Patent Application
20090065722
This application claims priority from German Application Serial No. 10 2007 042 890.3 filed Sep. 8, 2007.
The invention concerns a pressure control valve.
It is generally known from the prior art to utilize wet-running disk shifting elements for torque transmission in automatic transmissions of motor vehicles.
Here torque transmission is effected in a friction-driven manner by pressing on the disk sets of the shifting elements wherein, for this purpose, the required contact pressure on the disk set is generated via a hydraulically operated clutch piston, which is actuated via a pressure control valve (clutch valve). The pressure control valves of the shifting elements are either directly actuated or controlled via pressure limiting valves or precontrol valves connected upstream.
A magnetic force, which is generated in both cases, is proportional to the control current and by way of which the purely hydraulic pressure control valves of the shifting element are shifted. The working pressure of the clutch valves is produced by the equilibrium condition of the force that is proportional to the control current (=actuating force) and the return force (=reaction force) of the pressure control valve.
A closed-end pressure regulator (CE-DR), which features two valve seats arranged in hydraulic half-bridge circuit, wherein a ball seat geometry is used at the inlet side and a flat or ball seat geometry is used on the tank side, is frequently used according to the prior art for control in the case in which the pressure control valve is controlled via a pressure regulator connected upstream or via a pressure limiting valve (precontrol valve) connected upstream.
In an advantageous manner, a closed-end pressure regulator allows minimization of leakage oil flow in the end positions. At the desired minimal pressure, the inlet control edge is closed and the leakage oil flow from the inlet control edge to the tank edge is thus reduced to almost 0 ml/min. This is necessary, because one actuator should ideally be directly associated with each shifting element of an automatic transmission in order to be able to represent each possible shift change.
Without the closed-end function, each precontrol valve would have a maximum leakage between the inlet edge and the tank edge at minimal pressure requirement. With a large quantity of shifting elements to be controlled, the result would thus be a very high oil volume requirement in the hydraulic system of the vehicle's hydraulic pump
A precontrol valve such as this is known from DE 10342892 A1 of the Applicant. A proportional pressure limiting valve with a magnetic part and a valve part is described within the scope of DE 10342892 A1, wherein the valve part is provided with an inlet opening for the inlet volume flow, a first outlet opening for the filling volume flow and a second outlet opening for the tank volume flow and a ball seat, a flat seat provided with an opening, a closing part for controlling the flow rate through the opening of the flat seat and a stream diverter arranged between the ball seat and the flat seat.
WO 98/48332 of the Applicant also discloses a pressure control valve configured as closed-end pressure regulator, having a connection for a pressure line, a connection for a working pressure line and a connection for an outlet line to the ambient pressure and at least two aperture stages with defined and definable flow resistance, of which two aperture stages are variably coupled under mechanical or hydraulic action according to the principle of the hydraulic half bridge. Both variable aperture stages are provided as inlet and outlet apertures of a control pressure chamber and feature a sealing element, wherein the sealing element of the inlet aperture is configured as a ball or calotte or truncated cone or cylinder and/or the sealing element of the outlet aperture is configured as a ball or calotte or truncated cone or cylinder.
The current embodiment of the pressure control valves configured as a closed-end pressure regulator, has the problem that at low oil temperatures the inlet volume flow is greatly reduced due to the viscous behavior of the oil, which in a disadvantageous manner leads to a reduction of the valve dynamic, in particular in precontrolled clutch valves. Compensating for this effect by way of a larger inlet geometry has proven to be disadvantageous, since the leakage volume flow is greatly increased at high temperatures.
It is therefore an object of the present invention to disclose a pressure control valve configured as a closed-end pressure regulator, in which a sufficient inlet volume flow is also ensured at low oil temperatures, without the disadvantage of a greatly increased leakage volume flow at high temperatures.
A pressure control valve configured as a closed-end pressure regulator is accordingly proposed in which the cross-section of the inlet control edge (that is, the valve or ball seat) can be modified depending on the temperature in such a way that the cross-section is opened as widely as possible at low oil temperatures in order to make a large volume flow to the follow-up slide valves possible, while the cross-section of the inlet control edge is reduced at high oil temperatures such that a high valve dynamic of the follow-up slide valve is achieved and the leakage oil flow is not significantly increased.
Within the scope of a particularly advantageous embodiment of the invention, it is proposed that the ball seat be designed from a material whose heat expansion coefficient is considerably greater than the heat expansion coefficient of the push rod and which thus features a disproportionately greater geometric expansion in comparison with the material of the push rod at increasing temperatures. This ensures that the cross-section of the inlet control edge has an ever-smaller cross-section surface at increasing temperature.
The cross-section reduction in a circular cross-section is proportional to the square of the temperature, since the diameter of the cross-section is linearly reduced with the temperature and the surface of the cross-section and thus the flow through the cross-section are related to the square of the cross-sectional diameter.
According to a particularly advantageous further development of the invention, the ball seat is formed by an annular disk, wherein a stable supporting ring that is mounted in a fixed manner in a housing is provided on the outer diameter of the disk such that the thermal expansion of the annular disk is guided inward as viewed from the radial direction.
The supporting ring is preferably made of a material that has approximately the same heat expansion coefficient as the material of the push rod, whereby the cross-section of the inlet control edge can be determined in an advantageous way by selection of the material for the annular disk that forms the ball seat.
According to the invention, the annular disk that forms the ball seat can be composed of a plastic material which features non-linear heat expansion behavior above the glass transition point with a disproportionate reduction of the cross-section of the inlet control edge above the glass transition point of the plastic can be achieved in this way by utilizing a polyphenylene sulfide (PPS plastic); a typical value being around 80° C.
According to another embodiment of the invention, a material having a negative heat expansion coefficient, such as a GFK material (fiberglass-reinforced plastic) can be used for the ball seat as an alternative to a material having a large heat expansion coefficient for the ball seat. When the temperature increases, the cross-section of the inlet control edge is reduced by way of an annular disk of such a material, which forms the ball seat and is installed without a protective ring.
This embodiment has the additional advantage that the annular disk that forms the ball seat can subsequently be mounted or clipped on as an insert in the pressure control handle, which significantly simplifies the production process.
The known pressure control valves configured as closed-end pressure regulators must allow a high dynamic at the follow-up slide valve, while the leakage must be as low as possible.
The transition from the inlet seat to the tank seat occurs very abruptly so that the leakage volume flow of the pressure regulator increases abruptly without achieving a substantial pressure increase. This is necessary in order to keep the disturbing influences in the reducing pressure as far away as possible from the working pressure, but leads to the disadvantage that a high leakage oil volume is produced in the low pressure range of the pressure regulator, while a high volume flow requirement of the transmission is present at the same time in this pressure range for the purpose of filling the clutch.
The geometric configuration of the ball seat, which is actuated by way of a push rod, essentially determines the maximum leakage or the maximum volume flow of the pressure regulator while, according to the prior art, the cross-section of the inflow edge is reduced by way of the push rod, which has a cylindrical geometry that remains essentially the same when viewed from the axial direction.
When a high pressure and volume flow requirement occurs, the push rod of the pressure regulator is displaced to completely close the tank edge, wherein the maximum volume flow is required in this situation in order to bring the follow-up, slide valve into its control position. When the control position is reached, there is very little or no volume flow requirement at the pressure regulator with reference to the working pressure so that the inlet volume flow at the inlet control edge can be reduced.
According to a further development of the invention, the push rod is consequently configured at its end facing the ball seat such that the opening of cross-section of the inlet edge can be modified depending on the axial position of the push rod, in such a way that the cross-section is reduced when the target pressure is low in order to reduce the inlet volume flow, while the total cross-section of the inlet edge is available when the target pressure is high in order to satisfy the high volume flow requirements of the follow-up, slide valve and to be able to compensate for a high leakage in the working pressure.
Preferably the push rod has a geometric expansion in the area of its end facing the ball seat, which results in a position-dependent, cross-sectional constriction, wherein the pressure/flow/flowthrough behavior of the pressure regulator is determined by the axial position and contour of the geometric expansion. Here the geometric expansion can have the shape of a truncated cone that tapers in the direction of the ball seat or can have a cylindrical, concave or convex shape; a double cone shape is likewise possible.
With this configuration of the push rod, the transition of the inlet control edge to the tank control edge, which is abrupt without the geometric expansion, can be rendered more gentle, whereby a startup jump in the pressure control characteristic is prevented. Further, when the volume flow requirement is low, laminar flow can be converted into turbulent flow in this way, which facilitates the passage of the oil at low temperatures.
As an alternative or in addition to the configuration of the push rod, the ball seat can be designed in such a way that its diameter on the side facing the ball is smaller than its diameter on the side that faces away from the ball. The sharpened shape of the ball seat achieves the effect that laminar flow is converted to turbulent flow, which facilitates the passage of the oil at low temperatures.
The invention will now be described, by way of example with reference to the accompanying drawings in which:
The pressure control valve 1 that serves as a precontrol valve has an electromagnet 2, which customarily has a magnetic core, a magnetic coil 3, and an armature 4 that can be displaced toward the left against the Force of a spring, as well as an anchor rod 5, displaceable by the armature 4, for biasing the closing part 6, against a first valve seat preferably designed as a valve seat 7, and can close a through opening 8 incorporated in the valve seat 7. A push rod 9 is also provided, which is connected to the anchor rod 5 or can be designed as a single piece with the anchor rod 5, which can move a sealing element 10 designed as a ball out of a second valve seat designed as a ball seat 11. An inlet control edge is identified with reference numeral 12 and a tank edge is identified with reference numeral 13, while a stream diverter is identified with reference numeral 19.
The valve shown in
In order to avoid this disadvantage, it is proposed according to the invention that the ball seat 11 be made from a material whose heat expansion coefficient is considerably greater than the heat expansion coefficient of the push rod 9, and thus features a disproportionately greater geometric expansion in comparison with the material of the push rod at increasing temperature. The concept, according to the invention, ensures that the cross-section of the inlet control edge 12 has an ever-smaller, cross-section surface at increasing temperature.
A valve designed in this way is the object of
In the example shown in
As can be seen in
The object of
Exemplary pressure/volume flow characteristics of a pressure control valve 1, according to the prior art, and of a pressure control valve 1, designed according to the exemplary embodiment of
As can be seen in
It can also be seen in
The position of the push rod 9, depending on the pressure regulator flow and a pressure regulator force Fm in a conventional valve designed as a closed-end pressure regulator and in a valve according to
Here, lines H are lines of force with constant flow. In
It goes without saying that any constructive design, in particular any spatial arrangement of the components of the pressure control valve according to the invention, as well as in combination with another, and insofar as it is technically practical, falls under the scope of protection of the claims, without influencing the function of the pressure control valve as disclosed in the claims, even if these designs are not explicitly represented in the Figures or in the description.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 042 890.3 | Sep 2007 | DE | national |
