Fuel Injection System Control Systems
Rugged and easily serviceable, mechanical governors continue to be used all over the world, especially in off-highway applications and nonroad engines. An inline pump illustrates the basic functions of mechanical control.
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Fuel Injection System Control Systems Ulrich Projahn, Helmut Randoll, Erich Biermann, J¨org Bru¨ckner, Karsten Funk, Thomas Ku¨ttner, Walter Lehle, and Joachim Zuern
6.1
Mechanical Control
6.1.1
Functions of a Mechanical Speed Governor
Rugged and easily serviceable, mechanical governors continue to be used all over the world, especially in off-highway applications and nonroad engines. An inline pump illustrates the basic functions of mechanical control. The hallmark of closed loop control is feedback of a controlled variable to the actuated variable, e.g. the injected fuel quantity specified by the setting of the inline pump’s control rack. Increasing the injected fuel mass at a constant load causes the speed to increase. In turn, the centrifugal force acting on the control device also increases and reduces the amount of rack travel. This creates a closed loop control circuit. The basic function of every governor is to limit the maximum speed to prevent a diesel engine from exceeding its allowable maximum speed. Other functions of a mechanical speed governor are: – providing the starting fuel quantity, – controlling idle speed, – maintaining a specified speed at various engine loads and – adjusting the torque characteristic with torque control or auxiliary units.
6.1.1.1
Proportional Degree
When a diesel engine’s load is reduced without varying the accelerator pedal’s position, the speed in the control range may only increase by a quantity permitted by the engine manufacturer. The increase in speed is proportional to the change in load, i.e. the more the engine load is reduced, the more the speed changes. This is called proportional behavior or proportional degree. The proportional degree is defined as the difference between maximum no load speed nLo and maximum full load speed nVo divided by maximum full load
U. Projahn (*) Robert Bosch GmbH, Diesel Systems, Stuttgart, Germany e-mail: [email protected]
speed nVo (rated speed): d ¼ 100
nLO nVo in %: nVo
Common proportional responses are approximately 0–5% for generator engines and approximately 6–15% for vehicle engines.
6.1.2
Design and Function of a Mechanical Speed Governor
An articulated rod connection establishes a connection with the injection pump’s control rack. RQ and RQV(K) governors (Fig. 6-1) have two flyweights that act directly on the governor springs integrated in the control device, which are designed for the desired rated speed, proportional degree and idle speed. Increasing quadratically with the speed, the centrifugal forces of the rotating centrifugal weights are counteracted by elastic forces from the governor springs. The control rack’s setting corresponds to the particular deflection of the flyweights produced by the biasing of the governor springs resulting from the centrifugal forces.
6.1.2.1
Governor Designs
An RQ idle speed-maximum speed governor is described as an example of governor design. Usually, diesel engines for vehicle applications do not require any control in the speed range between idle and maximu
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