1
D4A Series Diesel Engine
Service Training Guide 1st Edition
Commercial Vehicle
Contents
2
Chapter I
Introduction
3
Chapter II
Structure
5
Chapter III Lubrication System
12
Chapter IV Cooling System
15
Chapter V Intake and Exhaust System
26
Chapter VI Fuel System
47
Chapter VII Troubleshooting
65
3
Chapter I
Introduction 1.1 Overview 1.2 Specification 1.3 Power and Displacement
1.1 Overview
4
This book will mainly introduce the engine mounted in the medium-size truck and bus We will focus on seeing D4A-series engine such as D4AF, D4AE, D4AL, which is mounted in the mediumsize truck and bus. D4AF Engine
D4AL Engine
These engines are equipped with RLD governor and PE-A(D)type injection pump and turbocharger(D4AE) or turbocharger intercooler(D4AL). D4AF is natural aspiration type engine and its cylinder bore inner diameter size is a little bigger than the other engines. Turbocharger and Intercooler
D4A-series are excellent fuel efficiency by direct injection, easy repair with its simple structure.
Direct Injection type
1.2 Specification
5
ITEM
D4AF
D4AE(D4AL)
Total Displacement
104 × 105,3.568cc
100× 105,3,298cc
Firing Order
1-3-4-2
1-3-4-2
Compression Ratio
17.5 : 1
16.5 : 1
Engine Speed Low/High
670±20/3800±50
730(750)±25/3850±50
Valve Clearance -In
0.4mm(cold)
0.4mm(cold)
Valve Clearance - Ex
0.4mm(cold)
0.4mm(cold)
Injection Pump/Governor
PE-AD/RLD-F
PE-AD/RLD-F
Injection pump Plunger O / D
10mm
9.5mm
Delivery Valve Open/pressure
20.8kg/㎠
11.3(25.3)kg/㎠
Timer Deg/rpm
5.5˚/ 1250~1700
4.5˚(4.0)/ 1100~1700
Injection Timing
10˚
9˚
Nozzle Open/pressure
220kg/㎠
220kg/㎠
Nozzle Orifice Hole
0.3mm×5
0.3mm×5
The power, torque and fuel injection timing of engine might be slightly different by the regional condition.
1.3 Power and Displacement
6
Each engine has different maximum power and torque. Check the part number carefully to select the correct part before use some part . Because each different engine can have different durability though they look same figure. engine
Intake type
total displacement
maximum power
maximum torque
D4AF
natural aspiration
3,568cc
96/3400ps/rpm
24/2000 kg·m/rpm
D4AE
turbocharger
3,298cc
118/3400ps/rpm
29/2000 kg·m/rpm
D4AL
turbocharger & intercooler
3,298cc
120/3400ps/rpm
30/2000 kg·m/rpm
Engine torque and power
D4AF engine
D4AE engine
D4AL engine
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Chapter II
Structure
2.1 Combustion Chamber 2.2 Valve Mechanism and Timing Gear 2.3 Piston & Rings,Con-Rod and Bearings
2.1 Combustion Chamber
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2.1.1 Combustion Chamber Combustion chamber is consists of cylinder head and pistons, 4 or 5-hole type injection nozzles are installed in the cylinder head . Combustion occurs when the fuel is directly injected into the combustion chamber when the air is compressed with high pressure in the chamber by piston. This combustion chamber is characterized by higher combustion efficiency and less loss in cooling.
2.1.2 Cylinder Sleeve Cylinder sleeve(liner) is tightened into the crank case which is made of special iron with high abrasion-resistance.
Sleeve Water jacket Piston Crank case
2.2 Valve Mechanism and Timing gear 2.2.1 Valve The angle of both intake and exhaust valve seats is 45˚.
2.2.2 Valve Spring Valve spring prevents the valve-surging phenomenon, by mounting a valve spring with a different pitch in the opposite direction of its coil to the inside and outside of the spring.
2.2.3 Valve Cap The cap is mounted between a rocker and a valve., and the rocker has a bushing for lubrication inside.
2.2.4 Valve Stem Seal The valve stem seal is installed on the top of each valve guide. If this oil seal is damaged, engine oil flows down into the combustion chamber easily , white color smoke is generated. Mean while this oil seal does very important role of apply engine oil on the surface of valve appropriately
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2.2 Valve Mechanism and Timing gear 2.2.5 Tappet The tappet is cylindrical, and its contact surface with camshaft is eccentrically designed to prevent the partial abrasion by contacting to the cam while rotating inside.
2.2.6 Camshaft and Bush Valves are lift by the camshaft located in the middle of crankcase. Three camshaft bushes to bear the camshaft are mounted in the crank case. The bush bore is designed by getting smaller backward to make it easy for the camshaft to be taken away in front of crank case. Camshaft
Basic Diameter: 40.080 Lobe Height : 6.81 ~ 6.91 L:6.36 Cam Height : 46.939 Shaft Journal Clearance : 0.05~0.09
Bushing
Order
Stamp/ No.
I/D
Width
1st
1
54.5
41
2nd
2
54.5
21
3rd
4
53
21
2.2.7 Timing Gear The timing gear is installed in a timing gear case in front of the engine. The timing marks engraved at each gear needs to be aligned when being reassembled.
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2.3 Piston & Rings,Con-Rod,Bearings 2.3.1 Piston The piston is made of an alloy of molded aluminum. The engraved mark at the upper part of the piston tells weight and product number of the piston. The ◀ mark indicates a direction toward the engine. In particular be sure the ◀ mark indicates its direction when replacing a piston. And make sure that 4 pistons should have same weight.
Part Number Weight Mark Front Direction Mark
2.3.2 Piston Ring Piston rings consist of two compression rings and one oil ring, and a slippery surface of the ring is chrome-plated through a hardening process. 2.3.3 Piston Ring Assembly The end of 1st compression is located on the longest distance position from the Oil Ring Expender combustion chamber. Joint And the end of 2nd compression ring is opposition position of 1st ring. The end of oil ring is located short distance position from the combustion chamber.
1st Compression Ring End
Front of Engine 2nd Compression
Oil Ring End
Ring End Location of piston ring end
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2.3 Piston & Rings,Con-Rod,Bearings 2.3.3 Connecting-rod The connecting rod has an oil passage to connect the large end and small end part, to play a part in lubricating small end part and in cooling the piston.
2.3.4 Main Bearing The main bearing is a sectioned plane bearing which is made of a special alloy, and the upper bearing is grooved inside to be correspond with an oil hole of crankshaft. The five pairs necessary for installation should be in the right direction when being reassembled.
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Chapter III
Lubrication System 3.1 Diesel Engine Oil 3.2 Parts Lubricating 3.3 Oil Pump 3.4 Oil Cooler 3.5 Oil Filter
3.1 Diesel Engine Oil Item
14 D4AF
D4AL
API CC or Higher
API CD or Higher
8.2 ℓ With Filter
<
Pressure at Idle Speed
1.5kg㎠ (0.5kg/㎠)
<
Pressure at Max Speed
3~5kg/㎠ (2kg/㎠)
<
Pump Relief Valve Opening Pressure
3.7~4.3kg/㎠
<
Cooler Bypass Open
1.8~2.2kg/㎠
<
Every 6,000~10,000km
<
Class Capacity
Oil & Filter Replace
Good engine oil maintenance is very closely related with engine life time. The oil quantity, replacement term and oil quality should be kept to the maker’s specification. If the engine oil quantity is insufficient in the oil pan total oil life time gets be shorten, if the oil quantity is excessive so much,engine rotating load is increased and carbon is generated much more than normal condition. Specially, severe driving ,driving before warming up in cold season and humid weather are very bad for engine oil. Consider to the environmental problem,replacement cost and the probability of inserting foreign material into engine, the frequent replacement of engine oil is also undesirable way. For natural aspiration type engine like D4AF engine, CC or higher quality API classification diesel engine oil is recommended. And for turbocharger diesel engine like D4AE and D4AL engine, CD or higher grade oil should be used. Appropriate viscosity of diesel engine oil should be selected between API 5W30 and 20W50 according to the regional temperature.
3.2 Parts Lubricating
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MAIN OIL PATH
OIL PRESSURE SWITCH
OIL FILTER
ORIFICE
INJECTION PUMP
VACUUM PUMP
OIL COOLER BYPASS VALVE OIL PUMP
CAMSHAFT BUSH ROCKER BUSH
CRANKSHAFT MAIN BEARING
CONN ROD BEARING
PUSH ROD TURBO CHARGER (D4AL)
TAPPET
IDLER GEAR BUSH
TIMING GEAR CONN ROD BEARING AUTO TIMER
COOL PISTON
REGULATOR VALVE OIL STRAINER
OIL PAN
The engine oil, which flows into its main passage of a crank case from the oil filter, through an oil cooler and oil filter by a gear-typed oil pump and lubricates all parts of engine before going back to the oil pan.
B OIL PUMP
OIL COOLER C BYPASS
REGULATOR
A
VALVE BYPASS
C
VALVE A
OIL FILTER
VALVE To Main Path
B
3.2 Parts Lubricating 3.2.1 Valves The engine oil flows into the cylinder head through the oil hole and the pipe at the upper part of crank case, after lubricating No.1 camshaft bush. The engine oil lubricates each rocker bush, flowing in the rocker shaft through the front rocker shaft bracket, while it lubricates the slippery surface of the valve cap at the rocker and valve stem with being sprinkled into the oil hole at the upper part of the rocker. Also it lubricates the tappet and the cam of the cam shaft for flowing back to the oil pan through the cylinder head and the push rod hole in the crank case. 3.2.2 Main Bearing and Connecting Rod Bearing The oil main passage has a oil passage to lubricate each main bearing. The oil flowing through the oil hole lubricates the main bearing and connecting rod bearing through the oil hole in crankshaft. Also it lubricates small end part bush of the connecting rod through the oil hole of the connecting rod, and then it cools the piston by being sprinkled from the oil jet.
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3.2 Parts Lubricating 3.2.3 Cam shaft The oil flowing through the oil passage from the oil main passage lubricates each cam shaft bush. It also lubricates the cam shaft gear and valves through the oil hole as a oil passage at the journal of the front engine.
3.2.4 Timing Gear The gear bush in the timing gear idler is lubricated by some of the oil from the oil main passage and the oil sprinkled into the oil hole of the idler gear.Also the oil lubricates the timing gear through the forced lubricating system with a automatic timer, or the oil pipe mounted at the idler shaft.
3.2.5 Injection Pump The engine oil lubricates the injection pump and governor and drops to the oil pan from the oil passage of bearing cover. Be sure to charge engine oil in the new serviced injection pump before installation and run the engine
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3.2 Parts Lubricating
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3.2.6 Turbo Charger The bearing is lubricated by engine oil. It takes 2～3 minutes to circulate the engine oil when starting the engine. So beware that the excessive increase in rpm may cause serious damage to the turbo charger.In order to lubricate and cool the turbocharger enough against its high speed revolution, also make sure that the ignition should be off after idling for 2~3 minutes, .
3.2.7 Vacuum Pump Flowing into the vacuum pump through the oil passage of the timing gear case from the oil main passage, the engine oil lubricates the vein parts. And then it flows back to the oil pan flowing into the timing gear case, with air from the air nozzle of the vacuum pump.
Shaft Bearing
3.3 Oil Pump 3.3.1 Engine Oil Pump The gear-typed oil pump is operated by a skew gear installed in a camshaft. The oil pump case has a hole for oil flow, and then the oil flowing out from it lubricates a skew gear in cam shaft and an oil pump gear. If engine oil is contaminated and much sludge is accumulated on the oil pan. Some of sludge can flow through the skew gear lubricating oil hole and clog It . As the result of it the surface of skew gear and oil pump gear are worn and broken. The camshaft also is bend and the cylinder block and pump case are broken.
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Oil Outlet
Relief Valve
3.3.2 Relief Valve Relief valve in the oil pump prevents the lubricating system from excessive high pressure by leaking some of the engine oil to the oil pan. The minimum oil pressure at idle speed is 0.5~1.5kg/㎠ and 3~5kg/㎠ at highest speed. 3.3.3 Oil Pressure Switch In case the engine oil pressure is lower than normal , the built-in oil pressure switch will be closed.If the engine oil warning lamp turns on at idle speed and disappears as the engine speed is increased oil pump, bypass filter or oil switch should be checked .
oil pressure switch
3.4 Oil Cooler
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3.4.1 Oil cooler element The engine oil transmitted by the oil pump is supplied to the oil cooler. The oil cooler is a device for heat exchange between the oil supplied from the oil pump and the coolant.
3.4.2 oil cooler bypass valve Oil cooler has a bypass valve which can be opened when the oil temperature is low . Particularly, in case that the oil viscosity is high at low temperature, the bypass valve will be opened in high resistance against the oil passage according to as how much the oil cooler element is loaded, in order to make the engine oil flow directly flown to the oil filter without going through the oil cooler. 3.4.3 Oil cooler element contamination . Sometimes the engine oil cooling efficiency become decrease in an old used engine because of a lot of oil sludge in the cooler. The oil cooler element needs to be clean inside when engine oil temperature is higher abnormally. Whenever the cooler element is reinstalled it needs to be careful to get the correct direction and o-ring condition.
Bypass Valve
3.5 Oil Filter
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The filtering capacity, amount and bypass valve(relief valve) opening pressure is specified by an engine maker. D4A series engine oil filter has dual structure with full flow filter and bypass filter in a can. Oil filters must be changed with a genuine part when engine oil is changed 3.5.1 Full flow Filter Most of engine oil is filtered by the full flow filter and flows into engine main path. A bypass valve is open when the filter is contaminated severely by the foreign material and carbon sludge.The viscosity of engine oil is very high in cold winter season, it also can be opened . If the bypass warning lamp turns on, sudden acceleration should not be done to avoid engine lubricating part damage. 3.5.2 Bypass Filter It is installed together with the full flow filter in a can , but outlet way is separate completely by an O-ring. Amount of oil filtered by this is very small because the filtering fine degree is very high. Smaller particles which can not be filtered by full flow filter is filtered by this
To Main Path
. To OIL Pan
By-pass Filter Full-flow Filter By-pass Valve
To Main Path To OIL Pan
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Chapter IV
Cooling System 4.1 Over View 4.2 Cooling System
4.1 Over View
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4.1.1 Coolant and Circulation The engine is cooled by the forcedcirculated coolant by the water pump. water pump draws up coolant and send it to cylinder block water jacket. if the engine temperature is low the coolant re-circulate through the bypass way,but if engine temperature increases the thermostat is open and the coolant flows out the radiator
Radiator Thermostat
Oil Cooler
4.1.2 Water Jacket Between cylinder and cylinder water jacket is located to contain the coolant and cool down down the engine heat . If cylinder block is cracked, coolant leak out into the cylinder head gasket and oil pan.
Water Jacket
Radiator upper hose
Thermostat
Cylinder head
Radiator Water pump
Radiator lower hose
Cylinder water jacket Oil cooler
,,
4.2 Cooling System
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4.2.1 Radiator and Cap Engine cooling radiator is composed of tube and fin type core. To get the radiator keep the best condition of cooling efficiency, 1. Dust and foreign material out side of the core should be cleaned. 2. Fin should not be damaged to flow the air. 3. Soft water and anti-rust liquid should be used for coolant. If sludge or scale is covered inside the tube of radiator, clean it with special cleaner. In the radiator cap there are two valve systems. The outside valve is designed only for outlet the coolant from the radiator to reservoir to prevent the radiator from swelling by the expansion of hot temperature. And the other one small valve in the center of the cap is designed to intake the coolant to prevent radiator from the shrinking during engine stop.If the the sealing rubber of each valve is damaged, the boiling point of the coolant is lowed.
Cap Upper Tank
Lower Tank Drain Cock
Radiator Cap
Overflowing to the reservoir
Absorbing from reservoir
And if any sealing problem in the coolant compensate way is happen from radiator cap to coolant reservoir tank , the coolant level in the radiator is getting lower.
Checking points for coolant compensation defect
4.2 Cooling System
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4.2.2 Water Pump The water pump is operated by the V-belt of crankshaft pulley. There are unit seals between the impeller and bearing prevent the coolant leak. . Small amount of leaking coolant can flow out through the vent hole bottom side of pump case so that the leaked water from the unit seal does not flow into the bearing. The water pump bearing can also be damaged by the over tension of fan belt.
4.2.3 Thermostat The thermostat is controlled by wax. The Coolant Hot wax controls the coolant flow with the change To Radiator Air in its volume, changing itself from the solid state into the liquid state when it is heated up. Also the opening volume of the thermostat From valve will be changed according to the Cool Cylinder change in temperature of the coolant, and it Head To adjusts the coolant temperature, controlling W/pump the amount of the coolant flowing into the radiator and the water pump. Jiggle valve on the thermostat case is closed during thermostat is closed on purpose of warm up the engine in short time and is opened by its weight during engine stop to vent the air to Engine Run the radiator. Stop
4.2 Cooling System
26
4.2.4 Cooling Fan and Coupling The cooling fan clutch controls its fan speed according to the coolant temperature, and it will be possible for the bimetal to change the liquid amount of fluid coupler by detecting temperature of air flowing through the radiator. Auto cooling fan clutch is filed with silicon oil. If the heat came from the radiator contact, the coil bimetal is shrunken to open the silicon fluid valve. This sticky material between two clutch discs hold together .
Cooling Fan Clutch Section
When the engine is start first all of the silicon fluid between two discs is accumulate in the reservoir room by the centrifugal force and pump but the valve is closed till heat contact the bimetal. As the result the fan side disc is free from the rotation of engine in 2 or 3 minutes. When checking the coupling of the automatic cooling fan, check the coupling first whether the cleanness of the bimetal and nut tightening condition are good or not. And then check the condition of coupling bearing.
Check and Cleanness
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Chapter V
Intake and Exhaust 5.1 Turbocharger and Intercooler
5.1 Turbocharger and Intercooler 5.1.1 Advantage of turbocharger The compressor wheel of the turbo charger compresses intake air by using wasted exhaust gas energy and then put the compressed air to combustion chamber by force. As a result, engine output power is increased. 5.1.2 Turbo-charging effect The turbo-charging effect happens when the engine runs from 1200～1400 rpm. And speed of turbocharger at this moment is 90,000～170,000 rpm. and 40,000 rpm when the engine is idling. Vehicles with turbo charger have characteristics such as high engine output power, excellent fuel efficiency and reduction of toxic gases. High temperature is generated from inside of the turbocharger while the turbocharger is rotating at high speed. Intake air temperature is increased by transmitting heat from the exhaust gas through turbine wheel, shaft and compressor wheel. And also the oxygen density in the actually inhaled air of the cylinder decreases as much as the temperature increases. The intercooler increases the density of oxygen by decreasing the temperature of the intake air. When the density of air increases, it will be able to improve the combustion efficiency and the engine's output power. The intercooler is installed on D4AL engine only.
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5.1 Turbocharger and Intercooler 5.1.3 Waste-gate The wastegate actuator mounted on the turbo charger prevents the turbocharger from over-running and excessive high pressure inside of the intake manifold. It controls the boosting pressure properly by applying the extra exhaust gas to the wastgate actuator. The turbocharger system will be seriously damaged if the wastegate actuator does not activate. 5.1.4 Maintenance The shaft bearing is lubricated by engine oil. It takes 2-3minutes to circulate the engine oil after starting the engine. The turbocharger engine is need to be careful to operate and maintenance it. Clean and high quality engine oil and appropriate fuel injection quantity are very important for turbocharger engine . Also beware that the sudden acceleration or excessive high rpm at the time of starting the engine may cause serious damage to the turbo charger. In order to lubricate and cool the turbocharger system enough, the engine should be kept idle 2-3minutes more before stop the engine.
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Chapter VI
Fuel System 6.1 Fuel Flowing 6.2 Injection Nozzle and Holder 6.3 Supply Pump and Feed Pump 6.4 Pump Construction 6.5 Governor 6.6 Timer 6.7 Boost Compensator 6.8 Aneroid Compensator(A.C.S)
6.1 Fuel Flowing 6.1.1 Fuel Flowing The fuel is drawn by the supply pump through fuel suction pipe in the fuel tank and sand it to the fuel filter. Between the fuel tank and supply pump a water separator is located to separate out water in the fuel. The supply pump feeds the fuel to the fuel injection pump. The fuel inlet port of injection pump is a kind of regulating pressure valve to keep somewhat pressure in the fuel chamber and make it easy to fill the fuel into the plunger barrel. 6.1.2 Fuel Compression When the plunger compresses the fuel the high pressure fuel reaches at the fuel nozzle and it overcomes the nozzle spring force. This nozzle spring is called nozzle opening pressure(N.O.P). The surplus fuel from the nozzle and plunger combines and returns to the fuel tank.
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6.2 Injection Nozzle and Holder 6.2.1 Fuel Injection Nozzle The hole type nozzle is used for D4A series direct combustion type engines. The nozzle consists of a needle valve and a body. T his valve and body is produced as a combination set in the factory that a valve or body should be mixed with others even if the part numbers are same. This nozzle has 5 holes and 160 degrees spray angle. Nozzle spring supports the needle valve. 6.2.2 Fuel Injection Pressure The fuel pressure to compress and overcome this spring force is called nozzle opening pressure. This N.O.P should be higher than 220kg/㎠. When the nozzle holder assembly is installed on the engine, the tightening torque of mounting bolt should be followed the specification. The excessive tightening torque can damage nozzle holder or stick the valve
Fuel Injection Nozzle
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6.3 Supply Pump, Feed Pump 6.3.1 Supply Pump The supply pump is installed on the injection pump body to draw fuel from the tank and feed it to the pump housing.
6.3.2 Feed Pump The tappet is moved by a special on the camshaft to operate the pushrod and the piston. The reciprocal motion of this of this piston delivers the fuel to the injection pump. A priming pump (feed pump) is also mounted in the same housing. After open and fit a fuel line, air bleeding is conducted manually by this pump. A filter is installed in the supply pump’s intake side bolt pipe joint to clean the fuel during suction.
6.2.3 The deflector It is mounted in front of the suction and discharge port. After fuel injection, high pressure fuel inside the nozzle and injection pipe momentarily returns through the suction and discharge port. This spill pressure strikes the deflector first to prevent the pump housing erosion.
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6.4 Pump Construction 6.4.1 Delivery Valve It is located on top of the plunger. When the force of the fuel pressurized by the plunger exceeds the delivery valve spring’s set force, it pushes the delivery valve up and the pressured fuel is delivered to the nozzle holder through the delivery valve holder and injection pipe. 6.4.2 Movement of Plunger The plunger is pushed up by the cam of the camshaft trough a tappet assembly. The plunger spring then pushes the plunger back, resulting in a constant reciprocal motion. It increases or decreases the injection rate by a slanted helix. Fuel oil chamber is always filled with fuel supplied by the supply pump.The plunger barrel’s suction and discharge port opens onto this fuel oil chamber. 6.4.3 Control Sleeve and Rack Control sleeve is fitted around the outside of the plunger barrel. It has a groove on the bottom which fits a flange on the bottom of plunger. It is also fitted with a pinion gear which moves together with the sleeve. The pinion gear engages the control rack. When the control rack is moved in an axial direction, the pinion gear rotates and the plunger results in rotation.
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6.5 Governor The main purpose of fuel injection pump governor is to decrease the fuel injection quantity as the engine speed increases in the governor range. The RLD governor is used for D4A series engine. It controls fuel injection quantity during all speed range. The RLD governor is composed of flyweight, tension lever and guide lever, floating lever, torque cam, start spring, idling spring and governor spring etc. . 6.5.1 Flyweight It is mounted on the end of injection pump camshaft . The flyweight assembly consists of two flyweights, opens and closes in response to the centrifugal force of generated by the rotation of the camshaft. The sleeve and shifter are moved in an axial direction by sliders mounted on the ends of the flyweight arms. 6.5.2 Tension Lever It is supported by the tension lever shaft and also is moved by movement of shifter pushed by the force which generated by the engine speed. When this tension lever overcomes the governor spring set force, the fuel control rack decreases the fuel injection quantity. The guide lever combined by a cancel spring is moved to the same direction of it.
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Adjusting lever Idling set bolt Supporting lever Floating lever Governor spring Qo Po Guide lever
Full speed set bolt Cancel spring B
Control rack
Ro Start spring Sensor lever
Governor shaft
Full load set lever
Cancel spring A Tension lever
Full load set bolt Torque cam Cam shaft
Idle screw Idler spring
Close
Sleeve Fly weight
Open
6.5 Governor 6.5.3 Idling spring It contacts the shifter and is located in the lower portion of the governor cover on the flyweight axis. If this spring compressed force is strong, the engine idle speed increases. The spring force is adjusted by a screw bolt. 6.5.4 The floating lever It is support by the supporting lever which is supported by the control lever shaft. Both end of floating lever are fork shaped. One end engages the guide lever ball joint, and the other engages the ball joint of the rack connecting link, which is attached to the control shaft. 6.5.5Control lever Accelerator pedal is linked to the control lever by a cable. The control lever and supporting lever are assembled so that they are moved together by the force of a cancel spring
6.5.6 Start spring Its one end is connected to the spring eye mounted on the governor housing and the other end is connected to the rack connecting link. It always work to pull the control rack in the fuel-increase direction..
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6.5 Governor 6.5.7 Torque cam Its shape is the limit position of the sensor lever. The fuel control rack is not only moved by the tension lever but also control lever during L-shaped lever is separated from the supporting lever which happens during the engine is loaded by the accelerator pedal(control lever).
At this moment fuel injection quantity is maximum and the maximum quantity is determined by the sensor lever touch position to the torque cam and the torque cam is turned by the tension lever moved according to the engine speed.
The circumference of this cam is designed specially to improve engine and diving performance.
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6.6 Timer
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An automatic timer SCDM (for D4AE engine) or SCZ (for D4AF engine) is mounted for D4A series engine. This is a mechanical timing device to automatically control the fuel injection timing according to the engine speed and load.
The flyweights in the timer assembly are spread out and compress the springs by the centrifugal force generated according to the engine speed.
Generally timer can advance the fuel injection timing maximum 7˚ to 10˚ according to the engine speed
Timer Operation
Timing Advance Angle
As the flyweights open the fuel compression start time (fuel injection timing ) is advanced. One of engine timing gears drives the timer directly and is lubricated by the engine oil.
pump Speed(RPM)
6.7 Boost Compensator
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6.7.1 construction The interior of the booster compensator chamber is divided into an atmospheric chamber and a pressure chamber. A booster compensator spring with a pre-determined set force is built into the atmospheric chamber. The pushrod moves together with the diaphragm, and a pin at one end connects it to the boost compensator spring. The other end is constantly held against a screw by the boost compensator spring. The bottom end of the compensator lever contacts the control rack and the top end contacts a spring capsule used for adjusting the control rack position. 6.7.2 Operation When the boost pressure is applied on the diaphragm the set spring is compressed. The bottom of the boost compensator lever is therefore moved in the direction of arrow(2). As the load control lever of the governor itself is in the full load position and the floating lever is fixed, the control rack is moved in fuel-increase direction by the force of cancel spring and a quantity of fuel adequate for the amount of intake air pressurized by the turbocharger is injected into the combustion chamber.
cancel spring
To increase amount of fuel
Full load set screw Push rod A
Lever
Sensor lever
Diaphragm
U- shaped lever Push rod B
Boost pressure Boost compensator
Torque cam
6.8 Aneroid Compensator(A.C.S)
700 650 600 550 500 450 1,000
0
Atmospheric pressure(mmHg)
6.8.2 Construction The ACS includes a bellows under which a spring and pushrod are assembled. A joint and cap with an air inlet are installed in the bellows. The bellows, which extends and retracts according to the atmospheric pressure moves the pushrod against the pre-adjusted spring. The adjusting bolt attached to the top of the bellows is used to adjust the spring force and the initial push rod position. The clevis at the end of the ACS is the connected directly to the ACS lever(1) of the governor, allowing the shaft to move together with ACS lever(2). When the ACS functions, ACS lever (2) contacts the pin of the floating lever(1/2)
Relationship atmospheric pressure and altitude
750
2,000
3,000
4,000
Dry air density 780 760 740 720
Full-load injection quantity(%)
6.8.1 Purpose 1. Relationship between atmospheric pressure and altitude-pressure decreases as altitude increases. 2. Relationship between dry air density and atmospheric pressure- air density decreases as the atmospheric pressure decreases. 3. A vehicle adjusted to function at low altitude may experience may experience the following problems due to excessive fuel injection when it is driven at high altitudes. -high level of black smoke - lowered engine out put and increased fuel consumption - carbon deposits in the combustion chamber and then the engine life is shorten.
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0.110 0.115 0.120 0.125 Density(kgS²/ m⁴)
0.130
100 90 80 70 60 50 0
1,000 2,000 3,000 4,000 Altitude(m)
1 1/2
2
