• Mar 5th 2009 at 11:51AM
  • 13
Over the past decade, if there is one word that has become synonymous with green motoring it is hybrid. Ever since Toyota launched the first modern commercially viable hybrid with the original Prius (above) in 1997, over one million of them have hit the roads. Of course, as is so often the case, this overnight sensation was anything but. In fact, the technology was nearly a century in the making.

The first known hybrid was developed by the original Ferdinand Porsche back around the beginning of the twentieth century. The hybrid, as we mostly know it today, was actually developed and patented by engineers at TRW in the late 1960s. While most people have by now heard of hybrids and know that they can improve efficiency, few understand how they work. Since the debut of the Prius, most automakers have been working on hybrids and have developed their own variations in an attempt to reduce the cost and/or improve the efficiency. Let's start (after the jump) with a look the power-split parallel hybrid as popularized by Toyota and Ford.

In the simplest terms, a hybrid drivetrain is one that uses two or more power sources for propulsion. Since the birth of the automobile in 1886, cars have generally used a single power source. The vast majority have been internal combustion engines running on either gasoline or diesel fuel with power being transferred through some kind of transmission. The modern hybrid car has added some sort of electric drive into the mix, along with an electro-chemical battery for energy storage. There are, of course, other combinations, some of which use hydraulic drives instead of electrical ones or hydrogen fuel cells instead of internal combustion engines.

Hybrid vehicles like those from Toyota, Ford, and GM's Two-modes can be described as power-split strong parallel hybrids. Strong hybrids are generally considered those that can be propelled by either the engine, electric motor or a combination of both. Further differentiating these vehicles from some other strong hybrids that are coming to market in the next few years is the power-split device.

These vehicles all use transmissions with planetary gear-sets that provide continuously variable ratio control. The electronically controlled variable ratio device is used to enable continuously variable blending of the drive torque from the engine and motor/generator. This allows for supplementing or replacing output torque from the engine seamlessly with electric motor torque.

The engines in hybrids are typically configured to operate on an Atkinson cycle. This differs from the traditional Otto cycle in that the intake valve closes late after the piston starts to go back up on the compression stroke. The result is that the power stroke becomes longer than compression stroke, resulting in increased efficiency. The problem is reduced torque output. The immediate and continuous torque output of the hybrid's electric motor can be applied at any time to supplement the lost torque of the Atkinson engine without reducing efficiency.

When the driver presses the accelerator and the battery has energy available, the electric motor can provide extra power without opening up the engine's throttle and burning more fuel. Or, when cruising at light load conditions, the engine can be slowed down or even shutoff with the motor providing the torque necessary to keep the vehicle moving. Similarly, the motor can accelerate the vehicle without the engine running at all, although this is usually only possible at very slow rates.

Electric motors have some very cool characteristics such as the ability to produce torque from zero rpm. More important is their generating capability. If electric current is applied to a motor, the motor will turn. If you mechanically drive a motor it becomes a generator and produces current. When the driver lifts off the accelerator, the wheels drive the motor which then generates electricity to charge the battery.

All current production hybrids use nickel metal hydride batteries for energy storage. Most manufacturers are currently testing lithium ion batteries which have greater energy and power density but are also a lot more expensive. There also concerns with the long-term durability and safety of the lithium batteries but these are rapidly being overcome and lithium batteries will start appearing in mass-produced hybrids in 2009. Mercedes-Benz hopes that its S400 BlueHybrid will be the first hybrid to market with li-ion batteries.

Click the S400 for a high res gallery

The true strength of the hybrid-electric power concept is the ability to use a smaller engine and provide torque on demand and then recover some of the kinetic energy that is normally converted to heat by the brakes. Because current hybrids have limited battery capacity (typically no more than 1.5-2kWh) they provide the greatest benefit when the driving cycle includes a lot of braking and accelerating (something not everyone understands). When a hybrid car is cruising at steady state on the highway, the ability of the hybrid system to provide assistance is limited by the battery capacity and limited regenerative braking.

Even in these conditions, however, a hybrid can be useful to some degree. The two-mode hybrid system used by General Motors on its full-size SUVs and pickup trucks also has a displacement on demand system on its V8 engine that is also used on non-hybrid versions. At light loads, four of the eight cylinders can be deactivated. The ability of the hybrid drive to provide extra drive torque when needed means that GM is able to keep the engine running on four cylinder mode more of the time. In situations where the non-hybrid would re-activate all cylinders such as passing or climbing a grade the hybrid can simply use the motor instead.

In a future Greenlings post, we'll look at non-power-split hybrids in both mild and strong flavors.

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    • 1 Second Ago
      • 6 Years Ago

      In the US, yes it was Honda to be the first in 2000. Toyota came out with the Prius in Japan back in 1997 beating the Insight.
      • 6 Years Ago
      Has anyone considered Volt (or other serial hybrid) owners who don't live in houses and therefore can't plug them in on most days? Many people park on the street or live in apartment buildings where the parking lots have no electrical jacks. I would think that's more than 30% of America right there. What will be the fuel economy for a Volt that's never plugged in? Will it better or worse than, say, a Toyota Prius?
        • 6 Years Ago
        I've heard it reported that in "Charge Sustaining Mode" [i.e., when the time-averaged energy content of the battery is steady] the Volt gets about 50mpg. This seems like a reasonable number, since it is very similar to the Prius in size and weight, and the two car at that point are operating in very similar modes.

        That being said, I suspect that the EPAs models used for that prediction are not well calibrated (never having had a series hybrid against which to calibrate) so I'd use that as a rough guess and wait and see what real people get.
      • 6 Years Ago
      The discussion on what constitutes a hybrid sure is tough, BUT

      A fuel cell vehicle is most definitely NOT a hybrid, by any definition. They're electric vehicles, range-extended EVs if there's a plug-in capacity (and frankly, not having that is idiotic because fuel cell cars require batteries for load balancing anyway)
        • 6 Years Ago
        Hold on here

        It's a pure EV if it does not plug in, and it's a RE-EV if it does?

        So then the plug is the range extender? (The plug is the only thing that's different)

        No, that's not right. The FC is the range extender if it plugs in. What is the FC if it doesn't plug in? It's the power source. Right? And the energy source is H2 (or whatever fuels the FC).

        So in what way is it NOT a series hybrid?

      • 6 Years Ago
      "In the simplest terms, a hybrid drivetrain is one that uses two or more power sources for propulsion."

      Which is why so called "hybrids" that can't be plugged in are NOT hybrids. The electrical energy in the battery comes from the kinetic energy of the car, which comes from the mechanical energy of the engine, which comes from the energy of gasoline only, not from "two or more power sources."

      Either plug it in, or you don't have a hybrid.
        • 6 Years Ago
        Dan, I think your interpretation is a bit restrictive. Would it not be logical to extend your reasoning? Would you say that since gasoline and coal are both fossil fuels, energy captured from the sun millions of years ago, that coal electricity and gasoline only count as once source?

        The hybridization refers to only the final step -mechanical power, the stuff that accelerates you- some of which comes from an electric motor, and some of which comes from a gas motor.

        ... or were you just being a troll?
        • 6 Years Ago
        I wasn't being a troll. If that is the argument for what a hybrid is, then all cars are hybrids because they use gravity as a power source to assist their propulsion down a hill. Today's version of a hybrid is just a way of improving the gas mileage of the vehicle. I'm all for that, and I love that vehicle manufacturers are learning so much about electric drive systems, because they're going to need that knowledge to move toward the goal of emission-free vehicles. I just don't think an article about what a hybrid actually is should have defined it the way that they did.

        And I don't believe in the usage of coal-fired power plants. Using solar, wind, hydro, geothermal and even nuclear power is sufficient to meeting our present and future energy needs.

      • 6 Years Ago
      That seems like a rather narrow interpretation of the word Hybrid. So what do you proposed we call all the existing Hybrids? What about a Volt that is never plugged in, but instead gets recharged by the gas motor? Is that no longer a hybrid?
        • 6 Years Ago
        Why would anyone drive a Volt if they're not going to plug it in?

        The Volt is supposed to be driven on grid electricity primarily, so I'd go with the "range extended electric vehicle" designation rather than hybrid.
      • 6 Years Ago
      Wasn't honda the first to launch "the first modern commercially viable" hybrid with the Honda Insight?
      • 6 Years Ago
      Trouble with hybrids is that they are still petroleum dependent.

      Trouble with rechargeables is that they're - rechargeable: they rely on an external energy source.

      "Gooble" for the phrase "Johnson magnatron motor" to read about a self-contained, self-generating power plant invented almost 30 years ago which should have replaced gasoline engines - and diesel engines, in large measure - by now, but was quashed by the US DOE.
      • 6 Years Ago
      The "power split" hybrids have characteristics common to both series and parallel hybrids. Some of the power from the IC engine is transferred mechanically to the wheel like a parallel hybrid, and some of the power goes to a motor/generator that converts it into electrical power that can be used by the 2nd motor/generator to power the wheels like a series hybrid. This gives "power split" hybrids the best characteristics of both parallel and series hybrids, and avoids most of the downsides of each.
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