6 of 7 describes the Prius

Like another of the seven blind men describing the 2010 Prius, this is my review. Curiously, two days later at the Detroit Auto Show, not by intent, I brought back only two photos of painted sheet metal. Hopefully these notes will provide some insights that might yet be of interest.

EXHAUST HEAT RECOVERY



Technically this is a heat exchanger that runs engine coolant through the hot exhaust. This warms up the engine quickly and provides additional heat in the winter for cabin and to keep the engine at an optimum temperature. It taps the 1/3d of the heat typically lost out the exhaust pipe.

Our 1.5L engines warm up at about 10C/minute until reaching 82C when the thermostat opens and the cooling system begins dumping heat. But the exhaust stream heat exchanger should increase the rate of warm-up to 20C/minute or better (no one has independently measured the efficiency, yet.) In contrast, one hour with a block heater will raise the temperature ~30C and save 3 minutes of warm-up if you have a power outlet. This technique works by using otherwise wasted exhaust heat.

EXHAUST GAS RECIRCULATION


You'll notice there are four exhaust ports feeding the manifold and a fifth that feeds to the exhaust gas cooling and control system.

The cooled exhaust gas feeds via a small pipe to the intake manifold where it can provide up to a 10% dilution of incombustible and now cooled exhaust gas. The reduces the peak flame temperature, which reduces NOx production and allows a leaner mixture to be used. This lean mixture provides part of the fuel economy savings.

Exhaust gas recirculation systems were used in the 1970s in some of the earliest air emissions systems. However, lacking computer control and timing, they often suffered from 'coking up' that led to higher maintenance and other problems. Hopefully this system will fare much better.

DUAL VARIABLE VALVES


Unlike the current Prius engine that only changes the intake valve timing angle, the new one tunes both the intake and exhaust timing. This allows the engine to be optimized over a wider rpm and power band.

ELECTRIC WATER PUMP


Ordinarily the water pump has excess pumping capacity and coolant temperature regulation comes from a constricted, mechanical thermostat. This increases the mechanical loss, which means the engine has to work harder. But an electroniclly managed water pump pushes through only as much coollant as needed. Best of all, it can run in hot temperatures to minimize 'cooking' as heat from the exhaust manifold seeps into the block.

1.8L ENGINE


The larger displacement and torque means the engine can generate the same power as the 1.5L engine at a lower rpm. This avoids the problem that drag losses are proportional to the engine rpm and higher speeds are often less efficient than a lower rpm.

20% MORE EFFICIENT TRANSAXLE

The previous photo also shows the smaller transaxle, which is 20% more efficient than the current transaxle. It does this by elimination of the chain and using 'forced lubrication' (also called 'dry sump.') So instead of a pool of lubricant that is stirred by the gears, oil is pumped to where lubrication and cooling is needed and no more.

MODULAR TRACTION BATTERY


The existing, proven NiMH battery modules are now housed in a smaller, separate battery housing from the control electronics. This modular approach makes future technology a lot easier to introduce.

SPRING AND SHOCK REAR SUSPENSION


Unlike the integrated, McPhearson strut, this allows changing just the shocks instead of the whole unit. This should lead to improved handling as they age by a simple, affordable shock replacement. Individuals will be able to 'tune' their rear suspension for their typical driving route and style.

REDUCED UNDER-BODY DRAG

The bottom is uniform and smooth. This helps reduce an often neglected source of aerodynamic drag. The body also has a more aerodynamic shape with 5 cu. feet more space.

CONCLUSION

This is an excellent kaizen refinement of the Prius. There is more that could have been done (hydraulic lifters, more exhaust energy capture, battery improvements) but this is enough for now and provides a reasonable upgrade path for new technology.

Bob Wilson

 

Hydraulic lifters are found in the Lexus 250h:


They are also found on the Ford Fusion and Escape engines:



Bob Wilson

 

Speculation: hydraulic lifters may not fit in the same cylinder head with the advanced Toyota patent on variable valve technology. The Toyota patent includes the ability to change the valve stroke and potentially eliminate the throttle plate. If I have a choice between valve click and elimination of the throttle plate, I'll eliminate the throttle plate every time.

Bob Wilson