Fig. 5-2
Operation modes
1
→
2
→
3
→
4
→
5
→
6
→
7
→
8
VALVE CLOSE
8
→
7
→
6
→
5
→
4
→
3
→
2
→
1
VALVE OPEN
White
ON
1
ON
2
OFF
3
OFF
4
Drive states
Table 5-1
5
OFF
OFF
6
OFF
7
ON
Yellow
OFF
ON
ON
ON
OFF
OFF
OFF
OFF
Orange
OFF
OFF
OFF
ON
ON
ON
OFF
OFF
Blue
OFF
OFF
OFF
OFF
OFF
ON
ON
ON
8
Expansion valve control involves detecting the temperature of the compressor head and adjusting the aperture to stabilize it to
the target temperature.
The control period is once every 20 seconds, at which time a few pulses are produced.
④
③
②
①
④
③
②
①
Pin No. of
CN15
Connector pin No.
12V
1.2V
50ms.
75ms.
200ms.
Lead wire
・
This circuit incorporates 2 shift register latch driver ICs (IC11 and IC12) of the 8-bit type that convert serial signal inputs in
parallel and produces the result.
・
A typical circuit operation when the expansion valve is driven is described by using the time chart in Fig. 5-3.
①
The product produces a clock signal (12 periods worth at 750
μ
s. per period) through pin
#2
of the microcomputer. (One
period of clock signal consists of being off for 500
μ
s. and on for 250
μ
s.)
②
Serial signal #1 of drive pattern is produced through pin
#4
of the microcomputer synchronously with the clock signal.
#1: A serial signal is a serialized version of the pattern of energizing 1 or 2 phases of the 4 phases of windings of the
expansion valve. A serial signal is outputted so that the middle of an ON signal (Hi level, 500
μ
s.) of the serial signal enters
at the rise of the clock signal.
The above actions
①
and
②
update the contents of the shift register in the IC.
Next, 250
μ
s after the ON signal output in the 12th period of the clock signal, the following is conducted.
③
The latch signal from pin
#3
of the microcomputer will be turned off (Lo level, 500
μ
s.) and on again (Hi level).
④
After the necessary energization time has elapsed, and if the expansion valve needs to be driven, the product will go back
to
①
and repeat this procedure.
The above steps will energize 1 or 2 phases of windings of the 4 phases of the expansion valve, while controlling the
expansion valve aperture according to the contents of the shift registers updated for one energization time. When the
expansion valve aperture reaches its target, step
②
above will become a stop pattern. The actions
①
to
④
will then be taken
to terminate the expansion valve control.
– 192 –
