30.12.
Tyre Pressure Warning.
Poorly inflated tyre causes loss of control and increase fuel consumption. Figure 30.65 shows the layout and circuit of the tyre pressure warning system. The main idea is to give the driver warning of reduced pressure.
There are three basic components used in the system. A pressure operated switch is mounted in the wheel rim, the contacts of which close when pressure falls. This is recognized by a high frequency sender, which the switch passes but does not contact as the wheel rotates. The high frequency pulsar transmits an appropriate pulse to the electronic evaluator. When the pressure drops below the set value, the switch contacts close. This causes the high frequency pulsar to interrupt its stream of pulses to the evaluation circuit so that the warning lamp lights up. The system measures the tyre pressure with an accuracy of + 5 kPa. The design of the switch is such that changes in the temperature of the air in the tyre do not cause false readings. If a tyre pressure warning system is used in conjunction with wheels fitted with limp home tyres, it provides a reminder that the limp home mode is in use.
