What Are the Valve Transmission Groups

Valve Transmission Set

The valve transmission group mainly includes camshaft, timing gear, tappet and its guide rod, push rod, rocker arm arm and rocker arm shaft, etc. Its function is to make the intake and exhaust valves open and close at the moment specified by the gas distribution phase and to ensure sufficient opening degree.

Camshaft

The camshaft is a key component of thevalve train parts, which controls the valve phasing and is used to drive the oil pump, gasoline pump and distributor in some engines.

The camshaft is mainly composed of intake and exhaust cams, support shaft, timing gear shaft, gasoline pump eccentric cam, oil pump and distributor drive gear.

In order to reduce the deformation of the camshaft during engine operation to avoid the malfunction of the gas distribution mechanism, the camshaft is mostly fully supported, while some engines are not fully supported, such as the Jiefang CA6102 and E suction 10 camshafts with four journals.

In order to ensure the normal operation of the gas distribution mechanism, the relative angular position of the cams on the camshaft has strict requirements. The relative angular position of each exhaust cam in the same cylinder ensures the phase of gas distribution in one working cycle; the relative angular position of the intake (or exhaust) cam in each cylinder should be consistent with the ignition sequence of the engine. Therefore, as long as we know the direction of rotation of the camshaft and the working order of the intake cams (or exhaust cams), it is not difficult to determine the ignition order of the engine. For a four-cylinder, four-stroke engine, the angle between the same-name cams is 360W=60/6=60. The camshaft is usually driven by the crankshaft through a pair of timing gears, and when assembling the crankshaft and camshaft, the timing marks must be aligned to ensure the correct mating phase and firing moment. In order to prevent axial movement of the camshaft, the camshaft must have an axial positioning device. The cams of modern automobile engines mostly use the thrust flange positioning device in the Jiefang CA6102, Dongfeng EQ6llJ, Toyota ZY and 3Y camshafts, which are all positioned in this way, that is, the thrust flange is mounted on the camshaft's first journal in front of the tab, which is thicker than the thrust flange to ensure that the axial clearance between the thrust flange and the timing gear is in accordance with the regulations (0.05~0.10S for cars). .

The material of camshaft is generally made of high quality steel die forging, or alloy cast iron or ductile iron casting can be used. The working surface of cam and shaft diameter is generally finely ground after heat treatment to improve wear resistance.

Valve tappet

The function of the tappet is to transmit the thrust of the cam to the push rod and to withstand the lateral force exerted by the rotation of the camshaft. For side-mounted valve train, the tappet is usually made into a bacterium type, and an adjusting screw is installed on the top of the tappet to adjust the valve lash. The tappet of valve top-mounted distribution mechanism is generally made into a cylinder type to reduce weight. The advantage is that it can reduce the lateral force on the tappet caused by friction. This tappet structure is complex and heavy. Generally used in large bore diesel engines. Tappet commonly used nickel-chromium alloy cast iron or cold-excited alloy cast iron manufacturing. Its friction surface should be heat-treated and finely ground.

Some engine tappet directly installed in the cylinder block corresponding to the drilling of the guide hole, there are engines tappet installed in the detachable tappet guide body.

Hydraulic tappet

In the tappet body 1 is equipped with a plunger 3, in the upper end of the plunger pressed into the support seat 5. the plunger is often pressed upward by the spring 8, its uppermost position by the ring 4 to limit. The oil in the engine lubrication system flows from the main oil channel through the oil hole on the side of the tappet body and often fills the inner cavity of the plunger and the cavity below it. when the valve is closed, the spring 8 is the plunger 3 together with the support seat pressed into the injection plug against the push rod, and there is no clearance in the whole exhaust mechanism.

When the tappet is pushed upward by the cam, the push rod acts on the support seat 5 and the plunger 3 on the counter force figure to make the plunger overcome the force of the spring 8 and move downward relative to the tappet body 1, so the oil pressure in the lower cavity of the plunger increases rapidly, so that the check valve 7 closes the valve. Due to the incompressibility of the liquid, the entire tappet as a rigid body up, so as to ensure the necessary valve lift. When the oil pressure is very high, there will be a little oil through the plunger and tappet body between the mating gap to leak out, but this does not affect the normal operation. Likewise, when the valve is heated and expanded, the plunger is pressurized and moves axially relative to the tappet body, and the oil is squeezed out from the lower chamber through the above gap. Therefore, when using the hydraulic tappet, it is possible not to leave the valve clearance, but to ensure that the valve can still close with the valve seat when the valve is heated and expanded.

When the valve begins to close or cooling contraction, the pressure on the plunger decreases, and due to the action of the spring 8, the plunger moves upward, always maintaining contact with the push rod. At the same time, the lower cavity of the plunger produces a vacuum, one-way valve 7 is sucked open, the oil will flow and again fill the entire tappet cavity.

Pusher

The role of the push rod is to transmit the thrust from the camshaft through the tappet to the rocker arm, which is the most easily bent part of the valve train. It requires high rigidity, and in engines with large dynamic loads, the pushrod should be made as short as possible. For the cylinder block and cylinder head part is made of aluminum alloy engine, the push rod is best made of hard aluminum. Push rod can be solid, or hollow. Steel solid push rod, generally with the ball bearing forged into a whole, and then heat treatment.