SAE paper review

Thank you!

Here are some papers from Toyota & Aisin realated to the Prius Gen IV (the list may be incomplete):
The New Toyota Inline 4 Cylinder 1.8L ESTEC 2ZR-FXE Gasoline Engine for Hybrid Car
Development of the Li-ion Battery Cell for Hybrid Vehicle
The New Generation Front Wheel Drive Hybrid System
Development of New Hybrid Transaxle for Compact-Class Vehicles
Development of Power Control Unit for Compact-Class Vehicle
Efficiency Improvement in Exhaust Heat Recirculation System
Development of Compact Electric Rear-Drive Unit
The full texts are not online yet, but most of them have 5-pages free preview already.
The new MG2 is 53kW/163Nm/17000rpm MAX (Gen III: 60kW/207Nm/13500rpm MAX).
But I haven't seen the numbers for MG1.​

The $25, papers are available as of April 5 and I've bought:

The New Generation Front Wheel Drive Hybrid System (SAE 2016-01-1167)

As a summary, this is a good introduction and overview of the changes. It touches on the technical changes without going down the rabbit hole:

• Transaxle - higher MG2 speed, 13500 rpm to 170000 rpm, reduces weight and improves efficiency. New stator winding technique and rotor reduced mass and improved power.
• Power Control Unit - improved cooling and a "Super Body Layer" IGBT reduces size and improves efficiency. The DC/DC converter for the 12V power supply is smaller with increased output voltage range.
• Battery - better packaging but not a lot of technical details.
• Fuel Economy improvements sources:
  • 4% - battery
  • 28% - engine
  • 13% - transaxle
  • 16% - motor
  • 13% - power control unit (power electronics)
  • 26% - HV control laws
• Maximum vehicle speed for engine stop, 110 km/h (68 mph)
• Hybrid driving perception - the "rubber band" feel, the high engine rpm for maximum acceleration is reduced by using more battery power. In effect, 'sounding more normal' to reviewers who castigate the CVT.

The New Toyota InLIne 4 Cylinder 1.8L ESTEC 2ZR-FXE Gasoline Engine for Hybrid Car (SAE 2016-01-0684)

This provides the details hinted at in the earlier Combustion Development to Achieve Engine Thermal Efficiency of 40% for Hybrid Vehicles (SAE 2015-01-1254). The take-aways:

• Tumble flow - improves use of higher, cooled EGR mixture and rapid combustion.
• Intake valve timing - larger opening and slight tweaks in timing.
• Exhaust manifold - YEA!!! They are pulling the exhaust after the catalytic converter. This significantly reduces the risk of carbon/oil blocking of the EGR valve and tube. This will improve the life of these important parts!
• Intake manifold - better paths to even the cooled EGR ratios to the cylinders.
• Spark plugs - adjusted to optimize ground wire and tumble fuel-air mixture and ignition.
• Dual passage cooling - shortens warm-up yet improves cooling. Includes some baffles around cylinders and exhaust port cooling to minimize knock risk.
• Friction reduction - bearings, new oil pump rotors, lower mass valve roller arms and spring, lower friction piston skirt coating, and lower friction cam chain.

Efficiency Improvement in Exhaust Heat Recirculation System (SAE 2016-01-0184)

Oh boy! Mechanical engineering talk! I loved it. I have to quote this:

"As vehicle fuel economy has improved, waste heat represented as cooling heat loss Qw has declined. As a result, engine warm-up delays and insufficient heat stupply for cabin heaters have become an issue. TOYOTA and SANGO believe that utilizing the exhaust heat loss Qex, which is also waste heat, would be effective in improving fuel economy further."​

At last, discussing a 'topping cycle' as the future direction. In effect, the efficiency of hybrids is reaching a point where future improvements are going to address getting useful work from the exhaust heat:

• Conventional exhaust heat recirculation
• High-efficiency exhaust heat recirculation
• Latent heat storage (aka., the Gen-2 thermos?)
• Chemical heat storage
• Thermoelectric power generation
• Rankine cycle
• Air-conditioner using waste heat (YEA!!!!!)
• Stirling engine

The rest of the paper goes into an excellent thermodynamic review of heat flows and how the new heat recovery system was developed. For example, knowing the boiling point and worst case heat flow with the valve closed, they balanced the tubes (i.e., no spot boiling); thinned the tubes for better transfer; added fins to improve heat transfer, and; reduced the amount of coolant in the tubes for faster transfers. Fully meets my mechanical engineering interest that concludes with:

" . . . exhaust heat recirculation system are expected to become even more important technologically in order to improve fuel economy and maintain heating performance."​

Development of New Hybrid Transaxle for Compact-Class Vehicles (SAE 2016-01-1163)

Things not discussed already:

• stator - rectangular wires; segmentation winding; new coating to handle high voltages; welding wire segments.
• rotor - high-speed, low-loss rotor reduced 15% saving materials yet improving performance.
• power cables - gone! It plugs in directly.
• cooling - ATF fluid handles cooling and goes to radiator so surface cooling is not as important.
  
• differential - press-fitting
• mechanical losses - reduced by better gears and bearings
• dynamic ATF cooling flow - two fluid catch tanks and a fluid dam so only as much fluid is in the gears when needed to reduce stirring losses.

There are some other papers I may buy for future reading and reporting in this thread. But for $100, these four were well worth it.

Bob Wilson