Hybrids are hybrids -- right? Well, no. I got a phone call after last week's article asking me which was better, the Honda Civic Hybrid and the Toyota Prius. The correct answer is that they are different. "But," was the reply, "they're both hybrids, aren't they?" Yes, they both are hybrids, but, in fact, the designs are quite different, and they operate differently. So which is best? That is a decision best left to the consumer.
It looks like this is going to be another technical article, and it is.
What is the difference between the Civic Hybrid and the Prius? Both have gasoline engines and electric motors and batteries. Right? Yes, but they are mechanically connected differently in the two cars.
The Civic Hybrid is a "mild" hybrid, which means that the engine and motor are on the same shaft and therefore must operate together all the time. Honda calls this "integrated motor assist", meaning that the electric motor is there to "help" the engine deliver extra power when it is needed. But it also means that the car can never operate on electric power alone. The word "never", in this case isn't a very long time, because Honda engineers have figured out how to shut the engine off, though everything still rotates inside the engine, so the car can run only on electric motor power. When the electric power isn't needed, the motor turns into a generator to charge the batteries, which it also does during braking (regenerative braking).
The Prius, on the other hand, is a "full" hybrid (or "parallel" hybrid). That means that the engine and the two electric motors are on separate shafts and can operate independently from each other. The engine can be completely shut off and the car can be run on electric motor power at any time that the computer thinks it is appropriate. This is why the Prius has a higher EPA city rating than EPA highway rating. Since the car starts with a full battery charge when it is rated, it can run a lot on the motor alone and not use any gasoline.
Given that this causes confusion in the marketplace, the battery industry has stepped in to help the consumer understand what kind of hybrid the car sitting in front of them is. They've established different categories of hybrids. I'll let you decide if this makes anything simpler for the consumer. Here are the five categories:
Micro hybrid -- The mildest of hybrids allows engine stop-start and power for idle loads only, along with regenerative braking and alternator support for the regenerated energy. The traditional lead-acid battery is the top energy-storage solution (though with advanced design). Nickel metal-hydride (NiMH) batteries are less attractive due to poor power characteristics at low temperatures. Ultracapacitors (UCAPs, favored by Honda) and lithium-ion (Li-ion) batteries look very good in this application, but are costly.
Mild hybrid -- This is one step beyond the micro hybrid and has added regenerative capabilities and launch assist for up to three seconds. For this "low cost" hybrid for city driving, lead-acid technology could be used, but only if technology improves. NiMH again has low temperature issues, while Li-ion seems to be an attractive long-term solution. A UCAP looks attractive with lead-acid batteries, but is costly.
Moderate hybrid -- This type of hybrid can typically provide a longer power assist (three to ten seconds). Batteries see moderately high power cycling, with a typical mid-size car's electrical/electronic system. NiMH is the current battery of choice, but other solutions show promise. More powerful Li-ion technology could provide energy if its power fade is reduced. UCAPs could be competitive if assist before charging is below five seconds. If assist is needed for five to ten seconds, the combined pulse of a UCAP and lead-acid battery could be attractive. If needs stretch beyond ten seconds, UCAPs coupled with an advanced battery, could be competitive.
Strong hybrid -- This technology is used if acceleration assist exceeds eight seconds, and it offers electric-only drive at low speeds. It also has a high power span, ranging from 30 to 70% state of charge. NiMH is the current solution, but Li-ion is starting to compete, at least in development projects, but cost, life, and abuse tolerance are still concerns.
Plug-in hybrid -- The potentially most fuel-efficient hybrid technology allows for additional electrical charging at home to allow a greater range of electric-only vehicle propulsion, but it requires more on-board battery storage capabilities and systems would see significant power cycling. A possible bridge to fuel-cell and battery-only electric vehicles, it is currently attractive for short-distance vehicle usage, but this duty cycle will affect battery choice. Lead-acid would be good for very short distances (and cheap), but NiMH is the short-term choice due to proven power throughput. Li-ion technology is attractive, but safety and life are concerns due to the deeper state-of-charge drain.
I'm sure glad that these people have made this so very clear to the consumer! I'm not sure why I need to know all of this, but maybe it really is intended only for engineers who design those vehicles.
Back to the real world of production vehicles, there is some more news about the GM-DC-BMW consortium hybrid technology. A prototype transmission, dual-motor system has been shown. It is intended for trucks, rather than cars. It will appear in production 2008 Chevrolet Tahoe, Dodge Durango, and GMC Yukon SUVs. The actual appearance will likely be mid-2007, so this isn't all that far off. The management decision was to improve fuel consumption where it was needed most, i.e. big trucky SUVs. The passenger car applications will follow.
As I said last week, this system operates even more efficiently than Toyota's current design. Toyota's hybrid design hasn't really changed from the original Prius. They have done a lot of refining of components, but the basic design and mechanic assemblies have remained the same in all the models.
In the GM-DC-BMW system, the gearing creates a mechanical system that is 20% more efficient at higher speeds when the vehicle is operated on engine power under sustained load. One-mode hybrids do a very good job in the city, but are somewhat challenged on the highway because they depend on maintaining an electrical power path to transmit most of the system's power. This is because the "one-mode" drives, such as used by Toyota and Ford (and licensed by Nissan), use a single planetary gearset with the system to split input torque for driving the wheels or charging the battery. This design works well in small to mid-sized vehicles carrying light loads (look at the tow rating of the Ford Escape hybrid or Toyota Highlander Hybrid). For larger vehicles with greater load carrying and towing requirements, the electric power flow needed for sustained-load operation would require bigger, heavier electric motors.
The two modes of this system allow mode 1 to propel the vehicle from a start to second gear. Mode 2 goes from second gear to overdrive 4th. Shifts between gears and the two modes are much like the driving feel of an automatic transmission.
Additional fuel economy will come from cylinder deactivation in the pushrod V-8s in Dodge and GM/Chevrolet trucks. With all those variables, the computer control will be like playing a symphony orchestra.
This transmission will be built in GM's Baltimore transmission plant, which has a capacity of 360,000 units per year.
The only "new" part of Toyota's hybrid system is seen in their L110 transmission used in the GS and LS rear-drive hybrids. It has an added two-speed reduction gear set. According to Toyota, this allows additional torque multiplication and reduced motor size.
Okay, who have we left out in the hybrid world? We have covered Ford, GM and Chrysler in the U.S. With Mazda part of Ford, and Nissan licensing technology from Toyota, we've got Japan covered. In Germany, Volkswagen hasn't been mentioned. Not to be left out, VW has partnered with Continental and ZF to produce hybrid drive systems. With nothing more than hand-waving, it seems rather ambitious of them to announce that the consortium will make it possible to have full hybrid systems in production in 2007. This group is worth watching because it seems all the good patents are already taken. Where will the technology come from?
No, I didn't leave Porsche out in Germany. They have announced that they will license technology from Toyota to build hybrid Cayennes. There will be no hybrid 911, Cayman, or Boxster models.
That's probably more than you ever wanted to know about hybrids. It looks like there clearly are hybrids from every manufacturer you can think of in our future. I didn't mention the Koreans, but I'm sure they are working on hybrids too.
