Electric motors in hybrids and EVs do more than just save gas; they have incredible potential for enhanced performance and safety. In fact, many hybrids have all-wheel drive systems that are better than what you would find in a gasoline car.
How does a Traditional All-Wheel Drive System work?
There are a number of ways all four wheels are motivated in different gasoline-powered, all-wheel drive vehicles. For example, in full-time all-wheel drive systems, power from the engine is sent to all four wheels constantly. It gets the job done, ensuring you have wheels turning, no matter what traction level you have, but this setup is inefficient in terms of fuel usage. In some cases, all-wheel drive systems can shuffle power to either axle as needed.
To combat unnecessary fuel usage and parasitic losses, some automakers offer cars with part-time all-wheel drive. These work by sending power to all four wheels once slippage is detected. Often called a slip-and-grip setup, these also have drawbacks, namely they aren’t very good for performance and wait to act until you are starting to slip.
How do Hybrid All-Wheel Drive Systems Work?
With the help of electric motors, all-wheel drive can be less compromised. In hybrid cars like the Lexus RX 450h, the electric motors augment the gasoline engine to deliver more power and help keep fuel consumption down.
In the RX450h AWD, an electric motor is paired to each of the axles. Like a part-time AWD system, the car can power additional wheels when grip is needed. In the Lexus RX450h’s case, the electric motor that operates the rear wheels only activates when starting from a stop for a stronger launch, during hard acceleration for more passing ability, sharp turning for more grip and if the front wheels slip for more traction.
This system is reactive like a traditional slip-and-grip system, but there’s one very important difference important part: electric motors are extremely responsive and offer instant torque.
Even if it’s not an all-wheel drive vehicle, the tiny Spark EV puts out 400 lb-ft of torque, blasting from a stop in a very satisfying fashion. The story is the same in the Tesla Model S P85 with 443 lb-ft of tire smoking torque, available instantly. An all-wheel drive version of the Model S will hit production in 2015 when its platform-sharing crossover sibling, the Model X, arrive in 2015.
But back to all-wheel drive hybrids, one final thought is that these electric all-wheel drive systems don’t have to be split between four wheels like a traditional all-wheel drive setup.
Hybrid AWD Gaining Traction (in unusual places)
This hybrid-electric all-wheel drive setup is gaining traction with other automakers than just Lexus and Toyota. Acura’s new RLX Sport-Hybrid flagship sedan features a similar layout, but with three electric motors assisting its 3.7-liter V6 engine. There is one at the front axle and two at the rear (one for each wheel). Those rear electric motors can operate independently from each other and have an extra trick too; they can provide both positive and negative torque to enhance handling and stability. In the upcoming Acura NSX supercar, the layout is flipped, with the two motors operating the front two wheels, while the mid-mounted V6 engine gets a single motor to help send power to the rear-wheels.
In fact, many high-performance cars are realizing the potential of electric-assisted all-wheel drive systems. Porsche’s awesome 918 Spyder pairs its potent mid-mounted V8 engine to an electric motor that turns the front wheels to help achieve an amazing lap time of just 6:57 at the famous Nurburgring.
The BMW i8 also uses this all-wheel drive hybrid setup to deliver an impressive 0-60 time of 4.4 seconds. This impressive time comes thanks to the combination of a small 1.5-liter turbocharged three-cylinder engine (boosted by a small electric motor) powering the rear wheels and a dedicated electric motor powering the front. This setup allows the i8 to earn 78 MPGe making the i8 one of the most fuel-efficient sports cars on the market today.
The Porsche 918 and i8 both boast all-electric modes, allowing them to scoot around without using fuel for a limited distance.
The potential for high-performance all-wheel drive vehicles is just being realized. Take a look at the most recent 24 Hours of LeMans, where the top cars (the Audi R18 e-quattro and the Toyota TS040) used hybrid all-wheel drive layouts. We can easily expect more race-cars like this in the near future.
Hybrid-electric all-wheel drive systems still come with a few issues, like added costs and the extra weight of the electric motors and batteries.
But those compromises may be liveable for the extra benefit of all-wheel drive and improved fuel economy. For example, the Lexus RX450h AWD gets a gain of eight MPG (in combined driving situations) compared to its non-hybrid counterpart the RX 350 AWD. The front-wheel drive RX450h nets buyers just one more MPG than the AWD version, hinting that the added weight in this application may not be affecting fuel economy in a huge way.
For road applications, hybrid AWD vehicles can provide more than just added MPGs. They enhance the driving dynamics and stability of the car as well with more sporty applications on the way.