Jeep four-wheel-drive systems

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This is the article about Jeep Four-Wheel drive systems by tradename. For the article on AMC and Jeep transfer cases, see AMC and Jeep transfer cases.

Jeep uses a variety of four-wheel drive systems on their various vehicles. These range from basic part-time systems that require the driver to move a control lever to send power to four wheels, to permanent four-wheel systems that monitor and sense traction needs at all four wheels automatically under all conditions.

Command-Trac[edit]

Command-Trac[edit]

Command-Trac was first introduced using the NP208 transfer case in the full-size Jeeps (SJ series) in 1980. The drive modes are the same as with the Dana 18 and 20 transfer cases: 2Hi, 4HI PT, and 4LO PT. The 4WD modes are not for use on high-traction surfaces such as dry roads. The NP208 was used through at least 1987.

More commonly, Command-Trac is used to refer to the NP/NV-231 or NP-207 transfer cases introduced along with the Jeep Cherokee (XJ) in 1984. The system offers a chain-driven, aluminum, "shift-on-the-fly" transfer case. The "shift-on-the-fly" feature provides manual ease and assist while engaging 4WD. Command-Trac should only be driven in 4WD on low-traction surfaces due to the front and rear axles being locked together (no differential action in the transfer case). Driving in 4WD on dry pavement causes excessive wheel and drivetrain wear. Four-wheel modes are most commonly used for wet/slick surfaces or extreme weather conditions (rain, snow, etc.) (4H), towing (N), and off-road activities (4L).

There are reports of a modified version known as NP-231J HD which was supposedly (SP) a "heavy duty" version for the Jeep Grand Cherokee ZJ with V8 engines. The NP/NV-231 case is a chain-driven unit that takes 21- or 23-spline input shafts. The 23-spline was for the AX-15 transmission, and the 21-spline was used for the AX-5 and BA 10/5 transmissions. Low range for this case was 2.72 and high range was 1.00.

The Command-Trac HD transfer case was used in 6-speed Liberty KJ's from 2005–2007. Although sometimes referred to as the "NV(NP)231HD," the transfer cases are actually the 241 series used in full-sized trucks from other makers (241D or 241C). The Jeep version is labelled "NV(NP)241J." This is not the NV241OR transfer case found in the Jeep Wrangler Rubicon, which uses a 4.0 low range and has a reinforced case. Dodge uses a 241DHD, which has a reinforced case but the 2.72 low-range.

The Jeep Grand Cherokee/Commander line no longer offers a part-time transfer case option. The reason behind this was its poor sales along with an improved Selec-Trac. Selec-Trac and a simplistic Quadra-Trac had the convenience and comfort of "Full-Time" all wheel drive that Command-Trac lacked for "luxury" SUV's that did not require the more rugged part-time system.

The terms "Command-Trac" and "Selec-Trac" were used in other Jeep lines and refer to different transfer cases in those lines.

Applications:

Command-Trac II[edit]

Command-Trac II works the same as Command-Trac but uses a console mounted switch to control the MP1522 transfer case as opposed to a floor mounted lever.[1]

Applications:

Rock-Trac[edit]

Rock-Trac is similar to Command-Trac but uses the New Venture Gear NV241 OR and adds locking differentials and 4:1 low gear ratio.[2] In 2007 an electronic front sway bar disconnect was added and the locking differentials switched from air-actuation to electronic actuation.

Applications:

Selec-Trac[edit]

Selec-Trac[edit]

Selec-Trac was first introduced in the full-size Jeeps (SJ) in 1983 using the New Process NP229 transfer case. This system has the same settings as Command-Trac but instead of locking the front and rear drive shafts together in the "4Hi" setting the drive shafts were coupled together using a viscous-type coupler that works the same way as a viscous limited-slip differential does; which allowed the vehicle to be driven in "4Hi" on dry pavement. It was used from 1983 to 1991 in some applications.

The AMC Eagle used the NP119 transfer case in 1980, a strictly full-time all wheel drive model. From 1981 to 1988, a similar system was employed, dubbed "Select-Drive", which allowed the vehicle to switch from all wheel drive to 2WD using the NP129 model transfer case. The NP129 contained a viscous coupling around an open differential for added traction in slippery conditions. The NP128 has also been found equipped in select model years, which does not feature a viscous coupling.

The NP228 Selec-Trac transfer case is closely related to the NP229. The only difference is that the NP228 does not have a viscous-type limited-slip coupling. It was used briefly in 1986.

The NP242 Selec-Trac transfer case debuted alongside the Fuel-Injected 4.0L Inline-6 in the compact Jeep Cherokee in 1987 (previous years used the NP228/229) It is a more common feature in the upscale Limited version and the XJ Jeep Wagoneer, and Dodge Durango models (1998–2000). It has a shift-on-the-fly transfer-case like Command-Trac but unlike it, Selec-Trac offers full-time all wheel drive in addition to the part-time 4WD of Command-Trac. Full-Time all wheel drive has the ability for the front and rear axles to rotate at different speeds, making driving on dry and wet surfaces possible year-round without shifting back to 2WD again. It still has the ability to lock the front and rear axles.

Other Jeep vehicles used Selec-Trac, for example, the Jeep Grand Cherokee, before being discontinued on that platform in favor of the electronically controlled Quadra-Drive II four-wheel drive system in 2005.

Selec-Trac uses the New Venture Gear NV242 transfer case[3] (formerly known as NP242).

Applications:

Selec-Trac II[edit]

Selec-Trac II is similar to Selec-Trac I but uses a console mounted switch to control the MP3022 transfer case as opposed to a floor mounted lever. Selec-trac II also differs with its lack of a part-time 4WD setting.[4]

Applications:

Quadra-Trac[edit]

Quadra-Trac transfer case in a 1993 Jeep Grand Cherokee ZJ
Quadra-Trac selector in a 1993 Jeep Grand Cherokee ZJ

The Quadra-Trac name is used on a variety of full-time 4WD systems. The first version used the Borg-Warner BW1339 transfer case and was produced from 1973 to 1979.[5] The next version used the New Process NP219 transfer case and was produced from 1980-1982. From 1993-1995 the New Process NP249 transfer case carried the name from 1996-1998 New Venture Gear started manufacturing it and it was renamed the NV249.

Quadra-Trac was the trade name for the Borg-Warner 1305 and 1339 gear case. It was a chain-drive system introduced in 1973 on the full-sized Jeep line which included the Wagoneer, Cherokee, and trucks behind the AMC-specific Turbo-Hydramatic 400 automatic transmission. CJ7s also received the Quadra-trac. This system included a differential to shift torque between front and rear which could be locked with vacuum. The Borg-Warner 1305 offered only 4WD Hi modes in full-time or part-time (locked) modes, while the 1339 offered a full-time and part-time low range of 2.57.

The Jeep Quadra-Trac was differentiated from the open "New Process" Gear NP203 used by Dodge, General Motors, and Ford in that it included a center limited slip differential feature, in this case a clutch pack.

Applications:

The Borg-Warner system was replaced with a "New Process Gear" NP219-based chain-driven system in 1980[6] The NP219 Quadratrac transfer case was used in full-size Jeeps from 1980 through 1982. It offered the following modes: 4HiFT, 4HiPT, and 4LoPT. In full-time 4WD High a viscous limited-slip coupling is used between the front and rear output shafts.

Applications:

In 1993 Jeep introduced Quadra-Trac on the Jeep Grand Cherokee using the NP249 transfer case. The transfer case utilizes a viscous coupler which provides smooth and efficient four-wheel drive operation on dry surfaces. When a differential in speed occurs between the axles, heat buildup causes the viscous coupler to transfer power to the slower axle. It is similar to several passenger car systems, but with a low-range gear for serious off-roading.[7] NP249 transfer cases used the viscous coupler to transfer power in both high and low ranges.

Applications:

In 1996 the NP249 was replaced with the New Venture Gear NV249 transfer case which added a low-lock capability, meaning a hard gear transferred power in 4LO (front and rear drive shafts are locked at same speed in low range).

Applications:

Quadra-Trac II[edit]

Quadra-Trac II was introduced in 1999 and it employs a two-speed chain-driven transfer case featuring three modes of operation, "4-All Time", "N" or neutral, and "4-Lo". In "4-All Time", torque is applied to the rear wheels under normal driving conditions. If the rear axle starts rotating at a significantly higher rate than the front axle, hydraulic pressure builds up in the gerotor and causes the clutch pack to progressively transfer torque to the front axle until both axles return to the same speed. "N" or neutral mode is intended for towing the vehicle. In "4-Lo", the front and rear axles are locked together through a 2.72 gear reduction ratio. In 2005 Jeep added traction control and replaced the New Venture Gear NV247 transfer case with the NV245 transfer case.

Applications:

Quadra-Trac I[edit]

Quadra-Trac I was introduced in 2004 and works similar to the Quadra-Trac II system, but eliminates the "4 Lo" and "N" or neutral modes. By excluding these modes it creates a system that requires no driver input.[8] In 2005 Jeep added traction control and replaced the New Venture Gear NV147 transfer case[3] with the NV140 transfer case.

Applications:

Quadra-Drive[edit]

The Quadra-Drive system was introduced in 1999 and is based on the Quadra-Trac II system but adds limited slip differentials to the front and rear axles to create a four-wheel drive system capable of not only directing torque to the axle with best traction but to the individual wheel on an axle with best traction.

Quadra-Drive[edit]

Quadra-Drive uses the New Venture Gear NV247 transfer case mated to front and rear axles containing Jeep's Vari-Lok which are gerotor style limited slip differentials. Applications:

Quadra-Drive II[edit]

Quadra-Drive II uses the New Venture Gear NV245 transfer case mated to front and rear axles containing electronic limited slip differentials or ELSDs. Jeep added traction control in 2005 and starting in 2011 only a rear ELSD is offered, while the front has an open differential.

Applications:

Freedom Drive[edit]

Freedom Drive is Jeep's four wheel drive system used in its compact crossover SUVs based on a front wheel drive platform, the Compass and Patriot. There are two versions of the basic Freedom Drive system for the US Market, called I and II.

Freedom Drive I[edit]

Freedom Drive I is a light duty full-time electronically controlled all wheel drive system with a locking mode to set the front/rear torque split for especially slippery conditions in the Jeeps derived from the Chrysler/Mitsubishi GS Platform.

Applications:

Freedom Drive II[edit]

Freedom Drive II uses the same hardware as the FDI system but adds a lower axle gear ratio in conjunction with the CVT to simulate the benefits of a 19:1 low-range transfer case for off-road use. This function is an alternate program in the CVT and is not a transfer case function. FDII also adds hill descent control system, off-road tuned traction control, and electronic stability program. The Patriot with FDII also feature longer suspension travel(all 4x4, post 2011 models have the same suspension), skid plates, tow hooks, and a full-size spare tire. This enables the FDII-equipped Patriot to wear the "Trail Rated" badge from Jeep. Trail Rated Jeep vehicles are determined by meeting several requirements of off-road conditions including water fording, articulation, and other tests.

Applications:

For the European Market there is a single version which combines elements of both U.S. versions. The European version is available with either a CVT gearbox or most commonly with a 6-speed manual gearbox and has two settings on the traction control and electronic stability program systems to cater for off-road activity, U.S. FDII suspension travel and a full-size spare tire. Skid plates and tow hooks are options in the EU, but the hill descent control system is not available.

Applications:

Active Drive[edit]

Active Drive I[edit]

Active Drive I is a full-time four-wheel drive system that requires no driver input. This system under normal conditions sends all available torque to the front wheels while monitoring the speed of the front and rear axles. If the system detects that the front axle is moving more quickly than the rear axle then the system will send power through the power transfer unit to the rear axle until the speeds are the same.[9]

Applications:

Active Drive II[edit]

Active Drive II includes all of the features of Active Drive I but adds a low gear range. When in "4-Low" mode the front and rear axles are locked together and power is sent to all four-wheels through a 2.92:1 gear reduction in the power transfer unit; providing a crawl ratio of 56:1 for four cylinder Jeep Cherokees and a 47.8:1 crawl ratio for six-cylinder Cherokees. All Cherokees with this system have a raised ride height of one inch.[9]

Applications:

Active Drive Low[edit]

Active Drive Low includes all of the features of Active Drive I but denotes a greater possible crawl ratio. When in "4-Low" mode the front and rear axles are locked together and power is sent to all four-wheels through the power transfer unit although no low range gear reduction occurs. Active Drive low relies on shorter axle gear ratios while holding first gear in the ZF9HP transmission to achieve a crawl ratio of 20:1; similar in effect to Freedom Drive II.

Applications:

Active Drive Lock[edit]

Active Drive Lock includes all the features of Active Drive II but adds "rock" mode to the Selec-terrain system and locking rear differential for better traction when used off-road. This four-wheel drive system combined with tow hooks, skid plates, and unique front and rear fascias allows the Jeep Cherokee Trailhawk models to obtain the "Trail Rated" badge from Jeep.[9]

Applications:

Selec-Terrain[edit]

Selec-Terrain is a system designed to calibrate the vehicle to provide the best on-road and off-road performance; depending on which terrain mode is selected. The modes are selected by a dial located near the center console and have five settings: "Auto", "Snow", "Sport", "Sand/Mud" and "Rock". This system was first offered in the 2011 Jeep Grand Cherokee. It also comes standard on all 2014 Jeep Cherokees with four-wheel drive and all Jeep Grand Cherokees with a two-speed transfer case.

Applications:

See also[edit]

References[edit]

  1. ^ "Jeep 4x4 Basics". jeep.com. Retrieved 2012-08-15. 
  2. ^ "Jeep 4x4 Basics". jeep.com. Retrieved 2012-08-16. 
  3. ^ a b WJ Four-Wheel Drive Systems, WJ Jeeps.com. Retrieved on 9 October 2010.
  4. ^ "Jeep 4x4 Basics". jeep.com. Retrieved 2012-08-15. 
  5. ^ Allen, Jim (1998). Jeep 4x4 Performance Handbook. MotorBooks/MBI Publishing. p. 90. ISBN 978-0-7603-0470-9. 
  6. ^ John, Full-size Jeep pages on wagoneers.com 25 February 2002. Retrieved on 9 October 2010.
  7. ^ McCraw, Jim (November 1992). "4x4 when the going gets tough". Popular Science 251 (5): 112. Retrieved 10 October 2010. 
  8. ^ "Jeep 4x4 Basics". jeep.com. Retrieved 2012-08-16. 
  9. ^ a b c Harley, Michael (27 March 2013). "2014 Jeep Cherokee flaunts its new contemporary curves". autoblog.com. Autoblog.com. Retrieved 27 March 2013.