Can anyone explain to me the differences between the hybrid tecnologies implemented in Toyotas (HSD) and Honda (IMA) ..

(may be a link to a website or to another thread where the differnces are esxplained ..)

Also, what is the definition of a 'mild' and a 'true' hybrid .. and what are Prius and HCH considered?

Thanks and cheers!

IMA is simple and easy to understand. Honda places a single fairly flat motor in line with the engine. This motor can also be used as a generator eliminating the need for an alternator. The IMA motor normally starts the car but the car does have a seperate 12 v battery and 12 v starter in case the big battery fails. The IMA motor provides assist when accelerating or going up steep hills and regenerates the battery when decelerating or going down hill. Some call IMA "mild". The original IMA could not power the car in electric only mode but I believe the newest version can.

The Toyota system is much more involved and includes 2 motor generators. Just like IMA, HSD provides assist when needed and regenerates the battery during decelerations and downhills. The technical details involve far more than I'd want to type in a day. The heart of HSD is the Split Power Device that combines the engine an the motors in such a way as to provide a CVT like transmission. HSD is nothing short of fantastic and it borders on magic. Some call the Toyota system "full". To learn more click here:

http://www.cleangreencar.co.nz/page/...technical-info
http://www.ecrostech.com/prius/origi...plitDevice.htm
http://www.ecrostech.com/prius/original/PriusFrames.htm

While the Toyota sysem is fantastic and complicated it really does not do all that much better than Honda's IMA if you check the database. All the versions of the Civics and Prius are within a couple mpg of each other.

http://www.greenhybrid.com/compare/mileage/

The Prius edges out the CVT based Civics but the manual tranny Civic (like mine) gets the best mileage of all by a tiny margin. One big IMA advantage is that the main pack can die and the car can still start and run and reverse. HSD requires the main battery to start and to reverse (HSD lacks a reverse gear and uses pure EV mode to reverse).

I can help with the HSD, Hybrid Synergy Drive. This is second generation of the transaxle in my Prius and simular to the Ford Escape hybrid transaxle.

In operation, the HSD drives just like an automatic. Computers handle operation of the engine and two motor generators to balance and pass power as needed. In some modes, power passes between the motor generators. The large traction battery provides or takes power to the motor generators as needed.

The front part consists of a computer controlled motor generator (MG1), about one third of the power of the engine that with the planetary gear works as continiously variable transmission. For example, in neutral, the car is stopped and the engine running and MG1 motor spins backwards under computer control. When put in "D", the computers apply power to MG1 to balance the engine torque and both pass power to the drive wheels.

The second, larger motor generator (MG2) has over half the power of the engine and is connected to the drive wheels and gears. Again under computer control, MG2 can move the car forward or reverse without the engine, electric vehicle (EV) mode. At speeds below 42 miles per hour, more noticable at slower speeds, the vehicle can silently slip into electric mode powered just by MG2 and the traction battery for over a mile.

Prius owners have run out of gas and driven short distances to gas stations in electric mode. In Europe and Japan, they come with an EV button for short trips, 1-2 miles. All Prius lack a reverse gear and and use MG2 to backup. In the morning, I turn on the car and the engine starts but as I back out of my driveway, the computers shutdown the engine until I'm in the street ready to drive forward. Then the computers spin up the engine and it powers me through the neighborhood.

The HSD vehicles have two batteries. The main traction battery, 200 VDC, provides power to and from the motor generators including starting and stopping the engine. The smaller, auxillary 12 VDC battery powers the control computers, lights and regular car accessories.

In summary, the IMA and HSD are marvels of computer technology that handle the engine, motor generator(s) and batteries so the cars work like a regular, automatic vehicle . . . except they don't burn much gas, have very low emissions and are powerfully quiet. In the case of the HSD, there is a limited range, electric only mode.

Bob Wilson

Operation Iraqi Oil Freedom:

Automatic, stock, project car.

My other 1500 cc car:

Automatic, stock, backup car.
Free speech, dialog and knowledge thrives without the poison of SPAM.

A couple of things I'd like to add:

Toyota's HSD really is a complete departure from traditional car designs. Honda's IMA is pretty much just turning your flywheel into a motor/generator and the rest of the car is perfectly normal.

HSD has two electric motors and a geartrain that boggles the mind, but when you add up all the parts, it's not significantly more complicated than an IMA system. It's got a great reliability record, so don't let its different-ness scare you.

HSD definitely whips IMA's butt in city driving. I can beat the Civic Hybrid's 51 highway rating, but I can't even get near the 49 city rating. (I'm lucky to get 34.)

There's a rumor that HSD's efficiency drops off at higher highway speeds due to the efficiency of the electric motors always being on, but it really doesn't appear to pan out to anything in the real world, at least not at U.S. speeds.

The dividing line between "mild" and "full" hybrids is whether the car can run in electric-only mode. Prius definitely can. HCH1 could not. HCH2 can, but really, it's just a gimmick. In EV mode, the HCH2 disconnects its valve rockers and shuts off fuel and spark, so the Internal Combustion Engine is still turning while the electric motor is running the car. It only happens for short periods, under a narrow set of circumstances (although it can happen at any speed). With the Prius' HSD, you can zip around the parking lot silently.

Would-be hypermiler

Thank you all for your inputs ... great replies ..

So basically, a "full" hybrid is a car which is able to run just on battery albeit for small distances ..

Do all the Toyota hybrids (Hylander and Prius) have HSD or does Hylander have some other techology inside? What does Ford Escape Hybrid have?

Any other known hybrid technologies known to exist?

Thanks again for your input!

Regards.

Highlander and Prius both have HSD drives. The Ford Escape is very similar. It's so similar, they had to license Toyota patents for the FEH.

GM is quite proud of their Belt Assisted hybrids in the Silverado and soon to be Saturn VUE green. These units turn off the engine at a stop and automaticly restart the engine when the foot comes off the brake pedal. So in stop and go traffic, they save the engine idling.

I don't know if they help on regenerative braking or power assist. In which case, they could perform somewhat like an IMA but with the electric motor on the other side of the crank shaft.

Rather than say anything more about BAS, I should stop here but in North Alabama, a bass is a type of fish.

Bob Wilson

Operation Iraqi Oil Freedom:

Automatic, stock, project car.

My other 1500 cc car:

Automatic, stock, backup car.
Free speech, dialog and knowledge thrives without the poison of SPAM.

Well, this was originally more significant on earlier versions of HSD, which were lower-geared overall, had less engine power, and had only one set of planetary gears. The newer models have multiple planetary gearsets to allow true shifting of the mechanical gear-ratio, and rely less on using the motor/generators to provide differing torques.

All the Toyota, and the Lexus Models (Rx 400, GS 450, etc. ) also run versions of HSD.

The do offer regenerative braking, and very slight assist (only a couple percent of total engine output), however, this is done to act more as a "smart" alternator, this braking is done to draw the electrical power used to power the headlights and accessories on the car, but instead of it being a constant load, they can "pulse" it to do heavier charging when the car is decelerating, or under a lighter load. (other hybrid systems do this too)

One difference about IMA that sets it apart from these smaller systems "mild" systems is that the motors represent a large enough percentage of total engine output that engineers can use smaller engines (less peak power) with more efficient valve timing (trading off low end torque and some power). These changes would be unreasonable in a standalone gasoline vehicle, but work well with the electric component aiding accelerations. This is also why many critics are wrong when they say hybrids don't help for steady highway driving -- those engines, made possible by electric boost, perform much more efficiently on the highway than a standard engine. The HSD system more than makes up for its greater geartrain losses at highway speed, with its more efficient atkinson cycle engine.

According to Saturn (Click "View Demo"), they do have assist and regenerative braking. But they don't have a mode where the electric motor is actually propelling the vehicle on its own, so they'd be a "mild" hybrid, at best.

Would-be hypermiler

I'm pretty sure the Silverado uses a 42volt FAS not BAS. If so, a FAS (Flywheel Alternator/Starter) is very similar to IMA except the GM version is much lower voltage...

From http://www.gm.com/company/gmability/...1_alt_hyb.html


See also: http://www.chevrolet.com/pop/silvera.../hybrid_en.jsp