CVAD Crankshaft – Improved Fuel Economy

Reduce energy consumption of belt driven engine accessories with a NuVinci® crankshaft-mounted Continuously Variable Accessory Drive (CVAD) The NuVinci CVAD is a power management system for engine accessory drives that enables unprecedented ability to change accessory loads and outputs instantaneously for improved performance, improved fuel economy, and higher accessory output on an as-needed basis.
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.		Green area shows NuVinci benefit. See larger chart below.

Problem:  Power Loss from Un-Optimized Accessories

The belt-driven accessories for a typical passenger car or truck usually include an alternator, power steering pump, water pump, AC compressor, and, in some cases, a hydraulic brake booster. Some may also include emissions control pumps, an oil pump, and a cooling fan. A fundamental characteristic of each of these devices is that each has a very narrow speed range for most efficient operation – typically a much smaller ranges of speeds than the engine itself operates over during normal driving. But in the effort to improve fuel economy, accessory optimization has been largely overlooked, simply because existing technology offered no practical alternatives for producing an accessory drive whose speed was continuously optimized for all conditions...until now!

Solution:  A crank-mounted CVAD using the NuVinci  CVP

NuVinci technology makes possible a practical CVAD that measurably improves fuel economy by separating accessory speed from engine speed, which allows operation of accessories within their most efficient speed ranges. When installed on the crankshaft, a NuVinci-based CVAD can be used to optimize the operation of front-end accessories and improve fuel economy, or to increase alternator power and coolant flow at idle. The CVAD also allows for the downsizing of components to reduce packaging and improve constant speed performance.

The diagram below illustrates the CVAD’s “U” drive power path configuration. Power comes in from the crankshaft, transfers it to one traction ring, through the planet balls, and brings the power out of the other traction ring to the belt. Tilting the balls provides a smooth ratio transition from underdrive to overdrive.

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.

During a typical drive cycle, engine speeds operate between idle and highway cruise depending upon conditions as illustrated in the chart below. For vehicles with belt-driven accessories, accessory speeds follow these transients, wasting power when the engine is accelerating or cruising. With the NuVinci-equipped CVAD mounted on the crankshaft, belt speeds may be varied independent of engine speed, reducing accessory speeds and power consumption.

The NuVinci-equipped CVAD offers:

• Increased fuel economy
• Smooth accommodation of engine speed transients
• Opportunities to add “smart” controls for accessory drives
• Ability to downsize accessory capacity

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