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Introduction to Structure and Systems of Weichai Diesel Engine

Jun. 05, 2019

2.1 Gear system and valve mechanism of Weichai Generating Diesel Engine

The valve mechanism comprises camshaft gear, camshaft, tappet, push rod and valve train, and it adopts a structure of overhead valve and underneath camshaft.

Camshaft gear1 is driven by crankshaft gear 6 through idle gear 2, and crankshaft gear 6 also drive fuel injection pump 3 through idle gear 2.The gears should be assembled according to the paired engagement marks. Each gear is marked with “.”, and the gears must be assembled with “.” marks aligned to ensure that the valve timing and fuel supply time are correct, as shown in Figure 2-1.

structure of gear train

Driven by the camshaft gear, the camshaft controlsthe opening and closing of intake and exhaust valves according to certain valve timing through the tappet and push rod.

2.2 Lubricating system

Lubricating system consists of oil strainer, oil pump, oil filter and all internal pipes. The diesel engine adopts a combined lubrication method: pressure lubrication and splash lubrication.For crankshaft main bearing, connecting rod bearing, camshaft bearing and rockshaft and other parts, pressure lubrication is adopted.Besides, some kinematic pairs, such as cylinder liner and piston, piston pin and connecting rod, and piston pin seat, valve and valve guide, gear and other parts rely on splash lubrication.

Oil is intake by oil pump through filter screen, and compressed into oil filter.Filtered oil lubricates the crankshaft main bearing, camshaft bearing and rocker arm bearing through engine block main oil gallery.Lubricate the connecting rod bearing through oil gallery in the crankshaft.

Oil filter adopts a totally-closed spin-on type, during operation, if filter element is blocked, the safety valve will automatically open and make oil flow into main oil gallery directly, but at this moment, it has lost its function of filtration, therefore, it is required to timely replace filter elements of oil filter according to "Technical Maintenance" requirements. A pressure regulating valve is set in the oil filter, which can adjust pressure in the main oil gallery, maintaining it within the range of (200~500) kPa.

2.3 Fuel system

Fuel system consists of fuel tank, coarse fuel filter, fuel delivery pump, diesel filter, fuel pump and fuel injector.The diesel enters into fuel delivery pump through coarse fuel filter, and it is delivered by the fuel delivery pump to the diesel filter; after further filtration, it enters into fuel pump, and the high-pressure fuel that comes out of fuel pump is injected into combustion room by the fuel injector; the low-pressure fuel that comes out of fuel pump and the diesel that leaks out of needle valve couple at port of fuel injector flow back to fuel tank, as is shown in Figure 2-2.

Weichai engine fuel system

Figure 2-2 Fuel Circulation in the Fuel System

1. fuel return pipe; 2. high-pressure fuel pipe; 3. diesel filter; 4. fuel tank; 5. fuel filter; 6. fuel injection pump

The fuel delivery pump is of single-functional piston type, and installed on the outer side of fuel injection pump, it is driven by the eccentric gear on the camshaft of fuel injection pump, what's more, there is a manual fuel pump on the fuel delivery pump, before start-up of diesel engine, loosen the bleeder screw, and unscrew the manual fuel pump handle, tilt it up and down reciprocally to pump fuel and exhaust the air, making the whole fuel pump filled up with fuel.After finishing the air bleeding, the handle should be screw up, in order to avoid fuel leakage.

Diesel filter is used for separating mechanical impurities in the diesel, and reducing wearing of plunger couple and nipple needle valve couple.Blockage or damage of filter element, it is necessary to replace it.

The fuel injection pump is a BQ pump, electronic governor.The fuel injection pump is driven by fuel injection pump timing gear, through the fuel injection pump camshaft, idler wheel and tappet, making the plunger move reciprocally in the plunger liner. The control mechanism which changes the fuel volume is made up of adjusting pull rod, shifting fork and adjusting arm pressed on the plunger, and the position of pull rod is controlled by the governor, when the pull rod move forward, the fuel supply raises, otherwise, declines.

Before delivery of engine out of factory, the fuel injection pump has been adjusted and lead-sealed by manufacturer; users shall not disassemble it at will.When it is necessary to disassemble or repair, adjusting test should be conducted on test bench for fuel pump.

The fuel injector is of P Series, which is compressed up by a compression bolt and a flat clamp, the height of nozzle sticking out of cylinder head bottom surface can be adjusted with a gasket.The fuel injector should be maintained as specified in these instructions, in which, the needle valve couple are ground in pair, when disassembling, they shall not be exchanged, and should be kept clean.

2.4 Cooling system

The cooling system is forced circulation water cooling, as is shown in Figure 2-3.

It includes radiator, water pump, fan, and thermostat and so on.When the temperature of cooling water in engine block is lower than 73°C, the thermostat does not open, and the cooling water is circulating inside the engine (namely small circulation), making the temperature of water in the engine rise rapidly so that the engine reaches thermostability as soon as possible. When the temperature of cooling water reaches 80°C, the thermostat gradually opens, at the same time, the small circulation is closed. Cooling water enters into radiator through thermostat, reenters water pump after cooled by fan, and then enters engine block, fulfilling the big circulation.

This engine adopts centrifugal water pump, and the water pump adopts self-lubricating inner integral ball bearing, so no need to fill in lubricating grease. During use, when the water seal is worn, and there is serious water leakage in the water hole below the water pump body, it is necessary to replace the water seal.

Weichai engine cooling system

2.5 Electric appliance

Electric system includes storage battery, starter, alternator, relay governor, electric lock, preheating start-up switch and ammeter, etc.

The alternator is of JFWZ13 (14V/25A, in-built governor and reserved speed sensor binding post) AC shunt excitation alternator.It is formed by rectifying three-phase alternator and silicon diode, connect the negative electrode to the earth, never connect in the opposite direction; otherwise, the alternator will be damaged.

The starter is a series excitation DC motor(12V/3kW) of type QDJ1408L-P.The once continuous service time of starter shall not be longer than 10s, and the interval between twice start-ups is 2 min, if consecutive 3 times of start-ups all fail, it is necessary to check and troubleshoot. For the overhaul and troubleshooting methods of starter, please refer to "Operation and Maintenance Instructions for Starter".

The storage battery is of type 6Q-140, and voltage is 12V. Before use, the storage battery should be initially charged by filling in battery solution according to the specification.During use of the storage battery, please note that:

1. Frequently check the height of battery solution at least once a week, when the height is lower than (10~15) mm, it is necessary to add distilled water or other purified water, and it is forbidden to use well water or river water.

2. Normally keep unblocked the small air hole in the nut cover over the port of solution, and the outer surface of battery should be kept clean and dry.

3. Normally keep the quantity of electric charge of storage battery not less than 75%.When the storage battery is discharged by up to 50%, and then it's time to charge it. The discharging degree of storage battery can be check by aerometer or discharging instrument.

4. If any used storage battery will not be used again temporarily, before parking, it should be fully charged, and be recharged once a month after that.In the parking period, do not pour out the battery solution.

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