Toyota on GM's 2 Mode Hybrid system.

GM's 2 Mode Hybrid System Explained

Well, Toyota has to come up with the Heavy Duty-Use HSD system soon. Or we're going to be in a tough selling competion environment...

We have to sell and compete with the GM and its affiliate on the Full size SUV's and Trucks with better Fuel Economy......Than current Toyota's
large platform vehicle lines such as: Sequoias, Tundras etc..

=General Motors Two-Mode Hybrid System.=

The GM Two-Mode Hybrid System is a full hybrid that can operate on gasoline-only, electric-only, or a
blend of gasoline and electric power. The Two-Mode system combines the following major components:
• A 332-horsepower 6.0-liter gasoline V8
• A 4-speed automatic transmission
• Two 60-kilowatt (kW) electric motor/generators
• One 300-volt nickel-metal hydride battery pack
• A regenerative braking system
Understanding the “Two” Modes
To the average consumer, the name Two-Mode Hybrid System might refer to gasoline power and electric
power. However, the “Two” modes are actually more complex. Simply stated, the two modes are a lowspeed
and a high-speed variable gear ratio arrangement in the transmission. The two modes can both
employ gas and electric power.

Mode One>
GM calls the low-speed arrangement “input split,” meaning the gas engine’s power is split between
mechanical and electric drive power, which together create variable transmission ratios via a
planetary gearset. The vehicle starts out in this mode.

Mode Two>
GM calls the high-speed arrangement “compound split,” which is similar to “input split” but uses a
second planetary gearset to apply continuously variable combinations of gas and electric drive power
at higher road speeds.

The system essentially operates like two Hybrid Synergy Drive transmissions: One continuously variable
gearset is used for low-speed driving, with another continuously variable gearset for high-speed driving.
As such, there are twice as many gearsets.
General MotorsTwo-Mode Hybrid System

A Unique Automatic Transmission
The key to GM’s Two-Mode Hybrid System is the vehicle’s new Electrically Variable Transmission (EVT).
Like a traditional automatic, this transmission uses planetary gearsets coupled with internal clutches. The
difference is that within the transmission case are two 60kW electric motor/generators. These
motor/generators provide three critical functions for the system.

1. They help accelerate the vehicle
The motor/generators can power the vehicle with no help from the gasoline engine (electric
power), they can power the vehicle in combination with the gasoline engine (electric and
mechanical), or they can assist the gasoline engine to provide additional power for acceleration,
hill climbing, and towing (mechanical with electric assist). In addition, the first motor/generator is
the gas engine starter.

2. They recharge the batteries
The motor/generators create electricity for the battery. When running, the gasoline engine can
drive one motor/generator for recharging as necessary. During braking and coasting, both
motor/generators can be used to slow the vehicle, converting the motion of the SUV into electrical
current that helps recharge the battery.

3. They provide variable gear ratios
Under light driving loads, the two electric motors work together to vary the gear ratio between the
gasoline engine and drive wheels. During high loads, like acceleration and towing, the
transmission can revert to its four fixed gear ratios. With fixed ratios, the engine delivers
mechanical power straight to the drive wheels. Even when operating in fixed gear ratios, the
motor/generators can still contribute electric assist for additional power when accelerating.

A Highly Modified V8 Engine
In addition to its complicated transmission, the 6.0-liter V8 also uses numerous additional technologies to
help it consume less fuel.

• Active Fuel Management (AFM). This allows the engine to switch from 8- to 4-cylinder operation
when cruising. Four cylinders shut down.
• Late Intake Valve Closing (LIVC). Also called an Atkinson cycle engine. This technology reduces
resistance against the pistons during the compression stroke to improve efficiency. Some power
and torque is sacrificed for fuel economy.
• Variable Valve Timing (VVT). This is a limited VVT system that can’t adjust the intake and
exhaust valve timing independently. In GM’s engine, one cam can’t accomplish both jobs.
• Auto Stop mode. The engine automatically turns off when the vehicle reaches 0 mph. The engine
is restarted by the first motor/generator when engine power is needed.

The Pros and Cons>

Customers and cross-shoppers will want to know the pros and cons of the new GM Two-Mode Hybrid
System, so the following points will be very important to understand.

The Pros>
• Tahoe and Yukon will be the first full-size SUVs offered with hybrid drive, making them unique
vehicles.
• 2WD models have EPA estimated fuel economy ratings of 21 mpg in the city and 22 on the
highway. This compares to 14/20 mpg for a comparable 5.3-liter non-hybrid model.
General MotorsTwo-Mode Hybrid System

• 4WD models have EPA estimated fuel economy ratings of 20 mpg in the city and 20 mpg on the
highway. This compares to 14/19 mpg for a comparable 5.3-liter non-hybrid model.
• Tahoe and Yukon can carry up to eight passengers or 1,560 lbs. of cargo.
• Tahoe and Yukon can pull from 6,000 lbs. (4WD) to 6,200 lbs. (2WD), though this is anywhere
from 200 to 1,300 pounds less than a 2WD 5.3-liter V8 Tahoe.

The Cons>
• The hybrid Tahoe and Yukon will only be available in limited markets, which may also mean
limited dealer service support.
• The GM Two-Mode Hybrid System is complicated, with a complex engine, transmission control
system.
• The transmission has four clutch packs that can and will wear out over the lifetime of the vehicle.
By comparison, Toyota’s Hybrid Synergy Drive® (HSD®) has no clutches.
• To save weight, GM had to use expensive and potentially expensive-to-repair aluminum hood
and cargo door panels.
• GM had to eliminate the opening rear cargo door window to save weight.
• GM had to eliminate the spare tire and jack to save weight, yet the vehicles do not use run-flat
tires.
• GM eliminated the roof rack and made many expensive body modifications to help reduce wind
resistance.
• Model-specific body panels are not interchangeable with non-hybrids.
• The Two-Mode system was developed via a complicated arrangement between GM, Allison
transmission, Chrysler and BMW.

What You Really Need To Know
GM should be applauded for developing environmentally sensitive technology. However, Toyota already
has over 1,000,000 hybrid vehicles on the road worldwide. Yes, that’s one million! This number speaks to
Toyota’s environmental commitment, and it demonstrates a track record that for the foreseeable future
simply can’t be beat by any other company.
Further, Toyota’s Hybrid Synergy Drive® (HSD®) is elegant in its simplicity, with many benefits:
• There is no traditional transmission or clutches, which reduces complexity.
• The gas engines do not need extra engineering to shut down cylinders.
• HSD® can be engineered for a wide range of economy and performance needs, as Prius, Camry
Hybrid and Highlander Hybrid demonstrate.
• HSD® is Toyota’s proprietary technology. This is an in-house design and Toyota has full
engineering control, which means world-class quality control.
• Finally, HSD® vehicles are available nationwide, and all Toyota and Lexus dealers are trained to
service and repair the vehicles.
By comparison, the GM system is highly complex, and the engineering contribution of four different
companies made for an involved development process. GM and Allison Transmission developed an
earlier version of this technology for large diesel busses, where it has served successfully for several
years.

However, GM, Chrysler, BMW and Allison Transmission had to “shrink” the engineering to fit into personal
vehicles, while also adding a conventional 4-speed truck transmission.
Also, a customer must wonder if a vehicle sold in limited markets will be welcome in the service bay of
Chevrolet and GM dealers across the nation.
General MotorsTwo-Mode Hybrid System

The Future of the GM System
Because the Two-Mode Hybrid System was developed in collaboration with Chrysler and BMW, this
technology will be used in a variety of vehicles, including:
• Chevrolet Silverado Hybrid pickup truck
• GMC Sierra Hybrid pickup truck
• Dodge Durango HEMI Hybrid SUV
• Chrysler Aspen HEMI Hybrid SUV
• And potentially the BMW X5 SUV
Toyota Hybrid Vehicles, To make the World a better place to live
for present and next generations to come.

Email: [email protected]

C.Rickey Hirose, The Hybrid vehicle's Ambassador.