Patent Description:
Traditional refrigerated cargo trucks or refrigerated tractor trailers, such as those utilized to transport cargo via sea, rail, or road, is a truck, trailer or cargo container, generally defining a cargo compartment, and modified to include a refrigeration system located at one end of the truck, trailer, or cargo container. Refrigeration systems typically include a compressor, a condenser, an expansion valve, and an evaporator serially connected by refrigerant lines in a closed refrigerant circuit in accord with known refrigerant vapor compression cycles. A power unit, such as a combustion engine, drives the compressor of the refrigeration unit, and may be diesel powered, natural gas powered, or other type of engine. In many tractor trailer transport refrigeration systems, the compressor is driven by the engine shaft either through a belt drive or by a mechanical shaft-to-shaft link.

In some systems, the an Eco-Drive® generator is connected to the vehicle engine to convert rotational energy of the vehicle engine into electrical power and distributes the electrical power to components of the transportation refrigeration unit for the use thereof. When Eco-Drive® is installed on truck and commissioned for operation, the system is set to provide a continuous and nominal power at 400V/<NUM>/<NUM> or 460V/<NUM>/<NUM> to the transportation refrigeration unit. As a consequence components of the transport refrigeration unit, such as a compressor and an evaporator fan, have only one fixed speed of operation. <CIT> discloses a refrigeration unit of an electrically powered trailer refrigeration system that includes an economized scroll compressor, and an engine driven generator to power the scroll compressor and other components of the system. <CIT> discloses a frequency control regulation system for a compressor, the rotation frequency thereof being controlled according to a set value. This is used to optimize power consumption in a motor vehicle.

A first aspect of the invention provides a transportation refrigeration unit as defined in the appended independent device claim <NUM>.

The drive unit may be configured to deliver electrical power in the range of <NUM> to <NUM>.

The one or more sensed parameters may include one or more of a difference between a cargo compartment temperature and a set point temperature or a door position of the cargo compartment.

The electrical power may be continuously variable between the minimum frequency and the maximum frequency.

A control unit may be operably connected to the drive unit to command the drive unit based on the one or more sensed parameters.

In another embodiment, a transportation refrigeration system may include a vehicle including a vehicle engine to drive the vehicle, a cargo compartment, and a transportation refrigeration unit configured to cool the cargo compartment.

A second aspect of the invention provides a method of operating a transportation refrigeration unit as defined in the appended independent method claim <NUM>.

The frequency may be varied based on one or more sensed operating parameters of the transportation refrigeration unit.

The one or more sensed parameters may include a difference between a cargo compartment temperature and a set point temperature.

The one or more sensed parameters may include a door position of the cargo compartment.

With reference to the accompanying drawings, like elements are numbered alike::.

Referring to <FIG>, a transport refrigeration system <NUM> of the present disclosure is illustrated. In the illustrated embodiment, the transport refrigeration system <NUM> includes a vehicle, for example, a truck <NUM>, having a cargo compartment <NUM>. An engineless transportation refrigeration unit (TRU) <NUM> is utilized to provide a desired temperature and humidity range. A vehicle engine <NUM>, such as a gasoline or diesel combustion engine, provides power to drive movement of the truck <NUM>, and a drive unit <NUM> is utilized to provide electrical power to the TRU <NUM>. The drive unit <NUM> is connected to the vehicle engine <NUM> such that the drive unit <NUM> converts rotational energy from the vehicle engine <NUM> into electrical power, which the drive unit <NUM> distributes to various components of the transportation refrigeration unit <NUM> to power the components. It is understood that embodiments described herein can be applied to shipping containers that are shipped by rail, sea, air, or any other suitable container, thus the vehicle can be a truck, train, boat, airplane, helicopter, etc..

Referring to <FIG>, in some embodiments the drive unit <NUM> is a hydraulic system including a hydraulic pump <NUM> connected to and driven by the vehicle engine <NUM> at a power take off <NUM>. An electrical generator <NUM> is connected to the hydraulic pump <NUM> and converts the hydraulic power to electrical power.

Referring to <FIG>, the cargo compartment <NUM> includes a top wall <NUM>, a bottom wall <NUM> opposed to and spaced from the top wall <NUM>, two side walls <NUM> spaced from and opposed to one-another, and opposing front and rear walls <NUM>, <NUM>. The cargo compartment <NUM> further includes doors (not shown) at the rear wall <NUM>, or any other wall.

Typically, transport refrigeration systems <NUM> are used to transport and distribute cargo, such as, for example perishable goods and environmentally sensitive goods (herein referred to as perishable goods). The perishable goods can include but are not limited to fruits, vegetables, grains, beans, nuts, eggs, dairy, seed, flowers, meat, poultry, fish, ice, blood, pharmaceuticals, or any other suitable cargo requiring cold chain transport. In the illustrated embodiment, the TRU <NUM> is associated with a cargo compartment <NUM> to provide desired environmental parameters, such as, for example temperature, pressure, humidity, carbon dioxide, ethylene, ozone, light exposure, vibration exposure, and other conditions to the cargo compartment <NUM>. In further embodiments, the TRU <NUM> is a refrigeration system capable of providing a desired temperature and humidity range.

The engineless TRU <NUM> is generally integrated into the cargo compartment <NUM> and is mounted to the front wall <NUM>. The cargo is maintained at a desired temperature by cooling of the cargo compartment <NUM> via the TRU <NUM> that circulates airflow into and through the cargo compartment <NUM>.

Referring now to <FIG>, the components of the engineless TRU <NUM> include a compressor <NUM>, an electric compressor motor <NUM>, a condenser <NUM> that is air cooled, a condenser fan assembly <NUM>, a receiver <NUM>, a filter dryer <NUM>, a heat exchanger <NUM>, a thermostatic expansion valve <NUM>, an evaporator <NUM>, an evaporator fan assembly <NUM>, a suction modulation valve <NUM>, and a control unit <NUM> that includes a computer-based processor (e.g., microprocessor). Operation of the engineless TRU <NUM> may best be understood by starting at the compressor <NUM>, where the suction gas, for example, a refrigerant gas, enters the compressor at a suction port <NUM> and is compressed to a higher temperature and pressure. The refrigerant gas is emitted from the compressor at an outlet port <NUM> and then flows into tube(s) <NUM> of the condenser <NUM>.

Air flowing across a plurality of condenser coil fins (not shown) and the tubes <NUM>, cools the gas to its saturation temperature. The air flow across the condenser <NUM> is facilitated by one or more fans <NUM> of the condenser fan assembly <NUM>. The condenser fans <NUM> are driven by respective condenser fan motors <NUM> of the condenser fan assembly <NUM> that are electric.

By removing latent heat, the gas within the tubes <NUM> condenses to a high pressure and high temperature liquid and flows to the receiver <NUM> that provides storage for excess liquid refrigerant during low temperature operation. From the receiver <NUM>, the liquid refrigerant passes through a sub-cooler heat exchanger <NUM> of the condenser <NUM>, through the filter-dryer <NUM> that keeps the refrigerant clean and dry, then to the heat exchanger <NUM> that increases the refrigerant sub-cooling, and finally to the thermostatic expansion valve <NUM>.

As the liquid refrigerant passes through the orifices of the expansion valve <NUM>, some of the liquid vaporizes into a gas (i.e., flash gas). Return air from the refrigerated space (i.e., cargo compartment <NUM>) flows over the heat transfer surface of the evaporator <NUM>. As the refrigerant flows through a plurality of tubes <NUM> of the evaporator <NUM>, the remaining liquid refrigerant absorbs heat from the return air, and in so doing, is vaporized.

The evaporator fan assembly <NUM> includes one or more evaporator fans <NUM> that are driven by respective fan motors <NUM> that are electric. The air flow across the evaporator <NUM> is facilitated by the evaporator fans <NUM>. From the evaporator <NUM>, the refrigerant, in vapor form, then flows through the suction modulation valve <NUM>, and back to the compressor <NUM>. A thermostatic expansion valve bulb sensor <NUM> is located proximate to an outlet of the evaporator tube <NUM>. The bulb sensor <NUM> is intended to control the thermostatic expansion valve <NUM>, thereby controlling refrigerant superheat at an outlet of the evaporator tube <NUM>. It is further contemplated and understood that the above generally describes a single stage vapor compression system that can be used for HFCs such as R-404a, R-134a, R452a, R448a, R453a, R454a and natural refrigerants such as propane and ammonia. Other refrigerant systems can also be applied that use carbon dioxide (CO<NUM>) refrigerant, and that can be a two-stage vapor compression system. It is to be appreciated, however, that the listed refrigerants are merely examples thereof, and other refrigerants can be utilized.

A bypass valve (not shown) facilitates the flash gas of the refrigerant to bypass the evaporator <NUM>. This will allow the evaporator coil to be filled with liquid and completely 'wetted' to improve heat transfer efficiency. With CO<NUM> refrigerant, this bypass flash gas can be re-introduced into a mid-stage of a two-stage compressor.

The compressor <NUM> and the compressor motor <NUM> are linked via an interconnecting drive shaft <NUM>. The compressor <NUM>, the compressor motor <NUM> and the drive shaft <NUM> are all sealed within a common housing <NUM>. The compressor <NUM> is a single compressor. The single compressor can be a two-stage compressor, a scroll-type compressor or other compressors adapted to compress HFCs or natural refrigerants. The natural refrigerant can be CO<NUM>, propane, ammonia, or any other natural refrigerant that can include a global-warming potential (GWP) of about one (<NUM>).

The drive unit <NUM> is connected to electrically-driven components of the TRU <NUM>, such as the compressor motor <NUM>, evaporator fan assembly <NUM> and condenser fan assembly <NUM>, and the control unit <NUM>, via a plurality of electrical pathways <NUM>. The control unit <NUM> is configured to command a frequency of operation of the drive unit <NUM>, such that sufficient electrical power is delivered to the TRU <NUM> components based on operational parameters of the transport refrigeration system <NUM>. The operational frequency of the drive unit <NUM> is variable, and in some embodiments is continuously variable in a frequency range between a minimum frequency and a maximum frequency. In some embodiments, the minimum frequency is <NUM> and the maximum frequency is <NUM>. Operating the drive unit <NUM> at the minimum frequency provides a minimum cooling capacity from the compressor <NUM> and a minimum airflow from the evaporator fan assembly <NUM> and condenser fan assembly <NUM>. Likewise, operating the drive unit <NUM> at the maximum frequency provides a maximum cooling capacity from the compressor <NUM> and a maximum airflow from the evaporator fan assembly <NUM> and condenser fan assembly <NUM>. In some embodiments, the drive unit <NUM> is operable at any frequencies between the minimum frequency and the maximum frequency to tune cooling capacity provided by the compressor <NUM> and airflow provided by the evaporator fan assembly <NUM> and the condenser fan assembly <NUM>.

The control unit <NUM> utilizes parameters such as set point temperature of the TRU <NUM>, actual temperature in the cargo compartment <NUM>, delta temperature between the actual temperature and the set point temperature, whether or not cargo compartment doors are opened or closed, etc., to determine an optimal drive unit <NUM> frequency within the frequency range to produce a desired level of electrical power to meet the electrical power needs of the TRU <NUM>. For example, in operating conditions where the delta temperature (cargo compartment temperature minus set point temperature) is relatively high, the control unit <NUM> will command the drive unit <NUM> to operate at maximum power at the maximum frequency until the set point temperature is reached and equaled by the cargo compartment temperature. Conversely, in operating conditions where the delta temperature is relatively low, the control unit <NUM> will command the drive unit top operate at maximum power at the minimum frequency until the set point temperature is reached.

Utilizing a drive unit <NUM> having variable frequency of operation has the technical effect of reducing set point recovery times especially in cases where the delta temperature is relatively high. Further, such capability improves efficiency of the TRU <NUM> and fuel efficiency of the vehicle engine <NUM>, and also reduces CO<NUM> emissions of the vehicle engine <NUM>. Further, controlling operating frequency at the drive unit <NUM> alleviates the need to incorporate complex variable speed components in the fan assemblies and the compressor, and is beneficially efficient and reliable compared to such components.

Claim 1:
A transportation refrigeration unit (<NUM>) for cooling a cargo compartment (<NUM>) comprising:
a compressor (<NUM>) configured to compress a refrigerant;
a compressor motor (<NUM>) configured to drive the compressor (<NUM>);
an evaporator (<NUM>) heat exchanger operatively coupled to the compressor (<NUM>);
an evaporator fan (<NUM>) configured to provide return airflow from a return air intake and flow the return airflow over the evaporator (<NUM>) heat exchanger; characterized in that:
a drive unit (<NUM>) is configured to deliver variable frequency electrical power between a minimum frequency and a maximum frequency to the compressor motor (<NUM>) and the evaporator fan (<NUM>), a frequency of the electrical power based on one or more sensed parameters of the transportation refrigeration unit (<NUM>);
wherein the drive unit (<NUM>) is an electrical generator (<NUM>) operably connected to a vehicle engine (<NUM>); and
the electrical generator (<NUM>) is operably connected to the vehicle engine (<NUM>) via a hydraulic pump (<NUM>), the electrical generator (<NUM>) converting hydraulic power to electrical power.