(a) Labeled Sketch:
- Scroll Housing: Houses the spiral groove (scroll).
- Spiral Groove (Scroll): Helical groove machined inside the housing.
- Rotor: Spool-shaped rotor with a tight fit inside the scroll.
- Eccentric Cam Follower Pin: Off-center pin on the rotor.
- Cam Follower Groove: Groove on the drive sleeve where the pin rides.
- Drive Sleeve: Connected to the engine, rotates the rotor.
- Inlet Port: Where fuel enters the pump.
- Outlet Port: Where fuel exits towards the engine injectors.
(b) Varying End of Delivery
The scroll type fuel pump sketched in part (a) doesn’t directly control the “end of delivery” (injection timing) of fuel. Fuel injection timing is typically controlled by a separate mechanism within the engine’s fuel injection system.
The scroll pump’s function is to meter the fuel quantity delivered per engine cycle based on load. Here’s how the pump design indirectly affects the end of delivery:
- High Load: As explained previously, larger pockets form at high load, delivering more fuel per pump revolution. This increases the volume of fuel available for injection during the injection window controlled by the separate injection timing mechanism.
- Low Load: Smaller pockets deliver less fuel per revolution, reducing the amount of fuel available for injection during the same injection window.
In essence, the scroll pump indirectly influences the end of delivery by providing a variable fuel quantity based on load, which can then be injected at the appropriate time determined by the injection timing control system.