Electric motors in series with unconnected shafts

[Nigel Goodwin]

The only 4X4 I ever had problems driving with 4WD engaged was my last Chevy S10. It had the front axle changed at some time in its life. The front had a different ratio in it than the rear, worked great off road but chattered badly on a paved surface with the front engaged.

I've had too many to count 4X4s in my life, starting with Jeeps and other than the last S10 have had no problems when driving at speeds under 55MPH in 4WD. The truck I'm driving now is a extended cab Chevy Silverado, and works just fine in 4WD on the road, did it just a couple of weeks ago during a bad snow fall here.

Stuff like you guys are talking about must not have the same ratio at both ends. I was in a 4WD club years ago and no one ever complained about what you guys are talking about, we drove Jeeps, Land Cruisers, Chevy trucks and Ford trucks All with no road complaints.

I'm talking about brand new vehicles, so no 'wrong parts', and the 'problem' is explained in the owners manuals. If you don't have some way of allowing the speed to vary between axles (like a centre diff) then you will get problems on high grip surfaces like clean roads.

Incidentally, I mentioned 'Vintage Voltage' above, and a vehicle they converted the other week was a series 2 Land Rover, and they removed all the diffs and replaced them with 'something else' - can't remember what they were called, but essentially three limited slip diffs, so all wheels were driven at all times, but not at the same speed.

 

[Diver300]

According to this:- https://www.caranddriver.com/chevrolet/silverado-1500/specs the Silverado has a curb to curb turning circle of 50.2 feet (wow, just over twice that of my first car!), which is a radius of 301.2 inches, a wheelbase of 156.95 inches, and a width of 81.24 inches. Assuming that the front wheels are about as wide as the car, I calculate that at full lock the front wheels travel 23.5% further than the rear wheels.

There is no way that amount of speed difference would be taken up without a lot of complaint from the tyres if there was no central differential or something similar.

I know that there are various different methods of dealing with the speed difference. There can be a manual dog clutch like the early Land Rovers, a centre differential, or a viscous coupling. Some cars had the front wheels geared to turn slower than the rear wheels, but driven with a freewheel so that the drive is only taken up when rear wheels slip.

 

[Nigel Goodwin]

According to this:- https://www.caranddriver.com/chevrolet/silverado-1500/specs the Silverado has a curb to curb turning circle of 50.2 feet (wow, just over twice that of my first car!), which is a radius of 301.2 inches, a wheelbase of 156.95 inches, and a width of 81.24 inches. Assuming that the front wheels are about as wide as the car, I calculate that at full lock the front wheels travel 23.5% further than the rear wheels.

There is no way that amount of speed difference would be taken up without a lot of complaint from the tyres if there was no central differential or something similar.

I know that there are various different methods of dealing with the speed difference. There can be a manual dog clutch like the early Land Rovers, a centre differential, or a viscous coupling. Some cars had the front wheels geared to turn slower than the rear wheels, but driven with a freewheel so that the drive is only taken up when rear wheels slip.

Years ago my boss where I used to work swapped his Audi Quatro for a Ford Sierra 4x4 (why? - always looked like a stupid idea). While the Quatro was flawless the Ford juddered and shook at various speeds, and eventually an engineer was send out from Ford to look at it, as the local dealer couldn't sort it. The Ford engineer simply explained that it only had two diffs, and a viscous coupling in the middle - this was the cause of the juddering, as it really needed a third diff - tough ****, it's just how they were.

 

[shortbus=]

I'm talking about brand new vehicles, so no 'wrong parts'

Just because they are new doesn't mean they necessarily have the same differential ratio.

All I'm saying is my experience has been very different than you guys. Either that or I've been very lucky.

 

[Pommie]

I calculate that at full lock the front wheels travel 23.5% further than the rear wheels.

I must be missing something. The outer wheels will have to travel further than the inner ones but why will the front wheels travel further than the back?

Mike.

 

[Diver300]

I must be missing something. The outer wheels will have to travel further than the inner ones but why will the front wheels travel further than the back?

Mike.

The short answer is that the front wheels run wider when turning a corner. If you cut a corner when driving, and clip a kerb on the inside, it's always the inside rear wheel that clips the kerb, because the front wheels are further away, and therefore turning faster.

A longer answer is that a car will be turning around a centre point. A line through the rear axle will go through that centre point. A right-angle triangle will be formed with apexes as the centre of the turning circle, the middle of the rear axle and the middle of the front axle. The hypotenuse, the longest side, joins the middle of the front axle with the centre of the turning circle.

As the whole lot is rotating at the same rate, the speed over the ground is proportional to the distance from the centre of the turning circle, so the front axle, which is further from the centre of the turning circle, is moving faster.

In this picture the inside front wheel is about as far from the centre of the turning circle as the middle of the rear axle. The outside front wheel is furthest from the centre. The average speed of the front wheels will be quite a bit more than the average speed of the rear wheels.

It's more complicated if the rear wheels steer. The wheels doing the most steering will be the ones turning fastest.

 

[Nigel Goodwin]

Just because they are new doesn't mean they necessarily have the same differential ratio.

But it does mean it will be correct, whatever it might be (you would hope).

All I'm saying is my experience has been very different than you guys. Either that or I've been very lucky.

Presumably you manually set it to 4WD? - so why if there's no need for it? - you're just wasting fuel, reducing performance, and increasing tyre wear.

Try reading the user manual, assuming you have it, see what it tells you about using 4WD.

 

[shortbus=]

The short answer is that the front wheels run wider when turning a corner

That would be true if the vehicle didn't use the Ackerman principal. And if in normal diving you went lock to lock with the steering, which you don't.

Like many things in the real world, there is engineering "theory" and then there is real world practicality. As a machinist my whole adult life I have been exposed to that, doing something to make a part that the text book says isn't possible or can't be done.

 

[Nigel Goodwin]

That would be true if the vehicle didn't use the Ackerman principal. And if in normal diving you went lock to lock with the steering, which you don't.

Like many things in the real world, there is engineering "theory" and then there is real world practicality. As a machinist my whole adult life I have been exposed to that, doing something to make a part that the text book says isn't possible or can't be done.

You didn't answer why you're selecting 4WD under normal road conditions?.

No one is suggesting that it's 'not possible', just that it's a very bad idea that causes increased wear and poorer performance.

You might like to have a look here:

4-Wheel Drive Jerks When Turning: SOLVED - 4-Wheel Drive Guide

4-Wheel Drive Jerks When Turning

4wheeldriveguide.com

 

[shortbus=]

You didn't answer why you're selecting 4WD under normal road conditions?.

I never said I did that, you seem to have missed where I said my latest use was during a heavy snow storm, before they got around to plowing the roads. I'm saying it doesn't do what you guys claim it will if it's done. And, that in selective 4WD, ones with a transfer case and NOT a center differential it works. The so called "AWD" all wheel drive, needs to have a center differential, because the vehicles driver never knows when the front axle will kick in. That kicking in, powering up the front wheels if not expecting it makes the center diff necessary. With a selective 4WD you know what to expect and drive accordingly.

 

[Diver300]

That would be true if the vehicle didn't use the Ackerman principal. And if in normal diving you went lock to lock with the steering, which you don't.

Ackerman steering is about pivoting the inside wheel more than the outside one, so that the centre lines of all the wheels intersect, which should eliminate the wheels being forced sideways. That has very little to do with the distance covered by the wheels. The illustration that I used was there to show what Ackerman steering does, but I used it because it also shows quite well that the front wheels are further from the centre of the circle than the rear wheels, and therefore travel further when cornering.

Steering at full lock will increase the margin by which the steered wheels go faster than the non-steered wheels. It's also non-linear, so the effect at half way to full lock will be less than half of the effect at full lock. However, it doesn't make much difference how quickly the steering is turned or what the car was doing before hand, so I can't see what you mean about going from lock to lock with the steering. On the Silverado that I used as an example, a U-turn at full lock will result in the front wheels travelling 70 feet and the rear wheels travelling 56 ft 8 inches (both figures are averages for the axle), and that difference has to be made up by either tyre slip or something in the drive mechanism.

I guess that very short distances at full lock, such as when doing a three-point turn, may mean that there is enough play in the driveline to allow for the difference. Also, if the drive-line play has been taken up in one direction, the play will be taken the other way when the car reverses, so going forwards and backwards will reduce any problems.

 

[Nigel Goodwin]

I never said I did that, you seem to have missed where I said my latest use was during a heavy snow storm, before they got around to plowing the roads. I'm saying it doesn't do what you guys claim it will if it's done. And, that in selective 4WD, ones with a transfer case and NOT a center differential it works.

So what are arguing you about? - you're agreeing with everything that's been said.

The issue is (as has been said throughout this thread) using 4WD under normal road conditions - driving in snow on a road using 4WD is perfectly fine, and what 4WD is designed for. As is driving on loose surfaces like gravel, or fields etc. anything where the wheels can slip easily.

I happily drove up the motorway in 4WD a few years ago, to fetch my daughter back from the airport -there were areas were the motorway was completely covered in snow, and others where it was clear - just switch 4WD on and off as required.

 

[shortbus=]

Steering at full lock will increase the margin by which the steered wheels go faster than the non-steered wheels.

But in the end that also works for all rear wheel drives to. Have you seen the videos or on TV of cars on asphalt or concrete doing "donuts"? 2WD cars with powerful engines spinning the rear wheels and basically rotating around the inside front wheel. So it is not just a 4WD thing.

And who makes a U turn at speed?

 

[shortbus=]

So what are arguing you about? - you're agreeing with everything that's been said.

The issue is (as has been said throughout this thread) using 4WD under normal road conditions - driving in snow on a road using 4WD is perfectly fine, and what 4WD is designed for. As is driving on loose surfaces like gravel, or fields etc. anything where the wheels can slip easily.

I happily drove up the motorway in 4WD a few years ago, to fetch my daughter back from the airport -there were areas were the motorway was completely covered in snow, and others where it was clear - just switch 4WD on and off as required.

Again your changing the topic. You say, "just switch 4WD on and off as required", that means it's not AWD, with AWD it chooses when to go into front and rear drive. Unless like many things your side of the pond is different than here.

My argument is you people saying you CAN'T use 4WD on normal surfaces, and that is just wrong. May not be something you want to do every day but it is possible, with no real problems other than wear on the drive train.

 

[Diver300]

But in the end that also works for all rear wheel drives to. Have you seen the videos or on TV of cars on asphalt or concrete doing "donuts"? 2WD cars with powerful engines spinning the rear wheels and basically rotating around the inside front wheel. So it is not just a 4WD thing.

And who makes a U turn at speed?

I know that donuts can be done, but the wheels are slipping so that's not what we are talking about.

I did mention speed in my earlier posts, but not in the post about a U-turn.

I've not meant to imply that any of the tight turns would be performed a high speeds. If a manoeuvre results in one wheel travelling, for instance 10% further than another wheel, then the one wheel will be at a 10% higher speed, even if the speeds are very low compared to highway driving.

I should have used the word "distance" instead of "speed" in a few cases.

 

[Nigel Goodwin]

Again your changing the topic. You say, "just switch 4WD on and off as required", that means it's not AWD, with AWD it chooses when to go into front and rear drive. Unless like many things your side of the pond is different than here.

We were talking about 4WD - not AWD.

My argument is you people saying you CAN'T use 4WD on normal surfaces, and that is just wrong. May not be something you want to do every day but it is possible, with no real problems other than wear on the drive train.

Massive wear on the drive train, high risk of it failing, poor (dangerous) handling, massive tyre wear, much higher fuel consumption, juddering is common - why on earth would you do it?.

Driving your car head on into a bridge is 'possible', but I wouldn't recommend that either?.

But in the end that also works for all rear wheel drives to. Have you seen the videos or on TV of cars on asphalt or concrete doing "donuts"? 2WD cars with powerful engines spinning the rear wheels and basically rotating around the inside front wheel. So it is not just a 4WD thing.

And who makes a U turn at speed?

In order to do that they simply weld the differential together, deliberately making a similar (but even worse) situation to using 4WD on normal roads Oh, and fit a huge powerful engine

As I understand it, it's very big in Japan - and one of the car restoration TV programmes over here has a very attraction young blond lady as part of the team, and she's a champion at the sport.

Seems pretty pointless to me, but you can't deny there's a huge amount of skill involved.

 

[shortbus=]

I give up. You guys will never see things from my point of view and from my own experiences, I can't see your point of view.