Highlander Hybrid 4-Wheel Drive With Intelligence
The Highlander Hybrid 4WD-i option is like no other. In a departure from conventional 4WD design, it sports an electric motor dedicated to powering only the rear wheels. With no mechanical linkage between the rear-wheel drive and the rest of the powertrain, it's a distinctive approach, unique to Hybrid Synergy Drive®.
In all 4WD vehicles, the front and rear wheels must "know" what the others are doing. Most 4WD systems use mechanical shafts, gears, and electronic controls to keep the power distribution and wheel speeds in sync. Toyota engineers faced a challenge in designing the Highlander Hybrid 4WD option without a physical distribution of power between the front and rear wheels.

It's all about electronics
The solution is called 4-Wheel Drive with intelligence, or 4WD-i, for a very good reason. Highlander Hybrid with 4WD-i is packed with electronic sensors, controls and vehicle systems that process real-time data on speed, direction and acceleration.

Onboard control units analyze data from throughout the vehicle so quickly that its inner workings are totally transparent to the driving experience. Safety is actively enhanced, especially in skids, emergency maneuvers and tight cornering.

How it works
The key 4WD-i components are the Motor Generator Rear sensors or "MGR" and electronic control units. The MGR resides in a housing between the rear wheels also containing gears and a differential unit for the rear axle. For the sake of fuel economy, the MGR will usually not power the rear wheels during much of normal driving. It's used for acceleration and to automatically help provide control and safety. The MGR also captures kinetic energy upon braking, deceleration, or coasting and uses it to charge the hybrid battery pack.

Highlander Hybrid's sensors are 4WD-i's "nerve endings," gathering information on vehicle motion and mechanics instantaneously. The four main sensors are:
  • Wheel Speed -- one in each of the four wheels
  • Steering Angle -- reads the position of the steering wheel and steering direction
  • Yaw Rate & Deceleration Rate -- detects acceleration and deceleration in the forward, rearward and lateral directions. It's located under the front passenger seat
  • Accelerator Pedal Position -- reports on how far the driver steps on the accelerator pedal
The sensors feed information to two control units: the THS ECU (Toyota Hybrid System Electronic Control Unit) and Skid Control ECU. The ECUs take in sensor data and communicate with each other, choosing how much force and torque are required from the front transaxle and the MGR. The THS ECU also controls the gasoline engine plus two motor/generators that are integrated into Highlander Hybrid's front transaxle.

The result is balanced power on demand, a high level of fuel economy performance, and improved driving stability in a wide range of road conditions.

Now, that's intelligence.

Click for more detailed information on 4WD-i and Hybrid Synergy Drive in Highlander Hybrid.











[1] Vehicle Dynamics Integrated Management (VDIM) is an electronic system designed to help the driver maintain vehicle control under adverse conditions. It is not a substitute for safe driving practices. Factors including speed, road conditions and driver steering input can all affect whether VDIM will be effective in preventing a loss of control. Please see your Owner's Manual for further details.