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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.

Outline of Electronic Fuel Injection and Idle Speed Control System

admin — Wed, 28 Jul 2010 07:08:36 +0000

EFI (Electronic Fuel Injection)System
The EFI system uses various sensors to detect the operating conditions of the engine and the vehicle. In accordance with the signals from these sensors, the ECU calculates the optimal fuel injection volume and operates the injectors in order to inject the proper volume of fuel. During ordinary driving, the engine ECU determines the fuel injection volume for achieving the theoretical air-fuel ratio, in order to ensure the proper power, fuel consumption, and exhaust emission levels simultaneously. At other times, such as during warm-up, acceleration, deceleration, or high-load driving conditions, the engine ECU detect those conditions with the various sensors and then corrects the fuel injection volume in order to ensure an optimal air-fuel mixture at all times. (1/1)
ESA (Electronic Spark Advance) System
The ESA system detects the conditions of the engine based on the signals provided by various sensors, and controls the spark plugs to generate sparks at the appropriate timing. Based on engine speed and engine load, the ESA precisely controls the ignition timing so that the engine can generate improve power, purify exhaust gases, and prevent knocking in an effective manner.
ISC (Idle Speed Control) System
The ISC system controls the idle speed so that it is always appropriate under varying conditions (warm-up, electrical load, etc.). To minimize fuel consumption and noise, an engine must operate at a speed that is as low as possible while maintaining a stable idle. Moreover, the idle speed must be increased to ensure the proper warm-up and drivability when the engine is cold or the air conditioner is being used.
Diagnostic System
The engine ECU contains a diagnostic system. The ECU constantly monitors the signals that are being input by various sensors. If it detects a malfunction with an input signal, the ECU records the malfunction in the form of DTCs (Diagnostic Trouble Codes) and illuminates the MIL (Malfunction Indicator Lamp). If necessary, the ECU can output the DTCs by blinking the MIL or displaying the DTCs or other data on the display panel of a handheld tester. The diagnostic functions that output the DTCs and datas of a malfunction on a hand-held tester are a highly advanced and complex form of electronics system. Because a diagnostic system must comply with the regulations of each country, its contents vary slightly by destination.

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.

Diesel Engine BACS (Boost and Altitude Compensator System)

admin — Mon, 26 Jul 2010 06:49:00 +0000

1. Description
The BACS is a device that provides both the functions of the turbocharger boost compensator and the HAC. The HAC valve maintains the constant pressure in the constant pressure chamber located below the diaphragm and thus has the function of the HAC.
2. Construction
The basic construction is the same as that of the turbochargerboost compensator.
3. Operation
(1) Low-altitude drivingThe air is introduced into the constant pressure chamber from the filter. Then, a vacuum is applied by the vacuum pump to make the pressure lower than normal atmospheric pressure at all times.
(2) High-altitude drivingThe atmospheric pressure, of the air which is introduced into the constant pressure chamber, is lower at high altitude. When the atmospheric pressure is low, the bellows expand to make the vacuum passage from the vacuum pump narrow. As a result, the vacuum pressure, which is applied to the constant pressure chamber, decreases. Thus, the pressure inside the constant pressure chamber stays the same at both the low-altitude and high-altitude driving. The HAC functions to maintain the pressure in the constant pressure chamber by moving the push rod in accordance with the change in atmospheric pressure on the top part of the diaphragm.
Diesel Engine PCS (Power Control System)
The PCS is a device that reduces the maximum injection volume when the vehicle is driven under a certain conditions such as 1st or reverse gear. Normally, the VSV is off and a vacuum from the vacuum pump is applied to the power control valve. Accordingly, the power control lever rotates clockwise causing the governor tension lever to separate. When the VSV is on, the air is let into the power control valve causing the power control lever to rotate counterclockwise. Thus, the power control lever causes the tension lever to rotate clockwise and this reduces the maximum fuel injection volume.

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.

VE Pump Options ACSD (Automatically-controlled Cold Starting Device)

admin — Fri, 23 Jul 2010 04:32:16 +0000

1. Description
The ACSD uses the contractive and expansive properties of thermo wax and the tension of a spring to automatically advance the injection timing in response to the coolant temperature, causing the engine to idle-up (fast idle). This improves the startability at low temperatures and the stability of idling.
2. Operation
(1) Cold engine
The thermo wax contracts and pulls the plunger. Lever A rotates clockwise by the spring tension. This causes lever B to push the adjusting lever toward the idle-up position, resulting in a faster idle speed. At the same time, the roller ring is rotated, advancing the injection timing.
(2) Warm engine
As the coolant temperature rises, the thermo wax gradually expands to push the plunger out. Lever A causes the plunger to rotate counter-clockwise, gradually decreasing the advance angle of the injection timing and lowering the idle speed. When the coolant temperature reaches about 5C (12F), both injection timing and idle speed return to normal.
HINT
The adjusting method is different between the engine with the ACSD and without the ACSD.

TCV (Timing Control Valve) of Fuel Injection

admin — Fri, 23 Jul 2010 04:30:59 +0000

The TCV renders the LST inactive if the vehicle is operated with a cold engine (coolant temperature below 6C (14F)) or at high altitudes (where the atmospheric pressure is below 93 kPa (70mmHg)). The purpose of providing a TCV is to prevent misfiring. If the injection timing is allowed to keep advancing at conditions where misfiring occurs easily (cold engine or high altitude), misfiring is prevented. Then, white smoke is also prevented. The emission control ECU determines the conditions of the engine using signals from the water temperature sensor and the atmospheric pressure sensor.

Then, the emission control ECU outputs signals that cause the TCV to close the fuel passage of the LST, thus rendering the LST inactive. TCV on Before the engine has warmed up (coolant temperature below 6C (14F)) or when the vehicle is driven at high altitudes (where the atmospheric pressure is below 93 kPa (700mmHg)), the emission control ECU outputs signals that cause the TCV to turn on and close the fuel passage. Therefore, even if the accelerator pedal is released and the engine load decreases, the LST becomes inactivated and does not retard the injection timing.

LST (Load-Sensing Timer) of Fuel Injection

admin — Thu, 22 Jul 2010 04:29:11 +0000

The LST changes the fuel injection timing in accordance with the engine load, and obtain the characteristic of advancing. The fuel is released from the orifice on the governor sleeve via the governor shaft passage to the inlet side of the feed pump. Therefore, the pressure inside the pump housing is lowered to retard the injection timing. When the load on the engine increases (increased injection volume), the flyweights remain closed. The pressure inside the pump housing is not lowered because the orifice on the governor sleeve and the governor shaft passage are not aligned. On the contrary, when the load on the engine decreases (decreased injection volume), the flyweights open. The orifice on the governor sleeve and the governor shaft passage are aligned causing the pressure inside the pump housing to be reduced and the timing to be retarded.

M-M (Minimum-Maximum) Speed Governor ofDiesel Engine injection pump

admin — Wed, 21 Jul 2010 04:19:59 +0000

The M-M speed governor controls the injection volume in accordance with the engine speed at minimum and maximum speeds. At other speed ranges, the fuel volume in accordance with the level of depression of the accelerator pedal is injected. (Except for the control spring, the construction of the all-speed governor and M-M speed governor are basically the same.)
Adjusting Screws
The injection pump has the following adjusting screws:
1. Maximum speed adjusting screwControls the maximum engine speed.
2. Idle speed adjusting screwAdjusts the engine speed during idling.
3. Full-load setting screwAdjusts the maximum fuel injection volume.
HINT:
As the maximum speed adjusting screw and full-load setting screw are adjusted to the proper position and sealed, normally they are not adjusted. However, if due to changes with the passing of time, adjustment becomes necessary, break the seal and perform an adjustment. After an adjustment, the maximum speed adjusting screw and full-load setting screw must be sealed.