Power Generation
Electrical power for heavy duty vehicles is supplied by an alternator that is attached to the engine via a belt or shaft. The nature of vehicle alternators is such that at low operating speed, they produce considerably less than full rated power. A typical curve of alternator power output versus engine speed is shown in Figure 1. The generator in this example is rated to 425 amps at an engine speed of 6000 rpm but only generates 250 amps at idle. Most commercial generators have a dual rating, listing the output at idle and a rated rpm.
Heavy duty engines can spend much of their time at idle but the system power demands are unchanged based on engine speed (or vehicle speed). The result is the alternator must be designed to meet the maximum power output at the minimum alternator speed. As an example, the standard HMMVV needs to generate at least 154 amps at idle to satisfy its mission requirement. The HMMVV is a 400 amp alternator installed because it will meet the power requirements at idle.
Orbital Traction’s Controlled Velocity Accessory Drive (CVAD) enables an alternator to generate full rated power at engine idle, and across the full range of engine speeds, by decoupling the speed of the alternator from the speed of the engine. The CVAD-enabled alternator is capable at standard vehicle idle of generating twice as much power as a traditional alternator, without sacrificing performance at higher speeds. An example of the resulting increase in alternator performance for a 400 amp alternator is illustrated in Figure 2.
The CVAD alternator is designed to be retrofittable on any heavy-duty engine, within current space confines and without specialized training or personnel. This includes heavy-duty engines that provide stationary power (standby generator, frac pump, etc), mobile equipment (tractors, bulldozers, etc) or commercial and military vehicles.
The benefits of the CVAD systems are: