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OBJECTIVESAfter 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 weightUse of the Atkinson cycle to increase efficiencyCrankshaft offset to reduce internal frictionOften do not use a conventional starter motorSome use spark plugs that are indexed so the open side of the spark is pointed toward the intake valve for maximum efficiencyEngine mounts are computer-controlled to counteract and eliminate undesirable engine vibrationThe 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 systemConventional 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 systemSame or similar engine lubrication system including the oil filter but with a lighter viscosity oil than used in similar conventional vehicles
ENGINE FUNDAMENTALSMost 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 CYCLEOne 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 SPECIFICATIONSEngine 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 RatioCompression 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.
CR = Volume in cylinder with piston at bottom of cylinderVolume in cylinder with piston at top center
TORQUE, WORK, AND POWERTorque 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-metersone 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).
PowerThe 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.
HorsepowerThe 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 nethorsepower 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. 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 FEATURESThe 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 CamshaftsA composite camshaft uses a lightweight tubular shaft with hardened steel lobes press-fitted over the shaft.
Variable Valve Timing and LiftThere 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 LiftersThe use of roller rocker arms decreases friction in the valve train and helps the engine produce optimum power and economy.
Cylinder DeactivationSome 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?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 SYSTEMLubrication PrinciplesLubrication 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. The principle just described is that of hydrodynamiclubrication. 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 OILThe 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 AdditivesAdditives 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.
