Air heating system of internal combustion engine-mounted motor vehicle

A damper door unit is swingably disposed in an air intake duct for selectively permitting outdoor intake introduction and indoor air introduction. The damper door unit comprises a main door which is swingably connected to the air intake duct to selectively close an outdoor air intake opening and an indoor air intake opening, and an auxiliary door which is swingably connected to the main door to selectively close and open an opening formed in the main door. When of warming of the passenger compartment is required, the main door takes a position to achieve outdoor air introduction. However, under low speed cruising of the vehicle or at standstill of the vehicle with the engine idling, the auxiliary door opens to a certain extent thereby permitting a certain degree of indoor air introduction.

FIELD OF THE INVENTION 
The present invention relates in general to an air heating system of an 
internal combustion engine-mounted motor vehicle for warming air in a 
passsenger or driver compartment of the vehicle, and more particularly to 
such an air heating system which uses as an air heating medium an engine 
cooling water of the internal combustion engine mounted on the vehicle. 
OBJECTS OF THE INVENTION 
It is an object of the present invention to provide an improved air heating 
system for an internal combustion engine-mounted motor vehicle, which 
shows a sufficient heating effect even when the vehicle runs at low speed 
or the vehicle is at a standstill with the engine idling. 
It is another object of the present invention to provide an improved air 
heating system which is constructed to permit introduction of the indoor 
air into a heater unit in addition to introduction of the outdoor air when 
the vehicle runs at low speed or the vehicle is at a standstill with the 
engine idling. 
It is still another object of the present invention to provide an improved 
air heating system which is constructed to assuredly close the outdoor air 
intake opening when the system takes an indoor air recirculation position. 
It is a further object of the present invention to provide an improved air 
heating system which can be constructed by slightly modifying a 
conventionally used air heating system. 
Other objects and advantages of the present invention will become clear 
from the following description when taken in conjunction with the 
accompanying drawings which will be outlined hereinnext.

DESCRIPTION OF PRIOR ART AIR HEATING SYSTEM 
Prior to describing in detail the construction of the motor vehicle air 
heating system of the present invention, outlined explanation of a 
conventionally used air heating system will be made with reference to FIG. 
1 in order to clarify the invention. 
Referring to FIG. 1, there is shown a conventionally used air heating 
system of an internal combustion engine-mounted motor vehicle, which is 
generally designated by reference A. Designated by reference R is a 
passenger compartment of the vehicle in which the heating system A is 
mounted. The heating system A generally comprises an air intake duct 10 
which has at its upper section an outdoor air intake opening 12 and at its 
side section an indoor air intake opening 14. The outdoor air intake 
opening 12 is connected to an air intake grille or a cowl box 16 through 
which surrounding air is introduced into the air intake duct 10. Within 
the duct 10, a damper door 18 is disposed which is operable to swing 
between two rest positions, one rest position being a position to close 
the outdoor air intake opening 12 (as illustrated by phantom lines) and 
the other rest position being a position to close the indoor air intake 
opening 14 (as illustrated by solid lines). Furthermore, within the duct 
10, more particularly within an enlarged portion 20 of the duct 10 is 
mounted an electric fan 22 which produces air flow directing air from the 
air intake duct 10 toward a heater unit 26 which will be explained 
hereinnext. The enlarged portion 20 has an outlet opening 23 which is 
communicated via a flexible tube 24 with a heater unit generally 
designated by numeral 26. The heater unit 26 includes a housing 28 having 
an inlet opening (no numeral) connected to the tube 24 and a plurality of 
outlet openings 30, 32, 34 and 36 from which heated air blows into the 
passenger compartment R. Within the housing 28 are disposed a heater core 
38 and damper doors 40, 42 and 44. Designated by phantom line 46 is a 
defroster tube which leads to lower portions of a front window shield (not 
shown) of the vehicle. The heater core 38 is of a type which uses as an 
air heating medium an engine cooling water which travels in a water jacket 
(not shown) of the engine to cool the engine. 
Under operation of the heating system A, the indoor air intake opening 14 
is kept closed by the damper door 18, permitting the outdoor air intake 
opening 12 to open, so that the outdoor air is forced to come through the 
air intake duct 10 into the heater unit 26 and is heated suitably by the 
heater core 38 before discharging into the passenger compartment R through 
the outlet openings 30, 32, 34 and 36. 
Apart from the above, modernized internal combustion engines for 
automobiles are designed to operate economically even under low speed 
operation of the engines. These engines however encounter a drawback, 
originating from the economization in fuel consumption appearing at the 
low speed operation of the engines, in which upon idling of the engine or 
low speed cruising of the vehicle, the temperature of the engine cooling 
water fails to rise to a level sufficient to normally operate the heater 
core 38 in the heater unit 26. Thus, when, under the low speed operation 
of the engine, the heating system A operates with the outdoor air intake 
opening 12 open, the air travelling through the heater unit 26 is not 
sufficiently heated by the heater core 38 thereby causing a failure in 
heating the passenger compartment at a comfortably heated level. This 
problem appears more markedly when the engine is of the Diesel type. 
The above-mentioned drawback may be solved by positioning the damper door 
18 to close the outdoor air intake opening 12 permitting openings of the 
indoor air intake opening 14. In this condition, the warm air in the 
passenger compartment is recirculated through the heater unit A without 
feeding of the cold outdoor air into the unit A. However in this 
condition, the inner surface of the window shield becomes cloudy by 
increased moisture mainly caused by the presence of passengers in the 
compartment (However, it should be noted that in very cold days, the 
damper door 18 is positioned to completely close the outdoor air intake 
opening 12 for heating the passenger compartment R at the comfortably 
heated level, without respect to the increased moisture in the compartment 
R.). 
As an alternative way to solve the above-mentioned drawback, a measure has 
been also employed in which operation of the damper door 18 is controlled 
by movement of an accelerator pedal of the motor vehicle such that when 
the accelerator pedal is depressed to a certain extent causing relatively 
high speed operation of the engine, the damper door 18 takes a position to 
open the outdoor air intake opening 12 and close the indoor air intake 
opening 14, but when the accelerator pedal is not depressed or only 
slightly depressed causing relatively low speed operation of the engine, 
the damper door 18 takes a position to close the outdoor air intake 
opening 12 and open the indoor air intake opening 14. However, this 
measure causes complicated and bulky construction of the device by which 
the measure is brought into practical use. 
Of course, a measure may be available in which operation of the damper door 
18 is manually controlled by a driver or a passenger in accordance with 
the vehicle running condition. This measure is not practical because of 
complicatedness in handling the damper door 18. 
Accordingly, elimination of the above-mentioned drawbacks encountered in 
the conventional air heating systems is an essential object of the 
invention. 
DESCRIPTION OF THE EMBODIMENT 
Referring to FIGS. 2 to 4, particularly FIG. 2, there is shown an air 
intake section of an air heating system according to the present 
invention. Substantially the same parts as in the case of the 
aforementioned conventional system are designated by the same numerals 
particularly in FIG. 2. 
According to the invention, an improved damper door unit is employed as a 
substitute for the damper door 18 in FIG. 1. As is seen from FIG. 2, the 
unit comprises a main door 48 swingingly connected at its upper section to 
the intake duct 10 by means of a pivot shaft 50. The main door 48 is thus 
operable to swing from one rest position to close the outdoor air intake 
opening 12 to the other rest position to close the indoor air intake 
opening 14. As is best seen in FIG. 3, the main door 48 is provided with 
an auxiliary door 52 thereon. The auxiliary door 52 is swingably connected 
at its upper section to the main door 48 by means of a pivot shaft 54 so 
that the auxiliary door 48 is operable to open or close an opening 56 
formed in the main door 48. For catching the shaft 54 two holders 57 are 
mounted to the main door 48. The auxiliary door 52 is arranged on the 
inside surface of the main door 52 so that when the main door 48 takes the 
position to close the indoor air intake opening 14, the auxiliary door 52 
is swingable within the intake duct 10. As will become clear as the 
description proceeds, the auxiliary door 52 is arranged to open to a 
certain extent by force of intake vacuum which is created in the intake 
duct 10 upon operation of the electric fan 22 when the main door 48 closes 
the indoor air intake opening 56. The opening movement of the auxiliary 
door 52 is made against the weight of the door 52. Thus, by selecting the 
weight of the door 52, the opening degree of the door 52 relative to the 
opening 56 of the main door 48 is suitably determined. Further, as is 
indicated by a phantom line 58, a tension spring may be used for biasing 
the door 52 to take its close position. Such tension spring 58, a spiral 
spring to be mounted about the pivot shaft 54. 
FIGS. 3 and 4 show a detailed construction of the damper door unit. As is 
clearly shown in these drawings, a sealing mat 60 constructed of for 
example a soft rubber film is attached or affixed to the inner surface of 
the main door 48 so that upon closing of the main door 48 relative to the 
outdoor air intake opening 12 of the intake duct 10, assured sealing is 
made between the door 48 and a door seat portion (10a, see FIG. 2) formed 
on the intake duct 10, and upon closing of the auxiliary door 52 relative 
to the opening 56 of the main door 48, assured sealing between these doors 
48 and 52 is also made. Thus, when in a very cold day the damper door unit 
is in a position to close the outdoor air intake opening 12 as is 
indicated by phantom lines in FIG. 2, there occurs no air flow in the 
direction from the outdoor air intake opening 12 to the heater unit 26. 
This induces sufficient heating of air in the passenger compartment R. 
The auxiliary door 52 is provided thereon with a locking arm 62 which is 
operable to lock the auxiliary door 52 in its closing position relative to 
the main door 48. In a hot day season such as in summer when use of the 
air heating system is not required, the damper door unit takes a position 
to close the indoor air intake opening 14, opening the outdoor air intake 
opening 12, and the auxiliary door 52 is locked by the locking arm 62 to 
the main door 48. 
Indicated by numeral 64 in FIG. 3 is a link which leads to a known control 
unit (not shown). By shifting a lever of the control unit in a 
predetermined direction, the link 64 moves in a given direction to swing 
the damper door unit about the shaft 50 permitting the damper door unit to 
take one of the above-mentioned two rest positions. 
The following description is directed to operation of the auxiliary door 52 
of the damper door unit under a condition wherein the electric fan 22 
operates and the damper door unit, more particularly the main door 48, 
takes the position to close the indoor air intake opening 14 as is shown 
in FIG. 2 by solid line, permitting introduction of the outdoor air into 
the heater unit 26 via the outdoor air intake opening 12. 
When the vehicle cruises at relatively low speed or is at standstill with 
the engine idling, which causes insufficient heating of the engine cooling 
water fed to the heater core 38 and causes a wind pressure applied to the 
air intake grille 16 to be small or substantially zero, the operation of 
the electric fan 22 produces a condition wherein the pressure in the 
intake duct 10 is lower than that of the passenger compartment R. Thus, 
the auxiliary door 52 is forced to open against its own weight (or against 
the biasing force of the spring 58) thereby to introduce the indoor air 
into the intake duct 10 for mixing the indoor air with the outdoor air 
which comes from the outdoor air intake opening 12. The mixed air is 
introduced by the electric fan 22 into the heater unit 26 to be heated by 
the heater core 38 and is discharged into the passenger compartment R via 
the outlet openings 30, 32, 34 and 36. It will be appreciated that the 
opening degree of the auxiliary door 52 relative to the opening 56 of the 
main door 48 depends on the pressure difference appearing between the 
intake duct 10 and the passenger compartment R, so that the rotational 
speed of the electric fan 22 and the vehicle speed will determine such 
opening degree. Now, it should be noted that the addition of the indoor 
air to the outdoor air in the air intake duct 10 causes a rise of 
temperature of the air directed to the heater core 38, so that the air 
disharged into the passenger compartment R from the outlet openings of the 
heater unit becomes to have sufficient heat energy to warm up the 
passenger compartment R to a sufficient level. Thus, even when the vehicle 
cruises at low speed or the vehicle is at standstill with the engine 
idling, the temperature in the passenger compartment R is kept at 
sufficient and comfortable level. 
When the vehicle cruises at relatively high speed, causing a wind pressure 
applied to the cowl box 16 to be increased, the pressure in the intake 
duct 10 becomes higher than that in the passenger compartment R even under 
operation of the electric fan 22. In this condition, the auxiliary door 52 
is kept closed by a force generated by pressure difference between the 
intake duct 10 and the passenger compartment R, so that the air directed 
toward the heater core 38 is only the outdoor air coming from the outdoor 
air intake opening 12. However, it should be noted that under high or 
medium speed cruising of the vehicle which causes high or medium speed 
operation of the engine, the heater core 38 is given with as a heating 
medium the engine cooling water which is heated to a sufficient level to 
warm up the cold outdoor air passing through the heater unit 33 to a 
sufficient level. 
From the above description, it will be appreciated that since the cold 
outdoor air is mixed with the warmed indoor air before introduction into 
the heater unit 38 when the heater core 38 is not given with sufficiently 
heated engine cooling water due to low speed operation of the engine, the 
air discharged into the passenger compartment R becomes to have a heat 
energy for warming the compartment R sufficiently. 
Since the air discharged into the passenger compartment R comprises at 
least the outdoor air, the undesired phenomenon in which the inner surface 
of the window shield becomes cloudy is eliminated. 
Further in the invention, since the opening degree of the auxiliary door 52 
relative to the opening 56 of the main door 48 is determined in accordance 
with the vehicle speed, the volume of the indoor air recirculated into the 
heater unit is automatically controlled depending on the vehicle speed. 
More particularly, within the range between the idling speed and the 
medium speed of the engine, the opening degree of the auxiliary door 48 
and thus the volume of the recirculated indoor air into the heater unit 
are decreased as the vehicle speed increases. 
Referring to FIGS. 5 and 6 there is shown a modification of the air intake 
section of FIG. 2. In this modification, the auxiliary door 52' has a 
projection 52' a integrally formed on the lower section thereof, as is 
best shown in FIG. 6. The projection 52' a is sized and positioned to be 
sandwiched between the door seat portion 10a of the intake duct 10 and the 
main door 48 when the damper door unit takes a position to close the 
outdoor air intake opening 12. Thus, when taking such position, the 
auxiliary door 52' is assuredly prevented from rattling, thereby assuring 
seal between the outdoor air intake opening 12 and the downstream section 
(such as the enlarged portion 20) of the intake duct 10. Referring to FIG. 
7, there is shown another modification of the air intake section of FIG. 
2. In this modifiation, an elongated member 66 made of a flexible material 
such as flexible rubber or polyurethane foam is fixed to the side wall of 
the outdoor air intake opening 12 to protrude downwardly as shown. 
Similarly to the case of FIG. 5, the provision of the elongate member 66 
assures the seal between the outdoor air intake opening 12 and the 
downstream section of the intake duct 10 under the condition that the 
damper door unit takes a position to close the outdoor air intake opening 
12, as will be understood from the drawing. 
Although in the aforementioned description, explanation has been made with 
respect to an air heating system employing a heater unit 26, the measure 
according to the invention is applicable to an air conditioning system 
(not shown) which comprises generally the same parts and constructions as 
in the case of the above-mentioned air heating system except that in the 
air conditioning system, a cooling core such as an evaporator is installed 
in an air conditioning unit which corresponds to the heater unit 26. Upon 
operation of the cooling core for cooling the passenger compartment R, the 
damper door unit takes the position to close the outdoor air intake 
opening 12 for introducing into the intake duct 10 only the indoor air via 
the indoor air intake opening 14. Under this condition, the auxiliary door 
52 assuredly closes the opening 56 of the main door 48 by its own weight 
as well as a force which is produced by ram effect occuring in the cowl 
box 16 under the vehicle cruising, thereby to assure sealing between the 
interior of the intake duct 10 and the atmospheric air surrounding the 
vehicle. Of course, application of the measure of FIG. 5 or FIG. 7 to the 
air conditioning system mentioned above improves such sealing.