(a) Sketch a scroll type fuel pump, labelling the main components.(6)
(b) Explain how the pump sketched in part (a) may vary the end of delivery.(4)
Sketching a Scroll Metering Pump
Key Components to Include:
A cross-section of a scroll metering pump should include the following essential components:
- Outer Scroll: The stationary part of the pump that forms the outer boundary of the pumping chamber.
- Inner Scroll: The moving part that rotates within the outer scroll, creating the pumping chambers.
- Pump Housing: The casing that encloses the scroll assembly.
- Inlet Port: The point where fuel enters the pump.
- Outlet Port: The point where fuel exits the pump.
- Seal: The component that prevents leakage between the pump housing and the rotating components.
- Drive Shaft: The shaft that connects to the engine and drives the inner scroll.
Additional Details:
- Pumping Chambers: Indicate the areas between the scrolls where fuel is trapped and compressed.
- Flow Direction: Show the direction of fuel flow through the pump.
- Clearances: Illustrate the clearances between the scrolls and the housing.
- Materials: If known, indicate the materials used for the different components.
Note: The specific design of a scroll pump can vary, so the exact components and their arrangement may differ. However, the above elements provide a solid foundation for your sketch.
Varying End of Delivery in a Scroll Metering Pump
While the scroll design itself primarily controls the quantity of fuel delivered, the end of delivery can be influenced by several factors:
1. Plunger Position:
- Rotation angle: By controlling the rotation angle of the plunger, the point at which fuel delivery ceases can be adjusted.
- Spill port: Some scroll pumps have a spill port that can be opened or closed to control the end of delivery.
2. Delivery Valve Lift:
- Valve timing: The timing of the delivery valve’s closure can affect the end of delivery. A delayed closure can extend the injection duration.
3. Fuel Pressure:
- Pressure regulation: Maintaining optimal fuel pressure is crucial for consistent fuel delivery and precise control of the end of injection.
4. Electronic Control:
- ECU intervention: Modern scroll pumps often incorporate electronic control units (ECUs) to precisely control the end of delivery based on engine operating conditions.
By carefully managing these factors, the end of delivery can be adjusted to optimize engine performance, emissions, and fuel economy.
It’s important to note that the specific methods for varying the end of delivery can differ depending on the design and application of the scroll metering pump.