Driving down the cost of hybrid systems, €10 at a time

I blogged last month about the 2015 aluminum body Ford F150, one of the most important innovations in vehicle design and manufacturing to happen in a very long time. Among other things, I was trying to call attention to how that innovation has happened, and specifically that it’s been driven by improvements in computer-aided-engineering. Hybrids also offer an great case-in-point for such computer aided improvements. Toyota’s Prius hybrids, seemingly at the apex of auto efficiency 10 years back, have delivered an approximate 10% efficiency improvement each new generation, every 6 years or so. In fact the Toyota achieved 20% and 35% efficiency increases in the redesigned RX and GS hybrids over their previous versions. Toyota’s Managing Officer Satoshi Ogiso rightfully boasts about how their hybrids keep achieving these still greater efficiencies with more compact packaging, lighter components, and lower cost. But of course this computer-driven kaizen isn’t confined to the F-150 and the Prius: they’re happening throughout the auto industry.

A recently completed report we commissioned from the consultancy FEV on hybrid costs provides another illustration. Three years ago, the U.S. EPA contracted with FEV to assess the cost of hybrid systems. FEV conducted tear-down cost assessments of the input powersplit system sold by Toyota and Ford, and also assessed the cost of a parallel hybrid system with two clutches, commonly referred to as a “P2” hybrid. These were detailed cost assessments of every part in the hybrid system, conducted on state-of-the-art hybrid systems.

This new report is an update of those P2 hybrid cost assessments from the three-year-old EPA study. This was nothing fancy, and also nothing speculative. FEV evaluated known cost reductions that have been implemented in the three years since their original P2 hybrid tear-down cost study. And FEV only assessed improvements in the motor/generator and clutch assembly subsystem. Cost-reduction opportunities on other hybrid systems, such as the electric power supply (i.e., high voltage battery), brake-by-wire, and climate control (i.e., electric air-conditioning compressor) were not considered in the analysis. FEV found five places where improvements have been made over the last three years:

  1. Better integration of the electric motor and clutches resulted in a smaller case. Savings: €19. (The report was commissioned as part of ICCT’s cost and efficiency assessments for Europe, so all cost reductions are reported in Euros.)
  2. Improvements in clutch design resulted in elimination of the hydraulic system for the clutch. Savings: €10.
  3. Oil accumulators have replaced auxiliary oil pumps. Savings: €19.
  4. Electric motors are more efficient, allowing a smaller traction motor to be used. Savings: €26.
  5. The auxiliary hybrid cooling system has been replaced with an expanded capacity engine cooling system and an electric pump. Savings: €30.

Again: this is all pretty simple stuff. Yet it reduced the cost of the motor/generator/clutch subsystem in a midsize European car by 105 Euros. That’s about 14% of the original cost of the P2 motor/generator and clutch assembly subsystem (5% of the cost of the total hybrid system). In just three years.

And manufacturers are just scratching the surface. There are many other potential cost reductions for P2 hybrid systems. One of the biggest opportunities is to make Li-ion battery designs with higher power density. Batteries are a significant part of the cost of hybrid systems (on average about €1,100 at present). Current hybrid batteries are oversized, in order to provide the power needed for acceleration assist and regenerative energy capture without excessive deterioration. Higher power density will allow future hybrid batteries to much smaller —and therefore a lot cheaper. Another big opportunity is to improve coordination between the friction brakes and regenerative braking: better designs should allow the current cost of €174 to be cut substantially. The air conditioning system represents a third opportunity: driving the air conditioning compressor off of the electric traction motor with a gear or belt drive, instead of using a separate electrically-driven compressor, would also have large cost reductions.

I could go on. The point is that even without considering not-quite-there-yet-but-soon step-changes in hybrid technology, FEV still found 14% cost reductions in the motor/generator/clutch system from incremental improvements in just three years.

No one’s about to propose a new version of Moore’s Law for passenger vehicles. But it’s increasingly clear that we’re in an era when the pace of innovation in vehicle technology is accelerating, thanks to computer-aided design and simulation. Technologies are getting both better, and cheaper. And that trend shows no sign of slowing down.

Engineering & manufacturing