Throttle-body fuel-injection systems use what type of injector driver?
a. Peak and hold
b. Saturated switch
c. Pulse-width modulated
d. Pulsed
The Correct Answer and Explanation is:
Correct Answer: b. Saturated switch
Explanation:
Throttle-body fuel-injection (TBI) systems were among the first electronic fuel injection systems used in vehicles to replace the older carburetors. In a TBI system, one or two fuel injectors are located at the throttle body—essentially where the carburetor used to be. These injectors spray fuel into the intake manifold, where it mixes with air before entering the combustion chambers.
The type of injector driver used in a TBI system is the saturated switch driver. This driver type is simpler and less expensive than other options like the peak and hold driver used in multiport or sequential fuel-injection systems.
A saturated switch driver sends a continuous, lower current (typically around 1 amp) to the injector when it is turned on. The injector solenoid requires less current to open and remains open as long as the current flows. Because of this, saturated drivers work well with high-impedance injectors (typically 12 to 16 ohms). These injectors do not require a large initial current pulse, making them suitable for TBI systems which operate under relatively low-pressure and lower-performance demands compared to modern systems.
In contrast, peak and hold drivers send a high initial current (peak) to open the injector quickly and then reduce the current (hold) to keep it open. These are more complex and are typically used with low-impedance injectors in high-performance, sequential fuel-injection systems.
While pulse-width modulation (PWM) is a technique used to control the duration of injector opening (and thus fuel delivery), it is not a type of driver but rather a method applied by both saturated and peak-and-hold drivers.
Therefore, because TBI systems use high-impedance injectors and operate under simpler conditions, they rely on the saturated switch driver, making option b the correct answer.