MDE Unit 5 Q7

Scroll metering pumps meter fuel by the volume displaced as the inner scroll rotates within the outer scroll. To accommodate varying engine loads, the pump’s design incorporates several mechanisms:

1. Plunger Position Control:

• Rack and pinion: A common method involves a rack and pinion system that adjusts the position of the inner scroll.
• High load: By advancing the rack, the inner scroll’s position is altered to increase the volume of fuel delivered per rotation.
• Low load: Retracting the rack reduces the fuel volume per rotation.

2. Spill Ports:

• Fuel bypass: Some scroll pumps have spill ports that can be opened or closed to control the amount of fuel delivered.
• High load: By closing the spill port, more fuel is delivered.   1. Helix Fuel Injection Pump Explained – saVRee www.savree.com
• Low load: Opening the spill port diverts excess fuel, reducing the amount delivered to the injectors.

3. Multiple Plungers:

• Load distribution: Some pumps have multiple plungers to handle varying load conditions.
• High load: By activating more plungers, the fuel delivery rate increases.
• Low load: Only a few plungers might be activated for lower loads.

4. Electronic Control:

• Precision metering: Modern scroll pumps often incorporate electronic control systems for precise fuel metering.
• Load compensation: The ECU can adjust fuel delivery based on engine parameters like speed, load, and temperature.

In summary, scroll metering pumps achieve varying fuel delivery for different engine loads by manipulating plunger position, spill ports, and, in some cases, using multiple plungers. Electronic control systems enhance the precision and responsiveness of these pumps.