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Gasoline Engine Electronic Control System

admin — Thu, 29 Jul 2010 07:10:45 +0000

The engine control system consists of three groups including sensors (and sensor output signals), engine ECU, and actuators. This chapter explains the sensors (signals), power circuitry and ground circuitry, and sensor terminal voltages. The engine ECU functions are divided into EFI control, ESA control, ISC control, diagnosis function, fail-safe and backup functions, and other functions. These functions and the actuator functions are explained in separate chapters.
Preliminary Knowledge
The power circuitry is the electrical circuits that supply power to the engine ECU. These electric circuits include the ignition switch, the EFI main relay, etc. The power circuitry actually used by the vehicle consists of the following two types.
1. Control by ignition switch
As shown in the illustration, the diagrams show the type in which the EFI main relay is operated directly from the ignition switch. When the ignition switch is turned on, current flows to the coil of the EFI main relay, causing the contacts to close. This supplies power to the +B and +B1 terminals of the engine ECU. Battery voltage is supplied at all times to the BATT terminal of the engine ECU to prevent the diagnostic codes and other data in its memory from being erased when the ignition switch is turned off.
2. Control by engine ECU
The power circuitry in the illustration is the type where operation of the EFI main relay is controlled by the engine ECU. This type requires that power be supplied to the engine ECU for several seconds after the ignition switch is turned OFF. Therefore, the turning ON and OFF of the EFI main relay is controlled by the engine ECU. When the ignition switch is turned ON, battery voltage is supplied to the IGSW terminal of the engine ECU, and the EFI main relay control circuitry in the engine ECU sends a signal to the M-REL terminal of the engine ECU, turning on the EFI main relay. This signal causes current to flow to the coil, closing the contacts of the EFI main relay and supplying power to the +B terminal of the engine ECU. Battery voltage is always supplied to the BATT terminal for the same reason as for the control by ignition switch type. In addition, some models include a special relay for the air-fuel ratio sensor heater circuitry which is required large amount of current.
REFERENCE:
In models where the engine ECU controls the engine immobiliser system, the EFI main relay is also controlled by the key unlock warning switch signal.
Ground Circuitry
The engine ECU contains the following three basic ground circuits.
1. Ground for engine ECU operation (E1)
The E1 terminal is the engine ECU unit ground terminal, and is normally connected close to the air intake chamber of the engine.
2. Sensor grounds (E2, E21)
The E2 and E21 terminals are sensor ground terminals, and these are connected to the E1 terminal in the engine ECU. These prevent the sensors from detecting erroneous voltage values by keeping the sensor ground potential and engine ECU ground potential at the same level.
3. Grounds for actuator operation (E01, E02)
The E01 and E02 terminals are actuator ground terminals, such as for the actuators, ISC valve, and air-fuel ratio sensor heater, and, as with the E1 terminal, they are connected close to the air intake chamber of the engine.

Computer Control of Gasoline Engine

admin — Tue, 27 Jul 2010 07:06:41 +0000

A gasoline engine produces power through the explosion of a mixture of gasoline and air. The three essential elements for a gasoline engine to produce power are the following
1. Good air-fuel mixture
2. Good compression
3. Good spark
To achieve these three elements simultaneously, it is important to precisely control the formation of the air-fuel mixture and the timing of the sparks. Before 1981, the only engine control system in existence was the EFI (Electronic Fuel Injection), which used a computer to control the fuel injection volume. In addition to the EFI, there are now various computer-controlled systems, including the ESA (Electronic Spark Advance), ISC (Idle Speed Control), diagnostic systems, etc.
REFERENCE:
Toyota uses a computer-controlled system called the TCCS (Toyota Computer- Controlled System) to optimally control the fuel injection, ignition timing, drivetrain, brake system, and other systems in accordance with the operating conditions of the engine and the vehicle.
Process of Computer Control
For the computer to function properly, it requires a comprehensive system comprised of various input and output devices. On an automobile, sensors such as a water temperature sensor or an air flow meter correspond to the input device. And actuators such as injectors or igniters correspond to the output device. At Toyota, the computer that controls a system is called an ECU (Electronic Control Unit). The computer that controls the engine is called an engine ECU (or ECM*Engine Control Module). The sensors, actuators, and the engine ECU are connected with wiring harnesses. Only after the engine ECU processes the input signals from the sensors and outputs control signals to the actuators can the entire system operate as a computer-controlled system. *The ECM is SAE (Society of Automotive Engineers) terminology.

Turbocharger Boost Compensator

admin — Sun, 25 Jul 2010 06:46:06 +0000

1. Description When the intake air volume (boost pressure) is increased by the turbocharger, the boost compensator increases the maximum fuel injection volume in accordance with the increased intake air volume, in order to maintain optimal combustion conditions and increase the engine output at all times.

2. Construction The boost compensator is installed above the governor of the injection pump. The diaphragm and push rod move up and down by the boost pressure. The push rod has a tapered construction, by which, the control arm is rotated via the connecting pin. This amount of movement becomes tension lever movement distance, and the spill ring movement distance (injection volume).

3. Operation

(1) When the boost pressure is low: The spring pushes the diaphragm upward. The injection volume does not increase because the connecting pin is in contact with the tapered bottom portion of the push rod.

(2) When the boost pressure is high: The diaphragm is pushed by the boost pressure to move the push rod downward. The tension lever is pulled by the control spring. Therefore, the connecting pin moves to the right toward the tapered portion of the push rod, and the control arm also rotates clockwise. The tension lever and control lever rotate counter-clockwise around fulcrum A and move the spill ring to increase the maximum fuel injection volume. (3) When the boost pressure is too high: Normally it is controlled at the area C and D. If the boost pressure rises above the intercept point on the graph, the connecting pin is pushed back to the left by tapered portion B of the push rod, reducing the maximum fuel injection volume. This prevents the boost pressure from rising too high in the case of a failure.

Diesel Engine High-Altitude Compensator (HAC)

admin — Sat, 24 Jul 2010 05:03:21 +0000

1. Description
At high altitudes, the air density decreases with the decrease in the atmospheric pressure. For this reason, if the fuel is injected under the same conditions as at low altitudes, the air-fuel mixture becomes too rich, making the engine susceptible to generating black smoke. Therefore, the HAC automatically reduces the maximum fuel injection volume in accordance with the vehicle’s present altitude.
2. Construction
The HAC, which is installed above the pump governor, consists of vacuum bellows, a push rod, connecting pin and control arm.
3. Operation
(1) Low altitude
As the bellows are contracted when the atmospheric pressure is high, the push rod is pulled upward by the spring. The spill ring is kept at the normal position.
(2) High altitude
When the atmospheric pressure is low, the bellows expand to push the push rod downward. This movement is transmitted via the connecting pin, the control arm and the tension lever, and serves to move the spill ring to the left. In this way, the maximum fuel injection volume is decreased.

Diesel Engine Automatic Timer (Injection Timing Control)

admin — Sun, 18 Jul 2010 03:45:09 +0000

As in the case of gasoline engine ignition timing, diesel engine injection timing must be advanced (or retarded) in accordance with the engine speed in order to obtain optimum performance. Advancing or retarding is controlled by the automatic timer in response to the engine speed.

Construction and operation

Fuel injection timing is controlled by changing the position of the roller, which touches the face cam. When the injection pump is not rotating, the roller is in the maximum retarding position. When the injection pump starts rotating and speed is increased, the timer piston moves to the left pushing the timer spring, as the fuel pressure inside the pump housing also increases. The slide pin connected to the piston converts the piston movement into the rotational movement of the roller ring. When the roller ring rotates in the opposite direction of the drive shaft, the injection timing advances. When the roller ring rotates in the same direction, the injection timing retards.

Diesel Engine Fuel Cut-off Solenoid

admin — Sat, 17 Jul 2010 08:58:59 +0000

The fuel cut-off solenoid valve opens and closes the fuel passage leading to the suction port. (The valve remains open while the ignition switch is on.)
1. Fuel cut-off solenoid on
The battery voltage is applied to the solenoid and the valve compresses the spring to be drawn upward. As a result, the suction port is opened and the fuel is supplied.
2. Fuel cut-off solenoid off
The current,which flows into the solenoid,is cut off, allowing the valve to retract downward by the spring. As the valve closes the suction port, the fuel supply to the cylinder will stop, causing the engine to stop.
Diesel Engine Anti-reverse Rotation
The diesel engine generally rotates in reverse. If the fuel is injected where the air is drawn from the exhaust side and compressed, the engine will rotate. However, the pump is designed to make reverse rotation for the engine impossible. If the pump rotates in reverse, the fuel will be returned back to the pump housing as the pump plunger moves upward and the suction port is opened. Also, the fuel is not compressed because the pump plunger moves downward, when the delivery port is opened. Therefore the fuel is not injected, making it impossible that the engine to rotate in reverse.

Diesel Engine Injection Pump System

admin — Thu, 15 Jul 2010 03:39:20 +0000

The injection pump pumps the fuel to each injection nozzle.

The injection pump functions to control the fuel injection volume and timing.

1. Fuel suction

The feed pump draws the fuel from the fuel tank, and compresses it into the pump housing.

2. Fuel pumping

One plunger is used to send the highly pressurized fuel to each injection nozzle by reciprocated movement with rotating.

3. Injection volume control

The governor controls the injection volume and the engine output. The governor functions to control the maximum engine speed to prevent the engine from overrunning and stabilize idling speed.

4. Injection timing control

The timer controls the injection timing in proportion to the engine speed. The internal parts of the injection pump are lubricated and cooled by the fuel.

Summary of Operation

Turning the ignition switch on causes the fuel cut-off solenoid valve to be pulled in and the passage between the pump housing and the plunger to open. When the feed pump rotates, the fuel is drawn up from the fuel tank, passes through the sedimenter and the fuel filter, and enters the pump housing after the pressure is regulated by the regulating valve. The plunger draws the fuel from the pump housing into the pressure chamber during its downward movement (moves to the left), and compresses the fuel highly to distribute it to each delivery valve during the upward movement (moves to the right). After passing through the delivery valve, the fuel is introduced into the nozzles via the high-pressure pipes, from which the fuel is injected into the cylinders. At the same time, the internal parts of the pump are lubricated and cooled by the fuel. A portion of the fuel returns to the fuel tank from the over flow screw, in order to control the increase of the fuel temperature in the pump.

Other Diesel Engine Equipment Intake Shutter

admin — Wed, 14 Jul 2010 03:36:14 +0000

1. Description

Some diesel engines use an intake shutter. The intake shutter has following functions.

(1) Stops vibration immediately after engine is turned off. In diesel engines, air continues to be drawn into the cylinder and compressed even after the ignition switch is turned off. To prevent vibration from occurring immediately after engine is turned off, the intake shutter is closed immediately after the ignition switch is turned off in order to shut the intake air off and stop the engine smoothly.

(2) Reduces intake air noise. During deceleration, or low speed and light load, the amount of the intake air is reduced by the intake shutter. The intake air noise is reduced without drawing unnecessary air into the intake manifold.

(3) Improves EGR performance. The intake shutter opening angle is controlled to attain the proper EGR effect, depending on the engine running condition.

HINT:

The intake shutter is also called throttle valve.

Deisel Engine Vehicles Glow System

admin — Tue, 13 Jul 2010 03:30:11 +0000

1. Glow indicator light description

The glow plug indicator light is mounted inside the combination meter. When the light goes off, it informs the driver the engine is ready to be started.

HINT:

The glow indicator light operates independently from the glow plug. Thus, it does not indicate whether plug has actually heated up or not. The light lighting time is approx. 0- 1seconds. The light lighting time varies according to the coolant temperature and according to the engine models.

2. Operation of glow system (Super glow type)

Timer 1 and 2 inside the preheating timer or the emission control ECU are turned on after the ignition switch is turned to ON when the temperature of the engine coolant is low. Timer 1 turns on the glow indicator light in the combination meter. Timer 2 turns on the glow plug relay to let the glow plug generate heat. Timer 1 and 2 are turned on during the time in accordance with the temperature of the coolant. Then, they are turned off. When timer 1 is turned off, the glow indicator light is turned off. When the ignition switch is turned to the START, the preheating timer or emission control ECU turns the glow plug relay on, in order to prevent the temperature of glow plug dropping during starting and improve startability. When timer 3 operates, it turns the glow relay on for the time depending on the coolant temperature and effects after-glow when the engine is started and the ignition switch is returned to ON from START.

REFERENCE:

Fixed-delay Type Circuit

For the preheating system of the fixeddelay type, the preheating timer controls the glow indicator light lighting time and the time that the glow plug relay is turned on (preheating time.)

Indicator light lighting timeApprox. 5 seconds

Preheating timeApprox. 18 seconds Both are controlled at the fixed time.

Variable-delay Type Circuit

For the preheating system of the variable- delay type, the preheating timer controls the glow indicator light lighting time and the time that the glow plug relay is turned on (preheating time) in accordance with the engine coolant temperature and alternator voltage (which acts as the engine running signals).

Light lighting time:

Approx. 2 – 28 seconds

Preheating time:

Approx. 2 – 55 seconds

Both vary according to the coolant.

Diesel EnginePreheating System

admin — Mon, 12 Jul 2010 03:26:50 +0000

1. Necessity of preheating system

At a cold engine starting, the compression heat escapes from the compression chamber even if there is adequate compression. In some cases, the injected fuel does not rise to the ignitable temperature. Therefore, the preheating system is necessary to improve ignition performance. By heating the air before a cold engine starting, the preheating system improves engine startability. Also, diesel knock and white smoke are reduced by heating the air for a certain amount of time according to the coolant temperature even after starting.

Glow Plug

The latest Toyota vehicles feature glow plugs with self-controlling temperature. A control coil is built into the glow plug, in which the resistance increases as temperature rises. The increased resistance of the coil reduces the amount of current to the thermal coil, which is connected in series to the control coil. By reducing the amount of current, the temperature of the glow plug does not rise as much. The temperature of glow plug rises to approx. 90C (1,472 F).

REFERENCE:

The previous glow plug, which did not feature self-controlling temperature featured a system when the glow plug resistors were set in series, reducing the current flowing into the glow plug.