Instant Torque (Electric Cars vs. Gas/Diesel Cars)

Ryuk1990
So I hear a lot about how electric cars are great because electric motors get instant max torque at 0 RPM.

However, can't the same be done with an internal combustion engine if you have a clutch?

Kozy
No. Run an ICE to slow and it will stall. Even below about 2000rpm in most engines, there is very little torque.

1 person
Staff Emeritus
Homework Helper
That pesky transmission is there for a reason, and it's not to give you an extra hand rest.

1 person
Ryuk1990
I'm not familiar with stick shift cars at all (or car mechanics in general) so bare with me as I have no idea what I'm talking about. But can't you rev up the engine to its max torque almost instantly using a clutch without moving the car and THEN hit the pedal to get that same feeling of instant torque that you would get from an electric car?

Gold Member
I'm not familiar with stick shift cars at all (or car mechanics in general) so bare with me as I have no idea what I'm talking about. But can't you rev up the engine to its max torque almost instantly using a clutch without moving the car and THEN hit the pedal to get that same feeling of instant torque that you would get from an electric car?

Yes, but this involves the clutch slipping. If you do that a lot, the clutch will wear out prematurely. Have you ever changed brake pads? Changing the clutch disk is about 100 times worse, as it involves removing the engine, transmission, or both.

Typical costs:
Having a clutch replaced can cost $400 -$3,000 or more, depending on the make, model and type of vehicle;

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Staff Emeritus
Homework Helper
More likely, you'll stall the engine.

Hit what pedal?

With a manual transmission, the clutch is disengaged to allow the engine to run without load. Consequently, it takes very little throttle to rev the engine to its max. torque RPM. If you put the transmission into its highest (1:1) ratio and engage the clutch, the engine still must overcome the inertia of the car before movement can take place. More often than not, doing this will stall the engine rather than getting the car to move. Also, since the clutch is a friction device, engaging it repeatedly at high RPM will rapidly burn out the friction plates, requiring a costly clutch replacement.

Doing the same thing with an automatic transmission may not stall the car, but soon you will need a new transmission, which is even more costly to replace than a clutch.

1 person
xxChrisxx
I think the main point to take is that there is a difference between having torque being produced at a specific high RPM and slipping something to achieve pull away, and having produced at zero RPM.

1 person
Highspeed
Ryuk1990, Yes, what you're talking about is possible. You can just dump the clutch at peak torque. You will get the results above though....fast wear and broken parts. You could also use a slipper clutch that will only lock-up above a certain rpm. It's not instant, but will allow the engine to rev up before being loaded at peak torque (or whatever rpm you set it for). You could also use a high-stall torque converter. It doesn't hammer the drivetrain like a clutch, but creates a whole lot of very hot transmission fluid, so you'll need a good cooler. Driveablitlity would be poor with a slipper clutch or converter that stalled that high, so daily use wouldn't be possible. Is there a point beyond a theoretical question? It's going to be a loooooooong time before a Prius can pull a travel trailer, or before an electric truck can pull a semi-trailer for 500 miles a day. ICE vehicles overcome the lack of instant torque through gearing, so there is really no need to turn an ICE into an electric motor.

1 person
Ryuk1990
Is there a point beyond a theoretical question? It's going to be a loooooooong time before a Prius can pull a travel trailer, or before an electric truck can pull a semi-trailer for 500 miles a day. ICE vehicles overcome the lack of instant torque through gearing, so there is really no need to turn an ICE into an electric motor.

It was more about having that fast smooth acceleration that the Tesla Model S offers with an ICE car.

Staff Emeritus
Homework Helper
Most cars with automatic transmissions accelerate quite smoothly from stop to highway speeds. The shift points of the transmission provide a momentary change in the sound of the engine as the revs drop, but other than that, everything is quite smooth. Also, new transmissions have up to eight speeds, rather than the three or four or older transmissions, making the process even smoother, as the engine revs do not need to drop as much between shifts.

It might be you are thinking of the so-called Continuously Variable Transmission (CVT), which doesn't operate using conventional reduction gears.

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

These transmissions allow the engine to maintain a constant speed as the vehicle accelerates. Although such transmissions have been used in a variety of automotive applications, several factors have kept them from replacing conventional transmission designs (see the article above for more details).

1 person
Homework Helper
It was more about having that fast smooth acceleration that the Tesla Model S offers with an ICE car.

Tesla S: 0-60 in 5.4 sec, top speed 125 mph, "handles like a sedan" (to quote the Tesla website)
Porsche 911S turbo: 0 - 62 mph in 3.1 sec, 0-124 mph in 10.3 sec, top speed 200 mph, handles like a car.

Homework Helper
But can't you rev up the engine to its max torque almost instantly using a clutch without moving the car and THEN hit the pedal to get that same feeling of instant torque that you would get from an electric car?

Yes, but this involves the clutch slipping. If you do that a lot, the clutch will wear out prematurely.

That depends on the design of the clutch. Back in the 1970s I used to drive a british-designed sports car with a 6 speed gearbox. More accurately, it had a 4 speed conventional box and pedal-operated clutch, and a separate epicyclic gearbox and clutch that was operated electrically from a switch in the top of the gearstick, to switch between gears 3 and 4, or 5 and 6. (The manual box and clutch selected either 1,2,3,5 or 1,2,4,6).

The epicyclic gear change was designed to operate at any engine RPM and throttle position, and changed gear in less than a second. Floor the throttle, flip the switch, and get a kick in the back ... (or on a bad hair day, over-rev the engine when changing down without first engaging brain).

xxChrisxx
That depends on the design of the clutch. Back in the 1970s I used to drive a british-designed sports car with a 6 speed gearbox. More accurately, it had a 4 speed conventional box and pedal-operated clutch, and a separate epicyclic gearbox and clutch that was operated electrically from a switch in the top of the gearstick, to switch between gears 3 and 4, or 5 and 6. (The manual box and clutch selected either 1,2,3,5 or 1,2,4,6).

The epicyclic gear change was designed to operate at any engine RPM and throttle position, and changed gear in less than a second. Floor the throttle, flip the switch, and get a kick in the back ... (or on a bad hair day, over-rev the engine when changing down without first engaging brain).

It doesn't make any difference on design, a slipping friction clutch transmissting lots of torque will wear prematurely.

And a British 70's sports car in the US.... an MGB?
What you are describing is an overdrive in 3rd and 4th.

The solenoid should automatically disengage the overdrive in 2nd and 1st. If/when it fails, and you can engage the overdrive in the lower gears, it slips and wears the cone clutch out. Also the overdrive is not designed to give you 'a kick in the back'. It's designed for cruising.

The reason for the lurch when you engage the overdrive whilst still having the throttle open is that wheels suddenly wanted to be travelling much faster than the road speed (as overdrive is effectively a longer gear). Two things can happen in this case, the wheels slip or the overdrive clutch slips to synchronise the road and engine speed. As it's rather dangerous for the wheels to start slipping at high speed, the clutch was designed to slip first.

This abuse of the overdrive clutch is what caused MG to stop the overdrive from engaging in 3rd on later cars

sgb27
More likely, you'll stall the engine.

Hit what pedal?

With a manual transmission, the clutch is disengaged to allow the engine to run without load. Consequently, it takes very little throttle to rev the engine to its max. torque RPM. If you put the transmission into its highest (1:1) ratio and engage the clutch, the engine still must overcome the inertia of the car before movement can take place. More often than not, doing this will stall the engine rather than getting the car to move.
The technique asked about by the OP involves flooring the throttle and then controlling the clutch pedal to ensure RPMs stay around max torque (gradually engaging it as car speed builds) - if you're stalling the engine you're engaging the clutch too quickly.

Staff Emeritus
Homework Helper
The technique asked about by the OP involves flooring the throttle and then controlling the clutch pedal to ensure RPMs stay around max torque (gradually engaging it as car speed builds) - if you're stalling the engine you're engaging the clutch too quickly.

Perhaps so, but it is a maneuver which I think could only be accomplished with not a little skill and a fairly robust clutch. All in all, even with the best technique, I still see a much shorter clutch life, perhaps shorter engine life to boot.

Tesla S: 0-60 in 5.4 sec, top speed 125 mph, "handles like a sedan" (to quote the Tesla website)
Porsche 911S turbo: 0 - 62 mph in 3.1 sec, 0-124 mph in 10.3 sec, top speed 200 mph, handles like a car.

That's not really a fair comparison though, since the Tesla is a much different car in a completely different category of size and performance (and is half the price of a 911 Turbo S). A BMW M5 or Audi RS6 would be a much better comparison (and should still win in all performance metrics).

Gold Member
No. Run an ICE to slow and it will stall. Even below about 2000rpm in most engines, there is very little torque.

Interesting. I just drove a Volvo semi-tractor with a Detroit diesel in it and it governs out when it approaches 2000 RPM. ALL the torque is below 2000. Yes, the thread is about diesels too.

xxChrisxx
That's not really a fair comparison though, since the Tesla is a much different car in a completely different category of size and performance (and is half the price of a 911 Turbo S). A BMW M5 or Audi RS6 would be a much better comparison (and should still win in all performance metrics).

It's ironic that you picked two cars with pretty much the same power as the 911 turbo s. New Golf R. 300bhp and 0-60 in 4.8 with the DCT.

Hot hatch progress... its mind bending.

Gold Member
Generally with ICE the larger the displacement the lower the rpm at which it makes max torque. If you want more torque without having to rev the engine just get a bigger engine.

Here's a 14 cylinder diesel that makes over five million foot pounds of torque at only 102 rpm
http://en.wikipedia.org/wiki/W%C3%A4rtsil%C3%A4-Sulzer_RTA96-C

sgb27
Perhaps so, but it is a maneuver which I think could only be accomplished with not a little skill and a fairly robust clutch. All in all, even with the best technique, I still see a much shorter clutch life, perhaps shorter engine life to boot.
Isn't this what everyone does when they try to pull away "quickly" in a manual transmission (eg pulling out onto a busy road)? You rev the engine up a bit (to around max torque), then release the clutch in a controlled manner whilst pressing the accelerator harder to keep the rpms more or less constant. In most cars the clutch will only slip for a fraction of a second until the car is moving fast enough to match the 2000-3000rpm. Yes it does wear the clutch more than a slower pull-away, but it's not going to destroy anything. Try the same technique in 2nd or 3rd gear, then you'll smell the clutch burning away :-)

Staff Emeritus
Homework Helper
Isn't this what everyone does when they try to pull away "quickly" in a manual transmission (eg pulling out onto a busy road)? You rev the engine up a bit (to around max torque), then release the clutch in a controlled manner whilst pressing the accelerator harder to keep the rpms more or less constant. In most cars the clutch will only slip for a fraction of a second until the car is moving fast enough to match the 2000-3000rpm. Yes it does wear the clutch more than a slower pull-away, but it's not going to destroy anything. Try the same technique in 2nd or 3rd gear, then you'll smell the clutch burning away :-)

Maybe you can do this all day in a little four-banger car, but you take a big torquey V8 and drop the clutch at 3000 rpm, you will wear out your tires. You don't always have to smell the clutch plate burning to bring the day for a new clutch closer to today.

Staff Emeritus
Homework Helper
Generally with ICE the larger the displacement the lower the rpm at which it makes max torque. If you want more torque without having to rev the engine just get a bigger engine.

Here's a 14 cylinder diesel that makes over five million foot pounds of torque at only 102 rpm
http://en.wikipedia.org/wiki/W%C3%A4rtsil%C3%A4-Sulzer_RTA96-C

The Sulzer engine is specially designed to operate at low RPM because it is directly connected to the propeller of a ship. A propeller of the size used to drive the ship operates most efficiently at this low speed. For smaller craft, higher speed diesels are used with reduction gears so that the engine can operate at its most efficient speed while the propeller operates at its most efficient but slower speed.

sgb27
Maybe you can do this all day in a little four-banger car, but you take a big torquey V8 and drop the clutch at 3000 rpm, you will wear out your tires.
The question was whether you can make an ICE generate peak torque at 0mph (as electric motors can), what happens at the tyres is exactly the same for electric and ICE. If you had a powerful enough electric motor and commanded it to generate peak torque from 0mph all day you would also wear out your tyres.

Gold Member
so there is really no need to turn an ICE into an electric motor..

Besides the 0 rpm torque question there is the advantage of efficiency. The electric motor is far more efficient tank to wheels than the ICE, and always will be.

Homework Helper
So I hear a lot about how electric cars are great because electric motors get instant max torque at 0 RPM.
Peak torque for an electric motor occurs at 0 rpm and decreases linearly until it become zero torque at max rpm. Internal combustion engines produce peak torque at some rpm, but with an ideal CVT (continously variable transmission), peak torque delivered to the rear wheels occurs at the rpm corresponding to peak power.

However, can't the same be done with an internal combustion engine if you have a clutch?
Yes, or with a CVT.

Note that the limiting factor for peak torque at the driven tires is limited to the amount of traction available. Dropping the clutch at high rpms or attempting to apply peak torque from an electic motor onto the driven wheels could result in the wheels spinning, assuming sufficient torque at low speeds is enough to spin the driven wheels.

Diesel electric locomotives use diesel engines to drive generators which in turn deliver electricity to electric motors directly attached to the driven wheels of the locomotive. It's a heavy equivalent to a CVT, but heavy is a good thing for locomotives (to get enough traction to pull the remainder of a train).

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Staff Emeritus
Homework Helper
Besides the 0 rpm torque question there is the advantage of efficiency. The electric motor is far more efficient tank to wheels than the ICE, and always will be.

I don't know what you mean by the statement that "The electric motor is far more efficient tank to wheels than the ICE, ..."

The electric motor is not a prime mover; it depends on an external source of energy, be it a battery, a fuel cell, Fred Flintstone running on a treadmill, whatever.

If you want to measure the efficiency of the electric motor compared to an ICE, you must compare like with like, i.e., for the electric motor, you've got to throw in the efficiency of the generating plant as well.

Gold Member
I ...
The electric motor is not a prime mover; it depends on an external source of energy
And that would be......
If you want to measure the efficiency of the electric motor compared to an ICE, you must compare like with like, i.e., for the electric motor, you've got to throw in the efficiency of the generating plant as well.

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It's ok to ban me. Really. I've things to do.

Gold Member
I don't know what you mean by the statement that "The electric motor is far more efficient tank to wheels than the ICE, ..."

The electric motor is not a prime mover; it depends on an external source of energy, be it a battery, a fuel cell, Fred Flintstone running on a treadmill, whatever.

If you want to measure the efficiency of the electric motor compared to an ICE, you must compare like with like, i.e., for the electric motor, you've got to throw in the efficiency of the generating plant as well.
"tank to wheels" is a common standard of efficiency found all throughout the literature. Its importance lies is due to the finite amount of energy is carried on board the platform. The efficiency of conversion of the on board energy source to motion is the critical measure of efficiency in determining both maximum range per energy carried and cost per unit distance traveled. Note this is the case regardless of the efficiency of the process used to make the carried energy.

So as I say, the typical electric motor as found in the currently available EVs has an efficiency of over 90%. The batteries are likewise about 90% efficient on discharge. The typical combustion engine and drive train currently on the road is around 15% efficient, moving to around 20% for the fleet of all new vehicles. The gap between the two, tank to wheels EV and ICE efficiency, will always be large due to thermodynamics.

Finally, we don't commonly see demands that ICE mpg calculations include the large energy overhead in refining oil to gasoline or the energy consumed in oil extraction.

Staff Emeritus
Homework Helper
That's what a prime mover is. You add fuel to the engine and get the work out. An electric motor has no tank, and you can't consider the charge in the battery to be the equivalent.

Gold Member
An electric motor has no tank, you can't consider the charge in the battery to be the equivalent.
Why not? It is commonly done.

Staff Emeritus
Homework Helper
A lot of things are commonly done, but that does not mean it is necessarily the correct way of doing things.

Look, a prime mover takes the potential energy stored in a quantity of fuel and turns that potential energy into useful work. We look at the work obtained versus the amount of energy contained in the fuel. The ratio of work obtained to energy input is the definition of thermal efficiency of a prime mover.

On the other hand, the electricity which charges a battery in an electric car doesn't come straight out of the ground. It has to be generated somewhere. In the US, with certain exceptions, electricity is generated by burning coal or natural gas. The potential energy contained in that coal or natural gas is the basis for ultimately generating the electricity which goes into the battery of an electric car. That must be the basis for realistically assessing the relative efficiency of two vehicles which use different means of propulsion.

Gold Member
A lot of things are commonly done, but that does not mean it is necessarily the correct way of doing things.

Look, a prime mover takes the potential energy stored in a quantity of fuel and turns that potential energy into useful work. We look at the work obtained versus the amount of energy contained in the fuel. The ratio of work obtained to energy input is the definition of thermal efficiency of a prime mover.

On the other hand, the electricity which charges a battery in an electric car doesn't come straight out of the ground. It has to be generated somewhere. In the US, with certain exceptions...

You mean like solar panels on your roof?

Gary Graunke said:
[Oeva-list] my first solar year with Leaf EV, solar PV, and TOU
...
I spent only $406 for over 11000 miles of travel and all the electrical needs of my house, including winter hot water. ... I think my favorite comment that he made was: The grid is a nice battery I can rent for$10.12 a month

Gary drives a Nissan Leaf, and has recently upgraded to a Tesla S. His garage mounted solar array is rated at 4900 watts.

I don't think he's into spinning tires though. We leave that, to Mr. Wayland.

Plasma Boy said:
...1250 foot pounds of torque, at zero [rpm]*

Only about 150 more than the \$2,500,000.00 Bugatti Veyron Super Sport.

*Trying to bring us back on topic.

Gold Member
Interesting article:

Jens Schulenburg claims that at full throttle the Super Sport/Vitesse engine will consume more air in one hour than a human does in a month, though that statistic is purely academic, because at full throttle the Vitesse's W-16 will gulp through an entire tank of gas -- 26.4 gallons -- in just eight minutes.

Good god. That's 3.3 gallons per minute.

Thank god it reaches 60 mph in only 2.5 seconds. Slightly less than a second slower than Mr. Wayland's '72 Datsun.

(Ha ha!)

Ryuk1990
Tesla S: 0-60 in 5.4 sec, top speed 125 mph, "handles like a sedan" (to quote the Tesla website)
Porsche 911S turbo: 0 - 62 mph in 3.1 sec, 0-124 mph in 10.3 sec, top speed 200 mph, handles like a car.

I just wanted to add that the Tesla Model S Performance goes 0-60 in 4.2 seconds.

Is the heaviness of lithium ion batteries what's slowing down electric cars? I mean, electric motors are superior to IC engines, right?

Gold Member
I just wanted to add that the Tesla Model S Performance goes 0-60 in 4.2 seconds.

Is the heaviness of lithium ion batteries what's slowing down electric cars? I mean, electric motors are superior to IC engines, right?

"superior" is a subjective term.

f=ma

which yields: a=f/m

therefore, with two vehicles with similar motive forces, the one with the smaller mass will have a higher acceleration value.

Tesla S:
Curb weight: 4,647.3 lbs
torque 430 Nm​

Porsche 911 S Turbo:
Curb weight: 3680 lb.
torque 710 Nm​

Given that the Porsche has both higher torque and weighs less, it's a no brainer that it's faster.

I don't believe the Tesla S was designed as an adrenalin pumper.

Tesla S mpge: 95
Porsche mpg: 19

You can try and power a car with a 99.99% efficient electric sewing machine motor.
That's much superior to the 25% efficiency of a 530 hp gasoline engine.

Yes?

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