Inside Chrysler's Two-Mode HEMI Hybrid SystemS

On the outside, a hybrid is usually just a badge and a smug driver. On the inside is where all the fun happens. In that spirit we bring you the internals of the Chrysler version of the two-mode hybrid system (after a long day of previews and reveals we thought you deserved a little mechanical pr0n). This system is considered "two-mode" because it utilizes a continuously variable transmission with two modes. When going slow and not carrying much the hybrid can use electric power, engine power or duel power to propel itself. At high speeds or with high loads, the system switches to full power from the HEMI with the electric assist. Full details below:

The Advanced Two-mode Hybrid System

Chrysler's advanced, state-of-the-art two-mode full hybrid system — developed in partnership with General Motors, Mercedes-Benz and The BMW Group — integrates proven automatic-transmission technology with a patented hybrid-electric drive system to deliver the world's first two-mode full hybrid.

As a result of low- and high-speed electric continuously variable transmission (ECVT) modes, the system is defined as a "two-mode hybrid." In addition, the sophisticated fuel-saving system incorporates four fixed-gear ratios for high efficiency and power-handling capabilities. During the two ECVT modes, the system can use the electric motors for acceleration, improving fuel economy, or for regenerative braking to utilize energy that would normally be lost during braking or deceleration. The energy is stored in the batteries for later use.

The system's two modes are optimized for city and highway driving.

In the first mode — at low speed and with light loads — the vehicle can operate in three ways:

• Electric power only

• Engine power only

• Any combination of engine and electric power

The two-mode hybrid provides all of the fuel-saving benefits of a full-hybrid system, including electric-only operation. In this mode, the engine is "shut off," with the vehicle moving under electric-only power at low speed. The result is a significant reduction in fuel consumption in heavy stop-and-go traffic.

The second mode is used primarily at highway speeds. In addition to electric assist, the second mode provides full power from the 5.7-liter HEMI® V-8 when conditions demand it, such as when passing, pulling a trailer or climbing a steep grade.

The two-mode programming integrates a host of technologies to improve efficiency including Chrysler's patented Multi-displacement System (MDS), standard on the 5.7-liter HEMI V-8.

An elegantly complex design, the two-mode system also allows for more proliferate packaging via compact and powerful electric motors designed to fit within a conventional automatic transmission space — a clear efficiency advantage compared with today's typical single-mode systems that rely on much larger electric motors.

A sophisticated controller determines when the vehicle should operate in the first or second mode. Input from the controller determines the necessary torque for the driving conditions and sends a corresponding command to the engine and electric motors. The engine and electric motors transfer torque to a series of gears in the transmission, which multiply torque similar to a conventional automatic transmission to propel the vehicle. Unlike conventional continuously variable transmissions, however, the two-mode full hybrid's electrically controlled system uses no mechanical belts or bands. Shifts between the two modes are synchronous — meaning no engine speed changes are necessary for the mode shift to occur — resulting in seamless accelerations.

The 300-volt battery pack provides electric power for the system, and is designed to fit in the vehicle without compromising passenger space. A rectifier located under the vehicle's hood converts AC to DC, to power conventional 12-volt accessories, such as interior lighting, climate control and the audio system. The vehicle's internal-combustion engine efficiently maintains the battery pack.

Hybrid Development Center

Located in Troy, Mich., the Hybrid Development Center (General Motors, Chrysler, Mercedes-Benz and The BMW Group) jointly developed the overall modular two-mode hybrid system and the individual components: electric motors, transmission, high-voltage battery, high-performance electronics, wiring, safety systems, energy management and hybrid-system control units. In addition, the Hybrid Development Center is responsible for system integration and project management.