2011 2-MODE HYBRID TRANSMISSION (M99)

Vehicle Applications

Cadillac Escalade Hybrid / Escalade Platinum Hybrid

Chevrolet Silverado Hybrid

Chevrolet Tahoe Hybrid

GMC Sierra Hybrid

GMC Yukon Hybrid / Yukon Denali Hybrid

Product Highlights

·  Transmission designed for rear- and all-wheel-drive hybrid applications

·  Hybrid two-mode architecture

·  Electrically variable transmission with two integral electric motors

·  Electric vehicle drive capability

·  Maximum engine torque rating of 367 lb.-ft. (498 Nm)

·  Maximum gearbox torque rating of 379 lb.-ft. (515 Nm)

Overview

General Motors’ patented 2-Mode Hybrid transmission (M99) is the lynchpin for technologically advanced, industry-leading hybrid propulsion for full-size trucks and SUVs. It is an integral component of the hybrid drive system – as well as an efficient 6.0L V-8 (LZ1) with Active Fuel Management, variable valve timing and late intake valve closing technologies – for the following vehicles:

·  Cadillac Escalade Hybrid and Escalade Platinum Hybrid

·  Chevrolet Silverado Hybrid

·  Chevrolet Tahoe Hybrid

·  GMC Sierra Hybrid

·  GMC Yukon Hybrid and Yukon Denali Hybrid

The 2-Mode Hybrid transmission enables electric drive up to about 27 mph, helping deliver about 33 percent greater fuel economy in the city when compared with non-hybrid models. It also helps the vehicles deliver the capability and towing capacity expected of full-size trucks and SUVs – including electric drive when towing.

In simple terms, the 2-Mode Hybrid system is like two transmissions connected in parallel: One transmission is continuously variable by way of an electric motor used to vary ratios; and the other is a conventional stepped-ratio transmission. The fixed gears take over when power demand from the combustion engine is higher than the electric motor’s ability to maintain a ratio.

The 2-Mode Hybrid transmission is available in both two and four-wheel drive configurations. In 4WD applications, it is matched with the BorgWarner 4485 transfer case, which was developed with General Motors; it features an open planetary differential. Traction control and wheel-slip monitoring are performed by the stability control and anti-lock braking systems.

Electric Motors

The 2-Mode Hybrid transmission contains two electric motors, three planetary gear sets, and four wet-plate clutches. Three, 300-volt AC cables are connected to each of the two motors, which attach to the transmission housing via a rigid conduit around the transmission and are connected to an inverter that drives the motors.

The hybrid transmission can operate in multiple modes, including propelling the vehicle electrically with the combustion engine off. The first EVT mode (Mode-1) is designed for maximizing fuel economy and performance for city driving, while the second EVT mode (Mode-2) is designed for optimizing highway fuel economy and performance.

Four fixed ratios of 3.7:1, 1.7:1, 1.0:1 and 0.7:1 may be selected to balance performance and fuel economy. The system computes and chooses the optimum drive ratios to maximize highway fuel economy. Fixed gear changes are accomplished with synchronous shifts, using the EVT modes to transition between the fixed ratios.

Electric Vehicle (EV) Drive Operation

In typical EV drive operation, the vehicle initially accelerates with the engine off, using only electrical power from the 300V nickel metal hydride (NiMH) battery pack for propulsion. As the acceleration continues, the electric motors will simultaneously propel the vehicle and start the engine. With the engine running, the control system will blend the electrical power with the engine power, operating in the most efficient range to maximize fuel economy.

When decelerating, the regenerative braking system can capture much of the vehicle’s kinetic energy through the electric motors that are now acting as generators. The regenerative braking energy is stored in the NiMH battery and can be used later for EV drive.

The control system calculates whether to propel the vehicle with the 300-volt electric motor or the 6.0L gas engine. When the vehicle driving power is not high, and the engine operating efficiency is low, the control system stops the engine, and the hybrid system operates as a pure electric vehicle. When more driving power is required, the engine is quickly restarted to provide the dynamic response expected of a V-8-powered truck. The hybrid system therefore has two power sources, the gasoline internal-combustion engine and the electric drive system, and the control system proportions the two for optimum fuel economy and performance.

Specifically for EV drive operation, additional features were added to the main transmission case to minimize noise and vibration. Additional ribbing was added to the main case, while structure has been added to the input housing, enabling the mounting of the electric motors. Also for EV drive operation, an externally mounted electric oil pump supplies oil pressure to the hydraulic system when the engine is stopped.

Under higher load, such as towing, the control system shifts to fixed-gear operation.

Low Maintenance

Automatic transmission fluid is used as a lubricant and to cool the electric motors. For normal use there is no fluid change scheduled for the life of the vehicle.

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