LO 9-6 Identify and explain the purpose, construction, and operation of the camshaft

1.1. Overhead Camshafts

Overhead Camshafts

More recently designed overhead camshaft engines often use two camshafts. The Detroit DD13 and DD15 engines use one camshaft for the intake valves, a second camshaft for the exhaust valves, and an additional lobe for each cylinder on the exhaust cam to operate the compression release brake. The rear-mounted geartrain does not use timing marks to synchronize cam-to-crank operation. Instead, it uses special fixtures to lock the camshaft and geartrain in place Figure 51. The first generation of Cummins ISX with unit injectors uses two camshafts as well. One camshaft operates the valves, having lobes for the intake, exhaust, and compression release brake. The other, larger-diameter camshaft contains lobes to actuate the unit injectors Figure 52. The high pressurization of fuel inside the unit injector of the older ISX requires a wider lobe to distribute the injection actuation force. Space on the camshaft would not allow the use of three or four lobes on a single camshaft.

A	B		FIGURE 09-52: The wider injector lobe needed on the Cummins ISX requires a separate camshaft for the injector and valves.
FIGURE 09-51: A. The Detroit DD15 engine crankshaft is positioned at TDC and the geartrain is locked in place to synchronize cam and crank operation. B. This wedge tool is placed between the two Detroit DD15 camshafts to properly phase camshaft operation.