Self-pumping hydropneumatic spring strut with internal level control

An oil-filled working cylinder is divided into first and second working spaces by a working piston, the first working space being connected to a high pressure chamber. A piston pump includes a pump rod received in a pump cylinder formed by the hollow piston rod, the pump rod having a bore connected to a low pressure chamber via a discharge valve, a distal end provided with a suction valve, and a down-regulating opening connecting the bore to the first working space as a function of the position of the working piston, the pump cylinder being connected to the first working space by an outlet valve. At least one of the valves is a check valve including a housing having a bore, a ball reciprocably guided in the bore by guide ribs, and a resilient retaining element capturing the ball in the bore and spring-loading the ball toward a valve seat.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention pertains to a self-pumping hydropneumatic spring strut with internal level control, especially for motor vehicles, with an oil-filled working cylinder under the pressure of at least one gas cushion located in a high-pressure chamber and acting as a spring, the working cylinder being divided into two working spaces by a working piston carried by a hollow piston rod. A piston pump is driven by the movements of the spring and conveys oil from a low-pressure chamber into the working space connected to the high-pressure chamber, the pump cylinder of the piston pump being formed by the hollow piston rod, into which a hollow pump rod, which is attached to the working cylinder and carries at its forward end a suction valve, travels, the bore of the hollow pump rod being connected to the low-pressure chamber. A down-regulating opening can be closed as a function of the position of the working piston in the working cylinder, and connects the working space connected to the high-pressure chamber to a down-regulating channel, which is itself equipped with a throttle and/or check valve and which opens out into the low-pressure chamber. Fluid flows through the check valve and/or the throttle in the suction direction, and that the pump cylinder is connected to the high-pressure-side working space by an outlet valve.

2. Description of the Related Art

Self-pumping hydropneumatic spring struts with internal level control are already known (e.g., U.S. Pat. No. 6,234,462, DE 196 48 859 C2), in which the working cylinder is divided by a working piston carried by a hollow piston rod into two working spaces, and in which a piston pump, which is driven by the movements of the spring and conveys oil from a low-pressure chamber into the working space connected to the high-pressure chamber, is provided. The piston pump consists of a pump cylinder, which is formed by the hollow piston rod, into the forward end of which the hollow pump rod, which carries a suction valve, travels. In this state of the art, a total of three spring-loaded check valves is provided, i.e., an inlet valve, an outlet valve, and a discharge valve. The inlet and outlet valves are necessary for the pumping work of the piston pump, and the discharge valve is necessary for the throttled discharge of the damping medium when the load being imposed by the vehicle body is removed. The disadvantage is that each of these valves has a different design, which means that the associated multiplicity of parts requires a not inconsiderable amount of work with respect to logistics and assembly. In particular, spring-loaded plate valves are so large that they cannot be installed in a relatively small-diameter pump rod.

SUMMARY OF THE INVENTION

An object of the invention is to create a low-noise check valve which can be operated at high-frequency, which occupies a minimum of space, and which can be produced at low cost under mass production conditions.

To accomplish this task, at least one valve (discharge valve, inlet valve, outlet valve) is designed in such a way that a ball is provided as the valve body, which is guided in the bore by at least two guide ribs, and that a retaining element located in the terminal area of the bore captures the ball and simultaneously spring-loads it.

It is advantageous here that a ball is used as the valve body and that this ball is guided with precision between the guide ribs. The retaining element, in the form of a contoured spring disk with an opening in the center, acts on the ball in such a way that the ball can open the valve against the force of the spring but is limited in its stroke at the same time. To minimize noise, the stroke of the ball is also limited elastically.

According to another feature, the guide ribs are distributed uniformly around the circumference of the bore.

According to another essential feature, the retaining element has at least one radially inward-directed projection, which serves to limit the stroke of the valve body. It is advantageous here for the stroke of the ball to be limited by the projections, which are designed to act as springs, but which, as a result of their progressive spring characteristic, are also able to limit the stroke in the desired manner.

According to another embodiment, the retaining element has at least one radially inward-directed spring tongue, which keeps the valve body under elastic pretension. It is advantageous here that the spring tongue is also an integral part of the retaining element, so that the projections, the spring tongue, and the retaining element can be produced out of a single piece of material. To ensure that the flow is throttled to the least possible extent, the guide ribs extend axially over only part of the bore. It is advantageous here for the guide ribs to have a free area underneath the retaining element, so that the fluid can flow smoothly through the check valve.

According to another embodiment, the retaining element is held positively in place in the housing. It is advantageous here to hold the retaining element positively in place by peening over parts of the material of the housing.

According to another embodiment, the radial projections are capable of elastic movement in the axial direction.

The retaining element can be held in place positively in the valve housing, but it is also possible for the retaining element to be bonded to the housing with an adhesive. It is advantageous to use an adhesive, but welding or soldering is also conceivable.

According to another exemplary embodiment, the housing is an undercut-free, as-molded part.

According to another embodiment, there is at least a partial free area between the guide ribs of the housing and the retaining element.

It is advantageous here for the housing to be produced by sintering or pressing.

According to another feature, the retaining element is a disk-shaped component which allows a flowing medium to pass through, while its center part exerts elastic force on the valve body.

According to another essential feature, the retaining element has a closed, circular outer area, from which a spring tongue extends all to the way to the center.

It is advantageous for the spring tongue to be in the form of a circle or spiral so that a softer spring characteristic can be obtained.

The retaining element may be produced by stamping or may be shaped out of a piece of spring wire.

According to another embodiment, the retaining element has a compression-resistant outer area suitable for the peening process.

It is advantageous for the retaining element to be held in place on the housing by means of a claw-type connection.

According to another feature, the housing has a cutting edge on at least one end surface, so that it can be installed tightly in a receiving bore.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

The spring strut for motor vehicles shown inFIG. 1includes a the working cylinder18, in which a piston19, mounted on the end of a piston rod20, slides. The working cylinder18is connected underneath the piston19to the high-pressure chamber25. The unit is attached to the body of a vehicle and to the axle of the vehicle in a manner not shown in the figure. During the operation of the vehicle, the damping forces are generated by the damping valves21.

The spring strut according toFIG. 1shows an oil pump, which consists of the pump rod22and the pump cylinder23, which is formed by the hollow piston rod20. The movements of the vehicle axle caused by irregularities in the pavement actuate this oil pump, which continuously conveys oil in a controlled manner through the suction valve1b, out of the low-pressure chamber24via the outlet valve1cinto the working cylinder and thus into the high-pressure chamber25. As a result, the piston19and the piston rod20are pushed outward until the dynamic level control begins through the formation of a bypass. When the load on the system is removed, the down-regulating opening26in the pump rod22is released, and the vehicle is down-regulated, i.e., returned to its original level.

The essential purpose of the discharge valve1ais to open wide in the suction direction and to produce a throttling effect in the discharge direction, so that the vehicle body can be down-regulated gently. The advantage of this valve is that the discharge notch27can be opened by the rising valve body28during the suction stroke and thus can be flushed free of dirt particles. This helps to prevent the danger of clogging at this narrow throttle point. The down-regulating opening26has no throttling effect because of its size and is therefore not subject to the danger of clogging.

FIG. 2shows part of a piston rod20, a pump rod22, and the valves1a,1b, and1cin isolation. The down-regulating opening26, as already described on the basis ofFIG. 1, can also be seen in the pump rod22.

FIG. 3shows the check valve1with a housing2, which preferably can be produced without any undercuts, i.e., as-molded, without the need for any finish machining, ready for use just as it comes from the mold. A sintering or pressing technique is preferred for the production of this housing.

The housing2has a central inflow bore3, which forms the valve seat4at the transition to the bore17. In the area of its valve seat4, the inflow bore3is closed by the valve body5, designed as a ball. Above the valve body5there is a retaining element6, in the form of an internally contoured spring disk, which is arranged in such a way that its outer edge is permanently connected to the housing2, while its inner area exerts elastic force either directly or at least approximately on the center of valve body5.

The housing2has a cutting edge29on at least one end surface, which allows it to be installed tightly in a receiving bore.

FIG. 4shows the check valve1ofFIG. 3in the open position, where the valve body5has been lifted from the valve seat4against the elastic force of the retaining element6, i.e., the force of its spring tongue7, by the flow arriving through the inflow bore3.

The valve body5is centered by guide ribs8. The flow passes around the valve body5at least partially via longitudinal channels9on the circumference and then passes through the remaining open area of the retaining element6, the stroke of the valve body5being limited by the three projections10of the retaining element6.

The end stop of the valve body5can be spring-loaded and thus also have the effect of minimizing noise. To ensure that the flow is throttled to the minimum possible extent, the guide ribs8have a free area11underneath the retaining element6, especially in the case of the smallest sizes of these check valve designs. The shape of the free area can be individually adapted.

FIG. 5shows a top view of the check valve1illustrated inFIG. 1with a housing2and a retaining element6, which is designed in the form of a flat spring disk. The retaining element6is flat, because this facilitates handling in bulk, and it can thus be placed in the centering recess12of the housing2by machine without having to worry about its angular orientation or having to determine which is the right side and which the wrong side. The retaining element6has a spring tongue7, which acts elastically on the valve body5, where the three projections10serve as an end stop for the valve body5in the axial direction. Depending on the stiffness of the spring tongue7, the projections10can be eliminated entirely, because the maximum outward travel of the valve body5caused by the flow is often very short. The spring tongue7will then stop the valve body5by itself by virtue of its own stiffness.

The opening pressure of the check valve and the stroke can be varied as desired by appropriate choice of the retaining element6, e.g., through choice of its inner contours and/or its thickness. The retaining element6is permanently attached to the housing2by a positive connection, for example, or by a claw-type connection, by adhesive bonding, or by welding.

FIG. 6shows an exploded perspective of a highly miniaturized check valve1with the housing2, the valve body5, and the retaining element6. To optimize the flow, the guide ribs8have a free area11at the top, so that the retaining element can be inserted into the centering bore12of the housing2without having to occupy any predetermined position.

FIG. 7shows the completely assembled check valve1, where the retaining element6is permanently connected to the housing2by localized peening13.

FIG. 8shows the retaining element6together with the valve body5in a position in which the valve body5has actuated the spring tongue7in such a way that the projections10are acting as an end stop.

FIGS. 9-9dshow various ways in which the retaining element6can be attached to the housing2.FIG. 9shows the principle, illustrated inFIG. 3, of fastening the retaining element6to the housing2by means of localized peening. A magnified view of this localized peening13can be seen inFIG. 9a. The localized peening can be provided at several points distributed around the circumference of the housing2.

FIG. 9bshows a housing2, in which a peening14has been performed all the way around; that is, the entire circumference has been peened over.FIG. 9cshows a welded or adhesively bonded joint15.

FIG. 9dshows a retaining element6with an angled area at the outer edge, which forms a claw-type connection16when the element is pressed into the housing2. The retaining element6is therefore held positively in place in the centering bore12of the housing2by means of the corresponding interference fit.

FIG. 10is a cross-section showing a retaining element6, which is supported elastically by its spring tongue7on the valve body5.

FIG. 11shows a top view of the retaining element6ofFIG. 10. A projection10, which ultimately limits the stroke of the valve body5, can be omitted, depending on the stiffness of the spring. Depending on the design of the spring tongue7, it is also possible for the valve body5to make early contact with the retaining element6, if desired, so that the stroke can be limited in the desired manner. The spring tongue7is designed here with a circular or spiral shape because of the desire for a softer spring.

FIG. 12shows a retaining element6of spring steel wire. The outer edge is circular and designed to be resistant to deformation to allow peening of the housing.