Piston unit of a working cylinder

Abstract

A piston unit of a working cylinder has first and second coupling partners. The first coupling partner is a piston. The second coupling partner a piston rod. The piston rod is inserted axially into the piston. Each of the coupling partners has an annular groove. The groove of the piston rod is an external groove. The groove of the piston is an internal groove. The grooves of the coupling partners lie opposite one another. The unit has a coupling strand which engages in the grooves of the coupling partners and is placed into engagement by insertion into an annular groove gap defined by the grooves. The engagement of the coupling strand in the grooves produces a form-locking connection between the partners. The piston rod is oversized in relation to the piston and provides an additional frictional connection.

Claims

1. A piston unit of a working cylinder, comprising: a first coupling partner being a piston and a second coupling partner being a piston rod, said second coupling partner being coaxially inserted into a bore within said first coupling partner along a longitudinal axis; said first and second coupling partners each having a respective annular groove formed therein, said annular groove of said second coupling partner being an external groove on an outer surface of said piston rod and said annular groove of said first coupling partner being an internal groove on an internal surface of said bore in said piston, said annular grooves of said first and second coupling partners being disposed opposite one another and defining an annular-groove chamber, said first coupling partner having an access opening extending from an outer surface of the piston to said annular-groove chamber; a coupling strand for engaging into said annular grooves of said first and second coupling partners, said coupling strand being insertable into said annular-groove chamber through said access opening, an engagement of said coupling strand into said annular grooves of said first and second coupling partners effecting a positive locking connection between said first and second coupling partners; said second coupling partner having an oversize in relation to an internal diameter of said bore of said first coupling partner, for providing an interference fit effecting a non-positive locking connection between said first and second coupling partner, said interference fit preventing relative movement between said first and second coupling partners for preventing damage to seal elements of the piston unit; a hybrid coupling action produced by said interference fit and said coupling strand, said hybrid coupling action including a frictional locking between said first and second coupling partners resulting from said interference fit for axially and rotational locking said first and second coupling partners to one another, said coupling strand for accommodating axial forces acting on said first and second coupling partners.

2. The piston unit according to claim 1, wherein said first and second coupling partners have further, axially offset annular grooves for receiving further, axially offset coupling strands.

3. The piston unit according to claim 1, wherein said coupling strand (4) has a circular cross section.

4. The piston unit according to claim 1, wherein said first and second coupling partners have different moduli of elasticity, a first area of overlap between said engaged coupling strand and a side wall of said annular groove of one of said coupling partners, which has the higher modulus of elasticity, is smaller than a second area of overlap between said coupling strand and a side wall of said annular groove of the other coupling partner, which has a lower modulus of elasticity.

5. The piston unit according to claim 1, wherein said annular-groove chamber has a conical arrangement.

6. The piston unit according to claim 1, wherein an end section of said coupling strand is accessible to pull said coupling strand out of said annular-groove chamber.

7. The piston unit according to claim 1, wherein said first and second coupling partners define contact surfaces of said interference fit that are dimensioned to accommodate axial forces generated in normative load states.

8. The piston unit according to claim 7, wherein said coupling strand is constructed to accommodate critical overloads beyond the normative load states and prevents said first and second coupling partners from being pulled apart by the critical overloads.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) The invention will be explained in more detail below, on the basis of exemplary embodiments, with reference to:

(2) FIG. 1 which shows a sectional illustration of a piston unit without a coupling strand,

(3) FIG. 2 which shows a sectional illustration of a piston unit with a coupling strand,

(4) FIG. 3 which shows a half-section of a piston unit with two coupling strands,

(5) FIG. 4 which shows a half-section of a piston unit with a circular coupling strand,

(6) FIG. 5 which shows a half-section of a piston unit with a conical annular-groove chamber and a conical coupling strand,

(7) FIG. 6 which shows a sectional illustration of a piston unit in a plan view,

(8) FIG. 7 which shows a partial enlarged sectional illustration of a coupling strand region of a piston unit,

(9) FIG. 8 which shows another partial enlarged sectional illustration of a coupling strand region of a piston unit.

DESCRIPTION OF THE INVENTION

(10) FIG. 1 shows a piston unit according to the invention, without a coupling strand, in a full section.

(11) The piston unit is of multi-part form and has a piston 1 and a piston rod 2, wherein the piston rod 2 has been partially inserted into the piston 1.

(12) Below, the piston 1 and the piston rod 2 will also be described collectively as coupling partners.

(13) The piston 1 and the piston rod 2 each have a first annular groove 3.1 and 3.3, wherein the first annular groove 3.1 of the piston 1 is in the form of an encircling internal groove and the first annular groove 3.3 of the piston rod 2 is in the form of an encircling external groove, and wherein the annular grooves 3 form an annular-groove chamber 7.

(14) In order to facilitate the insertion of the piston rod 2 into the piston 1, the piston rod additionally has, on the end facing toward the piston 1, a run-on bevel 5 of encircling form.

(15) According to the invention, the piston 1 and piston rod 2 are coupled to one another by means of a positively locking connection.

(16) As illustrated in FIG. 2, the positively locking connection is in the present case realized by virtue of a coupling strand 4.1 being arranged within the annular-groove chamber 7 of the piston unit.

(17) In the present case, the coupling strand 4.1 has a rectangular cross section, wherein according to the invention, coupling strands with other forms of cross section may also be used.

(18) The positive locking of the coupling of the piston 1 and of the piston rod 2 is realized according to the invention in that, in the final position of the piston rod 2 in the piston 1, that surface of the coupling strand 4.1 which faces toward the piston-side end of the piston rod 2 bears against those walls of the annular grooves 3.1 and 3.3 which face toward the coupling strand 4.1.

(19) As a special technological feature, the external diameter of the piston rod 2 has an oversize in relation to the internal diameter of the piston 1.

(20) The oversize has the effect that, in the final assembled position of the piston rod 2, an interference fit and thus frictional locking is produced between said piston rod and the piston 1.

(21) Owing to the frictional locking that is provided, the piston rod 2 and the piston 1 are fixed axially in their position relative to one another without a clearance, whereby the piston 1 is prevented in an effective manner from moving axially relative to the piston rod 2. In this way, abrasion grinding phenomena can be prevented.

(22) Furthermore, owing to the interference fit that is provided, undesired twisting of the piston 1 relative to the piston rod 2 is prevented.

(23) In the present exemplary embodiment, the forces arising during the intended operation of a working cylinder in which the piston unit is received are accommodated entirely by way of the frictional locking that is provided. In the present exemplary embodiment, the positively locking connection of the coupling partners 1 and 2 by means of the coupling strand 4.1 thus serves for realizing a securing action in order, even in extreme load states of the working cylinder, for example in the event of incorrect operation and the frictional locking possibly being overcome as a result, to prevent detachment of the piston 1 from the piston rod 2. The operational reliability is thus increased without an increase in dimensions of the interference fit.

(24) FIG. 3 shows an exemplary embodiment of a piston unit according to the invention in half-section, wherein, to increase the axial load-bearing capacity, the piston unit has two coupling strands 4.1 and 4.2.

(25) In the present case, the coupling strand 4.1 is arranged in the annular-groove chamber between a first annular groove 3.1 of the piston 1 and a first annular groove 3.3 of the piston rod 2.

(26) The coupling strand 4.2 is arranged in a further annular-groove chamber which is formed by a second annular groove 3.2 of the piston 1 and a second annular groove 3.4 of the piston rod 2.

(27) In a further exemplary embodiment as per FIG. 4, the coupling strand 4.1 has a circular cross section.

(28) Such a circular cross section is, in a particularly advantageous manner, associated with a reduction in production costs for the coupling strand 4.1 and with an optimization of the profile of the internal stresses in the coupling strand 4.1 during the bracing thereof.

(29) To realize as large a region as possible in which there is a positive locking action between the coupling strand 4.1 and the annular grooves 3, said annular grooves are adapted in terms of their contour to the cross-sectional geometry of the coupling strand 4.1.

(30) The adaptation of the annular groove contours to the cross section of the coupling strand 4.1 furthermore has the technological advantage that, owing to the resulting roundings of the annular groove contours, notch effects that arise when the positively locking connection is subjected to load can be substantially eliminated.

(31) As a further exemplary embodiment, FIG. 5 shows a piston unit according to the invention with a coupling strand 4.1 which is of conical form and which has multiple segments.

(32) In this case, the annular grooves 3.1 and 3.3 are geometrically shaped such that, between them, there is formed a conical annular-groove chamber to which the coupling strand 4.1 adapts, by deformation, as it is inserted.

(33) FIG. 6 shows a piston unit according to the invention in a sectional plan view with a piston rod 2 in the form of a hollow element.

(34) As can be seen in FIG. 6, the externally situated piston 1 has a tangential access opening 6 via which the coupling strand 4.1 can be inserted into the annular-groove chamber formed by the annular grooves 3.1 and 3.3.

(35) As shown in FIGS. 7 and 8, the first and second coupling partners have different moduli of elasticity E(1) and E(2), a first area of overlap between the engaged coupling strand and a side wall of the annular groove of one of the coupling partners, which has the higher modulus of elasticity, is smaller than a second area of overlap between the coupling strand and a side wall of the annular groove of the other coupling partner, which has a lower modulus of elasticity.

REFERENCE NUMERALS USED

(36) 1 Piston 2 Piston rod 3.1 First annular groove, piston 3.2 Second annular groove, piston 3.3 First annular groove, piston rod 3.4 Second annular groove, piston rod 4.1 First coupling strand 4.2 Second coupling strand 5 Run-on bevel 6 Access opening 7 Annular-groove chamber