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Working Principle And Classification Of Accessories For TOYOTA Forklift Valve Train
Oct 23, 2018

First, summarize.

1, the valve train is the control mechanism of intake and exhaust. It opens and closes the intake and exhaust valves of each cylinder regularly according to the work order of each cylinder and the requirements of each cylinder working cycle, so that the combustible mixture (gasoline engine) or air (diesel engine) enters the cylinder in time, and the exhaust gas is removed from the cylinder in time.

2, the composition of valve train. The valve train is composed of valve group and valve drive group.

3. Classification of valve train. According to the installation position of the valve, it can be divided into two basic forms: overhead valve type and side valve type. At present, the forklift auger adopts overhead valve type valve distribution mechanism. According to the position of the camshaft, it can be divided into camshaft undermounting, camshaft middle mounting and camshaft mounting. According to the camshaft transmission mode, it can be divided into gear transmission, chain transmission and toothed belt transmission. In the form of valve actuation, it can be divided into rocker arm driving type, rocker driving type and direct driving type. According to the number of valves per cylinder, it can be divided into two valve type and multi valve type.

4. The working principle of valve train. The crankshaft rotates through the timing gear to drive the axle. Every four-stroke engine completes a working cycle, the crankshaft rotates two weeks, and the intake and exhaust valves of each cylinder are opened once. At this time, the camshaft rotates only one cycle. Therefore, the transmission ratio of crankshaft to cam is 2:1. When the camshaft is in the course of rotation, the tappet does not rise when the cam base circle contacts with the tappet. When the convex part of the cam contacts with the tappet, the tappet is lifted, and the rocker arm swings around the shaft through the push rod and adjusting screws, compressing the valve spring, leaving the valve seat and opening the valve. When the highest point of the cam bump is in contact with the tappet, the valve opens most, and when turned around, the valve begins to close under the action of the valve spring. When the cam protruding part leaves the tappet, the valve is completely closed.

Two. Valve group. 1, composition. The valve group mainly includes TOYOTA forklift accessories such as valve, valve spring, valve seat and valve guide. A and valve are made up of head and rod. The valve head operates at very high temperatures (up to 570-670 degrees for intake and 1050-1200 degrees for exhaust) and is subjected to gas pressure, valve spring tension and motion inertia, as well as poor cooling and lubrication conditions. Therefore, the valve structure and performance requirements are very high. The intake valve is usually made of alloy steel (chromium steel or nickel-chromium steel, etc.) and the exhaust valve is made of heat-resistant alloy steel (silicon-chromium steel, etc.). The cone angle of the valve sealing cone is called the valve cone angle. The intake valve cone angle is generally 30 degrees, and the exhaust valve cone angle is generally 45 degrees. Most engine intake valves have larger head diameters than exhaust valves. In order to ensure good sealing between valve head and valve seat, the sealing cones of both sides should be grinded each other before assembling, and the grinded valves can not be interchanged. B and valve guide ensure that the valve and valve seat can be properly closed when the valve is reciprocating. There is usually a 0.05-0.12mm gap between the valve stem and the conduit. Valve springs, mostly cylindrical helical springs, are made of high carbon steel and other cold drawn steel wires. In order to prevent the spring from resonance, a variable pitch cylindrical spring or double spring can be adopted. 2, function. Ensure that the cylinder seal is achieved. The valve head should be tightly attached to the valve seat, the valve duct should be well directed, the upper and lower end faces of the valve spring should be perpendicular to the center line of the valve stem, and the valve spring should be properly elastic.

Three. Valve drive group. 1. The valve train mainly consists of camshaft, timing gear, tappet and its pipe. There are push rod, rocker arm and rocker arm shaft in valve top mounted valve train. 2, function. The intake and exhaust valves can be opened and closed according to the timing of the valve timing and ensure sufficient opening. The camshaft is mainly equipped with cylinder intake and exhaust cams to enable the valve to open and close in a certain order of operation and valve timing, and to ensure that the valve has enough lift. When assembling crankshafts and camshafts, timing marks must be aligned to ensure correct valve timing and ignition timing.

Four, valve clearance. 1. Valve clearance is defined as the clearance between the tail end of the valve rod and the rocker arm (or tappet, cam) when the valve is completely closed. 2. Function, valve clearance is to give the valve mechanism spare parts when heated expansion of the room to ensure valve sealing. 3, classification, valve clearance is divided into two types of hot gap and cold gap. The former is the data of check and adjustment when the engine reaches the normal working temperature, and the latter is the data of check and adjustment when the engine reaches the normal working temperature. Generally, in the cold state, the intake valve clearance is 0.25-0.30mm and the exhaust valve clearance is 0.30-0.35mm. The valve distribution mechanism with hydraulic tappet can automatically adjust the length of hydraulic tappet and compensate the thermal expansion of valve at any time, so there is no need to leave valve clearance. 4, adjustment. Normal valve clearance will be changed due to wear and tear of valve train parts. Too large or too small valve clearance will affect the normal operation of the engine. In order to adjust valve clearance, the rocker arm is equipped with adjusting screws and locking nuts.