Air-conditioning system for motor vehicles

An air-conditioning system for motor vehicles having an evaporator and a heat exchanger arranged successively in the air flow. A separate air duct having an air outlet opening for the central jet, is connected on the one hand via a cold-air opening to an air-chamber upstream of the heat exchanger and, on the other hand, via a hot-air opening to an air chamber downstream of the heat exchanger. The cross-section of the bypass openings can be controlled by bypass flaps which are coupled with actuators. A control unit with stored characteristics is provided which indicate the correlation between the air quantity and air temperature of the air issuing at the central jet and the position of the bypass flaps. The control unit applies actuation values to the actuators, which actuation values effect a setting of the bypass flaps redetermined by characteristics for a preselected air quantity and air temperature.

BACKGROUND AND SUMMARY OF INVENTION 
The present invention relates to an air-conditioning system for vehicles, 
in particular passenger cars. 
In a known air-conditioning system of this type (W. Frank and H.-D. 
Oe.beta. "Mehr Klimakomfort im Personenwagen" [More Climatic Comfort in 
the Passenger Car], special publication from ATZ, Automobiltechnische 
Zeitschrift [Automotive Journal] No. 9/1987, p. 4, FIG. 2), 
temperature-controlled air is fed to the central plane of the passenger 
compartment by a central jet arranged in the dashboard in a so-called 
reheat operation. In a reheat operation, the air taken in is first cooled 
by the evaporator and thus dehumidified and then heated to the desired 
temperature in the heat exchanger. The air quantity fed to the passenger 
compartment is controlled by a shut-off flap at the air outlet opening for 
the central jet, which shut-off flap throttles the air flow to a greater 
or lesser extent, dependent on its position. In the operation mode 
"maximum cooling", cold air is additionally drawn off via the cold-air 
flap, also called the draw-off flap, from the space downstream of the 
evaporator or upstream of the heat exchanger, and fed to the passenger 
compartment via the air duct. In contrast, in heating operation, the air 
outlet is shut off via the central jet since the air--by virtue of the 
concept--is either too cold (less than approx. 5.degree. C.) or very hot 
(more than 40.degree. C.). 
In a further air-conditioned system know from the same literature reference 
(p. 5, illustration 5), the hot-air flap has been omitted and the cold-air 
flap has the function of an air-mixing flap, by means of which cold air is 
mixed in with the hot air flowing into the air duct from the hot-air 
opening in order to achieve the desired air temperature. By a shut-off 
valve at the air outlet opening for the central jet, the desired air 
quantity is, in turn, set infinitely variably by lesser or greater 
throttling. In this air-conditioning system, various pressure conditions 
can arise in the air-conditioning box due to the throttling of the mixed 
air at the air outlet opening of the central jet, thereby leading to 
reverse flows; that is, cold air in the direction downstream of the heat 
exchanger, with the result that then undesirably cold air also issues from 
the air outlet openings located downstream of the heat exchanger for 
defroster, lateral and foot-room jets. This can only be avoided by 
additional return flaps at the cold-air and hot-air openings. 
The object of the present invention is to provide an improved 
air-conditioning system in which temperature control and metering of the 
air issuing from the central jet is possible with relatively small 
construction expenditure. 
This object is achieved in the air-conditioning system according to the 
invention, by a departure from the principle generally used in 
air-conditioning systems of temperature control by mixed-air flaps and 
quantity regulation by a shut-off flap. Instead, each bypass opening 
(hot-air and cold-air openings) is throttled individually. Since no 
further shut-off flap is arranged downstream of the bypass flaps for the 
bypass openings in the air flow direction, in all modes of operation only 
a single flow results in the direction of the passenger compartment. 
Return flaps, as in the air-conditioning system described above, therefore 
are unnecessary. The actuators for the bypass flaps are infinitely 
variable. Vacuum elements with a feedback potentiometer or electric 
stepping motors can be used as actuators. 
A further advantage of the air-conditioning system according to the 
invention also lies in the reduction of noise as the bypass flaps are 
located relatively remotely from the central jet. 
If a capability for separate setting of the air-conditioning on the 
driver's side of the passenger side in the passenger compartment is 
desired (right/left separation), separate bypass flaps for two separate 
central jets, that is to say a total of four bypass flaps, must be 
provided. In the know air-conditioning system described above, in the case 
of a right/left separation, a total of two mixed-air and four return flaps 
as well as two shut-off flaps for the quantity control would be required, 
which means that, in the case of the air-conditioning system according to 
the invention, a considerable savings of costs can be achieved with the 
same comfort. 
Other objects, advantages and novel features of the present invention will 
become apparent from the following detailed description of the invention 
when considered in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE DRAWING 
The air-conditioning system illustrated diagrammatically in longitudinal 
section in FIG. 1 for a motor vehicle has a usually double-flow fan 10, an 
evaporator 11, a heat exchanger 12 and an air distributor 13. The 
components mentioned are arranged in a so-called air-conditioning box 14, 
in the specified sequence with respect to the direction of flow. The 
air-conditioning box 14 projects with its air distributor 13 into the 
passenger compartment 20 of the motor vehicle, and here has air outlet 
openings (not illustrated) which allow air to enter the passenger 
compartment 20 at various points via defroster jets, lateral jets and 
foot-room jets. A first intake opening 15, which is usually provided with 
a filter, allows the fresh air to enter the air-conditioning box 14 while 
so-called circulating air can be taken in from the passenger compartment 
20 via a second intake opening 16. The two intake openings 15, 16 can 
alternately be closed or opened by an air flap 17. At the top side of the 
air-conditioning box 14 above the heat exchanger 12 and air distributor 
13, a separate air duct 18 leads to the passenger compartment 20 and opens 
out there with an air outlet opening 19, on which a central jet 21 is 
placed which integrated in the dashboard of the passenger compartment 20. 
The air duct 18 is connected via a cold-air opening 22 with the chamber 
section 141 of the air-conditioning box 14, which is located between the 
evaporator 11 and the heat exchanger 12, and via hot-air opening 23 with 
the air distributor 13. Each of the two bypass openings 22, 23 can be 
closed by a bypass flap 24 or 25 which can be actuated infinitely variably 
by an actuator 26 or 27. The two actuators 26, 27 are connected to a 
control unit 28 which is connected on the input side to nominal value 
selectors 29, 30. The nominal value selector 29 serves for the selection 
of the air temperature and the nominal value selector 30 for the selection 
of the quantity of the air flowing into the passenger compartment 20 via 
the central jet 21. The nominal value selectors 29, 30 are constructed, 
for example, as potentiometers with an actuation range of 0-5 V, a maximum 
air temperature or air quantity being assigned in each case to the top 
limit. Stored in the control unit 28 are characteristics which indicate 
the correlation between the air quantity and air temperature of the air 
issuing at the central jet 21 and the position of the bypass flaps 24, 25. 
In this case, the control unit 28 operates in such a manner that it 
applies actuation values to the actuators 26, 27, which actuation values 
effect a setting of the bypass flaps 24, 25, determined by the 
characteristics, for the air quantity and temperature by means of the 
nominal value selectors 29, 30. 
An example of the characteristics stored in the control unit 28 is 
illustrated in the diagram according to FIG. 2. The characteristics 
illustrated in dot-dashed lines for the hot-air flap 25 are given by the 
function 
##EQU1## 
and the characteristic illustrated in a uninterrupted line for the 
cold-air flap 24 by the function 
EQU U.sub.K =U.sub.M -U.sub.W (2) 
In these equations, U.sub.W and U.sub.K are the actuation voltages from 
control unit 28 transmitted to the actuators 27 and 26 of hot-air flap 25 
and cold-air flap 24 respectively. U.sub.T is the setting voltage within a 
setting range corresponding to an air temperature T selected by the 
nominal value selector 29. U.sub.M is the setting voltage within the same 
setting range corresponding to an air quantity M selected by the nominal 
value selector 30 and U.sub.max is the actuation voltage for the actuators 
26, 27 to move the bypass flaps 24, 25 into the open end position in which 
the whole cross-section of the cold-air opening 22 and of the hot-air 
opening 23 is open. If, for example, the voltage of U.sub.m =2 V is 
predetermined by means of the nominal value selector 30, which corresponds 
in the case of a setting range of 5 V to a mean air quantity and a voltage 
U.sub.T =4 V is predetermined by means of the nominal value selector 29, 
which corresponds in the case of a setting range of 5 V to a top 
temperature, at a maximum setting voltage U.sub.max =5 V for complete 
opening of the bypass flaps 24, 25 according to equation (1) and equation 
(2), the characteristics of the control unit 28 identified as a and b in 
FIG. 2 are predetermined. With the voltage U.sub.T =4 V the control unit 
28 thus supplies an actuation voltage U.sub.W =1.6 V to the actuator 27 
for the hot-air flap 25 and an actuation voltage U.sub.K =0.4 V to the 
actuator 26 for the cold-air flap 24. The two actuation voltages are 
identified in FIG. 2 on the characteristics a and b by two small circles. 
Corresponding to the actuation values U.sub.W, U.sub.K, the hot-air flap 
25 is opened to such an extent that slightly less than half the air 
passage cross-section of the hot-air opening 23 is exposed while the 
cold-air flap 24 very considerably throttles the cold-air opening 22. The 
sum of the air quantities flowing to the central jet 21 via the two bypass 
openings 22, 23 corresponds to the value determined by means of the 
nominal value selector 30. If, for example, the desire air temperature T 
is decreased by means of the nominal value selector 29, e.g., the voltage 
is set at U.sub.T =2 V, the actuation voltage U.sub.W for the actuator 27 
for the hot-air flap 25 drops to 0.8 V while the actuation voltage U.sub.K 
for the actuator 26 of the cold-air flap 24 rises to 1.2 V. Accordingly, 
the hot-air opening 23 is throttled and the cold opening 22 is opened 
further. With an unchanged setting of the nominal value selector 30 for 
the desired air quantity, namely U.sub.M =2 V, the total air quantity, 
which is composed of the two air flows via the bypass openings 22, 23 and 
which flows into the passenger compartment 20 via the central jet 21, is 
turn unchanged. 
Although the invention has been described and illustrated in detail, it is 
to be clearly understood that the same is by way of illustration and 
example, and is not to be taken by way of limitation. The spirit and scope 
of the present invention are to be limited only by the terms of the 
appended claims.