Field of the Invention

The present invention concerns a hydraulic switching valve for a switched inertance hydraulic circuit. The invention also concerns a switched inertance hydraulic circuit comprising a hydraulic switching valve.

Background of the Invention

In hydraulic systems driven by a constant supply pressure, the hydraulic pressure at a load is typically controlled by throttling the flow of hydraulic fluid, for example by using a metering orifice. In a hydraulic actuator, for example, this allows the actuation speed and/or force to be controlled. This is a simple but energy inefficient way of controlling the hydraulic fluid, as the excess energy is lost as heat. The efficiency of such systems can be particularly poor at relatively low load pressures.

Switched inertance hydraulic systems provide a different approach to controlling the flow of hydraulic fluid. Switched inertance hydraulic systems typically comprise a fluid switch which is used to alternately accelerate and decelerate fluid flow in a channel to achieve a desired time-averaged pressure at the load. Inertance tubes and accumulators can be used to smooth the fluid flow and thereby reduce fluctuations in fluid pressure at the load. A switched inertance hydraulic system can be considered analogous to an electrical switched inductance transformer (e.g. a switched-mode transformer).

Figure 1 shows a first example switched inertance hydraulic circuit 1. The switched inertance hydraulic circuit 1 comprises a high pressure supply 2 connected to a first inlet of a fluid switch 3. A second inlet of the fluid switch 3 is connected to a reservoir 4 held at a low pressure. An outlet of the fluid switch 3 is connected to a load 5 via an inertance tube 6 and an accumulator 7. The fluid switch 3 alternately puts the load 5 in fluid communication with the high and low pressure inlets in order to achieve a desired time-averaged pressure at the load 5. Figure 2 shows a second example switched inertance hydraulic circuit 11. The switched inertance hydraulic circuit 11 comprises a high pressure supply 12 connected to a first inlet of a fluid switch 13 via an inertance tube 16. A first outlet of the fluid switch 13 is connected to a load 15 via an accumulator 17. A second outlet of the fluid switch 13 is connected to a reservoir 14 held at a low pressure. The fluid switch 13 alternately brings the load 15 into and out of fluid communication with the high pressure inlet in order to achieve a desired time-averaged pressure at the load 15.

Switched inertance hydraulic systems can provide various advantages over the aforementioned conventional hydraulic systems. In particular, such systems may be more energy efficient. For example, switched inertance hydraulic systems can avoid the need to dissipate energy as heat in order to reduce hydraulic pressure.

The fluid switches used in switched inertance hydraulic systems should ideally have a low resistance to fluid flow, low leakage, and the ability to switch at high frequencies. Scaling existing fluid switch designs so they can handle the flow rates and provide the switching speeds required for practical applications can be difficult.

The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved hydraulic switching valve.

Summary of the Invention

The present invention provides, according to a first aspect, a hydraulic switching valve (e.g. for a switched inertance hydraulic circuit), the hydraulic switching valve comprising: a manifold comprising a cavity, there being a first port, a second port and a third port opening into the cavity; a spool mounted for translational movement within the cavity, the hydraulic switching valve having a first state in which the spool is positioned such that the first port is in fluid communication with the second port, and a second state in which the spool is positioned such that the first port is in fluid communication with the third port; a (electric) motor arranged to drive movement of the spool via a crank mechanism, the crank mechanism being configured to convert rotary motion in a first direction provided by the motor into reciprocating linear motion of the spool. The hydraulic switching valve may comprise a controller configured to control the rotation of the motor so as to operate the hydraulic switching valve in a repeating pattern of switching cycles, each switching cycle having a total cycle time including a first time period in which the hydraulic switching valve is in the first state and a second time period in which the hydraulic switching valve is in the second state, wherein a ratio of the first time period to the total cycle time is a switching ratio.

Valves comprising a linearly translating spool may be capable of withstanding high speed movement. Furthermore, they may have relatively large port sizes for relatively small stroke lengths, and may have relatively low leakage. By using a crank mechanism, the high speed and precise rotational motion of an electric motor can be used to drive translational movement of a spool. This may allow the spool to be driven at the high switching frequencies required in switched inertance hydraulic circuits, while also providing sufficient control of the spool position during the switching cycle for there to be control of the switching ratio.

The switching ratio may be controllable (e.g. changeable, variable, adjustable). The controller may be configured to control (e.g. change, vary, adjust) the switching ratio by controlling the angular velocity of the motor during each switching cycle. The controller may be configured to control the switching ratio by controlling the torque applied by the motor during each switching cycle. The controller may be configured to control the torque applied by the motor so as to control the angular velocity of the motor, and thereby control the angular velocity of the crank mechanism.

During each switching cycle, there may be a first portion of a rotation of the crank mechanism and a second portion of the rotation of the crank mechanism. During the first portion of the rotation the motor may be controlled to apply an accelerating torque, and during the second portion of the rotation the motor may be controlled to apply a decelerating (i.e. retarding) torque. The accelerating torque may be a torque that acts (in the direction of motion) to increase the angular velocity of the crank mechanism. The decelerating torque may be a torque that acts (opposite to the direction of motion) to decrease the angular velocity of the crank mechanism. The accelerating torque may be applied when the spool is travelling in one direction (e.g. in a direction from a first end to a second end of the cavity). The decelerating torque may be applied when the spool is travelling in the other direction (e.g. in a direction from the second end to the first end of the cavity). The first portion of a rotation may be a first 180 degree portion, and the second portion of the rotation may be a second 180 degree portion. The accelerating torque and decelerating torque may be required when operating at switching ratios above and below 50%.

The controller may be configured to change the switching ratio (e.g. during the repeating pattern of switching cycles) by controlling the motor so as to change one of (e.g. the longer of) the first and second time periods and keep the other of (e.g. the shorter of) the first and second time periods substantially constant. It may be that over successive switching cycles, the first time period is changed and the second time period is kept constant, or vice versa. The first time period and/or second time period may be changed by changing the average angular velocity of the crank mechanism over the respective time period.

Above a switching ratio of 50% the switching ratio may be changed by the second time period being kept substantially constant and the first time period being changed. Below a switching ratio of 50% the switching ratio may be changed by the first time period being kept substantially constant and the second time period being changed. The second time period may be the same for substantially all switching ratios above a switching ratio of 50%. The first time period may be the same for substantially all switching ratios below 50%.

It may be that the first time period commences when the spool passes its midpoint whilst travelling in a first direction (and opens the first port) and ends when the spool returns to its midpoint whilst travelling in a second direction (and closes the first port); and the second time period commences when the spool passes its midpoint whilst travelling in the second direction (and opens the first port) and ends when the spool returns to its midpoint whilst travelling in the first direction (and closes the first port).

It has been found that, in a switched inertance hydraulic circuit, flow losses may be reduced where the shortest pressure pulse, e.g. due to the fluid switch putting a load into fluid communication with a higher pressure supply or lower pressure supply, is equal to the wave propagation time from the hydraulic switching valve to the load. The wave propagation time, T, may be taken to be T = 2L/c, where L is the propagation distance (e.g. pipe length) and c is the wave propagation speed (e.g. the speed of sound in the hydraulic fluid). The time period which is kept constant may thus have a length which is based on (e.g. dependent upon) a wave propagation time within the switched inertance hydraulic circuit (that the hydraulic switching valve is used in). The time period which is kept constant may have a length which is approximately equal to the wave propagation time from the hydraulic switching valve to the load. It is thought that, in at least some practical applications, for example in hydraulic excavator arms or the like, the propagation distance may be in the region of Im to 2m. With c = 1350m/s, the wave propagation time is approximately 1ms to 3ms. Hence, the time period which is kept constant may have a length in the range 1ms to 3ms, for example 2ms.

The controller may be configured, when operating the hydraulic switching valve at a switching ratio within a first range, to drive the motor such that during each switching cycle the crank mechanism rotates continuously in a first direction. The first range may be centred on a switching ratio of 50%. During the first range the controller may be configured to change the switching ratio by controlling the motor so as to change the longer of the first and second time periods and keep the shorter of the first and second time periods substantially constant.

The first range may have a lower limit and an upper limit. The lower limit of the first range may be a switching ratio in the range 20% to 40%, or optionally in the range 25% to 35%, for example the lower limit may be a switching ratio of 30%. The upper limit of the first range may be a switching ratio in the range 60% to 80%, or optionally in the range 65% to 75%, for example the upper limit may be a switching ratio of 70%.

The controller may be configured, when operating the hydraulic switching valve at a switching ratio within a second range, to drive the motor such that during the shortest of the first and second time periods the crank mechanism rotates continuously in a direction (e.g. the first direction), and during the other of the first and second time periods rotation of the crank mechanism comprises a pause during which the crank does not rotate. The pause may take place when the spool is at a position of maximum travel (away from its midpoint). The pause may take place when the first port is fully open to the second or third port, as the case may be. The pause in the rotation of the crank mechanism may provide more angular distance over which to accelerate back up to the speed required for the shorter time period, in comparison to a situation in which the crank mechanism continues to rotate. During the second range the controller may be configured to change the switching ratio by controlling the motor so as to change the longer of the first and second time periods and keep the shorter of the first and second time periods substantially constant.

There may be an upper second range (e.g. having switching ratios above the first range), wherein during the second time period the crank mechanism rotates continuously, and during the first time period the rotation of the crank mechanism comprises a pause during which the crank does not rotate.

The upper second range may have a lower limit and an upper limit. The lower limit of the upper second range may be a switching ratio in the range 60% to 80%, or optionally in the range 65% to 75%, for example the lower limit may be a switching ratio of 70%. The upper limit of the upper second range may be a switching ratio in the range 80% to 100%, or optionally in the range 85% to 95%, for example the upper limit may be a switching ratio of 90%.

There may be a lower second range (e.g. having switching ratios below the first range), wherein during the first time period the crank mechanism rotates continuously, and during the second time period the rotation of the crank mechanism comprises a pause during which the crank does not rotate.

The lower second range may have a lower limit and an upper limit. The lower limit of the lower second range may be a switching ratio in the range 0% to 20%, or optionally in the range 5% to 15%, for example the lower limit may be a switching ratio of 10%. The upper limit of the lower second range may be a switching ratio in the range 20% to 40%, or optionally in the range 25% to 35%, for example the upper limit may be a switching ratio of 30%.

The controller may be configured, when operating the hydraulic switching valve at a switching ratio within a third range, to drive the motor such that during the shortest of the first and second time periods the crank mechanism rotates in one direction and then back in the opposite direction such that the spool does not travel a full stroke length. During the other of the first and second time periods the rotation of the crank mechanism may comprise a pause during which the crank does not rotate. Alternatively, during the other of the first and second time periods the crank mechanism may rotate continuously. When the switching ratio is within the third range, the switching frequency may be substantially constant. It may be that during the third range the shorter of the first and second time periods is not substantially constant. There may be an upper third range (e.g. having switching ratios above the upper second range), wherein during the second time period the crank mechanism rotates in one direction and then back in the opposite direction such that the spool does not travel a full stroke length. During the first time period the rotation of the crank mechanism may comprise a pause during which the crank does not rotate. Alternatively, during the first time period the crank mechanism may rotate continuously.

The upper third range may have a lower limit and an upper limit. The lower limit of the upper third range may be a switching ratio in the range 85% to 95%, for example the lower limit may be a switching ratio of 90%. The upper limit of the upper third range may be a switching ratio of 100%.

There may be a lower third range (e.g. having switching ratios below the lower second range), wherein during the first time period the crank mechanism rotates in one direction and then back in the opposite direction such that the spool does not travel a full stroke length. During the second time period the rotation of the crank mechanism may comprise a pause during which the crank does not rotate. Alternatively, during the second time period the crank mechanism may rotate continuously.

The lower third range may have a lower limit and an upper limit. The lower limit of the lower third range may be a switching ratio of 0%. The upper limit of the lower third range may be a switching ratio in the range 5% to 15%, for example the upper limit may be a switching ratio of 10%.

The hydraulic switching valve may be operable at a switching frequency. The switching frequency may be the inverse of the total cycle time. The switching frequency may be at a maximum at a switching ratio of 50%. At a switching ratio of 50%, the switching frequency may, for example, be in the range 150Hz to 500Hz, or optionally in the range 350Hz to 200Hz, for example the switching frequency may be approximately 250Hz.

The controller may be configured to control the switching ratio in response to a control signal. The controller may be an electronic controller. The controller may comprise a memory and/or a processor. The control signal may be digital signal. The control signal may be generated as a result of user input. The control signal may be generated automatically, for example as a part of a closed control loop. The crank mechanism may comprise a crank rotatable about an axis of rotation. The crank mechanism may comprise a connecting member (e.g. a connecting rod) mounted to the crank at a position offset from the axis of rotation of the crank. The connecting member may be arranged to convert a rotational motion of the crank into a reciprocating linear motion. The crank may be in the form of a crank disk. The crank may be in the form of a crank arm. The crank may be directly driven by the motor. Alternatively, the crank may be driven via further drive components, such as a gearbox. The connecting member may connect the crank to the spool.

The controller may be arranged to determine the position of the crank mechanism, spool, and/or motor, for example on the basis of input from one or more sensors. The hydraulic switching valve may comprise an encoder for use in determining the position of the crank mechanism, spool, and/or motor.

The first port may comprise a plurality of apertures opening into the cavity. The second port may comprise a plurality of apertures opening into the cavity. The third port may comprise a plurality of apertures opening into the cavity. For the first, second and/or third port, the plurality of apertures may be distributed circumferentially around the spool/cavity, and optionally the plurality of apertures are positioned at the same longitudinal position along the spool. For the first, second and/or third port, the plurality of apertures may be connected via a flow gallery extending circumferentially around, and optionally encircling, the spool. By providing one or more of the ports with a plurality of apertures, it may be possible to increase the overall area of the port, and thereby improve fluid throughput.

The hydraulic switching valve may comprise a plurality of first ports distributed along a longitudinal axis of the spool. The hydraulic switching valve may comprise a plurality of second ports distributed along the longitudinal axis of the spool. The hydraulic switching valve may comprise a plurality of third ports distributed along the longitudinal axis of the spool. Each first port may be associated with a corresponding second port and third port. Translation of the spool may put each first port into fluid communication with one of the corresponding second port and third port. In the first state, the spool may be positioned such that each first port is in fluid communication with the corresponding second port. In the second state, the spool may be positioned such that each first port is in fluid communication with the corresponding third port. The plurality of first ports, second ports and third ports may provide a plurality of parallel flow paths through the cavity. This may increase the effective port area and reducing the resistance to fluid flow.

The plurality of first ports may be connected (outside the cavity) via one or more first flow galleries. Each of the first flow galleries may taper outwards along the longitudinal axis of the spool. The plurality of second ports may be connected (outside the cavity) via one or more second flow galleries. Each of the second flow galleries may taper outwards along the longitudinal axis of the spool. The plurality of third ports may be connected (outside the cavity) via one or more third flow galleries. Each of the third flow galleries may taper outwards along the longitudinal axis of the spool. The flow galleries may taper such that the cross-sectional area of the flow gallery increases as more ports meet the flow gallery.

It may be that the first ports are not in fluid communication with each other via the cavity. The first ports may be separated from each other by a land of the spool. Likewise, it may be that the second ports are not in fluid communication with each other via the cavity. The second ports may be separated from each other by a land of the spool. Likewise, it may be that the third ports are not in fluid communication with each other via the cavity. The third ports may be separated from each other by a land of the spool.

The first port may be an output port. The first port may be for connection to a load. The second port may be an input port. The second port may be for connection to a higher pressure input (i.e. supply). The third port may be an input port. The third port may be for connection to a low pressure input (i.e. supply).

Alternatively, the first port may be an input port. The first port may be for connection to a supply. The second port may be an output port. The second port may be for connection to a load. The third port may be an output port. The third port may be for connection to a reservoir.

The hydraulic switching valve may further comprise a fourth port opening into the cavity. In the first state, the spool may be positioned such that the fourth port is in fluid communication with the third port. In the second state, the spool may be positioned such that the fourth port is in fluid communication with the second port.

The motor may be a brushless motor (e.g. a permanent magnet brushless motor). Brushless motors may advantageously have a longer operating lifetime in respect of the number of switching cycles, for example in comparison to brushed motors. The motor may comprise a permanent magnet rotor and an electromagnet stator. The motor may be an axial flux motor.

The manifold may be formed by an additive manufacturing process. The manifold may be of a single piece construction. That is to say, the manifold may be formed as a single piece such that the cavity, the first port(s), the second port(s), and the third port(s) are each defined within the same single piece of material. Said single piece of material may also include the one or more first flow galleries, the one or more second flow galleries, and/or the one or more third flow galleries.

The present invention provides, according to a second aspect, a hydraulic switching valve (e.g. for a switched inertance hydraulic circuit), the hydraulic switching valve comprising: a manifold comprising a cavity, there being a first port, a second port and a third port opening into the cavity; a spool mounted for translational movement within the cavity, the hydraulic switching valve having a first state in which the spool is positioned such that the first port is in fluid communication with the second port, and a second state in which the spool is positioned such that the first port is in fluid communication with the third port; a (electric) motor arranged to drive movement of the spool; a controller configured to control the rotation of the motor so as to operate the hydraulic switching valve in a repeating pattern of switching cycles, each switching cycle having a total cycle time including a first time period in which the hydraulic switching valve in in the first state and a second time period in which the hydraulic switching valve is in the second state, wherein a ratio of the first time period to the total cycle time is a switching ratio; and wherein the controller is configured to vary the switching ratio by keeping one of the first and second time periods substantially constant and varying the other of the first and second time periods.

The present invention provides, according to a third aspect, a hydraulic circuit comprising a hydraulic switching valve according to the first aspect and/or the second aspect. The hydraulic circuit may be a switched inertance hydraulic circuit. The switched inertance hydraulic circuit may further comprise one or more of: an inertance tube, an accumulator, and a reservoir.

The hydraulic circuit may be arranged to provide a fluid from the first port to a load, optionally via the inductance tube and/or the accumulator. The hydraulic circuit may be arranged to provide a higher pressure fluid to the second port. The hydraulic circuit may be arranged to provide a lower pressure fluid to the third port. In such an arrangement, the second and third ports are used as input ports, and the first port is used as an output port.

In an alternative arrangement, the hydraulic circuit may be arranged to provide a fluid at a supply pressure to the first port, optionally via the inductance tube. The hydraulic circuit may be arranged to provide the fluid from the second port to a load, optionally via the inductance tube and/or the accumulator. The hydraulic circuit may be arranged to provide the fluid from the third port to a return (e.g. a reservoir) (and not via the load). The reservoir may be at a return pressure lower than the supply pressure. In such an arrangement, the first port is used as an input port, and the second and third ports are used as output ports.

It will thus be appreciated that in either of the above cases, changing the amount of time the first port is in fluid communication with the second port, in comparison with the amount of time the first port is in fluid communication with the third port, may change the average pressure at the load.

The hydraulic circuit may be a switched inertance hydraulic circuit as shown in figures 1 or 2, with the fluid switch 3 or 13 being replaced by the hydraulic switching valve according to the first aspect and/or the second aspect.

The present invention provides, according to a fourth aspect, a controller for a hydraulic switching valve according to the first aspect and/or the second aspect. The controller may have any of the features set out in relation to the first aspect and/or the second aspect.

The present invention provides, according to a fifth aspect, a method of controlling a switched inertance hydraulic circuit using a hydraulic switching valve according to the first aspect and/or the second aspect. The method comprises the steps of connecting a load to the first port, connecting a higher pressure supply to the second port, connecting a lower pressure supply to the third port, using the controller to control the rotation of the motor so as to operate the hydraulic switching valve in the repeating pattern of switching cycles. The method may comprise a step of changing the switching ratio so as to change an average hydraulic pressure at the load.

The present invention provides, according to a sixth aspect, a method of controlling a switched inertance hydraulic circuit using a hydraulic switching valve according to the first aspect and/or the second aspect. The method comprises the steps of: connecting a higher pressure supply to the first port, connecting a load to the second port, connecting a lower pressure return to the third port, using the controller to control the rotation of the motor so as to operate the hydraulic switching valve in the repeating pattern of switching cycles. The method may comprise a step of changing the switching ratio so as to change an average hydraulic pressure at the load.

The present invention provides, according to a seventh aspect, a hydraulic switching device comprising a first hydraulic switching valve and a second hydraulic switching valve. The first hydraulic switching valve may be a hydraulic switching valve according to the first aspect and/or the second aspect. The second hydraulic switching valve may be a hydraulic switching valve according to the first aspect and/or the second aspect.

The manifold of the first hydraulic switching valve and the manifold of the second hydraulic switching valve may together define a body. The manifold of the first hydraulic switching valve may be integrally formed with the manifold of the second hydraulic switching valve. The manifold of the first hydraulic switching valve and the manifold of the second hydraulic switching valve may together be of a single piece construction such that the cavities, the first ports, the second ports, and the third ports (of the two valves) may each be defined within the same single piece of material. Said single piece of material may also include the one or more first flow galleries, the one or more second flow galleries, and/or the one or more third flow galleries.

The controller of the first hydraulic switching valve and the controller of the second hydraulic switching valve may be provided together in the same control unit. The motor of the first hydraulic switching valve and the motor of the second hydraulic switching valve may be independently controllable. In embodiments, the motors, cranks, and/or spools may be driven synchronously.

The hydraulic switching device may comprise a plurality of external ports (e.g. for connection to other elements of a hydraulic circuit). The external ports may be provided by the body. The external ports may open to an exterior of the body.

The first port(s) of the first hydraulic switching valve and the first port(s) of the second hydraulic switching valve may be connected to different (first) external ports. This may allow the first port(s) of the first hydraulic switching valve to be connected to a first load, and separately for the first port(s) of the second hydraulic switching valve to be connected to a second load, the loads being independently controllable. Therefore, it may be that the first port(s) of the first hydraulic switching valve are not in fluid communication with the first port(s) of the second hydraulic switching valve.

The second port(s) of the first hydraulic switching valve and the second port(s) of the second hydraulic switching valve may be connected to the same (second) external port. This may allow the second port(s) of both the first and second hydraulic switching valves to be connected to the same supply (or return) line. Therefore, it may be that the second port(s) of the first hydraulic switching valve are in fluid communication with the second port(s) of the second hydraulic switching valve.

The third port(s) of the first hydraulic switching valve and the third port(s) of the second hydraulic switching valve may be connected to the same (third) external port. This may allow the third port(s) of both the first and second hydraulic switching valves to be connected to the same return (or supply) line. Therefore, it may be that the third port(s) of the first hydraulic switching valve are in fluid communication with the third port(s) of the second hydraulic switching valve.

In alternative embodiments, the first port(s) of the first hydraulic switching valve and the first port(s) of the second hydraulic switching valve are connected to the same (first) external port. Therefore, it may be that the first port(s) of the first hydraulic switching valve are in fluid communication with the first port(s) of the second hydraulic switching valve.

The present invention provides, according to an eight aspect, a hydraulic circuit comprising a hydraulic switching device according to the seventh aspect. The hydraulic circuit may be a switched inertance hydraulic circuit. The switched inertance hydraulic circuit may further comprise one or more of: an inertance tube, an accumulator, and a reservoir.

The first hydraulic switching valve and/or the second hydraulic switching valve may be arranged within the hydraulic circuit in the manner set out above in relation to the third aspect. For example, the hydraulic circuit may be arranged to provide a fluid from the first port to a (e.g. respective) load, a higher pressure fluid to the second port, and a lower pressure fluid to the third port.

It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

It will be appreciated that the switching ratios may be expressed either in percentage form or in decimal form. For example, a switching ratio of 10% could be expressed as 0.1, and vice versa.

Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

Figure 1 shows a circuit diagram of a first example switched inertance hydraulic system;

Figure 2 shows a circuit diagram of a second example switched inertance hydraulic system;

Figure 3 shows a schematic diagram of a hydraulic switching valve according to a first embodiment of the invention;

Figures 4a to 4c show the spool and crank mechanism of the hydraulic switching valve according to the first embodiment of the invention in different positions;

Figure 5 shows the spool and crank mechanism of the hydraulic switching valve according to the first embodiment of the invention with directions of torque and angular velocity indicated;

Figure 6 shows the switching frequency and maximum port opening against the switching ratio for the hydraulic switching valve according to the first embodiment of the invention;

Figures 7 to 13 show rotor velocity against time, control torque against time, and flow spring torque against time for the hydraulic switching valve according to the first embodiment of the invention when operated at various switching ratios;

Figure 14 shows a schematic diagram of a hydraulic switching valve according to a second embodiment of the invention;

Figure 15 shows a side cross-sectional view of a hydraulic switching device according to a third embodiment of the invention; Figure 16 shows a plan cross-sectional view of the hydraulic switching device according to the third embodiment of the invention;

Figures 17 to 19 show cross-sectional views through a first port, second port and third port, respectively, of a hydraulic switching valve according to the third embodiment of the invention; and

Figure 20 shows the path of the flow galleries within the manifolds of the hydraulic switching valves according to the third embodiment of the invention.

Detailed Description

Figure 3 shows a hydraulic switching valve 100 according to a first embodiment of the invention. The hydraulic switching valve 100 comprises a manifold 102 comprising a cavity 104. The manifold 102 defines a first port 106, a second port 108, and a third port 110 which open into the cavity 104. A spool 112 is mounted for translational movement within the cavity 104. The movement of the spool 112 is linear and in a direction parallel to the longitudinal axis of the spool 112.

A motor 114 is arranged to drive the movement of the spool 112 via a crank mechanism 116. The motor 114 is a permanent magnet brushless motor. The crank mechanism 116 comprises a crank 118 and a connecting member 120. The crank 118 is in the form of a crank disk and is mounted to the motor 114. In embodiments, a gearbox is provided between the motor 114 and the crank 118. A first end of the connecting member 120 is rotatably mounted to the crank 118 at a position offset from the axis of rotation of the crank 118. A second end of the connecting member 120 is rotatably mounted to the spool 112. The crank mechanism 116 converts rotational motion generated by the motor 114 to linear motion of the spool 112.

The spool 112 comprises a plurality of lands which can block the ports, and a plurality of grooves which can allow fluid flow between the ports. The position of the spool 112 within the cavity 102 determines the flow path through the hydraulic switching valve 100. The hydraulic switching valve 100 has a first state in which the spool 112 is positioned such that the first port 106 is in fluid communication with the second port 108, and a second state in which the spool 112 is positioned such that the first port 106 is in fluid communication with the third port 110. The hydraulic switching valve 100 also comprises a closed state in which the first port 106 is not in fluid communication with either then second port 108 or third port 110.

Figure 4a shows the spool 112 at its maximum travel in one direction. Fluid can flow between the first port 106 and second port 108 via a groove in the spool 112. The hydraulic switching valve 100 is thus in the first state. Figure 4b shows the spool 112 at its central position. The first port 106 is blocked by a land thereby preventing fluid flow through the hydraulic switching valve 100. The hydraulic switching valve 100 is thus in a closed state. Figure 4c shows the spool at its maximum travel in the other direction. Fluid can flow between the first port 106 and third port 110 via another groove in the spool 112. The hydraulic switching valve 100 is thus in the second state.

The hydraulic switching valve 100 further comprises a controller 122. The controller 122 is configured to control the rotation of the motor 114 so as to operate the hydraulic switching valve 100 in a repeating pattern of switching cycles. Each switching cycle has a total cycle time including a first time period in which the hydraulic switching valve 100 is in the first state and a second time period in which the hydraulic switching valve 100 is in the second state. A ratio of the first time period to the total cycle time is a switching ratio.

The controller 122 controls the rotation of the motor 114 by controlling the torque applied by the motor 114. By controlling the torque, the controller 122 is able to control the angular velocity of the crank mechanism 116 during each switching cycle. The lengths of the first and second time periods, and thus the switching ratio, are thereby also controlled.

To operate the hydraulic switching valve 100 at a switching ratio of 50%, the motor 114 applies a constant torque such that the angular velocity of the crank mechanism 116 is kept substantially constant throughout each switching cycle. To operate the hydraulic switching valve 100 at a switching ratio above or below 50%, the motor 114 applies an accelerating torque in the direction of rotation during a first portion of a rotation of the crank mechanism 116, and the motor 114 applies a decelerating torque opposite to the direction of rotation during a second portion of a rotation of the crank mechanism 116.

Figure 5 shows the crank 118 rotating clockwise. Arrows indicate where an example accelerating torque (r _a ) and decelerating torque (id) are applied. In this example, the accelerating torque is applied in a clockwise direction as the pivot point 119 on the crank 118 travels from the nine o’clock position to the three o’clock position, and the decelerating torque is applied as the pivot point 119 travels from the three o’clock position to the nine o’clock position. Consequently, the angular velocity (co) will be highest when the pivot point 119 is at the three o’clock position and the spool 112 is at its maximum travel to the right, and the angular velocity will be lowest when the pivot point 119 is at the nine o’clock position and the spool 112 is at its maximum travel to the left. The first time period will therefore be shorter than the second time period, giving a switching ratio of less than 50% (0.5) in this example.

Figure 6 shows the switching frequency (line 124) that the hydraulic switching valve 100 is configured to operate at for all switching ratios from 0% to 100%. Figure 6 also shows the maximum port opening against the switching ratio (line 126) for the hydraulic switching valve 100. The switching ratios can be broken down into a first range 128, a second range 130 and a third range 132. Across the different ranges, the crank mechanism 116 and spool 112 are driven in different ways.

In the first range 128 of switching ratios, the controller 122 is configured to drive the motor 114 such that, during each switching cycle, the crank mechanism 116 rotates continuously in a first direction of rotation. At the switching ratio of 50%, the controller 122 drives the motor 114 such that, in use, the first and second time periods are each approximately equal to the wave propagation time from the hydraulic switching valve to the load in the switched inertance hydraulic circuit. Above a switching ratio of 50% the second time period is kept substantially constant (at its length at the switching ratio of 50%) and changes to the switching ratio are made by the first time period being changed. Below a switching ratio of 50% the first time period is kept substantially constant (at its length at the switching ratio of 50%) and changes to the switching ratio are made by the second time period being changed. Keeping at least one of the time periods approximately equal to the wave propagation time can help minimise flow losses in the system, and thereby improve the efficiency of the system.

In the second range 130 of switching ratios, the controller 122 is configured to drive the motor 114 such that, during the shortest of the first and second time periods, the crank mechanism 116 rotates continuously in the first direction; and during the longer of the first and second time periods, rotation of the crank mechanism 116 comprises a pause during which the crank 118 does not rotate. The pause occurs when the pivot point 119 is at the three o’clock or nine o’clock position, and the spool 112 is at its maximum travel to the right or left. A pause at the three o’clock position will lengthen the first time period, and a pause at the nine o’clock position will lengthen the second time period. Similarly to the first range 128, above a switching ratio of 50% the second time period is kept substantially constant (at its length at the switching ratio of 50%) and changes to the switching ratio are made by the first time period being changed. Below a switching ratio of 50% the first time period is kept substantially constant (at its length at the switching ratio of 50%) and changes to the switching ratio are made by the second time period being changed.

In the third range 132 of switching ratios, the controller 122 is configured to drive the motor 114 such that, during the shortest of the first and second time periods, the crank mechanism 116 rotates in one direction and then back in the opposite direction such that the spool 112 does not travel a full stroke length and the ports are not fully opened. The out-and-back motion during the shortest time period starts and ends with the pivot point 119 at either the twelve o’clock or six o’clock position. The shortest time period also departs from being approximately equal to the wave propagation time and the switching frequency is held substantially constant. In comparison, across the first and second ranges the switching frequency decreases linearly from a maximum at a switching ratio of 50%. During the longer of the first and second time periods rotation of the crank mechanism 116 comprises a pause during which the crank 118 does not rotate.

In this embodiment, the first range 128 comprises switching ratios (r) falling within 30% < r < 70%; the second range 130 comprises a lower second range of switching ratios falling within 10% < r < 30%, and an upper second range of switching ratios falling within 70% < r < 90%; and the third range 132 comprises a lower third range of switching ratios falling within 0% < r < 10%, and an upper third range of switching ratios falling within 90% < r < 100%.

Figures 7 to 13 show example plots of rotor velocity against time (line 134), control torque against time (line 136), and flow spring torque against time (line 138) for the hydraulic switching valve according to the first embodiment operated at switching ratios of 50%, 52%, 54%, 56%, 60%, 72% and 75% in a switched inertance hydraulic circuit with a load connected to the first port, a high pressure supply connected to the second port, and a low pressure supply connected to the third port. The unshaded areas indicate the time periods in which the hydraulic switching valve is in the first state, and the shaded areas indicate the time periods in which the hydraulic switching valve is in the second state.

At the switching ratio of 50% (see Figure 7), each of the first and second time periods have a length of 2.25ms, giving a total cycle time of 4.5ms and a switching frequency of 222Hz. The rotor velocity is near constant with a velocity oscillation due to flow forces in the system. As the switching ratio increases, the second time period is held constant at 2.25ms but the length of the first time period increases. The total cycle time thus increases and the switching frequencies reduce to 116Hz at 75% (see Figure 13).

Figure 14 shows a hydraulic switching valve 200 according to a second embodiment of the invention. The hydraulic switching valve 200 has similar features to the hydraulic switching valve 100 according to first embodiment, including: a manifold 202 comprising a cavity 204, a spool 212 mounted for translational movement within the cavity 204, and a motor (not shown) arranged to drive the movement of the spool 212 via a crank mechanism 216. The motor is controlled by a controller (not shown) in the manner described in relation to the hydraulic switching valve 100 according to the first embodiment.

The hydraulic switching valve 200 differs from the first embodiment in that it comprises a four first ports 206 distributed along a longitudinal axis of the spool 212, four second ports 208 distributed along a longitudinal axis of the spool 212, and four third ports 210 distributed along a longitudinal axis of the spool 212. Each first port 206 is associated with a corresponding second port 208 and third port 210.

The hydraulic switching valve 200 has a first state in which the spool 212 is positioned such that each first port 206 is in fluid communication with the corresponding second port 208. The hydraulic switching valve 200 has a second state in which the spool 212 is positioned such that each first port 206 is in fluid communication with the corresponding third port 210.

The first ports 206 are connected outside the cavity by a first flow gallery 240 in the manifold 202, the second ports 208 are connected outside the cavity by a second flow gallery 242 in the manifold 202, and the third ports 210 are connected outside the cavity by a third flow gallery 244 in the manifold 202. The hydraulic switching valve 200 provides a plurality of parallel flow paths via which fluid can flow through the cavity 204. This increases the effective port area and reduce the resistance to fluid flow without needing to increase the stroke length of the spool 212.

Figures 15 and 16 show a hydraulic switching device according to a third embodiment of the invention. The hydraulic switching device comprises two hydraulic switching valves 300. The hydraulic switching valves 300 each comprise a manifold 302. The manifolds 302 are together integrally formed as a single piece by an additive manufacturing process. Therefore there is a single body which defines the manifold 302 of both the hydraulic switching valves 300. The manifolds 302 each comprise a cavity 304. A spool 312 is mounted for translational movement within each of the cavities 304. The movement of each spool 312 is driven by a motor 314 via a crank mechanism 316. Each of the motors 314, and thus each spool 312, can be driven and controlled independently. The motors 314 are each controlled by a controller (not shown) in the manner described in relation to the hydraulic switching valve 100 according to the first embodiment.

Similarly to the hydraulic switching valve 200 of the second embodiment, four first ports 306, four second ports 308, and four third ports 310 open into each cavity 302. The four first ports 306, four second ports 308 and four third ports 310 are distributed along a longitudinal axis of the respective spool 312. Each first port 306 is associated with a corresponding second port 308 and third port 310.

Each hydraulic switching valve 300 has a first state in which the spool 312 is positioned such that each first port 306 is in fluid communication with the corresponding second port 308, and a second state in which the spool 312 is positioned such that each first port 306 is in fluid communication with the corresponding third port 310.

Figure 17 shows a cross section through one of the first ports 306 taken in a direction perpendicular to the longitudinal axis of the spool 312. The first port 306 comprises a plurality of apertures 346 opening into the cavity 304. The plurality of apertures 346 are distributed circumferentially around the spool 312 (not shown in Figure 17) at the same longitudinal position. The plurality of apertures 346 are connected via a circumferential flow gallery 348 that encircles the spool 312. At each of four equispaced angular positions, the circumferential flow gallery 348 connects to one of four first longitudinal flow galleries 340 (also labelled 1.1-1.4) which at least partially extend parallel to the longitudinal axis of the spool 312. The first longitudinal flow galleries 340 for a particular spool 312 all connect to the same first external port 350 opening to an exterior of the single piece (i.e. body) which forms the manifolds 302. The first longitudinal flow galleries 340 each taper outwards (i.e. increase in cross-sectional area) along the longitudinal axis of the spool 312, in a direction towards the first external port 350, as more first ports 306 connect to the flow gallery 340. Each spool 312 is associated with a different first external port 350.

Figure 18 shows a cross section through one of the second ports 308 taken in a direction perpendicular to the longitudinal axis of the spool 312. Similarly to the first port 306, the second port 308 comprises a plurality of apertures 352 opening into the cavity 304 which are distributed circumferentially around the spool 312 and are connected via a circumferential flow gallery 354. At each of four equispaced angular positions, the circumferential flow gallery 354 connects to one of four second longitudinal flow galleries 356 (also labelled 2.1-2.4). The second longitudinal flow galleries 356 for both spools 312 all connect to the same second external port 358 opening to an exterior of the single piece (i.e. body) which forms the manifolds 302. Thus the second ports of the two hydraulic switching valves are in fluid communication.

Figure 19 shows a cross section through one of the third ports 310 taken in a direction perpendicular to the longitudinal axis of the spool 312. Similarly to the second port 308, the third port 310 comprises a plurality of apertures 360 opening into the cavity 304 which are distributed circumferentially around the spool 312 and are connected via a circumferential flow gallery 362. At each of four equispaced angular positions, the circumferential flow gallery 362 connects to one of four third longitudinal flow galleries 364 (also labelled 3.1-3.4). The third longitudinal flow galleries 364 for both spools 312 all connect to the same third external port 366 opening to an exterior of the single piece (i.e. body) which forms the manifolds 302. Thus the third ports of the two hydraulic switching valves are in fluid communication.

Figure 20 shows the path of the flow galleries within the manifold 302. As can be seen, the flow galleries, in particular the second longitudinal flow galleries 356 and third longitudinal flow galleries 364, have a curvilinear path along at least a portion of their length. This allows the flow galleries to be more densely packed within their manifold 302 and the body. This geometry is made possible by the use of additive manufacturing processes to form the manifolds 302.

In use in a switched inertance hydraulic circuit, the hydraulic switching valve 300 can be placed in fluid communication with a load via one of the first external ports 350. The second external port 358 can be placed in fluid communication with a high pressure supply, and the third external port 366 can be placed in fluid communication with a low pressure supply. The controller can then drive the relevant motor 314 to so as to operate the hydraulic switching valve 300 in a repeating pattern of switching cycles, the switching ratio being controlled in order that the load experiences the desired time-averaged pressure.

In alternative embodiments, the load can be placed in fluid communication with both of the first external ports 350, and the motors 314 driven in phase. Alternatively, the first external ports 350 can be connected to different loads and the motors 314 driven independently.

Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

In alternative embodiments, there is no range of switching ratios in which rotation of the crank mechanism comprises a pause. Instead, there is only a range of switching ratios in which the crank mechanism rotates continuously throughout each switching cycle (previously defined as a first range), and a range of switching ratios in which during the shortest of the first and second time periods the crank mechanism rotates in one direction and then back in the opposite direction such that the spool does not travel a full stroke length (previously defined as a third range).

Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.