GB2498369A - Hydraulic control unit with graduated control of flow-rate - Google Patents

Abstract

A hydraulic control unit includes: a first input port (1), for receiving fluid from a hydraulic supply; a first output port (2), for returning the fluid to the supply; a second output port (4), for supplying fluid to drive a hydraulic tool; a second input port (3), for receiving fluid returned from the hydraulic tool; and a valve (70) arranged to control a flow-rate of fluid supplied from the first input port (1) to the second output port (4) and returned via the second input port (3) to the first output port (2). The valve is variable so as to provide graduated control of the flow-rate. The tool may be a vibroflot and there may be a relief valve (42) arranged to allow fluid to flow through a bypass path from the first input port and the first output port.

Description

DESCRIPTION

HYDRAULIC CONTROL UNIT

This invention relates to a hydraulic control unit, for controlling the supply of hydraulic power to a hydraulic tool from a hydraulic supply. It is particularly relevant to the supply of hydraulic power to a vibroflot.

A vibroflot is a long, vertically-suspended vibrating probe for improving the strength of the ground prior to construction taking place. Typically, the vibrating poker is from 7m to 30m in length and from 300mm to 400mm in diameter and is suspended either from a crane or from a purpose-made or adapted mobile base machine (which is usually mounted on caterpillar tracks and hydraulically-powered).

Vibroflots of different types can be powered either hydraulically or electrically. The present invention concerns hydraulically powered vibroflots, in particular, but is also potentially relevant to other similar hydraulically powered tools.

The basic method of supplying hydraulic power to the vibroflot is from a standalone hydraulic power-pack with a built-in, customised control system, manufactured by the vibroflot manufacturer. It is known for users of vibroflots to design and build their own control systems for their own power-packs, however very few have this capability.

A standalone hydraulic power supply typically comprises a diesel engine coupled to a hydraulic pump. In order to operate the vibroflot correctly and safely, the pump is controlled by a control system to generate a variable flow-rate. That is, the control system sets the pump to different speeds -in particular, during a start-up phase. The control system preferably also includes sensors and control logic to detect and mitigate problems while the vibroflot is in use.

A more sophisticated method of supplying the hydraulic power for the vibroflot is to modify the pre-existing hydraulic system built into the mobile base-machine (or crane) which suspends the vibroflot, and thereby to divert some of the base machine's built-in hydraulic power to operate the vibroflot.

This bespoke modification of the base-machine is done by the vibroflot manufacturer.

In general, it is not possible to power a vibroflot directly from an arbitrarily chosen conventional hydraulic power-pack (without modification), because such a standard hydraulic supply will lack the sensing and control systems desired for safe operation of the vibroflot and its output parameters (such as flow-rate, which is usually fixed) will not be suitable to meet the hydraulic input requirements of the vibroflot.

According to an aspect of the present invention, there is provided a hydraulic control unit comprising: a first input pod, for receiving fluid from a hydraulic supply; a first output pod, for returning the fluid to the supply; a second output pod, for supplying fluid to drive a hydraulic tool; a second input pod, for receiving fluid returned from the hydraulic tool; and at least one valve arranged to control a flow-rate of fluid supplied from the first input pod to the second output pod and returned via the second input port to the first output port, wherein the valve is variable so as to provide graduated control of the flow-rate.

The present inventors have recognized that it would be desirable to provide a plug and go" hydraulic control unit which could be attached to any power-pack of sufficient performance and used to drive a vibroflot or similar hydraulic tool. The control unit enables the output of the power-pack to be adapted to the needs of the tool. In particular, the variable valve enables the flow-rate to the tool to be modulated by the control unit.

A control unit according to an embodiment of the invention can be provided as a standalone unit, hydraulically coupled between the hydraulic tool and a standard power-pack. This avoids the need to provide a bespoke power-pack. A control unit according to another embodiment can be attached to a base machine (again, assuming that the base machine has sufficient performance to drive the tool). This avoids the need to customize the integrated hydraulic supply of the base-unit. Consequently, the hydraulic control unit provides greater flexibility by allowing an existing hydraulic supply to power the hydraulic tool without modification of the supply, thereby avoiding the cost of customizing the supply or purchasing a specific power-pack.

The valve is preferably continuously variable. That is, the valve is capable of being set to any arbitrary desired position (degree of opening) by the application of a suitable a control input. This means that an arbitrary rate of flow can be selected, by applying appropriate control to the valve.

Preferably, the valve is controlled such that a maximum desired flow-rate can be set in a configuration mode and in a normal operation mode the set maximum flow-rate cannot be exceeded. That is, in the normal operation mode, the valve is preferably controlled to prevent it opening to more than a configurable maximum degree. The configurable maximum flow and corresponding valve position are preferably reconfigurable. This allows the control unit to be reconfigured for use with different vibroflots and hydraulic supplies. Control of the valve is preferably electronic.

Preferably, the hydraulic control unit further comprises a bypass path coupling the fluid supplied to the first input port to the first output port without circulating through the second output and input ports, wherein the bypass path preferably comprises a pressure relief valve arranged to allow fluid to flow through the bypass path when the pressure at its input side exceeds a predefined threshold.

The bypass path allows excess hydraulic fluid to return to the supply (pump source) without flowing through the valve and the hydraulic tool. This means that the hydraulic supply can deliver a fixed, constant flow-rate. The valve is used to select the (lesser or equal) flow-rate to be delivered to the tool.

When the flow-rate delivered by the supply is greater than the flow-rate passing through the valve, fluid pressure increases upstream of the valve. The pressure relief valve automatically opens in this case, to permit the recirculation of the "unused" fluid back to the supply.

The hydraulic control unit may further comprise a check valve, wherein one port of the check valve is coupled to the second output port and the other port of the check valve is coupled to the second input port, the check valve being arranged to prevent fluid flowing through it from the second output port to the second input port but to permit fluid to flow in the opposite direction.

This provides protection against cavitation in a motor of the hydraulic tool in the event of a sudden loss of hydraulic fluid pressure delivered by the external hydraulic supply. When the main fluid supply is lost, the anti-cavitation check valve allows fluid to "free-wheel" -that is, continue to circulate through the hydraulic tool, so as to allow the kinetic energy in the tool to dissipate.

The valve is preferably electronically actuable.

This allows electronic control of the flow-rate, for example, using an electronic controller included in the hydraulic control unit. The electronic controller may be a Programmable Logic Controller, for example. The electronic controller is adapted to supply a control signal to the valve, which controls the valve position and thereby the flow-rate through the valve. For example, in a solenoid-controlled proportional valve, a current signal flowing to the solenoid may determine the valve position. Preferably, the electronic controller may be adapted to supply a control signal having a plurality of discrete, non-zero levels. This enables stepped opening and/or closing of the valve. Preferably, the discrete signal levels are reconfigurable by an operator, so that a set of desired flow rates can be implemented for arbitrary pairings of a hydraulic supply with a vibrofiot. Preferably, the controller provides at least one first signal level suitable for warming up the vibrofiot at the start of use.

Preferably, the controller also provides at least one second level suitable for normal operation of the vibroflot. The at least one second signal level may comprise a signal level corresponding to the maximum desired flow-rate set during a configuration phase. The controller may be configured to smoothly increase the level of the control signal from the first level to the second level in response to operator input. This enables the flow of hydraulic fluid to be increased steadily (rather than suddenly) to the normal operating flow.

The valve is preferably remotely electronically controlled, preferably via the electronic controller, from a remote control device in wired or wireless communication with the hydraulic control unit. A control panel may be provided in the cab of the base machine, for example. This enables the rig driver to control the hydraulic tool. The remote control device is preferably also operable to configure the electronic controller. This allows the rig driver to set up the hydraulic control unit from the cab of the base machine, as well as control it when the vibroflot is in use. The configuration functions of the remote control device may be protected, for example by password, to ensure that only properly qualified personnel are permitted to modify the configuration.

The hydraulic control unit preferably further comprises: a third input port for receiving fluid from a second hydraulic supply; a third output port, for returning the fluid to the second supply; a fourth output port, for supplying fluid to a lubrication or cooling circuit of the hydraulic tool; a fourth input port, for receiving fluid returned from the lubrication or cooling circuit of the hydraulic tool; and at least one second valve arranged to control the flow of fluid from the third input port to the fourth output port and from the fourth input port to the third output port.

This provides the integrated connections and control necessary to create a secondary hydraulic circuit, for lubricating and/or cooling a vibroflot (or similar tool). The second valve is preferably electronically actuable by the same electronic controller as the first valve. This allows control of the primary (power delivery) circuit and secondary (lubrication/cooling) circuit to be integrated in the same device, under common control.

The hydraulic control unit may further comprise at least one further pair of ports for circulating fluid through an auxiliary hydraulic element; and a further valve arranged to selectively couple the further pair of ports to the third input port and third output port and thereby to control the flow of fluid to and from the auxiliary element.

This provides the integrated connections and control to create auxiliary hydraulic circuits. These may be useful for driving subsidiary hydraulic actuators (such as hydraulic cylinders) associated with the hydraulic tool. For example, some vibroflots have these additional actuators. Preferably, the control of the actuators is provided by the same electronic control system used to control the primary and secondary hydraulic circuits. This allows all aspects of the vibroflot operation to be controlled in an integrated manner.

The second valve and the further valve may be coupled to the third input port through a variable priority valve adapted to control the proportion of fluid flowing from the third input port to each of these valves.

This allows the auxiliary hydraulic circuits to be supplied by the same hydraulic supply as the secondary (lubrication/cooling) circuit.

The hydraulic control unit may further comprise a filter coupled in series with at least one of the input ports, preferably a plurality of filters, each being coupled in series with a respective one of the input ports.

This protects the hydraulic control unit (in particular, its valves) from contamination originating from the supply or the tool, respectively.

The hydraulic control unit may further comprise at least one of: a first pressure transducer arranged to measure a fluid pressure at the input side of at least one filter and communicate the measured pressure to an electronic control system; and a pressure switch arranged to measure a differential fluid pressure across the filter and output a warning signal to the electronic control system if the differential pressure exceeds a preset threshold.

The control system is preferably configured to alert an operator and/or to automatically deactivate the hydraulic control unit if the pressure exceeds a predefined threshold.

The pressure transducer and/or pressure switch can be used to detect blockage of the filter, since the blockage will cause an increase in the pressure at the input side of the filter and an increase in the differential pressure between the filter input and output. The control system can then automatically power-down the unit. This functionality may be particularly useful at the input ports facing the hydraulic tool, because a failure of the hydraulic tool may cause debris to block these input ports. This may be relevant, in particular, at the input pod for returning lubrication/cooling fluid from the tool, because a failure of the tool may cause contamination of the lubricating/cooling fluid. Note that the pressure transducer and/or pressure switch may be provided in addition to a bypass valve for the filter. The bypass valve opens at a predetermined pressure, in order to protect the filter from damage. However, bypassing the filter may cause debris to contaminate the control unit (especially the valves) and any connected hydraulic supply. Therefore, it may be preferable to shut down the control unit before the bypass valve opens (that is, at a lower pressure than would open the bypass valve). Thus, the control system receiving measurements from the transducer or receiving a warning signal from the pressure switch should preferably be configured to shut off the control unit at a lower pressure than that which would cause the bypass valve to open.

The hydraulic control unit may further comprise a second pressure transducer arranged to detect an increase in pressure due to a blockage in the hydraulic tool.

The pressure transducer is preferably arranged in electronic communication with the control system, wherein the control system is configured to alert an operator and/or to automatically deactivate the hydraulic control unit if the pressure exceeds a predefined threshold. This can help to prevent damage or failure of components in the event of a blockage.

The control unit may further comprise a third pressure transducer arranged to monitor a pressure at which hydraulic fluid is delivered to the hydraulic tool.

The hydraulic control unit may further comprise a temperature sensor arranged to measure a temperature of hydraulic fluid returning from the hydraulic tool.

The temperature sensor is preferably arranged to measure fluid temperature returning from the lubrication or cooling circuit of the tool. It is preferably arranged in electronic communication with the control system, wherein the control system is configured to alert an operator and/or to automatically deactivate the hydraulic control unit if the temperature exceeds a predefined threshold. This can help to prevent damage or failure of components in the event of overheating.

Alternatively or in addition, the control system may be configured to provide an interlock function based on the temperature measurements, wherein the valve controlling the supply of hydraulic power to the tool will not be allowed to open beyond its warm-up position until the measured temperature has reached a predefined safe operating threshold. This prevents the operator from mistakenly supplying a higher flow-rate when the hydraulic tool is cold. Supplying too much driving hydraulic fluid when the tool is cold could damage the tool, due to the increased viscosity of the fluid at low temperatures.

The hydraulic control unit may be specially adapted for use with a vibroflot as the hydraulic tool.

According to another aspect of the invention, there is provided a kit of parts comprising a vibroflot and a hydraulic control unit for the vibroflot as summarised above.

According to still another aspect of the invention, there is provided a method of configuring a hydraulic control unit as summarised above, the method comprising: coupling the first input and output pods to a hydraulic supply; coupling the second input and output ports to the vibroflot; activating the hydraulic supply; opening the valve, thereby allowing a flow of fluid to circulate through the vibrofiot; varying the valve position, thereby varying the flow rate of the fluid; measuring a vibration of the vibroflot while varying the valve position; determining when a desired vibration has been achieved; and fixing the associated valve position as the maximum for use with the vibroflot.

If the vibroflot is being configured from a cold start, the method preferably comprises gradually opening the valve, thereby gradually increasing the flow of fluid circulating through the vibroflot; measuring a vibration of the vibroflot while gradually opening the valve; determining when a desired vibration has been achieved; and fixing the associated valve position as the maximum for use with the vibroflot.

This method allows the control unit to be set up for use with a substantially arbitrary pairing of a given vibroflot and a given power-pack.

Neither the power-pack nor the vibroflot needs to be modified. It is assumed that the power pack is able to deliver at least enough performance (power and flow-rate) to satisfy the operating requirements of the vibroflot. The method determines the valve position which delivers the correct flow of hydraulic fluid to the vibrofiot for its desired operating point. This position is then set as the maximum valve position for the given combination of power-pack and vibroflot.

If either the power-pack or vibrofiot is replaced, the configuration procedure should be repeated.

The configuration method may further comprise measuring the flow rate through the second output port of the hydraulic control unit using an external flow-meter. This may be helpful if the flow rate output from the hydraulic supply is not known in advance. The flow meter can be used to calibrate the position of the valve (and the corresponding level of the control signal, for an electronically actuable valve) against the actual flow rate being delivered to the vibroflot. This can allow a set of valve positions (and signal levels) to be established which provide a set of specific desired flow rates to the vibroflot.

The vibration of the vibroflot is preferably measured using a sirometer.

The invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a diagram symbolically illustrating a primary hydraulic circuit of a hydraulic control unit according to an embodiment; Fig. 2 shows a secondary hydraulic circuit included in the same hydraulic control unit; and Fig. 3 shows an auxiliary hydraulic circuit which branches from the secondary hydraulic circuit illustrated in Fig. 2.

Fig. 1 shows a primary hydraulic circuit of a hydraulic control unit according to an embodiment of the invention. The primary circuit comprises four external connection pods: a first input port 1 is provided for receiving hydraulic fluid from the power-pack; a first output port 2 is provided for returning the fluid to the power-pack; a second output port 4 is provided for delivering fluid to the vibroflot; and a second input port 3 is provided for receiving the fluid returned from the vibroflot. The primary hydraulic circuit is completed by the connections to the power-pack and vibrofiot, and the fluid circulating through the second output pod 4 and input port 3 delivers hydraulic power to the vibroflot motor. In the presently described embodiment, the first input port 1 and the second input and output pods 4, 3 are two-inch SAE 6000 flange ports. The first output pod 2 is a two-inch SAE 3000 flange port. Oil, such as mineral oil according to ISO VG 46/68, contamination class ISO 18/15, is used as the hydraulic fluid.

A filter 20 is provided at the first input port 1. In this embodiment, the filter component 22 is a two-inch British Standard Pipe (BSP) SAE flange pressure filter of 10pm type. The filter 20 also includes a bypass valve 24, which allows hydraulic oil to bypass the filter component 22 if the pressure exceeds 6 bar. This safety feature means that the filter component 22 is protected from excessive pressure -for example, if the filter becomes partially or completely blocked. An electrical indicator switch 26 is provided to detect a pressure difference across the filter in excess of a predetermined threshold (5 bar). If the pressure differential exceeds this threshold, the switch is closed and a warning indicator is activated on a control panel to alert the user that a filter blockage may have occurred. An electronic control system can then automatically power-down the hydraulic control unit. The differential threshold of the pressure switch 26 (set to 5 bar) is less than the pressure threshold of the bypass valve 24 (set to 6 bar) so that the control unit can be turned off safely before the bypass valve 24 opens, in normal operation when both safety features are functioning properly. Opening of the bypass valve 24 may allow debris to contaminate downstream hydraulic components, so this should be allowed only a last resort, if the protection provided by the switch 26 has not been able to shut down the unit fast enough.

Downstream of the filter 20, a panel mounted pressure gauge 250 is provided. This is coupled to the hydraulic circuit via a quarter-inch BSP inline gauge isolator valve 240. The pressure gauge 250 allows the input pressure to be inspected.

From the filter 20, the filtered hydraulic oil flows to an input port P of a proportional valve 70. In the present embodiment, this is a CETOP 8 two- stage, two-position proportional valve, allowing graduated control of the flow-rate. The valve is electrically controlled by means of a solenoid b. When the control unit is inactive, the valve 70 is in its first position (as illustrated in Fig. 1). In this configuration, fluid flow to the input port P is blocked. In order to supply hydraulic power to the vibroflot, the valve spool is moved (gradually) towards its second, open position. In the open configuration, fluid can flow from the input port P to the output port A and returning fluid can flow from input port B to output port T. The valve 70 allows graduated control of the flow rate, under the control of a programmable logic controller 220.

Two paths are provided for hydraulic oil to bypass the valve 70. That is, these paths couple the output of the filter 20 to the first output port 2. One bypass path is provided by a solenoid-controlled cut-off valve 44. The other bypass path is provided by a pressure relief valve 42. In the present embodiment, the pressure relief valve 42 is configured to open at a pressure of 300 Bar. The cut-off valve 44 enables all of the hydraulic oil to circulate back to the power-pack, when the power-pack is active but the hydraulic control unit is switched off. When the control unit is in use, PLC 220 causes the cut-off valve 44 to close. Meanwhile, the pressure relief valve 42 allows excess flow of hydraulic oil to re-circulate to the power-pack, when the hydraulic control unit is in use. This means that oil flows through the proportional valve 70 at the desired rate and the remainder of the oil delivered by the power-pack flows through the relief valve 42, back to the power-pack.

The output port A of the valve 70 is coupled to the second output port 4.

This output port delivers oil to drive the vibroflot motor. When the hydraulic oil returns from the vibroflot, via second input port 3, it is filtered by filter 30. This filter 30 is of a similar type to filter 20, described above. From the output of the filter, the hydraulic fluid flows back to the valve 70, where it enters port B and emerges at port T. From here, the oil combines with any oil flowing through the relief valve 42 in the bypass path and continues to exit the unit via first output port 2.

The primary hydraulic circuit is adapted to accommodate a maximum flow rate of 500 litres per minute, in the present embodiment. Typically, a vibroflot will require a flow-rate in the range from 190 1/mm to 450 1/mm. The pipes used to connect the components of this circuit have an internal diameter (bore) of 76mm and a wall thickness of 12.5mm ("76mm x12.5mm"). Those skilled in the art will be able to choose suitable pipe specifications according to the requirements of specific applications.

A pressure transducer 110 is provided, coupled to the second output port 4. This provides measurements of the output pressure delivered to the vibroflot to the programmable logic controller (PLC) 220. In this embodiment the transducer 110 has an operating range of 0-400 bar and produces an output current of 4-2OmA. Two quarter-inch BSP line-mounted test points are provided for diagnostic purposes. One test point 80 is provided coupled to the second output port. This allows direct measurement of the pressure which is also measured by the pressure transducer 110. This is useful since the readout of the transducer pressure will usually be at a control panel that is remote from the hydraulic control unit Another test point 90 is provided at the output of the filter 30, for testing the pressure of hydraulic oil returning from the vibroflot.

A further safety feature is provided by bypass valve 46. This is coupled between the second output port 4 and port T of the valve 70. The bypass valve 46 is a check valve (non-return valve). In normal operation, the pressure at the second output port 4 will be greater than the pressure at the second input port 3. Note that the second input port 3 is coupled to the other side of the check valve 46 via the filter 30 and return path through valve 70. Under this normal operating condition, the check valve 46 is closed. However, if the supply of hydraulic oil from the power-pack is suddenly lost, a pressure drop will occur at the second output 4. Without the presence of check valve 46, cavitation could occur in the vibroflot motor. However, check valve 46 prevents this by opening in response to the reversal in differential pressure and allowing oil to circulate through the vibroflot. In this anti-cavitation mode, the hydraulic oil is flowing into the control unit via second input port 3; through filter 30; through the valve 70, via ports B and T; through the (open) check valve 46; and back to the vibroflot via second output pod 4.

In the presently described embodiment, the connections to the proportional valve 70 are implemented by a ported manifold 40. This ported manifold therefore incorporates the bypass path provided by the relief valve 42; the bypass path provided by the cut-off valve 44 and the anti-cavitation check valve 46. The connections for test points 80, 90; the gauge isolator valve 240 and the pressure transducer 110 are provided by the ports of the manifold. In this embodiment, the manifold 40 is a CETOP 8 SAE ported manifold.

The hydraulic control unit of the present embodiment also comprises a secondary hydraulic circuit, which is illustrated in Fig. 2. The secondary circuit comprises four external connection pods: a third input port 5 is provided for receiving hydraulic oil from a second supply (power-pack); a third output pod 6 is provided for returning the oil to the supply; a fourth output pod 8 is provided for delivering oil to a lubrication and cooling circuit of the vibroflot; and a fourth input port 7 is provided for receiving oil returning from this lubrication and cooling circuit. The secondary hydraulic circuit is completed by the connections to the second power-pack and the vibroflot lubrication circuit. In the present embodiment, the third input pod 5 is implemented as a half-inch BSP female port; the third output pod 6 and fourth input port 7 are provided by three-quarter-inch BSP female ports; and the fourth output port 8 is implemented as a half-inch BSP female port. The third input pod 5 and output port 6 are also shared with an auxiliary circuit of the hydraulic control unit. This auxiliary circuit will be described in greater detail below, with reference to Fig. 3.

A filter 120 is provided at the third input port 5. This protects the secondary circuit of the hydraulic control unit -especially the valve -from contamination due to particulate material in the oil supplied by the second power-pack. In this embodiment, the filter 120 is a half-inch BSP pressure filter. The filter component 122 of the filter 120 is of the 10 micron type.

Similarly to the filters 20 and 30 described previously, the filter 120 also includes a bypass valve 124 configured to allow oil to bypass the filter at pressures greater than 6 bar (to protect the filter component 122 against excess pressure, particularly if it becomes blocked; and an electrical pressure-sensing indicator switch 126, for alerting the operator to potential blockage of the filter. The switch 126 is set to activate if the differential pressure exceeds 5 bar. The third input port 5 and the filter 120 are adapted for a hydraulic oil flow from the supply of up to 30 1/mm.

From the filter 120, the filtered oil flows to a variable priority valve 140.

This divides the flow of oil between the secondary circuit and the auxiliary circuit (to be described subsequently below). In this embodiment, the filter 120 and the variable priority valve 140 are connected by a pipe of internal bore 12mm, thickness 1.5mm. The same pipe dimensions are used to carry the outputs from the valve 140. The variable priority valve 140 is implemented as a three-quarter-inch BSP line-mounted valve, which is configured to allow a flow of 15 1/mm to the secondary circuit and to separate off the remainder, of between 0 and 15 I/mm, for the auxiliary circuit.

After the variable priority valve 140, the oil flows to an input port F of a control valve 160. In this embodiment, this valve 160 is a CETOP 3 subplate mounted single directional control valve. The valve has two configurations, controlled by means of a solenoid, a. In the first configuration, oil entering via the port P exits the valve via port T. From here, it flows to the third output port 6, from where it is returned to the second hydraulic supply. Thus, in this configuration, the hydraulic oil is circulated from third input 5 to third output 6 without any oil being directed to the vibroflot lubrication circuit. In order to supply oil to the vibroflot lubrication circuit, the valve 160 is switched to its second configuration. In this configuration, the oil entering via port P flows out through port B, and from there to the fourth output port 8, which is connected to the vibroflot. Oil returning from the vibroflot enters the valve 160 through port A and is directed to pod T. It then continues, as before, to the third output port 6. The flow out of port T of the control valve 160 is carried by a pipe of 15mm bore and 1.5mm wall thickness.

A pressure relief valve 150 provides a bypass path between the input port P of the valve 160 and the output port T of that valve. This provides a bypass route for oil to flow from the variable priority valve 140 essentially directly to the third output port 6. A pressure transducer 230 is also provided at the input port P of the valve 160. This transducer 230 has an operating range of 0 to 60 Bar. If the pressure increases above 40 Bar, the operator of the vibroflot is warned and the PLC 220 shuts down the system. This protects the components of the secondary circuit and the lubrication circuit of the vibrofiot against damage due to excessive pressures. The pressure relief valve 150 provides a backup to the pressure transducer 230. The relief valve 150 is configured to open if the input pressure exceeds 50 Bar. With this arrangement, if the pressure suddenly spikes above 50 Bar, too quickly for the pressure transducer 230 and PLC 220 to react, the relief valve 150 will open immediately to protect the other components. A pressure spike may be caused by a blockage in the hydraulic circuit. In the present embodiment, the relief valve 150 is implemented as a CETOP 3 line mounted subplate with a relief valve cartridge.

Upon returning from the vibroflot lubrication circuit, via fourth input port 7, the lubricating oil passes through a filter 130, before entering the valve 160, via port A. In the current embodiment, the filter 130 comprises a three-quarter-inch BSP return filter of 10pm type, having a bypass valve and an electrical indicator switch. It functions similarly to the filters 20, 30 and 120, described previously above. However, the bypass valve of this filter 130 is set to open if the differential pressure exceeds 1.75 bar and the electrical pressure switch is set to activate if the pressure exceeds 1.2 bar. This is because the hydraulic oil returning from the vibroflot lubrication circuit is found to be at a lower pressure than that experienced by the other filters 20, 30. This filter 130 protects the components of the secondary hydraulic circuit from contaminants introduced while the oil was flowing through the vibroflot lubrication and cooling system.

If the vibroflot fails, significant amounts of debris may flow into the hydraulic control unit, via fourth input 7. These will be collected in the filter 130 and may block it. The electrical pressure switch of the filter 130 detects this condition. If the differential pressure exceeds 1.2Bar, the switch activates and the PLC 220 alerts the operator of the vibroflot that the filter 130 has become blocked and the system shuts down. This controlled shut down will occur before the bypass valve in the filter 130 opens at a threshold differential pressure of 1.75 bar (which would allow debris to enter the valve 160 and ultimately reach the second hydraulic supply via third output port 6). As an optional addition (or potential alternative to the pressure switch), a pressure transducer 170 can be provided between the fourth input port 7 and the filter 130. The pressure transducer 170 has a scale of 0 to 60 Bar. The PLC 220 receives measurements from the transducer 170 and is configured to pre-warn the operator of the blockage of the filter 130 if the pressure at the input port 7 exceeds an absolute threshold (in this example, 3 bar). Monitoring absolute pressure at the input side of the filter 130 (input port 7) provides an alternative detection means to monitoring the relative pressure difference across the filter.

A temperature sensor 260 is provided to measure the temperature of the oil in the lubrication circuit before it returns to the hydraulic supply via third output port 6. In this embodiment the sensor is a half-inch BSP temperature transducer with a temperature range of 0 to 100°C and an output current in the range 4 to 20 mA. The sensor 260 communicates its measurements to PLC 220, which enables the operator to be alerted if the lubrication and cooling oil begins to overheat. The PLC 220 may be configured to automatically shut down the system if the temperature measured by sensor 260 exceeds a predetermined threshold (in this example, 86°C). In the present embodiment, the PLC 220 is also configured to monitor the temperature during a start-up phase of the vibroflot. The PLC will prevent the control valve 70 opening beyond a pre-configured "warm up" position until the oil in the lubrication circuit has reached a minimum safe operating temperature (in this example, 20°C).

Only when the oil has warmed up will the operator be allowed to increase the primary oil flow to bring the vibroflot motor up to its full operating speed. This prevents damage to the vibroflot by accidentally driving it with cold, viscose oil at a high flow-rate. Note that the temperature of the oil in the main circuit of the vibroflot motor will usually be closely related to the temperature in the lubrication circuit.

A test point 280 is provided at the output port B of the control valve 160.

This allows connection of gauge, for diagnostic purposes. The test point 280 is provided as a CETOP 3 tapping module with A and B ports, which is arranged between the sub plate mounted valve 160 and the sub plate 150 containing the pressure relief valve cartridge in the bypass path.

Fig. 3 shows an auxiliary circuit of the hydraulic control unit according to the present embodiment. Oil flows into this circuit from the variable priority valve 140 described earlier above. The auxiliary circuit comprises several control valves, which can be used to operate auxiliary hydraulic elements in the vibroflot, such as hydraulic cylinders. Oil returning from these auxiliary elements recombines with the oil flowing in the secondary hydraulic circuit and returns to the second hydraulic supply via third output port 6. By way of example, the auxiliary circuit illustrated in Fig. 3 comprises three control valves 190, 200, and 210.

Control valve 190 is a CETOP 3 subplate mounted single directional control valve, which is identical to the control valve 160 of the secondary circuit. With the valve 190 in its first position (as illustrated) oil enters via port F and exits again via port T. From here, it recombines with the flow of oil in the secondary circuit (flowing to output port 6). When the valve is actuated by the solenoid, a, it switches to its second configuration, in which oil flows from port P to port B. In Fig. 3, port B is shown as leading to a plugged pressure connection Bi. This plug stops the flow of oil, allowing pressure to build up.

The control valve 190 is therefore switched to this configuration at the same time that either of the valves 200 or 210 (described below) is opened.

Two identical control valves 200 and 210 are connected in parallel with the control valve 190. Each of these comprises a CETOF 3 subplate mounted double-directional control valve. Control valve 200 allows oil to be circulated through auxiliary ports 9 and 10, in either direction. Likewise, control valve 210 allows oil to be circulated through auxiliary ports 11 and 12, in either direction.

In the present embodiment, auxiliary ports 9, 10, 11, and 12 comprise half-inch s BSP male ports. Oil is delivered to each of valves 200 and 210 from the variable priority valve 140, via ports P. Oil is returned from both valves 200 and 210 via ports T, to recombine with the oil flowing out through third output port 6. Since the control valves 200 and 210 are double directional (that is they are adapted to direct the fluid flow in either of two directions), they are suitable for driving hydraulic elements which can move in two directions, such as hydraulic cylinders.

In this embodiment, the connections to the control valves 190, 200, and 210 are provided by a CETOP 3 three station manifold block 180, which includes a relief valve cartridge 182, set to 150 Bar. The relief valve cartridge 182 provides a bypass path, leading directly from the input of the auxiliary circuit (output of the variable priority valve 140) to the third output port 6. This allows oil to flow back to the second hydraulic supply, in the event of excess pressure, thereby protecting the valves 190, 200, and 210 as well as the connected auxiliary hydraulic elements from damage. The manifold block 180 also provides a test point 100, for diagnostic purposes.

The manifold block 180 receives hydraulic oil for the auxiliary circuit through a 12.5mm x 1.5mm pipe connected to one output of the variable priority valve 140, as mentioned previously above. Port T2 of the manifold block is connected to port P of the sub-plate comprising the relief valve 150, by a 15mm x 1.5mm pipe. Furthermore, port Ti of the manifold block 180 is connected to the third output port 6 by another 15mm x 1.5mm pipe.

All components of the hydraulic control unit are mounted on a base frame (or "crash frame"). All solenoids are controlled by 24 Volt DC signals from the PLC 220. The PLC 220 communicates with a control panel, preferably in the cab of the base machine, from which the operator can control the vibroflot. In this embodiment, the control panel and the hydraulic control unit are connected via an umbilical electrical cable.

A method of operating the control unit will now be described. All connections to the input and output ports are completed, at the outset. The hydraulic supply for the primary and secondary circuits is turned on. Initially, the oil flow into the first input port 1 flows to the valve 70 and is blocked at port P. The oil instead flows through the solenoid-controlled valve 44 and back to the first output port 2. The oil flow to the third input port 5 flows to valve 160 and manifold 180. These two flows combine and return to the second hydraulic supply through third output port 6. Note that oil is flowing through valve 160 (into port P and out of port T) and through the manifold 180 (in through port T2 and out through port Ti). In the auxiliary circuit, oil will be flowing through the valve 190, in its first configuration, as described earlier above.

Power is then switched on, using the control panel. The oil flow for the vibroflot lubrication and cooling circuit is activated using the control panel, to allow oil to flow to fourth output port 8. That is, valve 160 is switched to its second (open) configuration. Pressure in the lubrication circuit will be sensed using the pressure transducer 230.

The primary oil flow (to the vibrofiot motor) can now be activated, from the control panel. An electrical interlock prevents the primary oil flow from being directed to the vibroflot if the lubrication pressure measured by transducer 230 is below a preset threshold. This is because adequate lubrication is essential for safe operation of the motor. Assuming there is sufficient lubrication pressure, the valve 70 will be opened, to allow oil to pass to the vibroflot. Simultaneously with the opening of valve 70, the cut-off valve 44 is closed to stop the bypass flow. The oil flows out through the second output port 4 to the vibrotlot (driving the vibroflot motor) and returns via second input port 3 and filter 30. The returning oil then flows back via the valve 70 (into port B and out through port T) and onwards via the first output port 2 to the tank. The flow-rate of oil to the vibroflot is controlled from the control panel.

This has a button which steps the position of valve 70 to increase the oil flow.

The correct maximum oil flow is set in a configuration phase, to be described later, below. Buttons are also provided on the control panel to operate any connected auxiliary hydraulic elements, by actuating the valves 190, 200, and 210 of the auxiliary circuit.

Before the hydraulic control unit is used for the first time with a selected vibroflot and hydraulic power-pack, it should be configured by a competent engineer. This configuration phase will now be described. The hydraulic control unit of the present embodiment can accommodate a main flow of up to about 450 1/mm. A given vibroflot will typically require a flow in the range 190 I/mm to 450 1/mm, to drive its motor. It is desirable to avoid supplying the vibroflot with too great a flow of oil.

If the flow provided by the primary hydraulic supply is not known, a flow meter should be fitted in series with the second output pod 4 and the flow-rate measured. The flow-rate delivered by the main hydraulic supply must be sufficient to drive the vibroflot. Preferably, the flow-rate delivered by the supply should be slightly greater than the requirement of the vibroflot, because this helps valve control. This may not be essential, but can help to compensate for losses in the hydraulic system.

Once the flow-rate of the main supply is known, and the vibroflot is connected and running, the position of the valve 70 can be adjusted (using the buttons on the control panel). The valve 70 is opened in steps, to allow incrementally greater amounts of oil to flow. During this process, the vibration of the vibroflot is measured using a sirometer. This measures the frequency of oscillations of the vibroflot motor. When the desired vibration is achieved -in this example 50Hz -the corresponding setting of the valve 70 is determined to be the maximum setting for this particular combination of vibroflot and hydraulic supply. This means that when the control unit is in use, the operator will be unable to open the valve 70 to permit any greater flow rate. In normal operation, therefore, the vibroflot can be slowly speeded up to warm up the oil and then the speed (flow-rate) increased gradually to the maximum setting.

In order to safely stop the vibroflot, the flow-rate of oil should be gradually stepped down to 0, using the control panel to control the valve 70, in order to allow the vibroflot motor to stop spinning. The lubrication and cooling circuit can then be deactivated and the hydraulic control unit turned off.

When in operation, the hydraulic control unit is protected by several safety systems. In the event of a blockage of the vibroflot lubrication circuit, pressure transducers 170 and 230 will trigger the PLC 220 to shut off the system in order to protect it and will also give a visual warning on the control panel. If the oil temperature in the lubrication circuit becomes too high, the temperature sensor 260 will give a warning and if the temperature increases further it will automatically shut down the system. If there is a sudden loss of hydraulic oil from the main supply, the ball check valve 46 will allow oil to circulate around the vibroflot motor in a loop, to prevent cavitation of the motor.

The control panel in the cab will also alert the operator if the pressure differential across any of the filters increases (indicating that the filter has begun to block) and if the pressure increases further, the PLC 220 will automatically shut down the system and provide a visual alarm to the operator.

The control panel also provides a reset function, which the operator will use to bring the system back into operation, after the problem which caused the warning I shutdown has been fixed.

The hydraulic control unit of the embodiment described above can be used either with standalone hydraulic supplies or with the on-board hydraulic supply of a base machine carrying the vibroflot. As described above, embodiments of the present invention provide a "plug and go" vibroflot hydraulic control unit in either case.

The control unit comprises a dual-circuit hydraulic control system, to control the hydraulic power supplied to both the vibroflot drive circuit and the lubrication & auxiliary actuation circuits. It is mounted within a frame which can be either free-standing or attached to a mobile base unit, and has a control panel suitable for mounting in the driver's cab of the mobile base unit or the crane which suspends the vibroflot.

Hydraulic power for the primary (driving) and secondary (lubrication) circuits can be supplied to the control unit from separate hydraulic supplies.Depending upon the requirements of the vibroflot and the capacity of the supply, the primary supply may come from a tandem pump -that is, a pair of linked pumps driven by the same motor -using the combined output flow of the pair.

The control unit has a PLC (Programmable Logic Controller) built into the frame which controls the various valves and monitors the different sensors in the unit. In other embodiments this electronic controller may be implemented in other ways, such as using a microcontroller or microprocessor.

The unit has filtration to ensure that the base machine does not contaminate the vibroflot control valves and also to ensure that if the vibroflot fails it does not contaminate the base machine.

To control the unit from cab of the base machine or crane, it has a control panel which can be programmed to set the unit to the range of different vibroflot speeds and also to display system parameters and safety warnings.

A hydraulic control unit according to the present invention can be advantageously used to control a vibroflot for ground improvement. However, other hydraulic tools may also be controlled -in particular where it is desirable or essential to provide graduated control of the flow of hydraulic fluid to the tool.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

The word "coupled" is used herein to indicate fluid communication between hydraulic components. It is not necessarily essential that two components which are said to be coupled are directly coupled -other components may be connected in between the first two components. However, as those skilled in the art will appreciate, in some cases direct coupling may be the preferred embodiment.

Claims (1)

1. <claim-text>CLAIMS1. A hydraulic control unit comprising: a first input port (1), for receiving fluid from a hydraulic supply; a first output port (2), for returning the fluid to the supply; a second output port (4), for supplying fluid to drive a hydraulic tool; a second input port (3), for receiving fluid returned from the hydraulic tool; and at least one valve (70) arranged to control a flow-rate of fluid supplied from the first input port (1) to the second output port (4) and returned via the second input port (3) to the first output port (2), wherein the valve (70) is variable so as to provide graduated control of the flow-rate.</claim-text> <claim-text>2. The hydraulic control unit of claim 1, further comprising a bypass path coupling the fluid supplied to the first input port (1) to the first output port (2) without circulating through the second output and input pods, wherein the bypass path preferably comprises a pressure relief valve (42) arranged to allow fluid to flow through the bypass path when the pressure at its input side exceeds a predefined threshold.</claim-text> <claim-text>3. The hydraulic control unit of claim 1 or claim 2, further comprising a check valve (46), wherein one port of the check valve is coupled to the second output port (4) and the other port of the check valve is coupled to the second input port (3), the check valve being arranged to prevent fluid flowing through it from the second output port (4) to the second input port (3) but to permit fluid to flow in the opposite direction.</claim-text> <claim-text>4. The hydraulic control unit of any of claims 1 to 3, wherein the valve (70) is electronically actuable.</claim-text> <claim-text>5. The hydraulic control unit of any of claims 1 to 4, further comprising: a third input port (5) for receiving fluid from a second hydraulic supply; a third output port (6), for returning the fluid to the second supply; a fourth output pod (8), for supplying fluid to a lubrication or cooling s circuit of the hydraulic tool; a fourth input port (7), for receiving fluid returned from the lubrication or cooling circuit of the hydraulic tool; and at least one second valve (160) arranged to control the flow of fluid from the third input port (5) to the fourth output port (8) and from the fourth input port (7) to the third output port (6).</claim-text> <claim-text>6. The hydraulic control unit of claim 5, further comprising: at least one further pair of ports (9, 10; 11, 12) for circulating fluid through an auxiliary hydraulic element; and a further valve (190, 200, 210) arranged to selectively couple the further pair of ports to the third input port (5) and third output port (6) and thereby to control the flow of fluid to and from the auxiliary element.</claim-text> <claim-text>7. The hydraulic control unit of claim 6, wherein the second valve (160) and the further valve (190, 200, 210) are coupled to the third input port (5) through a variable priority valve adapted to control the proportion of fluid flowing from the third input port (5) to each of the valves.</claim-text> <claim-text>8. The hydraulic control unit of any preceding claim, further comprising a filter coupled in series with at least one of the input ports, preferably a plurality of filters each being coupled in series with a respective one of the input ports.</claim-text> <claim-text>9. The hydraulic control unit of claim 8, further comprising at least one of: a first pressure transducer (170) arranged to measure a fluid pressure at the input side of at least one filter and communicate the measured pressure to an electronic control system; and a pressure switch arranged to measure a differential fluid pressure across the filter and output a warning signal to the electronic control system if the differential pressure exceeds a preset threshold.</claim-text> <claim-text>10. The hydraulic control unit of any preceding claim, further comprising a second pressure transducer (230) arranged to detect an increase in pressure due to a blockage in the hydraulic tool.</claim-text> <claim-text>11. The hydraulic control unit of any of any preceding claim, further comprising a temperature sensor (260) arranged to measure a temperature of hydraulic fluid returning from the hydraulic tool.</claim-text> <claim-text>12. The hydraulic control unit of any of claims 9, 10, or 11, wherein the control system is preferably configured to alert an operator andlor to automatically deactivate the hydraulic control unit if the measured pressure or temperature exceeds a predefined threshold or increases by more than a predefined amount.</claim-text> <claim-text>13. The hydraulic control unit of any preceding claim, adapted for use with a vibroflot as the hydraulic tool.</claim-text> <claim-text>14. A kit of parts comprising a vibroflot and a hydraulic control unit for the vibroflot according to any preceding claim.</claim-text> <claim-text>15. A method of configuring a hydraulic control unit according to any of claims 1 to 13 for use with a vibroflot, the method comprising: coupling the first input and output ports to a hydraulic supply; coupling the second input and output ports to the vibroflot; activating the hydraulic supply; opening the valve, thereby allowing a flow of fluid to circulate through the vibroflot; varying the valve position, thereby varying the flow rate of the fluid; measuring a vibration of the vibroflot while varying the valve position; determining when a desired vibration has been achieved; and fixing the associated valve position as the maximum for use with the vibroflot.</claim-text> <claim-text>16. A hydraulic control unit for a vibroflot, substantially as described herein with reference to the accompanying drawings.</claim-text> <claim-text>17. A vibroflot coupled to a hydraulic control unit as claimed in claim 16.</claim-text>