Abstract:
A heating/cooling control system that can effectively control the temperature of the air discharged at the rear interior of the motor vehicle. The heating/cooling control system includes a front control and a rear control. The front control is capable of operating within a predetermined temperature range. The temperature range of the rear control is determined by the set point of the front control.

Description:
TECHNICAL FIELD OF THE INVENTION 
     This invention relates to a Heat Ventilation and Air Conditioning (HVAC) system installed in a motor vehicle. More specifically, this invention relates to a control strategy for controlling temperature of the air discharged at the rear of the motor vehicle. 
     BACKGROUND OF THE INVENTION 
     Typically in today&#39;s HVAC system installed in motor vehicles, controls are provided for controlling the front climate control and the rear climate control. However, the current technology for rear temperature control from the front control normally utilizes slide lever controls or rotary knobs, which allows for infinite temperature selection over a wide range. 
     The current problems associated with using rocker or push buttons to control the temperature of the rear climate control system from the front climate control is that the temperature change that corresponds to one increment of the rocker button selection is very large due to the large operating range of the HVAC system and limited indicators directed by styling. To achieve appropriate indication to the customer regarding temperature selection over the entire operating range would require a large amount of displays, these solutions are costly and may be difficult to package. For example, typical discharge air temperature range of the rear climate control system is 120° F. (160° F. to 40° F.). Typically the number of LED indicators allowed is limited by styling direction and cost. For example if the styling dictates five LED buttons, the temperature gradient per LED (assumed evenly distributed and one LED per button push) is 120° F./5=24° F. As seen, this temperature gradient per button push is much too large to achieve occupant comfort. 
     Therefore, there is a need in the industry to control the rear climate control system such that the temperature gradient of the rear system has smaller increments. 
     SUMMARY OF THE INVENTION 
     In accordance with the preferred embodiment of the present invention, a control strategy for controlling the temperature of the rear climate control system is disclosed. Preferably, the temperature range of the rear system is controlled by the front control system set point. 
     Preferably, the temperature selected in the front control system determines the selectable temperature range of the air discharged from the rear control system. According to the preferred embodiment, the temperature of the front system is set as the median temperature of the rear control system. Therefore, any temperature range of the rear control system is measured from the set point of the front control system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features of the invention will become apparent from the following discussion and the accompanying drawings in which: 
     FIG. 1 is a front view of the instrument panel as installed in a motor vehicle in accordance with the teachings of the present invention; 
     FIG. 2 is a view of the HVAC system having the front air flow system installed in a motor vehicle in accordance with the teachings of the present invention; 
     FIG. 3 is a view of the HVAC system having the rear air flow system installed in a motor vehicle in accordance with the teachings of the present invention; and 
     FIG. 4 is a flow chart representation of the control strategy of the rear control system in accordance with the teachings of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention or its application or uses. 
     Referring in particular to the drawings, an instrument panel incorporating the temperature control strategy of the present is shown and designated by reference numeral  10 . 
     As shown in FIG. 1, the instrument panel  10  is installed in the interior  21  of a motor vehicle and includes a steering wheel  12 , a glove compartment  14 , an audio system  16 , an HVAC system (not shown in FIG.  1 ), controlling inputs  20  and front vents  44  for discharging air into the interior  21  of the motor vehicle  21 . 
     As shown in FIG.  2  and will be explained in details later, the controlling inputs  20 , include a rocker button  24  and a display unit  26  that display the temperature selected. Although in the drawings LED indicators are shown as the display unit  26  it must be understood that the display units  26  are not limited to this form. The controlling inputs  20  provide controls to regulate the temperature of the air discharged into the interior  21  of the motor vehicle and can be operated by the front occupants (driver and the front passenger) of the motor vehicle. 
     Referring in particular to FIG. 2, an HVAC system is generally shown and represented by reference numeral  18 . Preferably, the HVAC system  18  of the present invention is a combination HVAC system that can both heat and cool the interior  21  of the motor vehicle. The HVAC system  18  includes a front air flow system  28  to control the flow of the air into front interior of the vehicle  21 , and a rear air flow system  61  (as shown in FIG. 3) to control the flow of the air into rear interior of the vehicle  21 . The HVAC system  18  also includes a fluid transport and heat exchanger system  30  that acts as a transfer medium for heat energy and a system for a controlling inputs  20 . 
     The front air flow system  28  includes a duct  32  that provides the air into the interior of the motor vehicle  21 . Further, it also includes a blower  34  for introducing air into the duct  32 , a re-circulation door  36  for controlling the proportion of the fresh air to the re-circulated air and a set of duct vents  38  for discharging air into the passenger compartment. The duct vents  38  include a defrost vent  40  for directing air towards the windshield  42  (shown in FIG.  1 ), a front vent  44  for directing the air towards the front occupants in a motor vehicle, and a floor vent  46  for directing air towards the feet of the occupants of the motor vehicle. 
     As shown in FIG. 3, the rear air flow system  61  includes a duct  62  that provides interior vehicle air into the rear HVAC system. Further, it also includes a blower  63  for introducing air into the duct  62 , and a set of duct vents  64  for discharging air into the passenger compartment. The duct vents  64  include an upper vent  65  for directing air towards the occupants face level and a lower vent  66  for directing air towards the occupants feet. 
     The controlling inputs  20  on the instrument panel  10  are connected to a front control  50  that controls the temperature of the air discharged from the front air control system  28  and a rear control  52  that controls the temperature of the air discharged from the rear air control system  61 . As will be explained later, the temperature range of the rear control is always controlled by the temperature of the front control. 
     As shown in FIG. 2, the fluid transport and heat exchanger system  30  is operable in a heating mode and a cooling mode and includes a compressor  54 , a switch  56  for controlling the operation of the compressor  54 , an internal heat exchanger  58  for transferring energy between the refrigerant and the air flowing into the interior of the motor vehicle  21 . In addition the fluid transport and heat exchanger system  30  also includes an external heat exchanger  60  for interfacing with the outside environment. 
     As explained above the HVAC system  18  is connected to a microprocessor (not shown) that typically regulates the temperature of the air discharged through the front vents  44  and the rear vents  64 . In accordance with the teachings of the present invention and as shown in FIG. 3, the front seat occupants can select a particular temperature for the rear seat occupants by pressing the rocker buttons  24 . The temperature selected as the set point temperature by the front control  50  (or driver in a dual zone system) is determined to be the reference point for setting the temperature range of the rear control  52 . Therefore, the temperature range over which the rear control  52  can be operated is a subset of the temperature range of the front control  50 , wherein the temperature of the rear control  52  can either be increased or decreased from the temperature set point of the front control  50 . Since the temperature range of the rear control  52  is now a subset of the overall range, the temperature gradient associated with an incremental button push can be reduced, therefore rear occupant comfort level can be more readily achieved. 
     With reference to FIG. 4, if the front control is selected to a set point of 70° F. The median rear temperature would be the same 70° F. The front control  50  has the ability to increase or decrease the set point of the rear control  52  referenced from the front set point. If the front control  50  selected a set point of 75° F., the median temperature for the rear control  52  would change to 75° F. and the actual discharge temperature would change since the median reference changed. 
     In order to explain how the rear control  52  reference point is set by the front control  50 , 3 different examples are presented. These examples are only to illustrate the point and are in no way limiting the present invention. In Case  1  let us assume that the front control selected the extreme cold set point (i.e. 60° F.). In Case  2  let us assume that the front control temperature set point is 72° F. and in Case  3  let us assume that the front control is selected at extreme hot set point (i.e. 90° F.). Further, assume that for all the three cases there is a 2° F./increment with 4 total increments. This implies a subset temperature range of +/−8° F. In the first case since the front control is selected at the extreme cold set point (i.e. 60° F.) the rear system reference would change to the low end and therefore the temperature of the rear control can only be increased from this reference point. Therefore the temperature range of the rear control is 60° F. to 68° F. Similarly, in the second case, since the front control set point is the median reference point of the rear control, and the temperature can be increased or decreased from this reference point. Therefore, the temperature range of the rear control is 68° F. to 76° F. On the other hand, in Case three where the front control is selected at extreme hot set point (i.e. 90° F.) the rear system reference would change to the high end and therefore the temperature of the rear control can only be decreased from this reference point. This implies a subset temperature range of −8° F., therefore the temperature range of the rear control is 82° F. to 90° F. Therefore the temperature range of the rear control is 82° F. to 90° F. 
     As explained above, the button logic and the temperature gradient associated per push button can be easily changed through software logic. For example, in the above cases, if it is desired that the temperature gradient desired 3° F. instead of 2° F., or some proportional change per step, merely changing the software logic can do this. 
     As any person skilled in the art will recognize from the previous description and from the figures and claims, modifications and changes can be made to the preferred embodiment of the invention without departing from the scope of the invention as defined in the following claims.