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Hybrids are the hot development in the automotive marketplace. They offer the chance to have better fuel economy while maintaining vehicle designs – especially size – that American motorists have come to expect. Certainly $4-plus per gallon gasoline (close to $5 for diesel) has made the hybrid much more attractive.

Many with SUVs and pickup trucks are feeling insecure about their vehicle choices right now. For them, the hybrid is just a dream since retrofitting is not that likely, although one entrepreneur in Florida is converting luxury sports cars (e.g. Porsche) to pure electric from internal combustion engines. His system is a plug-in, battery-powered electric motor conversion which can deliver performance (119 mph) at a dollar cost in the low-to mid-five figures!

Just how does the hybrid do it and what level of fuel economy improvements can we expect to see? I want to share some of the workings of the hybrid and what it means for engine oil, as well as other lubricants.


The system now being sold by General Motors, Toyota and others captures braking energy by powering a generator which stores the electricity created in batteries. The basic premise of this parallel hybrid is that we can capture some of the energy normally lost when braking or decelerating, and put it to use when accelerating. How much we gain depends, but it can be up to a 30 percent fuel economy improvement versus the engine-only operation. There are also emissions reductions of 10 percent to 20 percent due to the fact that the engine is not working as hard.

(Rather than exhaustively go through all of the configurations, I recommend that the reader go to under the heading of hybrid vehicle drives. There are diagrams of all the proposed and commercial hybrid systems in this article.)

One of the advantages of the electric hybrid design is the relatively small space taken up by the electrical apparatus. Currently (no pun intended) plug-in hybrids are being developed to take advantage of your home electrical system to fully charge the battery. This will allow you to start up and drive for several minutes without even starting the engine. The system is quiet, especially when operating on electricity. Thats an additional advantage for the neighbors of those early-rising commuters.

One concern is that the batteries are expensive. And, like most rechargeable batteries, they have a finite life. Estimates range from four to six years and the cost to replace the battery is currently more than $2,000. Just about the time you think you might want to trade the vehicle in, the battery will need to be replaced. The question becomes, do you trade it and take a hit on battery cost, or do you replace it first and take the hit that way? The outcome is the same: You will pay.

One ingenious proposal is for hybrid drivers to lease the battery. The purchase decision would then be battery lease cost versus fuel prices and mpg. Another benefit is that lithium-ion batteries, which are proposed for use in plug-in electric vehicles, can be recycled for other uses.

Hydraulics Promise

But wait, there is more! Not only is there an electric hybrid, there is also a hydraulic hybrid. This vehicle operates on the same concept of capturing energy that would otherwise be lost and using it for acceleration. The difference is that it uses a hydraulic system rather than a battery to capture the energy. The HLA system is one such system, developed by Eaton and being employed by Ford in some 2009 models.

This system uses a hydrostatic drive to capture the energy from deceleration and stores it in an accumulator which pressurizes a gas (in this system, nitrogen). When the vehicle accelerates, the gas depressurizes to help drive the hydrostatic motor. (See the diagram to the left.)

Hydraulic hybrids have been tested by the EPA in UPS delivery trucks and show improvements in fuel economy of up to 70 percent with emissions reductions of 40 percent! These results are admirable in both respects.

One benefit of the hydraulic hybrid system is there is no battery that must be replaced. Another is that the hardware is currently available and doesnt represent significant stretches in technology.

On the downside, there is the issue of compactness. The hydraulic/hydrostatic components do take up more room. That would suggest that passenger cars might not be suitable for this type of hybrid configuration. However, large SUVs, pickup trucks and commercial vehicles seem to be logical candidates. Even more attractive is the concept of a hydraulic hybrid in the construction and agricultural markets, where efficiency and fuel economy are extremely important.


By now, you are wondering, When do we get to the oil part? The question of engine lubrication in hybrids is actually not a surprise at all. The combustion engine side of the hybrid still needs to be lubricated. For that, the OEMs are recommending current ILSAC GF-4 formulations. They point out that every bit of fuel economy is important, and that the engine design is the same as those vehicles operating on gasoline only. For larger vehicles using a diesel engine, API CJ-4 is the current choice. These engines have no unique technical needs, so the latest recommendations are correct.

One could argue that the fuel-burning engines in hybrid systems might not be as severely stressed, since they are getting a boost from the electric or hydraulic portion of the hybrid system. However, the passenger car lubricant system (under ILSAC or API) is really not designed to go backwards to a less-severe standard. Rather, it is conceivable that in the future new categories might not be coming quite as fast. There is still going to be a significant portion of vehicles (both commercial and personal) that will not be hybrids and will need to be lubricated with the most advanced engine oils. That says no change in engine oil category development.

One interesting additional feature of the hydraulic hybrid is the fluid to be used in the hydraulic system. It might not be necessary to use as sophisticated an oil as automatic transmission fluid (ATF). Hydrostatic drives that are now being used in commercial equipment use hydraulic fluids which are not as highly formulated, since hydrostatics dont have clutch packs requiring friction modification as do automatic transmissions.

The concept of maximum efficiency hydraulic fluids (MEHF) has been proposed, and a tentative performance description published. Data from RohMax Oil Additives, an additive supplier that has been a proponent of this concept, have shown that fuel economy gains in excess of 10 percent can be achieved using MEHF products versus conventional hydraulic fluids. This result came from a field test in a tracked hydraulic excavator.

Of course this is only one test, and the operating conditions of other applications could result in a different level of performance and fuel savings. The idea is pretty good though. If you can capture mechanical efficiency by the proper formulation of a hydraulic fluid, why not use it? Certainly, ATF might give the same or better results and would be available in any dealers service area. However, ATF could also be overkill.

The bottom line

With gasoline costing more than $4 per gallon and diesel at close to $5, every bit of fuel economy that can be squeezed from a vehicles powerplant/lubrication system is highly desirable. Engine oils that deliver fuel economy – however little – and hydraulic fluids that provide additional mechanical efficiency are promising areas of concentration for the oil and additive industries.

Through continued development, we might be able to give the OEMs a few percent in improvements. That translates to reduced dollars spent at the gas pump (although each of us might not be able to easily detect the change in our own vehicles). It also gives the OEMs a cushion in their ongoing struggle to meet federally mandated fuel economy limits.

In the longer run, it is obvious that all-electric vehicles and fuel cell vehicles will mean a significant loss of engine oil demand. The time is coming when Do-It-Yourself and Do-It-For-Me will mean changing wires and cleaning connections – not draining and disposing of engine oil.

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