Toyota's new low-friction Rav4/Venza engines 1AR-FE & 2AR-FE

[Daox]

I was just reading about Toyota's new engines for the Rav4 (2AR-FE) and Venza (1AR-FE). While quite oversized (IMO), they do implement some interesting technologies that backup Toyota's claim that its a 'low-friction design'.

It incorperates:

• An offset crankshaft
• Roller rockers for the valvetrain
• Three stage variable oil pump
• Reduced tension piston rings (I can see Metro going OOOOohhh as he reads this one)
• Reduced tension auxiliary belt drive
• Tumble air control valve (enhances combustion while the engine is cold)
• 12 hole high atomizing long nozzle fuel injectors

It also has all the normal goodies like VVT on intake and exhaust cams as well as ACIS intake system (dual runner intake manifold).

Too bad they don't quantify any of the gains.


source, and this too.

[Tygen1]

Motorcycles, 4-stroke dirt bikes in my expierience, have been using offset cranks for a number of years so they could use tiny slipper pistons. They offset the crank to take some of the side load forces off of the piston sidewall during the power stroke. Useing that, they can make tiny and light wieght motors. Seems Toyota is using it to reduce friction.

[metromizer]

Good to see the "Kaizen" philosophy at work toward FE improvements, roller rockers are always good for recuced parasitic losses. The variable length/volume intake tract is great to see being used on more production cars, independant VVT (intake AND exhaust) is a step in the right direction. Racers have long known the benefits of low tension piston rings with respect to parasitic frictional losses, but often a crankcase vacuum pump is needed to get the rings to seal. I wonder how Toyota is dealing with that? Three-stage variable oil pump is news, I've never heard of that, but it makes sence so long as it's bullet-proof simple (some experimental oil pump warrenty problem could really hurt if it doesn't work out). Increased compression ratio while still burning regular fuel means they are improving combustion control, I attended a recent update on similar resarch that sounded promising. Same with new injectors.

The marketing guy who wrote the press release lost me when he said "Key low-friction technologies include an offset crankshaft..." the term offset crankshaft used as if it were some sort of FE improving feature (they likely increased the crank stoke to increase the displacement from 2.4 to 2.5 liters, slightly increasing torque but nothing to do with lower friction, FE improvements) don't mind me, it's just a peive of mine to see this repeated more than once in automotive marketing circles.

[metromizer]

Originally Posted by Tygen1

They offset the crank to take some of the side load forces off of the piston sidewall during the power stroke...

can you educate me? I don't know what this is...

[rmay635703]

Originally Posted by Tygen1

Originally Posted by Tygen1
They offset the crank to take some of the side load forces off of the piston sidewall during the power stroke...

Originally Posted by metromizer

can you educate me? I don't know what this is...

.

[some_other_dave]

It's similar in concept to using pistons with offset wrist-pin holes. Though those are, from what I recall, used more to reduce piston slap than to reduce friction. Still, reduced side-loads are reduced side-loads.

-soD

[MetroMPG]

Neat.

I think the fist gen. Insight 1.0 litre engine had an offset crank as well. (Plus roller rockers and other stuff.)

Yup: InsightCentral.net - Encyclopedia - Honda Insight Offset Cylinder

The engine block has a unique, offset cylinder design in which the bore center is offset 14mm from the crank center. Maximum combustion pressure occurs at a point where the connecting rod is straight up and down in the cylinder. In this position there is zero lateral force so friction and piston slap are reduced.

As a result of the offset construction, the combustion pressure is used more efficiently since the rod is near it maximum leverage point with the crankshaft.

[Daox]

I wonder why all engines don't do this? Loss of power maybe?

[some_other_dave]

I don't think there's any loss of power. I think the main reason is that it's more expensive to build. No, I don't know that for a fact, but I would suspect that it is more expensive to machine things so they are offset like that, and there may be extra steps (or checks) during assembly.

That's definitely the reason that all cars don't yet have roller lifters or the equivalent. They are significantly much more expensive than solid lifters, and more complex (so more stuff to design, to manufacture, to assemble, to engineer, to break), even though they have obvious advantages.

-soD

[Formula413]

Originally Posted by metromizer

variable length/volume intake tract

I have heard of this before but never seen it in practical application, how does it work?