GB2258905A

GB2258905A - Piston cylinder for use in vehicle power steering mechanism.

Info

Publication number: GB2258905A
Application number: GB9117671A
Authority: GB
Inventors: Barry John Millard
Original assignee: Adwest Engineering Ltd
Current assignee: Adwest Engineering Ltd
Priority date: 1991-08-16
Filing date: 1991-08-16
Publication date: 1993-02-24
Anticipated expiration: 2011-08-16
Also published as: GB9117671D0; GB2258905B

Abstract

A piston cylinder having a single casing wall which has an axial end having a fluid port defining an inlet/outlet 110 into the interior of the cylinder and an associated fluid conduit 115 formed within the casing wall and extending longitudinally thereof to communicate with said port. <IMAGE>

Description

The present invention relates to a fluid driven power steering system for a vehicle.

A typical known power steering system is illustrated in Figure 1. The system 9 includes a piston cylinder 10 housing a piston which drives a rod 12 for causing steerage of road wheels 14. The rod 12 is connected to a rack (not shown) which is in engagement with a pinion (not shown).

The pinion is in driving connection with a steering wheel 21 of the vehicle via a control valve 20.

A hydraulic pump 16 provides pressurised hydraulic fluid which is fed to one or other end of the cylinder 10 via conduit 18, control valve 20 and one or other of the conduits 22,24.

As shown it is conventional for conduits 22,24 to be connected to the upper side of the cylinder 10 via connectors 26,28.

It is well known in the industry that problems exist in providing fluid connectors between the housing block of the control valve and the relevant ends of the piston cylinder.

These problems arise because of the restricted space between the piston cylinder and the underside of the engine or transmission casings of the vehicle.

The inlet/exit ports to the piston cylinder must ideally be in the top part of the cylinder to ensure expulsion of air on filling with hydraulic fluid since air in the system is totally unacceptable because of its adverse effect on the performance of the steering.

Conventional solutions employ minimum port height connections with tight pipe bends in the fluid pipes. Bend radii are naturally limited to the practical or acceptable amount of flattening or distortion in the pipe away from roundness. Another method avoiding pipe bends is to employ "Banjo" connections. Height is still a consideration and additionally this solution is more costly and involves more points of sealing and components and hence increases cost.

A further method to avoid pipe bends is to employ "Elbow" connectors being of similar proportion to the Banjo system but avoiding the difficulty of making satisfactory joints in the Banjo. Brazing of Banjo to pipe is usual but this is undesirable as it negates corrosion protection on the pipes.

Other more costly designs have been employed such as twin dual cylinders where the fluid is conducted through the annulus between the two walls.

In accordance with one aspect of the present invention we provide a piston cylinder having a single casing wall which has a fluid port defining an inlet/outlet into the interior of the cylinder and an associated fluid conduit formed within the casing wall and extending longitudinally thereof to communicate with said port.

The wall of the casing may be provided with a longitudinally extending rib or protrusion within which the conduit is located. The rib or protrusion is preferably integrally formed with the casing wall.

According to another aspect of the present invention we provide a power assisted steering system for a motor vehicle, the system including a rack having a piston connected thereto for assisting movement of the rack, the piston being housed in a piston cylinder as defined above, and a fluid control valve in driving connection with a pinion in engagement with the rack, the control valve being connected to respective conduits in said cylinder for supplying/discharging fluid to the cylinder. Preferably the connections to the conduits are located at one axial end of the cylinder.

The piston cylinder is preferably connected at one axial end to a rack housing and a first expandable bellow mounted at the opposite axial end of the piston cylinder and a second expandable bellow mounted at the axial end of the rack housing remote from the cylinder, the cylinder being provided with a fluid conduit for providing fluid communication between the interior of the first and second bellows.

Various aspects of the present invention are hereinafter described with reference to the accompanying drawings, in which: Figure 2 is a schematic side view of a power steering mechanism according to one embodiment of the present invention; Figure 3 is a perspective view of a piston cylinder casing according to one embodiment of the present invention; Figure 4 is a sectional view taken along line IV-IV in Figure 3.

Referring initially to Figure 2, in accordance with the present invention, pipes 22,24 are shown being connected into one axial end of the piston cylinder 100 and thereby avoids the disadvantages associated with connecting the pipes 22,24 on the upper side of the cylinder 10 as illustrated in Figure 1.

Connection of pipes 22,24 to one end of the cylinder 100 is achieved, as illustrated in Figures 3 and 4 by incorporating fluid conduits 40,41 within the casing wall 101 of the cylinder 100.

Preferably, as illustrated, the casing wall 101 is provided with a longitudinally extending rib or protrusion 102 in which an associated fluid conduit 40,41 is located.

The provision of such ribs or protrusions 102 enables the wall thickness of the remainder of the casing wall 101 to be relatively thin and thereby minimise use of material.

Ports 110 (only one of which is visible in Figure 4) are provided in the inner surface of the cylinder 100 at locations 111,112 respectively which provide fluid communication between the interior of the cylinder and an associated conduit 40 or 41.

The conduits 40,41 each extend from their associated port 110 to one end of the cylinder 100 to define a connection port 115. Each connection port 115 may be internally threaded to receive a conventional pipe connector 116. Thus, in use, the pipe connection does not project above the exterior of the cylinder 100. The cylinder 100 may be manufactured by drawing or extrusion with the conduits 40,41 being simultaneously formed during the drawing/extrusion process. Alternatively the conduits 40,41 may be subsequently formed by for example drilling.

The conduits 40,41 may extend throughout the full length of the cylinder 100 in which case at least one longitudinal end of each conduit would be plugged.

Ports 110 may be formed by drilling from the interior of the cylinder 100 outwardly to communicate with the associated conduit 40,41 or alternatively may be formed by drilling from the exterior of the cylinder 100 inwardly as illustrated in Figures 3 and 4. In this case the outer portion of the resulting bore is closed by a plug 117.

The preferred material from which the cylinder 100 is formed is an aluminium alloy but other materials such as steel or plastics could be used. It will also be appreciated that the cylinder 100 may be formed by casting or moulding techniques as opposed to drawing or extrusion.

Although in the illustrated embodiment only two ribs 102 are shown it will be appreciated that any number may be provided for accommodating conduits extending longitudinally along the cylinder 100.

It is also envisaged that the pipes 22,24 may be dispensed with by mounting the block of the control valve 20 onto the cylinder 100 with its fluid conduits in direct communication with conduits 40,41.

It will be appreciated that in accordance with the present invention damage to pipework is reduced and that wear or corrosion surface treatments can be applied to the aluminium alloy by for example oxidizing or plating. The use of aluminium alloy for this part of a rack and pinion steering is advantageous in that it can show weight savings over the more usual steel tubing and is more compatible with the use of aluminium casings making up the remainder of the rack assembly.

It will also be appreciated that fluid conduits running along the cylinder casing may be used for fluid communication between components located at opposite ends of the cylinder 100. For example, in the example illustrated in Figure 2, an additional conduit and associated rib may be provided with the conduit communicating at one end with the interior of bellows 50.

The opposite end of the conduit would be adapted to communicate with the interior of the rack housing 54 by for example appropriate cross-drilling and plugging. This effectively provides an air passageway between the interior of bellows 51,50.

Claims

1. A piston cylinder having a single casing wall which has an axial end having a fluid port defining an inlet/outiet into the interior of the cylinder and an associated fluid conduit formed within the casing wall and extending longitudinally thereof to communicate with said port.

2. A piston cylinder according to claim 1, wherein the wall of the casing is provided with a longitudinally extending rib or protrusion within which the conduit is located.

3. A piston cylinder according to claim 2, wherein the rib or protrusion is integrally formed with the casing wall.

4. A piston cylinder according to claim 1,2 or 3, wherein the port is internally threaded to receive a pipe connector.

5. A piston cylinder according to any preceding claim, wherein the casing wall is formed by extrusion or drawing.

6. A piston cylinder substantially as herein described with reference to and as illustrated in the accompanying drawings.

7. A power assisted steering mechanism for a motor vehicle, the system including a rack having a piston connected thereto for assisting movement of the rack, the piston being housed in a piston cylinder according to any preceding claim, and a fluid control valve in driving connection with a pinion in engagement with the rack, the control valve being connected to respective conduits in the cylinder for supplying/discharging fluid to the cylinder.

8. A system according to claim 7, wherein the connections to the conduits are located at one axial end of the cylinder.

9. A power assisted steering mechanism substantially as herein described with reference to and as illustrated in the accompanying drawings.

9. A system according to claim 7 or 8, wherein the piston cylinder is connected at one axial end to a rack housing and a first expandable bellow mounted at the opposite axial end of the piston cylinder and a second expandable bellow mounted at the axial end of the rack housing remote from the cylinder, the cylinder being provided with a fluid conduit for providing fluid communication between the interior of the first and second bellows.

AMUIDMENTS TO THE CLAIMS HAVE BEEN FLED AS FOLLOWS CLAIMS 1. A power assisted steering mechanism for a motor vehicle, the mechanism including a rack having a piston connected thereto for assisting movement of the rack, the piston being housed in a piston cylinder, the piston cylinder having a single casing wall which has a fluid port located in an axial end face of the casing wall for providing an inlet/outlet connection into the interior of the cylinder and an associated fluid conduit formed within the casing wall and extending longitudinally thereof to communicate with said port and a fluid control valve in driving connection with a pinion in engagement with the rack, the control valve being connected to said fluid port for supplying/discharging fluid to the cylinder.

2. A mechanism according to claim 1, wherein the wall of the casing is provided with a longitudinally extending rib or protrusion within which the conduit is located.

3. A mechanism according to claim 2, wherein the rib or protrusion is integrally formed with the casing wall.

4. A piston cylinder according to any preceding claim, wherein the casing wall is formed by extrusion or drawing.

5. A mechanism according to any preceding claim wherein the fluid control valve is connected to said fluid port via a fluid conducting pipe.

6. A mechanism according to claim 5, wherein the port is internally threaded to receive a pipe connector.

7. A mechanism according to any of claims 1 to 4 wherein the control valve includes a block having fluid conduits formed therein and is mounted onto the cylinder with its conduits in direct communication with respective fluid ports in the casing wall.

8. A mechanism according to any preceding claim, wherein the piston cylinder is connected at said axial end to a rack housing and a first expandable bellow is mounted at the opposite axial end of the piston cylinder and a second expandable bellow mounted at the axial end of the rack housing remote from the cylinder, the casing wall of the cylinder being provided with a further fluid conduit for providing fluid communication between the interior of the first and second bellows.