Operation of Transport Refrigeration Systems to Prevent
Engine Stall and Overload
Cross-Reference to Related Application
[OOOl] This application claims priority to U.S. Provisional Patent
Application Serial No. 611387,177, entitled "Operation of Transport Refrigeration
Systems to Prevent Engine Stall and Overload," filed on September 28,2010. The
content of this application is incorporated herein by reference in it entirety.
Field of the Invention
[0002] This invention relates generally to the operation of a transport
refrigeration system and, more particularly, to maintaining cooling performance of a
transport refrigeration system while preventing engine stalls as well as overload of
the engine.
Background of the Invention
[0003] Fruits, vegetables and other perishable items, including meat, poultry
and fish, fresh or frozen, are commonly transported in the cargo box of a truck or
trailer, or in an intermodal container. Accordingly, it is customarily to provide a
transport refrigeration system in operative association with the cargo box for cooling
the atmosphere within the cargo box. The transport refrigeration system includes a
refrigerant vapor compression system, also referred to as a transport refrigeration
unit, and an on-board power unit. The refrigerant vapor compression system
typically includes a compressor, a condenser, an expansion device and an evaporator
serially connected by refrigerant lines in a closed refrigerant circuit in accord with
known refrigerant vapor compression cycles. The power unit includes an engine,
typically diesel powered.
[0004] In many trucwtrailer transport refrigeration systems, the compressor
of the transport refrigeration unit is driven by the engine shaft either through a belt
drive or by mechanical shaft-to-shaft link. More recently, all electric transport
refrigeration systems have been developed for trucwtrailer applications wherein the
engine drives an on-board generator for generating sufficient electrical power to
drive an electric motor operatively associated with the compressor of the transport
refrigeration unit. For example, U.S. Patent 6,223,546, assigned to Carrier
Corporation, the same assignee to which this application is subject to assignment,
the entire disclosure of which is incorporated herein by reference in its entirety,
discloses an electrically powered transport refrigeration unit powered by an engine
driven synchronous generator capable of producing sufficient power to operate the
compressor drive motor and at least one fan motor. With respect to intermodal
containers, clip-on power units, commonly referred to as generator sets or gensets,
are available for mounting to the intermodal container, typically when the container
is being transported by road or rail, to provide electrical power for operating the
compressor drive motor of the transport refrigeration unit associated with the
container. The genset includes a diesel engine and a generator driven by the diesel
engine.
[OOOS] During transport of such perishable items the temperature within the
cargo box of the truck, trailer or container must be maintained within strict
temperature limits associated with the particular items being transported, regardless
of potentially severe operating conditions imposed by the local environment in
which the system is operating. For example when the transport refrigeration system
is operated at high ambient temperatures and/or high altitude operation, the power
demanded by the refrigeration unit at high cooling capacity demand may exceed the
limited shaft power available from the engine, raising the potential for an engine
stall or engine overload. In the event of an engine stall or engine overload, the loss
of power from the generator will result in an undesired shutdown of the refrigeration
unit.
[0006] In conventional transport refrigeration systems, the control system is
open loop in that the system controller is unaware of the actual operating engine
load. Rather, the transport refrigeration system controller uses algorithms that
include safety margins to limit the engine shaft power demand in an attempt to
prevent overload of the engine. However, at times, such as under aggravated service
conditions and during transient operations, a lost in refrigeration unit performance
and engine stalls or overload can still occur. A need exists for controlling the
operation of the refrigeration unit in response to actual engine operating conditions
so as to avoid engine stall or engine overload.
Summary of the Invention
[0007] In an aspect, a method is provided for optimizing the performance of
a transport refrigeration system having a transport refrigeration unit powered by a
diesel engine, including the step of matching a capacity output of the transport
refrigeration unit to an available shaft power of the diesel engine. The method may
also include the step of operating the transport refrigeration system at the capacity
output necessary to meet a current refrigeration demand load so as long as both an
operating fuel rack position of the diesel engine is not at 100% and an operating
speed of the diesel engine does not drop more than five percent.
[OOOS] In an aspect, a method is provided for controlling the power
consumption of a transport refrigeration unit having a refrigerant mass flow
circulating within a refrigerant circuit having a refrigerant compressor and having a
diesel engine for powering the transport refrigeration unit. The method includes the
step of selectively limiting refrigerant mass flow through the refrigerant circuit in
response to an operating fuel rack position on the diesel engine and on an operating
speed of the diesel engine. In an embodiment, the method may include the further
steps of: monitoring the operating fuel rack position for the diesel engine;
monitoring the operating engine speed of the diesel engine; and selectively adjusting
the refrigerant mass flow through the refrigerant circuit of the transport refrigeration
unit to maintain the operating fuel rack position at a position less than 98% of the
maximum fuel rack position and to simultaneously maintain the operating engine
speed at a speed of at least 98% of a maximum engine operating speed. In an
embodiment, the method may include the further steps of: monitoring the operating
fuel rack position for the diesel engine; monitoring the operating engine speed of the
diesel engine; determining whether the monitored fuel rack position is at a position
of at least 90% of a maximum fuel rack position; determining whether the monitored
engine speed is at a speed of at least 98% of a maximum engine speed; and if both
the monitored fuel rack position is at a position of at least 90% of a maximum fuel
rack position and the monitored engine speed is at a speed of at least 98% of a
maximum engine speed, restricting an increase in refrigerant mass flow through the
compressor.
[0009] In an aspect, a method is provided for controlling the operation of a
transport refrigeration unit having a refrigerant mass flow circulating within a
refrigerant circuit having a refrigerant compressor and a compressor suction
modulation valve and having a diesel engine for powering the transport refrigeration
unit. The method includes the steps of: determining whether a change in a system
operating condition has been requested; and if a system operating condition change
has been requested, restricting an increase in refrigerant mass flow by reducing a
maximum rate open of the suction modulation valve to 0.1 percent per second.
Brief Description of the Drawings
[OOl 01 For a further understanding of the disclosure, reference will be made
to the following detailed description which is to be read in connection with the
accompanying drawing, wherein:
[OOll] FIG. 1 shows a schematic diagram of an exemplary embodiment of a
transport refrigeration system wherein the compressor is by a motor powered by a
electric generator driven by a diesel engine;
[0012] FIG. 2 shows a schematic diagram of an exemplary embodiment of a
transport refrigeration system wherein the compressor is driven by a diesel motor
through a belt drive; and
[0013] FIGS. 3 (a) & (b) show a block diagram illustration of an exemplary
embodiment of a control method as disclosed herein.
Detailed Description of the Invention
[0014] Referring initially to FIGS. 1 and 2 of the drawing, there are depicted
exemplary embodiments of transport refrigeration systems for cooling the
atmosphere within the cargo box of a truck, trailer, container, intermodal container
or similar cargo transport unit. The transport refrigeration system 10 includes a
transport refrigeration unit 12 including a compressor 14, a refrigerant condenser
heat exchanger 16, an expansion device 18, a refrigerant evaporator heat exchanger
20 and a suction modulation valve 22 connected in a closed loop refrigerant circuit
including refrigerant lines 24,26 and 28 and arranged in a conventional refrigeration
cycle. The transport refrigeration system 10 further includes an electronic system
controller 30, a diesel engine 32 and an engine controller 34. The transport
refrigeration system 10 is mounted as in conventional practice to an exterior wall of
the truck, trailer or container with the compressor 14 and the condenser heat
exchanger 16 with its associated condenser fan(s) (not shown) and diesel engine 32
disposed externally of the refrigerated cargo box.
[0015] As in conventional practice, when the transport refrigerant unit 12 is
operating in a cooling mode, low temperature, low pressure refrigerant vapor is
compressed by the compressor 14 to a high pressure, high temperature refrigerant
vapor and passed from the discharge outlet of the compressor 14 into refrigerant line
24. The refrigerant circulates through the refrigerant circuit via refrigerant line 24 to
and through the heat exchange tube coil or tube bank of the condenser heat
exchanger 16, wherein the refrigerant vapor condenses to a liquid, thence through
the receiver 36, which provides storage for excess liquid refrigerant, and thence
through the subcooler coil 38 of the condenser. The subcooled liquid refrigerant
then passes through refrigerant line 24 through a first refrigerant pass of the
refrigerant-to-refrigerant heat exchanger 40, and thence traverses the expansion
device 18 before passing through the evaporator heat exchanger 20. In traversing
the expansion device 18, which may be an electronic expansion valve ("EXV") as
depicted in FIG. 1 or a mechanical thermostatic expansion valve ("TXV") as
depicted in FIG. 2, the liquid refrigerant is expanded to a lower temperature and
lower pressure prior to passing to the evaporator heat exchanger 20.
[0016] In flowing through the heat exchange tube coil or tube bank of the
evaporator heat exchanger 20, the refrigerant evaporates, and is typically
superheated, as it passes in heat exchange relationship return air drawn from the
cargo box passing through the airside pass of the evaporator heat exchanger 20. The
refrigerant vapor thence passes through refrigerant line 26 to the suction inlet of the
compressor 14. In passing through refrigerant line 26, the refrigerant vapor
traverses a second refrigerant pass of the refrigerant-to-refrigerant heat exchanger 40
in heat exchange relationship with the liquid refrigerant passing through the first
refrigerant pass thereof. Before entering the suction inlet of the compressor 14, the
refrigerant vapor passes through the suction modulation valve 22 disposed in
refrigerant line 26 downstream with respect to refrigerant flow of the refrigerant-torefrigerant
heat exchanger 40 and upstream with respect to refrigerant flow of the
compressor 14. The controller 30 controls operation of the suction modulation valve
22 and selectively modulates the open flow area through the suction modulation
valve 22 so as to regulate the flow of refrigerant passing through the suction
modulation valve to the suction inlet of the compressor 14. By selectively reducing
the open flow area through the suction modulation valve 22, the controller 30 can
selectively restrict the flow of refrigerant vapor supplied to the compressor 14,
thereby reducing the capacity output of the transport refrigeration unit 12 and in turn
reducing the power demand imposed on the engine 32.
[0017] Air drawn from within the cargo box by the evaporator fan(s) (not
shown) associated with the evaporator heat exchanger 20, is passed over the external
heat transfer surface of the heat exchange tube coil or tube bank of the evaporator
heat exchanger 20 and circulated back into the interior space of the cargo box. The
air drawn from the cargo box is referred to as "return air" and the air circulated back
to the cargo box is referred to as "supply air". It is to be understood that the term
"air' as used herein includes mixtures of air and other gases, such as for example,
but not limited to nitrogen or carbon dioxide, sometimes introduced into a
refrigerated cargo box for transport of perishable product such as produce.
[0018] Although the particular type of evaporator heat exchanger 20 used is
not limiting of the invention, the evaporator heat exchanger 20 may, for example,
comprise one or more heat exchange tube coils, as depicted in the drawing, or one or
more tube banks formed of a plurality of tubes extending between respective inlet
and outlet manifolds. The tubes may be round tubes or flat tubes and may be finned
or un-finned.
[0019] The compressor 14 may comprise a single-stage or multiple-stage
compressor such as, for example, a reciprocating compressor as depicted in the
exemplary embodiments shown in FIGS. 1 and 2. However, the compressor 14 may
be a scroll compressor or other type of compressor as the particular type of
compressor used is not germane to or limiting of the invention. In the exemplary
embodiment depicted in Fig. 1, the compressor 14 comprises a reciprocating
compressor having a compressing mechanism, an internal electric compressor motor
and an interconnecting drive shaft that are all sealed within a common housing of
the compressor 14. The diesel engine 32 drives an electric generator 42 that
generates electrical power for driving the compressor motor which in turn drives the
compression mechanism of the compressor 14. The drive shaft of the diesel engine
drives the generator shaft. In an electrically powered embodiment of the transport
refrigeration unit 10, the generator 42 comprises a single on-board engine driven
synchronous generator configured to selectively produce at least one AC voltage at
one or more frequencies. In the embodiment depicted in FIG. 2, the compressor 14
comprises a reciprocating compressor having a compressing mechanism having
shaft driven directly by the drive shaft of the diesel engine 32, either through a direct
mechanical coupling or through a belt drive 38 as illustrated in FIG. 2.
[0020] As noted previously, the transport refrigeration system 10 also
includes an electronic controller 30 that is configured to operate the transport
refrigeration unit 12 to maintain a predetermined thermal environment within the
interior space defined within the cargo box wherein the product is stored during
transport. The controller 30 maintains the predetermined thermal environment
selectively powering the various components of the refrigerant vapor compression
system, including the compressor 14, the condenser fan(s) associated with the
condenser heat exchanger 16, the evaporator fan(s) associated with the evaporator
heat exchanger 20, and various valves in the refrigerant circuit, including but not
limited to the suction modulation valve 22. The controller 30 also controls the
operation of the compressor 14 to selectively varying the output capacity of the
compressor 14 to match the cooling demand to maintain the desired product storage
temperature for the particular products stored within the refrigerated cargo box.
[0021] In one embodiment, the electronic controller 30 includes a
microprocessor and an associated memory. The memory of the controller 30 may be
programmed to contain preselected operator or owner desired values for various
operating parameters within the system. The controller 30 may include a
microprocessor board that includes the microprocessor, an associated memory, and
an inputloutput board that contains an analog-to-digital converter which receives
temperature inputs and pressure inputs from a plurality of sensors located at various
points throughout the refrigerant circuit and the refrigerated cargo box, current
inputs, voltage inputs, and humidity levels. The inputloutput board may also include
drive circuits or field effect transistors and relays which receive signals or current
from the controller 30 and in turn control various external or peripheral devices
associated with the transport refrigeration system. The particular type and design of
the electronic controller 30 is within the discretion of one of ordinary skill in the art
to select and is not limiting of the invention.
[0022] The system controller 30 is also in communication with the electronic
engine controller 34. For example, the system controller 30 may be in closed loop
communication with the electronic engine controller 34 by way of a controller area
network (CAN) system. The system controller 30 determines the operating load
state of the engine 32 based on input received from the electronic engine controller
34. For example, in an embodiment, the electronic engine controller 34 senses the
position of the mechanical fuel rack, which essentially represents a fuel throttle
position, and is indicative of the level of fuel flow being supplied to the engine 32
relative to the maximum permissible fuel flow fuel, which is indicative of the
operating engine load relative to the maximum operating engine load. The
electronic engine controller 34 also senses the operating engine speed, that is engine
revolutions per minute (RPM), of the engine 32 in real time. The system controller
30 monitors both the fuel rack position and the operating engine speed through
interrogation of the electronic engine controller 34. For example, in an embodiment,
the electronic engine controller 34 may detect the fuel rack position and the
operating engine speed (RPM) at one second intervals, and the system controller 30
may determine engine load based on a running average of the past thirty seconds of
readings for both fuel rack position. Engine operating speed (RPM) may also be
based on a running average of RPM measurements taken over a time interval, for
example the past thirty seconds.
[0023] In accordance with an aspect of the disclosure, the system controller
30 optimizes the performance of the transport refrigeration system 10 by matching
the capacity output of the transport refrigeration unit 12 to an available shaft power
of the diesel engine, which equates to matching the power demand of the refrigerant
unit 12 to an available shaft horsepower of the diesel engine 32. By doing so,
enhanced fuel economy and improved system capacity control can be realized.
Additionally, engine output can be maximized while avoiding engine overload and
engine stalls. Controlling the power consumption of the transport refrigeration
system can also permit a smaller engine, that is an engine having a lower maximum
available shaft power, to be used. By monitoring both the fuel rack position and the
operating engine speed, the system controller determines the real time operating load
state of the engine 32 and can adjust the capacity output of the transport refrigeration
unit 12 to match the available shaft power of the engine 32 as necessary. For
example, the system controller 30 can adjust the capacity output of the transport
refrigeration unit 12 by selectively adjusting the suction modulation valve (SMV) 22
to adjust the flow of refrigerant vapor to the suction inlet of the compressor 14. The
system controller 30 can also adjust the capacity output of the transport refrigeration
unit 12 by other techniques known in the art such as, but not limited to, unloading
the compressor 14 to reduce the flow of high pressure refrigerant through the
refrigerant circuit, ceasing operation in an economizer mode, throttling the
evaporator expansion valve closed or a combination thereof.
[0024] In determining the operating state of the engine 32, the system
controller 30 analysis the operating fuel rack position, expressed as a percent of the
fuel rack position at a 100% fuel flow setting, and the operating engine speed in
RPM, expressed as a percent of the target engine RPM, which is an indication of
engine RPM droop, that is a drop-off in the real-time operating engine RPM relative
to the target engine RPM. Thus, as used herein, an engine RPM droop of 98%
would mean that the operating engine RPM is two percent below the target engine
RPM. Similarly, an engine RPM droop of greater than 98% would indicate an
operating engine RPM that is less than 2% below the target engine RPM and an
engine RPM droop of less than 98% would indicate an operating engine RPM that is
more than 2% below the engine target RPM. In many applications, the diesel engine
32 may have two operating RPM points, that is a relatively lower RPM for low
speed operation and a relatively higher RPM for high speed operation. In such case,
the target RPM would be selected by the system controller 30 based upon whether
the engine 32 was currently operating in a low speed mode or a high speed mode.
[0025] In an aspect of the method of optimizing the performance of the
transport refrigeration system as disclosed herein, the system controller 30 operates
the transport refrigeration system in a normal operating mode at a capacity output
necessary to meet a current refrigeration demand load so as long as the operating
fuel rack position is not at 100% with the engine operating speed dropping no more
than a few percent, for example dropping no more than two percent (i.e. an engine
RPM droop of no less than 98%). An operating engine RPM of less than 98% of the
target engine RPM could indicate an impending engine stall condition. In the
normal operating mode, the system controller 30 will permit engine speed shifts,
changes in unloader state (onloff), rapid opening or closing of the suction
modulation valve 22, and other normal operations. However, when the fuel rack
position reaches or exceeds 90% and the operating engine RPM simultaneously
drops to 98% of the target engine RPM, the controller 30 unload the compressor 14
and/or close the suction modulation valve 22 to reduce engine load and return the
fuel rack position to less than 85% and raise the operating engine RPM to greater
than 98% of the target engine RPM. Under these conditions the system controller 30
will allow the rate at which the SMV may be further closed to reach its maximum
closing speed. Once the engine load has been reduced, so long as a system change
request is not active, the system controller 30 will limit the maximum opening speed
of the suction modulation valve (SMV) 32, that is the rate at which the SMV may be
further opened, to 0.1 % per second and employ as a control limit logic maintaining
the fuel rack position at less than 90% and maintaining the engine operating RPM
equal to or greater than 98% of the engine target speed.
[0026] If under these conditions wherein the fuel rack position reaches or
exceeds 90% and the operating engine RPM simultaneously drops to 98% of the
target engine RPM, system change is called for, for example a speed shift or a
change in unloader state, the system controller 30 will unload the compressor 14
and/or close the suction modulation valve (SMV) 22 to further reduce the engine
load to bring the fuel rack position to less than 70% and raise the operating engine
RPM to greater than 98% of the target engine RPM. The system controller 30 will
also engage control limit logic and bring the engine operating state to a fuel rack
position of less than 90% and maintain the operating engine RPM at least 98% of
the target RPM, thereby ensuring against an engine stall or engine overload
condition occurring. Once the engine load has been reduced, the system controller
30 will allow the system change request but will limit the maximum opening speed
of the suction modulation valve (SMV) 32, that is the rate at which the SMV may be
further opened, to 0.1% per second and employ as a control limit logic maintaining
the fuel rack position at less than 90% and maintaining the engine operating RPM
equal to or greater than 98% of the engine target speed.
[0027] Referring now to FIG. 3, there is depicted in a process schematic
block diagram illustrating an exemplary embodiment of a method of the disclosure.
At block 300, the controller 30 initiates the process by determining at step 302 both
the operating fuel rack position (Rack) as a percent of the maximum fuel rack
position at 100% fuel flow to the engine 32 and the operating engine speed as a
percent of the maximum engine speed (RPM droop). Both determinations are made
based on real time engine operating data obtained from the electronic engine
controller 34. As explained earlier, both determinations may be running averages
over a selected time interval, such as , for example, the average over a 30 second
running period of individual readings made at one second intervals during that
period. At block 302, a determination is made as to whether the operating fuel rack
position (Rack) is less than 85% and whether the operating engine speed (RPM ) is
at least 98% of the target engine operating speed (RPM droop). If yes to both
conditions, i.e. the operating fuel rack position (Rack) is less than 85% and the
operating engine speed is equal to or greater than 98% of the target engine operating
speed (RPM droop), the controller 30 maintains normal operation (block 3 18) of the
transport refrigeration system 12.
[0028] However, if either one or both of the conditions at block 302 is no,
then the system controller 30, at block 304, determines whether the operating fuel
rack position (Rack) is at or greater than 90% and whether the operating engine
speed is less than 98% of the target engine operating speed (RPM droop). If no to
both conditions, i.e. the operating fuel rack position (Rack) is less than 90% and the
operating engine speed is at least 98% of the target engine operating speed (RPM
droop), the controller 30 maintains normal operation (block 318) of the transport
refrigeration system 12.
[0029] If, at block 304, the controller 30 determines that the operating fuel
rack position (RACK) is at or greater than 90% and the operating engine speed is
less than 98% of the target engine operating speed (RPM droop), the system
controller 30, at block 306, will reduce the cooling output capacity of the
refrigeration unit 12, for example by initiating an unload of the compressor 14 or
closing the suction modulation valve (SMV) 22, to bring the operating fuel rack
position (Rack) to less than 85% and the operating engine speed to at least 98% of
the target engine operating speed (RPM droop). Next, at block 308, the system
controller 30 checks to determine whether a system change request is active. A
system change request could be, for example, for purposes of illustration but not
limitation, a change in engine speed, a compressor unload, or transient condition. If
a change request is not active at block 308, the system controller 30 proceeds
directly to block 312, and restricts the maximum rate of opening of the suction
modulation valve (SMV) 22.to 0.1 percent per second, thereby limiting the rate of
increase in refrigerant vapor flow to the suction inlet of the compressor 14, which in
turn limits a change in capacity output of the transport refrigeration unit 12. At
block 314, the system controller 30 now implements as its control limit logic
maintaining the operating fuel rack position (Rack) to less than 90% and the
operating engine speed at at least 98% of the target engine operating speed (RPM
droop). The system controller 30 will continue to monitor, block 316, the operating
fuel rack position (RACK) and the operating engine speed, and permit normal
operation (block 318) of the refrigeration system, including the refrigeration unit 12,
so long as both the operating fuel rack position (Rack) remains less than 90% and
the operating engine speed is at least 98% of the target engine operating speed (RPM
droop).
[0030] However, if a system change request is active at block 308, the
system controller 30, at block 310, will reduce the cooling output capacity of the
refrigeration unit 12, for example by initiating an unload of the compressor 14 or
closing the suction modulation valve (SMV) 22, to bring the operating fuel rack
position (Rack) to less than 70% and the operating engine speed to at least 98% of
the target engine operating speed (RPM droop). The system controller 30 then
proceeds to block 312 and restricts the maximum rate of opening of the suction
modulation valve (SMV) 22.to 0.1 percent per second, thereby limiting the rate of
increase in refrigerant vapor flow to the suction inlet of the compressor 14, which in
turn limits a change in capacity output of the transport refrigeration unit 12. At
block 314, the system controller 30 now implements as its control limit logic
maintaining the operating fuel rack position (Rack) to less than 90% and the
operating engine speed at at least 98% of the target engine operating speed (RPM
droop). During the period of operation of the refrigerant unit at reduced cooling
capacity and with restriction on the rate of opening of the suction modulation valve
(SMV) 22, the system controller 30 will allow the requested system change occur
with little or no risk of an engine overload or engine stall occurring that would lead
to insufficient shaft horsepower output from the engine 30. Thus, the risk of a
shutdown of the refrigerant system 14 occurring as a result of the system change
being implemented is greatly reduced, if not eliminated.
[0031] Additionally, at block 3 16, the system controller 30 continues to
monitor whether the operating fuel rack position (Rack) is less than 90% and
whether the operating engine speed (RPM) is at least 98% of the target engine
operating speed (RPM droop). If, at block 316, the system controller 30 determines
that the operating engine speed drops below 98% of the target operating engine
speed (RPM droop) or the operating fuel rack position rises above 90%, a system
alarm is activated, at block 320, to warn of a potential impending engine stall or
engine overload.
[0032] The terminology used herein is for the purpose of description, not
limitation. Specific structural and functional details disclosed herein are not to be
interpreted as limiting, but merely as basis for teaching one skilled in the art to
employ the present invention. Those skilled in the art will also recognize the
equivalents that may be substituted for elements described with reference to the
exemplary embodiments disclosed herein without departing from the scope of the
present invention.
[0033] While the present invention has been particularly shown and
described with reference to the exemplary embodiments as illustrated in the
drawing, it will be recognized by those skilled in the art that various modifications
may be made without departing from the spirit and scope of the invention. For
example, in other embodiments, a different indicator of operating engine load, other
than fuel rack position, could be used to monitor the operating engine load, in
combination with operating engine speed in carrying out the concept of the method
disclosed herein.
[0034] Therefore, it is intended that the present disclosure not be limited to
the particular embodiment(s) disclosed as, but that the disclosure will include all
embodiments falling within the scope of the appended claims.
We Claim:
1. A method for optimizing the performance of a transport refrigeration
system having a transport refrigeration unit powered by a diesel engine, comprising
the step of matching a capacity output of the transport refrigeration unit to an
available shaft power of the diesel engine.
2. The method of claim 1 wherein the transport refrigeration unit
includes a compressor having a compression mechanism drive shaft driven by a
shaft of the diesel engine.
3. The method of claim 2 wherein the engine shaft directly drives the
compression mechanism drive shaft.
4. The method of claim 2 wherein the engine shaft drives an electric
generator for generating electrical power to power a compressor drive motor for
driving the compressor.
5. The method of claim 1 further comprising the step of operating the
transport refrigeration system at the capacity output necessary to meet a current
refrigeration demand load so as long as both an operating engine load of the diesel
engine is not at 100% and an operating speed of the diesel engine is at least 98% of a
target engine operating speed..
6. A method for controlling the power consumption of a transport
refrigeration unit having a refrigerant mass flow circulating within a refrigerant
circuit having a refrigerant compressor and having a diesel engine for powering the
transport refrigeration unit, the method comprising the step of selectively limiting
refrigerant mass flow through the refrigerant circuit in response to an operating
engine load on the diesel engine and an operating speed of the diesel engine.
7. The method of claim 6 further comprising the steps of:
monitoring the operating engine load of the diesel engine;
monitoring the operating engine speed of the diesel engine; and
selectively adjusting the refrigerant mass flow through the refrigerant circuit
of the transport refrigeration unit to maintain the operating engine load less than
98% of the maximum operating engine load and to simultaneously maintain the
operating engine speed at a speed of at least 98% of a target engine operating speed.
8. The method as recited in claim 6 further comprising the steps of:
monitoring the operating engine load of the diesel engine;
monitoring the operating engine speed of the diesel engine;
determining whether the monitored operating engine load is less than 90% of
a maximum engine load;
determining whether the monitored engine speed is at a speed of at least 98%
of a maximum engine speed; and
if both the monitored engine operating load is at a position of at least 90% of
a maximum operating engine load and the monitored engine speed is at a speed of at
least 98% of a target engine operating speed, restricting an increase in refrigerant
mass flow through the compressor.
9. The method as recited in claim 8 wherein the refrigerant circuit of the
transport refrigeration unit includes a suction modulation valve and the step
restricting an increase in refrigerant mass flow through the refrigerant circuit
comprises reducing a maximum rate open of the suction modulation valve to 0.1
percent per second.
10. The method of claim 6 wherein the step of selectively limiting
refrigerant mass flow through the refrigerant circuit in response to an operating
engine load of the diesel engine and an operating speed of the diesel engine
comprises the step of limiting refrigerant mass flow through the refrigerant circuit in
response to an operating fuel rack position on the diesel engine and an operating
speed of the diesel engine
11. The method of claim 10 further comprising the steps of:
monitoring the operating fuel rack position for the diesel engine;
monitoring the operating engine speed of the diesel engine; and
selectively adjusting the refrigerant mass flow through the refrigerant circuit
of the transport refrigeration unit to maintain the operating fuel rack position at a
position less than 98% of the maximum fuel rack position and to simultaneously
maintain the operating engine speed at a speed of at least 98% of a maximum engine
operating speed.
12. The method as recited in claim 10 further comprising the steps of:
monitoring the operating fuel rack position for the diesel engine;
monitoring the operating engine speed of the diesel engine;
determining whether the monitored fuel rack position is at a position of at
least 90% of a maximum fuel rack position;
determining whether the monitored engine speed is at a speed of at least 98%
of a maximum engine speed; and
if both the monitored fuel rack position is at a position of at least 90% of a
maximum fuel rack position and the monitored engine speed is at a speed of at least
98% of a target engine operating speed, restricting an increase in refrigerant mass
flow through the compressor.
13. The method as recited in claim 12 wherein the refrigerant circuit of
the transport refrigeration unit includes a suction modulation valve and the step
restricting an increase in refrigerant mass flow through the refrigerant circuit
comprises reducing a maximum rate open of the suction modulation valve to 0.1
percent per second.
14. A method for controlling the operation of a transport refrigeration
unit having a refrigerant mass flow circulating within a refrigerant circuit having a
refrigerant compressor and a compressor suction modulation valve and having a
diesel engine for powering the transport refrigeration unit, the method comprising
the steps of:
determining whether a change in a system operating condition has been
requested; and
if a system operating condition change has been requested, restricting an
increase in refrigerant mass flow by reducing a maximum rate open of the suction
modulation valve to 0.1 percent per second.
15. The method as recited in claim 14 further comprising the steps of:
determining an operating engine load on the diesel engine;
determining whether the operating engine load exceeds 90% of a maximum
operating engine load;
if the operating engine load exceeds 90% of the maximum operating engine
load, reducing the power demand of the refrigerant unit to reduce the operating
engine load on the diesel engine to about 70% of the maximum operating engine
load; and
executing the system change request.
16. The method as recited in claim 15 wherein the step of reducing the
power demand of the refrigeration unit comprises unloading the compressor.
17. The method as recited in claim 15 wherein the step of reducing the
power demand of the refrigeration unit comprises throttling down refrigerant flow
through the suction modulation valve.