Mobile rescue stretcher and hydraulic system for a mobile rescue stretcher

Abstract

The invention relates to a hydraulic system 1 for a mobile rescue stretcher, having a hydraulic cylinder 2, a tank 3 and a pump 4. The hydraulic cylinder 2 comprises a piston 5 with a piston rod 6, a first working chamber 7 and a second working chamber 8. The first working chamber 7 is connected to the pump 4 via a first line device 9, and the second working chamber 8 is connected to the pump 4 via a second line device 10. Furthermore, the invention relates to a mobile rescue stretcher having such a hydraulic system 1.

Description

[0001] This invention relates to a hydraulic system for a mobile rescue stretcher, the hydraulic system comprising a hydraulic cylinder, a tank, and a pump. Furthermore, this invention also relates to a mobile rescue stretcher having such a hydraulic system.

[0002] A hydraulic cylinder typically includes a piston with at least one piston rod, a first working chamber, and a second working chamber, the second working chamber being separated from the first working chamber by the piston. The first working chamber is typically the piston working chamber, and the second working chamber is typically the piston rod working chamber.

[0003] The first chamber is connected to the pump via a first piping connection, and the second chamber is connected to the pump via a second piping connection. Depending on whether the hydraulic cylinder is retracted or extended, the first chamber can be pressurized by the pump via the first piping connection, or the second chamber can be pressurized by the pump via the second piping connection. When pressure is applied to the second chamber, hydraulic fluid can flow out of the first chamber via the first piping connection, which has a first check valve that opens when pressure is applied to the second piping connection. When pressure is applied to the first chamber, hydraulic fluid flows out of the second chamber via the second piping connection. The hydraulic fluid flowing out of the chamber flows to a tank or is directly drawn back into the pump.

[0004] In mobile rescue stretchers, these hydraulic systems are used to change the height of the patient support relative to the stretcher's base. Typically, such rescue stretchers have a scissor jack structure, one end of which is connected to the patient support and the other end to the base. To change the height of the patient support, hydraulic cylinders extend or retract accordingly. Such rescue stretchers are known, for example, in WO 2019 / 201579 A1.

[0005] However, a drawback of the known solution is that if the additional force acts in the retraction direction of the hydraulic cylinder, the first check valve may become "stuck" when the cylinder retracts. This condition is referred to below as traction load and can be caused, for example, by a patient lying on a patient support.

[0006] When the hydraulic cylinder retracts, pressure is applied to the second piping system and consequently to the second working chamber (i.e., the piston rod working chamber), creating a control pressure that opens the first check valve. The amount of hydraulic fluid discharged from the first working chamber (i.e., the piston working chamber) is greater than the amount to be delivered to the second working chamber, so only a portion of the discharged hydraulic fluid is directly returned to the second working chamber. The excess fluid must be removed from the hydraulic circuit and sent to a tank. However, due to the traction load, the subsequent pump flow rate may no longer be sufficient to deliver the required amount of hydraulic fluid to the second working chamber. This weakens the control pressure applied to the first check valve, causing it to close. The retraction motion of the hydraulic cylinder then stops. Once sufficient back pressure is established, the pump flow rate becomes sufficient again, and the control pressure is restored. The first check valve reopens, and the hydraulic cylinder continues to retract. However, because the traction load is still in effect, the control pressure weakens rapidly again, and the first check valve closes once more.

[0007] This jamming of the first check valve can damage the check valve seat and cause the entire hydraulic system to vibrate. Furthermore, it can cause discomfort to the operator and patient.

[0008] To prevent this, the nozzle can be integrated into the first piping assembly to reduce the retraction speed of the hydraulic cylinder. Figure 1 An exemplary hydraulic circuit diagram is shown in the figure.

[0009] Hydraulic system 101 includes hydraulic cylinder 102, tank 103, and pump 104. Hydraulic cylinder 102 includes piston 105 with piston rod 106 that space a first working chamber 107 from a second working chamber 108. Hereinafter, the first working chamber 107 is the piston working chamber, and the second working chamber 108 is the piston rod working chamber. Piston rod 106 is connected to a patient support (not shown) to change the height of the patient support relative to a base frame (not shown). Piston working chamber 107 may be selectively connected to pump 104 or tank 103 via a first conduit 109. Therefore, piston rod working chamber 108 may also be connected to pump 104 or tank 103 via a second conduit 110. As shown, the connections between conduits 109, 110 and tank 103 or pump 104 are achieved via corresponding valves, but other options are also conceivable, such as those known in WO 2019 / 201579 A1.

[0010] Furthermore, a first check valve 111 is disposed in the first piping assembly 109, and a second check valve 112 is disposed in the second piping assembly 110. The first check valve 111 is connected to the second piping assembly 110 via a first control line 113, and the second check valve 112 is connected to the first piping assembly 109 via a second control line 114, such that when pressure is applied to the respective piping assemblies 109 and 110, the corresponding check valves 111 and 112 open. For example, if pressure is applied to the second piping assembly 110 to retract the hydraulic cylinder 102, the pressure in the second piping assembly 110 is signaled to the first check valve 111 via the first control line 113, thereby opening the check valve 111. Therefore, the hydraulic fluid from the piston chamber 107 can flow out to the tank 103 via the first piping assembly 109. Additionally, a nozzle 115 is disposed in the first piping assembly 109 between the first check valve 111 and the piston chamber 107. The nozzle 115 limits the fluid volume, thereby limiting the retraction speed of the hydraulic cylinder 102.

[0011] refer to Figure 1 The described solution effectively prevents the first check valve from jamming. However, the nozzle 115 functions during both the retraction and extension of the hydraulic cylinder 102. In other words, the nozzle functions not only when the patient is lying on the patient support (so-called "low load") and when the support is lowered, but also when the underframe retracts rapidly (e.g., when the patient support is connected to the ambulance) (so-called "retraction"). This consumes unnecessary energy, generates heat, and slows down the retraction process.

[0012] In light of this, the object of the present invention is to provide a hydraulic system for a mobile rescue stretcher, wherein, when a traction load is present, the check valve can be effectively prevented from jamming without limiting the function of the rescue stretcher.

[0013] This problem can be solved by the hydraulic system according to claim 1. Preferred embodiments are described in the dependent claims.

[0014] The hydraulic system according to the invention is characterized by a scheme known in the prior art, particularly the second piping assembly comprising a first branch line and a second branch line. The first branch line is connected to a pump, and the second branch line is connected to a tank. According to the invention, a pressure valve is disposed in the second branch line, which opens when pressure is applied to the second piping assembly via the pump, thereby limiting the pressure in the second piping assembly to a level sufficient to open the first check valve. The pressure valve is preferably a pressure reducing valve, and preferably opens at a pressure of up to 100 bar, particularly at a pressure of up to 75 bar.

[0015] Therefore, the pressure in the second piping system is limited to the set pressure of the pressure valve, which is lower than the pump pressure. This limited pressure is sufficient to open the first check valve. Simultaneously, excess liquid can flow through the pressure valve to the tank, thus removing it from the circuit. Therefore, even under traction loads, the control pressure applied to the first check valve does not decrease, preventing it from jamming. This also allows for sufficient speed during retraction and lower load periods.

[0016] Preferably, as seen in the flow direction from the pump to the hydraulic cylinder, the second check valve is disposed in the first branch line, and the second branch line branches off from the second line assembly downstream of the second check valve. When the hydraulic cylinder extends, the second check valve releases the piston rod working chamber into the tank via the pressure valve.

[0017] Preferably, the second piping assembly includes a third branch line, which is connected to the tank and branches off from the first branch line. According to the invention, a nozzle is disposed in the third branch line. This nozzle ensures that the control pressure used to open the first check valve is released when the hydraulic cylinder stops retracting and the first check valve is safely closed. This effectively prevents the patient stent from sinking.

[0018] Preferably, the third branch line includes a bypass line that uses a fourth check valve bypass nozzle disposed in the third branch line. This allows a larger volume of hydraulic fluid to be pumped from the tank when the first chamber is pressurized.

[0019] Preferably, the first piping assembly includes a fourth branch line connected to the tank, and the fourth check valve can open when the second piping assembly located in the fourth branch line is pressurized. In this document, it is particularly advantageous if the hydraulic resistor (specifically, a nozzle) is located in the fourth branch line upstream of the fourth check valve in the flow direction from the first working chamber to the tank. This ensures that a portion of the excess liquid is directly delivered to the tank. Consequently, overall power consumption can be reduced because the entire excess liquid does not need to flow to the tank via a pressure valve.

[0020] Furthermore, this problem can be solved by the mobile rescue stretcher according to claim 10. According to the invention, the rescue stretcher has the aforementioned hydraulic system.

[0021] The invention will now be described in more detail with reference to the accompanying drawings. Hereinafter, it is shown schematically:

[0022] Figure 1 The hydraulic circuit diagram of the hydraulic system known in the prior art is shown above;

[0023] Figure 2 A hydraulic circuit diagram of a hydraulic system provided according to the present invention is shown;

[0024] Figure 3 A side view of a rescue stretcher with a hydraulic system provided according to the present invention is shown.

[0025] Figure 2 A hydraulic circuit diagram of a hydraulic system 1 for a mobile rescue stretcher 50 according to the present invention is shown. (Refer to below) Figure 3 The rescue stretcher 50 is described in more detail. The hydraulic system 1 includes a hydraulic cylinder 2, a tank 3, and a pump 4. In this exemplary embodiment, the tank 3 is configured as a hydraulic accumulator, but other configurations are also possible, such as... Figure 1 As shown.

[0026] The hydraulic cylinder 2 includes a piston 5 with a piston rod 6, which separates a first working chamber 7 from a second working chamber 8. In this exemplary embodiment, the first working chamber 7 is the piston working chamber, and the second working chamber 8 is the piston rod working chamber. The piston working chamber 7 is connected to a pump 4 via a first conduit 9, and the piston rod working chamber 8 is connected to the pump 4 via a second conduit 10. The pump 4 is configured to pressurize the piston working chamber 7 via the first conduit 9 or the piston rod working chamber 8 via the second conduit 10. Therefore, unpressurized hydraulic fluid from the respective other working chamber 7, 8 flows out via the respective conduits 9, 10.

[0027] Therefore, the hydraulic system 1 includes a first check valve 11 disposed in a first piping assembly. The first check valve 11 is configured as a spring-loaded check valve and is connected to the second piping assembly 10 via a first control line 23, such that the first check valve 11 opens when pressure is applied to the second piping assembly 10 or the piston rod chamber 8 to retract the hydraulic cylinder 2. Thus, hydraulic fluid discharged from the piston chamber 7 can be directly and at least partially drawn in via the first piping assembly 9 and the pump 4.

[0028] Because of the piston rod 6, when the hydraulic cylinder 2 retracts as described above, not all the hydraulic fluid in the piston chamber 7 can be directly pumped into the piston rod chamber 8. To remove excess hydraulic fluid from the circuit, the second piping assembly 10 includes a first branch line 13 and a second branch line 14. The first branch line 13 is connected to the pump 4, and a second check valve 12 is disposed in the first branch line 13. In this exemplary embodiment, the second check valve 12 is also configured as a spring-loaded check valve. In the flow direction from the pump 4 to the piston rod chamber 8, the second branch line 14 branches downstream of the second check valve 12. The first control line 23 branches upstream of the second check valve 12.

[0029] The second branch line 14 connects to the tank, and a pressure valve 15, configured as a pressure reducing valve, is located in the second branch line 14. The pressure reducing valve 15 limits the pressure in the second line assembly 10 to a maximum of 100 bar, specifically a maximum of 75 bar. This pressure is sufficient to open the first check valve 11 via the first control line 23. Simultaneously, when the hydraulic cylinder 2 retracts, excess hydraulic fluid is delivered to the tank via the pressure reducing valve 15. This prevents the first check valve 11 from jamming due to the reduced control pressure in the first control line 23.

[0030] To prevent sinking when the hydraulic cylinder 2 stops retracting, the second piping assembly 10 includes a third branch line 16, which branches off from the first branch line 13 between the pump 3 and the second check valve 12 and connects to the tank 3. A nozzle 17 is disposed in the third branch line 16. A smaller nozzle 17 is selected. When the hydraulic cylinder stops retracting, the second check valve 12 closes, and residual pressure remains between the pump 4 and the second check valve 12. The residual pressure present in the second piping assembly 9 and signaled via the first control line 23 can now be safely released via the nozzle 17, allowing the first check valve 11 to close safely, thereby preventing further movement of the hydraulic cylinder 2.

[0031] Furthermore, the third branch line 16 has a bypass pipe 18, which uses a third check valve 19 to bypass the nozzle 17. This third check valve is also configured as a spring-loaded check valve. When the first pipeline assembly 9 is pressurized to extend the hydraulic cylinder 2, hydraulic fluid can be drawn directly from the tank 3 via the third branch line 16 and the bypass pipe 18.

[0032] The first piping assembly 9 includes a fourth branch line 20 connected to the tank 3. The fourth branch line 20 branches in the flow direction from the pump 3 to the piston chamber 7 downstream of the first check valve 11. The fourth check valve 21, also configured as a spring-loaded check valve, is disposed in the fourth branch line 20 and connected to the second piping assembly 10 via a second control line 24, such that the fourth check valve 21 opens when the second piping assembly 10 is pressurized. The second control line 24 branches from either the second piping assembly 10 between the pump 3 and the second check valve 12 or the first branch line 13. A nozzle-type hydraulic resistor 22 is disposed upstream of the fourth check valve 21. This allows a defined portion of the hydraulic fluid discharged from the piston chamber 7 to be drawn out of the circuit when the hydraulic cylinder 2 retracts. This enables a faster overall retraction of the hydraulic cylinder 2.

[0033] As shown in the figure, the hydraulic system 1 has a manually operable safety valve 25, which directly connects the piston chamber 7 and the piston rod chamber 8 to the tank 3. To prevent unobstructed sinking when the safety valve 25 is actuated, a nozzle 26 is positioned between the piston rod chamber 8 and the safety valve 25.

[0034] Furthermore, the hydraulic system 1 includes a safety pressure reducing valve 27 that connects the first piping assembly 9 to the tank 3. The safety pressure reducing valve 27 has a set pressure greater than 200 bar and prevents damage to the hydraulic system 1 should the hydraulic cylinder 2 be obstructed from the outside or moved to its stop. Additionally, the pressure may increase due to factors such as temperature or solar radiation. The hydraulic system 1 also has an optional external connection 28 and optionally includes a pressure gauge 29.

[0035] The hydraulic system 1 also includes a suction device 30, through which the pump 4 can directly draw hydraulic fluid from the tank 3. The figure shows a configuration with two spring-loaded check valves, but other configurations, such as those with directional valves, are also possible.

[0036] Figure 3 A side view of a mobile rescue stretcher 50 provided according to the present invention is shown. The rescue stretcher 50 has a patient support 51, a base frame 52, a scissor jack structure 53, and a hydraulic system 1 as described above. A hydraulic cylinder 2 is connected to the scissor jack structure 53 and the base frame 52, such that pressurization of the first conduit 9 and therefore the piston chamber 7 raises the patient support 51 relative to the base frame 52. Thus, when the second conduit 10 and the piston rod chamber 8 are pressurized, the patient support 51 descends relative to the base frame 52.

[0037] The lifting of the patient stent 51 is described below. For this purpose, pump 4 is controlled by pressurizing via the first piping device 9. This opens the first check valve 11, allowing hydraulic fluid to flow into the piston chamber 7, and the hydraulic cylinder 2 extends. Hydraulic fluid discharged from the piston rod chamber 8 can flow into the tank 3 via the second piping device 10 and the second branch line 14 because the pressure exceeds the set pressure of the pressure reducing valve 15, and the pressure reducing valve 15 therefore opens. Pump 3 draws hydraulic fluid from the tank 3 via the fourth branch line 16 and the bypass line 18, and via the suction device 30. Once the desired height of the patient stent 51 is reached, pump 3 is shut off, and the position of the hydraulic cylinder 2 is maintained via the first check valve 11 and the fourth check valve 21.

[0038] To lower the patient stent 51, the control pump 4 pressurizes the second tubing assembly 10. Control pressure, signaled via the first control line 23 and the second control line 24, controls the opening of the first check valve 11 and the fourth check valve 21. Therefore, hydraulic fluid discharged from the piston chamber 7 can be directly drawn back by the pump 4, or partially discharged into the tank 3 via the fourth branch line 20. Due to the pressure in the second tubing assembly 10 or the first branch line 13, the second check valve 12 opens, allowing hydraulic fluid to flow into the piston rod chamber 8. Excess hydraulic fluid flowing out of the piston chamber 7 is delivered to the tank 3 via the pressure reducing valve 15, and the pressure in the second tubing assembly 9 is limited to the set pressure of the pressure reducing valve 15.

[0039] Once the desired height of the patient stent 51 is reached, pump 4 is stopped. The second check valve 12 closes, and the control pressure in the first control line 23 and the second control line 24 is released into the tank 3 via the third branch line 16 and the nozzle 17. Therefore, the first check valve 11 and the fourth check valve 21 are closed, and the position of the patient stent 51 is maintained.

[0040] The above description of the functions of the mobile rescue stretcher 50 also applies accordingly to the rapid retraction (“retraction”) or extension (“extension”) of the base frame 51, i.e., to situations where no patient is accommodated on the patient support 51. This is necessary, for example, when the patient support 51 is to be connected to or removed from an ambulance.

[0041] List of reference numerals

[0042] 1. Hydraulic System

[0043] 2 Hydraulic cylinders

[0044] 3 cans

[0045] 4 pumps

[0046] 5 pistons

[0047] 6 Piston rod

[0048] 7 First Studio / Piston Studio

[0049] 8 Second Studio / Piston Rod Studio

[0050] 9 First Piping Unit

[0051] 10 Second Piping Device

[0052] 11 First check valve

[0053] 12 Second check valve

[0054] 13 First branch pipeline

[0055] 14 Second branch pipeline

[0056] 15 Pressure valve / pressure reducing valve

[0057] 16 Third branch pipeline

[0058] 17 Nozzles

[0059] 18 Bypass pipe

[0060] 19 Third check valve

[0061] 20 Fourth branch pipeline

[0062] 21 Fourth check valve

[0063] 22 Hydraulic resistors / nozzles

[0064] 23 First control line

[0065] 24 Second control line

[0066] 25 Safety valve

[0067] 26 nozzles

[0068] 27 Safety pressure reducing valve

[0069] 28 External Connections

[0070] 29. Pressure gauge

[0071] 30 Suction Device

[0072] 50 rescue stretchers

[0073] 51 bracket

[0074] 52 base frame

[0075] 53. Scissor jack structure

[0076] 101 Hydraulic System

[0077] 102 Hydraulic Cylinder

[0078] 103 cans

[0079] 104 pump

[0080] 105 Piston

[0081] 106 Piston Rod

[0082] 107 First Studio / Piston Studio

[0083] 108 Second Studio / Piston Rod Studio

[0084] 109 First Piping Unit

[0085] 110 Second Piping Unit

[0086] 111 First check valve

[0087] 112 Second check valve

[0088] 113 First control line

[0089] 114 Second control line

[0090] 115 nozzle

Claims

1. Hydraulic system (1) for a mobile rescue stretcher (50), the hydraulic system (1) having a hydraulic cylinder (2), a tank (3) and a pump (4), the hydraulic cylinder (2) comprising a piston (5) with at least one piston rod (6), a first working chamber (7) and a second working chamber (8), the second working chamber (8) being separated from the first working chamber (7) by the piston (5), the first working chamber (7) being connected to the pump (4) via a first line device (9), the second working chamber (8) being connected to the pump (4) via a second line device (10), the first working chamber (7) being pressurized by the pump (4) via the first line device (9) or the second working chamber (8) being pressurized by the pump (4) via the second line device (10), hydraulic liquid flowing out of the first working chamber (7) via the first line device (9) when pressure is applied to the second working chamber (8), wherein the first line device (9) comprises a first non-return valve (11) which opens when pressure is applied to the second line device (10); hydraulic liquid flowing out of the second working chamber (8) via the second line device (10) when the first working chamber (7) is pressurized, characterized in that the second line device (10) comprises a first branch line (13) connected to the pump (4) and a second branch line (14) connected to the tank (3), a pressure valve (15) being arranged in the second branch line (14) and opening when pressure is applied to the second line device (10) such that the pressure in the second line device (10) is limited to a pressure sufficient to open the first non-return valve (11); the pressure in the second line device (10) is limited to a pressure set at the pressure valve (15), excess hydraulic liquid from the first working chamber (7) is directed to the tank (3) through the pressure valve (15) when the pressure set at the pressure valve (15) is lower than the pump pressure and the pump (4) pressurizes the second working chamber (8) through the second line device (10); wherein a second non-return valve (12) is arranged in the first branch line (13) so that the pressure of the second line device (10) is released through the pressure valve (15) to the tank (3) when the hydraulic cylinder (2) is extended.

2. Hydraulic system (1) according to claim 1, characterized in that the pressure valve (15) is a pressure relief valve.

3. Hydraulic system (1) according to claim 1 or 2, characterized in that the pressure valve (15) opens at a pressure of at most 100 bar.

4. Hydraulic system (1) according to claim 1, characterized in that the second line device (10) comprises a third branch line (16) connected to the tank (3), the third branch line (16) branching off from the first branch line (13) and a nozzle (17) being arranged in the third branch line (16).

5. Hydraulic system (1) according to claim 4, characterized in that The third branch line (16) comprises a bypass pipe (18) which bypasses the nozzle (17), wherein a third non-return valve (19) is arranged in the bypass pipe (18).

6. Hydraulic system (1) according to claim 1, characterized in that The first line arrangement (9) comprises a fourth branch line (20) which is connected to the tank (3), wherein a fourth non-return valve (21) opens when pressure is applied to the second line arrangement (10) arranged in the fourth branch line (20).

7. Hydraulic system (1) according to claim 6, characterized in that A hydraulic resistor (22) is arranged in the fourth branch line (20), wherein the hydraulic resistor (22) is in particular a nozzle.

8. Hydraulic system (1) according to claim 7, characterized in that The hydraulic resistor (22) is arranged upstream of the fourth non-return valve (21) in the fourth branch line (20) in the flow direction from the first working chamber (7) to the tank (3).

9. Mobile rescue stretcher (50) with a hydraulic system (1) according to any one of the preceding claims.

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