what heavy trucks are doing...
http://fleetowner.com/equipment/behr-s-visco-technology-diesel-engines-promises-fuel-savingssample quote
Variable-speed Visco fan drives for truck engines have been available since the 1970s, but this is the industry’s first coolant-pump application.
Heavy-truck coolant pumps today are almost exclusively tied linearly to engine-speed via belt drives. Since these pumps are designed to meet coolant requirements under maximum load conditions, flow rates at many operating points exceed actual need with a resulting drain on fuel economy.
Behr’s trademarked Visco technology covers variable-speed, fuel-saving air- and coolant-flow products by hydraulically isolating engine-input speeds and minimizing power consumption under high-speed operation and light-engine loads where maximum flow rates are not required.
The Visco pump’s control logic is embedded in an engine-control module.
Although the pump is tied to a belt drive, energy is transferred hydraulically to an impeller.
The amount of energy transfer depends on the amount of silicone oil in an operating chamber managed through a closed-loop control system.
The fully variable-speed Visco clutch operation allows for precise coolant flow rates. Continuous impeller-speed feedback is the key to providing immediate coolant flow adjustments when required by engine conditions.
The Visco coolant pump is designed for the life of the vehicle and does not require periodic maintenance. Estimated fuel-economy savings of 1% for long-haul truck applications is based on average engine power of 100 kW.
