Are All Hybrid Systems Created Equal?

There are two types of systems in the marketplace:

Parallel Hybrid System – The vehicle starts with the electric generator and uses the gas motor to assist on acceleration, help to maintain speed and recharge the batteries when needed.

Series Hybrid System – The vehicle starts with the gas motor which mantains speed and recharges the batteries and has the electric motor to assist on acceleration.

Both system have the generators recapturing energy and putting it back into the batteries when the vehicle is in motion.

The interesting thing about these two different system is how much difference there is in the fuel economy for city driving.

The Parallel Hybrid System, which is the choice of Toyota and Ford, offers the greatest improvement in city fuel economy, between 50% to 100%. (depending on comparison of the Prius, Lexus 400h, Highlander Hybrid and Ford Escape)

The Series Hybrid System, which is the choice of Honda, G.M. and other auto makers offers the least amont of improvement as for city fuel economy, between 15% to 50%.(depending on the comparison of Honda Civic, Honda Accord, GM Silverado & Sierra)

So if you want the best fuel economy in city driving look for the Parallel Hybrid System, for all hybrids are not created equally.

Andrew Grant is the world’s first hybrid taxi driver. He introduced his Prius taxi to the not-so-mean streets of Vancouver in 2000, and logged 200,000 miles in just 25 months. Andrew’s Prius was snatched by Toyota. The automaker wanted a chance to study the durability of the hybrid batteries and other components, which held up amazingly well. See this video for details. He’s now driving his third Prius. Andrew has taken a break from taxi-driving, and now works as a professional coach helping his clients achieve personal excellence in various fields of endeavor.

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  • Guest

    This is rubbish; a series hybrid transmits ALL its power electrically. You can’t buy one. There is no point to this article.

  • Guest

    Are you sure you have your facts correct? AFAIK, series hybrids are systems where the ICE drives a generator which in turn powers the electric motors in conjunction with the batteries. Parallel systems can be driven by either the ICE and/or the electric motors. None of the existing hybrids are series hybrids. The difference in fuel economy is due to differing implementations of parallel systems.

  • Guest

    agree on first 2 comments;
    B(u)y the way…
    Prius is a smart computer-driven
    series AND parallel drivetrain.

  • gottfried.staubach

    Quite right, there is NO true series hybrid vehicle available today. The Prius is a series/parallel hybrid, while the Civic Hybrid is a pure parallel hybrid.
    Both the Prius AND the Civic Hybrid start their combustion engines with an electric motor/generator.

    Seems the author hasn’t made himself familiar with hybrid concepts …

  • paul

    Sorry, Andy, but I’ll jump on you too – you blew it. True series hybrid cars were around over a century ago, but there aren’t any today.

    Check for a simple explanation of series versus parallel in the context of hybrid automobiles.

    When I was trying to decide a couple of years ago whether to buy a Prius or a Honda Civic Hybrid, I chose the Honda because it was mechanically simpler and got better highway versus city mileage. So far, I was right: My 2003 HCH has 85,000 miles on it and runs like a fine watch – including an 80-MPH roundtrip run from the SF Bay are to San Diego and back a couple of weeks ago at 40+ MPG.

  • Guest

    My information is taken directly from the Toyota University Prius New Car features maual Copyright 2001.

    In the technical description page 22.

    In a series hybrid system, the engine runs a generator, and the electric motor to drive the wheeels. This type of vehicle can be described as an electric car that is equipped with an engine-driven generator.

    Equipped with a low- output engine, the engine is operated at a pratically constant speed in its most effective range, inorder to efficiently rechage the battery while the vehicle is in motion.

    Parallel Hybrid System

    This system uses both the engine and electic motor to directly drive the wheels is called the parallel hybrid system. In addition to supplementing the motive force of the engine, the electric motor in this system can also serve as a generator to recharge the battery while the vehicle is in motion.

    These to points are written exactly as they are in the manual.

    The Honda system is unable to start from a stand still on electric only and can run on electric only under certian conditions for brief periods, where as the Toyota system can start and maintain its speed for sustained periods of time.

    The reason the Prius gets exceptional city fuel economy is due to the fact of being able to run on electric only from a dead stop and the Honda cannot.

    So if there is anything not clarified yet concerning about the information about the differences concerning the two different systems I hope this has cleared it up. Everything I talk about is based from the two Toyota University manuals i have for the Classic Prius and the current model.

  • Guest

    well obviously folks disagree with the technical specifics. But it is a common view that Prius is best for city driving while Civic Hybrids are best choice for highway & rural driving… (and Insight gets the best mpg of anything, if you don’t mind not having a backseat, but I digress). For suburban driving, it’s probably a tossup between the two, with minor differences depending on what your typical sustained speeds are, and if you’re on flatland vs hilly.

  • Richard.Selle

    No one seems to say that the 2006 Civic hybrid can start and run on the electric motor like the Prius.

  • Guest

    I don’t want to harp on this post but what you paraphrased in your blog is not what you quoted from the manual. This is a technicality but in a true series hybrid motive power would only come from the electric motor.

  • Guest

    It seems to me that the given definitions of parallel and series are not very good ones. Definitions that I would prefer are:

    Series: the gasoline and electric motors always turn together in lock-step. Honda is an example, where the electric motor is in the bell housing between the motor and the transmission and is directly coupled to the crankshaft, so that the electric motor always turns at the same speed as the gasoline engine.

    Parallel: any other arrangement, where “the” electric motor and gasoline engine can rotate independently. Prius is in this catetory.

    The “parallel” systems are really quite different, and raise many questions which don’t arise in the “series” systems. If the electric motor and gasoline engine can turn independently, then new elements (clutches, gears, or something) are required to “hook them together” and to control how power is transmitted between each of these elements (the gas engine and the eletric motor) and the wheels. Toyota calls this arrangement “Synergy Drive” – Ford salesmen that I have talked to seem not have any understanding of their product and cannot describe it coherently.

    In the Prius, the system is really more complex that usually described. There is a “three shaft device” (the logical equivalent of a differential) where the total work input to the three shafts is always zero (e.g., if power is being INPUTTED to one shaft and one shaft is being held still, the third shaft will be OUTPUTTING power equal to inputted power on the first shart).

    In the case of the Prius, the “three shaft device” (implemented as a planetary gear set) has the gasoline engine connected to one shaft (the planet carrier), the wheels (via fixed gearing) to the second shaft (the ring gear), and has a SECOND electric motor/generator connected to the third shaft (the sun gear). (The “first” electric motor on a Prius is connected to the wheels, via fixed gearing.) For some reason, Toyota rarely mentions the existence of the second motor/generator. But the second motor generator does many things – for example, it applies a “load” (or completely stops) the third shaft as a mechanism to force the “three shaft device” to deliver power from gas engine to the wheels (this is similar to the problem as with a conventional differential – when one wheel of a car with a differential is “off the ground,” gunning the engine runs that wheel at double speed, but no energy is delievered to the second wheel — to deliver energy to the second wheel, the “free” wheel must be contrained from turning freely).

    In fact, the Prius has a continuum of modes where the second motor generator either receives or sends “mechanical power” from/to the “three shaft device.” In conjunction with this, the second motor generator is outputting or receiving electrical energy, either to/from the NiMH battery and/or to/from the first motor. For example, to get the equivalent of a lower gear (e.g., let the gas engine run faster and get torgue multiplication), the second motor/generator acts as a generator, lets its shaft spin (which allows the gas engine to turn faster and hence deliver more power), and then delivers the resulting generated electrical energy to the first electrical motor to increase torgue to the wheels. This kind of activity is what is Toyota calls the ‘eCVT’ (Continuously Variable Transmission) (apparently because that is the kind of terminology that buyers are use to, but I don’t think it is a tranmission at all).

    The two system deliver comparable results in terms of fuel economy, but they are extremely different in terms of “how they work.” There are arguments for both, especially in the areas of product cost and failure modes.

  • Guest

    Thank-you Wally for your explination, the way you explain it is very clear…I should have went into explaining about Mg1 + Mg2 and elaborated more so on the other areas involved that make the difference in the systems.

    Thank-you again Wally

  • Guest

    The only problem with Andy’s description is that it’s backwards. A series hybrid requires the engine’s power to be transmitted through the traction motor; a parallel hybrid has a mechanical connection between the engine and wheels which allow torque to be transmitted directly. The Honda hybrids are all parallel, the Prius has a split power pathway so it is described as series-parallel, some of the hybrid transit buses are series hybrids as are the Green Goat hybrid switch locomotives.

  • Guest

    Please correct me if I’m wrong, but my understanding was that series hybrids are similar, though not identical, to a diesel-electric locomotive drivetrain…… an ICE moves a generator, whose electricity powers an electric motor that moves the wheels….the key here is that the ICE’s torque NEVER touches the motive wheels in a MECHANICAL fashion.

    Now, before I get flamed, I know a locomotive is not a hybrid, since it won’t move if the ICE is not operational. I am only pointing at the similarities of a series hybrid drivetrain and a diesel-electric locomotive.

  • david407

    All of this information sounds great, but another consideration for comparisons should be the warranties.

  • Guest

    You’re correct, Fernando, but there actually are series-hybrid locomotives. Google for “Green Goat” or take a gander at (but be quick about it while it’s still on the main page).

  • Guest

    One point I want made clear that this was a vehicle that was being used as a taxi not a private vehicle….if you were to also take in consideration that the vehicle is on the road 22-24 hours a day 7 days a week and was never built to be used as a taxi. I think if you talked to other taxi owners around the world about the amount of money they would spend in parts and labour in the same distance driven as on this Prius, you would find that they are spending more money and down time then those that own Prius’s as taxis….in all fairness if you were to make a comparison should it not be with a Toyota truck? One of the reasons I love Toyota is that when you replace a part outside the warranty period you recieve a lifetime parts and labour for no charge replacement if it needs to be replaced again…that includes taxi’s.

  • smtowntxguy

    well andrew you made a believer out of me i’ve been a cab driver in san antonio, texas for 5 years now and i will have my toyota prius online in san antonio by 15 nov…….it took a few months and a lot of talking with the city council to allow me to do this but i’m looking forward to it and thank you for all the use information you have put out there with this car it helped with convincing the city of san antonio to get this done ….once again thanks….

  • Guest

    Glad I could be of help in getting more hybrids on the road…especially aa taxi’s…they’re great for the environment and excellent on the bottom line…

  • hybridtraining

    “My information is taken directly from the Toyota University Prius New Car features maual Copyright 2001.”

    Now we know why there are fact checkers. This is a perfect example of the dangers of the Internet: people copy material they don’t understand from a trusted source and then present it as fact. I have the 2001 Toyota University documents that Mr. Grant quoted. THEY ARE WRONG. Don’t believe me? Keep reading…

    The definitions of series and parallel hybrids were settled decades ago. Toyota made the mistake of calling the Prius a parallel hybrid when they first launched it in North America. They never made that mistake again. Here’s a quote from a document that Toyota released in 2004 on its THS-II system:

    3 types of Hybrid Systems

    The following three major types of hybrid
    systems are being used in the hybrid vehicles
    currently on the market:


    The engine drives a generator, and an electric
    motor uses this generated electricity to drive the
    wheels. This is called a series hybrid system
    because the power flows to the wheels in series,
    i.e., the engine power and the motor power are in
    series. A series hybrid system can run a small-
    output engine in the efficient operating region
    relatively steadily, generate and supply electricity
    to the electric motor and efficiently charge the
    battery. It has two motors—a generator (which has
    the same structure as an electric motor) and an
    electric motor. This system is being used in the
    Coaster Hybrid.


    In a parallel hybrid system, both the engine
    and the electric motor drive the wheels, and the
    drive power from these two sources can be utilized
    according to the prevailing conditions.This is called
    a parallel hybrid system because the power flows
    to the wheels in parallel. In this system, the battery
    is charged by switching the electric motor to act as
    a generator, and the electricity from the battery is
    used to drive the wheels. Although it has a simple
    structure, the parallel hybrid system cannot drive
    the wheels from the electric motor while
    simultaneously charging the battery since the
    system has only one motor.


    This system combines the series hybrid
    system with the parallel hybrid system in order to
    maximize the benefits of both systems. It has two
    motors, and depending on the driving conditions,
    uses only the electric motor or the driving power
    from both the electric motor and the engine, in order
    to achieve the highest efficiency level. Furthermore,
    when necessary, the system drives the wheels while
    simultaneously generating electricity using a
    generator. This is the system used in the Prius and
    the Estima Hybrid.

    Now double-check it against other sources. A quick check of the Bosch Automotive Handbook, to give just one example, will confirm this.

    Please, please take down this webpage, or replace it with another one. I’ll even write it if you want. I teach automotive technicians about hybrid technology, and I don’t want to spend my teaching time undoing myths.

    For an example of someone else who got it wrong, see

  • smit

    parallel are better in my opinion…since they are better at fuel..


  • security831

    What about a differntial motor generator with two rotors and one stator. It can be used series or parallell

  • Guest

    Why do they make two hybrid systems when they basically do the same thing and they still use gas to maintain speed charge batteries and help accelerat.

  • Guest

    The reason there is more than one type of hybrid system is that the auto makers are creating systems that serve particular needs. Example General Motors have hybrid systems on their trucks which only give a 10 – 20% improvement in fuel economy, yet the main target market are those that need a mobile power source they can plug into while the truck is stationary. As far as Toyota and Honda are concerned they have different systems in that the Toyota system is able to start on electric only and maintain speeds of 35 mph for up to 5 min depending on the load and road conditions, where as the Honda system starts always on gas but can go for brief periods on electric only at speeds between 30 – 35 mph.

  • hybridtraining

    Andrew, please stop. You’ve been told by half a dozen people responding to this column alone that you got almost everything wrong. I don’t have the energy to go through the mistakes you made in your most recent post (March 22). I’m sure you mean well, but if you’re going to try and explain how these cars work, please take the time to learn how these cars work. Spreading misinformation is inexcusable when accurate information is so readily available. Buy a book.

  • Guest

    Jack, thank-you for your comments. I have acquired my information from the training manuals provided by Toyota Canada and other manufactures news releases. Concerning the posting on March 22, I explained how other auto makers are applying the hybrid technology in different types of vehicles. The point of this particular posting was to talk about different types of hybrid systems and their benefits, not to go into detail of the exact workings of the particular systems. If you think what I have been posting has been almost everything wrong I would be happy to stop submitting any future articles and allow you to step up and take over my blog. I have never intended to spread misinformation in any way shape or form….my intentions are to share my experiences and data that I have acquired from having 3 Toyota Prius’s as taxi’s since November 2000 which have in total to date accumilated 868,000 kms (approx. 542,000 miles),to help people get an overview of how they perform in those type of conditions and pass on any tips on how to maximize their fuel economy, service reliability and performance of the vehicle. Nothing more and nothing less.

  • amtoro

    There has been a few true series-hybrids developed by OEM’s, almost none lived to see the day light; look back 10 years at Daewoo in Korea, they built an hybrid Nubira that was powered solely by an electric motor and had a small (Daewoo Tico’s 800c.c.) gasoline engine under the trunk floor that kicked in only to replenish the batteries.