Your Online Mechanic » Gasoline

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.

What is Diesel Knock and Gasoline Knock ?

admin — Thu, 01 Jul 2010 09:01:57 +0000

The fuel accumulated during the ignition delay period is burned at one time during the flame propagation period. Thus the pressure inside the combustion chamber rises sharply. The pressure inside the combustion chamber rises sharply in proportion to the amount of the fuel injected during the ignition delay. This pressure wave causes the engine to vibrate and make a noticeable noise. This is called as diesel knock. The diesel engine uses a self-ignition combustion system, so to a certain extent, diesel knock is unavoidable. Causes of diesel knock are as follows:

Engine temperature is low.

Intake air temperature is low.

Fuel ignition temperature is high. (Cetane number is low.)

Injection timing is early. (The fuel is injected when the compression temperature is still low.)

Injection condition is not good. (The fuel does not mix well with the air.)

To prevent diesel knock, shortening the ignition delay, thus avoiding a sudden rise in pressure.

The following methods are employed:

Using fuel with a high cetane number.

Raising the compression pressure and the intake air temperature until the beginning of the fuel injection.

Raising the combustion chamber temperature.

CO/HC Inspection and Adjustment

admin — Sun, 20 Jun 2010 05:03:31 +0000

1. Necessity

Determination of engine condition. By measuring CO/HC, it is possible to determine the engine condition, including the effectiveness of the airfuel ratio, and the operation of the emission control system. It can be determined that the engine and emission control system are normal when the CO and HC are within the standard value, and the engine operates smoothly. When the engine does not operate smoothly or HC levels are high, engine misfire is a probable cause. Causes of engine misfire are improper air-fuel ratio, poor compression, ignition system trouble, or emission control system trouble, etc. For meeting regulations.

2. With TWC/oxygen sensor

It is not necessary to adjust the CO level because the engine control system increases and decreases the fuel injection volume coming out of the injector to adjust the air-fuel ratio to more closely match the theoretical air-fuel ratio, using the oxygen sensor signal.

Most of CO and HC are purified by the TWC even if some misfiring occurs.

When CO and HC are detected, the following are probable causes: Poor or insufficient warm-up of TWC, rich air-fuel mixture, a high rate of misfire.

3. Without TWC/oxygen sensor

It is necessary to adjust the CO level within the standard value in order to meet the regulations and use the engine in good condition.

The air-fuel mixture is rich when CO/HC concentration is high and the engine runs smoothly. It is necessary to adjust the CO concentration in order to keep emission gases clean, even though the engine operates more smoothly when the CO concentration is higher than the standard value.

When the CO concentration is too low, the HC concentration is high and the engine does not operate smoothly, causing misfires to occur.

What is an Automotive Catalytic Converters?

admin — Mon, 14 Jun 2010 04:48:11 +0000

Outline

The catalytic converter makes harmful substances (CO, HC and NOx) react chemically with harmless ones (H2O, CO2, N2) according to the exhaust gas passed. Generally platinum, palladium, iridium and rhodium, etc., are used as catalysts for automobiles.

(1) Types of catalyst

Oxidation catalystOxidize HC or CO and form nonpolluting H2O or CO2.

Deoxidization catalystRemove oxygen from NOx and form non-polluting N2.

Oxidation/Deoxidization catalystPerform above two functions at the same time. (Oxidation/Deoxidization catalyst for automobiles is called Three-Way Catalytic Converter (TWC)because three harmful substances, CO/HC/NOx, are transformed into non-polluting substances at the same time. Oxidation/Deoxidization catalyst is used for most automobiles nowadays.)

(2) Operating temperature catalyst

For the catalyst, the purification rate changes according to the temperature. As shown in the graph, the purification rate is close to 100% and purifies the exhaust gas effectively when the catalyst temperature rises over 40C.

NOTICE:

Vehicles equipped with the catalytic converter need to use unleaded gasoline, because lead adheres to the surface of catalyst and the oxygen sensor (O2 sensor), and the appropriate effect cannot be attained if leaded gasoline is used.

(3) Three-Way Catalyst (TWC) system

The TWC is the system that oxidizes CO and HC in the exhaust gas and deoxidizes NOx at the same time, to purify them into CO2, H2O and N2. Recently the monolithic type is used as shown in the illustration. Alumina or catalytic substances coat the grated pattern of monolith which has many holes. The harmful substances are purified by passing through the holes. There are two types of monolith; ceramic type and metal type. The thinner the grate is, the higher the purification ability becomes. The TWC can be most effective around the theoretical air-fuel ratio. Therefore, the air-fuel ratio feedback system is needed to keep the air-fuel ratio around the theoretical air-fuel ratio. The air-fuel ratio feedback system detects oxygen in the exhaust gas, using the oxygen sensor attached in the exhaust manifold. Then the fuel injection volume is adjusted by the engine ECU to control the air-fuel ratio at all times so that the TWC performs properly.

Principle of Production of Exhaust Gases

admin — Fri, 11 Jun 2010 04:41:52 +0000

Theoretical Air-fuel Ratio

The theoretical air-fuel ratio is the ratio of the minimum amount of fuel and air (which contains oxygen) needed to fully burn the fuel. Gasoline is a mixture of several types of hydrocarbons of which is the most predominant octane (C8H18). 2C8H18 + 25O2 !16CO2 + 18H2O In order for 1g of octane to produce water (H2O) and carbon dioxide (CO2) when burned, 15g of air is necessary. The actual fuel is not pure octane but octane and various HCs. Therefore the theoretical air-fuel ratio is about 14.7.

Graph Showing the Generation of CO/HC/NOx

The graph on the left, shows the air-fuel ratio and theamounts of CO/HC/NOx generated.

1. Richer

CO/HCIncrease

NOxDecrease

2. Leaner

CODecrease

HCDecrease

However it increases because of the misfire when the air-fuel ratio is too lean. NOxThe amount generated is greatest when the actual air-fuel ratio is slightly leaner than the theoretical air-fuel ratio. When the ratio becomes even leaner, the amount decreases because the combustion temperature decreases. The generated amounts of CO/HC/NOx increase under the following conditions, except for the graph on the left.

3. While engine is cold

The generated amounts of CO/HC increase because the rich air-fuel mixture is supplied.

4. At heavy load

The emission gas is increased because both the fuel and the air are increased.

The generated amounts of CO/HC increase because the rich air-fuel mixture is supplied.

The generated amounts of NOx increase becausethe combustion temperature rises.

HINT:

PPMAbbreviation for Parts Per Million. Used as a unit to indicate concentration or content.

Harmful Gases Produced by Automobiles

admin — Wed, 09 Jun 2010 04:40:34 +0000

1. What is emission control system?

The emission control system reduces the emissions, which are harmful to the environment and human beings produced by automobiles.

2. What are emissions?

The term emission gas means the evaporated fuel from the fuel tank and the blow-by gas, which passes between the piston and the cylinder wall, including the exhaust gas. The emission gas is harmful to the environment and human beings because it includes such harmful substances as CO (carbon monoxide), HC (hydrocarbon) and NOx (nitrous oxides). Vehicles equipped with diesel engines emit not only gases such as CO, HC, NOx but also carbon particles, which also affect the environment and human beings.

(1) CO (crbon monoxide)

CO is generated when an insufficient amount of oxygen is taken the combustion chamber (incomplete combustion).

2C (carbon) + O2 (oxygen) 2CO (carbon monoxide)

When CO is inhaled into the human body, it disolves in the blood and the blood’s ability to deliver oxygen is hindered. Breathing in large amounts of CO will result in death.

(2) HC (hydrocarbon)

HC is generated during incomplete combustion in the same way as CO. Also, HC is generated in the following cases

<1>When the temperature of the quenching zone is low, it does not reach the combustion temperature.

<2>The intake gas blows through when the valve timing overlaps. The richer the air-fuel mixture is, the more HC is generated. The leaner it is, the less HC is generated. The generated amounts of HC become greater because it cannot burn when the air-fuel mixture is too lean.

When HC is inhaled into the human body, it becomes cancer-causing agent. It also causes the photochemical smog. Blow-by gas HC :25% Exhaust gas CO :100% HC 55% NOx :100%

(3) NOx (nitrous oxides)

NOx is generated by the nitrogen and oxygen in the air of the air-fuel mixture when the temperature of the combustion chamber rises above about 1,80C (3,272 F). The higher the combustion temperature rises, the more NOx is generated. When the air-fuel mixture is lean, more NOx is generated because the ratio of oxygen in the air-fuel mixture is too high. Therefore, NOx is generated according to the two factors of the combustion temperature and oxygen concentration.

N2 (nitrogen) + O2 (oxygen) 2NO (NO, NO2 or

N2… NOx)

When NOx is inhaled into the human body, it irritates the nose and throat. Also it causes the photochemical smog.

1. Exhaust gas

Exhaust gas is emitted from the exhaust pipe. In theory, only CO2 (carbon dioxide) and H2O (vapor) are generated when burning gasoline. However, all of the gasoline does not react according to the chemical theory due to such factors as air-fuel ratio, N2 (nitrogen) in the atmosphere, combustion temperature, combustion duration, etc. That is how harmful substances such as CO, HC or NOx are generated.

2. Evaporated fuel

Evaporated fuel is emitted into the atmosphere afterthe fuel evaporates from the fuel tank, carburetor, etc. Its main component is HC.

3. Blow-by gas

Blow-by gas blows from the gap between the piston and cylinder wall into the crankcase. It consists of mostly fuel of unburned gas (HC).

Elements of a Gasoline Engine

admin — Sun, 21 Mar 2010 09:05:37 +0000

All gasoline engines mounted on Toyota automobiles are four-stroke engines. Four-stroke engines operate by continuous and regular repetition of the following sequence:

1. Intake stroke

2. Compression stroke

3. Combustion stroke

4. Exhaust stroke

Basic principle of four-stroke engine

In order for an engine to operate smoothly under a wide range of operating conditions, the following three conditions must be satisfied:

Good air-fuel mixture

Good compression

Good spark

What is a GoodEngine Compression?

admin — Sat, 13 Mar 2010 09:19:15 +0000

Necessity of compressing the airfuel mixture

When an uncompressed air-fuel mixture is ignited, it burns slowly due to the low density of fuel and air. However, when compressed air-fuel mixture is ignited, the high density causes the mixture to suddenly burn (explode). Even when the fuel mixture is the same, a compressed mixture will release more power than an uncompressed mixture when ignited. Furthermore, compressing the air-fuel mixture causes the fuel and air to mix more thoroughly, resulting in a higher rate of vaporization of the gasoline and higher temperature when ignited. The compressed air-fuel mixture also burns more easily than before. The level of compression of the air-fuel mixture is expressed in the compression ratio. Generally, the greater explosive pressure can be attained when the compression pressure is higher. However the knocking occurs if the pressure is too high. Therefore, the compression ratio of the gasoline engine is normally designed to be between to 11.

Good Spark

The gasoline engine converts the combustion of the air-fuel mixture to motive force. In order for the air-fuel mixture to burn well, it is important to have a powerful enough spark with proper ignition timing.

Conditions for a good spark

(1) Ability to generate a powerful spark enough for the air-fuel mixture to burn (explode) The spark plug in a gasoline engine generates a spark to burn the air-fuel mixture. If the spark is weak, there will not be enough energy to ignite the air-fuel mixture. For that reason, a powerful spark is essential.

(2) Ability to keep the proper ignition timing for every engine condition The ignition timing changes according to engine speed or load to ensure that there is always proper ignition timing.

Components of a standard Automotive Engine

The engine is made of many components to help it convert heat energy into mechanical energy efficiently when the air-fuel mixture is burned.

1. Cylinder head

(1) Cylinder head

(2) Cylinder head gasket

2. Cylinder block

3. Crankshaft

(1) Crankshaft

(2) Bearing cap

4. Connecting rods

(1) Connecting rod

(2) Bearing cap

5. Bearings

(1) Connecting rod bearing

(2) Crankshaft bearing

(3) Thrust washer

6. Pistons

(1) Piston

(2) Piston pin

(3) Piston rings

7. Valve mechanism etc.

(1) Exhaust camshaft

(2) Intake camshaft

(3) Valve lifter

(4) Keeper

(5) Valve spring retainer

(6) Valve spring

(7) Valve stem oil seal

(8) Spring seat

(9) Valve

(10)Timing chain

(11)Chain tensioner slipper

(12)Chain vibration damper

(13) Timing chain tensioner

(14)Crankshaft timing sprocket

When these components function correctly, motive force is produced.

Engine Cylinder Head

admin — Fri, 12 Mar 2010 09:22:06 +0000

The cylinder head is located on top of the cylinder block. The bottom of the cylinder head is indented and combines with the piston to form the combustion chamber. Internally, there are a oil hole and a water jacket to cool the valves and the spark plugs. Most gasoline engines have cylinder heads made of aluminum alloy. Aluminum alloy is lighter than cast iron, and it has excellent heat conduction properties. In between the cylinder block and the cylinder head is the cylinder head gasket, which acts to seal the junction of the two parts in order to prevent leakage of highly pressurized gasses, combustion gasses, coolant and engine oil.