Regulatory agencies such as the Environmental Protection Agency and the Engine Manufacturers Association require strict emission requirements for heavy-duty diesel engines. One method used to reduce emissions of engines is an Exhaust Gas Recirculation ("EGR") system. The EGR system controls the amount of exhaust gas that is introduced into the engine's air intake system by a valve that adjusts the flow rate based on various engine operating parameters.
In addition to the normal operation of the EGR system, most EGR systems also have a fail-safe mode that drives the EGR valve either fully closed or fully open, depending on the design of the EGR system. Typically a spring is added to the EGR system to move the EGR valve when in fail-safe mode. The spring, however, is permanently affixed, and continuously exerts a biasing force on the EGR valve, i.e., during both normal and fail-safe operation. This places a large and unnecessary load on the actuator during normal operation. The additional load increases the likelihood of the actuator overheating, or requires a more powerful actuator than would otherwise be needed.
Further, because of the high powered actuators, conventional EGR systems typically use hydraulic or pneumatic powered actuators to adjust the position of the EGR valve. Both hydraulic and pneumatic systems are, however, susceptible to leaking.