The manifold-pressure compensator (LDA) reacts to the charge-air pressure generated by the exhaust-gas turbocharger, or the (mechanical) supercharger, and adapts the full-load delivery to the charge-air pressure AssignmentThe manifold-pressure compensator (LDA) is used on pressure-charged diesel engines. On these engines the injected fuel quantity is adapted to the engine’s increased air charge (due to pressure-charging). If the pressurecharged diesel engine operates with a reduced cylinder air charge, the injected fuel quantity must be adapted to the lower air mass. This is performed by the manifold-pressure compensator which, below a given (selectable) charge-air pressure, reduces the full-load quantity.Design and constructionThe LDA is mounted on the top of the distributor pump. In turn, the top of the LDA incorporates the connection for the charge-air and the vent bore. The interior of the LDA is divided into two separate airtight chambers by a diaphragm to which pressure is applied by a spring. At its opposite end, the spring is held by an adjusting nut with which the spring’s preload is set. This serves to match the LDA’s response point to the charge pressure of the exhaust turbocharger. The diaphragm is connected to the LDA’s sliding pin which has a taper in the form of a control cone. This is contacted by a guide pin which transfers the sliding-pin movements to the reverse lever which in turn changes the setting of the full-load stop. The initial setting of the diaphragm and the sliding pin is set by the adjusting screw in the top of the LDA.Method of operation In the lower engine-speed range the charge-air pressure generated by the exhaust turbocharger and applied to the diaphragm is insufficient to overcome the pressure of the spring. The diaphragm remains in its initial position. As soon as the charge-air pressure applied to the diaphragm becomes effective, the diaphragm, and with it the sliding pin and control cone, shift against the force of the spring. The guide pin changes its position as a result of the control cone’s vertical movement and causes the reverse lever to swivel around its pivot point . Due to the force exerted by the governor spring, there is a nonpositive connection between tensioning lever, reverse lever, guide pin, and sliding-pin control cone. As a result, the tensioning lever follows the reverse lever’s swivelling movement, causing the starting lever and tensioning lever to swivel around their common pivot point thus shifting the control collar in the direction of increased fuel delivery. Fuel delivery is adapted in response to the increased air mass in the combustion chamber. On the other hand, when the charge-air pressure drops, the spring underneath the diaphragm pushes the diaphragm upwards, and with it the sliding pin. The compensation action of the governor lever mechanism now takes place in the reverse direction and the injected fuel quantity is adapted to the change in charge pressure. Should the turbocharger fail, the LDA reverts to its initial position and the engine operates normally without developing smoke. The full-load delivery with charge-air pressure is adjusted by the full-load stop screw fitted in the governor cover.
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