IDENTIFICATION Exhaust gases from the front three cylinders on six cylinder engines (all four cylinders on four cylinder engines) are routed from the exhaust manifold through the EGR cooler, past control and reed valves, and mixed with the intake manifold charge air. The addition of cooled exhaust gases back into the combustion airflow reduces the peak in cylinder combustion temperature. Less oxides of nitrogen (NOx) are produced at lower combustion temperatures. The two systems operate independently of each other and in combination. Exhaust back pressure is used by the exhaust brake to increase braking performance.
The constant-throttle valves use the air that escapes through them on the compression stroke to provide braking force. The constant-throttles valves are small valves which are built into the cylinder head and positioned opposite the exhaust valve. When open, a link is created between the combustion chamber and the exhaust port. Exhaust Brake/Constant-Throttle Valves, Optional When the engine brake is switched on, the constant-throttle valves are put under pressure, which in turn opens the valves. To increase braking performance, the engine can be equipped with an exhaust brake on the turbocharger in conjunction with constant-throttle valves in the cylinder head. See Figure 15.
On the 6-cylinder model, the constant-throttle valves are activated by engine oil pressure. On 4-cylinder engines, the constant-throttle valves are activated by compressor air pressure. The engine brake is activated by the DDEC-VCU and can be activated only at engine speeds up to 2700 rpm. Figure 15 Constant Throttle Activation 24 All information subject to change without notice. (Rev. 04/08) DDC-SVC-MAN-0055 04/08 Copyright © 2008 DETROIT DIESEL CORPORATION