Rate of change temperature control for transport refrigeration systems
First Claim
1. A method of controlling the load temperature of a transport refrigeration system to a selected set point temperature, by operating modes which include a high capacity cooling mode and a lower capacity cooling mode, comprising the steps of:
- switching between the higher capacity cooling mode and the lower capacity cooling mode at predetermined load temperatures relative to set point,starting a timer having a programmable time-out period when the operating mode changes to the lower capacity cooling mode,monitoring the load temperature relative to set point during the lower capacity cooling mode,programming the time-out period of the timer in response to predetermined differences between the load temperature and set point, with the length of the time-out period varying indirectly with the magnitude of the predetermined difference temperature,said monitoring step including the step of providing a control signal when set point is not reached within a period of time after entering the lower capacity cooling mode which is a function of time and load temperature relative to set point, and to the programmed time-out period of the timer,and forcing a change from the lower capacity cooling mode to the higher capacity cooling mode in response to said control signal.
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Abstract
Methods and apparatus for controlling the load temperature of a transport refrigeration system to a selected set point temperature by operating modes which include a high capacity cooling mode and a lower capacity cooling mode. The rate of change of the load temperature is monitored by time and temperature integration when the lower capacity cooling mode is entered, to insure that the lower capacity cooling mode has adequate capacity to reduce the load temperature to set point within an acceptable period of time. If the set point temperature is not reached within a period of time which is a function of time, load temperature relative to set point, and the rate of change of load temperature relative to set point, a signal is provided which forces the system to the higher capacity cooling mode until the set point temperature is reached.
76 Citations
9 Claims
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1. A method of controlling the load temperature of a transport refrigeration system to a selected set point temperature, by operating modes which include a high capacity cooling mode and a lower capacity cooling mode, comprising the steps of:
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switching between the higher capacity cooling mode and the lower capacity cooling mode at predetermined load temperatures relative to set point, starting a timer having a programmable time-out period when the operating mode changes to the lower capacity cooling mode, monitoring the load temperature relative to set point during the lower capacity cooling mode, programming the time-out period of the timer in response to predetermined differences between the load temperature and set point, with the length of the time-out period varying indirectly with the magnitude of the predetermined difference temperature, said monitoring step including the step of providing a control signal when set point is not reached within a period of time after entering the lower capacity cooling mode which is a function of time and load temperature relative to set point, and to the programmed time-out period of the timer, and forcing a change from the lower capacity cooling mode to the higher capacity cooling mode in response to said control signal. - View Dependent Claims (2, 3, 4, 5, 7)
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6. The method of claim 6 including the steps of successively setting the time-out periods of the timer to the second, first and third values in response to a rising temperature in which the timer starting step started the timer in response to the lower capacity cooling mode being entered from the set point.
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8. Rate-of-change control apparatus for monitoring and controlling the load temperature of a transport refrigeration system having different capacity cooling modes, to insure that operation at a lower capacity cooling mode is adequate to reduce the load temperature to a selected set point temperature within an acceptable period of time, comprising:
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timer means having a programmable time-out period, means activating said timer means when a predetermined lower capacity cooling mode is entered, means programming the time-out period of said timer means to provide different time-out periods in predetermined different temperature bands above set point, with the time-out period of each temperature band being responsive to the location of the temperature band relative to set point, increasing as the temperature bands become closer to set point, and means responsive to the timing out of the timer means for switching the transport refrigeration system from the lower capacity cooling mode to the high capacity cooling mode. - View Dependent Claims (9)
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Specification