seb146
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Engine And Transmission Questions

Tue Sep 05, 2017 4:07 am

I thought I would ask some random and non political questions:

What is the advantages of rear engine, mid engine, and front engine? Why do hybrids and alternative fuel vehicles not have standard transmissions? Would there be an advantage for hybrid and alternate fuel vehicles to have rear or mid engines? Or rear wheel as opposed to front wheel drive?
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WIederling
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Re: Engine And Transmission Questions

Tue Sep 05, 2017 7:19 am

Engine sitting over the driven axle has obvious advantages.
Much weight at the back creates a less stable vehicle.

Engine and gearbox between axles gives perfect roadhandling
_but_ has a knack for a much harder to handle type of control loss.

Front engine with front drive allows good traction and
accomodates the average thumbfisted driver quite well.

I don't see "alternative fuel vehicles" having different gearboxes.
( you will see a prevalence of the more efficient gearbox designs
like oldstyle regular stick shift, double clutch or CVT designs.)

The gearbox with electric dual generator/motor setup
you see on Toyota hybrids adds the electric drive part
but also enhances the gearbox with CVT features.
( you see a similar arrangement of variable bypass in
agricultural tractor designs.)
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Aesma
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Re: Engine And Transmission Questions

Tue Sep 05, 2017 9:49 am

Electric cars have 1 gear or 2 gears max, lots of torque, standard transmissions are of no use.

Hybrid cars usually need a transmission able to link the electric and gas engines together and allow them to work independently too.

Peugeot did something simpler with the hybrid 508 and 3008 (and I think BMW with the i8, but in the opposite direction), diesel engine in the front with standard FWD transmission, and battery and electric engine in the back linked to the rear wheels, no mechanical link between the two.
New Technology is the name we give to stuff that doesn't work yet. Douglas Adams
 
seb146
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Re: Engine And Transmission Questions

Tue Sep 05, 2017 4:00 pm

Aesma wrote:
Electric cars have 1 gear or 2 gears max, lots of torque, standard transmissions are of no use.

Hybrid cars usually need a transmission able to link the electric and gas engines together and allow them to work independently too.

Peugeot did something simpler with the hybrid 508 and 3008 (and I think BMW with the i8, but in the opposite direction), diesel engine in the front with standard FWD transmission, and battery and electric engine in the back linked to the rear wheels, no mechanical link between the two.


From what I am understanding here, alternate fuel and hybrid vehicles have different transmissions than gas or diesel engines?

I thought there had been three speed manual transmissions on some cars. I know it would not make much of a difference in every day driving, but what about downshifting for hills? I have an automatic and downshift sometimes when I am in San Francisco to make it up some of those hills. I know it is rare and not practical for nearly all cars, but it is just a random question.
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Aesma
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Re: Engine And Transmission Questions

Tue Sep 05, 2017 5:58 pm

With an electric engine you get maximum torque at 0rpm so going uphill is no problem.
New Technology is the name we give to stuff that doesn't work yet. Douglas Adams
 
seb146
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Re: Engine And Transmission Questions

Tue Sep 05, 2017 11:58 pm

Aesma wrote:
With an electric engine you get maximum torque at 0rpm so going uphill is no problem.


I doubt a Nissan Leaf or any Tesla would roll uphill. I don't think that is what you meany, anyway.

I think my mind is working the wrong way about the hills. I am thinking there is more power needed to drive uphill. That power comes from the engine. The higher RPM of the engine makes the car go and accelerate uphill. I am missing something, but what?
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Tugger
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Re: Engine And Transmission Questions

Wed Sep 06, 2017 12:36 am

seb146 wrote:
Aesma wrote:
With an electric engine you get maximum torque at 0rpm so going uphill is no problem.


I doubt a Nissan Leaf or any Tesla would roll uphill. I don't think that is what you meany, anyway.

I think my mind is working the wrong way about the hills. I am thinking there is more power needed to drive uphill. That power comes from the engine. The higher RPM of the engine makes the car go and accelerate uphill. I am missing something, but what?

It sounds like you are meaning "engine braking" where you use the engine to slow you going down a hill. And yes higher revs (sans fuel!) do slow you down more as there is more friction and resistance at the higher rate.

As to driving uphill, yes more power OR lower gear ratios are needed to perform the task. Gearing is indeed magical, it is right up there with levers (you know "give me a lever long enough and I will move the world"...). Give me the right gear ratio and I can move basically anything. Not fast necessarily, but it will move. Modern commercial trucks have 400+ HP and pull 88,000lbs+ and have 10 to 18 gears.

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Re: Engine And Transmission Questions

Wed Sep 06, 2017 3:58 am

seb146 wrote:
Aesma wrote:
With an electric engine you get maximum torque at 0rpm so going uphill is no problem.

I am thinking there is more power needed to drive uphill. That power comes from the engine. The higher RPM of the engine makes the car go and accelerate uphill. I am missing something, but what?


I'm not sure where I read/heard it, but possibly the best explanation of the difference between "power" and "torque" when talking about cars is this: Torque is what gets you to the speed you want to be at, power is what keeps you there.

Torque is the ability of the engine to turn the wheels -- so for going uphill, torque is a bigger player than pure power. Power is the engine's ability to keep the wheels turning and is more related to maintaining a given speed than getting to that speed.

Torque is the reason why almost all heavy trucks have diesel engines (and it's the reason why almost all ultra-heavy trucks and trains are diesel-electric). They need masses of torque to get the wheels turning under load. My car is a diesel -- it's not particularly fast, but it will get to any speed limit in an impressively short time. It will also pull its way up a hill/mountain with a lot less fuss than my previous gas-engined car would.

Internal combustion engines work efficiently in a relatively narrow RPM band (between about 1,500 and 7,000 RPM for most gas cars), and they need gearboxes to make the most of the power and torque that are available in that band.

All-electric cars like the Tesla and even the Nissan Leaf have all their torque available from rest -- there's not the significant torque curve seen with an internal combustion engine. That's the reason why "Ludicrous Mode" is so much fun in a Tesla. They don't need a gearbox because they have all the torque they need from rest, and that torque is available through almost all the operational band (there is some tail-off at insanely high RPM).

Diesel-electric haul trucks and locomotives use the engine as a generator to power electric motors in the wheels, once again making good use of the fact that there's no significant torque curve in electric drive trains.
 
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BreninTW
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Re: Engine And Transmission Questions

Wed Sep 06, 2017 4:25 am

And some thoughts on your initial question on engine placement ...

Front engine/front-wheel drive (FF):
Pros:
    Better packaging. Most FF cars have the engine mounted longitudinally, so it takes up less room in the front of the car, meaning you can have a larger passenger cabin in the same footprint. You also don't have a huge transmission tunnel.
    It's more difficult to induce oversteer where the back of the car tries to pass the front of the car in a bend.
Cons:
    Having all the weight at the front of the car lends itself to understeer -- the car wants to go straight instead of following a bend.
    The mechanics of having the same set of wheels driving and turning leads to a larger turning circle, and also slightly more expensive maintenance and components.

Front engine/rear-wheel drive (FR):
Pros:
    Relatively simpler and cheaper to design and build.
    Many drivers prefer the feeling of being "pushed" rather than "pulled".
    Engine bay is less crowded.
    Smaller turning circle.
Cons:
    It's easy to induce oversteer, which most drivers are unable to counter effectively. This quickly leads to spin-outs.
    Packaging is more challenging: Engines are mounted front-to-back and a transmission tunnel is required. This can make the cabin more cramped.
    Ultimate handling requires expensive independent suspension and a complicated drive system at the rear.

Mid-engine/rear-wheel drive (MR):
Pros:
    Better weight distribution leads to better handling characteristics.
    Smaller turning circle.
Cons:
    It's almost impossible to have more than two seats.
    Engine access can be a pain.

Rear engine/rear-wheel drive (RR):
Pros:
    Better packaging. The engine is typically mounted longitudinally, so it takes up less room, meaning you can have a larger passenger cabin in the same footprint. You also don't have a huge transmission tunnel.
    Many drivers prefer the feeling of being "pushed" rather than "pulled".
    Smaller turning circle.
Cons:
    Engine access can be a pain.
    It's easy to induce oversteer, which most drivers are unable to counter effectively. This quickly leads to spin-outs.
    Requires most complex controls and independent rear suspension.
    Engine controls can be challenging to maintain.

I occasionally drove an ambulance based on a 1974 VW transporter (RR layout) -- forward of the engine it was wonderful and easy to work in, but loading patients over that engine at the back was insanely difficult (and yes, we did have to carry a patient a time or two!)
 
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Aesma
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Re: Engine And Transmission Questions

Wed Sep 06, 2017 6:44 am

I did manage to oversteer once in my FF car, unintentionally I mean (I had done it on purpose once and spun it in a wet street), at about 100Km/h in a bend, with two passengers in the back changing the dynamics I'm used to, well, that was scary, but I managed to recover somehow.
New Technology is the name we give to stuff that doesn't work yet. Douglas Adams
 
tommy1808
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Re: Engine And Transmission Questions

Wed Sep 06, 2017 7:03 am

BreninTW wrote:
It's easy to induce oversteer, which most drivers are unable to counter effectively. This quickly leads to spin-outs.


In fairness, that is just because most people never learn how to handle it. It is not exactly part of the normal driving school curriculum. I positively loved that my driving school offered to take every former student to an ADAC safety training two years after getting the licence for free (aside of the ADAC fee). It really takes just 2 or 3 spins with someone telling you what to do, before you know how to catch it.

Of course today ESP does the catching in most cars quite efficiently.

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Channex757
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Re: Engine And Transmission Questions

Wed Sep 06, 2017 8:43 am

Just to be awkward, some Aston Martins and Ferraris have confused the issue too with a front mounted engine and gearbox at the rear. Apparently this helps with weight distribution.
 
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Re: Engine And Transmission Questions

Wed Sep 06, 2017 11:57 am

Channex757 wrote:
Just to be awkward, some Aston Martins and Ferraris have confused the issue too with a front mounted engine and gearbox at the rear. Apparently this helps with weight distribution.


Transaxle : All Daf "Variomatic" types, VW/Porsche 924

there seem to actually be two definitions around on what makes a "transaxle".
1: gearbox on the driven axle with engine detached and a long transmission shaft
Porsche 924 yes, beetle and all frontdrive cars no

2: gearbox combined with differential and wheel drive independent of where the engine sits.
essentially all cars that have a gearbox that includes differential and wheel drive
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Aesma
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Re: Engine And Transmission Questions

Wed Sep 06, 2017 2:15 pm

For me a transaxle is indeed what you find in a Porsche 924/944, but according to wikipedia, most cars have a transaxle.
New Technology is the name we give to stuff that doesn't work yet. Douglas Adams
 
WIederling
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Re: Engine And Transmission Questions

Wed Sep 06, 2017 2:51 pm

Aesma wrote:
For me a transaxle is indeed what you find in a Porsche 924/944, but according to wikipedia, most cars have a transaxle.


The various Wikipedia pages differ.
DE references the 924 and DAF arrangement, i.e. engine/clutch on one end gearbox on the other connected via a long power shaft
EN has the any gearbox with integral differential.

No looked at other languages.
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BreninTW
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Re: Engine And Transmission Questions

Wed Sep 06, 2017 11:51 pm

WIederling wrote:
Channex757 wrote:
Just to be awkward, some Aston Martins and Ferraris have confused the issue too with a front mounted engine and gearbox at the rear. Apparently this helps with weight distribution.


Transaxle : All Daf "Variomatic" types, VW/Porsche 924

there seem to actually be two definitions around on what makes a "transaxle".
1: gearbox on the driven axle with engine detached and a long transmission shaft
Porsche 924 yes, beetle and all frontdrive cars no

2: gearbox combined with differential and wheel drive independent of where the engine sits.
essentially all cars that have a gearbox that includes differential and wheel drive


My Mazda 6 claims to have a transaxle gearbox (it's FWD). As long as it works, I don't really care what they call it.

My second car was an Alfetta 159i (seems to be a model unique to South Africa) -- it had a rear-mounted gearbox. Handled like a dream, but changing the clutch was an absolute nightmare!
 
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Re: Engine And Transmission Questions

Tue Sep 12, 2017 6:49 pm

tommy1808 wrote:
In fairness, that is just because most people never learn how to handle it. It is not exactly part of the normal driving school curriculum.


Surprised it's not mandatory in Germany. It wasn't either when I got my license, but these days students in my neck of the woods are not even allowed tuition on the road before they've been on a closed track, including time on a skidpad where they learn to handle over- and understeer. They also have to pass a mandatory 1st aid course, sit a minimum hours of theoretical training and minimum hours of driving tuition. Which is all good; the youngster getting a license these days are standing on a very solid foundation, which leads to fewer accidents and injuries.

Downside is the rather high cost of a license; which is around 2000EUR on average.
From receips and radials over straight pipes to big fans - been there, done that, got the hearing defects to prove
 
Flighty
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Re: Engine And Transmission Questions

Tue Sep 12, 2017 7:30 pm

BreninTW wrote:
And some thoughts on your initial question on engine placement ...

Front engine/front-wheel drive (FF):
Pros:
    Better packaging. Most FF cars have the engine mounted longitudinally, so it takes up less room in the front of the car, meaning you can have a larger passenger cabin in the same footprint. You also don't have a huge transmission tunnel.
    It's more difficult to induce oversteer where the back of the car tries to pass the front of the car in a bend.
Cons:
    Having all the weight at the front of the car lends itself to understeer -- the car wants to go straight instead of following a bend.
    The mechanics of having the same set of wheels driving and turning leads to a larger turning circle, and also slightly more expensive maintenance and components.

Front engine/rear-wheel drive (FR):
Pros:
    Relatively simpler and cheaper to design and build.
    Many drivers prefer the feeling of being "pushed" rather than "pulled".
    Engine bay is less crowded.
    Smaller turning circle.
Cons:
    It's easy to induce oversteer, which most drivers are unable to counter effectively. This quickly leads to spin-outs.
    Packaging is more challenging: Engines are mounted front-to-back and a transmission tunnel is required. This can make the cabin more cramped.
    Ultimate handling requires expensive independent suspension and a complicated drive system at the rear.

Mid-engine/rear-wheel drive (MR):
Pros:
    Better weight distribution leads to better handling characteristics.
    Smaller turning circle.
Cons:
    It's almost impossible to have more than two seats.
    Engine access can be a pain.

Rear engine/rear-wheel drive (RR):
Pros:
    Better packaging. The engine is typically mounted longitudinally, so it takes up less room, meaning you can have a larger passenger cabin in the same footprint. You also don't have a huge transmission tunnel.
    Many drivers prefer the feeling of being "pushed" rather than "pulled".
    Smaller turning circle.
Cons:
    Engine access can be a pain.
    It's easy to induce oversteer, which most drivers are unable to counter effectively. This quickly leads to spin-outs.
    Requires most complex controls and independent rear suspension.
    Engine controls can be challenging to maintain.

I occasionally drove an ambulance based on a 1974 VW transporter (RR layout) -- forward of the engine it was wonderful and easy to work in, but loading patients over that engine at the back was insanely difficult (and yes, we did have to carry a patient a time or two!)


This is a really good summary. About seb's question, why do hybrids not have manual transmissions? Actually, the Honda Insight and (IIRC) Honda Civic Hybrid DID come with manual transmissions. There is no real reason why you can't do it. But today's automatic gearboxes are now more efficient than manual transmissions, partially because they have more gear ratios. In the past, a 4 speed automatic was pretty inefficient.

Another thing to note is that hybrids often use Atkinson cycle engines. My understanding is they have less torque. But the electric motor's torque can mask this, allowing you to use the more efficient Atkinson cycle, which seems to be a simple engineering change.

Why does a Toyota Prius have a CVT rather than a conventional automatic? Probably many reasons. Hybrids tend to more often have CVT compared to normal cars. This leads me to think the engineers at Toyota (and Ford, Hyundai and others) are able to strike the best efficiency and drivability compromise with CVT as opposed to an automatic. But that it mainly applies to hybrids. All those manufacturers still prefer to use conventional automatics for their gas cars. I guess automatic is less good at marrying up with hybrid.
 
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BreninTW
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Re: Engine And Transmission Questions

Tue Sep 12, 2017 11:58 pm

Flighty wrote:
Why does a Toyota Prius have a CVT rather than a conventional automatic? Probably many reasons. Hybrids tend to more often have CVT compared to normal cars. This leads me to think the engineers at Toyota (and Ford, Hyundai and others) are able to strike the best efficiency and drivability compromise with CVT as opposed to an automatic. But that it mainly applies to hybrids. All those manufacturers still prefer to use conventional automatics for their gas cars. I guess automatic is less good at marrying up with hybrid.


Hybrids are mostly about efficiency -- especially your daily-driver hybrids (Prii, etc.) CVTs are up to 20% more efficient than a traditional automatic. That alone makes the CVT + Hybrid drivetrain an engineer's wet dream.

Big problems with CVTs is that they feel like exactly what they are (in effect) -- big rubber bands! Apparently the latest generation CVTs are much better feeling, but I have no experience with them. The last CVT I drove was a Mitsubishi Lancer which was a couple of years old. I must admit that I felt very little difference between the CVT in that car, and the auto in my older Nissan. I have noticed that Toyota has switched from CVT to 8-speed auto in the latest generation Camry, which was, I believe, due to customer feedback. Toyota seems to have stuck with CVTs in its smaller cars.

Hyundai uses a DCT with its hybrid drivetrain. Ford uses a CVT in the Fusion (I think the Ford platform is Toyota sourced though). Nissan has stuck with the CVT for now. Mazda is bonded to the traditional auto for life apparently (and it's a fine piece of engineering, I have to say!)

The fine print: Drivetrains and gearboxes may vary depending on which country you are in. I tend to follow what's available in Taiwan and Europe more than what's available in the US.
 
tommy1808
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Re: Engine And Transmission Questions

Wed Sep 13, 2017 4:50 am

B777LRF wrote:
Downside is the rather high cost of a license; which is around 2000EUR on average.


oh.. that is about what you pay for your 30 or so driving lessons plus theory plus test fee in Germany as well. But i was still out on a main street within one or two minutes after the beginning of my first lesson.

I do however agree with my former driving teacher that some driving experience is needed before a safety driving training is really meaningful, which is why he insisted on those ~2 years waiting time.

Thinking about myself being young, i am not sure if some sliding fun wouldn´t have made me overconfident.

best regards
Thomas
Times are changing: 70 years ago the USA went to war to defeat the Nazis, now they elect them to run their country.
 
WIederling
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Re: Engine And Transmission Questions

Wed Sep 13, 2017 8:29 am

B777LRF wrote:
.... including time on a skidpad where they learn to handle over- and understeer. T....
Downside is the rather high cost of a license; which is around 2000EUR on average.


Everything the same in Germany ( inclusive of excessive cost ) but for the skidpad training.

.. "no triggers", keep away from the taped areas! i.e. driving at the limit
is not trained because you are not supposed to ever go there ( dumb position, I know :-)

What I noticed here is that young drivers ( especially the female ) again sit much too near
the wheel to be able to have full control. This was last prevalent in the 60ties.
So close, bust was locking into the steering wheel rim and spokes.
Murphy is an optimist
 
WIederling
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Re: Engine And Transmission Questions

Wed Sep 13, 2017 8:35 am

"Why does a Toyota Prius have a CVT rather than a conventional automatic?"

For the Prius the CVT is an integral part of the electric parts of the drivetrain.
You have two electric motors in different positions in the gearbox and
transfer power not only from/to the battery but also between the two motors
creating the visible CVT properties.

It is not a mechanical CVT like:
https://en.wikipedia.org/wiki/Continuou ... triebe.png
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Aesma
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Re: Engine And Transmission Questions

Wed Sep 13, 2017 8:50 am

What about mechanics ? The driving license course in France was altered recently so that students must know what's under the hood, my sister just passed it so I questioned her, you could put her behind the wheel of an electric car and tell her it's an automatic, she wouldn't even notice there is no IC engine !
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