What is the difference between 4WD part time and Center Lock?

[Grenadian]

Hi,
I own a Wrangler and a Grenadier.
Would you like to someone explain to me in detail what the difference is between
the Wrangler's 4WD part time and the IG's High Center Lock?

 

[Dokatd]

4wd part time allows you to direct power to the rear axle only. This may be done in the transfer case or the front axle via hubs. There are variations of this including auto hubs. In any case, the front and rear power output potential is 100% at either the front or rear axle. Meaning the front and rear driveshafts are solidly interconnected without a differential or limited slip device. If the back axle turns then the front axle turns.

The IG is full time 4wd. There is a differential inside the transfer case and power is always sent to both the front and back axle. You cannot disengage power to the front axle. Output potential with the center differential unlocked is variable. Meaning you can stop the front axle from spinning and 100% of the power is now being sent to the rear axle only. This usually means the back axle has less traction than the front axle. This also means you are likely not moving forward anymore. This action can cycle from the front to back axle instantly and is accomplished by a passive differential. However if you lock the center differential then you will get 100% power potential to both the front and rear axle at all times. This is the same as your part time 4wd truck when it's in 4wd.

The purpose of this is to allow the front and rear axles to rotate at different speeds as needed to go around a turn. The front axle will travel a shorter distance over the ground than the back axle when you execute a turn and reduces binding in the drive train. If you didn't have this center differential the truck would tend to buck and bind when turning. And if you couldn't lock that differential you would be severely limited in your off-road performance.

Hopefully that explains it without images and such. There are alternative scenarios such as the Range Rover and Subarus etc that have what amounts to a torque converter in their transfer case to allow the vehicle to act effectively as both locked and unlocked to a degree. This is typically called "All Wheel Drive".

 

[Grenadian]

Wow!
It was a clear answer, but I read it 20 times because I lack basic knowledge, but I didn't fully understand it.
So,
1. IG's Center Lock (4H lock) = Wrangler's 4WD Part time
2. IG's fulltime 4WD + Wrangler's 4WD AUTO

Does it mean?

 

[landmannnn]

Wow!
It was a clear answer, but I read it 20 times because I lack basic knowledge, but I didn't fully understand it.
So,
1. IG's Center Lock (4H lock) = Wrangler's 4WD Part time
2. IG's fulltime 4WD + Wrangler's 4WD AUTO

Does it mean?

For practical use, you are correct.
1. IG 4H lock is just the same as Wrangler 4WD engaged.
2. IG fulltime 4WD is similar to Wrangler 4WD auto. Actually the IG sends power to both axles in this situation, the Jeep only engages the front when it detects it is needed. You probably wouldn't notice the difference between the two when driving.

 

[Max]

The Centre Lock should not be engaged when you are traveling on bitumen, concrete or any other hard surface...the wheel must be able to spin to eliminate binding. Typical use is dirt roads, sand, grass and rocky areas

 

[Tinerfeño]

The IG is full time 4wd. There is a differential inside the transfer case and power is always sent to both the front and back axle. You cannot disengage power to the front axle. Output potential with the center differential unlocked is variable. Meaning you can stop the front axle from spinning and 100% of the power is now being sent to the rear axle only. This usually means the back axle has less traction than the front axle. This also means you are likely not moving forward anymore. This action can cycle from the front to back axle instantly and is accomplished by a passive differential. However if you lock the center differential then you will get 100% power potential to both the front and rear axle at all times. This is the same as your part time 4wd truck when it's in 4wd.

The term "power" is difficult. It is torque x revolutions. If torque is zero, also power is zero, or if revolutions are zero, power is zero.

An open differential is a torque equalizing device. This is the way it allows cornering. But the same way it may reduce driving force created by low traction on one tyre as the lower traction is also present on the other tyre (despite better traction). If the low traction will cause one tyre slip and the other not there is still same torque (and driving force) on both tyres. Power will be different as the other speed is zero. If the lower traction tyre is in air the torque is zero and this also causes zero torque on the other.

Constant 4WD with all three differentials open (not locked) is sensitive in loosing traction on one tyre as this will cause zero driving force on all four tyres. Locking centre differential connects propeller shafts (Am. drivce shafts) and improves driving force which will be 2 x lower front + 2 x lower rear. Locking axle differentials the driving force will be lower front + greater front + lower rear + greater rear. If one front and one rear tyre are in the air the driving force will be greater front + greater rear.

As there is always some traction available if a tyre has contact with ground a good suspension is very important in creating maximum driving force, Suspension lifts are usually made with stiffer springs (greater spring rate) which reduces wheel travel. This affects negatively driving force on uneven surfaces.

In off-road I always lock center differential when there is:

• Low traction even on a relatively flat surface. Typically cold, wet, gravel, mud, snow, ice, or any combination of these.
• Uneven surface regardless of the traction conditions. Like rock crawling on dry and warm conditions.

On higher speeds locking the center differential will change the behaviour of the car and it should be used with caution. I often use it on-road when there is snow or ice.