CVAD Alternator – Rated Power at Idle

Extracting more power from an alternator using NuVinci® technology and a Continuously Variable Accessory Drive (CVAD) NuVinci® CVAD - Alternator Model: 43CVP-A01 U-Drive Now Available for Beta Fleet Tests (click here for the specification sheet)		(click chart for larger version below)
		Green area shows NuVinci benefit
The NuVinci CVP is a power management system for engine-driven alternators that enables unprecedented ability to change alternator output on the fly for improved performance (up to 75% improvement demonstrated) at low engine speeds while maintaining reliable accesory operation at high engine speeds. The NuVinci CVP does this by offering an infinite number of speed ratios between its high and low ratio extremes, with programmable instantaneous, smooth and continuous ratio changes. Operation is completely seamless and transparent to the driver.

Problem:  Underpowered alternators for mission-critical needs

Military, transit bus and commercial vehicles share a common alternator problem – namely that a belt-driven alternator doesn’t make anywhere near its rated electric power at engine idle. This is because the alternator’s speed at idle falls below its rated speed. Sizing the pulley ratio to spin the alternator faster at idle will cause the alternator to over-speed and fail during normal engine operation. Inadequate electrical power during prolonged idle can result in high levels of battery maintenance and replacement, the need to carry multiple batteries, poor or inadequate electrically powered equipment performance, and in some cases, even premature failure of sensitive onboard electronics.

Solution:  A CVAD alternator using the NuVinci  CVP

A NuVinci-based CVAD improves alternator power at low engine speeds, with minimal complexity, easy bolt-on installation and low cost. The diagram below illustrates the CVAD’s “U” drive power path configuration. Power comes in from the belt, goes thru the input traction ring, through the planet balls, and then out of the output traction ring. Tilting the balls provides a smooth ratio transition from overdrive, providing high alternator speeds at low engine speeds, to underdrive, when the alternator might be operated at speeds slower than engine speed.

The CVAD enables control of output speed (see red line in the chart below), independent of engine speed (the white line). At engine idle, output speeds may be increased, providing more power to the alternator. At higher engine speeds (such as accelerating from a stop or cruising), accessory speeds may be reduced, saving energy. The NuVinci CVP also shifts quickly, helping to smooth out transients.

Results:

The graph below illustrates the improvements possible with a NuVinci CVAD. A typical-high performance alternator (grey curve) does not provide full power at low engine speeds (less than 1200RPM). A NuVinci-equipped CVAD alternator (red curve) enables optimal alternator operation, even at low engine speeds. The green area represents the increase in alternator current generated at low RPM, as compared to a standard alternator. Depending upon the duty cycle, this can result in 75% more delivered power.

The NuVinci-equipped alternator offers:

• Rated alternator power at idle
• Reduce or eliminate the need to carry multiple batteries
• Opportunity to downsize accessory capacity
• Improved battery life

Click here for a Alternator-mounted CVAD datasheet (PDF) (contents of this page in printer format)

Click here to read the NuVinci Development Briefing: A Continuously Variable Accessory Drive for Alternators and Other Engine-Driven Accessoriesesults:

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