Once the computer’s programming instructs that a correction or adjustment must be made in the controlled system, an output signal is sent to an actuator. This involves translating the electronic signals into mechanical motion.
An output driver is used within the computer to control the actuators. The circuit driver usually applies the ground circuit of the actuator. The ground can be applied steadily if the actuator must be activated for a selected amount of time. For example, if the BCM inputs indicate that the automatic door locks are to be activated, the actuator is energized steadily until the locks are latched. Then the ground is removed.
Other systems require the actuator to be turned either on and off very rapidly or for a set amount of cycles per second. It is duty cycled if it is turned on and off a set amount of cycles per second. Most duty cycled actuators cycle ten times per second.… READ THE REST
The air charge temperature (ACT) sensor input will be used as an example of how the computer processes information. If the air temperature is low, the air is denser and contains more oxygen per cubic foot. Warmer air is less dense and therefore contains less oxygen per cubic foot. The cold, dense air requires more fuel compared to the warmer air that is less dense. The microprocessor must supply the correct amount of fuel in relation to air temperature and density. An ACT sensor is positioned in the intake manifold where it senses air temperature. This sensor contains a resistive element that has an increased resistance when the sensor is cold. Conversely, the ACT sensor resistance decreases as the sensor temperature increases. When the ACT sensor is cold, it sends a high-analog voltage signal to the computer, and the A/D converter changes this signal to a digital signal.
When the microprocessor receives this ACT signal, it addresses the tables in the ROM.… READ THE REST
The computer requires a means of storing both permanent and temporary memory. The memories contain many different locations. These locations can be compared to file folders in a filing cabinet, with each location containing one piece of information. An address is assigned to each memory location. This address may be compared to the lettering or numbering arrangement on file folders. Each address is written in a binary code, and these codes are numbered sequentially beginning with 0.
While the engine is running, the engine computer receives a large quantity of information from a number of sensors. The computer may not be able to process all this information immediately. In some instances, the computer may receive sensor inputs that the computer requires to make a number of decisions. In these cases, the microprocessor writes information into memory by specifying a memory address and sending information to this address. When stored information is required, the microprocessor specifies the stored information address and requests the information.… READ THE REST
FIGURE. Main components of the computer and the Microprocessor.
The microprocessor is the brain of the computer. The microprocessor is constructed of thousands of transistors that are placed on a small chip. The microprocessor brings information into and out of the computer’s memory. Hie input information is processed in the microprocessor and checked against the program in memory. The microprocessor also checks memory for any other information regarding programmed parameters. The information obtained by the microprocessor can be altered according to the program instructions. The program may have the microprocessor amicroprocessorly logic decisions to the information. Once all calculations are made, the microprocessor will deliver commands to make the required corrections or adjustments to the operation of the controlled system.
The program guides the microprocessor in decision making. For example, the program may inform the microprocessor when sensor information should be retrieved and then tell the microprocessor how to interpret this information.… READ THE REST
Remembering the basics of electricity, voltage does not flow through a conductor; current flows and voltage is the pressure that “pushes” the current. However, voltage can be used as a signal; for example, difference in voltage levels, frequency of change, or switching from positive to negative values can be used as a signal.
The computer is capable of reading only voltage signals. A program is a set of instructions the computer must follow to achieve desired results. The program used by the computer is “burned” into integrated circuit (1С) chips using a series of numbers. These numbers represent various combinations of voltages that the computer can understand. The voltage signals to the computer can be either analog or digital. Many of the inputs from the sensors are analog variables. For example, ambient temperature sensors do not change abruptly. The temperature varies in infinite steps from low to high. The same is true for several other inputs such as engine speed, vehicle speed, fuel flow, and so on.… READ THE REST
A computer processes the physical conditions that represent information (data). Hie operation of the computer is divided into four basic functions:
- Input: A voltage signal sent from an input device. This device can be a sensor or a switch activated by the driver or technician.
- Processing: The computer uses the input information and compares it to programmed instructions. Hie logic circuits process the input signals into output demands.
- Storage: The program instructions are stored in an electronic memory. Some of the input signals are also stored for later processing.
- Output: After the computer has processed the sensor input and checked its programmed instructions, it will put out control commands to various output devices. These output devices may be the instrument panel display or a system actuator. The output of one computer can also be used as an input to another computer.
Understanding these four functions will help today’s technician organize the troubleshooting process.… READ THE REST