Pump assembly, in particular for generating pressure in a brake circuit of a controllable power brake system of a motor vehicle

Abstract

A pump assembly for generating pressure in a brake circuit of a controllable power brake system of a motor vehicle. The pump assembly has, as a pressure generator, a piston-cylinder unit in which a piston is actuated with the aid of a piston drive. The piston drive converts a rotational movement, with which a nut of this piston drive is driven, into a translatory movement of a spindle, which is in turn connected to the piston in a rotationally fixed manner. The piston is a steel component in which a plastic deformation at a piston head forms a device for connecting the spindle to the piston in a rotationally fixed manner.

Claims

1. A pump assembly for generating pressure in a brake circuit of a controllable power brake system of a motor vehicle, the pump assembly comprising: a piston-cylinder unit including: a hollow steel piston; and a cylinder in which the piston is displaceably received and that delimits a working chamber; a piston drive that is configured to drive the piston and that includes: a nut configured to be driven for rotational movement; and a spindle that executes a translatory movement, cooperates at least indirectly with the nut, and is connected to the piston in a rotationally fixed manner; and at least one first guide element; wherein: the piston has: a piston skirt that is open at one axial end of the piston and that has a radially outwardly extending circumferential lip having an exterior circumferential edge, which, in at least one circumferential region of the piston, is an axial and radial terminating edge of the piston; and a piston head having a plastic deformation forming a device by which the spindle is connected to the piston in a rotationally fixed manner; and each of the at least one first guide element: is positioned at a respective distinct circumferential position of the lip in a respective other circumferential region of the piston; extends radially outward from the lip at a radial position of the lip that is radially the same as a radially outermost position to which the lip extends in the at least one circumferential region of the piston, so that an entirety of the respective first guide element is radially exterior to all of the lip; and is integrally formed with the exterior circumferential edge of the lip.

2. The pump assembly as recited in claim 1, wherein the plastic deformation forms a cup-shaped receptacle, which is open towards an interior of the piston and a wall of the deformation is formed by an inwardly bent first and second material layer of the piston head.

3. The pump assembly as recited in claim 2, wherein the first and second material layers of the wall are connected to one another at an end situated in an interior of the piston and, enclose a gap between the first and second material layers, the gap being open towards a surrounding environment of the piston.

4. The pump assembly as recited in claim 3, wherein the plastic deformation forms a circumferential channel that is radially exterior to, surrounds, and is separated by the first and second material layers from, the cup-shaped receptacle.

5. The pump assembly as recited in claim 4, wherein: the channel and the cup-shaped receptacle each forms: a respective interior surface of the piston that is perpendicular to a central longitudinal axis that extends axially and about which the nut rotates and that faces towards the open axial end of the piston skirt; and a respective exterior surface of the piston that is perpendicular to the central longitudinal axis and that faces away from the open axial end of the piston skirt; the respective interior surfaces of the channel and the cup-shaped receptacle are at a same axial position of the piston as each other; and the respective exterior surfaces of the channel and the cup-shaped receptacle are at a same axial position of the piston as each other.

6. The pump assembly as recited in claim 1, wherein the plastic deformation has an inside diameter which is matched to an end of the spindle in such a way that, between the spindle and piston, a force fit is established via which the spindle is to be connected to the piston in a rotationally fixed manner.

7. The pump assembly as recited in claim 1, wherein each of the at least one first guide element is formed by deformation of a material extension which is integrally formed with the lip of the piston skirt.

8. The pump assembly as recited in claim 7, wherein the piston is radially supported against a second guide element on the pump assembly via the at least one first guide element.

9. The pump assembly as recited in claim 1, wherein each of the at least one first guide element includes a radially extending base surface and at least one wall extending axially from the base surface in a direction parallel to a central longitudinal axis about which the nut rotates.

10. The pump assembly as recited in claim 1, wherein each of the at least one first guide element includes a base surface and two walls (a) between which the base surface extends radially outward from the exterior circumferential edge and (b) that extend axially from the base surface in a direction parallel to a central longitudinal axis about which the nut rotates.

11. The pump assembly as recited in claim 10, wherein each of the two walls includes a respective first end connected to the base surface and a respective second end, which is a free end pointing in a direction away from the piston head.

12. The pump assembly as recited in claim 10, wherein the two walls and the base surface between the two walls form a u-shape whose base is at the open axial end of the piston skirt.

13. The pump assembly as recited in claim 10, wherein the two walls include respective interior surfaces that face each other and extend in respective planes that are parallel to each other.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An exemplary embodiment of the present invention is illustrated with the aid of the figures and will be explained in detail in the description below.

(2) The figures comprise a total of 4 figures, in which mutually corresponding components are denoted by the same reference signs.

(3) FIG. 1 shows, in a longitudinal section, a pump assembly which is conventional in the related prior art and acknowledged above.

(4) FIG. 2 shows a piston of s pump assembly in a longitudinal section, according to an example embodiment of the present invention.

(5) FIG. 3 shows a view into the hollow interior of the piston.

(6) FIG. 4 shows a piston according to an example embodiment of the present invention, in a perspective illustration looking obliquely onto its open end from the rear.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

(7) The pump assembly (10) illustrated in FIG. 1 belongs to the related art and has already been explained in detail above. As stated, it comprises a piston-cylinder unit (12) having a piston (14), which is received in a cylinder (16) and which can be driven for reciprocating translatory movement by an electric motor (24) via an interconnected planetary gearing (26) and a piston drive (22) arranged downstream. The following description discusses the structural design of this piston (14), which enables this piston to be produced from steel in a cost-effective and space-saving manner using a forming technique and without machining.

(8) According to FIG. 2, the piston (14) designed according to the an example embodiment of the present invention is a hollow piston which is open at one end. It is preferably produced from steel by deep drawing and is divided into a cylindrical piston skirt (50) and a closed piston head (52), which is integrally connected to this piston skirt (50) at one end thereof. The wall thickness of the piston (14) is at least substantially constant throughout, i.e. in the region of the piston skirt (50) and the piston head (52); transitions, such as those between the piston skirt (50) and the piston head (52), for example, are rounded.

(9) A deformation (54) is provided at the piston head (52), which deformation creates a device by which the piston (14) is to be connected to a spindle (38) of the piston drive (22) in an axially fixed manner. This deformation (54) is a double folding of the material of the piston head (52). This folding forms a circular cup, which is arranged concentrically to a longitudinal axis L of the piston (14) at the piston head (52) and projects into the interior of the hollow piston (14). The circumferential wall (56) of the deformation (54) can be seen in a plan view through the open end of the piston (14) (FIG. 3). This wall (56) encloses a base area (58) which, by way of example, is of planar design and is depressed with respect to the wall (56). On the outside of the piston (14), this base area (58) is flush with a remaining ring area (60) of the piston head (52), which surrounds the deformation (54) at its circumference. The remaining ring area (60) and the base area (58) together define the end face of the piston head (52) which is to be acted upon by a pressure medium.

(10) As a result of the folding, the wall (56) of the deformation (54) consists of a first material layer (62) of the piston head (52), which is turned inwards at a right angle, and a second material layer (64) of the piston head (52), which is turned in the opposite direction to the first material layer. Both material layers (62; 64) abut against one another and are connected to one another at their ends which are situated in the interior of the piston (14). Between them, they delimit a narrow gap (74), which is open towards the surrounding environment of the piston (14). The material layers (62; 64) of the wall (56) extend circumferentially such that they are approximately concentric to one another and concentric to the circumferential surface of the piston skirt (50).

(11) The open end of the piston (14) widens into a circumferential lip (66), which protrudes with respect to a circumference of the piston skirt (50). Material extensions (67) of this lip (66) form a plurality of first guide means (68), which protrude radially from the piston (14) as a result of bending the material extensions (67) at a right angle. The guide means (68) comprise a base (70), which is connected to the lip (66) in one piece and whereof the side edges are bent to form wings. These wings (72) are situated at a distance opposite one another in a plane-parallel manner and extend in the direction of the longitudinal axis L of the piston (14). In the exemplary embodiment, the wings (72) extend, for example, in a direction which points away from the piston head (52), although this is not compulsory for the invention. The wings (72) might likewise extend in the direction of the piston head (52). The first guide means (68) are provided for mounting so-called sliding blocks, made of plastic, on the piston (14). The piston (14) is received and radially supported in the second guide means (46) on the assembly via these sliding blocks, with little friction and noise. The sliding blocks in turn abut circumferentially against the wings (72) of the first guide means (68).

(12) Further details relating to the configuration of the first guide means (68) can be seen in FIG. 3. Accordingly, by way of example, precisely two first guide means (68) are provided on the piston, which are arranged in a diametrically opposed manner on the circumference of the piston (14).

(13) The wings (72) of a wing pair of the guide means (68) are connected to one another and to the lip (66) of the piston (14) via the common base (70). In a plan view, the guide means (68) have a u-shaped cross section, whereof the opening points away from the piston head (52) owing to the exemplary direction of extent of the wings (72).

(14) To illustrate the previously explained configuration of the piston, FIG. 4 shows this piston again in a view looking obliquely onto the open end from the rear.

(15) As mentioned, the explained steel piston can be produced in a deep drawing process and, theoretically, with a very good surface quality, However, with this production procedure, grooves may still occur in the circumferential surface of the piston skirt, which grooves extend in the longitudinal direction L of the piston (14) and therefore hinder the subsequent sealing of the piston (14) in the cylinder (16). It is possible to eliminate such grooves with little additional effort by post-treating, in particular, the circumferential or running surface of the piston (14) by compressed air blasting with a solid blasting medium after the deep drawing procedure. Such blasting methods are conventional.

(16) Modifications or additions to the exemplary embodiment which go beyond the explanations above are possible without deviating from the scope of the present invention.