Page 394 - Understanding Automotive Electronics

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FUTURE AUTOMOTIVE ELECTRONIC SYSTEMS 11

Power is transmitted from the driving shaft to the driven shaft by a belt
that couples a pair of split pulleys. The effective gear ratio is the ratio of pulley
radii at the contact point of the belt. The radii vary inversely with the spacings
of the split pulleys. The spacings are controlled by a pair of hydraulic cylinders
that push the left half of each pulley in or out.
The control strategy for an integrated engine and CVT system is relatively
complicated and involves measuring vehicle speed and load torque.
Considerable research effort has been and will continue to be expended to
develop a suitable control system, the technology of which will, undoubtedly,
be digital electronic controls.

SAFETY
Collision Avoidance Radar Warning System
Collision avoidance An interesting safety-related electronic system having potential for
radar systems use low- future automotive application is the anticollision warning system. An on-
power radar to sense board low-power radar system can be used as a sensor for an electronic
objects and provide collision avoidance system to provide warning of a potential collision with an
warnings of possible col- object lying in the path of the vehicle. As early as 1976, at least one
lisions. experimental system was developed that could accurately detect objects up to
distances of about 100 yards. This system gave very few false alarms in actual
highway tests.
For an anticollision warning application, the radar antenna should be
mounted on the front of the car and should project a relatively narrow beam
forward. Ideally, the antenna for such a system should be in as flat a package as
possible, and should project a beam that has a width of about 2˚ to 3˚
horizontally and about 4˚ to 5˚ vertically. Large objects such as signs can reflect
the radar beam, particularly on curves, and trigger a false alarm. If the beam is
scanned horizontally for a few degrees, say 2.5˚ either side of center, false alarms
from roadside objects can be reduced.
In order to test whether a detected object is in the same lane as the radar-
equipped car traveling around a curve, the radius of the curve must be
measured. This can be estimated closely from the front wheel steering angle for
an unbanked curve. Given the scanning angle of the radar beam and the curve
radius, a computer can quickly perform the calculations to determine whether
or not a reflecting object is in the same lane as the protected car.
For the collision warning system, better results can be obtained if the
radar transmitter is operated in a pulsed mode rather than in a continuous-wave
mode. In this mode, the transmitter is switched on for a very short time, then it
is switched off. During the off time, the receiver is set to receive a reflected
signal. If a reflecting object is in the path of the transmitted microwave pulse, a
corresponding pulse will be reflected to the receiver. The round trip time, t,
from transmitter to object and back to receiver is proportional to the range, R,

UNDERSTANDING AUTOMOTIVE ELECTRONICS 381