Patent Application
20100284841
The invention is based on a piston pump for delivering a fluid, as generically defined by the preamble to independent claim 1, which is used in particular in vehicle brake systems.
In vehicles with hydraulic or electrohydraulic vehicle brake systems, such piston pumps are preferably used as return feed pumps, for selectively lowering or raising a brake pressure in the wheel brake cylinders, and as a result the brake pressure in the wheel brake cylinders can be regulated. Such regulation can be performed for instance in an anti-lock brake system (ABS), a traction control system (TC system), and an electronic stability program, and so forth.
During an intake stroke of the piston assembly 2, fluid is aspirated radially via a filter sleeve 9 and via transverse bores 3 that are disposed in the first piston element 2.1, and the fluid is carried via the longitudinal bore 4 corresponding with the transverse bores 3 in the second piston element 2.2 and via the opened inlet valve 5 into the compression chamber 8.1, which is disposed in the cylinder 8 between the inlet valve 5 and the outlet valve 6. After top dead center is reached, the direction of motion of the piston group 2 is reversed, so that the second piston element 2.2 with the inlet valve seat 5.1 is pressed sealingly onto the inlet valve sealing element 5.3, via the first piston element 2.1 driven by an eccentric element 14 disposed in an eccentric chamber 15, and the inlet valve 5 is closed. In the compression chamber 8.1, a pressure buildup now takes place until such time as the pressure in the compression chamber 8.1 is greater than the spring force of the outlet valve 6, as a result of which the fluid under pressure is conducted out of the compression chamber 8.1 into an outlet line, not shown, via the outlet opening 8.3 and the open outlet valve 6.
After bottom dead center is reached, the direction of motion of the piston group 2 reverses again, so that the outlet valve 6 closes again, and the intake stroke begins again; a restoring force F2 of a restoring spring 10, disposed in the compression chamber 8.1 and guided by a cylinder wall 8.4, which spring is embodied for instance as a spiral spring with polished end windings and is braced on a cylinder bottom 8.2 and on a cage element 11, acts against the cage element 11 of the inlet valve 5 and thus against the second piston element 2.2, in order to move the piston assembly 2 back in the direction of top dead center. During operation, axial forces F1 and F2, which on the one hand are effected by the eccentric element 14 and introduced via the first piston element 2.1, and on the other are effected by the restoring spring 10 and introduced via the cage element 11, and radial forces F3, which are generated by the prevailing system pressure, therefore act on the second piston element 2.2, which has the inlet valve seat 5.1. The second piston element 2.2 embodied as a valve seat is therefore produced as a stable component, preferably as a metal component, and can be weakened only conditionally by intake bores in the form of transverse bores 3. The transverse bores are therefore made in the first piston element 2.1, resulting in a relatively long inlet region embodied as a longitudinal bore 4.
The piston pump of the invention as defined by the characteristics of independent claim 1 has the advantage over the prior art that a cage element, in which an inlet valve spring and an inlet valve sealing element are disposed, as a high-pressure sealing element which is embodied for absorbing for radially acting force components and for sealing off against the cylinder wall via a radial sealing element and for sealing off axially from a piston assembly via an axial sealing face, which piston assembly has at least one transverse bore and a longitudinal bore corresponding to the at least one transverse bore. Since the high-pressure sealing element absorbs the radially acting force components, the piston assembly coupled with the high-pressure sealing element now needs to absorb only the operative axial forces and experiences no further deformation from additional radial forces. This dividing up of the axial and radial force components each to one component advantageously leads to a reduction in component loads with respect to elongation and stress and makes it possible to embody the components with a lower component strength.
By the provisions and refinements recited in the dependent claims, advantageous improvements to the piston pump recited in the independent claim are possible.
The piston assembly includes a first piston element and a second piston element, and an inlet valve seat comprises a wear-resistant material and is disposed on the second piston element, which absorbs axially acting force components. At least one transverse bore corresponding to a longitudinal bore is made in the second piston element, and the elastic high-pressure sealing element seals off axially against the second piston element via the axial sealing face. Since there is no longer a nonpositive engagement between the cage element having the high-pressure sealing element and the second piston element having the inlet valve seat, in contrast to the conventional piston pump, one assembly step is advantageously omitted in the production of the piston pump of the invention. Moreover, stresses between the cage element and the second piston element that occur are reduced by the elimination of the nonpositive engagement. From the reduction in tension, the at least one intake bore embodied as a transverse bore and the corresponding longitudinal bore can be placed in the second piston element, and the cage element with the elastic high-pressure sealing element and the second piston element with the inlet valve seat can be made as plastic injection-molded parts. Embodying them as plastic injection-molded parts advantageously enables simple, economical production of the components, and complex shaping is possible. Overall, the piston pump of the invention makes an extreme reduction in the cost for the piston assembly possible and makes assembly easy. Moreover, the piston pump of the invention provides improved intake performance, greater pressure resistance, and an extremely short inlet region.
In a feature of the piston pump of the invention, the radial sealing face can be shaped by a pressure-dictated widening of the high-pressure sealing element. Moreover, the elastic high-pressure sealing element, toward the cylinder wall, can have a radial contact region for receiving and centering an upper end winding of a restoring spring for the piston assembly, which spring is disposed for instance in a compression chamber of the piston pump. The radial contact region can be embodied for instance as a radial receiving groove, which is shaped on the outer edge as a flexible sealing lip and closes off the compression chamber toward the cylinder wall in pressure-tight fashion.
In a further feature of the piston pump of the invention, the first piston element can be loosely coupled to the second piston element. Alternatively, the first piston element can be coupled to the second piston element by positive and/or nonpositive engagement. The first piston element is embodied for instance as a cylindrical needle roll and is advantageously available as a mass-produced standard part. Since the transmission of the driving force of an eccentric element is effected via a linear contact with the first piston part, embodied as a solid metal needle roll, preferably as a steel needle roll, wear can advantageously be reduced.
Advantageous embodiments of the invention, described below, and the conventional exemplary embodiments, described above for the sake of better comprehension of the invention, are shown in the drawings. In the drawings, identical reference numerals designate components and elements that perform the same or analogous functions.
A piston pump according to the invention, which can be used as a return feed pump in a vehicle brake system, essentially includes the same components as the conventional piston pump 1 described in conjunction with
As can be seen from
In a distinction from the conventional piston pump 1, the second piston element 22.2 now absorbs only the axially acting force components F1 and F2, so that a longitudinal bore 24 and transverse bores 23 that correspond to the longitudinal bore 24 can be made in the second piston element 22.2, without affecting the stability and strength of the second piston element 22.2. In the exemplary embodiment shown, the cage element 31 is embodied with the elastic high-pressure sealing element 31.1, and the second piston element 22.2 and the inlet valve seat 25.1 are both embodied as plastic injection-molded parts, thus advantageously making simple, economical production of the components possible, and complex shaping is also possible. Moreover, the first piston element 22.1, in the exemplary embodiment shown, is solidly coupled to the second piston element 22.2. In an embodiment not shown, the first piston element 22.1 can be loosely coupled to the second piston element 22.2. Overall, the embodiment of the inlet valve 25 according to the invention, in combination with the piston assembly 22, makes an extreme cost reduction for the piston pump possible along with simple assembly. Furthermore, the piston pump of the invention makes improved intake performance and greater pressure resistance available, and, by the dispositions of the transverse bores 23 in the second piston element 22, an extremely short inlet region as well.
As can be seen from
After bottom dead center is reached, the direction of motion of the piston group 22 is reversed again, so that the outlet valve closes again, and the intake stroke begins again, and a restoring force F2 of a restoring spring 30, disposed in the compression chamber 28.1 and embodied for instance as a spiral spring, presses against a radial contact region 31.4 that is disposed on the high-pressure sealing element 31.1. The restoring force F2 is axially against the second piston element 22.2 via the high-pressure sealing element 31.1 and the axial sealing face 31.5, and as a result the piston assembly 22 is moved back in the direction of top dead center. The radial receiving region 31.4, for instance in the form of a radial receiving groove, is embodied for receiving and centering an upper end winding 30.1 of the restoring spring, and the restoring spring 30 embodied as a spiral spring is braced in this receiving groove with its upper end winding 30.1. Via a lower end winding 30.2, the restoring spring 30 is braced on a cylinder bottom 28.2. As can also be seen from
In the piston pump of the invention, the axial and radial compressive force components are distributed each to a respective component, which advantageously leads to a reduction in component loads with respect to elongation and stress and makes it possible to embody the components with a lower component strength. Overall, the invention makes an economical piston pump, optimized in terms of installation space, possible that has components that are easy to produce and are embodied for instance as plastic injection-molded parts. The piston pump of the invention advantageously has improved suction performance, pressure resistance to 250 bar, and an extremely short inlet region.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 047 419.0 | Oct 2007 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2008/062458 | 9/18/2008 | WO | 00 | 6/1/2010 |
