Fuel Economy Improvements through Improved Automatic Transmission Warmup - Stand Alone Oil to Air (OTA) Transmission Cooling Strategy with Thermostatic Cold Flow Bypass Valve 2001-01-1760

The stand alone oil to air (OTA) transmission cooling strategy with thermostatic cold flow bypass valve has been shown to be an effective means of improving the warmup of an automatic transmission. Improving the system warmup rate of an automatic transmission significantly improves its efficiency by reducing losses resulting from extremely viscous transmission fluid and can allow for calibration changes that improve overall transmission performance. Improved transmission efficiency in turn allows for improved engine efficiency and performance. The improvements obtained from increased transmission and engine efficiency result in an overall increase in vehicle fuel economy.

Fuel economy and consumption are important parameters considered by the vehicle manufacturer and the customer. Fuel economy can be considered as important as reliability and durability. The stand alone OTA transmission cooling strategy with thermostatic cold flow bypass valve results in improvements to reliability, durability and fuel economy. Durability and reliability are improved due to improved transmission cooling during hot ambient conditions and improved transmission warmup during cold ambient conditions. Fuel economy is improved through using the stand alone OTA strategy due to the improved transmission warmup times, which results in improved powertrain efficiency and less fuel consumption.

The thermostatic cold flow bypass valve is the key to the stand alone OTA strategy being able to improve transmission warmup and improve fuel economy. The thermostatic cold flow bypass valve shuts off flow to the transmission oil cooler until a predetermined fluid temperature has been achieved. Once the predetermined transmission fluid temperature has been achieved, the bypass valve allows oil flow to the transmission oil cooler. This keeps the transmission from being unnecessarily cooled and therefore improves transmission efficiency.

As a follow up to previous testing conducted that quantified transmission warmup rates, fuel consumption measurements were taken for a 4X4 sport utility vehicle (SUV). The fuel consumed by the vehicle when using the stand alone OTA transmission cooling system with thermostatic cold flow bypass valve was compared to the fuel consumed by the vehicle when using the conventional oil to water (OTW) production transmission cooling system. Testing was conducted under a variety of ambient conditions ranging from 25 °C to -20 °C and for the following operating conditions: 50 kph and 100 kph road load operating conditions at 3250 kg GVW; 50kph and 80 kph 8% grade trailer tow operating conditions at 4500 kg GCW. Vehicle testing was conducted in an environmentally controlled wind tunnel with data acquisition occurring twice per second. Data measured included; fuel consumption, transmission system temperature and engine speed.

Fuel economy improvements were quantified for each operating condition and the entire drive cycle for a given ambient temperature. The decrease in fuel consumption for the stand alone OTA system is related to the improvements achieved in transmission warmup. The stand alone OTA transmission cooling strategy allows for improved transmission system warmup and more efficient transmission operation than the conventional OTW transmission cooling strategy. The result was a 4% improvement in vehicle fuel economy. If changes are made to the vehicle transmission calibration strategy, even greater fuel economy improvements can be obtained.