fluid between the cylinders takes place through the fluid passageway interconnecting the cylinders, said slave cylinder having a piston therein displaceable axially as a result of said fluid transfer, each piston dividing its cylinder into first and second chambers, and at least one of said cylinders including a piston-like member which is displaceable axially in its cylinder towards the piston under the influence of bias means so as to maintain the hydraulic working fluid in the first chambers of the cylinders under pressure, the piston in said one cylinder being associated with a piston rod passing through said first chamber and extending through said piston-like member.

2. A hydraulic apparatus according to Claim 1 in which the piston-like member forms an end wall of its cylinder.

3. A hydraulic apparatus according to Claim 1 or 2 in which the piston-like member is biased by a resiliently deformable washer.

4. A hydraulic apparatus according to Claim 3 in which the washer is located between the piston-like member and location means on its cylinder.

5. A hydraulic apparatus according to any preceding Claim in which a further said pistonlike member is displaceable axially in the other cylinder towards the piston in that cylinder.

6. A hydraulic apparatus according to Claim 5 in which a piston rod of the piston in the other cylinder passes through the first chamber of the other cylinder and extends through the further piston-like member.

7. A hydraulic apparatus according to Claim 5 or 6 in which the further piston-like member forms an end wall of its cylinder.

8. A hydraulic apparatus according to Claim 6 in which the further piston-like member is biased by a resiliently deformable washer.

9. A hydraulic apparatus according to Claim 4 or 8 in which at least one of said resiliently deformable washers is a Belleville washer.

10. A hydraulic apparatus according to any preceding claim in which a reservoir for working fluid is provided and communicates with said first chamber, the fluid in said reservoir being maintained under pressure by a resiliently loaded reservoir piston.

11. A hydraulic apparatus according to any preceding claim supplied as a unit prefilled with the working fluid under pressure and both the or each piston-like member urged against its bias by said working fluid.

12. A hydraulic apparatus constructed and arranged substantially as described herein with reference to the accompanying drawings.