Classifications

• • 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
• • 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
• • 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
• • 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
• • 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
• • 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 known from WO93/10345.
• The- disadvantage with the known drive system is that the pres- sure in the pressure conduit is the same for all users, which means that said pressure must always be greater or equal to the maximum pressure used by any one of the users . The oil flow to the other users will then have to be reduced, resulting in loss.
• Another disadvantage is that if the pressure required by a user increases due to a change of load, it may be necessary to raise the pressure in the pressure conduit, for which the pump requires some time. This prolongs the response time of the hydraulic drive system on load changes, which is disadvantageous. It is the object of the invention to eliminate the above disadvantages and to this end the hydraulic drive system is embodied in accordance with the characterizing part of claim 1.
• a low-loss and fast reacting hydraulic drive system By maintaining a constant level of pressure in the pressure conduit, which level may be higher than the pressure maximally required by a user, and by reducing said high pressure to the user pressure by means of a hydraulic transformer which involves little loss, a low-loss and fast reacting hydraulic drive system is provided.
• Hydraulic drive system with hydraulic transformers which are fed from a constant pressure supply system are known as such.
• the known hydraulic drive systems use adjustable pumps which, in order to realize the necessary dynamic performance, are necessarily of a very heavy design, which is a disadvantage.
• a fast reacting control system is required which uses much energy. Consequently, the possibility of saving energy is largely lost.
• the pump is executed in accordance with the characterizing part of claim 2.
• 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 3. 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.
• Another embodiment of the invention is executed in accordance with claim 4.
• a direct-current motor is used which can change gear quickly and quickly reaches full revolutions, thereby allowing quick reaction to changes regarding the load of the drive system.
• Another improvement is executed in accordance with claim 5. 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 hydraulic drive system is executed in accordance with claim 6. This prevents that during operating the decrease of liquid from the pressure conduit exceeds the amount of liquid maximally supplied by the pump, which would cause too great a pressure drop in the pressure conduit, which is undesirable.
• the power regulator is provided with means for selectively allocating power to certain users. This achieves that certain users in a drive system always have sufficient power at their disposal. This benefits the working of the apparatus or its safety.
• each pump is provided with a pressure accumulator possessing the necessary volume to limit the increase of pressure.
• a further improvement of the hydraulic drive system is executed in accordance with claim 9.
• 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 avoids flow losses in the pressure conduit.
• 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,
• FIG. 2 shows 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,
• FIG 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 vol- ume 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%
• 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.
• 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 pro- vided 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 .
• oil is supplied to the pressure conduit 1 for 11 msec.
• the amount of oil supplied to the pressure conduit 1 is 0.033 1, 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 1 and a residual volume of 0.1 1, thus 0.6 1 is avail- able 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.
• the starting valve 4 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.
• 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 trans- formers 9 and 11 to the higher pressures.
• Figure 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 con- stant 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 OJ OJ NJ to H H H
• H o p H- y- y - 0 r- 1 a H- y- y rr Hf
• 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)

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Applications Claiming Priority (2)

Related Child Applications (2)

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Cited By (15)

Families Citing this family (1)

Citations (8)

• 1997
  • 1997-05-28 NL NL1006143A patent/NL1006143C2/nl not_active IP Right Cessation
• 1998
  • 1998-05-27 WO PCT/NL1998/000305 patent/WO1998054450A1/nl active IP Right Grant
  • 1998-05-27 EP EP98925972A patent/EP0985087B1/en not_active Expired - Lifetime
  • 1998-05-27 DE DE69817343T patent/DE69817343T2/de not_active Expired - Fee Related

Patent Citations (8)

Non-Patent Citations (1)

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