Obstacle Avoidance Radar (Automobile)


Obstacle Avoidance Radar

This system, also called collision avoidance radar, can perform two functions. First, it is a reversing aid, which gives the driver some indication of how much space is behind the car. Second, it can be used as a vision enhancement system.
The technique of radar as a reversing aid (Fig. 30.63) in effect, is a range finding system. The output can be visible or audible, the latter being normally more appropriate. The audible signal is a “pip pip pip” type sound, the repetition frequency of which increases as the car comes nearer to the obstruction, becoming almost continuous as impact is imminent. This is because as the level of discrimination required is fairly low and the radar has to operate only over short distances. However, the main problem is to ensure that the whole width of the vehicles is protected.
Obstacle avoidance radar when used as a vision enhancement is somewhat different. Figure 30.64 demonstrates the principle of this system. This may also be linked with adaptive cruise control as discussed in section 30.7.4. Afrequency of 94 GHz has been used, known as millimeter wave.
Block diagram of obstacle avoidance radar when used as a vision enhancement.
Fig. 30.64. Block diagram of obstacle avoidance radar when used as a vision enhancement.
The operation of a basic radar system is that a radio transmitter generates radio waves, which are then radiated from an anten­na/lighting up’ the airspace with radio waves. A target, such as an other vehicle, that is in this space scatters a small portion of the radio energy back to a receiving antenna. This weak signal is amplified by an electronic amplifier and displayed,
often on a cathode ray tube. To determine the vehicle’s position the distance (range) and bearing must be measured. Since radio waves travel at a constant velocity (the speed of light, i.e.
3 x 108 m/s), the range can be obtained by measuring the time taken for a radio wave to travel from the transmitter to the obstacle and back to the receiver. For example, if the range is 150 meters, the time for the round trip becomes ((2 x 150)/(3 x 108) )= 1 us.
The relative closing speed can be calculated from the current vehicle speed. The radar signal is transmitted in the form of pulses, which is obtained by modulating the frequency of the signal. For this purpose, a triangular wave with a frequency of the order of 100 MHz may be used. This can also be used to trigger a display and for the calculation of distance. If required, the earthing
can be given by the relative position on the display device. Radar for vehicle use must meet the following general requirements.

(a) A range of at least 300 m in bad weather; this gives about 7 seconds warning at 160 kmph.
(b) Objects greater than 0.1 m2 must be detected.
(c) Data must be updated more than once per second.
(d) A beam spread of about 15 degrees horizontally and vertically.
(e) The driver’s display should not in­trude on concentration and act only as a warning.
The type of display or output required for use on a motor vehicle varies from an audible warning to a warning light or series of lights and possibly a display screen. If a large number of vehicles are fitted with obstacle avoidance radar, there may be interference from other vehicles, and drivers may go even faster be­
Layout and circuit of the tyre pressure warning system.
Fig. 30.65. Layout and circuit of the tyre pressure warning system.
cause they ‘know’ nothing is in the way. It soon becomes the norm to rely on the new technology.

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