GB2629168A

GB2629168A - Oil heater system for a generator set

Info

Publication number: GB2629168A
Application number: GB2305696.3A
Authority: GB
Inventors: John Futter Stephen; Appleby Andrew
Original assignee: Cummins Power Generation Ltd
Current assignee: Cummins Power Generation Ltd
Priority date: 2023-04-18
Filing date: 2023-04-18
Publication date: 2024-10-23
Also published as: GB202305696D0

Abstract

A generator-set 10 has an oil heater system 22, and the oil heater system is used to heat oil for an engine 12 of the generator-set, with the oil heater system including an oil heater 26 located external to the engine. In use, the oil is circulated through the engine using a pump 24, and the oil is heated by the oil heater connected in-line with the pump and outside of the engine. The pump and the oil heater are controlled by a control unit, such as the engine control module ‘ECM’ 18, and the control unit may also monitor the oil temperature via a temperature sensor 28, and/or may also monitor a sensed voltage and produce a fault signal if a power loss is detected. The system may be mounted via anti-vibration mounts (58 Fig. 6) onto a skid/bed frame (16 Fig. 1) of the generator set. The generator 14 is connected via a transmission system to the engine and the generator set may also include other components such as a clutch, an air handling system, etc. The arrangement allows preheating of oil for engine lubrication to a desired temperature range before starting the engine, and without first heating the entirety of oil in the sump.

Description

OIL HEATER SYSTEM FOR A GENERATOR SET

The present invention relates to an oil heater system for a generator set, and in particular an oil heater system for pre-heating oil prior to start-up of the generator set.

Some generator sets comprise an internal combustion engine, such as a gas, petrol or diesel engine, coupled to a generator. The internal combustion engine drives the generator in order to generate electrical power. The engine and generator run at a fixed speed of typically 1500 rpm or 1800rpm to provide 50Hz or 60Hz AC voltage to a load. The generator set may be used in prime-power mode as the main source of power to utility loads, or in standby mode to supply critical loads in case of main distribution grid failure. In either case, it may be necessary to shut down and subsequently restart the generator set, for example, for servicing or grid management.

Internal combustion engines typically require a lubricant such as engine oil to reduce friction and wear on moving parts. The oil creates a separating film between surfaces of adjacent moving parts to minimize direct contact between them, decreasing friction and reducing wear. In use, the oil is heated to a certain temperature in order to have a viscosity to properly coat the moving parts. While the engine is in operation, the oil is heated through conduction as it flows through the engine. However, when the engine is started, the temperature of the oil may be below that which is required to achieve the desired lubrication. This may lead to reduced engine efficiency, increased emissions, and/or reduced service life. Therefore, some generator sets include a heater to pre-heat the engine oil to a desired operational temperature before the engine is started.

A known oil heating system for a generator set comprises one or more immersion heaters in the engine sump (oil pan). The immersion heater is arranged to pre-heat the oil in the sump to a desired temperature before starting the engine. A system of this type is disclosed in WO 2019/152369.

Some known oil heating systems allow the temperature of the engine oil to be brought within a desired range before starting the engine. However, it would be desirable to provide an oil heater system for a generator set which can preheat the engine oil more quickly while avoiding or reducing premature degradation of the oil.

According to one aspect of the present invention there is provided an oil heater system for pre-heating oil in an engine of a generator set, the oil heater system comprising: a pump for circulating oil through the engine; an oil heater for heating the oil; and a control unit for controlling the oil heater, wherein the oil heater is connected in-line with the pump outside of the engine.

Embodiments of the claimed invention may provide the advantage that, by connecting the oil heater in-line with the pump outside of the engine, it may be possible for the oil to be heated more evenly and/or to avoid or reduce hotspots. This may help to reduce degradation of the oil and may help to ensure that all of the oil is within a desired temperature range. Furthermore, it may be possible to use a higher power heater than would otherwise be the case, which may help to reduce the engine preparation time prior to start-up.

By "in-line" it may be meant that the oil heater and the pump are in fluid communication and/or are connected in series. For example, the pump and the oil heater may be part of a fluid circuit, and one may be before the other in the fluid circuit. By "outside of the engine" it may be meant that the oil heater is not inside a main body of the engine, for example, not inside a sump or oil pan or engine block or other part of the main body of the engine. For example, the oil heater may be mounted on a skid, or mounted elsewhere such as on an outer surface of the engine.

The oil heater system may further comprise a temperature sensor arranged to sense a temperature of the oil. In this case, the control unit may be arranged to control an amount of heat produced by the oil heater in dependence on a sensed temperature. This may help to ensure that the oil is brought to and/or maintained at the correct temperature. The temperature sensor may comprise any suitable temperature sensing device, such as a thermocouple, a thermistor or a silicon bandgap temperature sensor.

The temperature sensor is preferably provided in line with the oil heater (and pump) outside of the engine. For example, the temperature sensor may be in fluid communication with the heater and/or the two may be connected in series. The temperature sensor and the oil heater may be part of a fluid circuit, and one may be before the other in the fluid circuit. By "outside of the engine" it may be meant that the temperature sensor is not inside a main body of the engine, for example, not inside a sump or oil pan or engine block or other part of the main body of the engine. This can allow the oil heater system to operate independently, and may help to achieve accurate control of the oil temperature. For example, the temperature sensor may be provided on or adjacent to the heater, or elsewhere such as on a skid or other component of the generator set. If desired, it would also be possible for the temperature sensor to be inside the engine, for example, in the sump.

In a simple case, the control unit may be arranged to turn the oil heater on and off in dependence on whether the sensed temperature is above or below a threshold. However, in a preferred embodiment, the control unit is arranged to control an amount of heat produced by the oil heater in dependence on a difference between the sensed temperature and a reference temperature. For example, the control unit may be arranged to compare the sensed temperature to a reference value, and to produce a control signal in dependence on the difference. This may be achieved, for example, by executing a control algorithm. The control signal may be used to control the amount of heat produced by the oil heater. This may help to reduce or avoid hysteresis in the oil temperature.

In one embodiment, the control unit is arranged to produce a control signal with at least a proportional term. In addition, the control signal may also have an integral and/or a derivative term. For example, the control unit may be arranged to execute a proportional integral derivative (PID) control algorithm.

This may help to ensure that the oil temperature reaches a desired temperature with minimal delay and overshoot.

The control unit is preferably arranged to maintain the temperature of the oil 5 within a predetermined range once the temperature of the oil has reached a reference temperature. This may help to ensure that the oil is at the desired temperature when the engine is started, even if there is a delay beforehand.

If desired, the control unit may also be arranged to control the pump in dependence on a sensed temperature. For example, the control unit may control the pump to have a higher flow rate when an amount of heat produced by the heater is high (or a difference between the sensed temperature and a reference temperature is high), and to have a lower flow rate when an amount of heat produced by the heater is low (or a difference between the sensed temperature and a reference temperature is low).

The oil heater system is preferably for pre-heating the oil during an engine preparation time. Thus, the oil heater system may be arranged to heat the oil and to circulate the oil through the engine during an engine preparation time.

Typically, an engine will comprise an engine control module (ECM) for controlling operation of the engine. A temperature sensor may also be provided in the engine's oil sump. The engine control module may monitor the temperature of the oil in the sump using the temperature sensor. When the engine is to be started, if the temperature of the oil in the sump is below a predetermined threshold, then the engine control module may inhibit starting of the engine, and issue an oil pre-heating command to the oil heater system. In response, the oil heater system may initiate an oil pre-heating process.

Thus, the control unit may be arranged to receive an oil preheat command and to initiate an oil pre-heating process on receipt of the oil preheat command. Preferably, the control unit switches on the pump and the oil heater on receipt of the oil preheat command.

The pump and/or the heater may be arranged to operate from an AC supply. The AC supply may be single phase, three phase, or any other appropriate number of phases. The oil heater system may comprise a switch with contactors, and the control unit may be arranged to close the contactors on receipt of an oil preheat command, thereby to supply AC power to the pump and the oil heater. This may allow a heater and/or pump with a relatively high power rating to be used. For example, in some embodiments, the heater may have a power rating of at least 2, 3, 4, 5 or 6 kW and the pump may have a flow rate of at least 5, 10, 15, 20 or 25 litres per minute, although of course other values less than or great than any of these values may be used instead.

The control unit is preferably arranged to switch off the pump and the oil heater when the oil preheat command is terminated. For example, the control unit may open the contactors in the switch when the oil preheat command is terminated. This can allow the engine to start up and operate as normal without the oil heater system once the oil in the sump is at the desired temperature.

The control unit may be arranged to monitor power loss and to produce a fault signal if power loss is detected. For example, the oil heater system may further comprise a voltage sensor for sensing a voltage of a power supply (such as an AC power supply) for supplying power to the heater and/or the pump, and the control unit may be arranged to monitor a sensed voltage to detect a power loss. A power loss may be, for example, a loss of power on one or more phases, or a drop in voltage to below a threshold level. If a power loss is detected, then the control unit may issue a fault signal to a user and/or another device such as a generator set interface box (GIB) and/or shut down the oil heater system, for example by opening the contactors of the switch.

The control unit may be arranged to monitor oil temperature and to produce a fault signal if the oil temperature exceeds a high limit set point. This may help to ensure that the oil does not overheat. The fault signal may be sent to a user and/or another device such as a generator set interface box (GIB) and/or used to shut down the oil heater system.

In one embodiment, the oil heater system further comprises a high limit temperature sensor, separate from a process temperature sensor. In this case, the control unit may be arranged to produce the fault signal if the temperature sensed by the high limit temperature sensor exceeds the high limit set point. This may provide redundancy and may help to improve the safety of the system. However, if desired, a single temperature sensor could be used to sense process temperature and high limit temperature.

The control unit may be arranged to calculate a rate of change of oil temperature (with respect to time), and to produce a fault signal if the rate of change of oil temperature is outside a predetermined range. This may allow the system to detect heater failure or other fault in the system. The fault signal may be sent to a user and/or another device such as a generator set interface box (GIB) and/or used to shut down the oil heater system.

The predetermined range may be fixed, or may be variable. For example, the predetermined range may be variable in dependence on a control signal for controlling an amount of heat produced by the oil heater. This may allow the control unit to detect if the rate of change in temperature is significantly different from that which would be expected if the heater is responding correctly to the control signal.

The control unit may be arranged to monitor various other potential fault conditions and respond accordingly. If desired, all of the fault signals could be grouped into one signal output and feed to another device such as a GIB. This output from the oil heater system may then be interpreted to flag a generic fault signal to other parts of the system.

The oil heater system may further comprise a display for displaying at least one of oil temperature, heater power and a fault signal. This may allow operation of the system to be monitored by a user. The oil heater system may also comprise an input device such as a keypad or touch screen for inputting parameters and other information.

The engine may comprise a sump (also known as an oil pan) for holding the oil which is to be used by the engine. Thus, the oil heater system may be arranged to be connected to a sump of the engine. Preferably, at least one fluid conduit (such as a hose, pipe, tube, channel, duct or any other means for conveying fluid) is provided for connecting the oil heater system to the sump. For example, the oil heater system may comprise a first conduit fluidly coupling the oil heater system to an outlet of the sump and a second conduit for fluidly coupling the oil heater system to an inlet of the sump. At least one further fluid conduit may be provided, for example, for fluidly coupling the pump to the heater.

The oil heater system may further comprise a first connector for removably connecting the first conduit to the sump and a second connector for removably connecting the second conduit to the sump. This may facilitate connection and disconnection of the oil heater system to and from the engine, and may allow a generator set to be provided either with or without the oil heater system depending on user requirements.

The oil heater system may further comprise means for mounting the oil heater system on a skid of the generator set. For example, the pump, the heater and/or the control unit may comprise one or more feet or brackets for mounting on the skid. The mounting means preferably comprise anti-vibration mounts. This may help to protect the oil heater system from vibrations produced by the generator set.

According to another aspect of the invention there is provided a skid for a generator set, the skid comprising an oil heater system in any of the forms described above mounted on the skid.

The skid may comprise a pair of opposing side members and a plurality of cross members. In this case, the pump and the heater may be mounted on at least one of the side members, preferably on an inner side of the side member. In one embodiment, the pump is mounted on one side member and the heater is mounted on the other side member, preferably opposing each other. In this case, a fluid conduit may be used to connect the pump and the heater. The fluid conduit may be supported by a cross member. This may allow the pump and heater to be contained within the existing envelope of the skid. The temperature sensor may be provided for example on the heater, or elsewhere.

According to another aspect of the invention there is provided a generator set comprising a generator, an engine, and an oil heater system or skid in any of the forms described above. The engine may comprise a sump and the oil heater system may be connected to the sump.

The engine may comprise an engine control module arranged to monitor a temperature of oil in the sump, and to issue an oil pre-heating command to the oil heater system when the engine is to be started and the temperature of the oil in the sump is below a predetermined threshold. The engine control module may be arranged to inhibit starting of the engine while the temperature of the oil in the sump is below the predetermined threshold. The engine control module may be arranged to terminate the oil pre-heating command when the temperature of the oil in the sump is above a predetermined threshold.

Corresponding methods may also be provided. Thus, according to another aspect of the invention there is provided a method of pre-heating oil in an engine of a generator set, the method comprising: circulating oil through the engine using a pump; heating the oil using an oil heater; and controlling the pump and the oil heater, wherein the oil heater is connected in-line with the pump outside of the engine.

Features of one aspect of the invention may be provided with any other aspect. Apparatus features may be provided with method aspects and vice versa.

Preferred features of the invention will now be described, purely by way of example, with reference to the accompanying drawings, in which: Figure 1 shows schematically parts of a generator set; Figure 2 shows parts of an oil heater system in an embodiment of the invention; Figure 3 shows one embodiment of a pump; Figures 4 and 5 show one embodiment of a heater; Figure 6 shows parts of an oil heater system in one embodiment; Figure 7 shows the oil heater system mounted on a generator set skid; Figure 8 shows some of the electrical components in the oil heater system; and Figure 9 shows steps taken by a heater control unit in one embodiment.

Figure 1 shows schematically parts of a generator set (genset). The generator set 10 comprises an engine 12 coupled to a generator (alternator) 14. The engine 12 is typically an internal combustion engine such as a gas, petrol or diesel engine. The engine 12 and generator 14 are both mounted on a skid (bed frame) 16. In operation, mechanical energy produced by the engine 12 is transferred to the generator 14 in order to generate an electrical output. Operation of the engine 12 is controlled using an engine control module (ECM) 18. The generator 14 has a three phase electrical output for connection to a grid. The generator set 10 may also include other components such as a clutch, transmission, air handling system and so forth in a manner known in the art.

When the engine is in operation, an oil pump 19 is used to circulate lubricating oil through the engine in order to reduce friction between moving parts. The engine 12 includes an oil pan or sump 20 which holds the oil. In general, it is desirable for the temperature (and hence viscosity) of the oil to be within a certain range for the engine to function correctly. A temperature sensor 21 measures the temperature of the oil in the sump and feeds the sensed value to the ECM 18.

During normal operation, friction produced within the engine causes the engine to heat up. The temperature of the engine is controlled using an engine cooling system (not shown). Heat produced by the engine is also transferred to the engine oil, which keeps the oil within the desired operating range. However, when the engine has not been used for a period of time, the temperature of the engine oil may be lower than that required for correct functioning of the engine.

Embodiments of the invention provide an oil heater system for pre-heating lubricating oil for a generator set before the engine is started. The disclosed oil heater system is able to control, monitor and regulate oil temperature to provide fast and efficient startup while avoiding hotspots which may cause oil degradation.

Figure 2 shows parts of an oil heater system in an embodiment of the invention. Referring to Figure 2, the oil heater system 22 comprises pump 24, heater 26, temperature sensor 28, heater control unit 30. The oil heater system may also include a plurality of hoses (or other type of fluid conduit) denoted generally by the reference numeral 32. A first hose 321 is used to connect an input to the oil heater system to an outlet of the sump 20 and a second hose 322 is used to connect an output of the oil heater system to an inlet of the sump 20.

In the arrangement shown, the outlet of the sump 20 is in fluid communication with an inlet of the pump 24 via the first hose 321. The pump 24 has an outlet which is in fluid communication with an inlet of the heater 26 via a third hose 32a. The heater 26 has an outlet with is in fluid communication with the inlet of the sump 20 via the temperature sensor 28 and the second hose 322. In this embodiment, the temperature sensor 28 is mounted on the heater 26, although it may also be provided elsewhere in the oil heater system. The sump 20, pump 24, heater 26, temperature sensor 28 and hoses 32 form a fluid circuit through which engine oil may be circulated.

In the arrangement shown, the oil heater 26 is connected in-line with the pump 24. The oil heater 26 is in fluid communication with the pump 24 (via the third hose 323) and the two are connected in series. Thus, the pump and the oil heater may be part of a fluid circuit, and one may be before the other in the fluid circuit. The temperature sensor 28 is connected in line with the oil heater 26. Thus, the temperature sensor is in fluid communication with the oil heater, and the two are connected in series. The pump, the oil heater and the temperature sensor may be part of a fluid circuit, and may be connected in any order. The oil heater 24 is outside of the engine. Thus, the oil heater is not inside the engine's sump or engine block or other part of the main body of the engine. For example, the oil heater may be on a skid, or elsewhere. The temperature sensor 28 is outside of the engine. Thus, the temperature sensor is not inside the engine's sump or engine block or other part of the main body of the engine. For example, the temperature sensor may be mounted on a skid, or may be mounted directly on the oil heater, or elsewhere. The pump 24 is also outside of the engine. Thus, the pump 24 is not inside the engine's sump or engine block or other part of the main body of the engine. For example, the pump may be on a skid, or elsewhere. However, if desired, it would be possible for at least one of the pump 24, oil heater 26 and temperature sensor 28 to be mounted (for example, bolted) to an outer surface of the engine or other part of the generator set. If desired, it would also be possible for the temperature sensor to be inside the engine, for example, in the sump.

The heater control unit 30 is arranged to receive temperature measurements from the temperature sensor 28 and to transmit control signals to the pump 24 and the heater 26. The heater control unit 30 is also in communication with the ECM 18 of the engine 12. The engine 12 is mechanically coupled to the generator 14 in the manner described previously.

The oil heater system of Figure 2 is arranged to heat the oil in the sump 20 to a predetermined temperature, and then to maintain the temperature within a predetermined temperature range, prior to starting the engine.

In operation, when it is intended to start the engine, a start command is received by the ECM 18. The start command may be issued by a human operator, or automatically by a system controller. On receipt of the start command, the ECM determines the temperature of the oil in the sump 20 using the sump temperature sensor 21. If the temperature of the oil in the sump is below a predetermined threshold, then the ECM 18 inhibits starting of the engine, and issues an oil pre-heating command to the heater control unit 30.

When the heater control unit 30 receives an oil pre-heating command, it turns on the pump 24. This causes oil from the sump 20 to circulate from the sump 20 through the pump 24, heater 26 and temperature sensor 28 back to the sump. The heater 26 is used to heat the oil returning to the sump. The temperature of the oil being circulated is monitored by the temperature sensor 28 and fed to the heater control unit 30. The heater control unit 30 controls the amount of heat produced by the heater 26 in dependence on the value of the temperature sensed by the temperature sensor 28. For example, in one embodiment, the heater control unit 30 controls the heater 26 to produce an amount of heat which is proportional to an error signal corresponding to a difference between the sensed temperature and a reference temperature (optionally with additional integral and/or derivative adjustments).

Optionally, the heater control unit 30 may also control the speed of the pump 24 in dependence on the value of the temperature sensed by the temperature sensor 28 or an amount of heat produced by the heater 26. For example, a flow rate produced by the pump may be increased when a difference between the sensed temperature and a reference temperature is high, and decreased when the difference is low. However, the pump may also operate at a single speed.

During the start-up period, the ECM continues to monitor the temperature of the oil in the sump 20 using the sump temperature sensor 21. When the ECM determines that the oil is at a suitable temperature, and any other necessary conditions for starting the engine are met, it terminates the oil pre-heating command to the heater control unit 30. In response, the heater control unit 30 turns of the pump 24 and the heater 26. The ECM is then able to start the engine 12. When the engine is running, oil is circulated through the engine using an oil pump in a conventional manner. Heat produced by the engine maintains the temperature of the oil, and hence its viscosity, within a desired range.

Although in Figure 2 the temperature sensor 28 is shown at the output of the oil heater 26, it could alternatively be provided at the input to the oil heater or elsewhere in the oil circuit. Furthermore, it will be appreciated that the pump 24, heater 26 and temperature sensor 28 may be provided in any appropriate order in the fluid circuit, and not necessarily that shown.

In one embodiment, the engine 12 shown in Figure 2 is a 4-cycle lean burn gas combustion engine and the generator 14 is a brushless, 4 pole. revolving field alternator. The engine may for example have a displacement of 60 litres and the generator may for example be able to produce an output of 1400kW. However, it will be appreciated that these values are given by way of example only, and the engine 12 and generator 14 may be of any appropriate type and rating. For example, in one embodiment, the engine and/or the generator may be of the type disclosed in WO 2019/152369, the subject matter of which is incorporated herein by reference.

Figure 3 shows one embodiment of the pump 24. Referring to Figure 3, the pump 24 includes an electric motor 34, a pump head 35, a pump inlet 36, a pump outlet 37, an electrical terminal box 38 and mounting feet 39. In operation, oil is drawn in through the inlet 36 and pumped out through the outlet 37 using an impeller in the pump head 35. In some embodiments, the pump 24 is able to produce a flow rate of up to 34 litres per minute (9 gallons per minute) and a pressure of up to 6.9 bar (100psi) although of course other values higher or lower than this are also possible.

Figure 4 shows an exterior view of the heater 26 in one embodiment.

Referring to Figure 4, the heater 26 comprises a jacket 42 housing a plurality of internal heating elements, a heater inlet 44, a heater outlet 45, mounting feet 46 and a flange assembly 47. The flange assembly 47 is used to connect the heating elements to a power supply. In operation, oil enters the heater inlet 44 and passes over the internal heating elements. As the oil passes the heating elements, heat is transferred to the oil. The heated oil exits the heater 26 through the heater outlet 45. In some embodiments, the heater is a 6kW heater with a watt density of 13 watts per square inch (2W/cm2) at 480V, 3-phase, although of course other values higher or lower than this are also possible.

Figure 5 shows an internal part of the heater 26 in one embodiment.

Referring to Figure 5, a plurality of heating elements 48 are provided which are housed inside the heater jacket. A plurality of baffles 50 are provided at spaced locations in the direction of fluid flow. The baffles 50 increase the flow path of the oil over the heating elements to increase the heat transfer.

Figure 6 shows parts of an oil heater system in one embodiment. In this embodiment, the oil heater system is arranged to be mounted to the skid of the generator set. This may facilitate attachment of the oil heater system to the engine, and can allow the oil heater system to be provided as an optional feature.

Referring to Figure 6, the oil heater system 22 comprises pump 24, heater 26, temperature sensor 28, heater control unit 30 and a plurality of hoses 32, all of which may be substantially in the forms described above. The oil heater system 22 is connectable to the sump of engine using first hose 321 and second hose 322. A sump outlet connector 52 is provided on the first hose 321 in order to connect it to an outlet of the sump. A sump inlet connector 54 is provided on the second hose 322 in order to connect it to an inlet of the sump. The sump outlet connector 52 and sump inlet connector 54 may each comprise, for example, a screw fitting and a gasket.

In this embodiment, the outlet of the sump is connectable to the inlet of the pump 24 using first hose 321. The outlet of the pump 24 is connected to the inlet of the heater 26 using third hose 323. In the arrangement shown, the temperature sensor 28 is integrated within the body of the heater 26, although it could also be mounted at the inlet or the outlet, or elsewhere. The outlet of the heater 26 is connectable to the inlet of the sump using hose 322. The oil heater 26 is connected in-line with the pump 24. Thus, the oil heater 26 is in fluid communication with the pump (via the third hose 32s) and the two are connected in series. The temperature sensor 28 is connected in line with the oil heater 26. Thus, the temperature sensor is in fluid communication with the oil heater, and the two are connected in series. The system also includes electrical leads 56. The electrical leads 56 are used to communicate electrical signals to and from the control unit 30 and other parts of the system.

In the arrangement of Figure 6, each of the pump 24, heater 26 and heater control unit 30 are arranged to be mounted to a skid of the generator set. The oil heater 26 is outside of the engine. Thus, the oil heater 26 is not inside the engine's sump or engine block or other part of the main body of the engine. The temperature sensor 28 is outside of the engine. Thus, the temperature sensor is not inside the engine's sump or engine block or other part of the main body of the engine. The pump 24 is also outside of the engine. Thus, the pump 24 is not inside the engine's sump or engine block or other part of the main body of the engine. Each of the pump 24, heater 26 and heater control unit 30 includes anti-vibration mounts 58 for mounting the oil heater system 22 to the skid of the generator set. In the arrangement shown, the anti-vibration mounts 58 are provided on the feet 39 of the pump and the feet 46 of the heater 26. Anti-vibration mounts are also provided on a bracket 59 which is used to attach the control unit 30 to the skid. The anti-vibration mounts help to protect the oil heater system from vibrations produced by the generator set.

Figure 7 shows the oil heater system mounted on a generator set skid in one embodiment. Referring to Figure 7, the skid 16 comprises a pair of opposing side members 60, a plurality of cross members 62, an engine mount 63, a pair of flywheel mounts 64 and a pair of generator mounts 66. The side members 60 and cross members 62 have an I-shaped cross section, and may be for example rolled steel joists. The side members 60 extend parallel to each other in a longitudinal direction. The cross members 62 extend between the pair of side members 60. The flywheel mounts 64 and generator mounts 66 are provided on top of respective cross members 62. The flywheel mounts are arranged to support the engine's flywheel and the generator mounts are arranged to support the generator. Other cross members and the appropriate mounts (not shown) may also be provided for mounting the engine and other components of the generator set to the skid.

In the arrangement of Figure 7, the pump 24 is mounted on the inside of one the side members 60 using anti-vibration mounts. The heater 26 is mounted on the inside of the opposing side member 60 using anti-vibration mounts. In Figure 7, part of the side member 60 is shown cut away so that the heater 26 is visible. The hose 323 which connects the pump 24 to the heater 26 runs alongside and is supported by the cross member 62 with the flywheel mounts 64. The control unit 30 is mounted to the top of one of the side members, on the same side of the bedframe as the heater 26. The various parts of the oil heating system are substantially as described above with reference to Figures 2 to 7.

When assembling the generator set, the oil heating system is first mounted on the skid 16 in the way shown in Figure 7. The engine 12 and the generator 14 are then mounted onto the skid 16. Once the engine has been mounted on the skid, the oil heating system 22 can be connected to the sump of the engine using the sump outlet connector 52 and sump inlet connector 54.

The arrangement of Figures 6 and 7 can allow the oil heater system to be provided without increasing the overall envelope of the generator set.

Furthermore, the oil heater system may be provided as an optional feature, and the skid 16 can be supplied either with or without the oil heater system.

Figure 8 shows in more detail some of the electrical components in the oil heater system. Referring to Figure 8, the oil heater system 22 comprises pump 24, heater 26, process temperature sensor 28, high limit temperature sensor 29, heater control unit 30, display 68, keypad 69, switch 72 and voltage sensor 80. In this embodiment, the heater control unit 30 comprises processor 70, transformer 74, temperature controller 76 and power switching device 78. The oil heater system 22 receives a three-phase AC supply which may be from, for example, a grid, another generator set, or another source of power such as inverter connected to a DC power supply. In one embodiment, the AC supply may be a 380 -480 volts, three-phase regulated power supply, although other values are also possible. The AC supply is connected to the switch 72. The switch in this embodiment is a three-phase switch with three contactors that can be opened or closed under control of the processor 70. The AC supply at the output of the switch 72 is connected to the transformer 74, the power switching device 78 and the pump 24.

The processor 70 comprises a central processing unit (CPU) and associated memory and peripherals, and is programmed with software to carry out the functions described herein. The processor and other low voltage components may be powered by a power supply unit and/or a battery.

In this embodiment, each of the temperature sensors 28, 29 is a thermocouple. A thermocouple is a sensor used to measure temperature and consists of two wire legs made from different metals joined together at their two ends to form two junctions. The measuring junction is connected to the body whose temperature is to be measured (in this case, the engine oil). The reference junction is connected to a body of known temperature. When the temperature difference between the measuring junction and the reference junction increases, a potential difference is produced between the measuring junction and the reference junction. This potential difference can then be converted into a temperature measurement using thermocouple reference tables. Alternatively, any other suitable type of temperature sensor, such as a thermistor or a silicon bandgap temperature sensor, may be used instead.

In operation, the processor 70 receives an oil pre-heating command from the ECM. On receipt of the oil pre-heating command, it closes the contactors in the switch 72. This causes three-phase AC power to be supplied to the pump 24 and power switching device 78. The pump 24 then begins pumping oil from the engine's sump, through the heater 26 and temperature sensor 28 and back to the sump. The oil pumped by the pump 24 is heated by the heater 26. The heater is activated when pump contacts are closed (the pump is operational), the system status is normal, and the oil temperature is below a low set point. The amount of heat produced by the heater is controlled using the power switching device 78. The power switching device 78 may comprise for example one or more thyristors or transistors. The power switching device 78 controls the proportion of each AC cycle which is fed to the heater 26, in order to control the amount of heat produced by the heater. In this embodiment, both the positive and negative parts of the AC cycle are controlled. The power switching device 78 is controlled by the temperature controller 76.

The temperature controller 76 in this embodiment is a PID (proportional integral derivative) controller which is used to control the temperature of the oil. The temperature controller 76 receives a signal indicating the temperature of the oil from the process temperature sensor 28 and compares it to a desired or reference temperature to produce an error signal. A PID control algorithm is used to control the switching of the power switching device 78, and thus the amount of heat produced by the heater, in order to keep the actual temperature as close as possible to the reference temperature. The value of the reference temperature may be predetermined, or set by a user via the keypad 69, or set by another device such as a generator set interface box (GIB).

The temperature controller 76 produces a high amperage power control output to control the switching of the power switching device 78. For example, in one embodiment, the temperature controller may be able to drive a 15A resistive load directly. The power for the temperature controller is provided by the transformer 74, which steps down one phase of the three phase AC supply to the required voltage for the temperature controller (for example, 120V AC).

The sensed temperature is fed to the processor 70, and the processor displays the sensed temperature on the display 68. This allows the user to be provided with real time values of the process temperature. In addition, values such as power, output and/or heater temperature may be displayed. If desired, other information such as an estimated time until the oil will reach the desired temperature may be displayed as well or instead. The keypad 69 is used to input data and commands to the oil heating system.

During the pre-heating process, the temperature of the oil is also sensed by the high limit temperature sensor 29. The output of the high limit temperature sensor 29 is fed to the temperature controller 76. The temperature controller compares the sensed temperature value from the high limit temperature sensor 29 to a high limit set point. If the sensed temperature exceeds the high limit set point, then this is signalled to the processor 70. In response, the processor 70 shuts down the oil heater system by opening the contactors in the switch 72. This provides a safety check to prevent the oil from overheating. The high limit set point may be any appropriate value and may be predetermined or set by a user or another device. The high limit set point may be variable, for example, in dependence on the type of oil. In some embodiments the high limit set point may be, for example, 100°C, 110°C or 120°C, although any other appropriate value could be used instead.

In this embodiment, the process temperature sensor 28 is used to sense the temperature of the oil during normal operation and the high limit temperature sensor 29 is used to detect if the oil temperature exceeds a high limit set point (for example, 100°C). Using a separate high limit temperature sensor may help to improve the safety of the system. However, if desired, a single temperature sensor could be used to sense process temperature and for high limit detection.

During the pre-heating process, the voltages of each of the three phases of the AC supply is sensed using the voltage sensor 80. The output of the voltage sensor is fed to the processor 70. The processor monitors the sensed voltages in order to detect a power loss, such as supply phase loss or a voltage drop to an inoperable level. If power loss is detected, the processor 70 generates a fault signal which may be sent to other devices (such as the GIB), displayed on the display 68 and/or used to open the switch 72.

The processor 70 is also able to detect heater failure (for example, due to open circuit) by analysing the rate of change (rise or fall) of temperature. To achieve this, successive values of the sensed temperature from the temperature sensor 28 are fed to the processor 70. The processor differentiates the sensed temperature values with respect to time, and compares the differential to a threshold value. If the rate of change exceeds an upper threshold, or is lower than a lower threshold, then a fault signal is generated. The fault signal may be sent to other devices, displayed on the display 68 and/or used to open the switch 72.

The processor 70 may also be arranged to monitor various other potential fault conditions and respond accordingly. If desired, all of the fault signals could be grouped into one signal output and feed to the GIB. This output from the oil heater system may then be interpreted to flag a generic fault signal to other parts of the system.

As discussed above, the ECM monitors the temperature of the oil in the sump and terminates the oil pre-heating command when the oil is at the desired temperature and other conditions for starting the engine are met. However, while the ECM continues to provide the oil heating command, the oil heater system maintains the oil temperature within a desired range (for example, between 90°C and 100°C). This can allow the engine to be started quickly when it is needed, for example, in response to an expected or actual increase in load on the grid, a disconnection of one or more other generator sets, and/or an actual or expected reduction in power generated by a renewable energy source.

When the oil pre-heating command terminates, the processor 70 opens the contactors in the switch 72. This cuts off the power supply to the pump 24, temperature controller 76 and power switching device 78. This shuts down the oil heater system, and the engine can then be started.

The power supply is also interrupted by opening the switch 72 if a fault condition arises, for example, if an emergency stop is initiated, if an oil level error is sensed by the ECM using an oil level switch, or if an emergency shutdown is initiated.

Figure 9 shows steps taken by the oil heater system 22 in one embodiment.

Referring to Figure 9, in step 100 an oil pre-heating command is received from the ECM. When the oil pre-heating command is received, the oil pre-heating process is initiated, and processing proceeds to step 102. In step 102 the contactors in the switch 72 are closed. This causes AC power to be supplied to the pump 24, the temperature controller 76 and the power switching device 78. The pump 24 then begins pumping oil from the engine's sump, through the heater 26, process temperature sensor 28, high limit temperature sensor 29, and back to the sump.

In step 104 a sensed temperature is received from the process temperature sensor 28. In step 106, the sensed temperature is compared to a threshold temperature TTH. The value of the reference temperature TTH may be predetermined or set by a user or another device. If the sensed temperature is less than the threshold temperature, then in step 108 the oil is heated using the heater 26. The amount of heat produced by the heater is controlled by the temperature controller 76. The temperature controller 76 controls the proportion of each AC cycle which is fed to the heater 26 by the power switching device 78. The temperature controller in this embodiment uses a PID (proportional integral derivative) control algorithm to control the power switching device 78, although other algorithms, such as proportional or proportional integral, could be used instead.

In step 110, the sensed temperature is compared to a high limit temperature threshold THL. This may be done using either a temperature sensed by the high limit temperature sensor 29 or the temperatures sensed by the process temperature sensor 28, or both. If the sensed temperature does not exceed the high limit temperature threshold THL, then processing proceeds to step 118. However, if the sensed temperature does exceed the high limit temperature threshold THL, then in step 112 a fault is indicated. This may be achieved, for example, by issuing a visual and/or audible alarm signal to the user and/or issuing a fault signal to another device such as a generator set interface box (GIB). Then in step 114 the contactors in the switch 72 are opened and in step 116 the oil pre-heating process is terminated.

In step 118, it is determined whether there is a loss of power, such as a supply phase loss or a voltage drop to an inoperable level. This is achieved by monitoring the voltages sensed by the voltage sensor 80 and comparing them to threshold values. If no power loss is detected, then processing proceeds to step 120. However, if one or more of the sensed voltages is below a threshold value, indicating a power loss, then in step 112 a fault is indicated, in step 114 the contactors in the switch 72 are opened and in step 116 the oil pre-heating process is terminated.

In step 120, a rate of change of the sensed temperature is analysed in order to detect a fault in the oil heater system, such as a failure of the heater 26 or the pump 24. This is achieved by first differentiating the sensed temperature with respect to time. The rate of change in temperature AT is then compared to a lower threshold ATL and an upper threshold ATH. If the rate of change in temperature AT is below the lower threshold ATL or above the upper threshold ATH, then this may indicate a fault.

For example, if the rate of change in temperature AT is below the lower threshold LTL, this may indicate a heater failure (heater failing to respond).

The value of the lower threshold ATL may be fixed (set in advance) or it may be varied, for example, in dependence on an output of the control algorithm which is used to control the amount of heat produced by the heater. For example, if the temperature controller 76 is controlling the heater 26 (via the power switching device 78) to produce a large amount of heat, then the value of the lower threshold ATL may be relatively high, and vice versa. In this way, it is determined whether the rate of change in temperature AT is significantly less than that which would be expected given the control signals which are being applied to the power switching device. If this is the case, it may indicate a heater failure or some other fault such as a fault in the power switching device 78.

On the other hand, if the rate of change in temperature AT is above the upper threshold ATH, then this may indicate a fault in the power switching device 78, or a fault in the heater 26, or a fault in the pump 24 (for example, pump failure) or some other fault. The value of the upper threshold ATH may also be fixed (set in advance) or varied, for example, in dependence on an output of the control algorithm which is used to control the amount of heat produced by the heater. Thus, the value of the upper threshold ATH may be higher if the expected change in temperature is high, and lower if the expected change in temperature is low.

If the rate of change in temperature AT is below the lower threshold ATL or above the upper threshold ATH, then processing proceeds to step 112. In step 112 a fault is indicated, in step 114 the contactors on the switch 72 are opened and in step 116 the oil pre-heating process is terminated. However, if the rate of change in temperature AT is between the lower threshold ATL and the upper threshold ATH, then processing proceeds to step 122.

In step 122 it is determined whether the ECM has terminated the oil pre-heating command. If the oil pre-heating command has not been terminated, then processing returns to step 104. In this case, the oil heater system continues to circulate the oil and bring its temperature to or maintain it in a desired temperature range. If on the other hand the oil pre-heating command has been terminated, then in step 114 the contactors in the switch 72 are opened and in step 116 the oil pre-heating process is terminated.

In addition, the contactors in the switch 72 are opened and the oil heating process is terminated if an emergency stop is initiated, if an oil level error is sensed, if an emergency shutdown is initiated, or if some other potentially hazardous fault is detected.

The embodiments described above may help to ensure even heating of the oil used in the engine, and may reduce engine preparation time prior to start-up.

Once the desired temperature has been reached, the system is able to maintain the temperature of the oil within a desired range.

Embodiments of the invention have been described above by way of example only, and various modifications are possible within the scope of the claims.

Claims

CLAIMS1. An oil heater system for pre-heating oil in an engine of a generator set, the oil heater system comprising: a pump for circulating oil through the engine; an oil heater for heating the oil; and a control unit for controlling the pump and the oil heater, wherein the oil heater is connected in-line with the pump outside of the engine.
2. An oil heater system according to claim 1, further comprising a temperature sensor arranged to sense a temperature of the oil, wherein the control unit is arranged to control an amount of heat produced by the oil heater in dependence on a sensed temperature.
3. An oil heater system according to claim 2, wherein the temperature sensor is connected in line with the oil heater outside of the engine.
4. An oil heater system according to claim 2 or 3, wherein the control unit is arranged to control the amount of heat produced by the oil heater in dependence on a difference between a sensed temperature and a reference temperature.
5. An oil heater system according to any of claims 2 to 4, wherein the control unit is arranged to control the amount of heat produced by the oil heater using a proportional integral derivative control algorithm.
6. An oil heater system according to any of claims 2 to 4, wherein the control unit is arranged to maintain the temperature of the oil within a predetermined range once the temperature of the oil has reached a reference temperature.
7. An oil heater system according to any of the preceding claims, wherein the control unit is arranged to receive an oil preheat command and to initiate an oil pre-heating process on receipt of the oil preheat command.
8. An oil heater system according to any of the preceding claims, further comprising a switch with contactors, wherein the control unit is arranged to close the contactors on receipt of an oil preheat command, thereby to supply AC power to the pump and the oil heater.
9. An oil heater system according to claim 7 or 8, wherein the control unit is arranged to switch off the pump and the oil heater when the oil preheat command is terminated.
10. An oil heater system according to any of the preceding claims, further comprise a voltage sensor for sensing a voltage of a power supply for the heater and/or pump, wherein the control unit is arranged to monitor a sensed voltage to detect a power loss and to produce a fault signal if a power loss is detected.
11. An oil heater system according to any of the preceding claims, wherein the control unit is arranged to monitor oil temperature and to produce a fault signal if the oil temperature exceeds a high limit set point.
12. An oil heater system according to claim 11, further comprising a high limit temperature sensor separate from a process temperature sensor, wherein the control unit is arranged to produce the fault signal if the temperature sensed by the high limit temperature sensor exceeds the high limit set point.
13. An oil heater system according to any of the preceding claims, wherein the control unit is arranged to calculate a rate of change of oil temperature, and to produce a fault signal if the rate of change of oil temperature is outside a predetermined range.
14. An oil heater system according to claim 13, wherein the predetermined range is variable in dependence on a control signal for controlling an amount of heat produced by the oil heater.
15. An oil heater system according to any of the preceding claims, further comprising a display for displaying at least one of oil temperature, heater power and a fault signal.
16. An oil heater system according to any of the preceding claims, wherein the oil heater system is arranged to be connected to a sump of the engine.
17. An oil heater system according to claim 16, wherein the oil heater system comprises a first conduit for fluidly coupling the oil heater system to an outlet of the sump and a second conduit for fluidly coupling the oil heater system to an inlet of the sump.
18. An oil heater system according to claim 17, further comprising a first connector for removably connecting the first conduit to the sump and a second connector for fluidly coupling the second conduit to the sump.
19. An oil heater system according to any of the preceding claims, further comprising means for mounting the oil heater system on a skid of the generator set.
20. An oil heater system according to claim 19, wherein the mounting means comprises anti-vibration mounts.
21. A skid for a generator set, the skid comprising an oil heater system according to any of the preceding claims mounted on the skid.
22. A skid according to claim 21, wherein the skid comprises a pair of opposing side members and the pump and the heater are mounted on at least one of the side members.
23. A generator set comprising a generator, an engine, and an oil heater system according to any of claims 1 to 20 or a skid according to claim 21 or 22, wherein the engine comprises a sump and the oil heater system is connected to the sump.
24. A generator set according to claim 23, wherein the engine comprises an engine control module arranged to monitor a temperature of oil in the sump, and to issue an oil pre-heating command to the oil heater system when the engine is to be started and the temperature of the oil in the sump is below a predetermined threshold.
25. A method of pre-heating oil in an engine of a generator set, the method comprising: circulating oil through the engine using a pump; heating the oil using an oil heater; and controlling the pump and the oil heater, wherein the oil heater is connected in-line with the pump outside of the engine.