EP2435712B1 - Controlled hydraulic systems comprising a variable drive ratio device - Google Patents
Controlled hydraulic systems comprising a variable drive ratio device Download PDFInfo
- Publication number
- EP2435712B1 EP2435712B1 EP10720663.3A EP10720663A EP2435712B1 EP 2435712 B1 EP2435712 B1 EP 2435712B1 EP 10720663 A EP10720663 A EP 10720663A EP 2435712 B1 EP2435712 B1 EP 2435712B1
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- EP
- European Patent Office
- Prior art keywords
- hydraulic system
- flow
- pump
- orifices
- speed
- 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
- 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
- F04B49/20—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 changing the driving speed
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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
- F04B49/06—Control using electricity
- F04B49/065—Control using electricity and making use of computers
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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
- F15B11/04—Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the speed
- F15B11/05—Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the speed specially adapted to maintain constant speed, e.g. pressure-compensated, load-responsive
- F15B11/055—Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the speed specially adapted to maintain constant speed, e.g. pressure-compensated, load-responsive by adjusting the pump output or bypass
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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
- F04B2203/00—Motor parameters
- F04B2203/02—Motor parameters of rotating electric motors
- F04B2203/0209—Rotational speed
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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
- F15B2211/205—Systems with pumps
- F15B2211/20507—Type of prime mover
- F15B2211/20515—Electric motor
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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
- F15B2211/205—Systems with pumps
- F15B2211/20507—Type of prime mover
- F15B2211/20523—Internal combustion engine
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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
- F15B2211/205—Systems with pumps
- F15B2211/2053—Type of pump
- F15B2211/20538—Type of pump constant capacity
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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
- F15B2211/255—Flow control functions
-
- 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
- F15B2211/60—Circuit components or control therefor
- F15B2211/63—Electronic controllers
- F15B2211/6303—Electronic controllers using input signals
- F15B2211/6306—Electronic controllers using input signals representing a pressure
- F15B2211/6309—Electronic controllers using input signals representing a pressure the pressure being a pressure source supply pressure
-
- 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
- F15B2211/60—Circuit components or control therefor
- F15B2211/63—Electronic controllers
- F15B2211/6303—Electronic controllers using input signals
- F15B2211/6306—Electronic controllers using input signals representing a pressure
- F15B2211/6313—Electronic controllers using input signals representing a pressure the pressure being a load pressure
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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
- F15B2211/60—Circuit components or control therefor
- F15B2211/63—Electronic controllers
- F15B2211/6303—Electronic controllers using input signals
- F15B2211/6346—Electronic controllers using input signals representing a state of input means, e.g. joystick position
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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
- F15B2211/60—Circuit components or control therefor
- F15B2211/665—Methods of control using electronic components
- F15B2211/6651—Control of the prime mover, e.g. control of the output torque or rotational speed
Definitions
- the present invention relates to controlled hydraulic systems for operating machinery. More particularly, the present invention relates to a controlled hydraulic system comprising a variable drive ratio device interposed between a prime mover and a fixed displacement pump for controlling the operating speed of the pump and hence the output flow in the hydraulic system.
- hydraulic pump flow is only required when a service is required to be operated but with a fixed displacement pump the flow is continuous whether the flow is required or not.
- the prime mover has a fixed speed, for instance an electric motor, and it can sometimes be advantageous to be able to vary the output flow from the fixed displacement pump.
- the present invention is difference in that pressure transducers are used to monitor the pressures at different parts of the circuit in order to adjust spool position and maintain a specific pressure difference and hence maintain an operating speed of an actuator.
- Devices in the prior art also use the fact that cylinders acting as actuators are asymmetric in the head area and are different to rod area when apportioning flow is concerned. This does not happen in the present invention.
- prior art devices relate to monitoring pressure difference across the actuator.
- It is yet a further object of at least one aspect of the present invention to provide and improved controlled hydraulic system comprising a variable drive ratio device interposed between a prime mover a fixed displacement pump for controlling the operating speed of the pump hence the output flow.
- a controlled hydraulic system comprising:
- the present invention therefore resides in the provision of a controlled hydraulic system comprising a variable drive ratio device interposed and/or positioned between a prime mover and a pump for controlling the operating speed of the pump and hence the output flow in the hydraulic system.
- the prime mover may be of a fixed or variable speed and may, for example, be a diesel engine or an electric motor.
- the variable ratio drive between the prime mover and the pump means that the speed of the pump may be controlled independently or substantially independently of the prime mover speed.
- Diesel engines typically run between a minimum speed of about 650-750 rpm and a maximum speed or about 2200-2300 rpm (Electric motors run at about 960, 1500 or 3000 rpm).
- variable ratio drive may be any suitable variable ratio drive unit.
- a pump flow with a minimum engine speed of about a 3:1 ratio may be used (assuming that the engine has appropriate torque capability at low engine speed).
- the variable ratio drive may also be able to substantially limit the flow output when flow is not required in order to limit power wastage (potentially about a 1:3 ratio).
- the pump may be a fixed displacement pump such as an external gear pump, an internal gear pump, a vane pump or any other such pump capable of delivering a fixed output flow in relation to its input drive speed.
- the pump may be driven by an electric motor or a variable speed electric motor.
- the ratio of the variable ratio drive may be controlled by any suitable type of remote means.
- any of the following may be used:
- Methods of controlling the variability of the variable speed drive may include:
- variable ratio drive may therefore be envisaged as essentially a variable speed drive where the variability may be infinite between its upper and lower limits or alternatively it may be variable in discrete steps between its upper and lower limits.
- the input to output ratio may be less than or greater than about 1:1.
- any form of motor and/or engine may be used as the prime mover such as an electric motor or a diesel engine and may be used as a variable or fixed speed prime mover.
- the present invention may therefore provide a prime mover such as a drive from a transmission of a diesel engine which may be of variable speed, variable torque and/or variable energy consumption.
- the present invention may therefore address the problem of facilitating the use of hydraulic systems by a user.
- the hydraulic system may be in a variety of machinery and vehicles.
- the hydraulic system may be in earth moving vehicles, construction equipment vehicles, mechanical handling equipment and the like, and also power units (which may use an electric motor as a prime mover).
- the system may comprise a flow control device.
- the pressure difference across one orifice e.g. a spool metering notch
- at least one orifice, three orifices or a plurality of orifices may be fixed.
- the orifices may be spool metering notches.
- the hydraulic system may also comprise one reservoir, at least one reservoir or a plurality of reservoirs for hydraulic fluid.
- the hydraulic fluid may, for example, be any suitable oil-based flowable material/liquid.
- There may also be a system of cables for the hydraulic fluid to flow around to allow the hydraulic system to function.
- the system of hydraulic pipework may form a circuit for the hydraulic fluid.
- in the hydraulic system there may be a steady state condition and there may be a fixed spool position.
- the fixed spool position there may be a fixed flow across one orifice, at least one orifice, three orifices or a plurality of orifices.
- the conditions may constantly change and an operator will be continually changing lever positions in order to control spool position so that the flow across all selected spools may be maintained under conditions of changing pressure and flow influences.
- the orifices used in the hydraulic system may be any suitable type of valves such as poppet valves or spool valves. Spool valves are simpler than poppet valves. Both poppet valves and spool valves may be independently controlled. By using simple valves such as poppet valves also allows the different components of the hydraulic system to be separated which may simplify manufacturing processes. Poppet valves may be used, but spool valves are preferred. For reference, the three metering elements which are all on one spool, and are therefore mechanically linked, may be split into separate elements and controlled individually (i.e. the different elements may be independently controlled).
- the present invention may use pressure monitors on at least one side or either side of any selected orifice(s). In particular, there may therefore be pressure monitors on either side of one orifice, at least one orifice, three orifices or a plurality of orifices.
- the orifices may be spool metering notches.
- the hydraulic system may be remotely controlled thereby providing a remote interactive control system.
- the hydraulic system may comprise a controller such as a joystick controller, an electronic control package and/or a main control valve.
- a controller such as a joystick controller, an electronic control package and/or a main control valve.
- There may also be a pressure monitor across an orifice or a series of pressure monitors across (e.g. on both sides) of a plurality of orifices. Pressure monitors may therefore be positioned on one side and/or both sides of any orifice(s).
- the joystick controller may be connected to the electronic control package which may allow the joystick controller to send a signal to the electronic control package.
- the electronic control package may then send a signal to a valve. This may allow the output signal from the electronic control package to be modified and changed in response to any change in signal from the pressure monitors on at least one or both sides of an orifice.
- the hydraulic system according to the present invention may therefore allow a user to automatically use a controller (e.g. a given joystick position) to constantly modify spool position in response to any change in the pressure loss or increase across a selected orifice and thereby maintain the required flow and actuator speed.
- a controller e.g. a given joystick position
- the system allows a user to select the desired operating speed of the service. The system may then monitor and control that operating speed (by modifying spool position) until such time as the input from the joystick is changed. This may be performed automatically.
- the hydraulic system according to the present invention may allow monitoring of the flow and in some situations it may be possible to link this into the Engine Management System to control engine speed and hence pump flow, thereby reducing unused flow to a minimum.
- the present invention may also use pressure transducers to monitor the pressures at different parts of the circuit in order to adjust spool position and maintain a specific pressure difference and hence maintain an operating speed of an actuator.
- a method of controlling the operating speed of a pump and hence the output flow in a hydraulic system comprising:
- the method of controlling the operating speed may comprise using a pressure monitor across an orifice or a series of pressure monitors across (e.g. on both sides) of a plurality of orifices as defined in the first aspect.
- the pressure monitors form a sensing system and are capable of sensing pressure in the hydraulic system and transmitting the information to facilitate a user in using the hydraulic system and hence in the operation of a hydraulic machine.
- machinery and/or a vehicle comprising a hydraulic system according to the first aspect.
- the machinery may be earth moving vehicles, construction equipment vehicles, mechanical handling equipment and the like, and also power units (which may use an electric motor as a prime mover).
- the present invention resides in the provision of a controlled hydraulic system comprising a variable drive ratio device interposed between a prime mover and a fixed displacement pump for controlling the operating speed of the pump and hence the output flow in the hydraulic system.
- the ratio of the variable ratio drive 214 may be controlled by any suitable type of remote means. For example any of the following may be used:
- variable ratio drive 214 is essentially a variable speed drive where the variability may be infinite between its upper and lower limits or alternatively it may be variable in discrete steps between its upper and lower limits.
- the input to output ratio may be less than or greater than 1:1.
- variable speed drive would potentially assume a pump drive speed close to zero so that the pump delivered either no or a minimal amount of flow.
- the ratio could vary between 1:3 and 3:1.
- the ratio can be adjusted in order to reduce the pump speed and hence reduce the flow.
- the ratio can be adjusted in order to increase the pump speed and hence the flow.
- the torque limit controls the ratio of the variable speed drive such that high flow is available as long as the associated pressure requirement together with that flow does not exceed the torque limit. In such a case the ratio, and so the pump flow, would adjust to ensure that the pump demand remained within the available torque limit.
- any form of motor and/or engine may be used as the prime mover such as an electric motor or a diesel engine and may be used as a variable or fixed speed prime mover.
- the present invention may therefore provide a prime mover such as a drive from a transmission of a diesel engine which is of variable speed, variable torque and/or variable energy consumption.
- the apparatus of the present invention may therefore be seen as an energy transformer which may comprise a converter such as a variable ratio drive which may provide constant speed output with variable torque.
- Figure 3 which is a representation of a diesel engine which has variable speed (i.e. the rpm on the x-axis) with resulting variable torque (as represented by 'A'), variable power (as represented by 'B') and variable energy consumption (as represented by 'C').
- Figure 4 represents a hydraulic system according to the present invention and shows how the flow and input power is variable against rpm.
- the present invention addresses the problem of facilitating the use of hydraulic systems by a user.
- the hydraulic system may be in a variety of machinery and vehicles.
- the hydraulic system may be in earth moving vehicles, construction equipment vehicles, mechanical handling equipment and the like, and also power units (which may use an electric motor as a prime mover).
- FIG. 5 is a representation of an open centre hydraulic circuit, generally designated 500 with an oil reservoir 510.
- an orifice e.g. a spool metering notch
- Figure 5 is a representation of an open centre hydraulic circuit, generally designated 500 with an oil reservoir 510.
- 500 With an oil reservoir 510.
- a steady state condition there will be a fixed spool position.
- the conditions will constantly change and the operator will be continually changing lever positions in order to control spool position so that the flow across all selected spools is maintained under conditions of changing pressure and flow influences.
- position P2 is a meter in centre notch position 514 which may increase in size with spool selection.
- Position P1 is an open centre notch 512 which reduces in size with spool selection.
- Position P3 is a meter out centre notch 516 which increases in size with spool selection.
- Figure 6 is a typical representation of apparatus 600 according to the present invention which shows a meter out notch 610, an open centre notch 612 and a meter in notch 614. A value housing 616 and a valve spool 618 is also shown.
- FIG. 7 is a representation of remote interactive control system 700 of the present invention.
- the system 700 comprises a joystick controller 710, an electronic control package 712, a main control valve 714 and a pressure monitor 716 across an orifice. Pressure monitors may therefore be positioned on at least one or both sides of any orifice.
- the joystick controller 710 is connected to the electronic control package 712 which allows the joystick controller 710 to send a signal to the electronic control package 712.
- the electronic control package 712 may then send a signal to a valve.
- This allows the output signal from the electronic control package 712 to be modified and changed in response to any change in signal from the pressure monitors on at least one or both sides of an orifice.
- the purpose of the orifice is to meter the flow between the pump and a selected service in order to control the speed of operation of that selected function.
- the open centre orifice progressively closes the flow path from the pump back to the oil reservoir in order to raise pressure, the meter in orifice progressively opens in order to allow that pump flow out to the selected function, and the meter out orifice progressively opens in order to allow oil from the opposite side of the selected function to return back to the oil reservoir.
- Movement of the valve spool within the valve housing therefore progressively moves this set of 3 orifices, changing the area of each simultaneously, in order to control the selected function. If the spool is selected in the opposite direction a similar set of 3 orifices achieve the same purpose in order to reverse the direction of operation of the selected function.
- FIG 8 is a flow chart which illustrates the operation of the remote interactive control system 700 according to the present invention.
- the system 700 may therefore allow a user to automatically for a given joystick position to constantly modify the spool position in response to any change in the pressure loss or increase across a selected orifice and thereby maintain the required flow and actuator speed. This is in contrast to prior art techniques with both open centre and load sense where a user selects the spool position in order to control the operating speed of the service.
- the system allows a user to select the desired operating speed of the service. The system may then monitor and control that operating speed (by modifying spool position) until such time as the input from the joystick is changed.
- FIG. 9 is a representation of a remote interactive control system 900 according to the present invention.
- the system 900 comprises joystick controls 910, an electronic control package 912; a series of spool valves 920,930,940,950 and a reservoir 918 of oil.
- oil is diverted inside the spool valves 920,930,940,950 to the selected service and returning oil is diverted back to the reservoir 918.
- pressure monitors 922,924; 932,934; 942,944; 952,954 which monitor the flow through an orifice in the spool valves 920,930,940,950.
- each of the orifices can be an individual component such as, for example, poppet valves or spool vales. It is preferred to use spool valves.
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Description
- The present invention relates to controlled hydraulic systems for operating machinery. More particularly, the present invention relates to a controlled hydraulic system comprising a variable drive ratio device interposed between a prime mover and a fixed displacement pump for controlling the operating speed of the pump and hence the output flow in the hydraulic system.
- Many fixed displacement hydraulic pumps are connected directly to a variable speed prime mover, for instance a diesel engine, and as such the rotational speed of the pump, and hence its output flow, is almost directly proportional to the rotational speed of the prime mover.
- In practice, this means that the speed of operation of any selected service on a machine being driven by such a principle is proportional to the speed of the prime mover. In the case of a diesel engine its low idle speed is approximately 1/3 of its high idle speed and as such it will take approximately three times as long to operate a service when the engine is running at low idle when compared to the time taken to operate the same service when the engine is running at high idle.
- Further to this, hydraulic pump flow is only required when a service is required to be operated but with a fixed displacement pump the flow is continuous whether the flow is required or not.
- In some applications the prime mover has a fixed speed, for instance an electric motor, and it can sometimes be advantageous to be able to vary the output flow from the fixed displacement pump.
- There are a number of prior art systems for controlling hydraulic systems. However, many of these types of systems describe a hydraulic metering mode transitioning technique for a velocity based control system. However, there are a number of fundamental differences to these types of prior art systems and the present invention. For example, in the prior art the process selects which metering mode to use at any point in time which involves determining a parameter (such as a hydraulic load) which denotes an amount of force acting on the actuator. In contrast, in the present invention the parameter which is selected is operating speed. Moreover, in the prior art there is use of pressure transducers in a number of location which are sensed. The present invention is difference in that pressure transducers are used to monitor the pressures at different parts of the circuit in order to adjust spool position and maintain a specific pressure difference and hence maintain an operating speed of an actuator. Devices in the prior art also use the fact that cylinders acting as actuators are asymmetric in the head area and are different to rod area when apportioning flow is concerned. This does not happen in the present invention. A further significant difference is that prior art devices relate to monitoring pressure difference across the actuator.
- US patents,
US 4 489 623 andUS 4 232 570 , describe the use of variable transmission unit operable to drive an axle shaft and pump unit for a vehicle. - It is an object of at least one aspect of the present invention to obviate or mitigate at least one or more of the aforementioned problems.
- It is a further object of at least one aspect of the present invention to provide an improved controlled hydraulic system for operating machinery.
- It is yet a further object of at least one aspect of the present invention to provide and improved controlled hydraulic system comprising a variable drive ratio device interposed between a prime mover a fixed displacement pump for controlling the operating speed of the pump hence the output flow.
- It is a further object of at least one aspect of the present invention to provide an improved method for controlling a hydraulic system.
- According to a first aspect of the present invention there is provided a controlled hydraulic system comprising:
- a prime mover;
- a fixed displacement pump; and
- a variable drive ratio device interposed between the prime mover and the pump;
- characterised by a flow control device; wherein the flow control device comprises a plurality of orifices and which is capable of fixing the pressure difference across the orifices; and
- a sensing system for measuring and/or sensing the pressure difference across each of the plurality of orifices;
- wherein the variable ratio drive device and the flow control device are operable to control the operating speed of the pump and hence the output flow in the hydraulic system.
- The present invention therefore resides in the provision of a controlled hydraulic system comprising a variable drive ratio device interposed and/or positioned between a prime mover and a pump for controlling the operating speed of the pump and hence the output flow in the hydraulic system.
- Typically, the prime mover may be of a fixed or variable speed and may, for example, be a diesel engine or an electric motor. By mounting the variable ratio drive between the prime mover and the pump means that the speed of the pump may be controlled independently or substantially independently of the prime mover speed. Diesel engines typically run between a minimum speed of about 650-750 rpm and a maximum speed or about 2200-2300 rpm (Electric motors run at about 960, 1500 or 3000 rpm).
- The variable ratio drive may be any suitable variable ratio drive unit. For example, a pump flow with a minimum engine speed of about a 3:1 ratio may be used (assuming that the engine has appropriate torque capability at low engine speed). The variable ratio drive may also be able to substantially limit the flow output when flow is not required in order to limit power wastage (potentially about a 1:3 ratio).
- In particular embodiments, the pump may be a fixed displacement pump such as an external gear pump, an internal gear pump, a vane pump or any other such pump capable of delivering a fixed output flow in relation to its input drive speed.
- The pump may be driven by an electric motor or a variable speed electric motor.
- The ratio of the variable ratio drive may be controlled by any suitable type of remote means. For example any of the following may be used:
- (1) The input to control the pump speed may be determined by varying the speed of the prime mover such that pump output flow remains constant within prescribed operating limits of all components within the system over a wide range of prime mover speeds;
- (2) The input to control the pump speed may be determined by other requirements, for instance the need to drive selected services at a specific speed, requiring a specific flow; and
- (3) The input to control the pump speed may be determined by whether there is a demand for flow.
- Methods of controlling the variability of the variable speed drive may include:
- (1) Electro-, hydraulic or electro-hydraulic signaling into the unit based on sensors relating to engine speed;
- (2) Electro-, hydraulic or electro-hydraulic signaling into the unit based on sensors relating to actuator operating speed; and
- (3) Electro-, hydraulic or electro hydraulic signaling into-the unit based on sensors relating to control valve selection.
- The variable ratio drive may therefore be envisaged as essentially a variable speed drive where the variability may be infinite between its upper and lower limits or alternatively it may be variable in discrete steps between its upper and lower limits. For example, the input to output ratio may be less than or greater than about 1:1.
- It should be noted that any form of motor and/or engine may be used as the prime mover such as an electric motor or a diesel engine and may be used as a variable or fixed speed prime mover. The present invention may therefore provide a prime mover such as a drive from a transmission of a diesel engine which may be of variable speed, variable torque and/or variable energy consumption.
- The present invention may therefore address the problem of facilitating the use of hydraulic systems by a user. The hydraulic system may be in a variety of machinery and vehicles. In particular, the hydraulic system may be in earth moving vehicles, construction equipment vehicles, mechanical handling equipment and the like, and also power units (which may use an electric motor as a prime mover).
- To control a hydraulic system which forms part of a hydraulic apparatus requires a certain flow of hydraulic fluid in the hydraulic system. In certain circumstances the system may comprise a flow control device. During this flow, the pressure difference across one orifice (e.g. a spool metering notch), at least one orifice, three orifices or a plurality of orifices may be fixed. The orifices may be spool metering notches.
- The hydraulic system may also comprise one reservoir, at least one reservoir or a plurality of reservoirs for hydraulic fluid. The hydraulic fluid may, for example, be any suitable oil-based flowable material/liquid. There may also be a system of cables for the hydraulic fluid to flow around to allow the hydraulic system to function. The system of hydraulic pipework may form a circuit for the hydraulic fluid.
- In particular embodiments, in the hydraulic system there may be a steady state condition and there may be a fixed spool position. During the fixed spool position there may be a fixed flow across one orifice, at least one orifice, three orifices or a plurality of orifices. There may also be a fixed pressure difference across one orifice, at least one orifice, three orifices or a plurality of orifices. However, in practice the conditions may constantly change and an operator will be continually changing lever positions in order to control spool position so that the flow across all selected spools may be maintained under conditions of changing pressure and flow influences.
- The orifices used in the hydraulic system may be any suitable type of valves such as poppet valves or spool valves. Spool valves are simpler than poppet valves. Both poppet valves and spool valves may be independently controlled. By using simple valves such as poppet valves also allows the different components of the hydraulic system to be separated which may simplify manufacturing processes. Poppet valves may be used, but spool valves are preferred. For reference, the three metering elements which are all on one spool, and are therefore mechanically linked, may be split into separate elements and controlled individually (i.e. the different elements may be independently controlled).
- To control a hydraulically operated apparatus at a certain speed may require a certain flow of hydraulic fluid. At this flow, the pressure difference across one orifice (e.g. a spool metering notch), at least one orifice, three orifices or a plurality of orifices may be fixed. However, problems for a user may then occur if the conditions change and it requires action from an operator to maintain the operating speed of the selected service. The present invention may use pressure monitors on at least one side or either side of any selected orifice(s). In particular, there may therefore be pressure monitors on either side of one orifice, at least one orifice, three orifices or a plurality of orifices. The orifices may be spool metering notches.
- In particular embodiments, the hydraulic system may be remotely controlled thereby providing a remote interactive control system.
- The hydraulic system may comprise a controller such as a joystick controller, an electronic control package and/or a main control valve. There may also be a pressure monitor across an orifice or a series of pressure monitors across (e.g. on both sides) of a plurality of orifices. Pressure monitors may therefore be positioned on one side and/or both sides of any orifice(s). The joystick controller may be connected to the electronic control package which may allow the joystick controller to send a signal to the electronic control package. The electronic control package may then send a signal to a valve. This may allow the output signal from the electronic control package to be modified and changed in response to any change in signal from the pressure monitors on at least one or both sides of an orifice.
- The hydraulic system according to the present invention may therefore allow a user to automatically use a controller (e.g. a given joystick position) to constantly modify spool position in response to any change in the pressure loss or increase across a selected orifice and thereby maintain the required flow and actuator speed. In the present invention, the system allows a user to select the desired operating speed of the service. The system may then monitor and control that operating speed (by modifying spool position) until such time as the input from the joystick is changed. This may be performed automatically.
- The hydraulic system according to the present invention may allow monitoring of the flow and in some situations it may be possible to link this into the Engine Management System to control engine speed and hence pump flow, thereby reducing unused flow to a minimum.
- The present invention may also use pressure transducers to monitor the pressures at different parts of the circuit in order to adjust spool position and maintain a specific pressure difference and hence maintain an operating speed of an actuator.
- According to a second aspect of the present invention there is provided a method of controlling the operating speed of a pump and hence the output flow in a hydraulic system, the method comprising:
- providing a prime mover;
- providing a fixed displacement pump; and
- providing a variable drive ratio device interposed between the prime mover and the pump;
- characterised by providing a flow control device; wherein the flow control device comprises a plurality of orifices and which is capable of fixing the pressure difference across the orifices; and
- providing a sensing system for measuring and/or sensing the pressure difference across each of the plurality of orifices;
- wherein the variable ratio drive device and the flow control device are operable to control the operating speed of the pump and hence the output flow in the hydraulic system.
- The method of controlling the operating speed may comprise using a pressure monitor across an orifice or a series of pressure monitors across (e.g. on both sides) of a plurality of orifices as defined in the first aspect.
- The pressure monitors form a sensing system and are capable of sensing pressure in the hydraulic system and transmitting the information to facilitate a user in using the hydraulic system and hence in the operation of a hydraulic machine.
- According to a third aspect of the present invention there is provided machinery and/or a vehicle comprising a hydraulic system according to the first aspect.
- Typically, the machinery may be earth moving vehicles, construction equipment vehicles, mechanical handling equipment and the like, and also power units (which may use an electric motor as a prime mover).
- Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:
-
Figure 1 is a schematic representation of a pump mounted directly onto a prime mover according to the prior art; -
Figure 2 is a schematic representation of a variable speed drive interposed between a prime mover and a pump according to an embodiment of the present invention; -
Figure 3 is a representation of a diesel engine which has variable speed (i.e. the rpm on the x-axis) with resulting variable torque (as represented by 'A'), variable power (as represented by 'B') and variable energy consumption (as represented by 'C'); -
Figure 4 represents a hydraulic system according to the present invention and shows how the flow and input power is variable against rpm; -
Figure 5 is a representation of an open centre hydraulic circuit according to an embodiment the present invention; -
Figure 6 is a representation of a meter showing different notch positions in an apparatus according to an embodiment the present invention; -
Figure 7 is a representation of remote interactive control system according to an embodiment the present invention; -
Figure 8 is a flow chart which illustrates the operation of a remote interactive control system according to an embodiment of the present invention; and -
Figure 9 is a schematic representation of a remote interactive control system according to a further embodiment of the present invention. - Generally speaking, the present invention resides in the provision of a controlled hydraulic system comprising a variable drive ratio device interposed between a prime mover and a fixed displacement pump for controlling the operating speed of the pump and hence the output flow in the hydraulic system.
-
Figure 1 represents the prior art situation where the prior art apparatus, generally designated 100, comprises aprime mover 110 and apump 112 mounted directly onto theprime mover 110. Theprime mover 110 may be of a fixed or variable speed and may be a diesel engine or an electric motor. Thepump 112 is mounted such that the drive between theprime mover 110 and thepump 112 is direct. This means that the speed of thepump 112 changes in proportion to the speed of theprime mover 110. -
Figure 2 is a general representation of apparatus according to the present invention generally designated 200. As shown inFigure 2 , avariable ratio drive 214 is mounted between aprime mover 210 and a pump 212 (e.g. a fixed displacement pump). Theprime mover 210 may be of a fixed or variable speed and may be a diesel engine or an electric motor. By mounting the variable ratio drive 214 between theprime mover 210 and thepump 212 means that the speed of thepump 212 can be controlled independently of theprime mover 210 speed. Thevariable ratio drive 214 may be any suitable variable ratio drive unit. - The ratio of the
variable ratio drive 214 may be controlled by any suitable type of remote means. For example any of the following may be used: - (1) The input to control the pump speed may be determined by varying the speed of the prime mover such that pump output flow remains constant within prescribed operating limits of all components within the system over a wide range of prime mover speeds;
- (2) The input to control the pump speed may be determined by other requirements, for instance the need to drive selected services at a specific speed, requiring a specific flow; and
- (3) The input to control the pump speed may be determined by whether there is a demand for flow.
- (1) Electro-, hydraulic or electro-hydraulic signaling into the unit based on sensors relating to engine speed;
- (2) Electro-, hydraulic or electro-hydraulic signaling into the unit based on sensors relating to actuator operating speed; and
- (3) Electro-, hydraulic or electro-hydraulic signaling into the unit based on sensors relating to control valve selection.
- The present invention therefore relates to the positioning/interposing of a variable ratio drive 214 between a
prime mover 210 and apump 212. Thevariable ratio drive 214 is essentially a variable speed drive where the variability may be infinite between its upper and lower limits or alternatively it may be variable in discrete steps between its upper and lower limits. For example, the input to output ratio may be less than or greater than 1:1. - There are a number of situations where the present invention may be of use. These include, but are not limited to, the cases described below:
- If the flow is not required then the variable speed drive would potentially assume a pump drive speed close to zero so that the pump delivered either no or a minimal amount of flow. Alternatively, we may use the situation where the ratio could vary between 1:3 and 3:1.
- If the system requires less flow than that the pump is delivering due to the speed it is being driven at then the ratio can be adjusted in order to reduce the pump speed and hence reduce the flow.
- Normal situation where flow required relates directly to speed of prime mover.
- If the system requires more flow than the pump is delivering due to the speed it is being driven at then the ratio can be adjusted in order to increase the pump speed and hence the flow.
- Where the pump is being driven by fixed speed prime mover and there is a requirement to vary the output flow which can be achieved by varying the pump speed.
- This applies to where an engine running at a lower speed has a torque limit. The torque limit controls the ratio of the variable speed drive such that high flow is available as long as the associated pressure requirement together with that flow does not exceed the torque limit. In such a case the ratio, and so the pump flow, would adjust to ensure that the pump demand remained within the available torque limit.
- It should be noted that any form of motor and/or engine may be used as the prime mover such as an electric motor or a diesel engine and may be used as a variable or fixed speed prime mover.
- The present invention may therefore provide a prime mover such as a drive from a transmission of a diesel engine which is of variable speed, variable torque and/or variable energy consumption. The apparatus of the present invention may therefore be seen as an energy transformer which may comprise a converter such as a variable ratio drive which may provide constant speed output with variable torque. In this regard we refer to
Figure 3 which is a representation of a diesel engine which has variable speed (i.e. the rpm on the x-axis) with resulting variable torque (as represented by 'A'), variable power (as represented by 'B') and variable energy consumption (as represented by 'C'). -
Figure 4 represents a hydraulic system according to the present invention and shows how the flow and input power is variable against rpm. The present invention addresses the problem of facilitating the use of hydraulic systems by a user. The hydraulic system may be in a variety of machinery and vehicles. In particular, the hydraulic system may be in earth moving vehicles, construction equipment vehicles, mechanical handling equipment and the like, and also power units (which may use an electric motor as a prime mover). - To control a hydraulic system which forms part of a hydraulic apparatus requires a certain flow of hydraulic fluid in the hydraulic system. During this flow, the pressure difference across an orifice (e.g. a spool metering notch) is fixed. To illustrate this function we refer to
Figure 5 which is a representation of an open centre hydraulic circuit, generally designated 500 with anoil reservoir 510. During a steady state condition there will be a fixed spool position. There will be a fixed flow across each orifice and a fixed pressure difference across each orifice. However, in practice the conditions will constantly change and the operator will be continually changing lever positions in order to control spool position so that the flow across all selected spools is maintained under conditions of changing pressure and flow influences. As shown inFigure 5 , position P2 is a meter in centre notch position 514 which may increase in size with spool selection. Position P1 is anopen centre notch 512 which reduces in size with spool selection. Position P3 is a meter out centre notch 516 which increases in size with spool selection. -
Figure 6 is a typical representation ofapparatus 600 according to the present invention which shows a meter outnotch 610, anopen centre notch 612 and a meter innotch 614. A value housing 616 and a valve spool 618 is also shown. - There are a number of problems with open center systems. For example, for a given spool position the operating speed of an actuator will vary due to:
- (1) Any change in the load on the actuator (by varying the pressure requirement) i.e. as is typical on many machines due to changing mechanical advantage;
- (2) Any change in the input flow to a valve i.e. as may occur during changes in the engine speed;
- (3) How many spools are selected i.e. selecting more spools affects the operating conditions of the first selected spool.
- To control a hydraulically operated apparatus at a certain speed requires a certain flow of hydraulic fluid. At this flow, the pressure difference across an orifice (e.g. a spool metering notch) is fixed. However, problems for a user then occur if the conditions change and it requires action from an operator to maintain the operating speed of the selected service. The present invention uses pressure monitors on at least one or both sides of any selected orifice. For example, we refer to
Figure 7 which is a representation of remoteinteractive control system 700 of the present invention. Thesystem 700 comprises ajoystick controller 710, anelectronic control package 712, amain control valve 714 and apressure monitor 716 across an orifice. Pressure monitors may therefore be positioned on at least one or both sides of any orifice. Thejoystick controller 710 is connected to theelectronic control package 712 which allows thejoystick controller 710 to send a signal to theelectronic control package 712. Theelectronic control package 712 may then send a signal to a valve. This allows the output signal from theelectronic control package 712 to be modified and changed in response to any change in signal from the pressure monitors on at least one or both sides of an orifice. The purpose of the orifice is to meter the flow between the pump and a selected service in order to control the speed of operation of that selected function. On an open centre valve there are typically 3 orifices which perform this action as depicted inFigure 5 andFigure 6 . The open centre orifice progressively closes the flow path from the pump back to the oil reservoir in order to raise pressure, the meter in orifice progressively opens in order to allow that pump flow out to the selected function, and the meter out orifice progressively opens in order to allow oil from the opposite side of the selected function to return back to the oil reservoir. Movement of the valve spool within the valve housing therefore progressively moves this set of 3 orifices, changing the area of each simultaneously, in order to control the selected function. If the spool is selected in the opposite direction a similar set of 3 orifices achieve the same purpose in order to reverse the direction of operation of the selected function. - In practice, these metering orifices will frequently be designed to suit a specific function in terms of their individual rate of change of opening with regard to spool position. The proposal with the new system is that these 3 orifices are separated and as such can be controlled individually for improved machine control.
-
Figure 8 is a flow chart which illustrates the operation of the remoteinteractive control system 700 according to the present invention. Thesystem 700 may therefore allow a user to automatically for a given joystick position to constantly modify the spool position in response to any change in the pressure loss or increase across a selected orifice and thereby maintain the required flow and actuator speed. This is in contrast to prior art techniques with both open centre and load sense where a user selects the spool position in order to control the operating speed of the service. In the present invention, the system allows a user to select the desired operating speed of the service. The system may then monitor and control that operating speed (by modifying spool position) until such time as the input from the joystick is changed. - In a prior art open centre system any flow not required is passed through the centre of the valve and back to the tank. In contrast, the present invention will allow monitoring of the flow and in some situations it may be possible to link this into the Engine Management System to control engine speed and hence pump flow, thereby reducing unused flow to a minimum.
-
Figure 9 is a representation of a remoteinteractive control system 900 according to the present invention. Thesystem 900 comprises joystick controls 910, anelectronic control package 912; a series of spool valves 920,930,940,950 and areservoir 918 of oil. In a selected position, oil is diverted inside the spool valves 920,930,940,950 to the selected service and returning oil is diverted back to thereservoir 918. On either side of the spool valves 920,930,940,950 there are pressure monitors 922,924; 932,934; 942,944; 952,954 which monitor the flow through an orifice in the spool valves 920,930,940,950. - In the prior art, it is conventional that spool valves having three orifices are machined onto the same component. Therefore, when an orifice needs to change area then the other two have to change at the same time. In the present invention, it becomes feasible to separate these various elements such that each of the orifices can be an individual component such as, for example, poppet valves or spool vales. It is preferred to use spool valves.
- Whilst specific embodiments of the present invention have been described above, it will be appreciated that departures from the described embodiments may still fall within the scope of the present invention. For example, any suitable type of pressure monitors may be used to measure flow in the valves. Moreover, any suitable type of variable drive ratio may be used.
Claims (12)
- A controlled hydraulic system comprising:a prime mover (210);a fixed displacement pump (212); anda variable ratio drive device (214) interposed between the prime mover and the pump;
characterised by:a flow control device (714); wherein the flow control device comprises a plurality of orifices; anda sensing system (716) for measuring and/or sensing the pressure difference across each of the plurality of orifices and which is capable of fixing the pressure difference across the orifices;wherein the variable ratio drive device and the flow control device are operable to control the operating speed of the pump and hence the output flow in the hydraulic system. - A controlled hydraulic system according to claim 1, wherein the prime mover is of a fixed or variable speed.
- A controlled hydraulic system according to any preceding claim, wherein the ratio of the variable ratio drive is capable of being controlled remotely.
- A controlled hydraulic system according to any preceding claim, wherein the controlled hydraulic system comprises a system of hydraulic pipework system capable of allowing the hydraulic fluid to flow.
- A controlled hydraulic system according to any preceding claim, wherein the plurality of orifices are formed from spool valves.
- A controlled hydraulic system according to any preceding claim, wherein the hydraulic system is remotely controlled thereby providing a remote interactive control system (700).
- A controlled hydraulic system according to any preceding claim, wherein the hydraulic system comprises a controller (900)(e.g. a joystick controller), an electronic control package (910) and a main control valve (920, 930, 940, 950).
- A controlled hydraulic system according to claim 7, wherein the controller is connected to the electronic control package which is capable of allowing the controller to send a signal to the electronic control package which allows the output signal from the electronic control package to be modified and changed in response to any change in signal from the pressure monitors (922,924; 932, 934; 942, 944; 952, 954) on at least one or both sides of an orifice.
- A controlled hydraulic system according to any preceding claim, wherein a user is capable of automatically using a controller (e.g. a given joystick position) to constantly modify spool position in response to any change in pressure loss or increase across a selected orifice and thereby maintain the required flow and actuator speed, and wherein a monitoring and/or sensing system is capable of continuously monitoring and sensing hydraulic flow and transferring this information to an Engine Management System to control engine speed and hence pump flow.
- A controlled hydraulic system according to any preceding claim, wherein the hydraulic system comprises pressure transducers capable of monitoring the pressures at different parts of the hydraulic system in order to adjust spool position and maintain a specific pressure difference and hence maintain an operating speed of an actuator, and wherein there is a pressure monitor across an orifice or a series of pressure monitors across (e.g. on both sides) each of a plurality of orifices.
- A method of controlling the operating speed of a pump and hence the output flow in a hydraulic system, the method comprising:providing a prime mover;providing a fixed displacement pump;providing a variable drive ratio device interposed between the prime mover and the pump;
characterised by:providing a flow control device (714); wherein the flow control device comprises a plurality of orifices and which is capable of fixing the pressure difference across the orifices; andproviding a sensing system (716) for measuring and/or sensing the pressure difference across each of the plurality of orifices;wherein the variable ratio drive device and the flow control device are operable to control the operating speed of the pump and hence the output flow in the hydraulic system. - A method of controlling the operating speed of a pump according to claim 11, wherein the method comprises using a pressure monitor across an orifice or a series of pressure monitors across (e.g. on both sides) each of the plurality of orifices in the hydraulic system, and wherein the pressure monitors form the sensing system and are capable of sensing pressure in the hydraulic system and transmitting this information to facilitate a user in using the hydraulic system and hence in the operation of a hydraulic machine.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GBGB0908982.2A GB0908982D0 (en) | 2009-05-26 | 2009-05-26 | Controlled hydraulic systems |
PCT/GB2010/050784 WO2010136785A2 (en) | 2009-05-26 | 2010-05-13 | Controlled hydraulic systems |
Publications (2)
Publication Number | Publication Date |
---|---|
EP2435712A2 EP2435712A2 (en) | 2012-04-04 |
EP2435712B1 true EP2435712B1 (en) | 2015-04-22 |
Family
ID=40862949
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP10720663.3A Not-in-force EP2435712B1 (en) | 2009-05-26 | 2010-05-13 | Controlled hydraulic systems comprising a variable drive ratio device |
Country Status (4)
Country | Link |
---|---|
US (1) | US20120070312A1 (en) |
EP (1) | EP2435712B1 (en) |
GB (1) | GB0908982D0 (en) |
WO (1) | WO2010136785A2 (en) |
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- 2009-05-26 GB GBGB0908982.2A patent/GB0908982D0/en not_active Ceased
-
2010
- 2010-05-13 WO PCT/GB2010/050784 patent/WO2010136785A2/en active Application Filing
- 2010-05-13 EP EP10720663.3A patent/EP2435712B1/en not_active Not-in-force
- 2010-05-13 US US13/322,135 patent/US20120070312A1/en not_active Abandoned
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US4232570A (en) * | 1976-12-22 | 1980-11-11 | The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland | Variable ratio transmission systems |
EP0275463A2 (en) * | 1987-01-20 | 1988-07-27 | Ford-Werke Aktiengesellschaft | Transmission clutch closed loop slip controller |
US5092824A (en) * | 1990-10-09 | 1992-03-03 | Connett Donald C | Pump output control system with high efficiency hydromechanical variable speed drive |
WO1998047732A1 (en) * | 1997-04-18 | 1998-10-29 | Transport Energy Systems Pty. Ltd. | Hybrid propulsion system for road vehicles |
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Also Published As
Publication number | Publication date |
---|---|
US20120070312A1 (en) | 2012-03-22 |
GB0908982D0 (en) | 2009-07-01 |
WO2010136785A2 (en) | 2010-12-02 |
EP2435712A2 (en) | 2012-04-04 |
WO2010136785A3 (en) | 2011-03-31 |
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