Fluid power distribution and control system

Abstract

A fluid power system comprises a pump with multiple independently variable outlets, each of which is capable of delivering fluid in individually controllable volume units and a plurality of hydraulic loads. A system of switching valves is configured to create fluid connections between the pump outlets and the loads. A control system commands both the pump and the switching valves, so as to create valve state combinations to satisfy load conditions as demanded by an operator. The number of pump outlets connected to one or more of the loads is changeable to satisfy the flow required of the load due to the operator demand, each pump outlet being commanded to produce a flow depending on the status of other outlets connected a load to which the outlet is connected and the operator demand for that load.

Claims

1. A fluid power system, comprising: a prime mover; a pump/motor unit connected to the prime mover and comprising a plurality of independently-variable fluid working machines for delivering and absorbing fluid flow, each of which is capable of delivering or absorbing fluid in individually-controllable volume units through a respective outlet; a plurality of hydraulic loads, each associated with a demanded load condition; a system of switching valves configured to create fluid connections between the outlets of the fluid working machines and the loads, each valve having discrete states, wherein the system of switching valves comprises a plurality of valve state combinations based on the state of each valve, wherein each valve state combination serves to selectively supply fluid to one or more loads from one or more said outlets in one or more distinct and separate fluid paths, and wherein at least one of the valve state combinations serves to simultaneously supply fluid to two or more loads from one of the fluid working machines; and a control system commanding both the plurality of independently-variable fluid working machines and the system of switching valves, so as to select a particular valve state combination of the plurality of valve state combinations to satisfy the demanded load conditions, the valve state combination being changeable such as to change the number of fluid-working machine outlets connected to one or more of the loads to satisfy flow required or pressure required of the demanded load conditions; each fluid working machine being commanded to produce a flow depending on feedback from the one or more loads to which the outlet of the fluid working machine is connected and the demanded load conditions for the one or more loads, and further comprising a plurality of pressure sensors, of which, at least one pressure sensor of the plurality of pressure sensors provides said feedback, wherein each pressure sensor of the plurality of pressure sensors is between a respective switching valve of the system of switching valves and a respective load of the loads, wherein the system of switching valves includes a plurality of discrete and independently switchable switching valves.

2. The fluid power system according to claim 1, further comprising a shaft, the shaft connected to the plurality of fluid-working machines of the pump/motor unit, the shaft being driven by the prime mover, the fluid working machines each comprising one or more working chambers, each working chamber including one or more commutating valves, the control system sending pulses to the commutating valves synchronised with the position of the shaft by means of a shaft position sensor.

3. The fluid power system according to claim 1, wherein the prime mover is a variable speed prime mover which receives a speed demand signal from the control system.

4. The fluid power system according to claim 1, wherein the prime mover is a variable speed prime mover and the control system takes into account the speed of the prime mover.

5. The fluid power system according to claim 1, wherein one of the loads is coupled to the outlet of the respective fluid working machine through one of said switching valves and no other valve.

6. The fluid power system according to claim 1, wherein a pressure sensor of the plurality of pressure sensors is connected in a selected one of said one or more fluid paths between the switching valves and a plurality of the loads connected to the same outlet.

7. The fluid power system according to claim 6, wherein the pressure sensor connected in the selected one of said one or more fluid paths is between the switching valves and a plurality of bidirectional control valves.

8. The fluid power system according to claim 6, wherein said selected one of said one or more fluid paths extends from said pressure sensor to a plurality of the loads, each having a load-control valve.

9. The fluid power system according to claim 6, further comprising a load sensing pressure sensor which feeds back the highest pressure required of any of said plurality of loads connected to the same outlet.

10. The fluid power system according to claim 1, wherein different load pressures of different loads are decoupled such that interactions between load responses are avoided.

11. The fluid power system according to claim 1, wherein at least one of said loads is an actuator having two fluid ports and the position of the actuator may be controlled by delivering fluid into either of the two fluid ports regardless of whether the direction of force on the actuator is against or with the direction of motion.

12. The fluid power system according to claim 1, wherein two or more fluid working machines of the fluid working machines have their respective outlets connected to a same load of the plurality of hydraulic loads, and wherein each of the two or more fluid working machines is commanded to produce or absorb a flow depending on the same load which it is connected to and the status of the other of the two or more fluid working machines connected to that same load and the demanded load conditions for that same load.

13. The fluid power system according to claim 1, wherein the commanded outlet flows are controlled to continuously maintain the flow required or pressure required due to the demanded load conditions when the switching valves are switched to connect another fluid working machine to a load of the one or more loads.

14. The fluid power system according to claim 1, configured to independently switch individual fluid working machines between flow control and pressure control of the individual fluid working machine depending on whether the outlets of the fluid working machines are connected to a pressure-controlled or a flow-controlled load.

15. The fluid power system according to claim 1, wherein the the demanded load conditions includes a demanded power output.

16. The fluid power system according to claim 1, wherein the loads comprise an accumulator, wherein one or more of the fluid working machines are controlled to deliver energy to or absorb energy from the accumulator so as to buffer the torque load exerted on the prime mover.

17. The fluid power system according to claim 16, the fluid power system comprising a shaft, the shaft being connected to the plurality of fluid-working machines of the pump/motor unit, the shaft being driven by the prime mover, wherein the control system causes fluid energy from the accumulator to be transferred to the shaft such that the sum of the fluid power supplied to the other loads can temporarily exceed the maximum power output of the prime mover.

18. The fluid power system according to claim 1, wherein the switching valves are solenoid valves in a matrix arrangement such that each of the fluid-working machine outlets is simultaneously selectively couplable to a plurality of loads.

19. A method of controlling a fluid power system, the fluid power system comprising: a prime mover; a pump/motor unit connected to the prime mover and comprising a plurality of independently-variable fluid working machines for delivering and absorbing fluid flow, each of which is capable of delivering or absorbing fluid in individually-controllable volume units through a respective outlet; a plurality of hydraulic loads, each associated with a demanded load condition; a system of switching valves configured to create fluid connections between the outlets of the fluid working machines and the loads, each valve having discrete states, wherein the system of switching valves comprises a plurality of valve state combinations based on the state of each valve, wherein each valve state combination serves to selectively supply fluid to one or more loads from one or more said outlets in one or more distinct and separate fluid paths, and wherein at least one of the valve state combinations serves to simultaneously supply fluid to two or more loads from one of the fluid working machines; and a control system, which commands both the plurality of independently-variable fluid working machines and the system of switching valves, so as to select particular valve state combinations of the plurality of valve state combinations to satisfy the demanded load conditions, the valve state combination being changeable such as to change the number of fluid-working machine outlets connected to one or more of the loads to satisfy flow required or pressure required of the demanded load conditions; and further comprising a plurality of pressure sensors, of which, at least one pressure sensor of the plurality of pressure sensor provides feedback, wherein each pressure sensor of the plurality of pressure sensors is between a respective switching valve of the system of switching valves and a respective load of the loads, wherein the system of switching valves includes a plurality of discrete and independently switchable switching valves; the method comprising: commanding each fluid working machine to produce a flow depending on said feedback from the one or more loads to which the outlet of the fluid working machine is connected and the demanded load conditions for the one or more loads.

20. A fluid power system, comprising: a prime mover; a pump/motor unit connected to the prime mover and comprising a plurality of independently-variable fluid working machines for delivering and absorbing fluid flow, each of which is capable of delivering or absorbing fluid in individually-controllable volume units through a respective outlet; a plurality of hydraulic loads, each associated with a demanded load condition; a system of switching valves configured to create fluid connections between the outlets of the fluid working machines and the loads, each valve having discrete states, wherein the system of switching valves comprises a plurality of valve state combinations based on the state of each valve, wherein each valve state combination serves to selectively supply fluid to one or more loads from one or more said outlets in one or more distinct and separate fluid paths, and wherein at least one of the valve state combinations serves to simultaneously supply fluid to two or more loads from one of the fluid working machines; and a control system commanding both the plurality of independently-variable fluid working machines and the system of switching valves, so as to select particular valve state combinations of the plurality of valve state combinations to satisfy the demanded load conditions, the valve state combination being changeable such as to change the number of fluid-working machine outlets connected to one or more of the loads to satisfy flow required or pressure required of the demanded load conditions; each fluid working machine being commanded to produce a flow depending on feedback from the one or more loads to which the outlet of the fluid working machine is connected and the demanded load conditions for the one or more loads, wherein the loads include an accumulator, wherein one or more of the fluid working machines are controlled to deliver energy to or absorb energy from the accumulator so as to buffer the torque load exerted on the prime mover, and further comprising a shaft, the shaft being connected to the plurality of fluid-working machines of the pump/motor unit, the shaft being driven by the prime mover, wherein the control system causes fluid energy from the accumulator to be transferred to the shaft such that the sum of the fluid power supplied to the other loads can temporarily exceed the maximum power output of the prime mover, wherein the system of switching valves includes a plurality of discrete and independently switchable switching valves.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings.

(2) FIG. 1 schematically shows a system according to an embodiment of the invention.

(3) FIG. 2 shows an exemplary embodiment of a control system.

(4) FIG. 3 shows an exemplary embodiment of a fluid working machine.

DETAILED DESCRIPTION

(5) The drawing shows a pump/motor with four independent fluid supplies, two of which 11, 12 are pump outlets, two of which 13, 14 are pump/motor outlets, and each of which is controlled by a controller 1. Mechanical power comes into the pump/motor unit via its shaft 22 from a prime mover 2, which may take a speed demand signal from the controller 1. The fluid working machines 11, 12, 13, 14 may be configured as pumps according to EP 0361 927 B1 or pump/motors according to EP 0494236 B1. Each fluid working machine 11, 12, 13, 14 comprises one or more working chambers 23 and one or more commutating valves 24. A control system 1 is provided to supply pulses to the commutating valves 24 of the fluid working machines 11, 12, 13, 14. The pump/motor unit uses the ability of pumps according to EP 0361 927 B1 or pump/motors according to EP 0494236 B1 to provide a number of independent and fully controllable fluid supplies from one compact package with a single input shaft 22.

(6) The switching circuit 6 in this embodiment consists of digital solenoid valves in a matrix arrangement such that any of the fluid outlets of the pump/motor 11, 12, 13, 14 may be coupled to any of the load ports 7, 8, 9, 10. These valves are controlled by the controller 1. Each of the load ports 7, 8, 9, 10 is protected from overpressure by a safety relief valve.

(7) The first load port 7 is connected to a single acting ram 15. The pressure supply has a pressure sensor feeding a signal to the controller. The operator demands a certain pressure be maintained on the ram, however the system is also capable of controlling the flow to the ram, for instance if the flow required to meet the pressure demand exceeds a preset flow limit. In the case of a double-acting ram or a bidirectional fluid motor, a directional control valve may be provided to allow bidirectional movement of the ram, and load-control valves such as overcentre valves may be provided such that the ram may be moved in both directions regardless of the direction of force on the ram.

(8) The second load port 8 is connected to a gas-charged accumulator. This is capable of storing energy as gas pressure and returning it back as fluid energy at a later time.

(9) The third port 9 is connected to a hydraulic motor 20. The operator demands a certain flowrate with a certain direction be supplied to the motor, however the system is also capable of controlling the pressure to the motor, for instance if the pressure required to meet the flow demand exceeds a preset pressure limit.

(10) In this example, the hydraulic motor 20 is a “Digital Displacement” pump/motor and the controller 1 sends pulses to the commutating valves of the motor, synchronised with the position of the motor shaft by means of a motor shaft position sensor 21. The direction of the rotation of this pump/motor is determined by the phasing of the commutating pulses relative to the shaft as implemented by the controller.

(11) The fourth load port 10 is connected to a pressure supply 18 to three separate flow-compensated proportional valves with a load sensing arrangement, each of which controls the flow to a separate hydraulic work function, each of which is provided with load-control valves. The operator controls the proportional valves, and an arrangement of shuttle and check valves feeds the highest pressure required of any of the loads back to the controller via a transducer. The pump is controlled to maintain the pressure in the supply line some margin above the pressure in the load sense line, however the system is also capable of controlling the flow to the valves, for instance if the flow required to meet the pressure demand exceeds a preset flow limit. It is also possible for one of the load ports to supply a network of open-centre valves, in which case the flow output of this load port may be adjusted according to the setting of the proportional valves such that the minimum excess flow is created.

(12) The controller 1 receives commands from the operator interface 3, receives the feedback from the shaft position sensor 5, receives a pressure signal from sensors connected to each of the load ports 7, 8, 9, 10, receives a pressure feedback signal from the load sense pressure line 19, sends commands to the digital valves which need to be activated inside the valve circuit 6 to connect the fluid supplies 11, 12, 13, 14 to the loads ports 7, 8, 9, 10, and sends pulses to the fluid working machines 11, 12, 13, 14 such that the load ports 7, 8, 9, 10 produce or absorb the fluid flow required by the operator through the interface 3 and the load sensing pressure feedback sensor 19, subject to limitation when the pressure in each of the load ports approaches the maximum pressure allowed on each of the load ports 7, 8, 9, 10 or when the total shaft power taken from the prime mover 2 exceeds the maximum which it can provide. The controller may also supply commands to directional control valves associated with one or more of the loads.

(13) The controller 1 can choose to transfer fluid energy from the accumulator 16 to the shaft of the pump/motor for the purposes of buffering the load on the engine such that the sum of the fluid power supplied to the other load ports 7, 9, 10 can temporarily exceed the maximum power output of the prime mover 2, and can provide fluid energy to the accumulator 16 to store energy when the fluid power demands on the other loads 7, 9, 10 are lower than maximum power output of the engine.

(14) In addition, the controller 1 must coordinate the commands to both the valves within the switching block 6 and the fluid working machines 11, 12, 13, 14. If the operator demands dictate that zero flow is required from the load ports 7, 9, 10 then the switching valves inside the block 6 may disconnect the load ports 7, 9, 10 from the fluid working machines 11, 12, 13, 14. When the operator demand dictates that fluid be either sourced from or absorbed to one of the load port 7, 9, 10 then the minimum number of fluid machines capable of fulfilling the flow demand is connected to that load port. As the operator demand changes then the number of fluid working machine ports which are connected to the load port can change depending on the instantaneous demand. In the case that the valves in the block 6 take significant time to change state, then optionally a forecast demand may be used in addition to the instantaneous demand, this forecast demand being based on an extrapolation of the trend of the operator demand or other knowledge which the controller has of the likely future demand, such that the future demand can be met without interruption.

(15) In addition, the controller 1 must balance the requirements of the operator against the limitations of the pump/motor and the switching circuit. The single-acting ram 15 can be supplied with fluid from any of the pump/motor ports 11, 12, 13, 14 via the switching circuit 6, but only certain of the pump/motor ports 13, 14 are capable of absorbing fluid from it.

(16) In addition, in the case of a variable speed prime mover, the controller can send a speed demand signal to the prime mover. This speed demand can be chosen such that the prime mover will at this speed be at its optimum operating point for energy consumption, given the load on the prime mover, but may be overridden under some operating conditions. If the flow demand from the operator for one of loads exceeds the ability of the system to satisfy, and all of the pump/motor units are already committed, then the speed setpoint may be increased above what would be optimum for fuel consumption. The torque on the prime mover and the maximum available torque can either be calculated from the outlet pressures and flows of all the pump/motor units which is known by the controller, or in the case of an electronically-controlled prime mover can be fed back to the controller from the prime mover electronic control unit.

(17) It may be that the variable speed prime mover does not include a speed governor; in this case the controller must supply to the prime mover a torque demand signal, and a feedback control loop is necessary within the controller to maintain the prime mover at the demanded speed. The speed of the prime mover is known to the controller by means of the shaft position sensor 5 or electronic feedback provided by the prime mover electronic control unit.

(18) The controller can operate according to different algorithms, e.g. having different ramp times, hysteresis, delay etc. depending on the nature of the load. For example, in a mobile work platform (manlift) a main lift cylinder can be controlled gently to avoid exciting the bounciness of the boom, whilst the auxiliary hydraulic cylinders can be more responsive.

(19) The functions of the controller 1 may be shared across several hardware microcontrollers. For instance, the function of generating the pulses to the commutating valves in the pump/motor, synchronised to the shaft by use of the position sensor signal, may be executed by a first controller. The function of controlling the overall system to the demands of the operator may be executed by a second controller, which may be asynchronous to the shaft. In this case the second controller may send to the first controller a flow rate demand or pressure demand, the generation of the pump/motor commutating valve pulses synchronised with shaft position being left to the first microcontroller. In this way the second controller may execute the overall system control function at regular fixed time steps asynchronous to the shaft position, facilitating rapid development of the system control software.