Input devices include various sensors and switches. See table 1-2 for the types and functions of vehicle sensors. Input signals are mainly electrical signals generated by sensors or switches. Generally, the signals input into the computer are voltage signals, which are divided into analog signals and digital signals, as shown in figure 1- 1.
Analog signal refers to the voltage signal with stepless change within a given range, and the signals from sensors are mostly analog voltage signals. Digital signal refers to one of two states: on-off, high and low, or on-off. In the automobile electronic control system, because of the computer technology, compared with the previous analog circuit, the speed and capacity of signal processing are greatly improved, and the signals received by the central processor in the computer are all digital signals.
A simple digital signal generator, such as a switch operated by the driver. When the switch is turned on, the voltage signal at point A in ECU is 5V; When the switch is closed, the voltage at point A in the electronic control unit is zero. This switch can only be used as an input signal under "Yes-No" or "On-Off" working conditions.
2.ECU consists of input interface, computer and output interface, as shown in figure 1-2. 1. input interface
The input interface is also called the input loop. As shown in figure 1-3, the signal from the sensor is filtered, shaped and amplified by the input loop, and then sent to the CPU for operation. Because the signals detected by the sensor include analog signals and digital signals, and the computer can only receive digital signals, it is necessary to use the input interface circuit to convert analog signals into digital signals, that is, use the A/D converter in the input interface, as shown in figure 1-4. 2. Computer computer
It consists of memory, CPU, address bus and data bus, as shown in figure 1-5. The computer receives the electrical signal from the sensor or switch and provides the reference working voltage to the sensor. The central processor collects input information and processes the input signal into an output signal through a logic circuit. Instructions, vehicle parameters, operating data and fault information are all stored in the memory.
1- sensor; 2- analog signal; 3- amplifier; 4-bit analog-to-digital converter; 5—CPU； 6-D analog-to-digital converter; 7- power triode; 8— Analog signal; 9- actuator; 10- memory; 1 1- composition of voltage regulator computer 3. output interface
After processing the input signal, the computer calls program instructions, and then sends control commands to the actuator or outputs other information to the dashboard. The electrical signal output by the computer is a digital signal, while some actuators need the computer to output an analog signal. Therefore, the output interface needs a digital-to-analog converter. At the same time, because the electrical signal output by the computer is weak, it is impossible to directly control the actuator. Therefore, most output circuits use output drivers composed of high-power transistors, as shown in figure 1-6. The output signal of the computer controls the on-off of the triode, thus controlling the grounding circuit of the actuator.
Third, the executive body.
According to the control signal output by the electronic control unit, the required mechanical action is completed, and the adjustment and control of a certain system are realized. There are many ways for actuators to convert electrical signals into mechanical motion, which can be divided into linear actuators and rotary actuators according to the forms of realizing mechanical motion. From the specific structure, the components that really realize this conversion are electromagnetic coils, micro-motors and so on. Figure 1-6 output circuit
1. Solenoid actuator
There are three common electromagnetic coil actuators: unidirectional electromagnetic coil, bidirectional electromagnetic coil and cross coil.
The unidirectional electromagnetic coil is shown in figure 1-7.
The spool of the direct electromagnetic coil is wound with many turns of enamelled thin copper wire, and the plunger core can be straight on the spool.
Usually, in order to reduce the long-term current consumption of electromagnetic coil, linear coil adopts two coils, namely closed coil and positioning coil, as shown in figure 1-8. When the switch is closed, the battery supplies power to the two coils at the same time until the plunger approaches the end of the stroke, and a pair of contacts are disconnected, cutting off the circuit of the closed coil. As long as the positioning coil is still energized, the plunger will remain at the end of the stroke. Fig. 1-8 working principle of unidirectional electromagnetic coil 1-On starter; 2- Connect the battery; 3- Turn off the coil; 4— Positioning coil double-acting electromagnetic coil, as shown in figure 1-9.
If the plunger moves linearly in two directions, two differential coils can be used. When the coil B is energized, the plunger moves to the right; When coil A is energized, the plunger moves back to the left. The force generated by the electromagnetic coil is very large, which can make the plunger move quickly, but the stroke is very short, only 8 mm, so the coil plunger is usually connected with an extended arm or lever to increase the stroke and make it more widely used.