Following closely on its introduction of the Japanese version of a hybrid Highlander (earlier post), Toyota has announced that it will introduce the seven-passenger hybrid SUV to the US market in June.
The Highlander Hybrid uses a new version of Toyota’s Hybrid Synergy Drive powertrain specifically developed for the mid-size SUV class. An all-new high-speed electric motor operates at twice the speed (up to 12,500 RPM) and delivers more than twice the power (123 kW) as the motor used in the Prius, producing 268 peak combined horsepower with a standard towing capacity of 3,500 pounds.
Toyota is offering two versions of the Highlander Hybrid: four-wheel drive (4WD-i) and two-wheel drive (4x2).
Toyota modified the 3.3-liter V6 engine in the conventional Highlander to integrate more smoothly with the hybrid system. Revisions include changes to calibrations of the Variable Valve Timing with intelligence (VVT-i) and Electronic Throttle Control (ETC) systems.
There are two electric motor-generators in the 4x2 models (as in the Prius) and three motor-generators in the 4WD-i models (as in the Lexus Rx 400h hybrid).
Internally referred to as MG1, MG2 and MGR for the rear electric motor in the 4WD-i, each has a specific function and each does double duty as both drive motor and generator (although MG1 is a starter and provides no motive force). The engine-driven generator (MG1) and rear electric motor (MGR) can charge the battery pack, which powers other electric motors as needed.
Power from the gas engine and front electric-drive motor (MG2) is distributed to the drive wheels via a planetary gear-type continuously variable transmission, which eliminates specific gear ratios. Two planetary gear units are used in the system. The Power-Split unit divides the engine’s drive force two ways: one to drive the wheels and the other to drive MG1 so it may function as a generator. The Motor Speed Reduction unit reduces the speed of MG2 and increases its drive torque, significantly boosting acceleration performance.
In addition to its motor-generator duties, the crucial MG1 adds two functions: one as a starter motor for the gas engine; and two, by regulating the amount of electrical power it generates (which varies its RPM), MG1 controls the output speed of the transaxle through the planetary gear set—without clutches or viscous couplings.
In conventional 4WD vehicles, the weight and friction of the additional drive components reduce the vehicle’s acceleration performance compared to the same model with 2WD. By contrast, the 50-kW MGR at the rear provides up to 96 lb.-ft. of additional drive torque as required. The system electronically varies front and rear torque distribution depending on driving conditions.
The Toyota hybrid technology also allows extended electric-mode operation during low speed or stop-and-go driving conditions. The permanent-magnet front electric drive motor (MG2) produces peak torque from zero-to-1,500 RPM, giving the Highlander Hybrid powerful and instantaneous response that will be especially felt in low- and mid-speed performance and in merging and passing maneuvers.
A regenerative braking system captures kinetic energy that would normally be lost as heat through the brakes and transforming it into useable electricity to recharge the batteries.
The hybrid system uses a 288-volt DC Nickel metal hydride (Ni-MH) battery pack. The battery’s power flows through a “boost converter” that bumps the voltage to 650V DC. An inverter changes this to 650V AC, providing its elevated power to the electric motors.
The Highlander Hybrid uses the all-new Vehicle Dynamics Integrated Management (VDIM) system. The new system goes beyond conventional traction control systems, which react to challenging conditions. Instead, VDIM anticipates loss of vehicle control in virtually any direction and makes corrections while allowing higher dynamic capability.
A critical component of VDIM is a new Electronically Controlled Braking system (ECB). The ECB system translates brake pedal stroke and pressure and generates the precise amount of combined electric regeneration and hydraulic pressure needed for virtually any driving condition.
Under guidance from VDIM, such precise brake control at individual wheels allows more optimized operation of the vehicle’s dynamic handling systems that employ the brakes: ABS, Brake Assist, Vehicle Stability Control (VSC) and traction control (TRAC). VDIM also interfaces with the Hybrid System, allowing it to modify vehicle power when needed, and a new Electronic Power Steering system (EPS) to optimize steering assist for each situation.
The EPS uses a DC motor and gear reduction system built into the steering gear housing to provide steering assist. This unit contributes to fuel economy by eliminating the traditional power steering pump and by providing its computer-controlled assist only when called for by the driver. EPS also allows a more precise and timely control of steering assist than conventional engine-driven hydraulic systems.
VDIM constantly calculates vehicle motion based on signals from a yaw rate and deceleration sensor, wheel speed sensor and steering angle sensor. Using these inputs, VDIM controls all of the vehicle’s dynamic handling systems and can employ them collectively and seamlessly, allowing it to quickly detect the onset of a loss of vehicle control and help correct it.
The Highlander Hybrid 4x2 carries an estimated EPA fuel efficiency rating of 33 mpg city, 28 mpg highway, 30 mpg combined. This more than doubles the fuel efficiency of most comparable V8-powered SUVs. The estimated EPA city/highway average for all 4WD-i models is an 31/27 with a combined rating of 29 mpg.
The Highlander Hybrid will be rated as a Super Ultra Low Emissions Vehicle (SULEV).
|Toyota 2006 Highlander Hybrid
|208 hp (155 kW)
|212 lb-ft (287 Nm)
|268 hp (200 kW)
|MG1 (Generator Motor)
|MG2 (Traction Motor) Power
|123 kW (167 hp)
|MG2 (Traction Motor) Torque
|335 Nm (247 lb-ft)
|MGR (4x4 Rear Traction Motor) Power
|50 kW (68 hp)
|MGR (4x4 Rear Traction Motor) Torque
|130 Nm (96 lb-ft)
|4x2 City/highway/combined mpg
|4x4 City/highway/combined mpg