Pneumatic/ vacuum actuated EGRS

In between the switchover from fairly unsophisticated pneumatic valves to purely electric units, fairly complex 'hybrid’ designs appeared. Here, the pneumatic EGR valve is equipped with an electronic potentiometer to provide the engine ECU with accurate data on EGR valve position. These types can be identified by both vacuum and electrical connections being present on the valve body. Pneumatic EGRS are less common than pure electric types, due to being fitted to older cars. These systems also have a number of separate electrically-controlled valves to control the vacuum, resulting in fairly complex circuits that can vary between car-makers.

Ford’s vacuum control solenoid is referred to as an electronic vacuum regulator (EVR). The differential pressure feedback electronic (DPFE) sensor measures the pressure on either side of the valve. The pressure difference is then converted into a voltage and sent to the ECU. This is compared against a reference map, so the ECU can adjust the EVR to control the quantity of exhaust gas that is passed into the inlet manifold.

Honda controls EGR rates based on information programmed within the ECU’S map and references various factors that include RPM, road speed, engine temperature and load. The ECU operates the EGR valve by earthing a separate solenoid valve that controls the vacuum. EGR valve position is assessed by a potentiometer with a 5-volts supply that passes a variable signal back to the ECU. The control unit pulses the earth path to the solenoid valve, regulating the supply of vacuum and, therefore, controlling the EGR valve position.

Vauxhall applications are similar to those of Honda, except the solenoid valve, EGR valve and valve position potentiometer are all contained within a single unit.