Pressure control valve having an axial supply port

A pressure control valve designed as a slide valve and having an axially situated supply port.

FIELD OF THE INVENTION

The present invention relates to a pressure control valve, in particular for an automatic transmission in a motor vehicle.

BACKGROUND INFORMATION

Hydraulically operated clutches are used for shifting gears in modern automatic transmissions of automobiles. To enable these switching operations to take place smoothly and without being noticeable to the driver, it is necessary to set the hydraulic pressure at the clutches with maximum precision according to predefined pressure ramps. Electromagnetically operated pressure control valves are used for this purpose. These valves may be designed either as seat valves or slide valves. As a rule, both structural designs have three hydraulic ports for inflow, control pressure and return flow. In seat valves, the ports may usually be situated both axially and radially.

A seat valve of this type is described in German Patent Application No. DE 197 33 660. The exemplary embodiments illustrated therein have both radial and axial inflow ports.

To maintain the pressure control function of slide valves, it is necessary for either tank pressure or control pressure to be present at the end faces of the slide or control piston. Therefore, the corresponding ports are usually situated radially. A slide valve of this type is described in German Patent Application No. DE 201 00 950 U1, it being possible to connect the tank port axially in one exemplary embodiment. A slide valve having an axially situated working port, at which the desired control pressure is present, is described in German Patent Application No. DE 198 47 021 B4.

Modern transmission control systems have hydraulic lines of high complexity. Due to the limited installation space, it is often not possible to separate the supply lines in a way that enables these lines to be routed to the pressure control valves in any manner.

SUMMARY OF THE INVENTION

The present invention provides a pressure control valve of the slide design in which the supply port is easily and economically mounted on the end face of the hydraulic part of the valve. Degrees of freedom in integrating the hydraulic system and in situating and mounting the pressure control valve are obtained thereby.

One advantageous embodiment of the present invention provides that a slide sleeve having a valve connecting element forms an annular inflow channel on the end face. This ensures that the inflow pressure is guided radially from the end face of the valve to the control piston.

In addition, it is provided that the slide sleeve has at least one radially situated opening. One of the radial openings is hydraulically connected to the annular inflow channel. Due to the radial openings, the various valve ports are hydraulically connected to the corresponding sections of the control piston, and the pressure control function of the control piston is implemented through simple means.

To ensure that the inflow pressure does not act upon the end face of the control piston and negatively influence the pressure control function thereof, the end face of the slide sleeve is sealed in a pressure-tight manner. An easy-to-manufacture approach is to press a sealing plug onto the end face of the slide sleeve. The sealing plug may be implemented from plastic or as a punched and bent part made of sheet metal. Both variants may be non-detachably and tightly mounted on the slide sleeve with the aid of a simple press connection.

The pressure control function is implemented by the fact that the valve has a control piston which hydraulically connects a working port to the supply port in an open end position and hydraulically separates the working port from a return port. In the non-activated state, this means that when the coil of an electromagnetic actuating device is not energized, its armature moves in the direction of opening with the aid of the helical spring mounted on the magnet and moves the control piston in the direction of an opened end position of the pressure control valve via a push rod. The first section of the control piston thus releases the inflow pressure opening, and the pressure medium flows into an annular chamber which is delimited by the slide sleeve and the control piston. Since the third section of the control piston simultaneously separates the return opening from the annular chamber, the pressure prevailing at the supply port is also present at the working port.

When the coil is energized, the electromagnetic force acts against the restoring force of the spiral spring on the magnet side, which has deflected the control piston in the direction of the end face. The control piston is moved back into the closed end position by the restoring spring mounted on the piston side. In the closed end position, the control piston seals the inflow pressure opening and simultaneously releases the return opening. Because tank pressure is present in the return opening and this tank pressure is lower than the working pressure prevailing in the annular chamber, the pressure medium flows to the return port via the return opening.

The same applies to an electromagnetic actuating device, which is not described in further detail herein and which operates without a spiral spring on the magnet side and whose electromagnet acts in the opposite direction. Through these means, the supply port is closed in the de-energized state and the return opening is closed in the energized state.

In the pressure control valve according to the present invention, the force which acts upon the control piston against the direction of opening depends on the pressure instantaneously prevailing at the control pressure opening. If the pressure drops at the control pressure opening, the force acting upon the control piston against the direction of opening is also reduced, and the control piston is moved in the direction of opening. However, if the pressure prevailing at the control pressure opening increases, the force acting upon the control piston against the direction of opening also increases, whereby it moves against the direction of opening. This self-control function of the control piston is achieved by the fact that the hydraulic surface acting in the direction of opening differs from the hydraulic surface acting against the direction of opening.

This difference between the hydraulic surfaces acting against and in the direction of opening is achieved by the stepped guide bore in the slide sleeve, which has a smaller diameter in the first section of the control piston than it does in the third section of the control piston.

All in all, a pressure control valve is obtained via the present invention, which provides a precise self-control function and simultaneously ensures a simple structural design and correspondingly low manufacturing costs.

It is also beneficial that the control piston has a first control edge which throttles the pressure medium flow which flows from the supply port to the working port when the control piston is in an intermediate position. The control piston also has a second control edge which throttles the pressure medium flow which flows from the working port to the return port when the control piston is in an intermediate position between the open and closed end positions. This makes it possible to implement a continuous pressure control characteristic of the valve.

It is particularly helpful if the present invention includes a control piston which has at least one channel which connects a first compensating volume, which is delimited by an end face of the control piston, in the area of the supply port to a second compensating volume at the opposite end of the control piston. As a result, the same hydraulic pressure, i.e., the tank pressure, is present at the end faces of the control piston. The movements of the control piston cause the hydraulic oil to move back and forth without pressure between the compensating volumes.

In addition, it is provided that the channel be designed as a combination of a longitudinal bore and a transverse bore. This makes the control piston for the pressure control valve according to the present invention easy and economical to manufacture.

An easy-to-manufacture approach provides that the valve connecting element is designed as an injection-molded plastic part. The control sleeve may thus be easily fixed within the valve housing.

DETAILED DESCRIPTION

Among other things, a hydraulic circuit10, to which an unpressurized hydraulic reservoir12and a hydraulic pump14belong, is used to control automatic transmissions as they are used in automobiles, for example. An outlet of hydraulic pump14forms a supply port16, to which a pressure control valve18is connected.

A return flow to a return port20, which leads back to a hydraulic oil reservoir12, leads from pressure control valve18. Furthermore, pressure control valve18is connected to a working port22at which the pressure to be controlled by pressure control valve18is present. In addition, pressure control valve18has an electromagnetic actuating device24.

FIG. 2shows the structure of a pressure control valve18according to the present invention. Pressure control valve18includes a valve connecting element26, which is preferably manufactured from plastic. Valve connecting element26has a concentric recess (without a reference numeral), into which a slide sleeve28is inserted in such a way that it forms an annular inflow channel30together with valve connecting element26. Slide sleeve28has a continuous and stepped guide bore32, which is used to accommodate a control piston34. On the left side inFIG. 2, the end face of slide sleeve28is sealed pressure-tight by a sealing cap36, which may be pressed on or shrunk-fitted, for example.

The opposite side (on the right inFIG. 2) of slide sleeve28is sealed by a bearing bush37. Three openings38,40and42are situated side by side in the axial direction on the circumference of slide sleeve28. The first opening, hereinafter referred to as inflow pressure opening38, in slide sleeve28opens guide bore32in the direction of inflow channel30and thus in the direction of supply port16when control piston34is correspondingly activated.

FIG. 2shows pressure control valve18in the equilibrium position, so that no hydraulic connection exists between inflow channel30and guide bore32. This equilibrium position is an intermediate position between the open and closed end positions.

The second transverse bore in slide sleeve28, which is identified below as control pressure opening40, connects guide bore32to working port22. The third transverse bore, hereinafter referred to as return opening42, establishes a hydraulic connection between guide bore32and return port20.

Control piston34is divided into four adjacent sections44,46,48and50in the axial direction. Outermost left and first section44inFIG. 2has a first diameter D1. Control piston34is guided within guide bore32with the aid of this first diameter D1.

The approximately centered second section46, which adjoins first section44, has a second diameter D2which is smaller than first diameter D1and which is smaller than the diameter of guide bore32in this area. This results in an annular chamber52.

Third section48, which adjoins second section46, has a larger diameter than first section44and is guided sealingly but axially slidable in guide bore32of slide sleeve28. This delimits annular chamber52in the axial direction.

In fourth and final section50, the diameter of control piston34is smaller than that of guide bore32. This results in a second compensating volume58, which is delimited in the axial direction by bearing bush37and push rod72.

Due to this particular form of control piston34, second section46of control piston34and slide sleeve28form an annular chamber52which communicates with working port22via control pressure opening40. The edge of first section44which faces second section46forms a first control edge54whose function is discussed in greater detail below.

The edge of third section48which faces second section46forms a second control edge56. Control piston34has a transverse bore60in the fourth section. A longitudinal bore62, which penetrates control piston34along its entire length, adjoins transverse bore60. As a result, the same pressure prevails in first compensating volume64and in second compensating volume58.

A first spiral spring66, which is supported against control piston34, on the one hand, and against sealing cap36, on the other hand, is located in first compensating volume64, the sealing cap sealing the end face of slide sleeve28.

InFIG. 2, electromagnetic actuating device24is situated on the right side of pressure control valve18. It includes, among other things, an annular coil68and a centrally situated armature70. A push rod72, which is situated coaxially to armature70, transmits the adjusting movement of armature70to control piston34.

First spiral spring66holds control piston34in contact with push rod72. Push rod72is guided sealingly but axially slidable in a through-opening76in bearing bush37, which seals slide sleeve28.

A second spiral spring78is pushed onto piston rod72in a concentric recess80of armature70. Spiral spring78is supported on armature70, on the one hand, and on a coil core82, on the other hand. Coil core82simultaneously forms a cover for a housing84in which electromagnetic actuating device24is situated. A slide bearing88, which accommodates the end of piston rod72facing away from armature70, is introduced into a coaxial bore86in coil core82.

Pressure control valve18operates as follows: When electromagnetic actuating device24pushes control piston34into the open position due to spiral spring78in the de-energized state of coil68(to the left inFIG. 2; not illustrated), hydraulic oil flows under high pressure from supply port16to annular chamber52via inflow pressure opening38and from the annular chamber to working port22via control pressure opening40. Return opening42in this case is largely covered by second control edge56. Return port20is thus largely separated from annular chamber52. As a result, the same pressure thus prevails at both working port22and supply port16.

However, if control piston34is in a rather right-hand position, for example when the coil is energized, inflow pressure opening38is covered by first control edge54, and annular chamber52is thus largely separated from supply port16. Instead, second control edge56now releases return opening42so that working port22communicates with return port20via control pressure opening40, annular chamber52and return opening42. In this way, the pressure prevailing at working port22is reduced via return port20because, in a first approximation, ambient pressure prevails there.

The different intermediate positions of control piston34make it possible to set any pressure in working port22; the pressure cannot be higher than in supply port16and not lower than in return port20.

The position of control piston34results from the equilibrium of forces between the hydraulic forces acting upon control piston34and push rod72and the restoring force of first spiral spring66, on the one hand, and between the force applied to control piston34by electromagnetic actuating device24via push rod72and the force present at armature70, due to second spiral spring78, on the other hand.

To maintain the pressure control function, it is important that the sum of the hydraulic forces applied to the end faces of control piston34is more or less zero in a state of equilibrium, as shown inFIG. 2. This is ensured by the fact that first compensating volume64, which is provided to the left of control piston34inFIG. 2and in which first spiral spring66is situated, communicates with return opening42via longitudinal bore62and transverse bore60as well as with second compensating volume58, which is provided to the right of control piston34inFIG. 2. Thus, the tank pressure present at return port20or in return opening42prevails in both compensating volumes58and64.

Sealing cap36of slide sleeve28ensures that the inflow pressure does not act upon an end face of control piston34.