Method and system for transferring hydraulic power between pump and actuator

Abstract

Methods and systems for transferring hydraulic power between a pump and an actuator. The actuator (3, 13) has an inlet (7) and an outlet (8) for hydraulic fluid, an actuator circuit between the inlet and the outlet and outside the actuator, in which the hydraulic fluid circulates from the outlet (8) to the inlet (7). The pulse pump (1) is used to generate a pressure pulse of a desired frequency and to transmit hydraulic power to the actuator (3, 13) by means of the pressure pulse by converting the pressure pulse into a flow to the inlet (7) of the actuator. The return flows from the actuators are returned during cycles between the pressure pulses for use in the pressure pulses following each return flow, whereby an amount of hydraulic fluid corresponding to the volume of the pressure pulses moves back and forth across the cross-sectional flow region in the power transfer conduit or hose (2) between the pulse pump (1) and the actuators (3, 13).

Description

Technical Field

[0001] The object of the present invention is a method and a system for transmitting hydraulic power between a pump and an actuator, the actuator having an inlet and an outlet for the hydraulic fluid and an actuator circuit between the inlet and the outlet and outside the actuator, in which the hydraulic fluid circulates under the pressure generated by the pump. Background Art

[0002] In conventional hydraulic systems, the goal is to maintain laminar flow in pipelines to avoid losses. For example, if the pressure in the pipeline is between 160 and 400 bar, the recommended maximum velocity of the fluid in the pipeline is 7 m / s. Conventional hydraulic systems require valve blocks to distribute oil to the various actuators, requiring large oil tanks and large coolers due to heat generation caused by pipeline resistance and flow regulation. Each pump in the system typically has multiple actuators, each with specific pressure and volume flow requirements that vary continuously during operation. If even one actuator requires high pressure, the pump must produce it, even if the others require lower pressure. If multiple actuators require high flow, and the pump output is insufficient for all of them, the system regulates a limited flow rate for all actuators. If the total power required by the actuators exceeds the total power of the pump, the system distributes the available power according to the specified settings. Overall, this regulation causes losses and therefore requires selecting a higher-powered pump when practical. Summary of the Invention

[0003] The object of the present invention is to provide a method and system operating on a principle that is substantially different from that of conventional hydraulic systems, whereby the total power requirement of the power system is minimized, since each actuator circuit operates completely independently and does not affect the operation of the other actuator circuits and the system in any way other than through power requirements, and the manufacturing costs are kept low compared to conventional systems, since the aforementioned valve blocks, large oil tanks, and large coolers are not required. Furthermore, fewer hydraulic lines or hoses are required compared to conventional systems.

[0004] This object is achieved by the present invention with the method disclosed in the appended claim 1 and the system disclosed in claim 11. Advantageous embodiments of the invention are disclosed in the independent claims.

[0005] In the present invention it has been recognized that hydraulic power is transmitted to the actuator by means of pressure pulses and by converting the pressure pulses into a flow into the actuator, whereby only an amount of hydraulic fluid corresponding to the volume of the pressure pulses moves back and forth in the power transmission conduit or hose. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] In the following, the invention is explained by way of a number of examples with reference to the accompanying drawings, in which:

[0007] Figure 1 shows a hydraulic diagram of a system according to an embodiment of the invention, in which the pressure pulses generated by a pulse pump 1 are converted in an actuator circuit connected to an actuator 3 into a flow towards the inlet 7 of the actuator;

[0008] Figure 2 Shown with Figure 1 The same otherwise, but between the pulse pump 1 and the actuator circuit connected to the actuator 3 there is connected a power transmission unit 11 which transmits the pressure pulses, this power transmission unit 11 also receiving the return flow from the actuator circuit and thus separating the actuator circuit from the power transmission pipe or hose 2; and

[0009] Figure 3 1 shows a hydraulic diagram of a system according to another embodiment of the present invention, wherein the actuator 13 is a piston-cylinder device whose operation is controlled by a directional valve 14. In addition, the diagram shows the corresponding Figure 2 The power transmission unit in the power transmission unit 11. DETAILED DESCRIPTION

[0010] In the method of the present invention, a pulse pump 1 is used to generate pressure pulses at a desired frequency. Hydraulic power is transmitted to the actuators 3, 13 via the pressure pulses by converting the pressure pulses into a flow that enters the actuator's inlet 7. Return flow from the actuators returns during the periods between the pressure pulses to be used in the pressure pulse following each return flow. An amount of hydraulic fluid corresponding to the volume of the pressure pulses is then moved back and forth across the cross-sectional flow area in a power transmission conduit or hose 2 located between the pulse pump 1 and the actuators 3, 13, which may also be referred to hereinafter as a pulse conduit.

[0011] The term pulse pump refers to any device or pulse generator that can generate pressure pulses in a fluid with a desired pulse frequency, desired stroke speed, and desired pulse size. A simple pulse pump is a piston that moves back and forth in a cylindrical space. The stroke motion of the piston can be generated by a cam on a rotating shaft, and the return motion can be generated by a spring. Multiple cams with corresponding pistons can be attached to the same shaft, allowing a single pulse pump or pulse generator to use multiple actuators by supplying pressure pulses to multiple power transmission pipes or hoses.

[0012] In accordance with Figure 1-Figure 3In the system, a pulse pump 1 is used to generate pressure pulses, which are used to generate a flow of hydraulic fluid to the inlet 7 of the actuators 3 and 13. The pulse pump 1 generates repetitive pressure pulses in the hydraulic fluid. The pressure pulses and components in the actuator circuit cause the hydraulic fluid to move back and forth in the power transmission pipes or hoses 2 between the pulse pump 1 and the actuators 3 and 13. Therefore, the power transmission pressure pulses and the return flow between them travel successively in opposite directions in the same pipes or hoses 2.

[0013] The hydraulic fluid returns during the return flow period from the outlet of the actuator 8 to the connecting channel 7b connected to the inlet 7 of the actuator. In this connecting channel 7b, the hydraulic fluid flows back and forth due to the alternation of pressure pulses and return flow.

[0014] exist Figure 1 and Figure 2 In the embodiment of FIG. 1 , the actuator 3 is a hydraulic motor having an external actuator circuit 9, 10, 7b, 4, 5, 6 between the outlet 8 and the inlet 7, wherein the hydraulic fluid that has passed through the motor is circulated by the pressure of the pressure pulses. The external actuator circuit is divided into a return flow circuit 9, 10 and a pressure circuit 4, 5, 6, which have a common connection channel 7b, through which the actuator circuit is connected to the power transmission pipe or hose 2 ( Figure 1 ) or connected to the power transmission unit 11 ( Figure 2 ), which will be explained below.

[0015] The outlet 8 of the actuator is connected to a pre-charged pressure accumulator 9 and, furthermore, via a non-return valve 10 to the inlet of the non-return valve 4 , the inlet of which is connected to the inlet 7 of the actuator.

[0016] The non-return valves 4 , 10 of the actuator circuit then ensure that the hydraulic fluid circulates from the outlet 8 of the actuator to its inlet 7 , while a portion of the hydraulic fluid of the actuator circuit with the size of the pressure pulses moves back and forth in the connecting channel 7 b at the pulse frequency.

[0017] Figure 3 The embodiment of differs from this in that the actuator is a piston-cylinder device 13, and the actuator circuit is connected to the piston-cylinder device 13 via a directional valve 14. The directional valve 14 can be used to control the direction of movement of the piston 13a. Figure 3, the piston 13a is connected in a stationary manner. The actuator circuit comprises a pressure circuit 4, 7a and a return circuit 8a, 9, 10 and a connecting channel 7b shared with them, via which the actuator circuit is connected to the power transmission unit 11. Here too, the non-return valves 4, 10 of the actuator circuit ensure that the hydraulic fluid circulates in the actuator circuit from the outlet 8 of the actuator 13 to its inlet 7. Not shown in the figure are chokes or other components that may need to be used. The accumulator 9 must be able to accommodate the fluid volume of the pressure pulse + the amount of fluid displaced by the piston rod. The entire system must be filled with hydraulic fluid in the initial stage. A small pre-pressure is charged into the accumulator 9, by means of which the fluid volume of the pressure pulse is returned to the connecting channel 7b. The hydraulic fluid can be oil.

[0018] exist Figures 1 to 3 In the embodiment of the embodiment, the hydraulic fluid returning from the outlet 8 of the actuator 3, 13 is directed to a pre-pressurized accumulator 9, which returns the hydraulic fluid through a non-return valve 10 to the connecting channel 7b connected to the inlet 7 of the actuator when the pressure in the hydraulic fluid drops below the pre-pressure of the accumulator 9. A pre-pressure of 2 bar to 10 bar is usually maintained in the accumulator 9 to enhance the return flow and prevent negative pressure. Preventing negative pressure is important so that the hydraulic fluid or the gas dissolved therein does not vaporize into bubbles. Since the power transmission is based on the pressure of the pressure pulses and the size (volume) of each pressure pulse can be small (for example, 0.1 liter), the compressibility of the hydraulic fluid must be as low as possible to avoid power losses. For this purpose, it is advantageous to remove air from the hydraulic fluid by vacuum treatment before closing the hydraulic fluid to the power transmission circuit and / or the actuator circuit.

[0019] exist Figure 1 and Figure 2 In the embodiment of the present invention, the pressure fluctuations of the pressure pulse are offset by a second pressure accumulator 5 connected to the inlet 7 of the actuator 3, which is capable of holding at least the volume of the pressure pulse, i.e. the volume of hydraulic fluid moved across the cross-sectional flow area by one pressure pulse. In addition, the flow of hydraulic fluid to the actuator 3 is balanced by a flow valve 6 connected to the inlet 7 of the actuator 3. Figure 3 In the embodiment of FIG. 5 , the corresponding pressure accumulator 5 or flow valve is not shown, because they are not necessary.

[0020] exist Figure 1-Figure 3In the embodiment of FIG, the cyclic flow generated by the pressure pulses is directed to a pressure circuit 7a, which is connected to the inlet 7 of the actuator 3, 13 via a first check valve 4. The return flow from the actuator is directed through a second check valve 10 to the inlet side of the first check valve 4. This allows the hydraulic fluid to circulate in the actuator circuit outside the actuator. The check valves can be replaced with synchronously controlled on-off valves, where one opens when the other closes. The advantage of check valves is that they operate automatically and do not require control.

[0021] exist Figure 2 and Figure 3 In this embodiment, a power transfer unit 11 is located between the power transmission pipe or hose 2 and the actuators 3 and 13. The pressure pulses received by the power transfer unit 11 are used to generate pressure pulses from the power transmission pipe or hose 2 into the individual actuator circuits. Return flow is also directed to the power transfer unit 11. Thus, the power transfer unit 11 receives both the pressure pulses and the return flow. The power transfer unit 11 can be a double-diaphragm accumulator, in which a movable diaphragm separates two pressure chambers 11a and 11b. The power transmission pipe or hose 2 connects to one pressure chamber 11a, and the connecting channel 7b of the actuator circuit connects to the second pressure chamber 11b. The diaphragm of the power transfer unit can be equipped with a return mechanism that returns the power transfer unit to its initial state when the pressure decreases. The power transfer unit 11 can also be a dual-circuit cylinder, in which a piston is moved by the pressure pulse and transfers hydraulic fluid to the actuator circuit on the other side of the piston, while simultaneously tensioning a spring that returns the piston and hydraulic fluid when the pressure pulse subsides. When the volume of the pressure space changes in accordance with the volume of the pressure pulse, the pressure pulse entering the first pressure space 11a also simultaneously pressurizes the second pressure space 11b behind the flexible diaphragm or movable intermediate piston. The actuator circuit is connected to the second pressure chamber 11b, where a volume of fluid equal to and at the same pressure as the pressure pulse passes through the check valve 4. In other words, in this power transmission unit 11, only the pressure and volume changes corresponding to the magnitude of the pressure pulse are transmitted between the power transmission pipe or hose 2 and the actuators 3, 13. The return flow of fluid occurs in the same manner as the entry flow, but the diaphragm or piston moves in the other direction, transferring fluid back to the power transmission pipe or hose 2.

[0022] If desired, the power transfer unit 11 can also be used as a pressure-volume converter. This is done, for example, such that the surface areas of the opposite ends of the piston moving between the fluid spaces 11a, 11b and the respective cylinder diameters are chosen to be different.

[0023] The power transmission unit 11 thus separates the actuator circuit from the power transmission pipe or hose 2. The pump pulse tube power transmission unit is its own circuit, and the actuator circuit is its own circuit. Several circuits can also be formed between these circuits: power transmission unit-pulse tube-power transmission unit, if power transmission over a large distance is desired.

[0024] The reason for separate fluid circuits is that it is then possible to manufacture the pump-pulse tube-power transmission unit (pulse circuit) as a prefabricated package that is subsequently connected to these actuator circuits. The pulse circuit can be prefilled with a fluid (such as oil) that has been degassed to reduce compressibility. When the oil is in a closed circuit, it remains gas-free by not coming into contact with air. Another reason for separate fluid circuits has to do with the propagation speed of the pulse wave in the pipe. For water at a temperature of 20°C, it is 1482 m / s, slightly lower for ethylene glycol, and about 1000 m / s for oil. For some liquid metals, the speed is even higher than that of water. Regardless of the speed, it limits the value of the pulse frequency because the wave must have time to travel back and forth through the pipe, and in addition, the filling of the fluid pulse takes time. For example, a wave traveling at 1000 m / s through a 10-m pipe requires 2×0.01s=0.02s, which corresponds to a frequency of 50 Hz. Frequencies faster than this cannot be used in a 10-m continuous pipeline, so for longer distances, if high frequencies are required, the pulse line must be divided into suitable sections.

[0025] The frequency of the pressure pulses can vary widely and, in typical applications, is in the range of 3 Hz to 45 Hz, preferably 7 Hz to 40 Hz. A frequency of 1 Hz is also possible, but at frequencies above 15 Hz or higher, the dynamic pressure of the pressure pulses and their smaller volume can be exploited to a greater extent. The volume of each pressure pulse (i.e., the amount of fluid that has passed through the cross-section of the power transmission pipe or hose 2 during the period between return flows) depends on the diameter of the pipeline, the length of the pipe, the maximum frequency determined by the propagation velocity of the hydraulic fluid pulse wave, and the power requirements, and it is impossible to define an average value for it because of the many variables involved. In underwater drilling operations, large-diameter hoses and high operating pressures of up to 5,000 bar are used to transmit hydraulic power, which is several orders of magnitude greater than in conventional machine and equipment construction. For these high-pressure hydraulic systems, pulse hydraulic systems using dynamic pressure as a single-hose system are well suited. The volume of the pulse is typically in the range of 1 / 3 to 1 / 40 of the volume of the pulse tube, and preferably in the range of 1 / 4 to 1 / 30. Furthermore, in order to transmit power with the help of pressure pulses, the volume of the pulses must be larger than the compressed volume of the fluid in the pulse tube at the pulse pressure. If the fluid is incompressible, smaller pulse sizes and higher frequencies are more advantageous and can better utilize the dynamic pressure.

[0026] Furthermore, actuator circuits typically require a pressure filter in the hydraulic fluid circuit. Pressure filters can also be found in the pulse pump or pulse generator circuit at the connection point of the power transmission pipes or hoses. Other known hydraulic circuit components can also be used, for example, to control the actuator and adjust power transmission parameters. The actuator circuit of a hydraulic motor can also be equipped with a directional valve to change the motor's direction of rotation. If necessary, a dedicated actuator cooler can also be added to the circuit.

[0027] The present invention is not limited to the exemplary embodiment described above. For example, connecting passage 7b may be replaced by fluid space 11b of power transmission unit 11, with the pressure side and return side of the actuator circuit separately connected to power transmission unit 11 via check valves. In this case, check valves 4 and 10 may be connected to the housing of the pressure accumulator or the head of a dual-circuit cylinder, and fluid space 11b may be directly used as a connecting passage between the circuit components of the actuator circuit.

[0028] In the following, the theoretical background of the power transmission according to the invention will be examined based on numbers and examples.

[0029] In the present invention, dynamic hydraulic pressure can be exploited by increasing the pressure pulse feed rate. In a standard hydraulic device, the velocity of the fluid is therefore in practice not greater than 7 m / s, at which speed a pressure of 850 kg / m 3 The dynamic pressure of oil with a density of 100 m / s is 0.21 bar. If this pulse is fed into the pipeline at a speed of 100 m / s, the dynamic pressure is 42.5 bar. If the speed is increased to 200 m / s, the dynamic pressure contribution is 170 bar. This can be exploited in energy transmission solutions because, with a pressure wave propagation speed of 1000 m / s and the high input speed of the pulse, high power can be transmitted. If the pulse size is, for example, 0.1 liter, the frequency is 20 Hz, and the pulse feed speed is 200 m / s, then, ignoring losses, the power transmitted solely by the dynamic pressure is approximately 34 kW. The total power is the sum of the dynamic pressure and the pressure generated by the pulse pump.

[0030] The power generated by conventional hydraulic pumps is manageable because the pressure depends on the load and the volume flow depends on the speed of the pump. In the pulse hydraulic device according to the invention, in addition to adjusting the frequency and pulse volume, the power can also be adjusted by adjusting the speed of the feed stroke to adjust the dynamic power.

[0031] If we compare conventional hydraulics and pulse hydraulics in power transmission, the previously mentioned maximum speed of 7 m / s for laminar flow in the pipe is a good starting point. If we take 3 / 4" (16 mm inner diameter) hydraulic pipes, then in conventional hydraulics, at a speed of 7 m / s, 84.4 liters / minute of oil will flow through the pipe. If the oil pressure is 100 bar, 14 kW of power is transmitted through the pipe. If pulse hydraulics are used, already with a pulse size of 0.11 liters at a frequency of 10 Hz and at the same normal hydraulic stroke speed of 7 m / s, 22 kW of power can be transmitted (losses are not taken into account in either case).

[0032] If the stroke speed increases above the 7 m / s, the dynamic pressure will transmit more power, and if the frequency or pulse size increases, the power also increases. The ratio of frequency to pulse size has limitations depending on the length of the pipe or hose, as waves travel at a finite speed in the pipe and the duration of the pulse stroke must be taken into account. For example, the lead time for a 10-m pipe at a wave speed of 1000 m / s is 0.01 s. The stroke speed of the 0.11-liter pulse stroke in our test setup is approximately 3 m / s. The measured duration of the pulse pressure from pressure increase to pressure decrease at the outlet end of the pulse tube is rise time 0.008 s + stabilization and fall time 0.024 s = 0.0032 s, from which the minimum total time from the start of a pulse to the start of a new pulse is calculated to be 0.0032 + 0.01 + 0.01 = 0.0232 s. This represents a maximum frequency of approximately 43 Hz with these initial values. We tested our device at frequencies up to 35Hz, which is the maximum speed for our device, and the pulses moved and transmitted power exactly as expected.

[0033] We cannot measure the loss accurately because the test equipment is designed to test theory in practice.

[0034] The following provides some additional information on the compressibility of hydraulic oil and its importance. In typical hydraulic systems, if the elasticity of cylinders and other components is not taken into account, oil compressibility is of little concern. At normal pressure and a temperature of 20°C, oil contains 9% air. This is the primary reason for the 0.7% compressibility of oil at a pressure of 100 bar. On the other hand, gas dissolves in the oil and bubbles if exposed to a negative pressure of 0.7 bar. If, in pulse hydraulic systems, air is removed from the oil through vacuum treatment and the power transmission system is filled with air so that the oil does not come into contact with the air, better efficiency is achieved using pressure pulses with a smaller volume, as the oil's compressibility is reduced. If the actuator circuit is separated into separate circuits, the power transmission system itself becomes closed. The actuator circuit can also be designed as a closed separate circuit.

Claims

1. A method for transmitting hydraulic power between a pump and an actuator, the actuator (3, 13) having an inlet (7) and an outlet (8) for the hydraulic fluid, an actuator circuit between the inlet (7) and the outlet (8) and outside the actuator, in which the hydraulic fluid circulates from the outlet (8) to the inlet (7), characterized in that A pulse pump (1) is used to generate pressure pulses of a desired frequency, the hydraulic power is transmitted to the actuator (3, 13) by means of the pressure pulses by converting the pressure pulses into a flow toward the inlet (7) of the actuator, and a return flow from the actuator returns during the period between the pressure pulses to be used in the pressure pulse after each return flow, whereby an amount of hydraulic fluid corresponding to the volume of the pressure pulse moves back and forth across the cross-sectional flow area in the power transmission pipe or hose (2) between the pulse pump (1) and the actuator (3, 13).

2. The method according to claim 1, characterized in that The hydraulic fluid returns from the outlet (8) of the actuator to the connecting channel (7b) connected to the inlet (7) of the actuator during a return flow period, in which the hydraulic fluid flows back and forth due to alternation of pressure pulses and return flow.

3. The method according to claim 1 or 2, characterized in that Hydraulic fluid from the outlet (8) of the actuator (3, 13) is directed to a pre-pressurized accumulator (9), and when the pressure in the hydraulic fluid drops below the pre-pressure of the accumulator (9), the pre-pressurized accumulator (9) returns the hydraulic fluid to the connecting channel (7b) connected to the inlet (7) of the actuator.

4. The method according to claim 3, characterized in that A pre-pressure of 2 to 15 bar is maintained in the pressure accumulator (9) to enhance the return flow and prevent negative pressure.

5. The method according to any one of claims 1 to 4, characterized in that The pressure fluctuations of the pressure pulse are counteracted by a pressure accumulator (5) connected to the inlet (7) of the actuator (3), the accumulator being capable of retaining at least the amount of hydraulic fluid moved across the cross-sectional flow area by one pressure pulse.

6. The method according to any one of claims 1 to 5, characterized in that The periodic flow generated by the pressure pulse is directed to the actuator (3, 13) through a first check valve (4), and the return flow from the actuator is directed to the inlet side of the first check valve (4) through a second check valve (10).

7. The method according to any one of claims 1 to 6, characterized in that The flow of hydraulic fluid to the actuator (3) is balanced by a flow valve (6) connected to an inlet (7) of the actuator (3).

8. The method according to any one of claims 1 to 7, characterized in that Air is removed from the hydraulic fluid before it is enclosed in the power transmission circuit and / or the actuator circuit.

9. The method according to any one of claims 1 to 8, characterized in that There is a power transmission unit (11) between the power transmission pipe or hose (2) and the actuator (3, 13), the power transmission unit (11) separates the actuator circuit from the power transmission pipe or hose (2), and the pressure pulse received by the power transmission pipe or hose is used to generate a pressure pulse to the actuator circuit, and the return flow is guided into the power transmission unit (11).

10. The method according to any one of claims 1 to 9, characterized in that The frequency of the pressure pulse is 3 Hz-45 Hz.

11. A system for transmitting hydraulic power between a pump and an actuator, the actuator (3, 13) having an inlet (7) and an outlet (8) for the hydraulic fluid, an actuator circuit between the inlet (7) and the outlet (8) and outside the actuator, wherein The hydraulic fluid is arranged in a circulation manner, characterized in that the pump is a pulse pump (1), which generates repeated pressure pulses in the hydraulic fluid, the hydraulic fluid moves back and forth in a power transmission pipe or hose (2) between the pulse pump (1) and the actuator (3, 13), the hydraulic fluid pressurized by the pressure pulses is arranged to flow into the inlet (7) of the actuator, and the outlet (8) of the actuator is connected to a pre-pressurized accumulator (9) and is further connected to the inlet of a check valve (4) or a switching valve connected to the inlet (7) of the actuator via a check valve (10) or a controlled switching valve.

12. The system according to claim 11, wherein: The pre-charged pressure accumulator (9) is arranged to facilitate return flow of hydraulic fluid to the pulse pump (1) during the periods between the pressure pulses.

13. The system according to claim 11 or 12, characterized in that The hydraulic circuit connected to the inlet of the actuator (7) comprises a check valve (4) or a controlled on-off valve.

14. The system according to claim 13, wherein: A pressure accumulator (5) and / or a flow valve (6) are connected between the check valve (4) or the controlled switching valve and the actuator.

15. The system according to any one of claims 11 to 14, characterized in that A power transmission unit (11) is provided between the power transmission conduit or hose (2) and the actuator (3, 13), which transmits pressure pulses and separates the power transmission conduit or hose (2) from the actuator circuit and receives the pressure pulses on the one hand and the return flow on the other hand.

16. The system according to claim 15, characterized in that The power transmission unit (11) is a double-sided diaphragm accumulator (11a, 11b) or a dual-circuit cylinder. In the double-sided diaphragm accumulator (11a, 11b) or the dual-circuit cylinder, a piston is moved by the pressure pulse and transmits the hydraulic fluid on the other side of the piston to the actuator circuit and simultaneously tensions a spring. When the pressure pulse decays, the spring returns the piston and the hydraulic fluid.

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