Hydraulic linear drive of a transmission actuator

A hydraulic linear drive for a hydraulic vehicle transmission actuator has a piston/cylinder unit in which an adjusting piston is arranged so it is longitudinally displaceable in a cylinder housing and subdivides the cylinder space into at least two pressure spaces which can receive hydraulic oil through control lines. The optional pressure action on the two pressure spaces is controllable by a shift valve. A connecting line is provided between the two control lines leading to the pressure spaces and a control valve is provided for optionally releasing or blocking the connecting line to further control the pressure force acting on the piston.

BACKGROUND AND SUMMARY OF THE INVENTION

This application claims the priority of German Application No. 10 2004 037 104.0 filed Jul. 30, 2004, the disclosure of which is expressly incorporated by reference herein.

This invention relates to a hydraulic linear drive. Preferred embodiments of the invention relate to a hydraulic linear drive for a transmission actuator comprising a piston/cylinder unit in which an adjusting piston is arranged to be longitudinally displaceable in a cylinder housing and to subdivide the cylinder housing space into at least two pressure spaces which can receive hydraulic oil through control lines, and a shift valve operable to control optional pressure action on the two pressure spaces.

Hydraulic linear drives are used in automatic transmissions, for example, for synchronizing the gears (see, for example, Johannes Loomann, Zahnradgetriebe [Gear Wheels], 2ndedition, pages 156 ff.).

With the generic hydraulic linear drives, the double piston bordered by two pressure spaces is displaced accordingly to the left or right by a pressure action, as described and explained in DE 198 34 955 A1 corresponding to U.S. Pat. No. 6,295,810, for example, the rate of adjustment of the hydraulic piston is adjustable through additional control valves integrated into the two control lines.

An object of this invention is to provide a circuit arrangement with which the adjusting force and/or adjusting speed of the double-acting hydraulic cylinder can be varied easily with only a few hydraulic components. This object is achieved according to certain preferred embodiments of the invention by providing a hydraulic linear drive for a transmission actuator comprising a piston/cylinder unit in which an adjusting piston is arranged to be longitudinally displaceable in a cylinder housing and to subdivide the cylinder housing space into at least two pressure spaces which can receive hydraulic oil through control lines, and a shift valve operable to control optional pressure action on the two pressure spaces, wherein a connecting line is provided between two control lines leading to the pressure spaces with a control valve for optionally releasing or blocking the connecting line.

Due to the fact that a connecting line in which a control valve optionally either releases or blocks the connecting line is provided between the two control lines leading to the pressure spaces, the volume flow to the pressure space acted upon by the pressure is controllable so that the adjusting rate and/or adjusting force of the hydraulic piston can be influenced in this way. For example, when using the linear drive as a hydraulic transmission actuator, a reduction in the synchronous force is possible. If comfortable shifting is desired, then the gear may be engaged with a low adjusting force whereas if a sporty shifting style is desired, the transmission actuator can be operated with a high synchronous force.

Other advantageous embodiments and refinements of the hydraulic linear drive are achieved through the features described herein and in the claims.

The control valve which is integrated into the connecting line has three shift positions in a first advantageous embodiment; in a first shift position, the connecting line is closed; in a second shift position, the connecting line is opened with a small opening cross section and in a third shift position it is opened with a larger opening cross section. In addition to the three discrete shift positions described above, it is also contemplated for the control valve to have an adjustable valve element which is continuously adjustable between a completely open shift position and a completely closed shift position.

In a further advantageous embodiment, the control valve has a first closed shift position and a second open shift position, whereby the control valve can be operated in cycles between these two shift positions. In this way it is also possible to vary the volume flow to the pressure chamber which is acted upon by hydraulic oil and thus to vary the adjusting force acting on the hydraulic piston.

Two exemplary embodiments of this invention are depicted in the drawing and described in greater detail below.

DETAILED DESCRIPTION OF THE DRAWINGS

The hydraulic linear drive depicted inFIG. 1can be used, for example as a hydraulic transmission actuator for an automatic transmission, and includes a cylinder housing2in which a double acting adjusting piston4is accommodated so that it is longitudinally displaceable, and having two piston rods4aand4bleading out of the cylinder housing2to the right and left. The adjusting piston4subdivides the cylinder space into two pressure spaces6aand6b, each being connected to a hydraulic control line8and10. The two control lines8and10are connected to two outputs of a 4/3 shifting valve12having two other connections at the input end connected to an oil tank14and a pressure source16, e.g., in the form of an oil pump.

Between the two control lines8and10leading to the pressure spaces6aand6bthere is a connecting line20in which a control valve22optionally releases or blocks the connecting line20. The control valve22has three shift positions, with the connecting line20being closed in a first shift position22a, while in a second shift position22bthe connecting line20to the pressure space6aand/or6bis throttled with a small opening cross section and in a third shift position22cit is throttled with a larger opening cross section. In addition to the three discrete shift positions shown, it is also contemplated for the control valve22to have a valve element that continuously monitors an opening between “completely open” and “completely closed” according to the other preferred embodiments of the invention.

The adjustment of the adjusting piston4and/or the choice of the adjusting force for the adjusting piston4is accomplished in the following manner. For example, if the pressure space6areceives hydraulic oil through the control line8via the 4/3 shifting valve12in its left shift position, then the pressure in the pressure space6acan be varied accordingly via the control valve22by supplying some of the oil volume flow back to the oil tank14through the connecting line20and through the control line10. The quantity of oil flowing back through the connecting line10is optionally adjustable via the control valve22.

The exemplary embodiment depicted inFIG. 2differs only in the design of the control valve22′, which has only two shift positions—a first closed shift position22′aand a second opened shift position22′b. Through cycled operation of this control valve22′ the function described previously for controlling the adjusting rate and/or adjusting force of the adjusting piston4can also be implemented.