Note: Descriptions are shown in the official language in which they were submitted.
1339~74
BACKGROUND OF THE INVENTION
The present invention relates to an air
conditioning apparatus for a motor vehicle which is
conventionally referred to as the car air conditioner.
5 More particularly, the invention is concerned with a
temperature control system suited preferably for use in
the car air conditioner of a reheat-air mix type.
The air conditioning apparatus for a motor
vehicle employed in the early stages was of a separate
10 type in which a cooler and a heater were operated
independently of each other. In recent years, an air
conditioner of a unitary structure referred to as the
reheat-air mix (blend) type air conditioner has been
developed arld is now used extensively. In this type of
15 air conditioner, temperature control can be performed
continuously from cooling to warming mode to maintain --
the intra-car temperature at a predetermined value
regardless of a wide change in the outside temperature.
Besides, the air conditioner can enjoy excellent tem-
~0 perature control in a continuous manner and can arovide
moisture removing capability, to further advantage.
A typical one of the reheat-air mix type air
conditioners for motor vehicles or cars is known, for
example, from Japanese Patent Application Laid-Open No.
25 136509/1983 (~P-A-58-136509) which corresponds to U. S.
Patent No. 4,456,166. In the discharge air
*
1339274
1 temperature control of this prior art air conditioner, a
difference between the actual temperature Td of the
discharged air and a desired temperature Tdo to be
attained is derived to determine the desired degree of
opening ~am of an air mixing or blend door, wherein the
control is so performed that a voltage value tapped from
a feed back potentiometer may assume a value correspond-
ing to the desired opening ~am.
As will be noted, in the prior art air condi-
tioner of the type under consideration, a sensor suchas a feedback potentiometer is employed for detecting
the opening of the air blend door, the reason for which
- may be explained by adoption of such arrangement in
which the discharge air temperature control is accom-
plished by deriving the difference between the desireddischarge temperature Tdo and the actual discharge
temperature Td through direct comparison of these tem-
peratures and controlling the opening of the air mixing
or blend door so that the temperature difference (Tdo -
Td) approaches or converges to zero.
However, notwithstanding of the fact that theopening of the air blend door, a mechanical quantity,
can vary within a relatively short time ~within about l
second or less), the air temperature at the discharge
port can vary only with a large delay in response (about
several seconds to several ten seconds) because of
influence exerted by the thermal capacity o~ passage walls
(walls of ducts and the like) in addition to the
1~39274
1 influence of the delay involved in the response of the
discharge temperature sensor itself.
Under the circumstance, when the control
system having the delay in response is to be operated
with stability and with high-speed response, as occasion
requires, it is necessary to detect the opening of the
air blend door and control it so that the door can
assume constantly the proper state or position. To this
end, a feedback potentiometer is employed as in the case
of the prior art temperature control system described
above.
With the arrangement in which the feedback
- potentiometer is employed as the sensor for detecting
the degree of opening of the air blend door, an arithmetical
determination of the desired opening ~am, processing
of the voltage signal produced by the door opening
sensor and other processing are required in the course
of the control process. Further, since correction must
be made on the possible nonuniformity in the positional
relationship between the door opening sensor and the
air blend door, the control procedure becomes ve ry
complicated, which also means that when a microcomputer
control is adopted, the program area is correspondingly
increased, giving rise to a problem. sesides~ assembling
and mounting of a linkage for interlinking the opening
sensor and the air blend door with each other, adjust-
ment thereof and other steps required for the setup Qf
the system are naturally accompanied with high
- 13392~4
1 expenditure, which gives rise to another problem.
SUMMARY OF THE INVENTION
An object of the present invention is to
provide an inexpensive discharge temperature control
system of a simplified structure, high reliability and
improved control accuracy by adopting an arrangement
in which the discharge temperature ~Td), the final
target item to be controlled, is controlled straight-
forwardly and which allows the door opening sensor for
the air blend door to be omitted while improving the
response capability and stability of the controlsystem.
The abovementioned object can be accomplished
by adopting at least one of the operational conditions
or criteria mentioned below:
(a) For a time of several seconds to several ten of
seconds following immediately the opening control of the
air blend door, the control output of the control
system is interrupted temporarily in view of an
inevitable delay involved in generation of the discharge
temperature sensor output signal in response to the
temperature of the current air stream as discharged.
(b) The output state of the discharge temperature
sensor in which the output signal has a large slope as
a function of time, i.e. the temperature detected by
the discharge temperature sensor changes from time to
time, the control output of the control system is
39~4
1 interrupted temporarily, since this state can be
regarded as the transient state of the whole system
including the mechanical and aerodynamic systems.
(c) Change in the desired discharge temperature
(Tdo) brought about by the operator or driver requires
the response of the control system without delay.
Accordingly, the control system is released from the
temporary stoppage state.
(d) When the actual discharge temperature (Td)
varies beyond the desired discharge temperature (Tdo)
as the result of operation of the air blend door, the
control system is released from the temporary stoppage
state so as to make response without delay.
(e) When the effect of the control output for
operating the air blend door as reflected on the dis-
charge temperature is insufficient (suppose, for
çxample, such a situation in which the discharge temper-
ature is not changed because the air blend door is not
moved at all due to a balanced state estahlished between
the spring force applied to the door and the force
applied by the actuator even when more or less amount
of the atmospheric air is introduced into the actuator
with a view to raising the discharge temperature in
the state where the maximum negative pressure is applied
to attain the maximum cooling), the control system is
released from the temporary stoppage state for the
purpose of obtaining the satisfactory response.
(f) When a differencc between the desired discharge
13392~4
1 temperature (Tdo) and the actual discharge temperature
(Td) is s~laller than a predetermined temperature
difference value (~T), no control output is produced,
because the above state means that the desired discharge
temperature is realized.
(g) When ¦Tdo - Td¦ > ~T, the control quantity
(control output or command) is determined as follows:
when Tdo - Td > 0, then Tdo = Td - ~T
when Tdo - Td < 0, then Tdo = Td +(-~T for
thereby assuring continuous (smooth) increasing/decreas-
ing of the control quantity.
(h) The actual control quantity is corrected on
the basis of the value determined as mentioned in the
paragraph (g) for thereby compensating for the non-
linearity of change in the discharge temperature inresponse to the change in the control quantity for the
air conditioning unit.
(i) Difference in the air flow (due to difference
in pressure) between the atmospheric pressure and the
negative pressure applied to the negative pressure
actuator is corrected.
(j) When the desired discharge temperature Tdo is
changed, the control output quantity is increased only
once for the purpose of enhancing the feeling of
~5 occupants to the response of the control system.
By adopting the operational criteria or
conditions (a) to tj) mentioned above, there can be
realized a control system having high stability and
133927~
high response speed without using the opening sensor for the
air blend door.
In other words, since the control of the means such
as the air blend door for regulating the heat exchange capa-
bility is performed intermittently in timing with the delayinvolved in the air temperature detection at the discharge
port, the air conditioner can be operated stably without
resorting to the control by using the door opening sensor.
According to the invention there is provided in an
air conditioner installed on a motor vehicle having a
temperature control system of a type in which a detected
temperature value of air discharged from the air conditioner
is controlled convergently to a desired temperature value by
regulating a thermal exchange capability of the air condi-
tioner through operation of an air blend door, said controlsystem comprising: arithmetic means for arithmetically
determining and updating sequentially a deviation of the
actual heat exchange capability from a requisite heat exchange
capability in accordance with a difference between the
detected temperature value and the desired temperature value;
control means operative in response to updated arithmetical
deviations to regulate the heat exchange capacity by
controlling operation of said blend door on a repeating basis;
decision means for determining whether or not an inhibit
signal is connected to said control means and inhibits a
control of operation of said blend door by said control means
for a period of time immediately after outputting a control
signal is produced; means for producing an inhibit signal as a
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~ 1339274
result of a decision by said decision means; and means for
suppressing production of said inhibit signal according to an
operational condition of said air conditioner.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a view showing schematically an
arrangement of a typical air conditioner for a motor vehicle
to which an automatic temperature control system according to
an embodiment of the present invention is applied;
Fig. 2 is a view for illustrating operation of the
system according to an embodiment of the invention;
Figs. 3 and 4 are views for illustrating some steps
shown in Fig. 2 in more detail; and
Fig. 5 is a view for illustrating the discharge
temperature control characteristic of a typical air
conditioning unit.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Now, the present invention will be described in
detail by referring to the annexed drawings which
1~39274
1 show a temperature control system for a car air condi-
tioner according to an exemplary embodiment of the
invention.
Fig. 1 shows schematically a general arrange-
ment of a car air conditioner provided with a temperaturecontrol system according to an embodiment of the inven-
tion. In the figure, an air conditioning unit 10, an
evaporator 11 and a heater core 12 are, respectively,
of conventional structures. As the elements which
partake directly in the discharge air temperature control
taught by the invention, there can be mentioned an air
blend (mixing) door 1, a negative pressure (vacuum)
~ctuator 2, an on/off valve 3, a three-way valve 4, a
discharged air temperature sensor 5 and a controller 6.
An intra-car (interior) temperature setting unit 7, an
atmospheric (exterior) temperature sensor 8, an intra-
car temperature sensor 9 and others are also connected
to the controller 6 although they bear no direct
relevance to the control proposed by the present inven-
tion.
Next, operation in general of the illustratedsystem will be described.
The controller 6 includes a microcomputer and
fetches a signal Ts tapped from the intra-car temperature
setting unit 7, a temperature signal Ta produced by the
atmospheric temperature sensor 8, a temperature signal
Tr produced by the intra-car temperature sensor 9 and
other parameters, if any, to thereby determine
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133927~
l arithmetically a desired (target) discharge temperature
Tdo and control various members (not shown) participat-
ing in the control of the air conditioner.- Among others,
the control of the air blend door 1 is performed in
such a manner in which the negative pressure actuator 2
is operated under the control of the controller 6 through
the on/off valve 3 and the three-way valve 4 which in
turn are controlled in response to signals Vs and V3
produced by the controller 6, whereby the operating
position of the air blend door l is correspondingly
established.
More specifically, the three-way valve 4 is
first connected to a negative pressure source in response
to the signal V3. Subsequently, the on/off valve 3 is
opened for a predetermined time in response to the
signals Vs. Thus, a negative pressure is introduced
into the negative pressure actuator 2, whereby the air
blend (mixing) door 1 is displaced toward the cooling
position by an angle of the magnitude corresponding to
the operating time duration of the on/off valve 3,
resulting in that the actual discharge temperature is
lowered. Reversely, when the three-way valve 4 is so
changed over as to communicate with the atmosphere with
the on/off valve 3 being subsequently operated to
thereby allow the atmospheric air to be introduced
into the negative pressure actuator 2, the air blend
door 1 is displaced toward the warming side, as the
result of which the output temperature rises. The
i~ 1339274
1 actual discharge temperature Td of the air discharged
through an outlet port OUT of the air conditioner is
detected by the discharged air temperature sensor 5
whose output signal is inputted to the controller 6 to
be utilized in the arithmetic determination of the
desired discharge temperature Tdo. The signals V and
V3 resulting from the above calculation are outputted
from the controller 6.
Next, arithmetic operation and control
procedure performed in this illustrated system will be
elucidated in conjunction with Fig. 2 which illustrates
the control procedure in a so-called program analysis
diagram (PAD in abbreviation).
Referring to Fig. 2, the optimum desired
discharge temperature Tdo is arithmetically determined
at a step 2.1 on the basis of the aforementioned intra-
car set temperature Ts, the atmospheric temperature Ta,
the actual intra-car temperature Tr and other parameters.
At the subsequent step 2.2, the actual discharge tem-
perature is determined on the basis of the signal Td
available from the discharge temperature sensor 5. So
far as the steps 2.1 and 2.2 described above are
concerned, the control procedure is the same as that of
the conventional air conditioner controlling system.
At a step 2.3, the timing at which the control
signal is to be outputted is determined. In actuality,
this step is a looped-back subroutine in which the
operational conditions (a) to (e) described hereinbefore
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133927 4
1 are evaluated, and a value "Yes" is set at the flag
"Stop" at the time when the control output is to be
stopped temporarily.
At the following step 2.4, the content of the
flag "Stop" is checked. When the value "Yes" is set at
this flag, the step 2.1 is regained without executing
any processing. On the other hand, when the content of
the flag "Stop" is found to be "No", the control is
transferred to a subsequent step 2.5 for releasing the
control system from the temporary stoppage state.
At a step 2.5, a control output or command
value indicative of the magnitude of displacement for
which the air blend door 1 is to be moved is arithmeti-
cally determined on the basis of the desired discharge
temperature Tdo and the actual discharge temperature Td
in accordance with the aforementioned operational
conditions or criteria (f) to (j).
When the control command or output value is
zero, no processing is executed at the next step 2.6
because no control output quantity is required to be
produced. Only when the control command value is not
zero, a control output signal corresponding to the
control command value is produced for controlling the
displacement of the air blend or mixing door 1.
The sequence of the individual steps described
above is repeated in an endless manner as indicated at
a step 2.2 to thereby control the discharge temperature.
Next, the decision made concerning the
l33927~
1 temporary stoppage of the control output at the step
2.3 will be elucidated in detail by referring to Fig. 3.
At a step 3.1, it is checked whether the
desired discharge temperature Tdo has undergone any
change. This step corresponds to the decision or
criterion (c) described hereinbefore. In the case of
the instant example, it is determined whether a change
has occurred in the desired discharge temperature since
the preceding arithmetical determination thereof. If
the desired discharge temperature has been changed, the
value "No" is set at the flag "Stop" to allow the
control output signal to be produced because importance
is put on the rapid response rather than the stability.
A step 3.3 corresponds to the evaluation with
reference to the operational decision (d) mentioned
hereinbefore, a step 3.5 corresponds to the evaluation
based on the condition (a), a step 3.6 corresponds to
the evaluation based on the operational condition (b),
and a step 3.9 corresponds to the evaluation based on
the operational condition (e).
In this manner, the value "Yes" is set at the
flag "Stop" when the temporary stoppage of the control
output is required with "No" being otherwise set at the
flag "Stop", whereupon the subroutine illustrated in
Fig. 3 comes to an end.
Next, arithmetical determination of the
control command value mentioned in conjunction with the
step 2.5 shown in Fig. 2 will be described in more
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133927 1
1 detail by referring to Figs. 4 and 5.
At a step 4.1 shown in Fig. 4, it is checked
whether or not the desired temperature Tdo is substan-
tially equal to the actual discharge temperature. This
step corresponds to the evaluation based on the condi-
tion (f) mentioned hereinbefore. In practice, there
can scarcely arise such a situation in which the desired
discharge temperature Tdo coincides perfectly with the
actual discharge temperature Td. Under the circumstance,
it is regarded that the actual discharge temperature Td
coincides with the desired discharge temperature Tdo
when the difference between these temperatures Tdo and
Td is smaller than a previously determined temperature
difference ~T. In this case, the control command value
is set to zero.
In this connection, the preset difference ~T
may assume a value of 0.3 to 5~C. When this value ~T is
small, the control system becomes more sensitive to
thereby produce the control command or output signal
more frequently. Reversely, when the preset temperature
difference ~T is selected at a large value, the control
accuracy is correspondingly degraded. In the case of
the illustrative embodiment, the value of ~T is set at
1~C.
At the subsequent step 4.3, it is decided
whether the negative pressure actuator is to be applied
with a negative pressure or to be communicated to the
atmosphere. This step corresponds to the decision
133927~
1 based on the condition (i) mentioned hereinbefore. In
this conjunction, it is noted in general that difference
between the pressure within the negative pressure
actuator 2 and the negative pressure source is usually
high at the time of application of the negative pressure,
which in turn means that even the control output of
small magnitude can cause the air blend door 1 to be
moved significantly, while in the state in which the
negative pressure actuator is communicated to the
atmosphere, the pressure difference under consideration
is relatively low, requiring thus the control output of
large magnitude for accomplishing the same displacement
of the air blend door as the case mentioned above.
Accordingly, it is necessary at this step 4.3 to decide
whether the negative pressure actuator is to be supplied
with the negative pressure or to be communicated to the
atmosphere.
Next, at a step 4.4 or step 4.5, the non-
linearity of the discharge temperature characteristic
of the air conditioning unit is corrected. This step
corresponds to the decision based on the criterion (h)
mentioned hereinbefore. In general, the discharge
temperature characteristic of the air conditioning unit
exhibits a non-linear characteristic as a function of
the opening of the air blend door 1, as is illustrated
in Fig. 5. In order to ensure the system stability,
it is important to correct the discharge temperature so
that the latter is proportional to the difference
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I33927~
1 between the desired discharge temperature Tdo and the
actual discharge temperature Td. Accordingly, correc-
tion of the characteristic with respect to its non-
linearity is performed at this step. At the same time,
in order to assure the continuity of the control output
for both the cases where ¦Tdo - Td¦ < aT is satisfied
and dissatisfied, respectively, correction of QT
indicated along the abscissa in connection with the
steps 4.4 and 4.5 is performed. This correction corre-
sponds to the decision based on the criterion (g)mentioned hereinbefore. Unless correction is performed,
then the control output value corresponding to ~T would
be produced abruptly or stepwise at the moment the value
of ¦Tdo - Td¦ exceeds the temperature difference ~T.
At the next step 4.6, a possible change in the
desired discharge temperature Tdo is checked. This
step corresponds to the decision based on the criterion
(j) mentioned hereinbefore. In the case of the illus-
trated embodiment, however, importance is put on the
system stability with the control output value being
usually set at a smaller value, and when the desired
discharge temperature Tdo is varied, the control output
value is immediately increased only temporarily. In
this manner, compromise and compatibility are established
and realized between the stability and the response
capability.
As will be appreciated from the foregoing, the
present invention provides an inexpensive temperature
1339274
1 control apparatus of simplified structure which can
nevertheless assure the discharge air temperature
control with high stability and response capability
without need for the use of a feedback potentiometer or
the like to great advantage. In the case of the
hitherto-known discharge air temperature control system
in which the feedback potentiometer is employed, the
amplification factor for the difference signal
(¦Tdo - Td¦) can not be set at an excessively high value
in view of the stability to be assured for the control
system. As a consequence, the temperature control
deviation or excursion becomes significant (5 to 10~C)
particularly in the vicinity of the m~X; mum cooling
position and the m~X; mum warming position, respectively.
According to the illustrated embodiment of the present
invention in which the desired discharge temperature
Tdo and the actual discharge temperature Td are directly
compared with each other and the control is performed
so that the difference ~T between the temperatures Tdo
and Td approaches to zero, the temperature control
deviation or excursion can be suppressed smaller than
the given value of the temperature difference ~T,
whereby the discharge air temperature can be controlled
with high accuracy.
Next, modifications and versions of the
illustrated embodiment of the invention will be
described.
In conjunction with the system shown in
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133927~
1 Fig. 1, the decisions made at the step 3.1 illustrated
in Fig. 3 and the step 4.6 in Fig. 4 can be modified as
follows.
In the case of the preceding embodiment of
the invention, it is decided whether the desired dis-
charge temperature Tdo has been changed relative to the
value determined by the preceding arithmetic operation
because much importance is placed on the response
capability. It is however possible that only when the
change of the desired discharge temperature Tdo greater
than a predetermined value ~T has occurred, decision is
made that change in the desired discharge temperature
Tdo has taken place. Furthermore, it is also conceiva-
ble that only when alteration of the desired intra-car
temperature and change-over of the discharge ports by
operator and switching of the operation mode of the air
conditioning unit take place simultaneously, the
decision that the desired discharge temperature Tdo has
been changed is rendered valid. In this connection, it
should be noted that rapid response is required only in
response to the operator's manipulation and switching
of the operation mode. For the other conditions, the
stability is more important factor. Thus, according to
this modification, the stability of the control system
can be further enhanced at the expense of slight
degradation in the response capability in the regions
where high response is of less importance.
Another modification of the preceding
133927~
1 embodiment of the invention is with respect to the
decision step 3.9 shown in Fig. 3. More specifically,
when some failure occurs in the air conditioning unit
or in the control system or when the air blend door has
reached the full stroke position, the discharge air
temperature does not vary in response to the control
output signal. Accordingly, when the insufficient
discharge temperature condition continues over a range
covering several degrees, it is decided that abnormal
temperature regulating condition prevails, and special
processings are performed as mentioned below. When the
discharge temperature is desired to be increased and
when the actual discharge temperature is sufficiently
high, it is decided that the air blend door 1 must have
been displaced to the maximum warming position. Reverse-
ly, when the discharge temperature is to be lowered and
when the actual discharge temperature is sufficiently
low, it is decided that the air blend door 1 must have
been displaced to the maximum cooling position. Accord-
ingly, under these conditions, the control outputsignal is interrupted for a predetermined time to inhibit
extraneous or unnecessary operations of the negative
pressure valves and others. On the other hand, when
the conditions mentioned above are not satisfied, it may
be decided that the system suffers from some failure.
In that case, a corresponding alarm may be produced to
alert the driver of this fact.
According to the modification described above,
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13392~4
1 no extraneous operations can take place, whereby use
life of the movable parts can be lengthened with
operating noise being reduced to advantages. Further-
more, due to the possibility of self-diagnosis and alarm
generation, the system reliability can be improved to
further advantage.
In still another modification of the illus-
trated embodiment of the invention, the negative pressure
actuator combined with the negative pressure valve for
driving the air blend door l may be replaced by an
electromagnetic actuator in which an electric motor is
made use of or an actuator operative on the basis of
the piezo-electricity principle or an actuator in which
thermal deformation is made use of or any other actuator
capable of moving continuously the air blend door to
the similar effects. The modified system in which any
one of the abovementioned actuators is used can be
controlled in accordance with the procedures illustrated
in Figs. 2 to 4 with one exception that the decision
step 4.3 is rendered unnecessary to simplify correspond-
ingly the control process.
As will now be understood, according to the
present invention which teaches that the desired
discharge air temperature (Tdo) and the actual discharge
temperature (Td) are directly compared with each other,
wherein the control is performed so that the difference
between these temperatures becomes zero, there can be
provided an inexpensive discharge temperature control
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133927~
system for a car air conditioner which enjoys various
advantages such as simplified structure, high reliability,
improve control accuracy and others.
Further due to the feature that the control
output command can be temporarily disabled and enabled in
dependence on the preestablished conditions, the control
system is imparted with both high response capability and
high stability.
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