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Hybrid hot rods — Can hybridization improve performance?

Wednesday, March 16, 2016 - 07:00
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Since 1999 when hybrid vehicles were introduced in the United States, they have gotten a bad name in terms of their performance. These vehicles have typically been recognized for their ability to get better than average fuel economy, but many automotive enthusiasts consider them to be slow and underperforming. In fact, many see them as having been designed solely for “tree huggers” that are only interested in saving fuel. Given the reputation these vehicles have developed, would you believe that hybrid technology actually has the ability to increase the rate of acceleration? Would you believe that this technology has been used in F1 race cars for going on seven years?  This article will focus on the following:

  • Why hybrids on the road are typically driven slowly
  • Why hybrid vehicle technology can actually increase the rate of acceleration
  • How hybrid technology is being implemented into race cars
Toyota 2013 F1 Hybrid
Toyota 2013 F1 Hybrid Top View

So, why do people drive hybrid vehicles so slowly? These vehicles are driven slowly so consistently that most people assume it’s that the vehicles are incapable of accelerating quickly. The reality however is that the vehicles are actually coaching drivers to accelerate slowly, not that the vehicles are incapable of going fast. This driver coaching is designed to help the driver achieve the advertised fuel economy. The coach in this case comes in many different formats, but they all have one thing in common. The commonality is the fact that they somehow “reward” the driver for operating the vehicle in a fuel efficient (slow) manner.  One example of this coaching was on the Ford Fusion hybrid. Ford chose to display an image of a digital plant in the dash display. The more efficiently the driver operated the vehicle, the more leaves the digital plant grew. I tend to think of these driver coaching systems as a type of video game. As with most video games, they are designed to draw the drivers in and subconsciously get them to play the fuel economy game.  

What a Prius and A Quattro E share     
You may still be reluctant to believe that hybrid technology has the ability to increase vehicle performance so let’s take a closer look. To begin with let’s look at the performance limitations of traditional internal combustion engines (ICE). We all know that a traditional ICE doesn’t create maximum torque immediately when the accelerator pedal is depressed. In fact, for most vehicles there is a significant delay while the engine speed increases to a peak performance RPM.  We refer to this as the ramp up of power as the engine’s torque curve.  For an ICE this torque curve looks somewhat like a mountain where it starts low, slowly builds up to a peak, and then drops back off.  So, how can hybrid technology improve this?  The key to this performance puzzle is the electric drive system in a hybrid.  Electric motors perform much differently than an ICE in terms of the torque curve.  Much like an ICE, the torque curve of an electric motor is dependent on the overall design.  The difference however is that, in general terms, electric motors produce high levels of torque beginning immediately from 0 RPM.  In fact, for most electric motors used in hybrid vehicles, the torque available starting at 0 RPM will be near the maximum possible torque the motor can produce. 

These unique electric motor torque characteristics can be used to supplement an ICE.  When a driver of a hybrid vehicle requests maximum acceleration (wide open throttle acceleration) the vehicle controllers begin a blending of power.  The typical sequence will involve the engine controller beginning to ramp up the ICE torque.  As previously mentioned, it will take some time for the ICE to reach peak torque output.  To improve acceleration during this ramp up of the ICE, the controllers will be commanding additional torque from the electric drive system of the hybrid.  Because the electric motors begin producing torque almost instantaneously, the vehicle will have improved acceleration.  Of course, there are limitations to all systems.  The electric drive system can’t sustain long term acceleration due to the limited power available (dictated by battery storage capacity).  In an ideal situation however, the ICE will have reached its maximum torque production range before the electric drive system runs out of power.

Because of this ability to increase the rate of acceleration, hybrid technology has been slowly making its way into performance applications.  Current examples of this trend include the Acura NSX, Porsche Panamera hybrid, Porsche Cayenne hybrid, and the Ferrari LaFerrari. All four of those vehicles are using hybrid technology, and it definitely isn’t just to improve fuel economy.  Because the Porsche models have both hybrid and non-hybrid versions they provide the opportunity for an apples-to-apples performance comparison. The Porsche Panamera hybrid for instance has a 0-60 mph time of 5.2s.  That is .8 seconds faster than the base model Panamera S. The performance difference is even more pronounced in the Porsche Cayenne. The hybrid version of that vehicle has a 0-60 mph time of 5.4s, while both the base model and the diesel versions of the Cayenne have much slower 0-60 mph times of 7.3s and 7.2s respectively.

The performance applications for hybrid technology however don’t stop with consumer vehicles. Race teams have been implementing hybrid technology for several years, and the latest versions of these systems are using some unique applications of this technology to improve performance beyond what is being done in the consumer market. Formula 1 (F1) racing is a perfect example of this. 

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