1.8 Petrol

[Jamesverso]

Any plans for toyota to put the new 1.8 Valvematic in the Prius as its still the older less powerful less efficient vvt engine?

[fuel miser]

Any plans for toyota to put the new 1.8 Valvematic in the Prius as its still the older less powerful less efficient vvt engine?

I doubt very much that they're due to replace the current (98bhp) engine, being that the Prius gen 3 has only been out for a year, and the same engine is used in the new Auris HSD. The 1.8 2ZR-FXE engine is unique to the Prius and Auris HSD as it uses the Atkinson cycle, which is much MORE efficient at the expense of low down power, which isn't a problem as the electric motor is designed to do the work at lower speeds, and increases the effective bhp output to a perfectly adequate 134.

[Grumpy Cabbie]

Fuelmiser is right and I will elaborate a little further. The engine in the Prius isn't designed for power but economy. It runs in a different way to a 'normal' car and this is the secret to its fuel efficiency. This different way is called the Atkinson cycle as opposed to a normal car engine which runs on the Otto cycle. The atkinson cycle system has been around for ages but hasn't really been popular because it lacks power when setting off etc. This isn't a problem with the Prius as the electric motor offers assistance to compensate.

So pretty much repeated what Fuelmiser said, but hope you can see why the Prius is a very economical vehicle yet still have a 1.8 petrol engine with an 'automatic' gearbox. Have added a couple links that will probably explain things better than me.

http://en.wikipedia.org/wiki/Atkinson_cycle

and

http://en.wikipedia.org/wiki/Four-stroke_cycle

[Sagitar]

It's not strictly an Atkinson cycle engine. The key thing about the Atkinson cycle is that it performs all four working strokes in a single revolution of the engine. The Prius engine certainly does not do that. The aspect of the Atkinson cycle that the Prius engine mimics is that it has a power stroke that is longer than its induction stroke. As a consequence it burns the charge more completely and down to a lower discharge pressure and is therefore more fuel efficient. But because it takes in a smaller charge than a conventional engine of the same swept volume, it generates less power.

The Prius engine achieves a similar effect by leaving the induction valve open for the first part of the compression stoke, allowing some of the charge to be pushed back out of the cylinder and having the same effect as if there was a shorter induction stroke. So in this regard it achieves a similar efficiency improvement (and a similar power reduction) as the Atkinson cycle. On the basis of this similarity Toyota describe the engine as an Atkinson cycle engine, but they are stretching the definition somewhat.

As others have said, the availability of additional power from the electric motors makes it possible to run with a less powerful I.C. engine that achieves greater fuel efficiency. This is a major benefit of the hybrid drive and putting in a more powerful but less fuel efficient I.C. engine would negate it.

[fuel miser]

So it's got an Atkinson cycle engine but it hasn't really got an Atkinson cycle engine. It's also got CVT transmission but then it hasn't really got CVT transmission.

It often baffles me why the Prius is so misunderstood!

[Grumpy Cabbie]

So it's got an Atkinson cycle engine but it hasn't really got an Atkinson cycle engine. It's also got CVT transmission but then it hasn't really got CVT transmission.

It often baffles me why the Prius is so misunderstood!

It also has an EV mode, but doesn't really. Well it does, but only when it wants, and oh it will go to 30 mph in EV, but again only when it wants.

It does do great mpg's though as well as a super smooth and quiet ride

[fuel miser]

So it's got an Atkinson cycle engine but it hasn't really got an Atkinson cycle engine. It's also got CVT transmission but then it hasn't really got CVT transmission.

It often baffles me why the Prius is so misunderstood!

It also has an EV mode, but doesn't really. Well it does, but only when it wants, and oh it will go to 30 mph in EV, but again only when it wants.

With the exception of those times when it'll do 40mph + in EV mode. I hope, between us, we're clearing up any confusion for all. :D

[kithmo]

So it's got an Atkinson cycle engine but it hasn't really got an Atkinson cycle engine. It's also got CVT transmission but then it hasn't really got CVT transmission.

It often baffles me why the Prius is so misunderstood!

It also has an EV mode, but doesn't really. Well it does, but only when it wants, and oh it will go to 30 mph in EV, but again only when it wants.

With the exception of those times when it'll do 40mph + in EV mode. I hope, between us, we're clearing up any confusion for all. :D

and don't forget the Power Mode that doesn't give you any more power

[Sagitar]

So it's got an Atkinson cycle engine but it hasn't really got an Atkinson cycle engine. It's also got CVT transmission but then it hasn't really got CVT transmission.

It often baffles me why the Prius is so misunderstood!

You cannot blame manufacturers for trying to find simple labels that get a concept over to the majority of the population. Most people have very little interest in the niceties. Engineers know that the Prius gear train has only one ratio. However, feeding power to a planetary gear set from multiple sources allows stepless variation of the rotational speed of the drive axle. To most people the effect is indistinguishable from that of a CVT, so why not call it a CVT? The only real problem that I see is that conventional CVTs depend upon variable friction drives of some kind and tend to have problems of wear and unreliability. I might be put off the Prius if I thought that it really did have a conventional CVT.

The term Atkinson cycle is now commonly applied to modified Otto cycle engines where the induction valve is held open during the first part of the compression stroke. These engines do not work anything like the original Atkinson cycle engine, but the theoretical thermodynamic cycle is very similar so it is not an inappropriate label, even though it brings a reaction from pedants like me . . . .

[johalareewi]

With the exception of those times when it'll do 40mph + in EV mode. I hope, between us, we're clearing up any confusion for all. :D

Isn't that stealth mode not EV mode ?

I'm still looking for the heretic mode switch. :)

[fuel miser]

And why is it that when a Prius is registered for taxi/private hire use, they don't have indicators?

(awaits abuse fronm G.C.)

[Grumpy Cabbie]

And why is it that when a Prius is registered for taxi/private hire use, they don't have indicators?

(awaits abuse fronm G.C.)

You can go off someone you know! :P

[johalareewi]

...To most people the effect is indistinguishable from that of a CVT, so why not call it a CVT? The only real problem that I see is that conventional CVTs depend upon variable friction drives of some kind and tend to have problems of wear and unreliability. I might be put off the Prius if I thought that it really did have a conventional CVT.

Which is why some people are trying to get it called eCVT to convey that it is CVT but done with electricity not mechanics.

[timberwolf]

So how many people here have owned a car with a conventional CVT? I suspect not many. So why try to name what Toyota have invented as an eCVT, when I am sure Toyota have their own name for what they built, why not call it that? (even if the name escapes me as I type this message).

[Sagitar]

So how many people here have owned a car with a conventional CVT? I suspect not many. So why try to name what Toyota have invented as an eCVT, when I am sure Toyota have their own name for what they built, why not call it that? (even if the name escapes me as I type this message).

There is an increasing number of vehicles with continuously variable transmission.

Interestingly, the July 2009 Prius brochure says on page 44:-

Gearbox type - Electronically controlled continuously variable transmission.

It's a good example of the kind of convenient labelling that I referred to earlier. Most people expect a car to have a gearbox, i.e. a unit that fits between the power source and the driven wheels and enables changes of the ratio of input shaft speed to output shaft speed, so Toyota list a gearbox type, even though the Prius hasn't really got one (but it does have something that does the same job). Elsewhere, the brochure describes the "Hybrid Synergy Drive" but that is a description of the combination of electric motors and petrol engine and includes specific mention of the CVT transmission as one of its elements.

Their marketing people must have had a real conundrum. Do we try to assure the market that this car is quite normal and they need not be worried by it; or do we emphasise the differences and play up the fact that it uses different technologies? My feeling is that they have gone mainly for the "it's normal" approach, but in doing so they have raised a whole series of questions for anyone trying to understand the details of the technology.

There is a little piece in Wikipedia that illustrates conventional thought on the matter:-

"CVTs should be distinguished from Power Sharing Transmissions (PSTs), as used in newer hybrid cars, such as the Toyota Prius, Highlander and Camry, the Nissan Altima, and newer-model Ford Escape Hybrid SUVs. CVT technology uses only one input from a prime mover, and delivers variable output speeds and torque; whereas PST technology uses two prime mover inputs, and varies the ratio of their contributions to output speed and power. These transmissions are fundamentally different. However the Honda Insight hybrid, the Nissan Tiida (only the SL model), Nissan Cube, Juke, Rogue, Altima, Murano, Maxima, and Jeep Patriot use CVT".

Toyota have clearly not read Wikipedia . . . . . . .

[timberwolf]

My spider sense should have been tingling when I wrote my last post.

In the April 2008 brochure, in the Specifications section under Hybrid Synergy Drive, there is a row "Transmission Electronic Controlled continuously Variable Transmission (CVT)". No mention of a gearbox. I see this as another example of Toyota taking a backward step to appeal to the more conventional car buyer with the design of the Gen 3.

[johalareewi]

Must admit, before I discovered Prius Chat, I thought the Prius had conventional CVT.

[Dave R.]

If you're interested in how the drive works, theres a rather good explanation here http://eahart.com/prius/psd/ (Complete with a working model to play with).