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Piston pump with improved efficiency

Piston pump with improved efficiency description/claims

The present invention relates to a piston pump for delivering hydraulic fluid with improved efficiency in which the piston pump is particularly inexpensive to manufacture.

A wide variety of piston pump designs are known from the prior art. Piston pumps for vehicle brake systems are frequently embodied in the form of radial piston pumps, in which at least one piston can be set into a reciprocating motion by means of a cam. Piston pumps of this kind are frequently used in connection with electronic stability systems (ESP) or electrohydraulic brake systems (EHB). Since the use of such systems is on the rise, even in smaller vehicles, it is necessary for the piston pumps to be very inexpensive to manufacture. Another requirement for such piston pumps is that they be as small and lightweight as possible. Since future brake systems will operate with higher pressures, the piston pump must also be able to generate these desired pressure levels.

The known piston pumps are usually equipped with a pressure chamber situated between an inlet valve and an outlet valve; the movement of the piston builds up an operating pressure in this pressure chamber. At its end oriented toward the piston, this pressure chamber must be sealed in relation to a low-pressure region of the piston pump. This is frequently accomplished by means of piston rings or sealing elements situated inside the cylinder. The inlet valve is situated in the pressure chamber and a supply line of hydraulic fluid can be provided by means of conduits integrated into the piston. The pressure chamber also contains a spring for returning the piston to its initial position; this placement of the spring can result in unfavorable flow conditions in the pressure chamber and in particular, can lead to problems due to gas evolution from the gases combined in the hydraulic fluid, and can also lead to noise problems.

The piston pump for delivering hydraulic fluid according to the present invention, with the defining characteristics of claim 1, has the advantage over the prior art that it is particularly compact and requires fewer parts. This enables a particularly inexpensive production of the piston pump according to the invention. According to the invention, this is achieved by the fact that a sealing element situated on the piston simultaneously also performs the function of the inlet valve. This makes it possible to reduce the number of parts and to achieve a particularly compact design of the piston pump. The sealing element is embodied in such a way that during a compression phase, its seals the pressure chamber in relation to a low-pressure region of the piston pump and during an intake phase, it produces a connection to the low-pressure region in order to draw hydraulic fluid into the pressure chamber.

Preferred modifications of the invention are disclosed in the dependent claims.

Preferably, the sealing element is situated on the piston so that it has an axial play. In other words, the position of the sealing element in relation to the piston can be changed in the axial direction of the piston by the amount of the axial play. This makes it possible to achieve a particularly simple embodiment for the combined inlet valve/sealing element. The sealing element can consequently assume two positions in relation to the piston, namely a first position for the intake phase and a second position for the compression phase.

In a particularly preferable embodiment, the sealing element on the piston is situated in a stepped region provided at the pressure chamber end region of the piston.

According to a preferred embodiment of the invention, the sealing element is embodied in such a way that its inner circumference has at least one raised region and one recessed region. During the intake phase, this permits an overflow of the sealing element along the recessed region between the sealing element and the piston. In a particularly preferred embodiment, the inner circumference of the sealing element is provided with a number of plane-like raised regions and a number of plane-like recessed regions situated between the raised regions. It is particularly preferable in this case for the arrangement of the raised and recessed regions to be symmetrical. This makes it possible to assure symmetrical pressure conditions against the sealing element. The size and depth of the recessed regions depends on the one hand on the inner diameter of the sealing element and on the other hand, also depends on the desired intake volume and stroke length of the piston.

In order to be able to achieve an intake of the piston pump as quickly as possible after the direction reversal of the piston once the top dead center has been reached, the inner circumference of the sealing element has a bevel on the edge oriented toward the low-pressure region of the piston pump. This bevel facilitates the opening of the sealing element for the intake phase, thus permitting a very short reaction time for the inlet function of the sealing element. It should be noted that it is also possible to provide a bevel on the inner circumference of the sealing element, at the edge oriented toward the pressure chamber. This makes it possible to improve guidance of the sealing element on the piston.

It is also preferable to provide a spring element in order to exert a spring force on the sealing element in the axial direction. In particular, this makes it possible to achieve an improved sealing by means of the sealing element during the compression phase of the piston pump. The spring element is preferably embodied in the form of a leaf spring with one or more spring tabs. Affixing the spring element to the piston in a preferable fashion achieves a particularly compact design. The spring element can, for example, be affixed to the piston by means of a plate-shaped retaining element; the retaining element is affixed to the pressure chamber end of the piston and protrudes beyond the stepped region of the piston in order to support the spring element.

Preferably, the piston has at least one flattened region on the circumference in order to supply hydraulic fluid from the low-pressure region to the sealing element. Preferably, three flattened regions are provided on the piston, each spaced equidistantly apart from adjacent flattened regions along the circumference of the piston.

In order to further improve efficiency, preferably a return spring for returning the piston to its initial position is situated outside the pressure chamber. Since the sealing element that performs the function of the inlet valve is also not situated in the pressure chamber, it is thus possible to obtain a clearance-optimized pressure chamber. Consequently, the pressure chamber can be easily designed for the desired pressure conditions and can have a simple geometry. According to the invention, a cylinder element is preferably provided for this, against the inside of which the sealing element is guided and against the outside of which the return spring for the piston is guided. The return spring in this case can be supported on the piston against an additional stepped region or against protruding projections. According to another preferred embodiment of the invention, the return spring is embodied in the form of a tapering, in particular conical spiral spring, which rests against a circumferential groove provided on the piston.

According to another preferred embodiment of the invention, the return spring for the piston is situated in a cam chamber of the piston pump. This, too, makes it possible to situate the return spring outside the pressure chamber of the piston pump. The return spring in the cam chamber is preferably fastened to the piston and particularly preferably, is embodied in the form of a leaf spring, which is supported against the walls of the cam chamber.

It is particularly preferable to use the piston pump according to the present invention in brake systems of motor vehicles, for example to control and regulate a pressure in a wheel brake cylinder. It is particularly preferable for the piston pump according to the present invention to be used in connection with electronic control and regulating systems of the brake system, e.g. ESB, EHB, TCS, etc. Since the piston pump according to the present invention is particularly inexpensive to produce, it is possible to significantly reduce the costs for equipping even small vehicles with such brake systems.

Preferred exemplary embodiments of the invention will be described below in conjunction with the accompanying drawings.

FIG. 1 is a schematic sectional view of a piston pump according to a first exemplary embodiment of the present invention,

FIG. 2 is a perspective view of several individual parts of the piston pump shown in FIG. 1,

• Provisional Patent
• Utility Patent

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