NO20150676A1 - Hydraulic system and a method for recuperating energy. - Google Patents
Hydraulic system and a method for recuperating energy. Download PDFInfo
- Publication number
- NO20150676A1 NO20150676A1 NO20150676A NO20150676A NO20150676A1 NO 20150676 A1 NO20150676 A1 NO 20150676A1 NO 20150676 A NO20150676 A NO 20150676A NO 20150676 A NO20150676 A NO 20150676A NO 20150676 A1 NO20150676 A1 NO 20150676A1
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- Norway
- Prior art keywords
- hydraulic
- pressure
- equipment
- accumulator
- machine
- Prior art date
Links
- 238000000034 method Methods 0.000 title claims description 21
- 238000006073 displacement reaction Methods 0.000 claims description 7
- 230000002349 favourable effect Effects 0.000 claims description 3
- 239000012530 fluid Substances 0.000 description 21
- 230000001276 controlling effect Effects 0.000 description 20
- 239000003921 oil Substances 0.000 description 19
- 238000004891 communication Methods 0.000 description 4
- 238000010586 diagram Methods 0.000 description 4
- 230000001419 dependent effect Effects 0.000 description 2
- 238000009825 accumulation Methods 0.000 description 1
- 230000003213 activating effect Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000010724 circulating oil Substances 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000003129 oil well Substances 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
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
- F15B1/00—Installations or systems with accumulators; Supply reservoir or sump assemblies
- F15B1/02—Installations or systems with 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
- F15B1/00—Installations or systems with accumulators; Supply reservoir or sump assemblies
- F15B1/02—Installations or systems with accumulators
- F15B1/024—Installations or systems with accumulators used as a supplementary power source, e.g. to store energy in idle periods to balance pump load
-
- 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
- F15B21/00—Common features of fluid actuator systems; Fluid-pressure actuator systems or details thereof, not covered by any other group of this subclass
- F15B21/14—Energy-recuperation means
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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Fluid Mechanics (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Other Liquid Machine Or Engine Such As Wave Power Use (AREA)
- Load-Engaging Elements For Cranes (AREA)
Description
Hydraulic system and a method for controlling hydraulic system
The present invention is related to a hydraulic system according to the preamble of claim 1.
The present invention is also related to a method for controlling a hydraulic system according to the preamble of claim 10.
Background
Hydraulic systems may be used in many fields of technology. A hydraulic system generally comprises a hydraulic machine, such as a hydraulic pump, arranged for supplying hydraulic power in the form of hydraulic flow and/or pressure to the hydraulic system. The hydraulic machine is powered by power source, such as an engine or an electric motor.
Presently also a second hydraulic machine has been introduced into the hydraulic system. Such system are disclosed in NO 331866 ( NATIONAL OILWELL VARCO NORWAY AS), US 2014123634 Al ( VOLVO CONSTRUKTIONS EQUIPMENT AB), US 8,209,975 B2 ( PARKER HANNIFIN AB) and US 2013111890 Al ( PARKER HANNIFIN AB).
From NO 331866 it is known an apparatus and method for recuperation of hydraulic energy from an actuator where a first drive of a first hydraulic machine and a second drive of a second hydraulic machine are mechanically connected, and where the first hydraulic machine is in hydraulic communication with an actuator, and where the second hydraulic machine is in hydraulic communication with an accumulator. This solution is mainly related to the possibility to supply hydraulic fluid from both hydraulic machines when the actuator works close to its maximal load and speed.
US 2014123634 discloses a hydraulic system for a working machine including a hydraulic actuator and a first hydraulic machine for supplying fluid to the hydraulic actuator. The hydraulic system further includes a hydraulic transformer for supplying fluid to the hydraulic actuator in parallel with the first hydraulic machine, and an accumulator for fluid. The hydraulic transformer includes a first port and a second port and the transformer is adapted to transform a first pressure and a first flow at the first port to a second pressure and a second flow at the second port. The second port of the hydraulic transformer is in fluid communication with the hydraulic actuator and the first port is in communication with the accumulator. This system is especially related to the use of a hydraulic actuator controller being adapted to determine a required hydraulic power for the hydraulic actuator, wherein the hydraulic actuator controller further is adapted to request a first power portion of the required hydraulic power from the hydraulic transformer and a second power portion of the required hydraulic power from the first hydraulic machine.
In US 8,209,975 is a fluid system described including a controllable first pump unit for supplying fluid pressure to at least one implement; a prime mover arranged to supply a driving torque to the first pump, where the first pump unit is arranged to supply fluid pressure to the implement. The fluid system further includes a controllable second pump unit connected to a fluid accumulator. The prime mover is arranged to supply a driving torque to the second pump unit in order to accumulate fluid pressure in the accumulator during periods of low demand. Fluid pressure from the accumulator is arranged to drive the second pump unit to assist the prime mover during periods of high demand in order to supply an additional driving torque in excess of the available driving torque from the prime mover.
From US 2013111890 it is known a start/stop arrangement in a fluid system comprising a controllable pump unit for supplying fluid pressure to at least one implement; a prime mover connected to a transmission device arranged to drive the pump unit; wherein the pump unit is installed on an outgoing power take off and is arranged to supply fluid pressure to the implement fluid system. The pump unit is arranged for accumulating fluid pressure in the accumulator. The fluid system further comprises a controllable motor unit connected to a fluid accumulator; that fluid pressure from the accumulator is arranged to drive the motor unit; and that the motor unit is connected to the prime mover by an overrun clutch, wherein the motor unit is arranged to supply torque to and start the prime mover when at least one predetermined condition is fulfilled. The motor is used to help the pump when the power requirement increases.
The above mentioned prior art solutions suffer from not being provided with energy efficient solutions as they do not have possibility to maintain and accumulate energy which normally is used to produce pressure without delivery to the load system. There is accordingly a need for providing energy efficient solutions for hydraulic systems, and particularly for large hydraulic power units.
Object
The main object of the invention is to provide a hydraulic system and method for controlling a hydraulic system solving the above mentioned drawbacks with prior art.
It is further an object of the present invention to provide a hydraulic system and a method for controlling a hydraulic system providing energy efficient solutions for the hydraulic system.
A further object of the present invention is to provide a hydraulic system and a method for controlling a hydraulic system providing possibilities for maintaining and accumulating energy which normally is used to produce pressure without delivery to the load system.
It is further an object of the present invention to provide a hydraulic system and a method for controlling a hydraulic system which are arranged for using only so much energy as the hydraulic system requires for proper working.
Further objects will appear by considering the following description, claims and drawings.
The invention
A hydraulic system according to the present invention is described in claim 1. Preferable features of the system are described in the claims 2-9.
A method for controlling a hydraulic according to the present invention is described in claim 10. Preferable features of the method are described in the claims 11-15.
The present invention provides a hydraulic system and a method for a novel and innovative way of controlling a hydraulic system, especially in standby mode, including accumulation of hydraulic energy and use of the accumulated hydraulic energy for maintaining required hydraulic pressure and flow in the hydraulic system.
The hydraulic system according to the present invention includes a first hydraulic machine and a second hydraulic machine, the hydraulic machines being arranged in series to a shaft of a common electric motor (e.g. AC) which is being controlled by a frequency converter for powering the hydraulic machines, and in this way forming a tandem machine unit.
The first hydraulic machine is preferably a variable hydraulic machine and is connected to hydraulic equipment while the second hydraulic machine is a hydraulic machine with a fixed or variable displacement range which is connected to an accumulator which again is connected to the hydraulic equipment.
The variable hydraulic machine is further arranged to a safety device including control valves, such as one or more pressure control valves and pressure relieve valves.
The hydraulic system further includes a control unit provided with means or software for controlling the hydraulic system. This includes controlling the hydraulic machines via the electric motor by controlling the frequency converter. The controlling is based on controlling speed of the electric motor by e.g. Direct Torque Control. The controlling further includes controlling the oil amount to the accumulator and the safety device and valves therein.
In operational mode of the hydraulic equipment the hydraulic system according to the present invention will work as prior art systems by that the variable hydraulic machine will provide required oil pressure and flow to the hydraulic equipment.
The main innovation over prior art is how the hydraulic system is controlled in stand by mode, i.e. when the hydraulic equipment is in stand by mode.
In stand by mode of the hydraulic equipment, the variable hydraulic machine will circulate without hydraulic pressure and flow, while the second hydraulic machine with fixed or variable displacement range chargés the pressure in the accumulator to a pressure higher than working pressure (designed system pressure) of the hydraulic system. The pressure in the accumulator is preferably charged to a pressure being approximately 5-10 % higher than working pressure of the hydraulic system, more preferably approximately 10-15 % higher than working pressure of the hydraulic system, and even more favorable approximately 15-25 % higher than working pressure of the hydraulic system. How much higher pressure the accumulator will need to have will be dependent on the properties of the hydraulic system/equipment, and e.g. will volume of the accumulator and response time be dependent on properties of the hydraulic pumps.
The oil amount delivered to the accumulator is controlled by the control unit and is proportional with the pressure in the accumulator. Pressure over the mentioned higher pressure in the accumulator is separated by a check valve, arranged between the safety device for the variable hydraulic machine and the hydraulic equipment.
The accumulator, by that it is provided with a pressure being higher than the working pressure, is arranged for supplying oil to the hydraulic equipment in a transitional period, further described below.
When it is detected that the delivered flow to the hydraulic equipment is over a predefined set point set in the control unit, the pressure control valve for circulating flow in the variable hydraulic machine in the safety device is disconnected and the variable hydraulic machine will start to deliver oil pressure and flow to the hydraulic equipment.
In the following transitional period between the disconnected pressure and flow in the variable hydraulic machine and the set point of the working pressure from a pressure relieve valve in the safety device, both pressure and flow in the hydraulic system are delivered by the accumulator. Oil delivered by the variable hydraulic machine is proportional with the oil flow which is required processed by the control unit and the control unit controls the frequency converter which drives the hydraulic machines via the electrical motor.
When the pressure from the variable hydraulic machine is according to the predefined set point for the working pressure, the accumulator is disconnected and the variable hydraulic machine will deliver the required oil pressure and flow until the hydraulic equipment/system again is set in stand by mode, whereupon the procedure as described above is repeated.
By the present invention it is possible to achieve a hydraulic system being up to ten times more energy efficient in stand by mode than what can be achieved by prior art. It can further be achieved a hydraulic system being more energy efficient and resulting in a longer operating live than what can be achieved by prior art. The present invention further provides a hydraulic system with lower working temperature and lower noise level compered to prior art solutions.
By the present invention, further can be achieved faster reaction for flow demand from the hydraulic system and lower pressure fall on hydraulic equipment load line.
Further preferable features and advantageous details of the present invention will appear from the following example description.
Example
The present invention will be further described with references to the attached drawings where:
Figure 1 is a functional diagram of a system according to the present invention, and
Figure 2 is a signal flow diagram of the system according to the present invention.
Reference is now made to Figure 1 which is a functional diagram of a hydraulic system according to the present invention and Figure 2 which is a signal flow diagram of the present invention. The main components of the hydraulic system according to the present invention includes a first 21 and second 22 hydraulic machine driving a hydraulic load system indicated by a hydraulic equipment 100 in the example.
The first hydraulic machine 21 is a variable hydraulic machine, in the example in the form of an axial piston pump 21. The second hydraulic 22 is a hydraulic machine with fixed or variable displacement range, in the example in the form of a pump 22 with fixed displacement range. Both hydraulic machines 21, 22 are arranged to a shaft 23 of an electric motor 24, and in this way forming a tandem pump unit connected to a common electric motor 24. In the shown example the electric motor 23 is an AC-motor which is controlled by a frequency converter 25.
Both hydraulic machines 21, 22 are by means of pipelines 26a, 26b communicating with a reservoir 30 for hydraulic fluid.
The variable hydraulic machine 21 is connected to load side of the hydraulic equipment 100 via an equipment pipeline 101. The variable hydraulic machine 21 is arranged for providing required oil pressure and flow to the hydraulic equipment 100 via the equipment pipeline 101, and where the hydraulic machine 21 will be controlled by a control unit 200, further discussed below. Accordingly, the variable hydraulic machine 21 will be adapted to the properties of the hydraulic equipment 100 for providing the required oil pressure and flow in the equipment pipeline 101 for powering the hydraulic equipment 100.
The hydraulic machine 22 with fixed displacement range is arranged to an accumulator 40, such as bladder accumulator, which further is arranged to the equipment pipeline 101, and is also controlled by the control unit 200, further described below. A bladder accumulator is the preferred solution, but also other solutions like a piston accumulator can be used, but a piston accumulator will have slower response and lower number of lifetime cycles. Accordingly, the hydraulic machine 22 and accumulator 40 will be adapted so as to be able to provide higher pressure than required oil pressure (working pressure) and flow in the equipment pipeline 101 for the hydraulic equipment 100 when the hydraulic equipment are in stand by mode.
The hydraulic system according to the present invention further includes a safety device 50 for the variable hydraulic machine 21 and a check valve 60 for the variable hydraulic machine 21, arranged in the equipment pipeline 101 between the variable hydraulic machine 21 and the connection of the accumulator 40 to the equipment pipeline 101, wherein the safety device 50 is arranged closest to the variable hydraulic machine 21.
The safety device 50 is provided with control valves 51-52 for controlling the system, in the example in the form of a pressure control valve 51 and a pressure relieve valve 52. The function of the different valves will be explained in further detail below.
Between the accumulator 40 and the equipment pipeline 101 is further arranged a pressure reducing valve 41, and a pressure sensor 42 is arranged in connection with the accumulator 40 to measure the pressure therein. The function of the pressure reducing valve 41 will be explained further below.
A pressure transducer 70 is further arranged in the equipment pipeline 101, before connection of the hydraulic equipment 100, but after the connection of the accumulator 40.
The first hydraulic machine 21 is further arranged to a load sense control 27 regulating maximal pressure. When maximal pressure is reached the first hydraulic machine 21 will angle down and reduce delivery of flow. By activating pressure control valve 51 pressure is reduced to minimum and the first hydraulic machine 21 is no longer delivering flow, i.e. it is disconnected.
The pressure relieve valve 52 of the safety device 50 is arranged for opening for oil pressure and flow from the variable hydraulic machine 21 when a predefined pressure is reached.
In addition the hydraulic system will be provided with filters (not shown) at suitable positions, which are well known for a skilled person a need no further description.
The control unit 200 is provided with means and/or software for controlling the hydraulic machines 21 and 22 by controlling the electric motor 24 via the frequency converter 25. The control unit 200 is further arranged for controlling the speed of the electric motor 24 by means of direct torque control (DTC). The control unit 200, as shown in Figure 2, will receive input from the pressure sensor 42 for the accumulator 40, the pressure transducer 70 in the equipment pipeline 101, and the hydraulic equipment 100. The control unit 200 will produce control signals for the safety device 50 and the valves 51-52 therein, and the frequency converter 25 for controlling the hydraulic machines 21, 22 via the electric motor 24.
When the hydraulic equipment 100 is in operational mode the hydraulic machine 21 will be controlled to provided required oil pressure and flow in the equipment pipeline 101 by that the control unit 200 controls the speed of the electric motor 24 via the frequency converter 25.
In stand by mode for the hydraulic equipment 100 the variable hydraulic machine 21 is adjusted via the pressure control valve 51 for circulating oil in the variable hydraulic machine 21 back to the reservoir 30 and by means of the load sense control 27. Further, the second hydraulic machine 22 will be charging the pressure in the accumulator 40 to e.g. approximately 20 % higher than working pressure. The pressure from the accumulator 40 being delivered to the equipment pipeline 101 is reduced to required oil pressure (working pressure) and flow by means of the pressure reducing valve 41. The pressure in the accumulator 40 is measured by a pressure sensor 42 and the hydraulic machine 22 is controlled by the control unit 200 via the frequency converter 25 and electric motor 24 so that the pressure in the accumulator 40 is e.g. 20 % higher than required pressure for the hydraulic equipment 100. The oil amount being delivered to the accumulator 40 is controlled by the control unit 200 and the delivered oil amount is proportional with the pressure in the accumulator 40.
Pressure over this mentioned higher pressure in the accumulator 40 is separated by the safety device 50 for the variable hydraulic machine 21 via the check valve 60.
After the oil amount delivered from the accumulator 40 to the equipment pipeline 101 reaches a predefined set point for the flow set in the control unit 200, pressure control valve 51 will be disconnected and the variable hydraulic machine 21 will start to deliver pressure.
In the following transitional period between the disconnected pressure and flow in the variable hydraulic machine 21 and set point of the required pressure from the relieve valve 52 in the safety device, both oil pressure and flow in the hydraulic system is delivered by the accumulator 40. When the set point is reached, the relieve valve 51 opens and the variable hydraulic machine 21 will deliver oil pressure and flow for powering the hydraulic equipment 100 while the flow from the accumulator 40 is disconnected by the pressure reducing valve 41.
When the hydraulic equipment 100 again is set in stand by the above described procedure is again repeated.
Claims (15)
1. Hydraulic system including a hydraulic equipment (100), a first hydraulic machine (21) and a second hydraulic machine (22), the hydraulic machines (21, 22) being powered by a common electric motor (24), where the first hydraulic machine (21) is in hydraulic connection with the hydraulic equipment (100) and the second hydraulic machine (22) is in hydraulic connection with the hydraulic equipment (100) via an accumulator (40), where the first hydraulic machine (21) is a variable hydraulic machine and is supplying oil pressure and oil flow to the hydraulic equipment (100) when the hydraulic equipment (100) is in operational mode,
characterized in thatthe second hydraulic machine (22) is a hydraulic machine with fixed or variable displacement range and that the second hydraulic machine (22) and the accumulator (40) are arranged for maintaining required oil pressure and flow and accumulating energy without delivery to hydraulic equipment (100) when the hydraulic equipment (100) is in stand by mode.
2. Hydraulic system according to claim 1,characterized in thatthe accumulator (40) is arranged for supplying the hydraulic equipment (100) with required oil pressure and flow in a transitional period after stand by mode of hydraulic equipment (100) until the hydraulic machine (21) is providing the required oil pressure and flow.
3. Hydraulic system according to claim 1,characterized in thatthe electric motor (24) is controlled by a frequency converter (25).
4. Hydraulic system according to claim 1,characterized in thatsystem further includes a safety device (50) arranged between the variable hydraulic machine (21) and the hydraulic equipment (100), the safety device (50) including at least one pressure control valve (51) and at least one pressure relieve valve (52), where pressure control valve (51) is arranged for circulating flow in the variable hydraulic machine (21) back to a reservoir (30) in stand by mode of the hydraulic equipment (100) and pressure relieve valve (52) is arranged for opening for oil pressure and flow from the variable hydraulic machine (21) when a predefined pressure is reached.
5. Hydraulic system according to claim 1,characterized in thata pressure sensor (42) is arranged to the accumulator (40) and that the second hydraulic machine (22) is arranged for providing the accumulator (40) with a pressure being 5-10 % higher than required pressure of the hydraulic equipment (100), more preferably 10-15 % higher than require pressure of the hydraulic equipment (100), and even more favorable approximately 15-25 % higher than required pressure of the hydraulic equipment (100).
6. Hydraulic system according to claim 5,characterized in thatthe system further includes a check valve (60) arranged between the safety device (50) and the hydraulic equipment (100), which check valve (60) is arranged for separating pressure over the higher pressure in the accumulator (40).
7. Hydraulic system according to claim 6,characterized in thata pressure reducing valve (41) is arranged between the accumulator (40) and the hydraulic equipment (100) being arranged for reducing pressure delivered from the accumulator (40) to required pressure of the hydraulic equipment (100).
8. Hydraulic system according to claim 1,characterized in thata pressure transducer (70) is arranged in front of the hydraulic equipment (100).
9. Hydraulic system according to any one of the claims 1-8,characterized in thatthe system includes a control unit (200) provided with means and/or software for controlling: a. the hydraulic machines (21, 22) by means of controlling the frequency converter (25) controlling the common electric motor (24), b. the safety device (50) and the valves therein (51-52), and c. oil pressure in the accumulator (40),
based on input from at least the pressure transducer (70), pressure sensor (42) and hydraulic equipment (100).
10. Method for controlling a hydraulic system including a hydraulic equipment (100), a first hydraulic machine (21) and a second hydraulic machine (22), the hydraulic machines (21, 22) being powered by a common electric motor (24), where the first hydraulic machine (21) is a variable hydraulic machine (21) in hydraulic connection with the hydraulic equipment (100) and the second hydraulic machine (22) is in hydraulic connection with the hydraulic equipment (100) via an accumulator (40), the method including, in operational mode of the hydraulic equipment (100), providing required oil pressure flow to the hydraulic equipment (100) by means of the variable hydraulic machine (21),characterized bythe method further including: in stand by mode of the hydraulic equipment (100) maintaining required oil pressure and flow and accumulating energy without delivery to hydraulic equipment (100) by means of the second hydraulic machine (22) with fixed or variable displacement range and the accumulator (40).
11. Method according to claim 10,characterized byfurther including, in transitional period between disconnected pressure in the variable hydraulic machine (21) and required oil pressure and flow, delivering both pressure and oil flow by the accumulator (40).
12. Method according to any one of the claims 10-11,characterized by, in stand by mode of the hydraulic equipment (100), increasing the pressure in the accumulator (40) to a pressure being approximately 5-10 % higher than working pressure of the hydraulic equipment (100), more preferably approximately 10-15 % higher than working pressure of the hydraulic equipment (100), and even more favourable approximately 15-25 % higher than working pressure of the hydraulic equipment (100).
13. Method according to claims 12,characterized byseparating pressure over the higher pressure in the accumulator (40) via a check valve (60).
14. Method according to claims 10-13,characterized bycirculating flow in the variable hydraulic machine (21) back to a reservoir (30) in stand by mode of the hydraulic equipment (100) by means of a pressure control valve (51).
15. Method according to claims 10-14,characterized bydetecting, by means of a pressure relieve valve (52), that the pressure delivered from the variable hydraulic machine (21) is according to required pressure for the hydraulic equipment (100) and disconnecting the accumulator (40) and delivering required pressure and oil flow for the hydraulic equipment (100) by means of the variable hydraulic machine (21) until hydraulic equipment (100) again is set in stand by mode.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NO20150676A NO20150676A1 (en) | 2015-05-27 | 2015-05-27 | Hydraulic system and a method for recuperating energy. |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NO20150676A NO20150676A1 (en) | 2015-05-27 | 2015-05-27 | Hydraulic system and a method for recuperating energy. |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| NO20150676A1 true NO20150676A1 (en) | 2016-11-28 |
Family
ID=61800041
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| NO20150676A NO20150676A1 (en) | 2015-05-27 | 2015-05-27 | Hydraulic system and a method for recuperating energy. |
Country Status (1)
| Country | Link |
|---|---|
| NO (1) | NO20150676A1 (en) |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20090266067A1 (en) * | 2008-04-29 | 2009-10-29 | Parker Hannifin Ab | Arrangement for operating a hydraulic device |
| US20100212521A1 (en) * | 2007-09-12 | 2010-08-26 | Markus Resch | Drive device for a bending press |
| US20130199168A1 (en) * | 2010-05-20 | 2013-08-08 | National Oilwell Varco Norway As | Apparatus and Method for Recuperation of Hydraulic Energy |
-
2015
- 2015-05-27 NO NO20150676A patent/NO20150676A1/en not_active Application Discontinuation
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20100212521A1 (en) * | 2007-09-12 | 2010-08-26 | Markus Resch | Drive device for a bending press |
| US20090266067A1 (en) * | 2008-04-29 | 2009-10-29 | Parker Hannifin Ab | Arrangement for operating a hydraulic device |
| US20130199168A1 (en) * | 2010-05-20 | 2013-08-08 | National Oilwell Varco Norway As | Apparatus and Method for Recuperation of Hydraulic Energy |
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