Comparison of Prius hybrid system to Tahoe hybrid system
#11
08-07-2009, 08:59 AM
Re: Comparison of Prius hybrid system to Tahoe hybrid system
I think there are significant differences between the Toyo and GM approach. Toyo uses independent electric motors on the wheels- I don't remember if it is front and rear or four motors, but it is a set up that allows power to be delivered more directly to wheels. This made the early Highlanders 4WD when the electric was on at low speeds. GM uses a gas engine, and an electric motor behind that, powering the drive train. Thus, regardless of which system is on, the drive shaft is being turned and then the diff, then the wheels. In the Toyo version, when on electric, power is directly to the wheels increasing torque, and avoiding the drive shaft, diff etc. I think this reduces friction and increases economy.
I have owned both, and this is my recollection of the manuals and what not. But as always, I could be wrong.
I have owned both, and this is my recollection of the manuals and what not. But as always, I could be wrong.
However, I believe the significant differences between the Highlander and the 2-Mode systems are slightly different than suggested. For the Highlander, the front wheels are driven the same as in the rest of the Toyota and Ford hybrid systems: engine and two electric motors operating through a planetary gearset driving a differential to drive shafts to the wheels. Some Toyota's have a 2-speed gear range between the planetary and the differential. Some Toyota's, such as the 4 wheel drive Highlander, have direct-drive rear wheels with additional electric motors on each rear wheel.
The 2-Mode GM system (and other manufacturers who use the 2-Mode system) has all these things except the direct-drive rear wheels. For their 4-wheel drive, they use multiple differentials to split the power from the engine/motor/planetary/transmission system to all four wheels, just as most 4-wheel drive systems. Also, the 2-Mode system, rather than having a fairly simple 2-speed transmission between the planetary gears and the differential, have a fairly normal multi-speed (4-speed, I believe) in parallel with the dual electric motor/planetary gear-set such that either the motor/planetary system is between the engine and the differential, or the normal transmission is between the engine and the differential. Additional clutches are used to switch between the two drive modes, engaging either the hybrid system, or the conventional transmission.
When the 2-Mode system is in "hybrid" mode, it is virtually identical in operation as the Toyota and Ford systems, save for minor differences, such as the way the rear wheels are driven. Note that the two electric motors are typically operating with one driving the wheels while the other is generating electricity for driving the other motor and/or charging the drive battery. In all electric mode, both motors are driving, while in braking mode, both motors may be acting as generators. The balance between the generating electricity and the driving the wheels effectively determines the gear ratio between the gas engine and the wheels. The Toyota rear electric wheels just tap the same power that the front wheels use: either power generated from one of the motors, or from the battery. The electronics control what each motor is doing at all times.
-- Alan
#12
08-07-2009, 01:09 PM
Re: Comparison of Prius hybrid system to Tahoe hybrid system
Alan,
You said in technically correct language what I was trying to convey- that the GM version has the electric in parallel rather than independent electric motors on the wheels. I don't disagree with your assessment one bit.
And on my 06 Toyo/Lexus versions, both had electric motors in the front and the rear. I believe that the front drive only version was either not available or not bought by me on the Toyo/Lexus models in 06.
You said in technically correct language what I was trying to convey- that the GM version has the electric in parallel rather than independent electric motors on the wheels. I don't disagree with your assessment one bit.
And on my 06 Toyo/Lexus versions, both had electric motors in the front and the rear. I believe that the front drive only version was either not available or not bought by me on the Toyo/Lexus models in 06.
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