Field of the Invention

The present invention relates to a high pressure fluid system. More particularly, the invention relates to a system for delivering a thick, highly viscous material such as mastic.

Background

Mastic materials are used increasingly as sealants in product manufacturing facilities, particularly in automotive manufacturing. Typically the mastic material will be applied to a product (e.g. parts of a vehicle) as the product is moved through different stages in the manufacturing process, for example at different stations on a production line.

When required to apply the mastic, an operator will simply reach for a mastic application gun, which is connected to an off-take on a mastic circuit that is supplied with the mastic at a high pressure. The high pressure is provided by a pump.

Conventionally, the pumps used have been hydraulic or pneumatic positive displacement pumps.

However, because mastics are very thick and viscous, the capacity and pressure available from conventional pumps has meant that the circuits have to be short such that the mastic pumps and the reservoirs of the mastic materials being pumped have hitherto had to be located close to the stations where the off-takes are located. A further problem is that the fluids tend to thicken, and may even solidify if left stationary for too long a time, such as overnight or at a week-end when the plant is not being used. On large production lines, these problems have meant that a large number of mastic pumping circuits have been installed close to the points where the mastic is used, with a correspondingly large number of pumps and storage vessels (reservoirs).

Similar problems can arise with other high viscosity fluids, such as epoxy materials or other types of adhesive.

This invention has therefore been conceived to provide an improved high pressure fluid delivery system that overcomes or alleviates the foregoing problems. Summary

According to a first aspect of the present invention, there is provided a system for delivery of a high viscosity fluid. The system comprises a variable speed pump. A circuit through which the fluid is pumped comprises a loop having a plurality of fluid off- takes from the circuit. A controller controls the operation and speed of the pump, (i) such that the pump pumps the fluid in the circuit in a high pressure mode in which fluid flows from the pump to the fluid off-takes through both ends of the loop. During the high pressure mode, the controller controls the speed of the pump to maintain the pressure of the fluid in the circuit. The controller also controls the operation and speed of the pump, (ii) such that the pump pumps the fluid around the circuit in a low pressure mode during periods when none of the fluid off-takes are being used.

Operating the system in the high pressure mode has the advantage that high pressure fluid is available at all of the off-takes for use in the manufacturing area. Operating the system in the low pressure mode has the advantage that the fluid is kept moving around the system, for example during periods when the plant in the manufacturing area is idle.

In an embodiment of the first aspect, in the low pressure mode, fluid flows from the pump through a first end of the loop and out through a second end of the loop.

In an embodiment of the first aspect, the system is installed in a manufacturing facility, with the fluid off-takes located at locations in a product manufacturing area. In an embodiment of the first aspect, the variable speed pump is located at a booster station, and the pump has an inlet for receiving fluid from a medium pressure pumping station.

In an embodiment of the first aspect, the medium pressure pumping station comprises a ram unit. The ram unit ensures that fluid is forced to enter the inlets of the pumps, such that the pumps are properly primed.

In an embodiment of the first aspect, the system further comprises an outlet pressure sensor for sensing fluid pressure at the outlet of the pump. The outlet pressure sensor provides a signal representing a sensed pressure to the controller, and the controller controls the speed of the pump based on the sensed outlet fluid pressure.

In an embodiment of the first aspect, the system further comprises a pressure switch responsive to fluid pressure at the outlet of the pump to confirm that operation of the pump is providing a fluid pressure below a maximum working pressure of the pump.

In an embodiment of the first aspect, the variable speed pump is an ac motor driven positive displacement pump.

In an embodiment of the first aspect, the ac motor is driven by an inverter. Preferably the inverter has a vector drive control, which may be a closed loop vector drive control.

According to a second aspect of the present invention, there is provided a method of operating a high viscosity fluid delivery system. The system comprises a circuit through which the fluid is pumped, a variable speed pump, and a plurality of fluid off-takes from the circuit. The method comprises a first step of (i) controlling the operation and speed of the pump, such that the pump pumps the fluid in the circuit in a high pressure mode to provide pressurised fluid to the off-takes. During the high pressure mode, the speed of the pump is controlled to maintain the pressure of the fluid in the circuit. The method comprises a second step of controlling the operation and speed of the pump, such that the pump pumps the fluid around the circuit in a low pressure mode during periods when none of the fluid off-takes are being used. In an embodiment of the second aspect, the fluid off-takes are off-takes from a loop in the circuit, and in the high pressure mode the fluid is pumped into the loop through both ends of the loop.

In an embodiment of the second aspect, in the low pressure mode, the fluid is pumped through a first end of the loop and out through a second end of the loop.

In an embodiment of the second aspect, the system comprises a pressure sensor monitoring a pressure of the fluid at an outlet of the pump. The method further comprises, in the high pressure mode, a step of detecting, by the pressure sensor, a drop in fluid pressure at the pump outlet below a pre-set fluid pressure. The method further comprises, in the high pressure mode, starting the pump, or increasing the speed of the pump, and restoring the pressure of the fluid at the pump outlet to the preset value. In an embodiment of the second aspect, the method further comprises the step of detecting, using the pressure sensor, that the fluid at the pump outlet has been restored to the pre-set value. The method further comprises the steps of reducing the speed of the pump to zero and, while the pump is at zero speed, using the pump to maintain a force on the fluid for a predetermined period of time.

According to a third aspect of the present invention, there is provided a system for delivery of a high viscosity fluid. The system comprises: a medium pressure pumping station; a booster station comprising a variable speed pump having an inlet receiving fluid from the medium pressure pumping station; a circuit through which the fluid is pumped; a plurality of fluid off-takes from the circuit; and a controller. The controller controls operation and speed of the pump (i) to pump the fluid in the circuit in a high pressure mode to provide pressurised fluid to the off-takes and wherein the controller controls the speed of the pump to maintain the pressure of the fluid in the circuit, and (ii) to pump the fluid around the circuit in a low pressure mode during periods when none of the fluid off-takes are being used.

The medium pressure pumping station may comprise a ram unit.

According to a fourth aspect of the present invention there is provided a method of operating a high viscosity fluid delivery system. The system comprises a medium pressure pumping station, a booster station comprising a variable speed pump, a circuit through which the fluid is pumped, and a plurality of fluid off-takes from the circuit. The method comprises: (i) pumping fluid from the medium pressure pumping station to the booster station; (ii) controlling the operation and speed of the variable speed pump to pump the fluid in the circuit in a high pressure mode to provide pressurised fluid to the off-takes and to control the speed of the variable speed pump to maintain the pressure of the fluid in the circuit, and (iii) controlling the operation and speed of the variable speed pump to pump the fluid around the circuit in a low pressure mode during periods when none of the fluid off-takes are being used. Brief Description of the Drawings

Figure 1 is a schematic layout of a high pressure fluid delivery system in a manufacturing facility in accordance with aspects of the invention.

Figure 2a shows the layout of Figure 1 with a flow path for a high pressure mode of operation highlighted.

Figure 2b shows the layout of Figure 1 with a flow path for a low pressure, recirculation mode of operation highlighted.

Figure 3 is a schematic illustration showing more detail of a booster station of the system of Figure 1 including a high pressure pump and associated controls

Figure 4 is an illustration of a high pressure positive displacement pump.

Referring to Figure 1 , there is shown a schematic diagram of an example embodiment of a high pressure system suitable for delivery of a fluid such as mastic. The system includes a circuit 20 around which the fluid is circulated. A number of pumps 24, 26 are used to pump the fluid. As shown, the pumps are arranged in two pumping stages. A first pumping stage includes a working medium pressure pumping station 23 including two medium pressure pumps 24a, 24b. As shown in Figure 1 , the medium pressure pumping station 23 is in the form of a ram unit, in which a vessel 22 (usually cylindrical) containing the mastic fluid is mounted. The pumps 24a, 24b are mounted in a fixed position, which is initially on top of a full vessel 22. When the fluid is pumped, rams 27 apply pressure to the fluid within the vessel 22 so that the fluid is forced to enter the inlets of the pumps 24a, 24b, thereby ensuring that the pumps are properly primed. Typically a pair of such medium pressure pumping stations 23 will operate in tandem, with, at any time one station pumping and the other on standby. Generally the working medium pressure pumping station 23 will operate until the ram unit reaches the top of its travel and the vessel 22 is almost empty. At that time the standby medium pressure pumping station will take over while the vessel 22 in the (previously) working station 23 is replenished or replaced with a full vessel.

A second pumping stage acts as a booster station 25 that includes a high pressure pump 26, an example of which will be described in more detail below. The second pumping stage has an outlet 29 through which fluid is pumped into and/or around the circuit 20.

The circuit 20 also includes a loop 30, which typically passes around a manufacturing area 31 , and has take-offs 32, each leading to a line 34 from which an operator or controlled machine, such as a robot, can operate an applicator (not shown), such as a mastic gun, to apply fluid when required to product parts in the manufacturing area 31. The circuit 20 includes a return line 40 back from the loop 30 to the medium pressure pumping station 23. A link valve 36 is provided in a short connecting line between the start of the loop 30 (at a point after the outlet 29 of the pump 26) and the end of the loop before the return line 40. A stop valve 38 in the return line 40 can be closed to prevent flow between the loop 30 and the return line 40.

The system is configured to operate in either a high pressure mode or a low pressure, recirculation mode. In the high pressure mode the link valve 36 is opened and the stop valve 38 is closed. Figure 2a shows the layout of Figure 1 with the flow path for the high pressure mode of operation highlighted. In this mode the pumps pump fluid into the loop 30 from both ends. This ensures that high pressure fluid is available at all of the off-takes 32 for use in the manufacturing area 31.

In the low pressure, recirculation mode, the link valve 36 is closed and the stop valve 38 is opened. In this mode the pumps pump fluid at a lower pressure around the loop 30 and back through the opened stop valve 38 and return line 40 to the medium pressure pumping stations 23. Figure 2b shows the layout of Figure 1 with the flow path for a low pressure, recirculation mode of operation highlighted. This ensures that the fluid is kept moving around the system, for example during periods when the plant in the manufacturing area 31 is idle.

In an alternative arrangement, in the high pressure mode the fluid is pumped into and around the loop in one direction - i.e. from one end only. In this case, the stop valve 38 remains closed and the link valve 36 is also closed (or may be dispensed with entirely).

Operation of the system is controlled by a controller 28. The controller 28 controls the speed of the pump 26 to pump the fluid/mastic around the circuit 20 in the high pressure mode during periods when one or more of the off-takes 32 are being used. In this mode the controller controls the speed of the pump 26 to maintain the pressure of the fluid/mastic in the loop 30. The controller also controls the pump 26 to pump fluid/mastic around the circuit 20 in a low pressure mode during periods when none of the off-takes 32 are being used.

Figure 3 illustrates more detail of the booster station 25, with high pressure pump 26. The high pressure pump 26 may typically be a positive displacement pump with pistons that reciprocate inside cylinders for pumping the fluid. The pistons are driven by a drive unit 42 (an example of which is described below in association with the pump illustrated in Figure 3). The drive unit is coupled to a variable speed motor 43, which in the example of Figure 4 described below is an ac motor. The operation and speed of the motor is controlled from a control panel 28, which houses a controller (such as a programmable controller, computer, etc.) and an inverter. As shown in Figure 3, the pump 26, drive unit 42 and motor 43 are supported on a floor mounted frame 41.

The pump 26 has an inlet 44 through which fluid is received from the medium pressure station 23 (see Figure 1), and an outlet 29 as described above with reference to Figure 1. An inlet pressure sensor 45 monitors fluid pressure at the pump inlet 44. An outlet pressure sensor 46 monitors fluid pressure at the pump outlet 29. The inlet pressure sensor 45 ensures that there is sufficient pressure in the fluid at the inlet 44 before the pump 26 starts pumping (i.e. that the pump 26 is primed). There is also a pressure switch 47 at the pump outlet which provides a safety feature to ensure that the pump does not continue pumping in the high pressure mode if a certain maximum pressure of the pump occurs. Signals from the pressure sensors 45, 46 and pressure switch 47 are provided to the controller in control panel 28. A valve 48 before the pump inlet 44 and another valve 49 at the pump outlet 29 can be used to isolate the booster station (e.g. for maintenance or repair purposes). Note that when operating in the high pressure mode, there may be short periods when production in the manufacturing area requires no, or very little, use of the fluid/mastic. At such periods the pumps, particularly the high pressure pump 26, may be required to operate at extremely low speeds, or even to be stationary, while still applying pressure to the fluid/mastic. The pumps that are described below have been developed to be particularly suitable for this type of operation. However, alternative pumps or pumping arrangements cold be used in a system similar to that shown in Figure 1.

Referring to Figures 1 and 2a and 3, in the high pressure mode, the pump 26 and its controller keep the pressure at the outlet of the pump 26 at a pre-set value, independent of the flow rate of the pump 26, as in a true pressure closed loop control system. Thus, at times when the fluid (e.g. mastic) is being used, or must be available for use in the manufacturing area 31 , the controller controls the pump to maintain the fluid pressure in the loop 30. If the outlet pressure sensor 46 detects a drop in pressure, the controller starts the pump 26, or if it is already running, increases the speed of the pump 26 to restore the outlet pressure to the pre-set value. When the fluid is actually being used at the off-takes 34 in the manufacturing area 31 , the motor 43 drives the drive unit 42 to move the pistons in the pump 26 and cause the fluid to be pumped into the loop 30. When use of the off-takes 34 ceases the controller still provides power to the motor for a short time to exert a torque on the drive unit that is transferred into a force on the pistons in the pump 26 so as to maintain pressure on the fluid in the loop 30. If there is then no further drop in outlet pressure detected by the sensor 46, the controller switches off the pump 26. While the operating mode remains the high pressure mode, the controller will then re-start the pump 26 if the outlet pressure sensor 46 detects a drop in pressure below the pre-set value.

With reference to Figures 1 and 2b and 3, in the low pressure mode the pump 26 is only required to provide enough pressure in the fluid for it to flow around the loop 30 and back through open valve 38 and return line 40 to the medium pressure station 23. This ensures that the fluid keeps moving and does not thicken or solidify in the pipelines, but because a high pressure is not required, less energy is consumed by the pumps.

Referring to Figure 4, there is shown an isometric view of an exemplary positive displacement pump 50, of a type particularly suitable for pump 26 described above in connection with Figure 1. The pump 50 is an example of a pump of the type described in the applicant's co-pending patent application, GB 1502686.7

As shown in Figure 4, the positive displacement pump 50 has 3 cylinders 52a, 52b, 52c, each of which has a respective piston (not visible) arranged for reciprocal movement inside it. The cylinders 52a, 52b, 52c are formed in a pump body 54, in which is formed an inlet passage 58 for connection to a supply of fluid to be pumped, and an outlet passage 56 out of which the fluid is pumped. Also housed within the pump body 54 is an arrangement of check valves, each cylinder having an associated inlet check valve and an associated outlet check valve, which ensure that the fluid flows into and out of the pump in one direction as the pistons are moved within the cylinders.

The positive displacement pump 50 is shown mounted to a frame 59, which also supports a variable speed ac motor drive 60 providing a rotational drive to the cam arrangement 62, via a gearbox 63, and a control panel 65. The cam arrangement 62 provides a reciprocating drive to the pistons in the cylinders 52a, 52b, 52c. During the reciprocal cycle, the pistons go through a drawing stroke and a pumping stroke. During the drawing stroke of a cylinder (e.g. cylinder 52a), the piston within the cylinder 52a moves upwards. The suction of the piston opens the inlet check valve and closes the outlet check valve associated with the cylinder 52a. Fluid is drawn along the inlet passage 56, through the associated inlet check valve and into the cylinder 52a.

During the pumping stroke, the pistons move downwards within the cylinders. While cylinder 52a is on its drawing stroke, the pistons in cylinders 52b, 52c are on their pumping strokes. The pistons within cylinders 52b, 52c increase the pressure of the fluid, which causes their associated inlet check valves to close and their associated outlet check valves to open. Fluid is pumped out of the cylinders 52b, 52c, through the outlet check valves and along the outlet passage 58.

The pistons are driven by a variable speed ac motor 60 coupled to a cam arrangement 62. The cams are shaped such that the drawing stroke occurs over a time period which is no more than half the time period of the pumping stroke. The cams are arranged to drive the pistons out of phase with one another such that at any position during the rotation cycle, at least two of the pistons are pumping. This means that twice the piston area is used to exert pressure on the fluid, thereby generating significantly higher pressure in the fluid than for a single cylinder. This arrangement also results in lower mechanical forces on the cam than would be the case if an equivalent fluid pressure was to be produced by a single piston. The ac motor 60, which drives the cam arrangement as described above so as to provide a reciprocating drive to the pistons, has an inverter with a closed loop vector drive control. For the pumps described above in a system such as that shown in Figure 1 , it is required to provide and maintain a high pressure to the fluid/mastic even when the quantity of mastic being used is very small (or zero). This means that the pump 26 of Figure 1 should be capable of maintaining a high pressure with the ac motor 60 maintaining a torque on the cam shaft even when this is not rotating, and this can only happen if the ac motor does not stall. The ac motor 60 is driven by an inverter. The inverter uses a vector control, preferably a closed loop vector control, in which a signal is provided to the inverter indicating the relative positions of the stator and rotor of the motor.