Why no 4 wheel drive on roads?

[Agvg]

When will a diesel electric drivetrain become std on small tractors? Then you could cheap and easy had the same system whith independent front and rear.

 

[RoostersGarage]

After clocking close to 200,000 miles in an AWD Subaru with the silicon drive technology, I can say that was a terrible design. Apply too much torque and the viscous coupling locks up, enabling 4 wheel drifts. When it got cold, it didn't work as well as when it was hot outside and I really wanted it to work better in the winter when driving on ice. I went a lot of places in that car and a lot of times didn't have to think about the road condition. However, I was in a loaner automatic while mine was in the shop and their automatic system was 100 times better than the old faithful silicon drive system. The automatic/electronic version was better in every way, except when something broke. I even noticed a power difference between the two and the automatic/electronic system seemed to have more power. I can only imagine there were mechanical losses in those couplers.

That's my point about tractors. They are already expensive enough, and for the average buyer the old faithful mechanic 4wd system is very good. When you're looking at a 35 hp tractor or less, there's not much power to lose. Not to mention those tractors are bought by homeowners and everything is already expensive enough. I can absolutely see a need for a full time 4wd system in big tractors that aren't trailered from one field to the next, or haul the crop to the market on the roads.

 

[LouNY]

When will a diesel electric drivetrain become std on small tractors? Then you could cheap and easy had the same system whith independent front and rear.

How about small trucks and tractors, that is a drivetrain that I have wished for for a long time.
A decent sized battery pak, a small diesel tuned for economy at a couple of different rpm's driving a generator
to power the vehicle and recharge the battery.
It could supply the AC power and the vehicle heat.

 

[Jims1025R]

One other thing to remember, on a hard surface, if you're in 4WD, too fast into a corner, and you come off the throttle quickly and/or apply [rear wheel] brakes, the front wheel is now providing braking through the drivetrain, which you did not intend. The now braking front wheel won't steer as well, and tends to want to induce a rollover in a turn when slowing.

 

[PILOON]

You will have no doubt noticed that most tractors have smaller wheels up front.
Being smaller they will wear faster than the rears and that's why they usually are slightly oversized than if a perfect match, usually by about 5%.
They refer to this as 'lead'. i.e., they lead by 5%.
I would assume when fronts are 'near bald' there is no longer any binding.

To have a true full time 4 wheel drive you'd need all 4 wheels to be the exact same size.

 

[RoostersGarage]

To have a true full time 4 wheel drive you'd need all 4 wheels to be the exact same size.

Always!! That means when mud is stuck on the backs but not the fronts, the full time 4wd system would be fighting this difference and have to allow slippage somewhere.

 

[Agvg]

How about small trucks and tractors, that is a drivetrain that I have wished for for a long time.
A decent sized battery pak, a small diesel tuned for economy at a couple of different rpm's driving a generator
to power the vehicle and recharge the battery.
It could supply the AC power and the vehicle heat.

Nissan e-power is close, no diesel but all electric drive train with a gas engine and battery.

 

[ning]

To have a true full time 4 wheel drive you'd need all 4 wheels to be the exact same size.

They could all 4 be different sizes, but you'd get a lot of wear in the differentials unless you had gearing to compensate for the different wheel sizes.

Note that I'm not saying it's reasonable to do what I stated.

 

[DieselBound]

I was advocating diesel-electric way back when Priuses were coming on the scene. But as far as for a tractor... Whereas a transportation vehicle can be viewed as operating two-dimensionally a tractor would be operating three-dimensionally.

How to load balance across travel and loader work (PTO operations tend to fairly constant) would be tricky. Maintaining sense of and actual fluidity might be tough.

Electrical stuff can be a lot more sensitive to harsh environments than flat-out metal.

 

[LouNY]

Big mine and off road equipment has been that way for years,