Machine element or mechanism – Control lever and linkage systems – Multiple controlled elements
Reexamination Certificate
2001-06-08
2004-07-27
Joyce, William C. (Department: 3682)
Machine element or mechanism
Control lever and linkage systems
Multiple controlled elements
C074S473360, C074S60600R, C092S248000
Reexamination Certificate
active
06766710
ABSTRACT:
DESCRIPTION OF THE PRIOR ART
The present invention relates to a hydraulic control device for operating a sliding selector shaft. In particular, the invention concerns a hydraulic control device for operating a sliding selector shaft of a gearbox for motor vehicles.
According to prior art, hydraulic control devices for motor vehicle gearboxes are known which have a control cylinder which serves to operate and position a selector fork attached to a sliding selector shaft of the gearbox for a gear shift. Traditionally, these control cylinders have a metal cylinder housing, which is bolted to the gearbox housing, today usually made from a light metal alloy, via a flange. At least one metal piston is disposed in the cylinder bore of the cylinder housing so that it can move axially and is actively connected to the sliding selector shaft to displace it when the control cylinder is supplied with hydraulic fluid.
In order to simplify this design, DE-A-34 10 802 suggests a control device for change gears of commercial vehicles where the ends of a sliding selector shaft which, for reasons of mechanical strength, is metal, and which carries a shift fork, are mounted in two guides in the form of a pressure medium cylinder, which can form part of the gearbox housing. In this case, the two ends of the sliding selector shaft serve as piston surfaces of equal size via which the sliding selector shaft can be exposed to the pressure medium in order to displace the sliding selector shaft, i.e. with this prior art, the sliding selector shaft itself is designed as a piston whose surfaces of equal size can be exposed to a pressure medium from opposite sides. One disadvantage of this prior construction is that the guides formed in opposite walls of the gearbox housing have to align with each other exactly, which involves a complicated manufacturing process, so that the singe piece sliding selector shaft in the form of a piston cannot jam in the guides when it makes its longitudinal movement.
In addition, bearing and guide systems for supporting the longitudinal movement of sliding selector shafts for vehicle gearboxes are known (Looman, Johannes: Toothed Gearing: Basic Principles, Designs, Applications in Vehicles; 3rd edition; Springer-Verlag 1996; Page 154, FIG. 6-10), which have bearing units disposed on both sides of the selector shaft and fork. These bearing units are two-part units and consist of a thin-walled sleeve with mounting trough and also an inside race sleeve with ball. The first sleeve, drawn from steel strip and case hardened, is used to line a corresponding bore in a wall of the gearbox housing, whereas the resilient internal race sleeve is allocated to the end of the selector shaft and fork. With a radial, essentially play-free guide, the bearing units do bring about a slight axial displaceability of the selector shaft and fork, but this requires considerable expense in terms of the fixture used.
Finally, the generic DE-A-197 25 226 discloses a piston-cylinder arrangement for the selector shaft and fork of a gearbox where pistons, which can consist of plastic, are disposed on the right and left end of the selector shaft and fork. Each piston is inserted into a cylinder pot which has an outside threaded section. The outside threaded section of the cylinder pot is screwed into an inside threaded section of a through or blind hole of the gearbox or clutch housing wall and has an element for damping the piston stop on the bottom. With this prior construction, the piston stop can be adjusted by turning the cylinder pot in the threaded hole of the gearbox or coupling housing wall. However, the design of the threaded sections demands in particular considerable production expense which increases the manufacturing in an undesirable way for the mass production of gearboxes for motor vehicles.
SUMMARY OF THE INVENTION
An object of the invention is to create a simpler and more compact hydraulic control device for operating a sliding selector shaft compared with prior art.
According to the present invention, there is provided a hydraulic control device for operating a sliding selector shaft, in particular of a gearbox for motor vehicles, with a bore made in a wall of a gearbox housing to accommodate a plastic piston actively connected to the sliding selector shaft, which delimits a pressure chamber and which, under hydraulic pressure, radially guides and axially displaces the sliding selector shaft, wherein the piston has a body and a plastic guide section via which the piston is guided directly on the bore, the bore being made as a non-reinforced cylinder bore in the wall of the gearbox and wherein the gearbox is made of a light metal alloy.
Consequently, the piston is used advantageously both for the displacement and for the defined guiding or bearing of the sliding selector shaft without additional expensive bearing
parts, like race sleeves with ball rings or similar being necessary. What is more, a space-consuming separate cylinder housing is no longer necessary, because the cylinder bore guiding the piston is made directly in a wall of a gearbox consisting of a light metal alloy, in particular an aluminum or magnesium alloy. Finally, expensive linings of the cylinder bore, possibly using steel sleeves or similar, can be omitted, because surprisingly, it has been found that under the given conditions, namely hydraulic system pressures of between 20 and 40 bar and ambient temperatures of more than 120° C. in the oil mist in some instances, the piston pair with guide section in plastic and cylinder bore in light metal alloy, with good wear behavior and also an adequate self-lubricating and venting property, guarantees the necessary guide properties. As a result, not inconsiderable space, weight and cost savings can be achieved with the embodiment of the control device according to the invention compared with traditional control device designs, which allows the use of such control devices in volume series.
The guide section of the piston can be made as one piece with the body in an advantageous manner from the manufacturing point of view. However, it is also possible that the guide section of the piston is formed by a guide ring disposed on a guide seat of the body.
The guide ring of the piston can be attached positively to the guide seat in an advantageously simple manner, i.e. without additional fastening means such as adhesive or similar. To do this, the piston can be provided with a collar formed on the piston body and at least one projection projecting slightly from the body in the radial direction, the guide ring being disposed between the collar and the projection on the guide seat of the body. To fit the sleeve shaped guide ring, this has to be pushed onto the body in a simple manner from the side of the body facing away from the collar and in the direction of the collar, with a slight partial expansion at the projection. A further positive connection can be made between the guide ring and the body which is favourable from the manufacturing point of view. According to this, the guide seat of the body is provided with a profile, possibly several radial grooves disposed next to each other, onto which the guide ring is rolled, the guide ring, in the form of an annular disc initially being transformed into a sleeve, the inside perimeter surface of which more or less presses into the profiling of the body.
If the guide section of the piston is integral with the body, fiber-reinforced polyphthalamide (PPA) or polyphenyl sulphide (PPS) have proved advantageous as a material for the body of the piston, particularly from the point of view of good abrasion resistance. If the guide section of the piston is formed by a guide ring disposed on the guide seat of the body, the body of the piston should preferably consist of long fiber-reinforced polyamide (PA) in a cost-effective manner. With reference to the good guide properties and good wear behavior, it is advantageous if polyphthalamide (PPA) or polyphenyl sulphide (PPS) is used as the material for the guide ring.
In the case of the piston embod
Kestler Günter
Reul Alexander
Stössel Roland
FTE automotive GmbH
Joyce William C.
McAndrews Held & Malloy Ltd.
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