OBJECTIVES After studying Chapter 3, the reader should be able to:. 1 OBJECTIVES After studying Chapter 3, the reader should be able to: 1. Explain how a four-stroke cycle gasoline engine operates. 2. Explain the Atkinson cycle and how it is affects engine efficiency. 3. List the various characteristics by which vehicle engines are classified and measured. 4. Describe how turbocharging or supercharging increases engine power. 5. Describe how the fuel injection and ignition work on hybrid gasoline engines. 6. Explain how active control engine mounts function.
HYBRID INTERNAL COMBUSTION ENGINES (ICE) The engine converts part of the fuel energy to useful power. This power is used to move the vehicle. Engines used in hybrid vehicles do differ from those used in conventional vehicles. These differences can include: Smaller displacement than most similar vehicles of the same size and weight Use of the Atkinson cycle to increase efficiency Crankshaft offset to reduce internal friction Often do not use a conventional starter motor Some use spark plugs that are indexed so the open side of the spark is pointed toward the intake valve for maximum efficiency Engine mounts are computer-controlled to counteract and eliminate undesirable engine vibration The use of low viscosity engine oil, such as SAE 0W-20
The engines are also similar to those used in non-hybrid vehicles and share the following features: Conventional fuel injection system Conventional engine layout and number of cylinders (except for the Honda Insight that uses a three-cylinder engine) Use the same engine parts as conventional engines except for those using CNG as a fuel. These engines utilize stronger internal parts, such as pistons and connecting rods, to better withstand the high compression used in these engines and to take advantage of the higher octane of the fuel. Same ignition system Same or similar engine lubrication system including the oil filter but with a lighter viscosity oil than used in similar conventional vehicles
ENGINE FUNDAMENTALS Most automotive engines use the four-stroke cycle of events, begun by the starter motor which rotates the engine. The four-stroke cycle is repeated for each cylinder of the engine.
ATKINSON CYCLE One key feature of the Atkinson cycle that remains in use today is that the intake valve is held open longer than normal to allow a reverse flow into the intake manifold. This reduces the effective compression ratio and, when combined with an increased stroke and/or reduced combustion chamber volume, allows the expansion ratio to exceed the compression ratio while retaining a normal compression pressure. This is desirable for good fuel economy because the compression ratio in a spark ignition engine is limited by the octane rating of the fuel used, while a high expansion ratio delivers a longer power stroke and reduces the heat wasted in the exhaust. This increases the efficiency of the engine because more work is being achieved.
The Atkinson cycle is up to 10% more efficient than a conventional four-stroke gasoline engine, and produces more torque than a conventional design engine at high engine speeds but it does reduce low-end engine torque. A typical hybrid electric vehicle can take advantage of this by using an electric motor to propel the vehicle at lower speeds. Electric motors excel at low RPM torque, so the hybrid transaxle makes up for the low-speed losses of the Atkinson cycle gasoline engine.
ENGINE SPECIFICATIONS Engine size is described as displacement ENGINE SPECIFICATIONS Engine size is described as displacement. Displacement is the cubic inch (cu. in.) or cubic centimeter (cc) volume displaced or swept by all of the pistons. The diameter of a cylinder is called the bore. The distance the piston travels down in the cylinder is called the stroke.
A liter (L) is equal to 1000 cubic centimeters; therefore, most engines today are identified by their displacement in liters. 1 L = 1000 cc 1 L = 61 cu. in. 1 cu. in. = 16.4 cc
Compression Ratio Compression ratio (CR) is the ratio of the volume in the cylinder above the piston when the piston is at the bottom of the stroke to the volume in the cylinder above the piston when the piston is at the top of the stroke.
If Compression Is Lower If Compression Is Higher Lower power Higher power possible Poorer fuel economy Better fuel economy Easier engine cranking Harder to crank engine, especially when hot More advanced ignition timing possible without spark knock (detonation) Less ignition timing advance required to prevent spark knock (detonation)
CR = Volume in cylinder with piston at bottom of cylinder Volume in cylinder with piston at top center
TORQUE, WORK, AND POWER Torque is the term used to describe a rotating force that may or may not result in motion. If ten pounds of force is applied to the end of a one-foot-long wrench to turn a bolt, then you are exerting 10 pound-feet of torque is being exerted.
The metric unit for torque is Newton-meters because Newton is the metric unit for force and the distance is expressed in meters. one pound-foot = 1.3558 Newton-meters one Newton-meter = 0.7376 pound-foot
Work is defined as actually accomplishing movement when torque or a force is applied to an object. A service technician can apply torque to a bolt in an attempt to loosen it, yet no work is done until the bolt actually moves. Work is calculated by multiplying the applied force (in pounds) by the distance the object moves (in feet). Applying 100 pounds of force to move an object 10 feet, accomplishes 1000 foot-pounds of work (100 pounds × 10 feet = 1000 foot pounds).
Power The term power means the rate of doing work Power The term power means the rate of doing work. Power equals work divided by time. Work is achieved when a certain amount of mass (weight) is moved a certain distance by a force. If the object is moved in 10 seconds or 10 minutes does not make a difference in the amount of work accomplished, but it does affect the amount of power needed. Power is expressed in units of foot-pounds per minute.
Horsepower The power an engine produces is called horsepower (hp) Horsepower The power an engine produces is called horsepower (hp). One horsepower is the power required to move 550 pounds one foot in one second, or 33,000 pounds one foot in one minute (550 lb. × 60 sec = 33,000 lb.). This is expressed as 500 foot-pounds (ft. lb.) per second or 33,000 foot-pounds per minute.
The actual horsepower produced by an engine is measured with a dynamometer. A dynamometer (often abbreviated as dyno or dyn) places a load on the engine and measures the amount of twisting force the engine crankshaft places against the load. The load holds the engine speed, so it is called a brake. The horsepower derived from a dynamometer is called brake horsepower (bhp). The horsepower is calculated from the torque readings at various engine speeds (in revolutions per minute or RPM). Horsepower is torque times RPM divided by 5252. Horsepower = Torque × RPM 5252 Torque is what the driver "feels" as the vehicle is being accelerated. A small engine operating at a high RPM may have the same horsepower as a large engine operating at a low RPM.
SAE horsepower rating. SAE gross horsepower is the maximum power an engine develops without some accessories in operation. SAE net horsepower is the power an engine develops as installed in the vehicle. Ratings are about 20% lower for the net rating method.
For the 2006 model year, all horsepower and torque specifications have been updated to reflect revised Society of Automotive Engineers (SAE) J1349 (Revised 8/04) net calculations that went into effect in January of 2005. These new calculations reflect a number of changes in the way horsepower and torque are measured and may cause SAE net horsepower and torque values published before to differ from the figures in previous years. The goal of the new standards is to ensure greater consistency in the way engines are tested in order to derive the horsepower and torque ratings advertised to the public.
Horsepower and altitude Horsepower and altitude. Because the density of the air is lower at high altitude, the power that a normal engine can develop is greatly reduced at high altitude. According to SAE conversion factors, a nonsupercharged or nonturbocharged engine loses about 3% of its power for every 1000 feet (300 meters [m]) of altitude.
HYBRID ENGINE DESIGN FEATURES The piston pin holes are usually not centered in the piston. They are located toward the major thrust surface, approximately 0.062 inch (1.57 millimeters) from the piston centerline.
Pin offset is designed to reduce piston slap and noise that can result as the large end of the connecting rod crosses over top dead center.
Offset Crankshaft The thrust side is the side of the cylinder that the connecting rod points to when the piston is on the power stroke. Most V-block engine (V-6 or V-8) rotates clockwise viewed from the front of the engine. The left bank piston thrust side faces the inside (center) of the engine. The right bank piston thrust side faces the outside of the block. This rule is called the left-hand rule and states: Stand at the rear of the engine and point your left hand toward the front of the engine. Raise your thumb straight up, indicating the top of the engine. Point your middle finger toward the right. This represents the major thrust side of the piston.
The offset usually varies from 1/16 inch to ½ inch, depending on make and model. Most gasoline engines used in hybrid gasoline/electric vehicles use an offset crankshaft.
Composite Camshafts A composite camshaft uses a lightweight tubular shaft with hardened steel lobes press-fitted over the shaft.
Variable Valve Timing and Lift There are two basic systems including: Variable camshafts such as the system used by Honda/Acura called Variable Valve Timing and Lift Electronic Control or VTEC. This system uses two different cam lobes for low and high RPM. When the engine is operating at idle and speeds below about 4000 RPM, the valves are opened by cam lobes that are optimized for maximum torque and fuel economy. When engine speed reaches a predetermined speed, depending on the exact make and model, the computer turns on a solenoid, which opens a spool valve. When the spool valve opens, engine oil pressure pushes against pins that lock the three intake rocker arms together. With the rocker arms locked together, the valves must follow the profile of the high RPM cam lobe in the center. This process of switching from the low-speed camshaft profile to the high-speed profile takes about 100 milliseconds (0.1 sec).
Variable camshaft timing is used on many engines including General Motors 4-, 5- and 6-cylinder engines, as well as engines from BMW, DaimlerChrysler, and Nissan. On a system that controls the intake camshaft only, the camshaft timing is advanced at low engine speed, closing the intake valves earlier to improve low RPM torque. At high engine speeds, the camshaft is retarded by using engine oil pressure against a helical gear to rotate the camshaft. When the camshaft is retarded, the intake valve closing is delayed, improving cylinder filling at higher engine speeds.
Roller Lifters The use of roller rocker arms decreases friction in the valve train and helps the engine produce optimum power and economy.
Cylinder Deactivation Some engines are designed to be operated on four of eight or three of six cylinders during low load conditions to improve fuel economy. When the computer determines that the cylinder can be deactivated, oil pressure is delivered to a passage, which depresses the pin and allows the outer portion of the lifter to follow the contour of the cam while the inner portion remains stationary, keeping the valve closed. The electronic operation is achieved through the use of lifter oil manifold, which is located in the valley between the banks of cylinders and contains solenoids to control the oil flow, which is used to activate or deactivate the cylinders.
How Are Engine Vibrations Controlled During Cylinder Deactivations How Are Engine Vibrations Controlled During Cylinder Deactivations? When a Honda V-6 equipped with cylinder deactivation is only running on three cylinders, there is a natural imbalance, which can produce drumming sounds and vibrations. To counteract this, the engine is mounted on special active control engine mounts (ACM) that electronically adjust themselves to counteract engine vibrations. The ACM vacuum solenoid valve (VSV) is controlled by a pulse signal transmitted from the engine control module (ECM). In normal operation, the frequency of this pulse signal is matched with engine speed to effectively dampen engine vibration.
Further booming sounds are reduced by an active noise control (ANC) system that automatically sends an out-of-phase sound through the loudspeaker system to cancel out engine noises. This system also works when the engine is idling and the counter sounds are produced by the speakers in the vehicle even if the radio is off.
HYBRID ENGINE LUBRICATION SYSTEM Lubrication Principles Lubrication between two moving surfaces results from an oil film that separates the surfaces and supports the load. If oil were put on a flat surface and a heavy block were pushed across the surface, the block would slide more easily than if it were pushed across a dry surface. The reason for this is that a wedge-shape oil film is built up between the moving block and the surface
Viscosity is the oil's thickness or resistance to flow Viscosity is the oil's thickness or resistance to flow. The principle just described is that of hydrodynamic lubrication. The prefix hydro- refers to liquids, as in hydraulics, and dynamic refers to moving materials. Hydrodynamic lubrication occurs when a wedge-shape film of lubricating oil develops between two surfaces that have relative motion between them.
Normal engine oil pressure range is from 10 to 60 psi (200 to 400 kPa) (10 psi per 1000 engine RPM). Conversely, hydrodynamic film pressures developed in the high-pressure areas of the engine bearings may be over 1000 psi (6900 kPa).
ENGINE OIL The oil must not be too thick at low temperatures to allow the engine to start. The lowest temperature at which oil will pour is called its pour point. An index of the change in viscosity between the cold and hot extremes is called the viscosity index (VI). All oils with a high viscosity index thin less with heat than do oils with a low viscosity index.
Engine Oil Additives Additives are usually classified according to the property they add to the oil. Antioxidants reduce the high-temperature contaminants. Corrosion preventives reduce acid formation that causes bearing corrosion. Detergents and dispersants prevent low-temperature sludge binders from forming and keep the sludge-forming particles finely divided.
Extreme pressure and anti-wear additives form a chemical film that prevents metal-to-metal seizure anytime boundary lubrication exists. Viscosity index improvers are used to reduce viscosity change as the oil temperature changes. Pour point depressants coat the wax crystals in the oil so that they will not stick together. A number of chemicals that will help each other can be used for each of the additive requirements. The balanced additives are called an additive package.
SAE Rating Engine oils are sold with an SAE (Society of Automotive Engineers) grade number, which indicates the viscosity range into which the oil fits. Oils tested at 212°F (100°C) have a number with no letter following. For example, SAE 20 indicates that the oil has only been checked at 212°F (100°C). This oil's viscosity falls within the SAE 20 grade number range when the oil is hot. Oils tested at 0F (-18C) are rated with a number and the letter W, which means winter and indicates that the viscosity was tested at 0F, such as SAE 5W. An SAE 5W-20 multi-grade oil is one that meets the SAE 5W viscosity specification when cooled to 0°F (-18°C) and meets the SAE 20 viscosity specification when tested at 212°F (100°C).
Most vehicle manufacturers recommend the following multi-viscosity engine oils for their hybrid engines: SAE 0W-20 SAE 5W-20 Thinner oil 1. Improved cold-engine starting 2. Improved fuel economy Thicker oil 1. Improved protection at higher temperatures 2. Reduced fuel economy
API Rating The American Petroleum Institute (API), working with the engine manufacturers and oil companies, has established an engine oil performance classification. Oils are tested and rated in production automotive engines. The oil container is printed with the API classification of the oil. The API performance or service classification and the SAE grade marking are the only information available to help determine which oil is satisfactory for use in an engine.
Gasoline Engine Rating In gasoline engine ratings, the letter S means service, but it can be remembered as being for use in spark ignition engines. The rating system is open-ended so that newer, improved ratings can be readily added as necessary (the letter I is skipped to avoid confusion with the number one). SA Straight mineral oil (no additives), not suitable for use in any engine SB Non-detergent oil with additives to control wear and oil oxidation SC Obsolete (1964) SD Obsolete (1968) SE Obsolete (1972) SF Obsolete (1980) SG Obsolete (1988) SH Obsolete (1993-1997) SJ Obsolete (1997-2001) SL 2001-2003 SM 2004+
Diesel Engine Rating Diesel classifications begin with the letter C which stands for commercial, but can also be remembered as being for use in compression ignition or diesel engines. CA Obsolete CB Obsolete CC Obsolete CD Minimum rating for use in a diesel engine service CE Designed for certain turbocharged or supercharged heavy-duty diesel engine service CF For off-road indirect injected diesel engine service CF-2 Two-stroke diesel engine service CF-4 High-speed four-stroke cycle diesel engine service CG-4 Severe-duty high-speed four-stroke diesel engine service CI-4 Severe-duty high-speed four-stroke diesel engine service (2002) CJ-4 For use in 2007 and newer diesels engine that operate on Ultra Low Sulfur Diesel fuel (ULSD)
ILSAC Oil Rating The International Lubricant Standardization and Approval Committee (ILSAC) developed an oil rating that consolidates the SAE viscosity rating and the API quality rating. If an engine oil meets the standards, a "star burst" symbol is displayed on the front of the oil container. If the star burst is present, the vehicle owner and technician know that the oil is suitable for use in almost any gasoline engine.
The original GF-1 (gasoline fueled) rating was updated to GF-2 in 1997, GF-3 in 2000 and GF-4 in 2004 and scheduled to be replaced in 2009 with GF-5.
European Oil Ratings The Association des Constructeurs European d'Automobiles (ACEA) represents most of the Western European automobile and heavy-duty truck market. The organization uses different engines for testing than those used by API and SAE, and the requirements necessary to meet the ACEA standards are different yet generally correspond with most API ratings. ACEA standards tend to specify a minimum viscosity rating and certain volatility requirements not specified by API.
Japanese Oil Ratings The Japanese Automobile Standards Organization (JASO) also publishes oil standards.
SYNTHETIC OIL According to the American Petroleum Institute, engine oil is classified into groups as follows. Group I - Mineral, non-synthetic, base oil with few if any additives. Group II – Mineral oils with quality additive packages. Most of the conventional engine oils are Group II. Group III – Hydrogenated (hydroisomerized) synthetic compounds commonly referred to as hydrowaxes or hydrocracked oil. This is the lowest cost of synthetic engine oils. Castrol Syntec is a Group III oil. Group IV – Synthetic oils made from mineral oil and monomolecular oil called polyalpholefin or POA. Mobil 1 is an example of Group IV synthetic oil. Group V – Non-mineral sources such as alcohol from corn called diesters or polyolesters. Red Line synthetic oil is an example of a Group V oil. Groups III, IV, and V are all considered to be synthetic because the molecular structure of the finished product does not occur naturally and is man-made through chemical processes.
OIL CHANGE INTERVALS All vehicle and engine manufacturers recommend a maximum oil change interval. The recommended intervals are almost always expressed in terms of mileage or elapsed time (or hours of operation), whichever milestone is reached first.
The important thing to remember is that these are recommended maximum intervals and they should be shortened substantially if any of the following operating conditions exists. 1. Operating in dusty areas 2. Towing a trailer 3. Short-trip driving, especially during cold weather (The definition of a short trip varies among manufacturers, but it is usually defined as 4 to 15 miles [6 to 24 kilometers] each time the engine is started.) 4. Operating in temperatures below freezing (32°F, 0°C) 5. Operating at idle speed for extended periods of time (such as normally occurs in police or taxi service)
Follow the Seasons A helpful method for remembering when the oil should be changed is to change the oil at the start of each season of the year. Fall (September 21) Winter (December 21) Spring (March 21) Summer (June 21)
HYBRID ENGINE IGNITION SYSTEM The ignition system includes components and wiring necessary to create and distribute a high voltage (up to 40,000 volts or more). All ignition systems apply battery voltage to the positive side of the ignition coil and pulse the negative side to ground, except for capacitor-discharge systems used on some vehicles. When the coil negative lead is grounded, the primary (low-voltage) circuit of the coil is complete and a magnetic field is created by the coil windings. When the circuit is opened, the magnetic field collapses and induces a high-voltage in the secondary winding of the ignition coil, which is used to generate a high-voltage arc at the spark plug.
Ignition Coils The heart of any ignition system is the ignition coil Ignition Coils The heart of any ignition system is the ignition coil. The coil creates a high-voltage spark by electromagnetic induction. Some ignition coils use windings that are electrically connected while other coils are true transformers in which the primary and secondary windings are not electrically connected.
What Is a “Married” and “Divorced” Coil Design What Is a “Married” and “Divorced” Coil Design? An ignition coil contains two windings: a primary winding and a secondary winding. These windings can be either connected together or kept separated. Married. These are also called a tapped transformer design.
Divorced. These are also called a true transformer design and are used by most waste-spark ignition coils to keep the primary and secondary winding separated.
To get a spark out of an ignition coil, the primary coil circuit must be turned on and off. This primary circuit current is controlled by a transistor (electronic switch) inside the ignition module (or igniter) that in turn is controlled by one of several devices, including: Hall-effect switch Magnetic crankshaft position sensors
Up-Integrated Ignition Control Most coil-on-plug ignition systems use the PCM for ignition timing control. This type of ignition control is called up-integrated because all timing functions are interpreted in the PCM, rather than being split between the ignition control module and the PCM. The ignition module, if even used, contains the power transistor for coil switching. The signal, as to when the coil fires, is determined and controlled from the PCM.
Coil-On-Plug Ignition Coil-on-plug (COP) ignition uses one ignition coil for each spark plug. This system is also called coil-by-plug, coil-near-plug, or coil-over-plug ignition. All hybrid electric vehicles use coil-on-plug-type ignition system.
There are two basic types of coil-on-plug ignition including: 2-wire There are two basic types of coil-on-plug ignition including: 2-wire. This design uses the vehicle computer to control the firing of the ignition coil. The two wires include ignition voltage feed and the pulse ground wire, which is controlled by the computer. All ignition timing and dwell control are handled by the computer. 3-wire. This design includes an ignition module at each coil. The three wires include: Ignition voltage Ground Pulse from the computer to the built-in module
Ion-Sensing Ignition In an ion-sensing ignition system, the spark plug itself becomes a sensor. The ignition control (IC) module applies a voltage of about 100 to 400 volts DC across the spark plug gap after the ignition to sense the burning gases called plasma inside the cylinder. The coil discharge voltage (10 to 15 KV) is electrically isolated from the ion-sensing circuit. The combustion flame is ionized and will conduct some electricity, which can be accurately measured at the spark plug gap. The purposes of this circuit include: Misfire detection (required by OBD-II regulations) Knock detection (eliminates the need for a knock sensor) Ignition timing control (to achieve the best spark timing for maximum power with lowest exhaust emissions) Exhaust gas recirculation (EGR) control Air-fuel ratio control on an individual cylinder basis Ion-sensing ignition systems still function the same as conventional coil-on-plug designs, but the engine does not need to be equipped with a camshaft position sensor, or a knock sensor, because both of these functions are achieved using the electronics inside the ignition control circuits.
Indexed Spark Plugs One hybrid engine, the three-cylinder Honda Insight, uses indexed spark plugs. Indexed spark plugs mean that the side electrode is facing away from the intake valve. With normal spark plugs, the side electrode may or may not block the spark (electrical arc). Honda has four different spark plugs available for this engine, labeled A, B, C or D. The specified plug for each cylinder is stamped next to the spark plug opening. The spark plugs also have a letter marked on the top with one of the letters.
OXYGEN SENSORS A conventional oxygen sensor is directly in the path of the exhaust gas stream where it monitors oxygen level in both the exhaust stream and the ambient air. In a zirconia oxygen sensor, the tip contains a thimble made of zirconium dioxide (ZrO2), an electrically conductive material capable of generating a small voltage in the presence of oxygen.
Atmospheric air enters through the other end of the sensor or through the wire of the sensor and contacts the inner side of the thimble. The inner and outer surfaces of the thimble are plated with platinum. The inner surface becomes a negative electrode; the outer surface is a positive electrode. Atmospheric air contains a relatively constant 21% of oxygen. Rich exhaust gases contain little oxygen. Exhaust from a lean mixture contains more oxygen. Negatively charged oxygen ions are drawn to the thimble where they collect on both the inner and outer surfaces.
When the concentration of oxygen on the exhaust side of the thimble is low (rich exhaust), a high voltage (0.60 to 1.0 volts) is generated between the electrodes. As the oxygen concentration on the exhaust side increases (lean exhaust), the voltage generated drops low (0.00 to 0.3 volts).
If the exhaust contains very little oxygen (O2S), the computer assumes that the intake charge is rich (too much fuel) and reduces fuel delivery.
There are several different designs of oxygen sensors, including: One-wire oxygen sensor. The one wire of the one-wire oxygen sensor is the O2S signal wire. The ground for the O2S is through the shell and threads of the sensor and through the exhaust manifold. Two-wire oxygen sensor. The two-wire sensor has a signal wire and a ground wire for the O2S. Three-wire oxygen sensor. The three-wire sensor design uses an electric resistance heater to help get the O2S up to temperature more quickly and to help keep the sensor at operating temperature even at idle speeds. The three wires include the O2S signal, the power, and ground for the heater. Four-wire oxygen sensor. The four-wire sensor is a heated O2S (HO2S) that uses an O2S signal wire and signal ground. The other two wires are the power and ground for the heater.
Oxygen sensors are numbered according to their location in the engine Oxygen sensors are numbered according to their location in the engine. On a V-type engine, heated oxygen sensor number 1 (HO2S1) is located in the exhaust manifold on the side of the engine where the number one cylinder is located.
WIDE-BAND OXYGEN SENSOR There are two types of oxygen sensors that can detect an actual air-fuel ratio in the exhaust gases as opposed to a conventional oxygen sensor, which simply changes voltage at exactly 14.7:1 air-fuel ratio. These sensors can measure the air-fuel ratio as rich as 12:1 and as lean as 22:1, depending on the exact type of sensor used.
A wide band oxygen sensor that uses a single cell is a four-wire unit used by Toyota and is called a linear air-fuel sensor. Another type of wide-band oxygen sensor uses a dual cell and has five or six wires. This type of sensor is called a lean air-fuel sensor (LAF) by Honda and a wide-range air-fuel sensor by Bosch. Both types of wide-band oxygen sensors need to be between 1200°F and 1450°F (650°C and 790°C) to operate efficiently. A typical dual cell wide band sensor usually uses five wires. One power wire One ground wire for the electric heater Three sensor wires
A wide-band oxygen sensor can be best described as having two oxygen sensors mated together with a diffusion layer between the two components. Just as in a conventional zirconium dioxide oxygen sensor, current flows from one side to the other and produces a voltage. In a wide-band oxygen sensor, an oxygen pump uses a heated cathode and anode to pull oxygen from the exhaust into a diffusion gap. The diffusion layer and the oxygen sensor elements are electrically connected so that it takes a certain amount of current (in milliamperes) to maintain a balanced oxygen level in the diffusion layer. When the air-fuel mixture is perfectly balanced at 14.7:1, the sensor produces no output current. When the air-fuel mixture is rich, the sensor produces a negative current ranging from zero to about 2 milliamps, which represents an air-fuel ratio of about 12:1. When the air-fuel ratio is lean, the sensor produces a positive current that ranges from 0 to 1.5 milliamperes as the mixture gets leaner up to about 22:1.
A linear air-fuel sensor is used on some Toyota brand vehicles and produces a voltage reading of 2.2 to 4.2 volts depending on the oxygen content of the exhaust. This type of oxygen sensor is used to detect mixtures as rich as 12:1 and as lean as 18:1.
A conventional zirconium oxygen sensor is also called a lambda sensor because the voltage changes at the air-fuel ratio of 14.7:1, which is the stoichiometric rate for gasoline. If this mixture of gasoline and air is burned, all of the gasoline is burned and uses all of the oxygen in the mixture. This exact ratio represents a lambda of 1.0. If the mixture is richer (more fuel or less air), the number is less than 1.0, such as 0.850. If the mixture is leaner than 14.7:1 (less fuel or more air), the lambda number is higher than 1.0, such as 1.130. Often, the target lambda is displayed on a scan tool.
SPEED DENSITY FUEL-INJECTION SYSTEMS Fuel-injection computer systems require a method for measuring the amount of air the engine is breathing in, in order to match the correct fuel delivery. There are two basic methods used: 1. Speed density 2. Mass airflow
The speed density method does not require an air quantity (mass air flow) sensor, but rather calculates the amount of fuel required by the engine based on information from sensors such as the MAP and TP. MAP sensor. The value of the intake (inlet) manifold pressure (vacuum) is a direct indication of engine load. TP sensor. The position of the throttle plate and its rate of change are used as part of the equation to calculate the proper amount of fuel to inject. Temperature sensors. Both engine coolant temperature (ECT) and intake air temperature (IAT) are used to calculate the density of the air and the need of the engine for fuel. A cold engine (low coolant temperature) requires a richer air-fuel mixture than a warm engine.
On speed-density systems, the computer calculates the amount of air in each cylinder by using manifold pressure and engine RPM. The formula used to determine the injector pulse width (PW) in milliseconds (ms) is: Injector pulse width = MAP/ ÷ BARO x RPM/ ÷ Maximum RPM The formula is modified by values from other sensors, including: Throttle position (TP) Engine coolant temperature (ECT) Intake air temperature (IAT) Oxygen sensor voltage (O2S) Adaptive memory
MASS AIR FLOW FUEL-INJECTION SYSTEMS The formula used by fuel-injection systems that use a mass air flow (MAF) sensor to calculate the injection base pulse width is: Injector pulse width = airflow ÷ RPM The formula is modified by other sensor values such as: Throttle position Engine coolant temperature Barometric pressure
Electronic fuel-injection systems use a solenoid-operated injector to spray atomized fuel in timed pulses into the manifold or near the intake valve.
GASOLINE DIRECT INJECTION Gasoline direct injection (GDI) systems inject fuel directly into the combustion chamber just before the spark. The fuel, under very high pressure, is injected in a fine mist into the closely packed air molecules. When ignition occurs, the fuel is moving, under pressure, throughout the cylinder. The flame front moves quickly through the compressed combustible swirling mixture. Gasoline direct injection systems, like diesel systems, require very high fuel pressures to overcome the combustion chamber pressures during injection.
MECHANICAL RETURNLESS FUEL SYSTEM The first production returnless systems employed the mechanical returnless fuel system (MRFS) approach. This system has a bypass regulator to control rail pressure that is located in close proximity to the fuel tank. Fuel is sent by the in-tank pump to a chassis-mounted inline filter with excess fuel returning to the tank through a short return line.
ELECTRONIC RETURNLESS FUEL SYSTEM This system is unique because it does not use a mechanical valve to regulate rail pressure. Fuel pressure at the rail is sensed by a pressure transducer, which sends a low-level signal to a controller. The controller contains logic to calculate a signal to the pump power driver. The power driver contains a high-current transistor that controls the pump speed using pulse width modulation (PWM). This system is called the electronic returnless fuel system (ERFS).
DEMAND DELIVERY SYSTEM (DDS) The demand delivery system (DDS) technology was developed. Having demand regulation at the rail improves pressure response to flow transients and provides rail pulsation damping. A fuel pump and a low-cost, high-performance bypass regulator are used within the appropriate fuel sender.
They supply a pressure somewhat higher than the required rail set pressure to accommodate dynamic line and filter pressure losses. Electronic pump speed control is accomplished using a smart regulator as an integral flow sensor. A pressure control valve (PCV) may also be used and can readily reconfigure an existing design fuel sender into a returnless sender.
Why Are Some Fuel Rails Rectangular Shaped Why Are Some Fuel Rails Rectangular Shaped? A port fuel-injection system uses a pipe or tubes to deliver fuel from the fuel line to the intended fuel injectors. This pipe or tube is called the fuel rail. Some vehicle manufacturers construct the fuel rail in a rectangular cross-section.
FUEL INJECTORS All fuel injection systems use solenoid-operated injectors.
This electromagnetic device contains an armature and a spring-loaded needle valve or ball valve assembly. When the computer energizes the solenoid, voltage is applied to the solenoid coil until the current reaches a specified level. This permits a quick pull-in of the armature when the injector is turned on. The armature is pulled off its seat against spring force, allowing fuel to flow through the inlet filter screen to the spray nozzle, where it is sprayed in a pattern that varies with application.
Not all injectors produce the same shape of spray pattern.
ELECTRONIC THROTTLE CONTROL The electronic throttle system has the following advantages over the conventional cable: Eliminates the mechanical throttle cable, thereby reducing the number of moving parts Helps reduce pumping losses by using the electronic throttle to open at highway speeds with greater fuel economy
The electronic throttle can be called Drive-by-Wire, but most hybrid vehicle manufacturers use the term Electronic Throttle Control (ETC), including General Motors, Ford, Honda, and Toyota. The ETC is used for the following functions. 1. Opens the throttle for cold-start fast idle 2. Is used to control the throttle opening while the driver is using the cruise control 3. Closes the throttle as needed to provide torque reduction for traction control 4. Limits throttle opening for engine speed control 5. Opens the throttle to maintain engine and vehicle speed as the Powertrain Control Module (PCM) leans the air-fuel ratio, retards ignition timing, and introduces addtitional exhaust gas recirculation (EGR) to reducing pumping losses
The typical Electronic Throttle Control (ETC) system includes the following components: 1. Accelerator Pedal Position (APP)sensor, also called Accelerator Pedal Sensor (APS) 2. The electronic throttle actuator (servomotor), which is part of the electronic throttle body 3. A Throttle Position (TP) sensor 4. An electronic control unit (usually the vehicle electronic control module)
The accelerator pedal position sensor uses two and sometimes three separate sensors, which act together to give accurate accelerator pedal position information to the controller, but also are used to check that the sensor is working properly. They function just like a throttle position sensor, and two are needed for proper system function. One APP sensor output signal increases as the pedal is depressed and the other signal decreases. The controller compares the signals with a look-up table to determine the pedal position. Using two or three signals improves redundancy should one sensor fail, and it allows quick recognition and diagnosis of a malfunction.
Electronic Throttle Body The actuator, often referred to as a servomotor is a DC electric motor. The voltage received by the servomotor is in the form of a square wave whose voltage and frequency remain the same. The servomotor responds to the change in duty cycle, which is the percentage reading between the on and off time.
SUMMARY 1. The four strokes of the four-stroke cycle are intake, compression, power, and exhaust. 2. Engines are classified by number and arrangement of cylinders and by number and location of valves and camshafts, as well as by type of mounting, fuel used, cooling method, and induction pressure. 3. Engine size is called displacement and represents the volume displaced or swept by all of the pistons. 4. Engine power is expressed in horsepower, which is a calculated value based on the amount of torque or twisting force the engine produces.
SUMMARY 5. The Atkinson cycle is used on most hybrid engines due to its greater efficiency. 6. Some hybrid engines use an offset crankshaft and low friction pistons to reduce internal friction. 7. All hybrid engines use coil-on-plug ignition systems and the Honda Insight uses indexed spark plugs. 8. All hybrid engines use electronically controlled port fuel injection.
REVIEW QUESTIONS 1. How does the Atkinson cycle differ from a conventional four-stroke cycle?. 2. What features are different between an engine used in hybrid vehicle and the engine used in a conventional vehicle? 3. What is an indexed spark plug? 4. How does the changing of the valve timing or opening affect the engine? 5. What is the difference between port-fuel injection and gasoline direct-fuel injection? 6. What is the difference between a conventional oxygen sensor and a wide-band oxygen sensor?