GB2348857A - A vent for a power-assisted rack-and-pinion steering system - Google Patents

Abstract

A power-assisted steering system for motor vehicles having a steering rack which is disposed in a longitudinally displaceable manner in a steering gear housing and having at least one gaiter connected to the steering gear housing and to an adjacent track rod, wherein the gaiter is manufactured at least partially from a gas-permeable, waterrepellent material.

Description

Vent for a power-assisted steering system The present invention relates to a power-assisted steering system for motor vehicles, in particular in the form of a rack-and-pinion steering system.

Power-assisted steering systems have a steering rack which is supported so as to be longitudinally displaceable in a steering gear housing and is provided at either end with a track rod tap. The track rods are generally connected by a screw thread and a ball joint to the steering rack. The steering rack, the screw thread and the ball joint are protected from dirt by means of bellows which are fastened by one end to the track rod and by the other end to the steering gear housing. In the course of a steering movement the volume enclosed by the bellows varies with the result that the air quantity contained there has to be compensated for. For this purpose, in known power-assisted steering systems a line is provided between the two air volumes arising on the left and right of the rack-andpinion steering system thereby enabling compensation between the two volumes on either side of the rack-andpinion steering system. The line is realized either by means of a longitudinal bore in the steering rack optionally combined with transverse bores or by means of a separate rigid line on the outside of the steering gear housing or bellows.

The constructional outlay for provision of such a connection is in practice relatively high. On the other hand, in the absence of such a connection some other way of removing the displaced air volume and/or supplying the necessary air volume is necessary.

The present invention seeks to provide a power-assisted steering system for motor vehicles in which the volumes enclosed by the bellows may be separately varied and/or compensated.

Thus viewed from one aspect the present invention provides a power-assisted steering system for motor vehicles having a steering rack which is disposed in a longitudinally displaceable manner in a steering gear housing and having track rods associated with the steering rack and having at least one gaiter connected to the steering gear housing and to the adjacent track rod, wherein the gaiter is manufactured at least partially from a gas-permeable, water-repellent material.

Preferably the material is a diaphragm which is diffusively permeable to gases.

Preferably the material is a foil provided with pores, preferably a plastic foil.

Preferably the material forms a substantially rotationally symmetric region of the bellows.

Preferably the material forms a region of the bellows of high elastic deformability.

Preferably the material is a hydrophobically coated net, fleece or woven material.

Viewed from a further aspect the present invention provides a power-assisted steering system for motor vehicles having a steering gear housing, a steering rack longitudinally displaceable in the steering gear housing, track rods associated with the steering rack and substantially gasproof bellows provided between the steering gear housing and the track rods, wherein the steering gear housing carries at least one connection which communicates with a space surrounded by the bellows, wherein the or each connection is sealed by a gas-permeable and liquid-proof diaphragm.

Preferably the diaphragm is disposed inside a screw cap and is screwable onto the connection.

Preferably the diaphragm is held in a substantially dimensionally stable ring.

Preferably the material is a hydrophobically coated net, fleece or woven material.

Embodiments of the present invention are described below in a non-limitative sense with reference to the drawings. The drawings show: Figure 1: bellows having a hydrophobic, gas-permeable diaphragm; Figure 2: a steering gear housing for a power-assisted steering system having a vent sealed by a diaphragm, and Figure 3: bellows having an associated flexible expansion chamber.

Figure 1 illustrates bellows 1 (which are known per se) for a power-assisted steering system. Such bellows are also known as"steering gaiters". The bellows 1 comprise a large-diameter connection 2 directed towards the steering gear housing as well as a small-diameter connection 3 directed towards the track rod. Both connections 2,3 are usually fastened by clamps to the respective component. In the case of steering gaiters, such bellows are not provided with pressure compensation openings.

According to Figure 1, in the region of the connection 3 the bellows carry an annular collar 4 made of rubber which is an integral part of the connection 3. A corresponding collar 5 of a larger diameter is likewise provided on the bellows, only outwardly offset from the collar 4 in the direction of the connection 2. The collar 5 is likewise integrally formed from the material used to manufacture the remainder of the bellows.

Extending between the two annular collars 4 and 5 is a diaphragm 6 fashioned in the shape of the envelope of a cone, wherein one open end of a smaller diameter is incorporated by its end face into the collar 4 and the other open end of a larger diameter is incorporated by its annular end face into the collar 5. During manufacture of the bellows, the material of the bellows is advantageously injection-moulded around the end faces or edges of the diaphragm 6.

A power-assisted steering system of a design generally known per se is shown in Figure 2. A steering gear housing 10 surrounds (in addition to other components not shown in detail) a steering rack 11. During operation, the open end 12 of the housing adjacent to the steering rack 11 is surrounded and sealed by the end 2 of the bellows 1. The consequently enclosed interior of the power-assisted steering system is aerated and de-aerated via a connection i3. In figure 2, a second connection 14 is provided for the right side of the rack-and-pinion steering system where bellows 1 are likewise disposed. The connections 13,14 in : : nown designs of power-assisted steering systems are connected to one another by a connection line screwed on there, with the result that a compensation of the air volumes on the left and right side of the power-assisted steering system is effected by means of said connection line. In the embodiment according to Figure 2, the connection 13 (similar to the connection 14) is provided with a screw cap 16 which is shown on an enlarged scale and has an opening 17 open towards the atmosphere. Inserted in the opening is a hydrophobic, gas-permeable diaphragm 18, the material of which may correspond to that of the diaphragm 6 according to Figure 1. The diaphragm 18 is secured in the screw cap 16 by means of a moulded plastic part 19 and pressed into its bearing surface by the axial force arising when the screw cap is screwed onto the connection 13, thereby rendering it both liquid-proof and loadable within specific limits.

A corresponding screw cap is screwed onto the connection 14 so that the air volume communicating therewith is also sealed in a liquid-and dirt-proof manner but is to a certain extent open to allow gases to pass through to the atmosphere.

Figure 3 shows a further embodiment of bellows 1 with steering-side connection 2 and track rod-side connection 3.

In said embodiment, an approximately round region 20 has been cut out of the bellows 1 and provided with a flexible expansion element 21. In the manner shown in Figure 3, this may comprise a bellows region having larger folds or greater lift as well as more closely adjacent folds. They may be formed from a different material to the actual bellows 1. In particular, it may also be the case that the region 21 is made of a similar gas-permeable and hydrophobic material to the diaphragms 6 and 18. In this case, both by virtue of its high expandability and by virtue of its relatively large surface the region 21 may allow gases to pass out of and into the interior of the bellows.

In practice, the embodiments described above operate as follows: When the steering rack travels into the steering gear housing, the bellows 1 according to Figure are contracted so that the air quantity surrounded by the bellows has less available space and an overpressure results. The overpressure may escape through the diaphragm 6 which is hydrophobic and gas-permeable. The rate of pressure relief is dependent upon the air volume, the pressure difference, the area of the diaphragm 6 and the mean pore size. When the steering rack travels out, the volume within the bellows 1 increases while the air quantity initially remains constant. The resulting partial vacuum (given previous escape of the enclosed air quantity) gives rise to a gas transfer from the atmosphere through the diaphragm 6 into the interior and hence to the necessary pressure compensation. The other air volume of the rack-and-pinion steering system undergoes the reverse process.

In the rack-and-pinion steering system according to Figure 2, the air volume in the region of the connection 12 is optionally also sealed off by conventional bellows which are incapable of air exchange with the atmosphere. In this case, a movement of the steering rack to the right gives rise to an overpressure on the left side which escapes to the atmosphere through the connection 13 and the diaphragm 18 situated therein. The diaphragm 18 is in this case likewise capable of repelling water, dirt and other undesirable impurities but not of impeding the gas transfer to any undesirable extent. Given the described movement of the steering rack to the right, the right air volume in Figure 2 is increased so that the required gas quantity is sucked in from the atmosphere through the connection 14 and a corresponding diaphragm 18. A locking of the steering the opposite direction by a movement of the steering rack 11 to the left leads to a reversal of the process with the result that the air to be displaced escapes through the connection 14, while a corresponding air volume is sucked in through the connection 13.

The bellows according to Figure 3 enable operation similar to the bellows according to Figure 1. However besides the possibility of diffusive gas transfer through the pores of the diaphragm 6, there is also the possibility of mechanical pressure compensation through enlargement of the region 21 in an inward or outward direction. In this case, for the purpose of pressure compensation a kind of expansion container is envisaged. When said region 21 is formed by a gas-permeable, hydrophobic diaphragm, the pressure building up there may ultimately escape or gas may be sucked in from the atmosphere. Such an application is preferred when rapid steering movements are anticipated and it is impossible for the volume flows (which are required within a very short time) to be transferred merely by diffusion through the diaphragms. In this case, the fastreacting, thin-walled expansion element 21 is preferred as a purely mechanical buffer.

The present invention may also be realized in other ways not described in the embodiments. Thus for example it is possible that the entire bellows 1 be manufactured from a gas-permeable, hydrophobic diaphragm. This has the advantage that the available diffusion surface is very large and enables a reliable gas transfer even in the event of a low overpressure. Suitable diaphragms are available (eg under the brand name GoretexTrom the company W L Gore & Associates, Putzbrunn, Germany). It is also possible to use other diaphragms, preferably based on halogenated hydrocarbons. Other materials may also be considered, provided that the required properties (gas permeability, water-repellent behaviour and imperviousness to liquids) are guaranteed.

Particularly in the embodiment according to Figure 2, it is possible to protide as a diaphragm (instead of the foil), a net, woven cloth or the like having a low mesh size and a hydrophobic surface or surface coating.

In power-assisted steering systems, the embodiments of the present invention described above make it possible to dispense with conventional longitudinal bores through the steering rack or a connection line provided outside the steering system for pressure compensation between the two volumes at either end.

Claims (1)

1. Claims . A power-assisted steering system for motor vehicles having a steering rack which is disposed in a longitudinally displaceable manner in a steering gear housing and having track rods associated with the steering rack and having at least one gaiter connected to the steering gear housing and to the adjacent track rod, wherein the gaiter is manufactured at least partially from a gas-permeable, water-repellent material.

   5. A power-assisted steering system as claimed in claim 1 wherein the material is a diaphragm which is diffusively permeable by gases.

   3. A power-assisted steering system as claimed in any one of the preceding claims wherein the material is a foil provided with pores, preferably a plastic foil.

   A A power-assisted steering system as claimed in any one of the preceding claims wherein the material forms a substantially rotationally symmetric region of the bellows.

   A A power-assisted steering system as claimed in any one of the preceding claims wherein the material forms a region of the bellows of high elastic deformability.

   . A power-assisted steering system for motor vehicles having a steering gear housing, a steering rack longitudinally displaceable in the steering gear housing, track rods associated with the steering rack, and substantially gas-proof bellows provided between the steering gear housing and the track rods, wherein the steering gear housing carries at least one connection which communicates with a space surrounded by the bellows, wherein the or each connection is sealed by a gas-permeable and liquid-proof diaphragm.

   7. A power-assisted steering system as claimed in claim 6 wherein the diaphragm is disposed inside a screw cap and is screwable onto the connection.

   8. A power-assisted steering system as claimed in either of claims 6 or 7 wherein the diaphragm is held in a substantially dimensionally stable ring.

   9. A power-assisted steering system as claimed in any of the preceding claims wherein the material is a hydrophobically coated net, fleece or woven material.

   10. A power assisted steering system as hereinbefore defined with reference to the accompanying Figures