MOBILE STRETCHER

Abstract

In a mobile stretcher, in order to change the height position of a patient support mounted on a chassis, the chassis geometry is modifiable by a hydraulic drive system. The drive system includes a linear actuator, a pressure supply unit, and a receiving space for hydraulic fluid. A manually actuatable unlocking valve unit directly connects a lifting working chamber of the linear actuator to the receiving space. The valve unit has a control space delimited by a piston element movably guided relative to the housing of the valve unit and which communicates with a lifting attachment, which communicates with the working chamber. The piston element is operatively connected to a valve body interacting with a valve seat of a relief valve between the lifting attachment and a tank attachment communicating with the receiving space. A mechanical actuation input acts on the valve body, with a spring element interposed.

Claims

1-13. (canceled)

14. A mobile rescue stretcher, comprising: a chassis having wheels and a chassis geometry; a patient stretcher supported by the chassis; a hydraulic drive system operable to change the chassis geometry in order to change a height of the patient stretcher above the wheels, the hydraulic drive system comprising; a pressure supply unit; a receiving chamber for hydraulic fluid; at least one linear actuator which can be acted upon by the pressure supply unit, the at least one linear actuator having a lifting working chamber; and a manually operable unlocking valve unit for directly connecting the lifting working chamber of the linear actuator with the receiving chamber for hydraulic fluid, the unlocking valve unit comprising; a housing having a lifting connection in communication with the lifting working chamber of the at least one linear actuator and a tank connection in communication with the receiving chamber; a piston element movably guided relative to the housing; a control chamber which is limited by the piston element, the control chamber communicating with the lifting connection; a relief valve formed between the lifting connection and the tank connection of the housing, the relief valve having a valve seat; a valve body cooperating with the relief valve, the piston element being operatively connected to the valve body; a mechanical actuation input operable to act on the valve body; and a spring element interposed between the mechanical actuation input and the valve body.

15. A rescue stretcher according to claim 13, wherein the piston element and the valve body are part of a rigid valve body unit.

16. A rescue stretcher according to claim 13, wherein the control chamber is of annular design and is limited by an annular effective surface of the piston element.

17. A rescue stretcher according to claim 13, wherein the spring element acts on the piston element.

18. A rescue stretcher according to claim 13, further comprising a mechanical stop for the mechanical actuation input, the mechanical stop preventing further movement of the actuation input in a position in which, with the relief valve closed, the capacity of the spring element is not yet exhausted.

19. A rescue stretcher according to claim 13, wherein: the at least one hydraulic actuator further comprises a lowering working chamber; the housing of the valve unit further comprises a lowering connection connected to the lower working chamber; the valve unit further comprising a shut-off valve arranged between the lowering connection and the tank connection and an actuating element coupled to the valve body and which can assume a position in which it opens the shut-off valve.

20. A rescue stretcher according to claim 19, wherein the shut-off valve is designed as a non-return valve with a shut-off direction from the lowering connection to the tank connection.

21. A rescue stretcher according to claim 13, further comprising a closing spring operable to close the relief valve and acting on the valve body.

22. A rescue stretcher according to claim 21, wherein the closing spring is disposed in the control chamber.

23. A rescue stretcher according to claim 13, further comprising a flow throttle disposed between the lifting connection and the tank connection in series with the relief valve.

24. A rescue stretcher according to claim 23, wherein the flow throttle is formed between the valve body and the valve housing.

25. A rescue stretcher according to claim 23, wherein the flow throttle is disposed between the control chamber and the relief valve.

26. A rescue stretcher according to claim 13, wherein the linear actuator has a pressure relief which is effective at the lifting working chamber of the linear actuator at its maximum volume.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In the following, the present invention is explained in more detail by means of a preferred embodiment illustrated in the drawing. Therein

[0017] FIG. 1 is a view of a mobile rescue stretcher with a hydraulic drive system for changing the height of the patient stretcher, illustrated with regard to its basic construction;

[0018] FIG. 2 is a circuit diagram of the hydraulic system of the rescue stretcher according to FIG. 1; and

[0019] FIG. 3 is a sectional view through the unlocking valve unit used with the hydraulic system according to FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The mobile rescue stretcher 1 illustrated in FIG. 1—in its fully erected configuration—which is used in particular for the transport of sick or injured persons (patients) in ambulance vehicles, comprises in a manner known as such a mobile rescue stretcher 1 a chassis 3 with four wheels 2 and a patient stretcher 4 supported by this chassis 3. In order to change the height H of the patient stretcher 4 above the wheels 2, the geometry of the chassis 3 comprising a base frame B and a scissors-type lifting structure S can be changed by means of a hydraulic drive system 5, which comprises an receiving chamber 6 for hydraulic fluid, a pressure supply unit 7 and at least one linear actuator 8 which can be acted upon by the pressure supply unit 7 and is effective between the base frame B and the scissors-type lifting structure S. The linear actuator 8 is formed as a double-acting differential cylinder 9. The double-acting differential cylinder 9 is installed in such a way that the piston working chamber 10 forms the lifting working chamber 11, that means that pressurization of the piston working chamber 10 acts in the sense of lifting the patient stretcher 4.

[0021] Conversely, the piston rod working chamber 12 forms the lowering working chamber 13, that means pressurization of the piston rod working chamber 12 has the effect of lowering the patient stretcher 4. To this extent the rescue stretcher 1 corresponds to the sufficiently known state of the art, so that further explanations are not necessary.

[0022] The hydraulic system, the other details of which—which can be readily seen in FIG. 2—are not important for the present invention beyond the following explanations, further comprises a manually operable unlocking valve unit 14. The manually operable unlocking valve unit 14 is suitable for establishing a direct fluidic connection of the lifting working chamber 11 and the lowering working chamber 13 of the linear actuator 8 with each other as well as with the receiving chamber 6 for hydraulic fluid, that means for providing a pressure equalization between lifting working chamber 11, lowering working chamber 13 and receiving chamber 6 for hydraulic fluid. From a functional point of view, the unlocking valve unit 14 comprises a relief valve 16—formed as a seat valve 15—which is arranged in a flow path 17 extending from the lifting working chamber 11 to the receiving chamber 6, as well as a shut-off valve 19—formed as a pilot-operated non-return valve 18—which is arranged in a flow path 20 extending from the lowering working chamber 13 to the receiving chamber 6.

[0023] The configuration of the unlocking valve unit 14 is illustrated in FIG. 3. It comprises a housing 21 with a receiving bore 22 for receiving the valve internals, into which three connections open, namely a lifting connection 23 communicating with the lifting working chamber 11, a lowering connection 24 communicating with the lowering working chamber 13 and a tank connection 25 communicating with the receiving chamber 6.

[0024] Between the openings of the lifting connection 23 and the tank connection 25, a valve seat 26 of the relief valve 16 is formed in the receiving bore 22. A valve body 27, which can be moved along the axis A in the receiving bore 22, interacts with the valve seat 26. The lifting connection 23 opens into an annular control chamber 28, which is limited radially outside by the housing 21 and radially inside by the valve body 27 and is axially limited on the one hand by a collar 29, in which the valve body 27 is guided, and on the other hand by a piston element 30, which is mounted on the valve body 27 and has an annular piston 31 guided sealingly in the receiving bore 22. A closing spring 32 is arranged in the control chamber 28, which is supported on the collar 29 and—in the area of its annular hydraulically effective surface 33—acts on the piston element 30 (and thus indirectly on the valve body 27, with which the piston element 30 is rigidly connected to form a rigid valve body unit 34) in the sense of closing the relief valve 16.

[0025] The unlocking valve unit 14 also has a mechanical actuation input 35 in the form of a plunger 36 which can be moved along the axis A in the receiving bore 22. The plunger 36 is approximately cup-shaped with an actuating pin 38 projecting from the base 37, onto which a lever 39 acts, which in turn can be coupled, for example, via a Bowden cable with an unlocking handle. A spring element 40 is interposed between the plunger 36 and the valve body unit 34, so that the plunger 36 can only act on the valve body unit 34 via the spring element 40. The spring element 40 is formed as a coil spring 41, which extends between the bottom 37 of the plunger 36 and the piston element 30 of the valve body unit 34. A step 42 formed in the receiving bore 22 represents a mechanical stop 43 for the plunger 36, which limits the movement path of the plunger 36 in a position in which the compression capability (capacity) of the coil spring 41 is not yet exhausted.

[0026] A valve insert 45 is also located in the receiving bore 22, adjacent to the plug 44 inserted at the front. This valve insert 45 contains the check valve 18, which is the above-mentioned shut-off valve 19 located between tank connection 25 and lowering connection 24.

[0027] The check valve 18 blocks the flow direction from the lowering connection 24 to the tank connection 25. It can be mechanically unlocked. For this purpose, the valve body 27 comprises an actuating element 46 in the form of an unlocking pin 49 which—if the valve body 27 is in the appropriate position—acts on the valve ball 47 and lifts it off the seat 48. If there is such a pressure in control chamber 28—which is above a predetermined pressure level—that the hydraulic force exerted on the piston element 30 is greater than the force transmittable by the coil spring 41, pressing in the plunger 36 causes the coil spring 41 to be compressed. The valve body unit 34 does not move and the relief valve 16 remains closed, as does the shut-off valve 19. If, however, there is such a pressure in control chamber 28—which is below a predetermined pressure level—that the hydraulic force exerted on the piston element 30 is less than the force that can be transmitted by the coil spring 41, pressing in the plunger 36 causes the valve body unit 34 to move and consequently the relief valve 16 and the shut-off valve 19 to open. The fluidic connection between the lifting connection 23 and the tank connection 25 is established via a flow throttle 50 arranged in series with the relief valve 16, which is formed by several ring sections in the area of the collar 29 between the valve body 27 and the valve housing 21.