Non-Turbocharged

Fig. 8 Exhaust gas recirculation (EGR) system.:

The EGR system reduces oxides of Nitrogen (NOx) emissions by recirculating a portion of the exhaust gasses back into the engine. A vacuum controlled (EGR) valve is used to regulate recirculation of exhaust gasses into the intake stream.


The system used on non-turbocharged engines consists of an engine speed (RPM) sensor, two load sensors mounted on the injection pump, an Electronic Control Module (ECM), three vacuum switching electro valves, a throttle flap vacuum motor and a dual diaphragm EGR valve, Fig. 8. The ECM monitors signals from the RPM and load sensor, computes the ideal amount of EGR for engine operating conditions and controls vacuum signals applied to the EGR valve and throttle flap motor through the three vacuum switching valves.

The two injection pump mounted sensors supply engine load information by monitoring injection pump lever position. A mobile sector, directly connected to the pump lever, passes in front of the load sensors as the injection pump lever moves through its travel. When the sensors are uncovered (light load conditions), a low voltage signal (approximately 2 volts) is transmitted to the ECM. As the sector covers the sensors (increasing load), a higher voltage (approximately 5 volts) is transmitted to the ECM. This allows the sensors to monitor 3 specific stages of engine loading: Light-load-no sensors covered; intermediate load-1 sensor covered; heavy load-both sensors covered.

The dual diaphragm EGR valve operates in one of three positions, depending upon vacuum applied by the switching valves. When no vacuum is applied to either chamber, the valve remains closed. When vacuum is applied to the upper chamber, the valve opens half-way until the upper diaphragm reaches a stop, partially raising the lower diaphragm rod which in turn controls the valve opening. In this position, spring tension applied to the lower diaphragm prevents the valve from opening fully. when vacuum is applied both diaphragm chambers the upper diaphragm rises until it contacts the stop, vacuum in the lower diaphragm chamber overcomes spring tension and the valve is opened fully. The throttle flap motor operates in conjunction with the EGR valve, limiting fresh air intake to increase EGR during light load conditions, and allowing full flow of intake air during intermediate and heavy load operation.

Vacuum applied to the EGR valve diaphragm chambers and throttle flap motor is controlled by separate switching valves which are operated by the ECM. When engine speed is below 1300 RPM, the switching valves are de-energized and no vacuum is applied to the EGR valve or throttle flap motor. During light load operation above 1300 RPM, both load sensors are uncovered and all three vacuum switching valves are energized. In this condition, the EGR valve is fully open and the throttle flap is partially closed providing operation above 1300 RPM, the lower load sensor is covered by the sector, and the ECM de-energizes the switching valve which controls the throttle flap motor. In this condition, vacuum is still applied to both EGR valve diaphragms but no vacuum is applied to the throttle flap motor, and EGR is reduced by the increased intake of fresh air. During high load operation both load sensors are covered, only the switching valve for the upper EGR valve diaphragm remains energized, and EGR is further reduced by the partial closing of the EGR valve operation. During Full load operation the lower load sensor remains covered, the ECM de-energizes all three switching valves and no EGR occurs.