Check valve assembly

Details Check valve assembly Check valve assembly

1999-05-19

2001-05-01

Michalsky, Gerald A. (Department: 3753)

Fluid handling

Systems

Supply and exhaust

C091S447000, C091S455000, C137S596160, C137S596200, C137S625680

Reexamination Certificate

active

06223773

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a check valve assembly and a valve assembly containing a check valve assembly.
In mobile hydraulics, such valve assemblies are i.a. used for controlling double-action pressure cylinders, such as employed, e.g., as front power lifts or rear power lifts of farming tractors. By means of these power lifters it is possible to operate various peripheral tools such as, e.g., cutter bars, balers, ploughs, cultivators, rollers etc.
Under certain operating conditions, a situation may arise in which a load must be sustained in the lifted condition, where it is desired for this condition to be maintained even when the hydraulic supply is deactivated. Thus, for example, a cutter bar must be immobilised in the lifted condition while the farming tractor travels to the meadow to be mown or while it is parked in the farmyard.
Customarily the power lifters are controlled by means of proportional valves possessing a Zero position wherein the work conduits communicating with the power lifters and a pump conduit are shut off. Such proportional valves are, however, generally designed as sliding valves, so that the hydraulic fluid cannot be shut off leak-free in the work conduits. Consequently, piloted or releasable check valves are provided in the work conduits, whereby the hydraulic fluid may be confined leak-free between the user and the check valve. By releasing the check valve, a return flow of the hydraulic fluid to the proportional valve is enabled.
DE 27 35 559 C2 discloses a valve assembly wherein a main poppet may be controlled open for release with the aid of a topping piston. The main piston is designed with a pilot hole which is closed by a closing member. The latter may be taken into its opened position by controlling the topping piston through the intermediary of a tappet, so that the spring side of the main poppet is de-pressurised and the main poppet is controlled open by the load pressure applied to its differential surfaces. At the same time, the topping piston controls open a tank port, so that the hydraulic fluid may flow from the user past the raised main poppet to the tank T without requiring a return connection to a directional control valve arranged upstream of the check valve assembly. By the known combination of directional control valve and check valve assembly, merely a single-action lifting cylinder may be connected, the cylinder chamber of which may optionally be connected through the control valve to a pump or through the topping piston to the tank.
With the closing member in the raised condition, the main poppet is controlled open instantaneously due to its area difference, so that the hydraulic fluid is de-pressurised toward the tank comparatively rapidly, without a possibility of influencing the velocity of return flow.
In DE-44 36 548 A1 a valve assembly for controlling double-action lifting cylinders is disclosed, wherein a check valve assembly is arranged in every work conduit. The valve assembly in turn contains a main poppet designed with an area difference (i.e., the valve seat diameter is smaller than the effective external diameter of the main poppet), which may be controlled open by means of a topping piston. Due to this valve assembly it is possible to control a double action user, however, as the main poppet is again designed with an area difference, the main poppet immediately following rising from its valve seat is instantaneously set to its open position, so that a maximum cross section of flow is provided at once. In this known valve assembly, too, it is not possible to influence the return flow.
SUMMARY OF THE INVENTION
The invention is based on the object of furnishing a check valve assembly and a valve assembly including a like check valve assembly, whereby the return flow of the hydraulic fluid from the user may be controlled at minimum expense in terms of circuit technology.
This object is attained by a check valve assembly containing a main poppet biased against a valve seat, which may be raised from said valve seat by a topping piston in which the diameter of the valve seat is about equal to the diameter of the main poppet on the seat side. In the check valve assembly, the main poppet is designed to include a pilot hole and a pilot hole closing body, which may be moved into its opening position by the topping piston. The present invention is also directed to a valve assembly containing such a check valve.
By the measure of designing the main poppet without an area difference and determining the opening process through abutment of the topping piston, abrupt opening of the main poppet may be prevented. The opening stroke of the main poppet may then be influenced through suitable control of the topping piston, providing the possibility of controlling the volumetric flow of the returning hydraulic fluid (drain control).
The main poppet is generally biased against its valve seat by a spring. In the case of one embodiment of the invention, this spring acts as a check valve spring on the one hand to enable flow to the user, and as a control spring on the other hand in order to control return flow from the user to the tank in the released condition of the check valve. As a check valve spring, this spring should have a lower spring constant and a comparatively weak design in order to avoid high pressure losses by way of the check valve. As a control spring, in contrast, this spring should have a steeper characteristic curve in order to present good response characteristics in running control. As a rule, a compromise is realised to the effect that the spring is designed to have a comparatively high spring constant while accepting the higher pressure losses in the checking function. This drawback may be overcome by arranging, instead of a single spring, a check spring and a control spring in series, as it were, so that a check spring of a comparatively weak design determines the check function, with a control spring having a steeper spring characteristic taking effect only after a predetermined axial displacement of the main poppet in order to control the control pressure acting on the topping piston.
In an alternative embodiment having an advantageous construction, one end of the control spring is supported on a spring retainer integral with the housing and, following a predetermined stroke of the main poppet, taken into contact with an inner annular end surface of the main poppet, so that the further opening displacement of the latter takes place against the force of the control spring.
The spring side of the main poppet may be connected to the tank by means of a connecting bore in the topping piston. The latter is controlled open during the axial displacement of the topping piston, so that the spring chamber of the main poppet is de-pressurised toward the tank and may thus be raised more easily from its valve seat.
The structural length may be minimised if the main poppet is designed with a hub-shaped projection into which a tappet of the topping piston plunges such as to raise the closing member of the pilot hole. The annular end surface of the hub-shaped projection serves as a contact surface for the adjacent end surface of the topping piston. These contact surfaces are processed such that they sealingly contact each other, so that the inner cavity of the hub-shaped projection and the outer circumference of the main poppet are sealed from each other, so that pressure compensation cannot take place between the pressures prevailing at the valve seat and at the pilot hole in the open condition of the connecting bore.
As was already explained above, the topping piston contacts an annular end surface of the main poppet. By a radial expansion of the hub-shaped projection in the range of the annular end surface to a diameter greater than the diameter of the seat of the main poppet and a corresponding enlargement of the annular end surface, the topping piston and the main poppet are pressed against each other by the resulting pressure forces, so that a sealing contact of the topping piston and thus optim

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