EP0985087B1 - Hydraulic drive system with constant pressure in pressure conduit - Google Patents
Hydraulic drive system with constant pressure in pressure conduit Download PDFInfo
- Publication number
- EP0985087B1 EP0985087B1 EP98925972A EP98925972A EP0985087B1 EP 0985087 B1 EP0985087 B1 EP 0985087B1 EP 98925972 A EP98925972 A EP 98925972A EP 98925972 A EP98925972 A EP 98925972A EP 0985087 B1 EP0985087 B1 EP 0985087B1
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- EP
- European Patent Office
- Prior art keywords
- pressure
- pump
- drive system
- hydraulic drive
- hydraulic
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B11/00—Servomotor systems without provision for follow-up action; Circuits therefor
- F15B11/02—Systems essentially incorporating special features for controlling the speed or actuating force of an output member
- F15B11/028—Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the actuating force
- F15B11/032—Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the actuating force by means of fluid-pressure converters
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
- F02B71/00—Free-piston engines; Engines without rotary main shaft
- F02B71/04—Adaptations of such engines for special use; Combinations of such engines with apparatus driven thereby
- F02B71/045—Adaptations of such engines for special use; Combinations of such engines with apparatus driven thereby with hydrostatic transmission
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
- F02B75/00—Other engines
- F02B75/04—Engines with variable distances between pistons at top dead-centre positions and cylinder heads
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
- F04B49/00—Control, e.g. of pump delivery, or pump pressure of, or safety measures for, machines, pumps, or pumping installations, not otherwise provided for, or of interest apart from, groups F04B1/00 - F04B47/00
- F04B49/22—Control, e.g. of pump delivery, or pump pressure of, or safety measures for, machines, pumps, or pumping installations, not otherwise provided for, or of interest apart from, groups F04B1/00 - F04B47/00 by means of valves
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B2211/00—Circuits for servomotor systems
- F15B2211/20—Fluid pressure source, e.g. accumulator or variable axial piston pump
- F15B2211/21—Systems with pressure sources other than pumps, e.g. with a pyrotechnical charge
- F15B2211/212—Systems with pressure sources other than pumps, e.g. with a pyrotechnical charge the pressure sources being accumulators
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B2211/00—Circuits for servomotor systems
- F15B2211/20—Fluid pressure source, e.g. accumulator or variable axial piston pump
- F15B2211/21—Systems with pressure sources other than pumps, e.g. with a pyrotechnical charge
- F15B2211/214—Systems with pressure sources other than pumps, e.g. with a pyrotechnical charge the pressure sources being hydrotransformers
Definitions
- the invention relates to a hydraulic drive system in accordance with the preamble of claim 1.
- Such a drive system is generally known from the Hydraulic Handbook, 7th edition, published by Trade and Technical Press ltd., 1979, page 363, figure 26.
- the disadvantage of this known system is that the first pressure has a fixed value and makes throttling necessary if a lower pressure is required by a user, so inducing energy loss.
- the power used by the users might exceed the power supplied by the pump which could cause an undesirable pressure drop in the pressure conduit and so function loss at one or more of the users.
- the present invention aims to provide an improved hydraulic drive system.
- the present invention provides the hydraulic drive system in accordance with the characterizing part of claim 1.
- the hydraulic transformer changes the available first pressure to the user pressure without losses and can return power into the pressure conduit.
- the hydraulic transformer controls together with the power regulator arranges that the power taken up by the users does not exceed the available power which includes power from the pump and power returned by a user. In this way the afore mentioned losses are avoided.
- the power regulator is provided with means for selectively allocating power to certain users. This achieves that certain users in a drive system keep sufficient power at their disposal. This benefits the working of the apparatus or its safety.
- each pump is provided with a first pressure accumulator. This results in less pressure fluctuations in the pressure conduit.
- a further improvement of the hydraulic drive system is executed in accordance with claim 4.
- pressure fluctuations over the length of the pressure conduit resulting from the pulsating oil supply are avoided, and the pulsating oil flow caused by the pump(s) mainly becomes a pulsating oil flow to the first pressure accumulator and oil flow through the pressure conduit is more even. This also avoids flow losses in the pressure conduit.
- the pump is executed in accordance with the characterizing part of claim 5. This provides a simple manner of obtaining a mobile drive.
- Another embodiment of the invention is executed in accordance with the characterizing part of claim 6. This provides a simple manner of realizing a hydraulic drive system quickly able to react to changing demand and consequently to changes in power use, while for instance the motor can keep turning at more or less constant or slowly altering revolutions.
- Still another embodiment of the invention is executed in accordance with claim 7.
- a direct-current motor is used which can be switched on quickly and quickly reaches full revolutions, thereby allowing quick reaction to changes regarding the load of the drive system.
- Figure 1 shows a high-pressure conduit 1 with a high-pressure accumulator 2 and a pressure pA and a low-pressure conduit 13 with a low-pressure accumulator 14 and a pressure pT.
- a hydraulic transformer 11 which is provided with a transformer control 7A is fed from the high-pressure conduit 1.
- a rotating hydromotor 10 having a regular stroke is fed from the hydraulic transformer 11 and is loaded with a torque M. Through the hydromotor 10 there is an oil flow at a pressure pB and an oil flow QB from the hydraulic transformer, the pressure pB depending, among other things, on the torque M and on the adjustment of the hydraulic transformer 11.
- the hydraulic transformer 11 is provided with transformer control 7A, which ensures that the transformer 11 is adjusted such that the motor assumes as much as possible the determined number of revolutions, which means that QB is as constant as possible, while the change of load is compensated by the torque M by means of adjusting the hydraulic transformer 11.
- a hydraulic transformer 9 interacting with a linear motor 8 is also fed from the high-pressure conduit 1, while in addition other, not shown users, may be placed between the high-pressure conduit 1 and the low-pressure conduit 13.
- the high-pressure conduit 1 is fed with compressed oil by a free-piston aggregate 15 which is known, for instance, from WO 93/10345, the content of which is to be considered included herein.
- a free piston mounted in the aggregate 15 is moved under the influence of a hydraulic drive system 3 and as soon as pA comes below the set value of, for instance 30 MPa, the movement of the free piston commences by means of a starting valve 4 . After 22 msec, the time required for the ignition of the air/fuel mixture in the motor, oil is supplied to the pressure conduit 1 for 11 msec.
- the amount of oil supplied to the pressure conduit 1 is 0.033 l, which at a maximum stroke frequency of 30 Hz and a high-pressure pA of 30 MPa produces a power of 30 kW.
- the high-pressure accumulator 2 has a volume of 0.7 l and a residual volume of 0.1 l, thus 0.6 1 is available as gas volume for cushioning the pulsations resulting from the pulsating oil supply. This volume suffices to limit the pressure changes during oil supply and lack of discharge to approximately 1 MPa, which is considered allowable.
- the high-pressure conduit 1 is equipped with a pressure gauge 5 which is connected with a pump control 6. If the pressure in the high-pressure conduit 1 drops below the adjusted value, the pump control 6 activates the free-piston aggregate 15 which will then supply oil until the pressure has regained the required level. If the demand for oil is smaller than the capacity of the free-piston aggregate 15, it will after each stroke stand still before making the next stroke. When the pressure has dropped below the adjusted value, the starting valve 4 will receive a signal from the pump control 6, in order for the next stroke to be made. Although this is not shown in Figure 1, it is also conceivable to parallel-connect several free-piston aggregates, which are all controlled by the pump control 6.
- the transformer controls 7A are connected with a maximum-power control 7.
- Said maximum-power control 7 ensures that the combined power taken up by the transformers does not exceed the capacity of the available pumps, for instance pump 15. This also takes into account the power returned by a transformer to the high-pressure conduit 1.
- An example of an application of this control in a fork-lift truck having a riding drive and a lift drive is that the capacity to ride or lift is limited when a load is being lifted, but that the capacity becoming available when the load is being lowered, can be made accessible to the riding drive. If power is returned by a hydraulic transformer to the high-pressure conduit 1 while there is no power demand, the pressure will rise above the adjusted value and a pressure-relief device 12 will open, and by throttling the energy it is converted into heat and is lost.
- a pressure accumulator 26 which may have a capacity of, for instance, 7 litres, affording the ability to recover much energy.
- a pulsating oil supply from the pump 15 would result in a pulsating oil flow with a relatively high flow rate to the pressure accumulator 26.
- the gas sides of the pressure accumulators 2 and 26 are in communication by means of a gas pipe 27, so that approximately the same pressure prevails in the entire pressure conduit 1.
- the pulsating flow of oil only flows to the pressure accumulator 2 located near the pump 15, and from there it flows evenly via the pressure conduit 1 to the users. In this manner high flow rates in pipes are avoided and the ensuing losses are limited.
- the transformer control 7A and the maximum power control 7 also receive the pressure information from the pressure gauge 5 and accordingly adapt the regulation of the hydraulic transformers 9 and 11 to the higher pressures.
- FIG. 2 shows a pump with a constant stroke volume, driven by a motor 16.
- the motor 16 may be a combustion motor whose revolutions can be varied only relatively slowly or, for instance, a three-phase motor having a constant number of revolutions. The torque to be produced by these known motors can vary very quickly.
- the delivery side and the suction side of the pump 17 can be short circuited by means of a short-circuiting valve 18 and the delivery side is in communication with the high-pressure conduit 1 via a non-return valve 19.
- a schematic representation of a return tank 20 is shown instead of the low-pressure conduit. Closure of the short-circuit valve 18 will cause the oil pumped by the pump 17 to flow to the high-pressure conduit 1, with the pump 17 pumping against the pressure pA. Once the high pressure pA has reached the required value, the pump control 6 activates the short-circuit valve 18 to open and the pump 17 pumps virtually without pressure, with the motor 16 hardly supplying any power any more.
- FIG. 3 shows a pump 22 with constant stroke volume, which can also function as motor.
- the pump 22 is coupled with a direct-current motor 21, which can also function as generator.
- the motor 21 is fed from electrical battery 23 via a switch 24.
- the fact that the motor 21 is fed from the electrical battery 23 makes this drive system especially suitable for a mobile application, for instance, a fork-lift truck.
- the pump control 6 then activates the valve 25 to open, after which the pump 22 commences to work as motor and the motor 21 commences to work as generator.
- the valve 25 shown is operated from the pump control 6, however, an embodiment it is also possible in which the valve 25 is operated hydraulically and opens when the pressure in the high-pressure conduit 1 rises above a value to be adjusted. The generated electrical current is returned to the electrical battery 23, but the manner in which this takes place is not explained.
- the fact that the hydraulic transformer is able to react quickly to the altered load conditions has been taken into account by executing the adjustment drive system of the hydraulic transformer such that in a drive system in which the speed of the motor is regulated by means of a control circuit, the band width of the adjusted drive system is approximately 7 Hz.
- Figure 4 shows the curve of pressure pB when the hydromotor 10 is connected, and which curve is especially the result of the load M and the adjustment of the hydraulic transformer 11.
- Figure 5 shows the curve of the oil flow QB from the hydraulic transformer 11 to the hydromotor 10, from which can be seen that due to the load the revolutions of the hydromotor drop (QB is lower).
- Figure 6 shows the curve of the oil flow QA from the high-pressure conduit 1 to the hydraulic transformer 11.
- Figure 7 shows a control signal ⁇ , representing the adjustment of the hydraulic transformer 10, triggered by the transformer control 7A.
- Figure 8 shows the pressure pA in the high-pressure accumulator 2. It can be seen that the free-piston aggregate starts when the pressure drops below the predetermined level of 30 MPa, and that after a delay of 22 msec the supply of oil commences and lasts 11 msec, the delay is caused by the free piston first having to carry out a compression stroke, subsequent to which energy developing at combustion, is during the expansion stroke given off to the hydraulic drive system. Because the waiting times between the starting moments vary, the adaptation to the different supplies is realized. It has also been clearly shown that when a small pressure accumulator is employed, there is very little pressure fluctuation and that by means of pulse modulation it is possible to quickly react to the changing energy demand.
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Physics & Mathematics (AREA)
- Fluid Mechanics (AREA)
- Fluid-Pressure Circuits (AREA)
Abstract
Description
- The invention relates to a hydraulic drive system in accordance with the preamble of
claim 1. - Such a drive system is generally known from the Hydraulic Handbook, 7th edition, published by Trade and Technical Press ltd., 1979, page 363, figure 26. The disadvantage of this known system is that the first pressure has a fixed value and makes throttling necessary if a lower pressure is required by a user, so inducing energy loss. Furthermore, during operating, the power used by the users might exceed the power supplied by the pump which could cause an undesirable pressure drop in the pressure conduit and so function loss at one or more of the users.
- To overcome these disadvantages of the known system, the present invention aims to provide an improved hydraulic drive system. To this end, the present invention provides the hydraulic drive system in accordance with the characterizing part of
claim 1. The hydraulic transformer changes the available first pressure to the user pressure without losses and can return power into the pressure conduit. The hydraulic transformer controls together with the power regulator arranges that the power taken up by the users does not exceed the available power which includes power from the pump and power returned by a user. In this way the afore mentioned losses are avoided. - In accordance with a further improvement of the invention, the power regulator is provided with means for selectively allocating power to certain users. This achieves that certain users in a drive system keep sufficient power at their disposal. This benefits the working of the apparatus or its safety.
- In accordance with a further improvement, if more than, one pump is involved each pump is provided with a first pressure accumulator. This results in less pressure fluctuations in the pressure conduit.
- A further improvement of the hydraulic drive system is executed in accordance with
claim 4. Hereby pressure fluctuations over the length of the pressure conduit resulting from the pulsating oil supply are avoided, and the pulsating oil flow caused by the pump(s) mainly becomes a pulsating oil flow to the first pressure accumulator and oil flow through the pressure conduit is more even. This also avoids flow losses in the pressure conduit. - In accordance with a still further embodiment of the invention, the pump is executed in accordance with the characterizing part of
claim 5. This provides a simple manner of obtaining a mobile drive. - Another embodiment of the invention is executed in accordance with the characterizing part of
claim 6. This provides a simple manner of realizing a hydraulic drive system quickly able to react to changing demand and consequently to changes in power use, while for instance the motor can keep turning at more or less constant or slowly altering revolutions. - Still another embodiment of the invention is executed in accordance with
claim 7. In such an embodiment, for instance, a direct-current motor is used which can be switched on quickly and quickly reaches full revolutions, thereby allowing quick reaction to changes regarding the load of the drive system. - Finally, another improvement is executed in accordance with
claim 8. This provides a simple manner for reconverting the energy brought into the pressure conduit by the hydraulic transformers into electrical energy, so that said energy is not lost. - The invention will now be explained with reference to a few exemplary embodiments which will be discussed with the aid of a drawing, in which
- Figure 1 shows a schematic diagram of a first embodiment of a hydraulic drive system with hydromotors having hydraulic transformers fed from a pressure conduit with a constant pressure, in which the pump is a free-piston aggregate,
- Figure 2 shown a schematic diagram of a second embodiment of a hydraulic drive system in accordance with Figure 1, in which the pump is a rotating pump driven by a motor,
- Figure 3 is a schematic diagram of a third embodiment of a hydraulic drive system in accordance with Figure 1, in which the pump is a rotating pump driven by a direct-current motor fed from a battery while also being capable of returning energy to the battery,
- Figure 4 is a diagram showing the pressure curve at the connection of a hydromotor shown in Figure 1, while said hydromotor undergoes an incremental loading of + 65%,
- Figure 5 is a diagram showing the curve of the volume flow through the hydromotor shown in Figure 1, during the incremental loading of + 65%,
- Figure 6 is a diagram showing the curve of the volume flow to the hydraulic transformer which is coupled to the hydromotor shown in Figure 1, during the incremental loading of + 65%,
- Figure 7 is a diagram showing the curve of the adjusting signal to the hydraulic transformer which is coupled with the hydromotor shown in Figure 1 during the incremental loading of + 65%, and
- Figure 8 is a diagram showing the curve of the pressure in the accumulator which is fed by a free-piston motor in accordance with Figure 1 during the incremental loading represented in Figures 4-7.
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- The diagrams are a schematic representation of the various parts, while the known, and in hydraulic systems customary constructions such as safety devices for motors and the like, are not shown. Where possible, similar parts in the various figures have been provided with the same reference numbers.
- Figure 1 shows a high-
pressure conduit 1 with a high-pressure accumulator 2 and a pressure pA and a low-pressure conduit 13 with a low-pressure accumulator 14 and a pressure pT. A hydraulic transformer 11 which is provided with atransformer control 7A is fed from the high-pressure conduit 1. A rotatinghydromotor 10 having a regular stroke is fed from the hydraulic transformer 11 and is loaded with a torque M. Through thehydromotor 10 there is an oil flow at a pressure pB and an oil flow QB from the hydraulic transformer, the pressure pB depending, among other things, on the torque M and on the adjustment of the hydraulic transformer 11. The hydraulic transformer 11 is provided withtransformer control 7A, which ensures that the transformer 11 is adjusted such that the motor assumes as much as possible the determined number of revolutions, which means that QB is as constant as possible, while the change of load is compensated by the torque M by means of adjusting the hydraulic transformer 11. - A hydraulic transformer 9 interacting with a
linear motor 8 is also fed from the high-pressure conduit 1, while in addition other, not shown users, may be placed between the high-pressure conduit 1 and the low-pressure conduit 13. - The high-
pressure conduit 1 is fed with compressed oil by a free-piston aggregate 15 which is known, for instance, from WO 93/10345, the content of which is to be considered included herein. A free piston mounted in theaggregate 15 is moved under the influence of ahydraulic drive system 3 and as soon as pA comes below the set value of, forinstance 30 MPa, the movement of the free piston commences by means of astarting valve 4 . After 22 msec, the time required for the ignition of the air/fuel mixture in the motor, oil is supplied to thepressure conduit 1 for 11 msec. The amount of oil supplied to thepressure conduit 1 is 0.033 l, which at a maximum stroke frequency of 30 Hz and a high-pressure pA of 30 MPa produces a power of 30 kW. The high-pressure accumulator 2 has a volume of 0.7 l and a residual volume of 0.1 l, thus 0.6 1 is available as gas volume for cushioning the pulsations resulting from the pulsating oil supply. This volume suffices to limit the pressure changes during oil supply and lack of discharge to approximately 1 MPa, which is considered allowable. - The high-
pressure conduit 1 is equipped with apressure gauge 5 which is connected with apump control 6. If the pressure in the high-pressure conduit 1 drops below the adjusted value, thepump control 6 activates the free-piston aggregate 15 which will then supply oil until the pressure has regained the required level. If the demand for oil is smaller than the capacity of the free-piston aggregate 15, it will after each stroke stand still before making the next stroke. When the pressure has dropped below the adjusted value, thestarting valve 4 will receive a signal from thepump control 6, in order for the next stroke to be made. Although this is not shown in Figure 1, it is also conceivable to parallel-connect several free-piston aggregates, which are all controlled by thepump control 6. - The
transformer controls 7A are connected with a maximum-power control 7. Said maximum-power control 7 ensures that the combined power taken up by the transformers does not exceed the capacity of the available pumps, forinstance pump 15. This also takes into account the power returned by a transformer to the high-pressure conduit 1. - An example of an application of this control in a fork-lift truck having a riding drive and a lift drive, is that the capacity to ride or lift is limited when a load is being lifted, but that the capacity becoming available when the load is being lowered, can be made accessible to the riding drive. If power is returned by a hydraulic transformer to the high-
pressure conduit 1 while there is no power demand, the pressure will rise above the adjusted value and a pressure-relief device 12 will open, and by throttling the energy it is converted into heat and is lost. - It is possible to equip the hydraulic drive system with large pressure accumulators, such as for instance, a
pressure accumulator 26 which may have a capacity of, for instance, 7 litres, affording the ability to recover much energy. A pulsating oil supply from thepump 15 would result in a pulsating oil flow with a relatively high flow rate to thepressure accumulator 26. To prevent this, the gas sides of thepressure accumulators gas pipe 27, so that approximately the same pressure prevails in theentire pressure conduit 1. As a consequence the pulsating flow of oil only flows to thepressure accumulator 2 located near thepump 15, and from there it flows evenly via thepressure conduit 1 to the users. In this manner high flow rates in pipes are avoided and the ensuing losses are limited. - It is also possible to adjust the overpressure-
relief device 12 to 10 MPa above the minimal pressure of 30 MPa, allowing much energy to be stored. Thetransformer control 7A and themaximum power control 7 also receive the pressure information from thepressure gauge 5 and accordingly adapt the regulation of the hydraulic transformers 9 and 11 to the higher pressures. - Figure 2 shows a pump with a constant stroke volume, driven by a
motor 16. Themotor 16 may be a combustion motor whose revolutions can be varied only relatively slowly or, for instance, a three-phase motor having a constant number of revolutions. The torque to be produced by these known motors can vary very quickly. The delivery side and the suction side of thepump 17 can be short circuited by means of a short-circuiting valve 18 and the delivery side is in communication with the high-pressure conduit 1 via anon-return valve 19. In this Figure a schematic representation of areturn tank 20 is shown instead of the low-pressure conduit. Closure of the short-circuit valve 18 will cause the oil pumped by thepump 17 to flow to the high-pressure conduit 1, with thepump 17 pumping against the pressure pA. Once the high pressure pA has reached the required value, thepump control 6 activates the short-circuit valve 18 to open and thepump 17 pumps virtually without pressure, with themotor 16 hardly supplying any power any more. - Figure 3 shows a
pump 22 with constant stroke volume, which can also function as motor. Thepump 22 is coupled with a direct-current motor 21, which can also function as generator. Themotor 21 is fed fromelectrical battery 23 via aswitch 24. The fact that themotor 21 is fed from theelectrical battery 23 makes this drive system especially suitable for a mobile application, for instance, a fork-lift truck. The moment the measurement of thepressure gauge 5 indicates that the pressure in the pressure conduit is lower than the setting, themotor 21 is activated and the oil is pumped via thenon-return valve 19 to the high-pressure conduit 1. While this takes place thevalve 25 is closed. When energy is recovered, for instance when a mobile device is braking, the pressure may exceed the adjusted value. Thepump control 6 then activates thevalve 25 to open, after which thepump 22 commences to work as motor and themotor 21 commences to work as generator. Thevalve 25 shown is operated from thepump control 6, however, an embodiment it is also possible in which thevalve 25 is operated hydraulically and opens when the pressure in the high-pressure conduit 1 rises above a value to be adjusted. The generated electrical current is returned to theelectrical battery 23, but the manner in which this takes place is not explained. - The embodiments described above demonstrate different possibilities, and it is also quite conceivable that embodiments, switches or other operating possibilities and the like described above for the one embodiment may also be applicable for one of the other embodiments. Apart from the described applications using the double-sided hydromotors, the invention may be applied unconditionally in situations involving hydraulic cylinders with single-sided load.
- How the controls described are to be realized, will be left aside for the moment. It is possible to use electromechanical controls, wherein sensors with respect to, for instance measuring a liquid flow, a number of revolutions, a movement or a pressure, electronically pass on the measured values to an electronic control, subsequent to which, for instance, the hydraulic transformer is adjusted by means of a stepping motor, a servomotor or a hydraulic servo-drive system. It is, however, also conceivable that a complete or partial hydraulic drive system is used, wherein, for instance, valves can be directly activated by a pressure or a pressure ratio.
- The different Figures 4-8 show how the drive system represented in Figure 1 reacts to an incremental loading of + 65% on torque M at a point in time t = 0.2 sec and an incremental loading back to the original moment M at the point in time t = 0.6 sec. The fact that the hydraulic transformer is able to react quickly to the altered load conditions has been taken into account by executing the adjustment drive system of the hydraulic transformer such that in a drive system in which the speed of the motor is regulated by means of a control circuit, the band width of the adjusted drive system is approximately 7 Hz. Such a band width is practicable if the adjustment drive system is of the heavy kind, or if the hydraulic transformer to be adjusted is executed in accordance with the hydraulic transformer described in the application PCT/NL97/00084 by the same applicant, which document is to be considered part of this document.
- Figure 4 shows the curve of pressure pB when the
hydromotor 10 is connected, and which curve is especially the result of the load M and the adjustment of the hydraulic transformer 11. - Figure 5 shows the curve of the oil flow QB from the hydraulic transformer 11 to the
hydromotor 10, from which can be seen that due to the load the revolutions of the hydromotor drop (QB is lower). - Figure 6 shows the curve of the oil flow QA from the high-
pressure conduit 1 to the hydraulic transformer 11. - Figure 7 shows a control signal δ, representing the adjustment of the
hydraulic transformer 10, triggered by thetransformer control 7A. - Figure 8 shows the pressure pA in the high-
pressure accumulator 2. It can be seen that the free-piston aggregate starts when the pressure drops below the predetermined level of 30 MPa, and that after a delay of 22 msec the supply of oil commences and lasts 11 msec, the delay is caused by the free piston first having to carry out a compression stroke, subsequent to which energy developing at combustion, is during the expansion stroke given off to the hydraulic drive system. Because the waiting times between the starting moments vary, the adaptation to the different supplies is realized. It has also been clearly shown that when a small pressure accumulator is employed, there is very little pressure fluctuation and that by means of pulse modulation it is possible to quickly react to the changing energy demand.
Claims (8)
- A hydraulic drive system comprising a pressure conduit (1) connected with several users, a pump (15;17;22) which, after being activated, has a substantially constant delivery for a supply of liquid, for instance oil, to the pressure conduit (1) which is under a first pressure (pA), a first pressure accumulator (2) coupled with the pressure conduit (1), wherein the active volume of the first pressure accumulator is of a size such that after the pump (15;17;22) is activated and immediately inactivated, the supply of liquid to the first pressure accumulator causes the first pressure (pA) to rise less than maximally allowed for a pulsatory pressure rise, a pressure sensor (5) for measuring the first pressure (pA), and pump control means (6) provided with switch means (4;18;24) for activating and inactivating the pump (15;17;22) and/or the pump's (15;17;22) supply of liquid to the pressure conduit (1), said pump control means (6) being connected with the pressure sensor for maintaining a substantially constant pressure in the pressure conduit (1) characterized in that each of the most important users is connected with the pressure conduit (1) via a hydraulic transformer (9,11) for transforming the first pressure (pA) into a user's pressure (pB), each hydraulic transformer (9,11) having a transformer control (7A) which is connected to a power regulator (7) for regulating the power to be supplied by said hydraulic transformers (9,11) taking into account the power returned by a hydraulic transformer into the pressure conduit (1).
- A hydraulic drive system according to claim 1, wherein the power regulator (7) is provided with means for selectively allocating power to certain users.
- A hydraulic drive system according to claim 2, wherein each pump (15;17;22) is provided with a first pressure accumulator (2).
- A hydraulic drive system according to one of the preceding claims, wherein the first, preferably small pressure accumulator (2) is coupled to the pressure conduit (1) near the pump (15;17;22), and at some distance thereto at least one second pressure accumulator (26,...) is coupled to the pressure conduit (1), and wherein the gas sides of the first and second pressure accumulators (2,26,...) are connected to a gas pipe (27).
- A hydraulic drive system in accordance with one of the preceding claims, in which the pump is a free-piston aggregate (15) comprising a freely movable piston, a hydraulic drive system (3) for controlling the movement of the free piston and a pump cylinder in which a pump piston connected with the pump cylinder can move, and wherein the switch means (4) form a part of the hydraulic drive system (3).
- A hydraulic drive system in accordance with one of the preceding claims, comprising a pump (17) driven by a motor (16), a valve (18) operated by the control means (6), for the communication between the suction side and the delivery side of the pump (17) and a non-return valve (19) provided in the connection with the pressure conduit (1).
- A hydraulic drive system in accordance with one of the preceding claims, comprising a pump (22) driven by a motor (21), and a non-return valve (19) provided in the connection with the pressure conduit (1), and switch means (24) for activating and inactivating the motor (21).
- A hydraulic drive system in accordance with one of the preceding claims, wherein by rotating in opposite directions pump (22) and motor (21) are capable of converting hydraulic energy into electrical energy, and means (25) are present for connecting the pressure conduit (1) with the pump (22) parallel to the non-return valve (19).
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
NL1006143A NL1006143C2 (en) | 1997-05-28 | 1997-05-28 | Hydraulic system with constant pressure in pressure line. |
NL1006143 | 1997-05-28 | ||
PCT/NL1998/000305 WO1998054450A1 (en) | 1997-05-28 | 1998-05-27 | Hydraulic drive system with constant pressure in pressure conduit |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0985087A1 EP0985087A1 (en) | 2000-03-15 |
EP0985087B1 true EP0985087B1 (en) | 2003-08-20 |
Family
ID=19765032
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP98925972A Expired - Lifetime EP0985087B1 (en) | 1997-05-28 | 1998-05-27 | Hydraulic drive system with constant pressure in pressure conduit |
Country Status (4)
Country | Link |
---|---|
EP (1) | EP0985087B1 (en) |
DE (1) | DE69817343T2 (en) |
NL (1) | NL1006143C2 (en) |
WO (1) | WO1998054450A1 (en) |
Families Citing this family (16)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6269783B1 (en) | 1999-02-22 | 2001-08-07 | Caterpillar Inc. | Free piston internal combustion engine with pulse compression |
US6152091A (en) * | 1999-02-22 | 2000-11-28 | Caterpillar Inc. | Method of operating a free piston internal combustion engine with a variable pressure hydraulic fluid output |
US6158401A (en) * | 1999-02-24 | 2000-12-12 | Caterpillar Inc. | Method of operating a free piston internal combustion engine with pulse compression |
US6360536B1 (en) * | 1999-03-16 | 2002-03-26 | Caterpillar Inc. | Control system for a hydraulic transformer |
US6374602B1 (en) | 1999-03-16 | 2002-04-23 | Caterpillar Inc. | Control system for a hydraulic transformer having variable pressure input |
US6293231B1 (en) * | 1999-09-29 | 2001-09-25 | Ingo Valentin | Free-piston internal combustion engine |
DE10026728A1 (en) | 1999-11-24 | 2001-05-31 | Mannesmann Rexroth Ag | Free piston motor for converting energy from petrol/oil into hydraulic energy has control piston to determine changeover from high pressure and low pressure reservoirs |
NL1013996C2 (en) * | 1999-12-30 | 2001-07-03 | Innas Free Piston Bv | Free piston unit for generating hydraulic energy. |
DE10120196A1 (en) * | 2000-05-19 | 2001-11-22 | Mannesmann Rexroth Ag | Free piston engine has engine piston driven by staged hydraulic piston, section of which with lesser diameter is arranged in work cylinder and section with greater diameter in compression cylinder |
CN1214179C (en) | 2000-05-19 | 2005-08-10 | 博世力士乐股份有限公司 | Free piston motor |
DE102009051204A1 (en) * | 2009-10-29 | 2011-05-19 | Muller, Katherina | Electro-hydraulic drive for motor vehicles |
US8887690B1 (en) | 2010-07-12 | 2014-11-18 | Sturman Digital Systems, Llc | Ammonia fueled mobile and stationary systems and methods |
FR2971013B1 (en) | 2011-01-27 | 2013-02-15 | Peugeot Citroen Automobiles Sa | METHOD FOR CONTROLLING A RECHARGE ENGINE INVOLVING A HYDRAULIC PUMP |
US9206738B2 (en) | 2011-06-20 | 2015-12-08 | Sturman Digital Systems, Llc | Free piston engines with single hydraulic piston actuator and methods |
US9464569B2 (en) | 2011-07-29 | 2016-10-11 | Sturman Digital Systems, Llc | Digital hydraulic opposed free piston engines and methods |
DE102012017004A1 (en) | 2012-08-28 | 2014-03-06 | Hydac Technology Gmbh | Hydraulic energy recovery system |
Family Cites Families (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4507054A (en) * | 1982-06-28 | 1985-03-26 | Carr-Griff, Inc. | Liquid dispensing system |
JP2776882B2 (en) * | 1989-04-27 | 1998-07-16 | 株式会社ユニシアジェックス | Pump device |
JPH02145679U (en) * | 1989-05-16 | 1990-12-11 | ||
JP2611566B2 (en) * | 1991-05-22 | 1997-05-21 | 株式会社島津製作所 | Hydraulic power recovery system |
NL9101934A (en) * | 1991-11-19 | 1993-06-16 | Innas Bv | FREE PISTON MOTOR WITH FLUID PRESSURE AGGREGATE. |
DE4316361C2 (en) * | 1993-05-15 | 1999-04-01 | Radosav Nikolic | Hydraulic industrial truck |
US5398506A (en) * | 1994-04-22 | 1995-03-21 | Diesel Equipment Limited | Control system for hydraulic pump system |
NL1002430C2 (en) * | 1996-02-23 | 1997-08-26 | Innas Free Piston Ifp Bv | Device for generating, using or transforming hydraulic energy. |
-
1997
- 1997-05-28 NL NL1006143A patent/NL1006143C2/en not_active IP Right Cessation
-
1998
- 1998-05-27 DE DE69817343T patent/DE69817343T2/en not_active Expired - Fee Related
- 1998-05-27 EP EP98925972A patent/EP0985087B1/en not_active Expired - Lifetime
- 1998-05-27 WO PCT/NL1998/000305 patent/WO1998054450A1/en active IP Right Grant
Also Published As
Publication number | Publication date |
---|---|
EP0985087A1 (en) | 2000-03-15 |
DE69817343T2 (en) | 2004-06-24 |
WO1998054450A1 (en) | 1998-12-03 |
DE69817343D1 (en) | 2003-09-25 |
NL1006143C2 (en) | 1998-12-01 |
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