Specifications
Transmission and Clutch Control Functions
Electric clutches can be added to automotive transmissions
to eliminate the 6% slip which typically occurs during cruise
and which results in a 6% loss in fuel economy. These de-
vices could be operated by a pair of LM2907’s as illustrated
in
Figure 29.
Magnetic pickups are connected to input and
output shafts of the transmission respectively and provide
frequency inputs f
1
and f
2
to the circuit. Frequency, f
2
, be-
ing the output shaft speed, is also a measure of vehicle road
speed. Thus the LM2907-8 No. 2 provides a voltage propor-
tional to road speed at pin 3. This is buffered by the op amp
in LM2907-8 No. 1 to provide a speed output V
OUT1
on pin
4. The input shaft provides charge pulses at the rate of 2f
1
into the inverting node of op amp 2. This node has the inte-
grating network R1, C3 going back to the output of the op
amp so that the charge pulses are integrated and provide
an inverted output voltage proportional to the input speed.
Thus the output V
OUT2
is proportional to the difference be-
tween the two input frequencies. With these two signalsÐ
the road speed and the difference between road speed and
input shaft speedÐit is possible to develop a number of
control functions including the electronic clutch and a com-
plete electronic transmission control. (In the configuration
shown, it is not possible for V
OUT2
to go below zero so that
there is a limitation to the output swing in this direction. This
may be overcome by returning R3 to a negative bias supply
instead of to ground.)
CONCLUSION
The applications presented in this note indicate that the
LM2907, LM2917 series devices offer a wide variety of uses
ranging from very simple low cost frequency to voltage con-
version to complex systems building blocks. It is hoped that
the ideas contained here have given suggestions which may
help provide new solutions to old problems. Additional appli-
cations ideas are included in the data sheet, which should
be referred to for all specifications and characteristics.
REFERENCES
1. Sociey of Automotive Engineers: Preliminary Recom-
mended Environmental Practices for Electronic Equip-
ment Design. October 1974.
2. See for example: Pollution Control Installers HandbookÐ
California Bureau of Automotive Repair No. BAR H-001
õ
5.5.4 NOX control systems.
3. TRW Globe Motors, 2275 Stanley Avenue, Dayton, Ohio
45404.
4. S.A.E. Paper
Ý
760018 Air Flow Measurement for Engine
ControlÐRobert D. Joy.
5. Code of Federal Regulations. Title 49 Transportation;
Chapter VÐNational Highway Traffic Safety Administra-
tion, Dept. of Transportation; Part 571ÐFederal Motor
Vehicle Safety Standards; Standard No. 121.
V
OUT1
e
V
CC
C2 R2 f2
V
OUT2
e
V
CC
(C2 R2 f2
b
C1 R1 f1)
TL/H/7451–52
FIGURE 29. Transmission or Clutch Control Functions
17