Variable exhaust valve

Yep, got that. Now where is the "main muffler" that it mentions? If it's the one at the back, then it's not the valve that the OP is talking about.

 

The OP misidentified the coolant heater as an "exhaust valve." Prius exhaust valves are mounted in the cylinder head and are operated by the overhead cam.

There is a spring-loaded, by-pass valve in the muffler at the rear of the car. The OP insists on calling an exhaust by-pass valve as an "exhaust valve."

• "exhaust valve" - a poppet valve located in the cylinder that is operated by the cam to let the very hot, glowing exhaust gasses out. It looks very similar to the intake, poppet valve.
• "by-pass valve" - a spring operated valve that opens in the muffler to reduce back pressure at high gas-flow rates (aka., power settings.)
• "exhaust coolant heater" - the part the original poster photographed that simply speeds up engine warm-up

Bob Wilson

 

Call it what you will... Not everyone knows everything, just yet.

Just a newbie learning here with interest as to what makes our cars go... and not having my "teacher" overlooking over my shoulder to describe what is explained as he is at work at the moment. I'm still in Hybrid Engine 101...

 

An engineer by training and habit, I tend to get a little persnickety about labels used for technology. Sad to say, the title "variable exhaust valve" remains somewhat misleading which is what first caught my eye. But there is history in tweaking the exhaust valve duration.

There has been some literature on exhaust valve duration being extended to increase the exhaust gas recirculation (EGR) to mitigate high power, exhaust temperatures. However, the higher temperatures inside the cylinder leads to a knock problem in spark ignition engines. This is why Toyota's 'cooled EGR' allows a higher ratio without inducing knock. In a diesel, EGR temperature is not a problem since ignition occurs with fuel injection timing.

Please understand I'm more interested in making sure we're all on the same sheet of paper. Shoot, I'm an older guy and am well aware of having 'a senior moment' when the precise term escapes me.

Bob Wilson

 

Correct. The OP was showing the exhaust heat recovery unit, which is right after the cat. The "variable exhaust valve" is part of the "main muffler". The main muffler is near the end of the exhaust pipe. Note that the engine also has variable exhaust valve timing (the poppet valves in the head).

And Bob is correct in insisting on using the correct name. This thread is a perfect example of this requirement as it has nicely confused the three "valves". There are -three- things that could be called an "exhaust valve" or "variable exhaust valve" so correct naming is necessary to keep them straight.

Note that one reason the GIII got the 1800cc engine is it has better "variable cam timing" or "variable exhaust valve timing" than the 1500cc engine. This allowed better control of the engine parameters for better power and fuel economy in the "Atkinson" configuration and hybrid system.

 

LOL!

Like GM calling their Belt-AsSisted (BAS) hybrids a hybrid. The more appropriate term was Belt-AsSisTed And RetArDed (BASTARD) hybrid.

Still, having studied Latin, French, and Japanese, I am sympathetic to the problem of language and finding an accurate translation.

Bob Wilson

 

A Gaelic translation might be a wee bit more of a challenge...

 

A Flux Capacitor, I know one when I see it!

 

You could say it but you couldn't speiligeadh.

 

Go Bob!!! In my world it is all about "Saoirse."

 

My TDI had an electrically controlled flapper valve in the middle of the exhaust system. It was there to force exhaust gases back through the EGR system. That's what I was thinking of when the OP thought there was a valve in the middle of the exhaust.