STEP 4V1833 - Caterpillar

Valve System Components
Illustration 3 g02138171
Valve system components
(23) Rocker arm
(24) Valve adjustment screw
(25) Rocker arm shaft
(26) Camshaft follower
(27) Camshaft
(28) Valve bridge
(29) Valve rotator
(30) Valve spring
(31) Valve
(32) Valve seat The valve train controls the flow of inlet air into the cylinders and the flow of exhaust gases out of the cylinders during engine operation. Machined lobes on the camshaft (27) control the following aspects of valve function:
Height of valve lift
Timing of valve lift
Duration of valve liftThe crankshaft gear drives the camshaft gear through an idler gear. The camshaft must be timed to the crankshaft in order to get the correct relation between the piston position and the valve position.The camshaft has three camshaft lobes for each cylinder. One camshaft lobe operates the inlet valves. One camshaft lobe operates the exhaust valves. There is also one camshaft lobe that operates the unit injector. Camshaft followers (26) roll against the surface of the camshaft lobes. The followers are used in order to transfer the lift that is machined into the camshaft lobe to the rocker arm (23).The camshaft lobes lift the camshaft follower of the rocker arm which actuates the valves (31). As the camshaft lobe lifts the follower, the rocker arm pivots at the rocker shaft (25). This applies the lifting action to the valve bridge (28). The valve bridge is used to transfer the lift from the rocker arm to the valves. The valve adjustment screw (24) is used in order to adjust the valve lash.Each cylinder has two inlet valves and two exhaust valves. Valve springs (30) are used to hold the valves in the closed position when lift is not being transferred from the camshaft lobe. The springs provide the force on the valve in order to ensure that the valves will close at high rpm and under high boost pressures.Valve rotators (29) cause the valves to rotate while the engine is running. The rotation of the valves prevents the valves from burning by constantly changing the contact area of the valve face and the valve seat (32). This rotation gives the valves longer service life.NOx Reduction System (NRS)
Illustration 4 g02134516
Components of the NRS (top view of the engine)
(7) NRS exhaust cooler
(33) Absolute pressure sensor
(34) Differential pressure sensor
(35) Oil return line from NRS actuator
(36) NRS venturi
(37) NRS valve assembly
(38) Solenoid for NRS actuator
(39) NRS actuator
(40) Oil supply for NRS actuator The NRS is used to reduce the amount of nitrogen oxide that is produced during combustion. The exhaust gas exits the combustion chamber and flows into the exhaust manifold. A portion of the exhaust gas from the first three cylinders of each bank flows into the NRS exhaust coolers (7). The NRS exhaust cooler (7) utilizes engine coolant, which flows through a heat exchanger in order to cool the exhaust gas. Heat is transferred from the exhaust gas to the engine coolant as the exhaust gas flows through cooler. The maximum temperature of the cooled exhaust gas is approximately 240° C (464° F).After the exhaust gas is cooled, the gas