Pressure Medium Drive With a Cylinder and a Plunger

The invention pertains to a pressure medium drive with a cylinder with a cylinder chamber, a radially guided piston, a sealing ring, and a replaceable support with a through-hole for the piston and a contact surface for the sealing ring.

Large numbers of pressure medium drives of this type, which are usually designed as hydraulic drives, are required for, for example, industrial trucks and forklifts, etc. At the end of the cylinder there is a support, which also serves at least in part as a guide for the plunger. This support also absorbs the axial forces of the sealing ring.

In the pressure medium drive of the general type described in DE 36 35 010 A1, a toothed rack, which is connected to a piston, passes through a support in the form of a plug, which closes off the working space. The support is provided with both an internal and an external thread and is held in place in the cylinder by means of a radially pretensioned locking ring consisting of round wire. Because the diameter of the piston is greater than that of the toothed rack, the toothed rack cannot be pulled out through the support. Thus a tool must be used to insert the locking ring into the narrow ring-shaped gap between the toothed rack and the cylinder, and when repairs are needed, it must be removed again from the same ring-shaped gap. Fabrication and repair are therefore complicated, and the round wire represents a weak point in numerous concrete applications where extremely high working pressures are involved.

U.S. Pat. No. 3,391,612 discloses a piston seal of larger cross section than the piston of a hydraulic motor, wherein the seal is connected to the piston by a dovetail joint. So that this connection can be made and taken apart again, a radial opening is provided in the cylinder wall, which is closed by a cover and secured with screws, which can be removed only by means of a tool. The piston itself must remain in the cylinder until the piston seal has been removed; nothing is said about pulling anything out through a hole in a support. With respect to a cover plate located at one end of the piston, which can be referred to as a support, this is also inserted and removed through a radial opening in the cylinder wall. The process of replacing the seals and the associated design are complicated, especially since there is no possibility of using extruded profiles to produce the cylinder. In addition, the radial assembly openings for the seals and their covers represent pronounced weak points with respect to high pressures.

All of the known means of attachment are either unspecific or complicated. It must be remembered that large numbers of pressure medium drives of this type are required.

The invention provides a pressure medium drive which can be produced easily from fewer parts, in which the support has a precise seat and the sealing ring can be easily replaced.

According to the invention,

(a) the piston is designed as a plunger, which can be pulled out through the through-hole and from the sealing ring without removing the support;

(b) the support is designed as a sliding body, which forms a diametral dovetail joint with the end of the cylinder; and

(c) the support, after it has been inserted, is held in place with respect to the cylinder by the piston.

It is especially advantageous for the dovetail joint to comprise two diametrically opposite sliding shoulders, which are fit in complementary transverse grooves in the cylinder.

It is also advantageous for the piston to be guided in a guide ring inserted in the cylinder chamber and for the sealing ring to be installed between the guide ring and the sliding body, especially when the guide ring consists of low-friction plastic and is installed in a stepped bore in the cylinder chamber.

Only a few parts are required for the object of the invention, one of these parts being the support, which occupies a precise seat in the open end of the cylinder and which assumes at least part of the job of guiding the piston. It also ensures the precise support of the sealing ring and can be replaced easily. No special collars or threaded bores are required at the end of the cylinder, nor are any additional sealing plates or sealing rings needed.

The plunger itself serves in this case in a surprisingly simple way as a retaining device for the sliding body; no other means of attachment are required. As long as the plunger is in the cylinder, the sliding body cannot be pushed out of the transverse grooves in the cylinder. After the plunger has been pulled out of the cylinder, the sliding body can be pushed out of the transverse grooves in the direction perpendicular to the longitudinal axis of the cylinder, so that then, without any special tools, the sealing ring can also be pulled out of its stepped bore and replaced with a new sealing ring. The sliding body can be reused as often as desired.

According to a variant of the invention, the sliding body has a rectangular outline (including a square outline), when seen in the axial direction, and the sliding shoulders are provided on two opposite sides of the rectangle.

According to another variant of the invention, the sliding body is provided with a ring-shaped groove inside the through-hole for the plunger and for a wiper ring to be inserted in this groove.

This wiper ring can also be easily pried out of the ring-shaped groove and replaced with a new one. As long as the wiper ring is in good condition, it can remain in the sliding body, and after the sealing ring has been replaced, it can be reinstalled together with the sliding body, which is inserted into the transverse grooves and held in place again by the plunger.

FIG. 1 is an axial cross section through a complete pressure medium drive;

FIG. 2 is an end view of the drive in the direction of arrow II in FIG. 1;

FIG. 3 is a partial axial section on an enlarged scale;

FIG. 3a is a partial axial section showing a dovetail joint;

FIG. 4 is a side cross section through the sliding body along line IV--IV of FIG. 5;

FIG. 4a is a side section through a sliding body having a dovetail;

FIG. 5 is an end view of the sliding body, in the direction of arrow V in FIGS. 4 and 4A;

FIG. 6 is an axial cross section through a double-sided pressure medium drive, of a type which can be used in so-called side loaders for the forks of forklift trucks;

FIG. 7 is an exploded perspective of the drive according to FIGS. 1-5 in conjunction with a double cylinder according to FIG. 6; and

FIG. 8 is an exploded perspective of an alternative embodiment.

FIG. 1 shows a cylinder 1 with a cylinder chamber 2, in which a piston 3 is provided, which is also referred to as a plunger. Because of the difference between the diameter of cylinder chamber 2 and the diameter of plunger 3, an annular gap 4 is created, into which a connecting bore 5 for a hydraulic line (not shown) opens.

The end of cylinder chamber 2 has a slightly expanded diameter, and a guide ring 6, which consists of a low-friction plastic such as polyamide, is inserted into this expansion. Following the expansion is a stepped bore 7, into which a sealing ring 8 is inserted, which is designed as a grooved ring or lip seal as shown.

Following after this stepped bore 7 are in turn two parallel transverse grooves 9, 10, which have a prismatic cross section and which extend crosswise through the entire cylinder 1; that is, they are open at both ends. Each of these transverse grooves 9, 10 is bordered on the side facing the end of cylinder 1 by a retaining shoulder 11, these shoulders being parallel to the associated transverse grooves 9, 10. Together, the shoulders and the grooves form sliding seats.

A sliding body 12 is inserted in the diametral direction into transverse grooves 9, 10, this body having a through-hole 13 for plunger 3. As can be seen in FIG. 1, sliding body 12 forms a support for sealing ring 8, which is subjected to the pressure of the hydraulic fluid, which can be as high as 300 bars, acting in the direction toward the cylinder opening, although this value does not represent a critical upper limit.

As can be seen from FIG. 2, sliding body 12 can be pushed out in either direction as shown by double arrow 14, perpendicular to axis A. In the axial direction, however, sliding body 12 is held reliably in position by transverse grooves 9, 10 and retaining shoulders 11.

As can be seen additionally from FIG. 3, sliding body 12 has a contact surface 15 for sealing ring 8 and, on the opposite side, an annular channel 16 (FIG. 4) inside through-hole 13, for the acceptance of a wiper ring 17. This wiper ring can be reused again if found in good condition; it does not require a metal holder, because sliding body 12 takes over this function as well. As can be derived especially well from FIG. 3, wiper ring 17 is held in all directions by the walls annular channel 16 and by plunger 3; it can be easily pried or rolled out, however, after plunger 3 has been removed.

As can be seen from FIGS. 4 and 5, sliding body 12 has a rectangular outline when seen in the axial direction according to arrow V, and two parallel sliding shoulders 18, 19 are provided on opposite sides of rectangle R. These Shoulders are also prismatic in cross section and are located and designed to fit into transverse grooves 8, 9. As shown in FIGS. 3a and 4a , the shoulders 18, 19 can be configured as dovetails for reception in correspondingly configured grooves 9, 10, which ensures that sliding body 12 is seated with extreme precision.

FIG. 6, furthermore, shows a double cylinder 20 with two cylinder chambers 2a, 2b, which are separated from each other by a partition wall 21. By means of two connecting holes 5a, 5b, the two cylinder chambers 2a, 2b can be actuated independently of each other. Because, in the case of plungers of this type, an external stop is required to limit their stroke, these types of pressure medium drives are frequently, although not exclusively, used for so-called side loaders with a side loading frame 22, the upper part of which as well as plungers 3a, 3b are shown in broken line in FIG. 6. By the alternating actuation of the two plungers 3a, 3b, side loading frame 22 can be shifted in either direction by a distance "s". For example, when plunger 3a is pushed out, plunger 3b is pushed in by the same distance. In any case, however, side loading frame 22, which fulfills the required stop function, prevents plungers 3a and/or 3b from escaping from their cylinders. After side loading frame 2 has been removed, sealing rings 8 and possibly also wiper rings 17 can be replaced as follows:

1. Remove plunger.

2. Push sliding body 12 sideways out of transverse grooves 9, 10.

3. Replace sealing ring 8 and possibly also wiper ring 17.

4. Push sliding body back into place from the side.

5. Reinsert plunger in the axial direction.

The idea of the invention is applicable both to cylinders with rectangular or square outlines (FIG. 7) and to cylinders which have, for example, a cylindrical external surface FIG. 8). In FIGS. 7 and 8, analogous parts are designated by the same reference numbers. In FIG. 8, cylinder 1 according to FIG. 1 is replaced by a cylinder 23 with a cylindrical external surface, the cylinder wall being thick enough to ensure that transverse grooves 9, 10 and sliding shoulders 18, 19 are of sufficient length.