Control system and method for an electronically controlled engine for a refrigeration system

Abstract

A transport refrigeration system (10) is disclosed that includes an electrically controlled engine (60) that drives a refrigeration circuit (80) of the transport refrigeration system (10). An engine control unit (65) is configured to operate the engine (60) in a differential operating mode in which engine speed is increased with a decrease in engine load from the refrigeration circuit (80) to maximize cooling capacity of the system (10) under low engine load conditions.

Description

TECHNICAL FIELD

[0001] The present invention relates to a refrigeration system comprising an electrically controlled engine, in particular to a control system and method for operating the electrically controlled engine of the system. BACKGROUND

[0002] Transport refrigeration systems (TRSs) generally include a transport refrigeration unit (TRU) connected to a transport unit (e.g., a truck, a container such as a container on a flatbed truck, a container on a railcar, a box truck, a semi-trailer, a bus, or other similar transport unit) to control one or more environmental conditions (e.g., temperature, humidity, air quality, etc.) of an interior space of the transport unit. Doing so can preserve perishable goods (e.g., produce, frozen food, pharmaceuticals, etc.) stored within the interior space of the transport unit.

[0003] The TRU generally includes a refrigeration circuit comprising a compressor, a condenser, an expansion valve, an evaporator, and a fan or blower to control heat exchange between air within the interior space and ambient air outside the TRU. An internal combustion engine is typically used to generate power that drives the compressor of the TRU to rotate to force refrigerant through the circuit. In some cases, the compressor is directly driven by the engine such that the rotational speed of the compressor is directly proportional to the rotational speed of the engine.

[0004] Current engine emission standards, such as the V-class regulation for non-road mobile machinery (NRMM) in Europe or the 4th stage standard in North America, limit the output of engine power, and thus limit the power value that can be used by the TRU from the engine. To meet such emission standards, the compressor engine is typically provided with a so-called “regulator”, i.e., a device configured to limit the power of the engine by limiting the fuel (e.g., air) to the engine, for example when the engine prime mover reaches its rated speed at full load (also referred to as rated load, i.e., the maximum load that the engine is manufactured to withstand at its rated speed). The rated speed is the engine speed (typically in revolutions per minute or RPM) of the full load engine at the maximum allowed power.

[0005] It is known to provide an electronic governor comprising one or more solenoid valves for controlling the flow of fuel to the engine, and which are actuated by appropriate control signals from an Engine Control Unit (ECU). Electronic governors for TRU engines are typically operated in a synchronous mode of operation, in which the ECU maintains a constant engine speed for varying engine loads. This is achieved by adjusting the position of the fuel valves so that the amount of fuel reaching the combustion chamber is increased or decreased in dependence on the load. In practice, the ECU can continuously monitor the engine speed via one or more sensors (as is known in the art), and adjust the position of the solenoid valves to compensate for any changes in speed arising from changes in load. The monitoring and valve actuation processes are performed sufficiently quickly to ensure that there are no appreciable differences in engine speed under varying loads.

[0006] The speed of an electronically controlled engine is typically capped at the rated speed of the engine to ensure that the engine does not exceed its power limit at full load. However, this also limits the speed of the compressor, and hence the flow of refrigerant that the compressor can pump around the refrigeration circuit, and as a result limits the cooling capacity of the TRU.

[0007] Accordingly, it is desirable to increase the cooling capacity of a TRU driven by a power-limited engine. SUMMARY

[0008] According to one aspect of the application, there is provided a transport refrigeration system comprising: an electronically controlled engine; a transport refrigeration unit comprising a refrigeration circuit configured to be driven by the engine; and an engine control unit configured to operate the engine in a differential mode of operation in which the engine speed increases with a reduction in engine load from the refrigeration circuit.

[0009] The Applicant has recognised that it is possible to maximise the cooling capacity of a power-limited TRU without increasing the power of the engine, and that this can be done by operating the electronically controlled engine of the TRU in a so-called "differential mode" of operation in which the engine speed is allowed to vary with different engine loads. This is in contrast to the synchronous mode of operation conventionally used in which the engine speed is kept constant when the engine load varies (although in embodiments, the engine can be operated in both modes, as described later). In particular, the speed of an electronically controlled engine can be increased (e.g. above its rated speed) without increasing the power of the engine in the event that the engine is not at full load. The increased engine speed will enable a greater amount of refrigerant to be pumped through the refrigeration cycle by the compressor of the refrigerant, thereby increasing the cooling capacity of the system.

[0010] The engine control unit can be configured to operate the engine in a differential operating mode and a synchronous operating mode, wherein in the synchronous operating mode the engine speed is maintained at a fixed speed for varying engine loads.

[0011] The engine control unit or the controller of the transport refrigeration unit can be configured to monitor an operating parameter indicative of engine load. The engine control unit can be configured to automatically alternate between the differential operating mode and the synchronous operating mode based on the operating parameter.

[0012] The engine control unit can be configured to operate the engine in the differential operating mode if the monitored operating parameter is at or below a predetermined threshold of the operating parameter. If the operating parameter is greater than the predetermined threshold, the engine control unit can be configured to operate the engine in the synchronous operating mode.

[0013] The operating parameter can be a case temperature of the transport refrigeration unit or a load acting on a prime mover of the engine.

[0014] The engine control unit can be configured to operate the engine in the differential operating mode when the transport refrigeration unit requires an engine speed above a rated speed of the engine to meet cooling demands of the system.

[0015] The engine control unit is configured to operate the engine in the synchronous operating mode when the transport refrigeration unit is operating in a continuous cooling modulation mode.

[0016] The engine control unit can be configured to operate the engine in the differential operating mode when the transport refrigeration unit is operating in a pull-down operating mode.

[0017] The system can include a user operable switch that causes the engine control unit to operate the engine in the differential operating mode when the switch is set to a first state and causes the engine control unit to operate the engine in the synchronous operating mode when the switch is set to a second state different from the first state.

[0018] According to another aspect of the present disclosure, there is provided a method of operating a transport refrigeration system, comprising: powering an electronically controlled engine to drive a refrigeration circuit in a transport refrigeration unit of the system; and operating the engine in a differential operating mode wherein the engine speed increases as engine load from the refrigeration circuit decreases.

[0019] The engine control unit can be configured to operate the engine in a differential operating mode and a synchronous operating mode, wherein in the synchronous operating mode the engine speed is maintained at a fixed speed for varying engine loads.

[0020] The method can include monitoring, using an engine control unit or a controller of the transport refrigeration unit, an operating parameter indicative of engine load. The method can include the engine control unit automatically alternating between a differential operating mode and a synchronous operating mode based on the operating parameter.

[0021] The method can include the engine control unit operating the engine in the differential operating mode if the monitored operating parameter is at or below a predetermined threshold of the operating parameter. The method can include the engine control unit operating the engine in the synchronous operating mode if the operating parameter is greater than the predetermined threshold.

[0022] As described above, the operating parameter can be a case temperature of the transport refrigeration unit or a load acting on a prime mover of the engine.

[0023] A user of the system can operate a switch of the system to cause the engine control unit to operate the engine in the synchronous operating mode or the differential operating mode.

[0024] The engine control unit can operate the engine in the differential operating mode when the transport refrigeration unit requires an engine speed above a rated speed of the engine to meet cooling demands of the system.

[0025] The engine control unit can operate the engine in the synchronous operating mode when the transport refrigeration unit is operating in a continuous cooling modulation mode.

[0026] The engine control unit can operate the engine in the differential operating mode when the transport refrigeration unit is operating in a pull-down operating mode.

[0027] Various “units” described herein, such as a unit controller or an engine control unit, can be coupled to one another via wireless links, and thus can include transceiver circuitry and one or more antennas. Additionally or alternatively, the units described herein can be coupled to one another via wired links, and thus can include interface circuitry, such as a universal serial bus (USB) socket. It will be appreciated that the modules described herein can be coupled to one another via any combination of wired and wireless links.

[0028] The various units described herein can include any suitable circuitry to cause the execution of the methods described and illustrated herein. These modules can include: at least one application specific integrated circuit (ASIC); and and / or at least one field programmable gate array (FPGA); and / or a single- or multi-processor architecture; and / or a serial (von Neumann) / parallel architecture; and / or at least one programmable logic controller (PLC); and / or at least one microprocessor; and / or at least one microcontroller; and / or a central processing unit (CPU); and / or a graphics processing unit (GPU) to execute these methods.

[0029] Each unit can include and / or be in communication with one or more memories, such as non-transitory computer-readable storage media, which store the data described herein, and / or store software (computer-readable instructions) to perform the processes described herein. BRIEF DESCRIPTION OF DRAWINGS

[0030] The present application will now be described by way of example with reference to the accompanying drawings in which:

[0031] Figure 1 is a side view of a TRS for a transport unit according to an embodiment.

[0032] Figure 2 is a schematic view of a TRS of Figure 1

[0033] Figure 3 is a schematic view of a plurality of torque-speed curves for an electronically controlled engine operating in a synchronous mode of operation according to an embodiment.

[0034] Figure 4 is a schematic view of a plurality of torque-speed curves for an electronically controlled engine operating in a differential mode of operation according to an embodiment.

[0035] Figure 5 is a flowchart schematically illustrating control logic of a unit controller and processing steps to be taken by the unit controller according to an embodiment. And

[0036] Figure 6 is a flowchart schematically illustrating control logic of a unit controller and processing steps to be taken by the unit controller according to another embodiment. DETAILED DESCRIPTION

[0037] Figure 1 is a side view of a transport refrigeration system (TRS) 10 for a transport unit 25 according to an embodiment. The transport unit 25 shown is a trailer-type transport unit. Embodiments described in this specification can be used with other types of transport units. For example, the transport unit 25 can represent a container (e.g., a container on a flatbed truck, a container for intermodal shipping, etc.), a truck, a boxcar, or other similar type of transport unit whose interior space can be controlled in terms of the environment.

[0038] ​The TRS 10 is configured to control one or more environmental conditions, such as, but not limited to, the temperature, humidity, and / or air quality of the interior space 50 of the transport unit 25. In one embodiment, the interior space 50 may alternatively be referred to as a conditioned space 50, a cargo space 50, an environmentally controlled space 50, a container 50, etc. The TRS 10 is configured to transfer heat between the air inside the interior space 50 and the surrounding air outside the transport unit 25.

[0039] According to one embodiment, the interior space 50 may include one or more partitions or inner walls (not shown) for at least partially dividing the interior space 50 into multiple zones or compartments. It should be understood that the interior space 50 can be divided into any number of zones and can be configured in any way suitable for cooling different zones. In some examples, each zone may have the same or different setpoint temperatures.

[0040] refer to Figure 1 and Figure 2 The TRS 10 includes a transport refrigeration unit (TRU) 15. For example... Figure 1 As shown, TRU15 is mounted on the front wall 30 of transport unit 25.

[0041] TRU 15 includes a programmable unit controller 35, which includes a single integrated control unit 40. It should be understood that in other embodiments, the unit controller 35 may include a distributed network (not shown) of TRS control elements. The unit controller 35 may include a processor, memory, clock, and input / output (I / O) interfaces (not shown). The unit controller 35 may include fewer or additional components.

[0042] TRU 15 also includes a closed cooling circuit ( Figure 2 (Ref. 80 in the accompanying drawings) This closed refrigeration circuit generally defines the flow of refrigerant through the refrigeration system 10. The refrigeration circuit 80 includes a compressor 90, a condenser (not shown), an expansion valve (not shown), and an evaporator (not shown). Relatively hot vapor refrigerant is transferred from the compressor 90 to the condenser, which is in thermal communication with the cooler ambient environment, thereby removing heat from the refrigerant. Cooler liquid refrigerant is transferred from the condenser (via the expansion valve) to the evaporator, which is in thermal communication with the space to be conditioned (e.g., the space to be cooled). As air circulates on the evaporator, liquid refrigerant droplets evaporate and absorb heat from the air to cool the space. To complete the refrigeration circuit, vapor refrigerant is transferred from the evaporator back to the compressor.

[0043] The unit controller 35 controls the refrigeration circuit of the TRS 10 to achieve a desired state (e.g., temperature, humidity, air quality, etc.) of the interior space 50. In particular, the unit controller 35 can be in wired or wireless communication with one or more sensing devices for measuring a number of operating conditions of the TRU, such as case temperature, ambient temperature, and operating parameters of the TRU 15, such as evaporator temperature, pressure, etc., in order to allow the unit controller 35 to draw conclusions as to what measures have to be taken in order to achieve the desired state within the interior space 50. For example, the unit controller 35 can compare the current state (e.g., case temperature and ambient temperature) with a target state (e.g., a set temperature of the case) and adjust the current cooling capacity of the TRU 15 accordingly. This can be done by sending control signals to various control devices of the TRU 15, such as a refrigerant throttling valve, an airflow regulator, etc., which control the movement of refrigerant through the refrigeration circuit.

[0044] The TRS 10 further comprises a power room (not shown) which houses a prime mover in the form of an internal combustion engine 60 (e.g., a diesel engine, etc.) which provides power to operate the TRU 15, in particular to operate the compressor 90. The power room can also or alternatively house an on-board electric motor and corresponding prime mover which can provide power to operate the TRU 15 when the internal combustion engine is inactive (e.g., when the transport unit is parked, e.g., at a warehouse or a ferry).

[0045] The unit controller 35 itself is powered by a power module (not shown) which can comprise a DC power source (e.g., a battery) for providing direct current to a plurality of DC components (not shown), etc. The DC power source can receive mechanical power and / or electrical power from, e.g., the prime mover of the power room, when the DC power source is coupled with a generator mechanical (e.g., a belt-driven alternator, a direct-driven generator, etc.). For example, in an embodiment, mechanical energy generated by a diesel engine is converted into electrical energy via a generator mechanical. The generated electrical energy is then converted into direct current via, e.g., a bi-directional voltage converter. The bi-directional voltage converter can be a bi-directional multi-battery voltage converter.

[0046] The power module is arranged in or separate from the TRU 15. The power module can power, e.g., a plurality of DC (direct current) components (not shown), a power management unit, etc. The direct current components can be accessories or components of the unit controller which require direct current for operation. Examples of DC components can include, e.g., a fuel pump, a drain heater, solenoid valves (e.g., controller pulse controlled valves), etc.

[0047] Engine 60 is an electronically controlled, power-limited internal combustion engine in that the speed of the engine 60, and thus the power output, is controlled by an engine control unit 65 via at least one electrically actuated solenoid valve 62, although other electrically actuated valves can be used instead. The position of the solenoid valve can be set to regulate the amount of fuel reaching the combustion chamber based on a control signal received from the engine control unit 65. During operation, the unit controller 35 can, for example, set a nominal engine speed at which the compressor 90 is to be driven and communicate the nominal engine speed to the engine control unit 65. The engine control unit 65 is, for example, a proportional-integral-derivative controller (PID controller) that provides speed control by continuously calculating an error value as the difference between the nominal engine speed and the current, measured engine speed and applies a speed correction based on proportional, integral, and derivative terms as is known in the art.

[0048] The engine control unit is operable to control the speed of the engine 60 in a synchronous mode of operation in which the engine control unit 65 maintains a constant engine speed for varying engine loads.

[0049] Figure 3 A set of torque and engine speed curves for an electronically controlled engine 60 operating in a synchronous mode of operation according to an embodiment of the present application is schematically illustrated.

[0050] The engine control unit 65 can be pre-configured with appropriate software, for example at the time of manufacture, to control the position of the solenoid valve 62 between a fully open position and a fully closed position, thus controlling the flow of fuel to the engine, to ensure that the engine speed remains constant at different loads (synonymously referred to as torque). In this regard, as Figure 3 illustrated, the engine control unit 65 is configured to operate the engine 60 in accordance with one of a plurality of predetermined torque-speed curves 41-45 stored in non-volatile memory by the engine control unit 65 for reference. While only five such curves are illustrated in Figure 3 it will be appreciated that the engine control unit 65 can store any number of such curves (and operate the engine accordingly in accordance with any number of such curves).

[0051] The engine 60 is configured such that the engine is manufactured to operate at a constant speed (between 0% and 100% of the engine rated speed) over the entire load range (0-100% of the rated load or torque) that the engine can sustain. Based on a nominal speed instruction received by the unit controller 35 of the TRU 15, the engine control unit 65 selects a torque-speed curve for operating the engine in the synchronous mode of operation.

[0052] When the engine control unit 65 operates the engine 60 according to one of the predetermined synchronous torque-speed curves, such as the curve 43 Figure 3 , the solenoid valve 62 (position) will be gradually opened or closed by the engine control unit 65 to provide the fuel injection rate required to maintain a constant engine speed (in this example, 60% of the engine rated speed) as the load on the engine 60 varies. In particular, as the load on the engine increases, the solenoid moves to a position that increases the mass flow of fuel to the engine. Conversely, as the load on the engine decreases, the solenoid moves to a position that decreases the mass flow of fuel to the engine.

[0053] For any fixed engine speed, the power output of the engine will be minimum when the engine load is 0% torque (or indeed as close to 0% torque as possible) and maximum when the engine load is 100% torque. Thus, for all load variations (as indicated by the torque-speed curve 45 Figure 3 , the engine control unit 65 limits the maximum speed of the engine to its rated speed (100% speed), i.e. the speed at which the power output of the engine operating at full load (100% torque) will reach its maximum value, to ensure that the power output of the engine does not exceed the limits set by emissions legislation.

[0054] When the engine control unit 65 operates the engine 60 in the synchronous mode of operation (at its rated speed, for example at the point of the curve 45 Figure 3 , if the load on the engine from the refrigeration circuit 80 is less than full load, the power output of the engine 60 will be below its maximum power limit. Under such low load conditions, the engine will have excess power generating capacity which the applicant has recognised can be advantageously utilised by the TRU 15 to increase its cooling capacity beyond that possible at those loads. For example, the excess capacity can be used to drive the engine at a speed higher than its rated speed, thereby increasing the speed at which the compressor can circulate refrigerant around the refrigeration circuit. In accordance with the present application, this is achieved by configuring the engine control unit 35 to be able to operate the engine not only in the synchronous mode of operation as described above, but also in a differential mode of operation in which the engine speed is allowed to vary with different engine loads, as will now be further described with reference to Figure 4 .

[0055] Figure 4 A set of torque and engine speed curves for an electronically controlled engine operating in the differential mode of operation in accordance with an embodiment of the application is shown schematically.

[0056] As in the case of the synchronous mode of operation, the engine control unit 65 can be pre-configured with appropriate software, e.g. at the time of manufacture, to operate the engine 60 in accordance with one of a plurality of predetermined torque-speed curves 51-56, which can be stored in non-volatile memory for use by the engine control unit 65. In particular, the unit controller 35 of the TRU 15 can set a nominal engine speed for the TRU 15 and send this to the engine control unit 65, which will in turn select the appropriate torque-speed curve to follow. Figure 4 Six such curves are shown in Figure 5, but it will be appreciated that any number of curves can be predetermined and stored in memory for use by the engine control unit 65.

[0057] As with the synchronous mode of operation described above Figure 3 In contrast to the synchronous mode of operation described above, in the differential mode of operation, the torque-speed curve allows the engine speed of the engine 60 to vary in dependence on the engine load. For example, as shown by curve 56, for an arrangement in which the engine is at full load (100% torque), the engine speed is set, in this example, to a first predetermined speed (100% speed) corresponding to its rated speed, but as the load of the engine decreases from full load, the engine speed is allowed to increase above the first speed. In this way, the engine can be operated at a speed above its rated speed when not at full load, which, as noted above, can be advantageous to maximise the cooling capacity of the TRU 15. Figure 4

[0058] In practice, the engine control unit 65 is pre-programmed to continuously monitor the load on the engine 60 (e.g. using conventional sensors known in the art) and automatically set the solenoid to a position corresponding to the speed indicated by the torque-speed curve. The extent to which the engine speed is allowed to vary for a given change in engine load can be pre-defined and set to ensure that the engine power output remains at or below the maximum power output set by emissions standards. In one embodiment, the engine speed is allowed to vary with engine load up to the first speed or, in this example, 7% above the rated speed.

[0059] It will be appreciated that, although the differential mode of operation is described above only in relation to increasing the engine speed above the rated speed of the engine, the differential mode of operation can be (and in embodiments is) used more generally to maximise the engine speed (by exploiting the excess power capacity of the engine at lower loads) even if this does not result in the speed exceeding the rated speed.

[0060] ​Furthermore, it will be appreciated that, although the differential operation mode has been described above as being provided in conjunction with the functionality of the synchronous operation mode, this dual functionality is not essential. Rather, according to embodiments of the application, the engine can be operated by the engine control unit in the differential operation mode only.

[0061] As mentioned above, by operating the electronically controlled engine in the differential operation mode, it is possible to advantageously exploit the excess power capability of the engine under low load conditions to maximise the cooling capacity of the TRU 15. This is particularly desirable in the case where the TRU 15 is operating in a so-called "pull down mode", which is a mode in which the unit controller 35 operates the TRU 15 to reduce the tank temperature to the set temperature as quickly as possible, as is known in the art. However, whenever the TRU 15 requires high speed cooling, when operating in the differential operation mode, the TRU 15 will benefit from the increased cooling capacity. For example, the differential operation mode can be employed when attempting to maximise cooling capacity during a so-called "ATP test", which is a known test designed to demonstrate that the cooling capacity of the TRU is suitable for the international transport of perishable foodstuffs.

[0062] Whilst it is desirable to automatically increase the engine speed (and hence increase the cooling capacity) for engine loads below full load of the engine when attempting to maximise cooling capacity, in other circumstances, for example when the TRU is operating in a so-called "continuous cooling modulation" mode, which is a mode of operation known in the art in which the unit controller 35 continuously modulates the current cooling capacity of the TRU to maintain a constant tank temperature, for example in response to ambient temperature fluctuations, this can not be desirable.

[0063] In this respect, as the cooling load required to maintain the set temperature within the tank decreases, for example due to a reduction in ambient temperature, the unit controller 35 of the TRU 15 will modify the position of the throttle valve of the refrigeration circuit 80 to throttle the flow of refrigerant pumped by the compressor 90 in an attempt to reduce the current cooling capacity of the TRU 15 to match the new cooling load. However, in the differential mode, the resulting reduction in engine load will cause the engine speed to increase, thereby increasing the cooling capacity above the level required to maintain the set temperature, thereby causing the engine 60 to work against the intention of the unit controller 35 of the TRU 15. As a result, the controller of the TRU will have to further throttle the refrigerant flow to prevent over-cooling of the interior space. This is clearly an inefficient use of engine fuel.

[0064] In those circumstances, it is desirable to instead operate the engine in the synchronous operation mode, thereby satisfying the reduction in engine load due to refrigerant throttling by reducing the flow of fuel to the engine (to maintain a constant speed). This will result in the refrigerant flow not being throttled as much as necessary to satisfy the cooling requirements of the interior space, whilst providing improved fuel economy.

[0065] To ensure that the most beneficial operating mode can be used at any given time when operating TRS, the engine control unit can be configured to alternate between differential operating mode and synchronous operating mode of engine 60.

[0066] In one embodiment, such as Figure 2 As shown in TRS 10, TRU 15 includes a user-operable switch 70 that allows the user to select any operating mode as the current mode for system 10. Accordingly, the switch can operate between a first state and a second state, in which the engine control unit 65 will operate the engine 60 only in differential operating mode, and in the second state, the engine control unit 65 will operate the engine 60 only in synchronous operating mode.

[0067] Switch 70 may be provided as part of TRU 15 and may communicate with its unit controller 35. Switch 70 may be a mechanical switch or an electronic switch, for example, a switch provided as a user-selectable option on a machine user interface as part of system 10. In either case, unit controller 35 communicates the current state of the switch to engine control unit 65 and, accordingly, the operating mode that engine control unit 65 will use to control engine speed.

[0068] However, instead of responding to a switch, for example, based on a control signal received from the unit controller 35, the engine control unit 65 may be configured to automatically switch between differential operating mode and synchronous operating mode.

[0069] Figure 5 This is a flowchart schematically illustrating the control logic and processing steps that the unit controller 35 according to such an embodiment is programmed to perform.

[0070] exist Figure 5 Step 71: The process begins when the unit controller 35 determines that the TRU 15 needs or is expected to be operated to achieve the operating mode at the set temperature. Specifically, the unit controller 35 will determine, based on several current operating conditions of the TRU 15 (such as chamber temperature and ambient temperature), whether the TRU 15 needs to be operated in pull-down mode or in continuous cooling operating mode to achieve the desired state within the internal space.

[0071] If it is determined in step 71 that TRU 15 will be operated in pull-down mode, the unit controller 35 will proceed to step 72 and instruct the engine control unit 65 to operate the engine 60 in differential operation mode to maximize cooling capacity for the entire pull-down operation. Alternatively, if it is determined in step 71 that TRU 15 will be operated in continuous cooling modulation operation mode, the unit controller 35 will proceed to step 72 and instruct the engine control unit 65 to operate the engine in synchronous operation mode to maximize fuel economy for the entire continuous cooling modulation operation.

[0072] In this way, for the current operating mode of TRS 10, the unit controller 35 will ensure that TRU 15 receives the most beneficial engine speed.

[0073] While the differential operating mode of the engine can be set at the start of the TRU 15's pull-down operation, in some installations it may be desirable to operate the engine in differential operating mode only after the load on the engine has dropped below a threshold. For example, it might be beneficial to operate the engine in a more fuel-efficient synchronous operating mode until the engine load drops to a level at which (if operating in differential operating mode) the engine speed can be increased sufficiently that the benefits of the increased cooling capacity will outweigh the increased fuel consumption associated with differential mode.

[0074] Figure 6 This is a schematic flowchart illustrating the control logic and processing steps that the unit controller 35 is programmed to perform when the TRU is to perform a pull-down operation, according to an embodiment of the present invention.

[0075] The unit controller 35 of the TRU 15 begins at step 81 by continuously monitoring the current value of an operating parameter that (directly or indirectly) represents the load applied to the engine 60 by the refrigeration circuit 80. Any suitable operating parameter indicating the engine load can be used.

[0076] In this regard, the applicant has recognized that as the evaporator temperature (i.e., the temperature of the refrigerant inside the evaporator) of TRU 15 decreases, the engine load decreases. For example, when the evaporator temperature is below freezing (e.g., at -20°C), the engine load is lower than when the evaporator temperature is merely cold (e.g., 0-5°C). Accordingly, in step 81, the evaporator temperature can be monitored (using a temperature sensor). However, in other devices, the chamber (internal space) temperature can be monitored instead of the evaporator temperature, because the chamber temperature is closely related to the evaporator temperature, and therefore closely related to the load on the engine.

[0077] Alternatively, the operating parameter monitored at step 81 can be a direct measurement of the engine load itself. As mentioned above, the engine control unit can already be configured to monitor the load on the engine 60, and in this case, at step 81, the current engine load can be communicated to the unit controller 35.

[0078] At step 82, the unit controller compares the current operating parameter to a predetermined threshold value for the operating parameter in question, and based on this comparison, selects whether to use the differential operating mode or the synchronous operating mode.

[0079] In the case where the monitored operating parameter is the evaporator temperature or the case temperature, the optimum operating parameter value at which the threshold value is set will vary for different transport refrigeration systems, for example, based on the size of the TRU (in terms of its maximum cooling capacity), the power threshold limit of the engine, etc. Thus, the threshold value used for comparison at step 82 can be predetermined on a system-by-system basis, using suitable experimental or analytical methods. For example, the system-specific analysis can be performed and the extent to which the engine load varies at different evaporator or case temperatures determined, and the optimum value at which the threshold value is set determined.

[0080] However, in the case where the monitored operating parameter is the engine load itself, the threshold value will be predetermined to be a value less than the full load of the engine. In embodiments, the threshold load value can be 80%, 60% or 40% of the full load of the engine.

[0081] If at step 82 it is determined that the monitored operating parameter is less than the predetermined threshold value, the unit controller 35 will proceed to step 83, at which the unit controller 35 sends an appropriate control signal to instruct the engine control unit 65 to operate the engine in the differential operating mode. However, if at step 82 it is determined that the operating parameter is greater than the predetermined threshold value, the unit controller 35 will proceed to step 84, at which the unit controller 35 sends an appropriate control signal to instruct the engine control unit 65 to operate the engine in the synchronous operating mode.

[0082] It will be appreciated that although the processing steps of Figure 6 have been described as being performed during a pull-down operation, embodiments of Figure 6 may be applied to any device in which maximum cooling capacity is desired.

[0083] The terminology used in the present description is intended to describe particular embodiments and is not intended to limit the application. Unless otherwise expressly stated, the terms "a," "an" and "the" do also include plural forms. The terms "including", "containing", "having" and "including" when used in this specification, mean the presence of the stated features, integers, steps, operations, elements, and / or components but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, and / or components.

[0084] With regard to the foregoing description, it is to be understood that detailed changes can be made in the construction materials and shapes, sizes and arrangements of the parts without departing from the scope of the present application. That is, the present application is not limited to the above-described embodiments, any feature can be used individually or in combination with any other feature except in cases of mutual exclusivity, and the disclosure extends to and embraces all combinations and sub-combinations of one or more features described herein.

[0085] The word "embodiment" as used in this specification means, but is not limited to, the same embodiment. The specification and described embodiments are merely examples. Other and further embodiments can be devised without departing from the basic scope thereof, and the present disclosure is not to be limited to the described embodiments and drawings.

Claims

1. A transport refrigeration system (10), comprising: Electronically controlled engine (60); and The transport refrigeration unit (15) includes a refrigeration circuit (80) and a controller. The refrigeration circuit (80) includes a compressor configured to be driven by the electronically controlled engine (60) to pump refrigerant around the refrigeration circuit. The controller is configured to set a nominal engine speed for driving the compressor and to transmit the nominal engine speed to an engine control unit (65) of the transport refrigeration system (10). The engine control unit (65) is configured to operate the electronically controlled engine (60) in a differential operation mode, in which: The engine control unit operates the electronically controlled engine (60) according to a predetermined torque-speed curve corresponding to the nominal engine speed; and The torque-speed curve indicates different engine speeds for driving the compressor for corresponding non-zero engine loads, wherein the torque-speed curve indicates the nominal engine speed at full engine load and one or more engine speeds above the nominal engine speed at engine loads below the full engine load, such that the engine speed will increase above the nominal engine speed as the engine load from the refrigeration circuit (80) decreases from the full engine load.

2. The transport refrigeration system (10) according to claim 1, wherein, The engine control unit (65) is configured to operate the electronically controlled engine (60) alternately in the differential operation mode and the synchronous operation mode. In the synchronous operation mode, the engine control unit operates the electronically controlled engine (60) according to the synchronous torque-speed curve to keep the electronically controlled engine (60) at a fixed engine speed for varying engine loads.

3. The transport refrigeration system (10) according to claim 2, wherein: The controller (35) of the engine control unit (65) or the transport refrigeration unit (15) is configured to monitor operating parameters indicating engine load; and The engine control unit (65) is configured to automatically alternate between the differential operating mode and the synchronous operating mode based on the operating parameters.

4. The transport refrigeration system (10) according to claim 3, wherein, The engine control unit (65) is configured to operate the electronically controlled engine (60) in the following mode: If the monitored operating parameter is equal to or lower than a predetermined threshold of the operating parameter, then it is the differential operating mode; and If the operation parameter is greater than the predetermined threshold, then it is the synchronous operation mode.

5. The transport refrigeration system (10) according to claim 4, wherein, The operating parameters are: The temperature of the container in the transport refrigeration unit (15); or The load acting on the prime mover of the electronically controlled engine (60).

6. The transport refrigeration system (10) according to any one of the preceding claims, wherein, The engine control unit (65) is configured to operate the electronically controlled engine (60) in the differential operating mode when the nominal engine speed is set to the rated speed of the electronically controlled engine (60), such that the engine speed will increase from an engine load below the rated load of the electronically controlled engine (60) to a speed above the rated speed.

7. The transport refrigeration system (10) according to claim 2, wherein, The engine control unit (65) is configured to operate the electronically controlled engine (60) in the synchronous operation mode when the transport refrigeration unit (15) is operating in the continuous cooling modulation mode.

8. The transport refrigeration system (10) according to claim 1, wherein, The engine control unit (65) is configured to operate the electronically controlled engine (60) in the differential operation mode when the transport refrigeration unit (15) is operating in the pull-down operation mode.

9. The transport refrigeration system (10) according to claim 2 further includes a user-operable switch (70) that, when the switch (70) is set to a first state, causes the engine control unit (65) to operate the electronically controlled engine (60) in the differential operation mode, and when the switch (70) is set to a second state different from the first state, causes the engine control unit (65) to operate the electronically controlled engine (60) in the synchronous operation mode.

10. A method of operating a transport refrigeration system (10), the transport refrigeration system comprising an electronically controlled motor and a transport refrigeration unit including a refrigeration circuit, the method comprising: Power is supplied to the electronically controlled engine (60) to drive the compressor of the refrigeration circuit (80) to pump refrigerant around the refrigeration circuit; as well as The controller sets the nominal engine speed for driving the compressor and transmits the nominal engine speed to the engine control unit (65) of the transport refrigeration system (10). The engine control unit operates the electronically controlled engine (60) in a differential operation mode, including: The engine control unit operates the electronically controlled engine (60) according to a predetermined torque-speed curve corresponding to the nominal engine speed. The torque-speed curve indicates different engine speeds to be used for corresponding non-zero engine loads, wherein the torque-speed curve indicates the nominal engine speed at full engine load and one or more engine speeds above the nominal engine speed at engine loads below the full engine load, such that the engine speed will increase above the nominal engine speed as the engine load from the cooling circuit (80) decreases from the full engine load.

11. The method of claim 10, further comprising: The engine control unit (65) alternately operates the electronically controlled engine (60) in the differential operation mode and the synchronous operation mode. In the synchronous operation mode, the engine control unit operates the electronically controlled engine (60) according to the synchronous torque-speed curve to maintain a fixed engine speed for varying engine loads.

12. The method of claim 11, further comprising: The engine control unit (65) or the controller (35) of the transport refrigeration unit (15) is used to monitor and indicate the operating parameters of the engine load. as well as Based on the operating parameters, the engine control unit (65) automatically alternates between the differential operating mode and the synchronous operating mode.

13. The method according to any one of claims 10 to 12, further comprising: When the nominal engine speed is set to the rated speed of the electronically controlled engine (60), the engine control unit (65) operates the electronically controlled engine (60) in the differential operation mode, such that the engine speed will increase from an engine load lower than the rated load of the electronically controlled engine (60) to a speed higher than the rated speed.

14. The method of claim 11, further comprising: When the transport refrigeration unit (15) operates in continuous cooling modulation mode, the engine control unit (65) operates the electronically controlled engine (60) in the synchronous operation mode.

15. The method of claim 10, further comprising: When the transport refrigeration unit (15) is operating in the pull-down operation mode, the engine control unit (65) operates the electronically controlled engine (60) in the differential operation mode.

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