Abstract:
The blower of an automotive air conditioning unit is energized according to a flexible schedule wherein the maximum and minimum voltages applied to the blower motor are varied in response to a plurality of sensed parameters which influence the environment controlled by the air conditioning unit so that during extremely hot and cold weather suitably powerful energization is realized while during milder weather the energization is limited to avoid unnecessary noise generation.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to an air conditioning unit of the type suitable for use in an automotive vehicle or the like, and more specifically to an improved blower control arrangement therefor. 
     2. Description of the Prior Art 
     In a previously proposed automotive air conditioner it has been arranged that the blower speed be varied according to a preset schedule so that when the temperature difference between the &#34;desired&#34; temperature and the &#34;actual&#34; cabin temperature reduces to a predetermined value, the blower speed is reduced at a given rate until reaching a minimum value. This minimum value is maintained while the above menttioned temperature difference remains within a predetermined narrow range. 
     However, this arrangement has proven only partially effective in that, if the maximum blower speed is selected to appropriately condition the vehicle cabin during extremely hot or cold weather, during milder weather this speed tends to be too high and produce an undesirable amount of noise under such conditions. When the rotational speed of the blower is selected so as to adequately maintain the desired vehicle cabin temperature during the aforementioned mild weather, however, the problem arises that during very hot and cold weather the blower power (especially the minimum power level) tends to be inadequate to maintain the cabin temperature and induces the blower speed to hunt. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the present invention to provide an improved blower control arrangement with which, for any given set of vehicle cabin environmental conditions, the most appropriate blower energization schedule may be derived and implemented. 
     In brief the present invention features an arrangement in which the blower of an air conditioning unit is energized according to a flexible schedule wherein the maximum and minimum voltages applied to the blower motor are varied in response to a plurality of sensed parameters which influence the environment controlled by the air conditioning unit, so that during extremely hot and cold conditions suitably powerful energization is realized while during milder conditions the energization is automatically limited to avoid unnecessary noise generation. 
     More specifically, the present invention takes the form of an air conditioning unit for a vehicle having a cabin, and which comprises: a blower for inducing air to flow through a duct of the air conditioning unit, a heat exchanger associated with the duct and arranged to vary the temperature of the air induced to flow through the duct, a sensor arrangement for sensing at least one parameter affecting the environment of the cabin and outputting an indication thereof, and a control circuit for controlling the energization of the blower according to an energization schedule, an extremum of which is selectively varied in response to the output of the sensor arrangement. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages of the arrangement of the present invention will become more clearly appreciated from the following description taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a schematic representation of a computer controlled air conditioning arrangement adapted for use with an enclosed space such as the passenger cabin of an automotive vehicle or the like; 
     FIG. 2 is a simplified flowchart illustrating the basic procedure followed by the embodiment of the present invention; 
     FIG. 3 is a flowchart showing in more detail the procedure which characterizes the embodiment of the present invention; 
     FIGS. 4 and 5 are graphs showing in terms of the voltage applied to the blower and the temperature difference between the &#34;desired&#34; temperature and the &#34;actual &#34; temperature, the temperature dependent control schedules derived in the program shown in FIG. 3.; 
     FIG. 6 shows a flowchart similar to that shown in FIG. 3, but wherein the minimum energization of the blower is modified in response to the sensed data; and 
     FIG. 7 is a schematic illustration of the functions of the microcomputer carried out in response to the inputted data from the various sensors employed in the various embodiments of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1, shows an air conditioning arrangement to which the present invention may be applied. In this arrangement &#34;air-conditioned air&#34; is discharged into a vehicle cabin 1 or the like by an air conditioning unit generally indicated by the numeral 2. This air conditioning system or unit is, by way of example, the type wherein air may be selectively inducted from the ambient atmosphere surrounding the vehicle or from the cabin 1 per se to be recirculated back thereinto, via a door 3 mounted at or near the upstream end of a duct 4. The duct 4 is as shown, provided with an atmospheric air induction port 5 and a recirculation port 6. The position of the door 3 is controlled by an actuator 7. 
     Located downstream of the door 3 is a fan or blower 8. 
     Located downstream of the blower 8 is a evaporator 9 via which heat may be extracted from the air forced to flow through the duct 4 by the blower 8. 
     Further downstream of the evaporator 9 is a mixing door 10 followed by a heater core 11 through which heated fluid such as engine coolant is circulated in a known manner. 
     As shown, the heater core 11 is disposed in a sub passage 12 of the duct 4 so that the mixing door 10 (under the motive influence of an actuator 13) may be set to vary the fraction of air directed to flow through and/or over the heater core 11 as compared to that fraction which is forced to flow through a sub passage 14. With this arrangement the amount of heat imparted to the air introduced into the cabin may be controlled. 
     In this air conditioning unit the previously mentioned actuators (7, 13) are controlled along with a blower motor actuator 16 by a microcomputer 18 which receives inputs via an analog-digital (A-D) converter 20 from a plurality of sensors including a cabin temperature sensor 22, a sunlight intensity or insolation sensor 26, an outside or ambient air temperature sensor 28 and a sensor which shall be referred to as a &#34;cabin calorific capacity&#34; sensor 29. This latter mentioned sensor is arranged to sense (for example) the number of people in the cabin and/or any sources of heat which will influence the attainment of the &#34;desired&#34; temperature. This sensor may of course include seat switches responsive a person sitting on the seat to which the switch is associated, an infrared radiation detector or the like. Alternatively, in lieu of a sensor per se, a predetermined value may be set into the RAM of the microcomputer 18 in the event that circuit simplification is required. This value may be of the order of 500 calories (merely by way of example). 
     The computer further receives data input from a manually operable terminal 30 disposed in the cabin. This device serves to enable the &#34;desired&#34; or target cabin temperature (T S ) to be inputted by the cabin occupant or occupants to the microcomputer 18. In this instance the terminal is arranged to generate a digital output signal and therefore need not be connected through the A-D converter 20. 
     For convenience, a liquid crystal display 32 or the like may be provided to indicate one or both of the selected &#34;desired&#34; temperature and and actual cabin temperature. 
     FIG. 2 shows a simplified flowchart illustrating the procedure followed by the embodiments of the present invention. As shown, following the START of the program, the various data necessary for calculating the amount of heat which must be added or removed from the cabin in order to obtain the &#34;desired temperature&#34; is read and subsequently processed. After the amount of heat which must be removed (or added) is established, the program proceeds to the determine the most appropriate voltage/temperature schedule with which to energize the blower and then in the last stage proceeds to output commands to implement the aforementioned schedule. 
     FIG. 3 shows in more detail the proceedure set forth in FIG. 2. As shown, following the START of the program the various necessary data are read in stage 101. Then, in stage 102 the program performs a calculation to determine the amount of heat which, in view of the manually selected &#34;desired&#34; temperature (T s ), must be added or subtracted from the cabin. The calculation is carried out using the following equation: 
     
         Q.sub.T =K.sub.1 (T.sub.A -T.sub.S)+K.sub.2 Z+Q.sub.I 
    
     wherein: 
     K 1  and K 2  are constants; 
     Q T  is the amount heat which must be added or removed from the cabin; 
     T A  is the temperature of the air outside the cabin; 
     T S  is the manually selected &#34;desired&#34; temperature; 
     Z is the degree of insolation; and 
     Q I  is the amount of heat produced by various sources within the cabin. 
     In stage 103 the program compares the actual cabin temperature T R  with the desired temperature T S  to ascertain the need to proceed alternatively to step 104 or 105. In the instance that the cabin temperature (T R ) is sensed to be equal to or greater than the desired temperature (T S ) the program will proceed to determine the most appropriate maximum voltage (V MAX ) with which to energize the air conditioner blower in the cooling mode. On the other hand, if the cabin temperature is lower than that required, the program will proceed in step 105, to determine the most appropriate maximum voltage with which to energize the blower in the heating mode. 
     As will apparent to those skilled in the art to which this invention pertains, steps 104 and 105 may be carried out using a simple two dimensional table look up. To this end it is possible to store a table of the nature shown in steps 104 and 105 in the ROM of the microcomputer. When using this table, if the value (Q T ) derived using the above mentioned equation falls (by way of example) between the predetermined values Q TO  and Q TI  then the look up will as shown in chain line, indicate the optimal voltage or V MAX  to be at the illustrated value; viz., in this example lower than the absolute maximum V O . 
     Alternatively, the optimal maximum energization voltage may be derived using a relatively simple program which does not involve a stored table. 
     In stage 106 the data derived in step 104 is utilized along with predetermined data such as the temperature difference range over which it is appropriate to reduce the blower speed (viz., θ O  -θ I ) to establish a new temperature dependent operation schedule. This newly established schedule will operate the blower using the above derived V MAX  voltage until the temperature difference reaches a preset value of θ 1  whereafter the energization of the blower will be gradually decreased until the minimum energization level V O  is reached at a second preset temperature difference of θ O . The energization of the blower motor is maintained at this level until such time as the temperature difference exceeds the θ O  value whereupon the voltage will be gradually increased. 
     Step 107 is deemed essentially the same as step 106 with the exception that it relates to a heating mode, and is considered as such to not require any explantion. 
     In step 108 the schedule determined in step 106 or 107 is implemented. 
     In order to allow for variations which occur in weather and/or time of day, the program is arranged to recycle as shown, so as to periodically establish a new control schedule. For example, if a given schedule is established during a hot summer day, after nightfall the factors affecting the cabin environment will have changed markedly and obviously induce the need for a different control schedule. Of course the program may be arranged so that recycling only occurs at given intervals to avoid overly frequent renewal of the control schedule. 
     FIGS. 4 and 5 show in more detail the temperature dependent shedules derived in steps 106 and 107. As will be appreciated it is advantageous to limit the degree to which the voltage V MAX  can be lowered. Hence, as shown, the the lower limit of V 2  is determined at approximately midway (merely by way of example) between the absolute maximum (V I ) and set minimum (V O ) voltages. This limitation, of course, can be effected in steps 104 and 105. Further as shown, the gradient of the sections interconnecting the maximum and minimum voltage levels (viz., the extrema) varies with the difference therebetween. As previously mentioned, the derivation of this section of the control schedule may be achieved using a simple equation (in program form). 
     FIG. 6 is a flowchart similar to that shown in FIG. 3 but wherein in order to maintain adequately low temperatures in extremely hot environments (for example a desert or the like) or keep the cabin adequately warm in freezing cold conditions, the normal minimum level of blower energization is advantageously raised. The decision as to how much to elevate the minimum voltage V O  is made using a technique similar to that used in deriving the voltage V MAX  in steps 104 and 105. viz., via table look up or by use of a suitable program. 
     FIG. 7 is a schematic illustration showing the operational interconnections between the various sensors, actuators and the microcomputer and which functionally shows the operations which take place within the microcomputer 18. However, it will be apparent that the function blocks shown in this figure, could be replaced with digital and/or analog circuits which would produce the same results, should it be desired to construct such a circuit.