Advanced Automotive Fault Diagnosis
part of the system should do in turn helps in deter-
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LÔØI NOÙI ÑAÀU, ledklok
- Điều hướng trang này:
- 2.7.3 Open loop systems
- 2.7.4 Closed loop systems
part of the system should do in turn helps in deter- mining how each part actually works. It is again important to stress that the links and interactions between various sub-systems are a very important consideration. Examples of this would be how the power demands of the vehicle lighting system will have an effect on the charging system operation, or in the case of a fault, how an air leak from a brake servo could cause a weak air/fuel ratio. To further analyse a system, whatever way it has been sub-divided from the whole, considera- tion should be given to the inputs and the out- puts. Many of the complex electronic systems on a vehicle lend themselves to this form of analy- sis. Considering the ECU of the system as the control element and looking at its inputs and out- puts is the recommended approach. 2.7.3 Open loop systems An open loop system is designed to give the required output whenever a given input is applied. A good example of an open loop vehicle system would be the headlights. With the given input of the switch being operated the output required is that the headlights will be illuminated. This can be taken further by saying that an input is also required from the battery and a further input of say the dip switch. The feature which determines that a system is open loop is that no feedback is required for it to operate. Figure 2.8 shows this example in block diagram form. 2.7.4 Closed loop systems A closed loop system is identified by a feedback loop. It can be described as a system where there is a possibility of applying corrective measures if the output is not quite what is wanted. A good example of this in a vehicle is an automatic tem- perature control system. The interior temperature of the vehicle is determined by the output from the heater which is switched on or off in response to a signal from a temperature sensor inside the cabin. The feedback loop is the fact that the out- put from the system, temperature, is also an input to the system. This is represented by Figure 2.9. The feedback loop in any closed loop system can be in many forms. The driver of a car with a conventional heating system can form a feedback loop by turning the heater down when he/she is too hot and turning it back up when cold. The feedback to a voltage regulator in an alternator is an electrical signal using a simple wire. tải về 7.07 Mb. Chia sẻ với bạn bè của bạn:
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