HYDRAULIC DRIVE UNIT FOR A STRETCHER AND STRETCHER WITH A HYDRAULIC DRIVE UNIT

Abstract

A hydraulic drive unit for a stretcher has a hydraulic circuit with a differential cylinder, a pump, a tank and a valve assembly. The differential cylinder includes a rod working chamber and a piston working chamber. The valve assembly is switchable into at least a first state and a second state, wherein the rod working chamber is connected to the tank in the first state and to the pump in the second state, and wherein the piston working chamber is connected to the pump in the first state and to the tank in the second state. The tank is a tank separated from the atmosphere with a variable tank volume, so that the hydraulic circuit is configured as a closed hydraulic circuit. A stretcher having such a hydraulic drive unit is also provided.

Claims

1. A hydraulic drive unit for a stretcher, the drive unit comprising: a hydraulic circuit with a differential cylinder, the differential cylinder having a rod working chamber and a piston working chamber; a pump; a tank; and a valve assembly switchable into at least a first state and a second state, wherein the rod working chamber of the differential cylinder is connected to the tank in the first state and to the pump in the second state, and wherein the piston working chamber of the differential cylinder is connected to the pump in the first state and to the tank in the second state; wherein the tank is a tank separated from atmosphere with a variable tank volume so that the hydraulic circuit is configured as a closed hydraulic circuit.

2. The hydraulic drive unit according to claim 1, wherein the tank is a flexible tank.

3. The hydraulic drive unit according to claim 2, wherein the flexible tank comprises a flexible membrane.

4. The hydraulic drive unit according to claim 3, wherein the flexible membrane is configured as a tank membrane.

5. The hydraulic drive unit according to claim 3, wherein the flexible membrane is configured as a bellows.

6. The hydraulic drive unit according to claim 1, wherein the tank is an elastic tank.

7. The hydraulic drive unit according to claim 1, wherein a maximum tank volume essentially corresponds to a differential volume of the differential cylinder.

8. The hydraulic drive unit according to claim 1, further comprising a rigid hollow body, wherein the tank is disposed within the hollow body.

9. The hydraulic drive unit according to claim 8, wherein the hollow body has a relief to the environment.

10. The hydraulic drive unit according to claim 9, wherein the relief is configured as a bore.

11. A stretcher comprising a hydraulic drive unit according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The invention is explained in more detail below with reference to exemplary embodiments shown in the figures. The figures show schematically:

[0019] FIG. 1 is a hydraulic circuit diagram of a hydraulic drive unit according to the invention;

[0020] FIG. 2 is a perspective view of a hydraulic drive unit according to the invention in accordance with a first embodiment;

[0021] FIG. 3 is a cross section through the hydraulic drive unit shown in FIG. 2 with minimum tank volume;

[0022] FIG. 4 is a cross section through the hydraulic drive unit shown in FIG. 2 with maximum tank volume;

[0023] FIG. 5 is a cross section through a hydraulic drive unit according to a second embodiment; and

[0024] FIG. 6 is a side view of a stretcher according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0025] FIG. 1 shows a hydraulic circuit diagram of a hydraulic drive unit 1 according to the invention for a stretcher 100. The stretcher 100 is described in more detail below with reference to FIG. 6. The drive unit 1 has a differential cylinder 2, a pump 3 driven by a motor M, and a tank 4. The differential cylinder 2 comprises a piston 13 with a piston rod 14, wherein the piston 13 separates a rod working chamber 10 (on the side of the piston rod 14) from a piston working chamber 11.

[0026] Furthermore, the drive unit 1 comprises a valve arrangement with a plurality of valves. The rod working chamber 10 is connected to the pump 3 via a first line arrangement 16 and the piston working chamber 11 is connected to the pump 3 via a second line arrangement 17. A first spring-loaded check valve 5 is disposed in the first line arrangement 16, which opens in the direction of flow from the pump 3 to the rod working chamber 10. A second spring-loaded check valve 6 is disposed in the second line arrangement, which opens in the direction of flow from the pump 3 to the piston working chamber 11. Furthermore, the second check valve 6 is a pilot operated check vale and thus hydraulically openable by a control line 15 branching off from the first line arrangement 16 between the pump and the first check valve 5 and acting on the second check valve 6 in the opening direction. Furthermore, a first return line 18 connected to the tank 3 branches off from the first line arrangement 16 between the first check valve 5 and the rod working chamber 10. A first pressure relief valve 7 is arranged in the first return line 18.

[0027] A third spring-loaded check valve 8 is arranged between the first line arrangement 16 or the pump 3 respectively, and the tank 4, which opens in the direction of flow from the tank 4 to the pump 3. Accordingly, a fourth spring-loaded check valve 9 is arranged between the second line arrangement 17 or the pump 3 respectively, and the tank 4, which also opens in the direction of flow from the tank 4 to the pump 3.

[0028] A second return line 19 connected to the tank 4 branches off between the fourth check valve 9 and the third check valve 6. A second pressure relief valve 20 is arranged in the second return line 19.

[0029] To extend the differential cylinder 2, the pump 3 is controlled in such a way that the second line arrangement 17 is pressurized. The pump 3 draws oil at least partially from the tank 4 via the third (open) check valve 8 and delivers it via the second line arrangement 17 and the (open) second check valve 6 into the piston working chamber 11. The piston 13 thus moves together with the piston rod 14 and forces the oil out of the rod working chamber 10 into the first return line 18. There, the first pressure relief valve 7 opens and the oil can flow off in the direction of the tank 4 or be drawn in again directly via the pump 3. This can also be referred to as the first state of the valve arrangement.

[0030] To retract the differential cylinder 2, the pump 3 is controlled so that the first line arrangement 16 is pressurized. The pressure present in the first line arrangement 16 is signaled via the control line 15 to the second check valve 6, which thus opens. Thus, the oil flowing off from the piston working chamber 11 can be partially sucked back in directly by the pump 3. Since the maximum volume of the rod working chamber 10 when the differential cylinder 2 is fully retracted is smaller than the maximum volume of the piston working chamber 11 when the differential cylinder 2 is fully extended, due to the piston rod 14, the excess differential volume thus formed is directed to the tank 4 via the first return line 18 and the first pressure relief valve 7. This can also be referred to as the second state of the valve arrangement.

[0031] Consequently, the tank 4 is filled when the differential cylinder 2 is retracted and emptied when the differential cylinder 2 is extended. In order to prevent air from being drawn in when the differential cylinder 2 is extended, the tank 4 is configured according to the invention as a tank 4 separated from the atmosphere with a variable tank volume, so that the hydraulic circuit as a whole is configured as a closed hydraulic circuit.

[0032] In the following, two embodiments of the inventive hydraulic drive unit 1 are described with reference to FIGS. 2 to 5, which differ in the design of the tank 4.

[0033] FIGS. 2 to 4 show a first embodiment example of a hydraulic drive unit 1 according to the invention. In this embodiment, the tank 4 is a flexible tank and comprises a flexible membrane configured as a tank membrane 12a. As shown in FIGS. 3 and 4, the tank membrane 12a is disposed within a hollow body 21 configured as a cap. The cap 21 protects the tank membrane 12a from damage. Further, the cap 21 has a relief 22 configured as a bore that connects the interior of the cap 21 to the environment. Here, the bore 22 passes centrally through the cap 21. However, various designs of the relief are possible, for example also a plurality of radial perforations. It should be noted that the cap 21 is not shown in FIG. 2.

[0034] The tank membrane 12a is initially completely folded in when the differential cylinder 2 is fully extended, see FIG. 3. The tank 4 thus has its minimum volume. When the differential cylinder 2 is retracted, oil is fed into the tank 4 as described above and the tank membrane 12a folds out. When the differential cylinder 2 is fully retracted, the differential volume is fully accommodated in the tank 4 and the tank membrane 12a is folded out to its maximum, see FIG. 4. In this example, the tank membrane 12a is configured so that the maximum tank volume is at least equal to the differential volume. Air inside the cap 21 can escape or be sucked in through the relief 22 when the tank membrane 12a is folded in or out. It should be noted that in FIG. 3 the piston rod 14 is only partially shown for clarity reasons.

[0035] FIG. 5 shows a second exemplary embodiment of a hydraulic drive unit 1 according to the invention. The second embodiment differs from the first embodiment shown in FIG. 4 in that the tank 4 comprises a bellows 12b instead of a tank membrane, whereby in FIG. 5 only the maximum tank volume is shown with the bellows 12b fully unfolded and thus with the differential cylinder 2 fully retracted. The bellows 12b is also configured so that the maximum tank volume corresponds at least to the differential volume.

[0036] FIG. 6 shows a side view of a stretcher 100 according to the invention. The stretcher 100 has a patient supporting surface 101, a chassis 102, a scissor jack structure 103, and a hydraulic system 1 described above. The differential cylinder 2 is attached to the scissor jack structure 103 and the chassis 102 such that pressurization of the piston working chamber 11 raises the patient supporting surface 101 relative to the chassis 102. Accordingly, when the rod workspace 10 is pressurized, the patient supporting surface 101 is lowered relative to the chassis 102.

LIST OF REFERENCE CHARACTERS

[0037] 1 hydraulic drive unit [0038] 2 differential cylinder [0039] 3 pump [0040] 4 tank [0041] 5 first check valve [0042] 6 second check valve [0043] 7 first pressure relief valve [0044] 8 third check valve [0045] 9 fourth check valve [0046] 10 rod working chamber [0047] 11 piston working chamber [0048] 12a tank membrane [0049] 12b bellows [0050] 13 piston [0051] 14 piston rod [0052] 15 control line [0053] 16 first line arrangement [0054] 17 second line arrangement [0055] 18 first return line [0056] 19 second return line [0057] 20 second pressure relief valve [0058] 21 hollow body/cap [0059] 22 relief/bore [0060] 100 stretcher [0061] 101 patient supporting surface [0062] 102 chassis [0063] 103 scissor jack structure [0064] M motor