Abstract:
A lateral heating or air conditioning unit has an electric heating device downstream of the heater core, spaced from it and in the mouth of the hot passage. Separate blend doors are disposed in each of the hot and cold passages. 
     The electric heater device is flush with the opening of the hot air passageway into the mixing chamber so as to prevent air flow disturbances.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a heating unit for a motor vehicle, and to an air conditioning unit for a motor vehicle. 
     BACKGROUND OF THE INVENTION 
     Heating and air conditioning units for vehicles are commonplace in the art. Two main configurations are used, one being the centre stack configuration and one the lateral configuration. In the centre stack configuration, a heater core is close to transverse an input duct and in the lateral configuration, the heater core is close to parallel to the axis of the input duct. 
     Many such units have an input air duct of a relatively large cross-section. The input air duct has a divider which defines two passageways, one of which contains a heat exchanger receiving engine coolant and the other of which contains no such heat exchanger. The two passageways combine again downstream of the heat exchanger in a mixing space and the air from the mixing space is distributed to different locations in the vehicle. One or more flow control devices is associated with the passageways, for example at the point of division of the input air duct so as to control the proportion of air flowing through the heat exchanger by comparison with the flow of air direct from the input air duct to the mixing space. The flow control devices are usually capable of substantially closing the air passages so that either all air flow in the input duct passes through the heat exchanger or all air flow in the input duct passes through the direct passageway to the mixing space. Intermediate positions allow proportion control. 
     It is possible to use a single door-type flow control device pivoting about the division point of the input air duct so that the door can be selectively across the heat exchange passageway, across the direct passageway or intermediate the two positions. Such single door type arrangements can however make the heating/air conditioning unit unduly large and also affect flow performance. It is alternatively possible to arrange separate doors across each of the passageways; where the doors are centrally pivoted in a butterfly formation, space may be saved. 
     Modern power units may not provide coolant which reaches the high temperatures that were formerly available and would be advantageous in supplying to the heat exchanger discussed above, known hereinafter as a heater core. Another problem arises during the warm up period of the power unit as during this time the coolant may provide little or no heating effect in the heater core. 
     It has therefore been proposed to additionally provide an electric heating device in the heating unit, this typically being a positive temperature coefficient (PTC) heating device. 
     Inclusion of such heating devices has a disadvantage in that it may adversely affect the flow of air through the heater core, and may also substantially increase the space occupied by the heating unit. 
     Object of the Invention 
     It is therefore an object of the present invention to address the difficulties of the prior art. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention there is provided a vehicle heating device comprising an inlet duct, and first and second passageways, said first and second passageways extending laterally from said inlet duct to a common mixing zone, a heater core, said heater core being disposed in the first passageway, said heater core being substantially laterally disposed with respect to said inlet duct, said first passageway having a mouth defined by two opposing wall portions, said mouth entering the common mixing zone, an electric heater disposed across said mouth and spaced from said heater core, a first blend door disposed in said first passageway, and a second blend door disposed in said second passageway. 
     Advantageously said electric heater has a first face disposed proximate said heater core and second face disposed remote from said heater core, said second face being substantially flush with said mouth and wherein an air flow in said second passage is substantially parallel to said second face. 
     Conveniently the device further comprises control devices for moving the blend doors between fully closed positions in which each blend door closes its respective passageway and fully opened positions in which each blend door is substantially aligned with the respective passageway. 
     Conveniently each blend door comprises two opposed wings mutually disposed at an obtuse angle to provide direction of air flow when the respective door is fully open. 
     Preferably the device further comprises an evaporator, said evaporator being disposed in said inlet duct to provide an air conditioning device. 
     Advantageously the device further comprises a flow separating device disposed in said inlet duct, whereby said inlet divides into first and second passageways. 
     Conveniently an extremity of said flow separating device forms one of said wall portions defining said mouth. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
     FIG. 1 shows a schematic cross-sectional view through a heating or air conditioning device in accordance with the invention, in a fully hot position. 
     FIG. 2 shows a view similar to that of FIG. 1 but with the device in the fully closed position. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the various figures, like reference numerals refer to like parts. 
     Referring first to FIG. 1, an air conditioning unit  1  has an input blower  2  of the centrifugal type, with a fan wheel  3  and providing an outlet  4 . The outlet  4  is in connection with a mouth of air inlet duct  10 , defined in part by a first wall portion  11  and an opposing second wall portion  12 . At the opening of the mouth of the duct  10  is a filter  15  followed by a evaporator  16 . 
     As known to those skilled in the art, the evaporator  16  is supplied with a cooling fluid whereby air downstream of the evaporator is cooled. 
     The device described here is an air conditioning unit, hence the evaporator. Those skilled in the art will realise that omission of the evaporator would instead provide a heating/ventilation unit due to the absence of the ability to cool. 
     The first and second wall portions  11 ,  12  are, as shown in FIG. 1, substantially parallel in the mouth region of the inlet duct  10 . However, upper, as shown in FIG. 1, wall portion  11  passes via a transition curve into a straight region  20  which tapers inward to a point  21  substantially on the axis A of the mouth region of the inlet duct  10 . The lower, as shown in FIG. 1, wall portion  12  also has a transition curve downwardly, diverging from the axis A before gently curving back to a straight region  22  substantially parallel to the axis A. 
     From the point  21 , the first wall portion makes a sharp transition to a portion  26  directed generally at right angles to the axis A before turning sharply back to a return portion  23  directed towards a lower edge, as shown, of the evaporator  16 . At the end  27  of the return portion, the first wall portion turns sharply back on itself to an outlet region  24  generally parallel to axis A. 
     A flow separating wall  30  is disposed within the air inlet duct  10 . The flow separating wall has a first extremity  31  which is slightly above the axis A and defines a shape which is generally convex towards the mouth of the air inlet duct  10 , passing from a point  32  nearest to the mouth and disposed on the axis A via a flow-directing region  33  to a second extremity  34 . The second extremity  34  is spaced from the innermost extremity  27  of the return portion  23  to define a mouth for housing an electric heating device  40 , such as a PTC heating device. The first extremity  31  of the flow separating wall  30  and the point  21  on the first wall portion  11  define a spacing receiving a heater bore  50 . As will be seen in FIG. 1, the heater core and the electric heating device are substantially parallel to one another and spaced apart. The electric heating device is substantially symmetrical about the axis of the heater core  50  with the straight return potion  23  and an inner wall  35  of the flow separating wall  30  defining a funnel-shaped air guide for air which passes through the heater core into and through the electric heating device  40 . 
     The outlet region  24  defines, with the straight region  22  of the said second wall portion, an outlet duct  25 . 
     A first butterfly-type door  51  is disposed between the first extremity  31  of the flow separating wall  30  and the first wall portion  12 . The first butterfly door has a central pivot  52  and two opposed shutter portions  53  dimensioned such that when the butterfly door  51  is in a first orientation the shutter portions abut respectively the first extremity  31  and the first wall portion  11 . The first wall portion has a stop  54  for the first door. The two shutter portions are not diametrically opposed but instead are disposed at an angle of about 160° so as to provide an air guide effect when the first butterfly door is in its open position, as shown in FIG.  1 . 
     Disposed between the flow directing region  33  of the flow separating wall  30  and the second wall portion  12  is a second butterfly door  61  having a central pivot  62  and two opposed shutter portions  63 . The shutter portions  63  are likewise disposed at an angle of around 160°. The second butterfly door  61 , as shown in FIG. 1 has a first orientation in which it substantially sealingly abuts the flow separating wall  30  and the second wall portion  12 . The second wall portion  12  has a stop  64  for the second door. The doors have associated control means to rotate them each clockwise by substantially 90° to the position shown in FIG.  2 . In these positions it will be seen that the obtuse angle defined by the two shutter portions  63  of the second door forms a flow guide for air, whereas the first door  51  is closed. 
     As will be understood by those skilled in the art, the device of the invention is a lateral system, in which the heater core is substantially aligned with the axis A. As shown in FIG. 1, when the first butterfly door is in the fully open position, an air flow  70  from the evaporator  16  has a generally smooth path between the inlet duct  10  and the outlet duct  25 . In the heater area air passes smoothly into the input of the heater core  50 , through the heater core  50  and then via the transition region of the space between the heater core and the parallel electric heating device, is concentrated into the electric heating device before passing out into the mixing space. 
     Referring now to FIG. 2, it will be seen that the first butterfly door  51  has been rotated by about 90° to abut the first wall portion  11  and also the first extremity  31  of the flow separating wall  30 . The second butterfly door is rotated to the fully open position and provides a generally smooth flow  71  between the air inlet duct  10  and the outlet duct  25 . It will be seen that the downstream face  41  of the electric heating device  40  is disposed so as to be generally flush with the mouth, thus it is collinear with the flow directing region  33  of the flow separating wall  30 , and the outlet region  24 . This ensures that no disturbance to air flow occurs due to additional turbulence and the like. The presence of the electric heating device  40  prevents the cool air in the air inlet duct from coming into contact with the heater core  50 . Specifically, the heater core  50  provides a number of generally parallel passageways between its fins  42  and the spacing between these fins is small by comparison with the spacing between the downstream face  41  of the electric heating device and the downstream face  51  of the heater core  50 . As a result, any turbulent effects in the spacing between the fins will not reach the heater core, thus effectively preventing pickup of heat from the heater core. 
     The particular embodiment shown has the electric heating device disposed parallel to the heater core. However it has been found that a deviation of plus or minus 15 degrees provides good flow properties. 
     The embodiment also uses butterfly doors, but other configurations such as shutters, flag doors, barrel doors or film doors can be used.