![]() One common approach is to meter the fuel drawn into the pump (inlet metering) with some type of inlet metering valve (IMV)-sometimes also referred to simply as a fuel metering valve (FMV). ![]() A number of pump metering approaches are possible. While this approach was used exclusively in some early fuel injection systems such as those with Bosch CP1 pumps (Figure 1 and Figure 2), poor efficiency and an excessively high fuel return temperatures can result.Īnother approach is to meter the fuel at the high pressure pump to ensure that only the amount of fuel required by the injectors is supplied to the common rail. In this approach, the pressure control valve position is the control system input. One way is to supply more fuel than is needed to the common rail and use a high pressure regulator-commonly referred to as a pressure control valve-in the high-pressure circuit to spill the excess fuel back to the fuel tank. There are a number of approaches to control the pressure in the common rail. In control terminology, the rail pressure is the system output while the position of the actuator used to control the rail pressure is the system input. This pressure is monitored by a pressure sensor and the difference between the nominal rail pressure value and the measured one is the input signal for the controller. The pump maintains the rail pressure by continuously delivering fuel to the common rail. Production common rail fuel systems are equipped with a closed-loop high pressure control-system that stabilizes the rail pressure within a relatively small margin to the nominal value specified by the electronic control unit for a given engine operating condition. Some practical common rail implementations utilize both approaches with the control strategy depending on the engine operating conditions. ![]() A variety of fuel metering can be used for the later. A more preferred approach is to meter the fuel at the high pressure pump in order to minimize the amount of fuel pressurized to the rail pressure. One early approach method was to supply more fuel than is needed to the common rail and use a pressure control valve to spill the excess fuel back to the fuel tank. Abstract: There are several approaches to control the pressure in the common rail.
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