What's The Auto 4 Wheel In Car

[sanny]

What is the auto 4 wheel in car

How it work with gear box

Advantages n disadvantages of having it

[Magnum]

The center differential will be present in most of the above setups but however locking the centre differential is a variable option from make to model. The center diff when locked provides an equal torque distribution to both the front and rear wheels, Useful when bogged down and aids traction and cornering in rally cars.

AFAIK the Fortuner lineage share the same part time 4wd setup as they are based on the pickup truck platform and internals, they do not have a centre differential, Some are factory fitted with a rear LSD or a Lockable rear differential, I'm not very sure about the Monterosport though.

Most of the newer vans are AWD rather than 4WD with a centre diff, where the front wheels engage automatically, but I've not seen the lock function though.

A bit of ignored trivia; all Defenders are AWD and come with a lockable center differential, completely mechanical almost to date and is activated by pulling the H-L shifter about 8" towards the driver, crude but effective

Is it the center diff which sends power between front and rear wheels in AWD?

bdw this is how the instrument cluster is in Montero Sport

You can see the 4WD display, notice the small box marked in between front and rear wheels That box blinks, I think when we put into 4L.

[iRage]

I had a V70 series Pajero sometime back and if I remember right the centre box blinks green when the diff is not locked and stay lit (and red ? might be a different car that turns red) when the diff is locked. I think in some modes the diff automatically gets locked.

As for the Fortuner and Hilux, I think the availability of a lockable centre diff is dependent on the market and model. I have seen both with and without a centre diff in different parts of the world. So...yeah....

In general, a diff basically lets axles on either side of it to spin at different speeds. For example in a normal car the diff would enable the right side wheel to spin at a different speed than the left side wheel and vice-versa when turning.

Okay so basics; you have your two axles front and back. You have your gear box and transfer case (which transfers power to the front, or rear depending on the car, when 4WD is engaged). In a 4WD system a part from the left and right side wheels turning at different speeds you have the added complexities of the rear set(axle) of wheels spinning at a different 'speed' than the front set (axle) of wheels. To deal with this the transfer case would need some apparatus like a centre diff or a viscous coupling.

A centre diff in a part time 4WD does the same thing as your normal diff; except now it deals with the rear set (axle) of wheels and the front set (axle) of wheels (turning at different 'speeds'). For clarity sake, imagine a drive shaft that goes from the front transfer case to the back with a differential in the centre splitting your front-rear drive shaft in to two parts. The centre differential will make it possible for the front half of the drive shaft to turn at a different 'speed' than the rear/back drive shaft part.

Some part time 4WDs have a center diff lock. When you engage the lock then both the front half and the rear half of the drive shaft will turn at the same 'speed', which helps the car to negotiate sticky (or slippery) situations.

EDIT: http://www.lcool.org/technical/diffs/diffs.html

Now in AWD systems you typically get a simple viscous coupling along with the transfer case which splits the 'speed' of the front and the rear wheels. Viscous couplings are less rugged than the standard old fashioned differential so you don't necessarily get viscous coupling systems in hardcore 4WD cars.

Why a simple viscous coupler or some sorts ? well..simpler...cheaper..lighter...and adequate for what most AWD cars are designed for.

So to answer your question...no you don:t get centre differentials in AWD cars (at least in its traditional sense). Granted the concept of viscous couplers have evolved over time where there are systems that mimic the functionality of an old school part time 4WD system including that of the centre differential.

Edited July 21, 2015 by iRage

[Magnum]

Thanks both of you! That was very helpfull

And yes Montero Sport has center diff lock as it has the Mitsubishi's Super Select 4WD system and yes our permit models have the same thing

http://www.offroadaussie.com/2013/06/mitsubishi-super-select-4wd/

[tiv]

Is it the center diff which sends power between front and rear wheels in AWD?

bdw this is how the instrument cluster is in Montero Sport

You can see the 4WD display, notice the small box marked in between front and rear wheels That box blinks, I think when we put into 4L.

Thanks both of you! That was very helpfull

And yes Montero Sport has center diff lock as it has the Mitsubishi's Super Select 4WD system and yes our permit models have the same thing

http://www.offroadaussie.com/2013/06/mitsubishi-super-select-4wd/

So is your Hiace an AWD? If I recall the KDH205 was AWD, considered one myself once, is the 206 the successor?

[Magnum]

So is your Hiace an AWD? If I recall the KDH205 was AWD, considered one myself once, is the 206 the successor?

Yeah its got auto AWD( turns on when needed) but im not sure if its got diff lock.

people say that the AWD comes only below 20km/h but I dont think thats tue, its suposed to come on at any speeds and it does feel very stable at high speeds.

KDH206 is AWD with 3litre 1KD engine and KDH205 is 2,5L 2KD engine with AWD. KDH200 and KDH205 re discontinued now

[iRage]

Yeah its got auto AWD( turns on when needed) but im not sure if its got diff lock.

people say that the AWD comes only below 20km/h but I dont think thats tue, its suposed to come on at any speeds and it does feel very stable at high speeds.

KDH206 is AWD with 3litre 1KD engine and KDH205 is 2,5L 2KD engine with AWD. KDH200 and KDH205 re discontinued now

You Hiace does not have a 'center diff' per say. I think it has a fancy 'viscous coupler' with the transfer case that handles 'speed' differences on either side. Even the likes of RAV4s and Vanguards don't have a 'center diff'.

As for the AWD and the speed. There probably is some truth to that. The RAV4s AWD system works only below 40kmph. The Vanguard and export model RAV4s which had the same system as the RAV4's had AWD lock mechanisms (see **note) but even that got turned off at speeds above 40kmph. The ones that come with traction control on the other hand had some fancy power distribution mechanism which utilized the AWD system (I am not 100% certain on this but I believe this traction control system was made standard in all AWD RAV4s towards the end; atleast in some markets. Again..not 100% certain on that...). EDIT : I am not entirely certain what speed thresholds that system has when utilizing the AWD system for traction control, if there are any.

**NOTE: This switch did nothing more than provide constant power to the electro magnetic coupler in the back so that it always engages the rear wheels. WIthout the switch, power is sent to the electro magnetic coupler only when slippage is detected in the front. This should not be confused with a 'center diff lock' as the icon printed on the switch looks similar to the 'center diff lock' switch in some vehicles. Granted with the coupler and the transfer case and the predefined power distribution ratios it can achieve the same function as a centre diff that is locked.

It is not just a Toyota thing even the Japanese outlander and Xtrail had some speed thresholds (sorry can:t remember what they are...)

Edited July 22, 2015 by iRage

[Magnum]

You Hiace does not have a 'center diff' per say. I think it has a fancy 'viscous coupler' with the transfer case that handles 'speed' differences on either side. Even the likes of RAV4s and Vanguards don't have a 'center diff'.

As for the AWD and the speed. There probably is some truth to that. The RAV4s AWD system works only below 40kmph. The Vanguard and export model RAV4s which had the same system as the RAV4's had AWD lock mechanisms (see **note) but even that got turned off at speeds above 40kmph. The ones that come with traction control on the other hand had some fancy power distribution mechanism which utilized the AWD system (I am not 100% certain on this but I believe this traction control system was made standard in all AWD RAV4s towards the end; atleast in some markets. Again..not 100% certain on that...). EDIT : I am not entirely certain what speed thresholds that system has when utilizing the AWD system for traction control, if there are any.

**NOTE: This switch did nothing more than provide constant power to the electro magnetic coupler in the back so that it always engages the rear wheels. WIthout the switch, power is sent to the electro magnetic coupler only when slippage is detected in the front. This should not be confused with a 'center diff lock' as the icon printed on the switch looks similar to the 'center diff lock' switch in some vehicles. Granted with the coupler and the transfer case and the predefined power distribution ratios it can achieve the same function as a centre diff that is locked.

It is not just a Toyota thing even the Japanese outlander and Xtrail had some speed thresholds (sorry can:t remember what they are...)

This is what the Toyota site says:

"Full-time 4WD system adopted center differential method the viscous coupling. The driving force is efficiently allocated, and supports running on a slippery road surface.

• Such as off-road and rally cars are not a purpose, it is 4WD that aims to contribute to excellent driving stability on a general road.

Seems like you are right about the viscous coupling. I dont understand why the AWD gas to be speed locked, to increase fuel economy?

bdw I also noticed my Hiace has a big turning radius, making U turns difficult. Do AWD/4WD vehicles have a large turning radius even when on 2WD mode?

and LSD is optional on 4WD

[iRage]

Well the old ravs had 50:50 and then 60:40 power distributionsat allspeeds whilst the CRV had the realtime system which made it a lot more fuel efficient than the RAV4s. So yeah, fuel efficiency would be a concern and Toyota them selves went with a realtime setup.

Seconfly, since the running gear is quite simple compared to what an Evo or WRX would have I dont think the couplers would be able to withstand constant high speed engagement. In fact, my RAV4, and quite a few others I've known of, the coupler started heating up after driving on some deep mud for about 2~3km (light starts blinking in a certain pattern although it keeps working). The CRVs my dad had had a tendency to whine under similar circumstances.

Also, on a side note, in the RAV4 the system works under three condition/modes. When wheel spin is detected, starting from a stand still and cornering (again relates to the first case when one wheel starts spinning more than the other). So the hiace might have something similar.

As for the turning radius, in old time 4wd when the system is engaged and locked-in it does effect the radius as the gearing of the axles, etc are put under strain when both front wheels try to turn at the same speed. In some, like the old hiluxes and stradas the setup itself effects the turning radius. To be honest I havent noticed much diff in the turning radius between 2wd and 4wd of cross overs, etc. So dunno.

[tiv]

This is what the Toyota site says:

"Full-time 4WD system adopted center differential method the viscous coupling. The driving force is efficiently allocated, and supports running on a slippery road surface.

• Such as off-road and rally cars are not a purpose, it is 4WD that aims to contribute to excellent driving stability on a general road.

Seems like you are right about the viscous coupling. I dont understand why the AWD gas to be speed locked, to increase fuel economy?

bdw I also noticed my Hiace has a big turning radius, making U turns difficult. Do AWD/4WD vehicles have a large turning radius even when on 2WD mode?

and LSD is optional on 4WD

Yes there is a turning radius compromise do to the articulation limit of front CVs, same story on Noahs and many Japanese Vans, and some AWD cars. Most SUVs in general do not have a good turning radius, thereby its not noticed.

Edited July 22, 2015 by tiv

[Magnum]

Well the old ravs had 50:50 and then 60:40 power distributionsat allspeeds whilst the CRV had the realtime system which made it a lot more fuel efficient than the RAV4s. So yeah, fuel efficiency would be a concern and Toyota them selves went with a realtime setup.

Seconfly, since the running gear is quite simple compared to what an Evo or WRX would have I dont think the couplers would be able to withstand constant high speed engagement. In fact, my RAV4, and quite a few others I've known of, the coupler started heating up after driving on some deep mud for about 2~3km (light starts blinking in a certain pattern although it keeps working). The CRVs my dad had had a tendency to whine under similar circumstances.

Also, on a side note, in the RAV4 the system works under three condition/modes. When wheel spin is detected, starting from a stand still and cornering (again relates to the first case when one wheel starts spinning more than the other). So the hiace might have something similar.

As for the turning radius, in old time 4wd when the system is engaged and locked-in it does effect the radius as the gearing of the axles, etc are put under strain when both front wheels try to turn at the same speed. In some, like the old hiluxes and stradas the setup itself effects the turning radius. To be honest I havent noticed much diff in the turning radius between 2wd and 4wd of cross overs, etc. So dunno.

Yes there is a turning radius compromise do to the articulation limit of front CVs, same story on Noahs and many Japanese Vans, and some AWD cars. Most SUVs in general do not have a good turning radius, thereby its not noticed.

I noticed how bad the turning radius in my Hiace is when I drove the car( the Hiace is only a lil bigger) few days before I got here, maybe the AWD system stays on always till 20km/h. The vehicle with best turning radius I know is those Suzuki Every, you can make a U-turn anywhere with them

bdw what about the front CVs??