Drivetrains Transmission Systems.................... 1 Manual transmissions Automatic transmissions Continuously variable transmissions (Xtronic CVT) Overdrive Transmission interlock Drivetrain Configurations.................. 4 Front-wheel drive Rear-wheel drive 4-wheel drive (includes part-time, full-time, and automatic) All-wheel drive (AWD) ATTESA E-TS Dana axles Traction and Stability Control.............. 7 Limited-slip differential (VLSD, HLSD) Locking rear differential Limited Slip (ABLS) Hill Descent Control (HDC) Hill Start Assist (HSA) Clutch start cancel switch Traction Control System (TCS) Vehicle Dynamic Control (VDC) For Additional Information................ 10 Manual transmissions Nissan/Infiniti manual transmissions consist of five or six forward gears and one reverse gear that are engaged by manually depressing the clutch and moving the shift lever. Like a brake pad, the clutch contains friction material that wears away every time the clutch slips due to overloading or incorrect timing of acceleration and clutch pedal release. Clutch hydraulic system parts and fluid are similar to the brake hydraulic system and may also require periodic service. Manual transmissions employ synchronizers that allow gears to mesh during shifting without grinding. Nissan and Infiniti transmissions use double- or triple-cone synchronizers on the gears that receive the most use (generally 2nd and 3rd gears). Double-cone synchronizers are two tapered rings, or collars, between the gears. They serve as internal braking mechanisms that enable gears rotating at different speeds to rotate at the same speed during upshifts and downshifts. The use of two rings rather than one allows the gears to mesh more smoothly and enhances the durability of the transmission. Proper selection and maintenance of manual transmission fluid also allows smooth, quiet operation and enhances service life. Transmission placement for rear-wheel-drive configurations Transmission Driveshaft DRIVETRAINS TRANSMISSION SYSTEMS The transmission manages the transfer of power from the engine s crankshaft to the driveshaft, which in turn sends it on to the axles and wheels. The transmission operates in a manner similar to a bicycle s rear wheel sprockets. Larger and smaller sprockets create faster and slower speeds from the same leg action. When the transmission shifts gears, it transfers and even multiplies the power from the engine to the driving wheels. Just as a bicyclist changes gears to match the pedal effort with riding conditions, the transmission changes gears to keep the engine operating in the most efficient rpm range. There are three types of transmissions: Manual transmissions Automatic transmissions Continuously variable transmissions Longitudinally mounted engine Rear differential With rear-wheel-drive vehicles, the driveshaft carries the power to a rear differential that then distributes the power to the rear wheels. Rear axle lubricant must be properly selected and periodically changed. Both manual transmission and rear axle fluid should be changed more frequently if the vehicle is used in severe service conditions (such as towing a trailer). (See Drivetrain Configurations in this chapter.) Encyclopedia I 1
Transmission placement for front-wheel-drive configurations Transversely mounted engine and transaxle With front-wheel-drive vehicles, there s no separate driveshaft or differential case. In their place is a transaxle, which is a combination of the transmission and axle with the clutch, gearbox, and differential gears integrated into a single unit between the front wheels. It functions like a differential, only the power doesn t need to be transmitted through a long driveshaft to the rear wheels. Transaxle fluid lubricates both the transmission and differential sections of the assembly. (See Drivetrain Configurations in this chapter.) 6-speed manual transmissions Certain Nissan and Infiniti vehicles offer 6-speed manual transmissions that are popular for performance-oriented driving. They make it possible to keep the engine at or near its torque peak during almost any driving situation. There are two variations on the 6-speed design: close-ratio and wide-ratio. A close-ratio design is similar to that used on many racing cars. It generally means that there is less than a 25% difference between each successive gear ratio. With this configuration, 1st through 4th are acceleration gears; 5th gear is close to a 1:1 driveshaft-to-camshaft turning ratio; and 6th is the overdrive or cruising gear. With the wide-ratio gearbox, 4th gear is nearly a 1:1 driveshaft to camshaft turning ratio, and both 5th and 6th gears are overdrive. Nissan has developed a 6-speed manual transmission for truck and SUV applications with a very low 1st-gear ratio for enhanced off-road and towing capability. On 4x4 models, a clutch start cancel switch allows the driver to start the vehicle without depressing the clutch, for use on steep inclines in off-road conditions. Automatic transmissions Automatic transmissions offer increased convenience, because they vary gearing automatically in response to driving needs. Nissan/Infiniti automatic transmissions have four or five forward gears, including an overdrive gear. Most 5-speed automatic transmissions also have a manual shift mode that provides a sportier shifting experience. Although the gears in an automatic transmission are arranged differently, they perform the same function as in a manual transmission. A combination of hydraulic and electronic controls react to throttle position, engine output, and road speed to select the correct gear. The automatic transmission is filled with a special fluid that should be checked and serviced per the maintenance schedule. Lockup torque converter All Nissan/Infiniti automatic transmissions have torque converters. A torque converter is a hydraulic clutch that transmits and multiplies engine torque while cushioning the flow of power through the transmission components. A lockup torque converter contains a special clutch that engages at a preset speed to form a solid connection between the engine output shaft and the transmission input shaft. The locking effect created by this special clutch reduces transmission friction. Reduced friction increases fuel efficiency, while promoting longer-lasting transmission parts. Also, because lockup torque converters allow the engine to turn at a consistently lower rpm, there is less cabin noise at highway speeds. Electronically controlled All current Nissan and Infiniti models have electronically controlled automatic transmissions. Electronically controlled automatic transmissions benefit from interaction between the Engine Control Module (ECM) and the Transmission Control Module (TCM). When the transmission is about to shift, the ECM retards ignition timing momentarily to reduce shift shock. The communication between the ECM and TCM provides smooth, efficient shifting. It also increases the service life of the transmission. Nissan/Infiniti electronically controlled automatic transmissions also feature a fail-safe mode that enables them to function in a reduced capacity in case of electronic malfunction, high transmission oil temperature, or low oil level. A warning light on the instrument panel signals the driver if the transmission goes into fail-safe mode. The vehicle should not be driven long distances or at high speeds in this condition, or further damage could occur. 2 I Encyclopedia
Manual shift mode The 5-speed automatic transmission with manual shift mode allows you to change gears by moving the shift lever forward to upshift or rearward to downshift. The driver can stay involved with the way the car shifts gears. On certain vehicles, Downshift Rev-Matching (DRM) raises engine rpm momentarily to provide smoother downshifts and a sportier feel, similar to heel and toe downshifting with a manual transmission. (Note: When the gearshift lever is in Drive, overdrive is engaged. When the lever is moved to manual shift mode, however, overdrive is disengaged, essentially downshifting into 4th gear.) Continuously variable transmissions (Xtronic CVT) Highstrength steel belt Pulley Full-size truck and SUV transmission The 5-speed automatic transmission available on Nissan and Infiniti full-size vehicles is specially engineered to meet the heavy-duty requirements of full-size vehicles. In addition to providing high acceleration performance, smooth shifting, and good fuel economy, it enhances the ability to match gearing to driving conditions. Lower gear ratios help provide good acceleration. Higher gear ratios help provide good fuel economy. Small step ratios (i.e. five speeds instead of four) create smoother shifting. On most vehicles, a gated shifter provides a sportier look and feel because it s mounted in the center console, not on the steering column like many other full-size vehicles. Its design provides precise control of gearshift selection. The gated shifter allows drivers to choose 1st or 2nd gear, and 4th or 5th gear, by moving the gearshift side to side. This is especially handy when hauling or towing a heavy load. The transmission also has a standard tow mode that revises the shift points to help reduce gear hunting when driving under a load or when towing uphill. Transmission oil cooler The automatic transmission on all Nissan/Infiniti vehicles has an oil cooler that maintains correct oil temperature to preserve its lubricating qualities, enhancing the transmission s durability. It is especially useful for heavyduty operating conditions like towing, hauling a heavy load at low speed, and during operation off-road. The transmission oil cooler is either a separate external radiator, or it is integrated into the lower half of the front radiator. Automatic transmission fluid replacement The 5-speed automatic transmission does not have a traditional pullout dipstick for checking the automatic transmission fluid level. Because the dipstick is bolted in place, the transmission fluid level should be checked and serviced at an authorized dealership. Also, only Nissan Matic-J fluid can be used in the transmission. Nissan has been building Continuously Variable Transmissions (CVTs) for more than a decade. In fact, today Nissan has more than a million CVTs in operation worldwide. In North America, Nissan introduced the advanced Xtronic CVT. How Xtronic CVT works A continuously variable transmission transmits power by means of two pulleys and a high-strength steel belt instead of traditional gears. One pulley receives the power generated by the engine and the other pulley transmits drive power to the tires. Both pulleys have V-shaped grooves in which the connecting belt rides. One side of the pulley is fixed; the other side is movable, actuated by a hydraulic cylinder. When actuated by various sensors, the cylinder can increase or reduce the amount of space between the two sides of the pulleys. This allows the belt to ride lower or higher along the walls of the pulleys, depending on driving conditions, thereby changing the gear ratio. The gear ratio varies continuously rather than in steps, like traditional transmissions. Advantages Xtronic CVT operates in much the same manner as a conventional automatic transmission, with some key differences. An automatic transmission typically has only four or five fixed gear ratios to choose from, but Xtronic CVT has an infinite number of ratios at its disposal. This virtually eliminates the shift shock that occurs when conventional automatic transmissions shift from one gear to another. It also eliminates hunting for the right gear when driving up a hill. When an automatic transmission shifts gears, engine rpm rises above or falls below the engine s optimum power and efficiency range. Xtronic CVT continuously adjusts the transmission s output to keep the engine in its optimum power and efficiency range at all times. This means immediate acceleration for passing because there s no waiting for the transmission to downshift. DRIVETRAINS Encyclopedia I 3
Xtronic CVT is much more efficient at transferring power from the engine to the drive-wheels because it has fewer moving parts than a conventional automatic transmission. Your customers get the best of both worlds the performance and fuel efficiency of a manual transmission with the ease of use of an automatic transmission. Overdrive All Nissan and Infiniti manual and automatic transmissions are overdrive transmissions. That is, they have a specific gear ratio that makes the engine s crankshaft turn slower than the driveshaft. For example, if the driveshaft were turning at 3000 rpm in overdrive gear, the engine s crankshaft would be turning at less than 3000 rpm. Because the engine can turn at a slower rate and still maintain the same driveshaft speed, overdrive allows the vehicle to operate more quietly and efficiently. The higher gear ratio increases economy through better fuel efficiency and reduced wear on the drivetrain. A slower-turning engine promotes a more comfortable, quieter ride. On many Nissan and Infiniti vehicles, a button on the gearshift lever allows drivers to control the overdrive gear. On vehicles with a gated console shifter, overdrive is disengaged when the lever is moved from the Drive to the 4th or 3rd gear position. On vehicles with manual shift mode, overdrive is disengaged when the manual shift mode is selected. Transmission interlock All Nissan and Infiniti manual and automatic transmissions have an interlock feature that helps prevent the transmission from engaging accidentally. On vehicles equipped with manual transmission, the interlock design prevents starting the engine unless the clutch pedal is fully depressed. On vehicles equipped with a conventional automatic transmission or the Xtronic CVT (Continuously Variable Transmission), the interlock design prevents shifting from Park until the brake pedal is depressed. DRIVETRAIN CONFIGURATIONS If the engine is the heart of a vehicle, the drivetrain is the legs, because it transmits the engine s power to the wheels. There are four basic drivetrain configurations: Front-wheel drive Rear-wheel drive 4-wheel drive (part-time, full-time, and automatic) All-wheel drive (AWD) Front-wheel drive Front-wheel drive became popular in North America during the early 1970s, when the first oil embargo dramatically raised the price of gasoline in the U.S. At that time, automakers began to reduce the size of their vehicles in order to improve fuel economy. But simply reducing the size of existing vehicles created a serious problem a reduction in the interior size as well. In part, this was due to the fact that conventional rear-wheel-drive powertrain configurations intruded significantly into the passenger compartment. To solve the interior size problem, automakers adopted front-wheel drive, which eliminates the longitudinal driveshaft, rear axle, and large longitudinal transmission hump. Vehicles with front-wheel drive also weigh less. Nissan and Infiniti vehicles with front-wheel drive use a transversely (side-to-side) mounted engine and a transaxle. Advantages Front-wheel drive places more mass (weight) over the front tires, which is an advantage when traction is poor, such as in snow or other slippery conditions. It allows more interior room for a given size. It reduces the weight of the vehicle, which enhances its power-to-weight ratio. Rear-wheel drive Driveshaft Transversely mounted engine and transaxle Longitudinally mounted engine Transmission Rear differential Rear-wheel drive has become the preferred configuration for performance vehicles, and it also allows trucks and 4 I Encyclopedia
utility vehicles to carry and tow heavier loads. Nissan/Infiniti vehicles with rear-wheel drive use a longitudinally (front-toback) mounted engine and transmission, with the driveshaft connected to a rear differential, which transfers power to the rear wheels. and 4-wheel-drive high range when the vehicle is traveling at speeds of up to 60 mph ( shift-on-the-fly ). The system is electronically actuated, which simplifies engaging and disengaging 4-wheel drive. A rotary switch on the dash allows drivers to change modes. Advantages The rear-wheel-drive layout distributes vehicle weight more evenly than front-wheel drive, providing precise handling and excellent driver feedback. (See also Front Midship (FM) platform on page 50.) It provides a dynamic advantage by dividing steering and power delivery functions between front and rear wheels, rather than making the front wheels responsible for both functions. Also, more braking force can be applied to the rear wheels. Finally, there is no torque steer with rear-wheel drive. With front-wheel drive, torque steer is the tendency for a vehicle to pull in one direction under hard acceleration. 4-wheel drive Engine Transmission Driveshafts Transfer case Axle With 4-wheel drive, the driveshaft transfers power to both the front and rear wheels. A separate gearbox mounted behind the transmission, called a transfer case, controls whether power is directed to the front axle (4-wheel drive) or just the rear axle (2-wheel drive). The transfer case also can include an additional low-range gear for use at low speeds over rough terrain. There are three main types of 4-wheel-drive systems: Part-time 4-wheel drive Full-time 4-wheel drive Automatic 4-wheel drive Part-time 4-wheel drive Part-time 4-wheel drive allows drivers to choose manually between 4-wheel drive for demanding conditions or rearwheel drive (2-wheel drive) for normal driving conditions. The ability to choose 2-wheel drive for normal on-road driving limits wear on drivetrain components, for reduced maintenance costs. Current Nissan vehicles with part-time 4-wheel drive have a system that allows drivers to shift between 2-wheel drive The system uses a 2-speed transfer case, with 4H (high range) and 4LO (low range). The low-range gear provides additional control during very low-speed operation, such as for severe off-road conditions. In 4LO, throttle sensitivity is reduced to allow better control in severe conditions. Due to the low-range gearing, maximum speed in 4LO is limited to 30 mph, and operating on dry pavement is not recommended. 4LO can be engaged/disengaged only when the vehicle is stationary and the transmission is in Neutral or Park. The previous-generation Frontier, Xterra, and Pathfinder used a mechanically actuated 4-wheel system operated by a transfer case lever. Frontier and Xterra used automatic locking front hubs. After shifting from 4-wheel to 2-wheel drive, drivers needed to back up approximately ten feet to disengage (unlock) the hubs from their axles. Pathfinder used permanently engaged hubs, which eliminated the need to back up to disengage locking hubs. Full-time 4-wheel drive Full-time 4-wheel drive provides power to all four wheels at all times, usually in a fixed front/rear proportion such as 50/50 or 38/62. Full-time 4-wheel-drive systems provide unnecessary power constantly to all four wheels, which increases steering effort and wear and also can affect fuel economy. Currently, no Nissan or Infiniti vehicles offer true full-time 4-wheel drive because Nissan and Infiniti automatic 4-wheel-drive systems perform the same functions without requiring driver intervention, and without incurring the wear of a full-time system. Automatic 4-wheel drive To address the disadvantages of full-time 4-wheel drive, certain Nissan and Infiniti vehicles offer a sophisticated automatic 4-wheel-drive system that provides the benefits of both part-time and full-time 4-wheel drive. Automatic 4WD (All-Mode) is an advanced automatic 4-wheel-drive system and is easy to operate. When driving on dry pavement (using the Auto mode), it directs power to the rear axles only, for optimal fuel economy. The system senses changes in surface conditions and instantly varies the distribution of power between rear and front axles to provide additional traction when needed. Automatic 4WD provides four modes of operation: Auto mode is the very heart of the Automatic 4-wheeldrive system. It is the preferred and recommended setting for all driving conditions. DRIVETRAINS Encyclopedia I 5
Auto mode automatically and instantly provides a 50/50 front/rear power split for stable, no-slip start-ups and varies power distribution between the front and rear axles for improved driving stability under various road conditions. During normal dry-surface driving conditions, Auto mode directs power only to the rear axle. However, if road surface conditions deteriorate, it automatically and instantly varies power distribution between the front and rear axles from 100% rear, to 50% rear and 50% front, or any proportion in between. Auto mode also enhances the operation of the Antilock Braking System (ABS), because it activates additional front and rear driveshaft sensors that are linked to the ABS Electronic Control Unit. It s important to point out to prospects that using the Auto mode does not increase fuel consumption or tire wear! It does provide an added level of control when unexpected driving situations occur. 2WD directs 100% of the power to the rear axle for driving on dry, paved roads. However, because the Auto mode does the same thing, the 2WD mode is intended mainly to facilitate rolling road emissions testing. 4H (Lock) mode directs an equal 50/50 power split between the front and rear axles for operation on dirt or severe road conditions. 4LO engages a super-low gear for use off-road and provides additional control when very low-speed operation is required. Throttle sensitivity is reduced to allow better control in severe conditions. Note: Beginning with 1999.5 QX4 and 2001 Pathfinder LE, all controls for All-Mode 4WD are activated using a single switch on the instrument panel. There s no longer a transfer case lever to engage 4LO. To select 4LO in earlier QX4 models, stop the vehicle, set the parking brake, place the automatic transmission in Neutral, and move the transfer case lever firmly (without hesitating) from 4H to 4LO. A 4LO symbol will illuminate to confirm that 4LO is engaged. As with many 4WD vehicles, leaving the transfer case in the Neutral position will allow the vehicle to roll freely. Always use the parking brake whenever shifting the transfer case or parking the vehicle. If the transfer case lever is not completely shifted from High to Low or from Low to High, the lever may stick in the Neutral position. If this occurs, switch the engine off, move the lever to the desired position, and restart the engine. All-wheel drive (AWD) Like automatic 4-wheel drive, AWD has the capability to vary the amount of power directed to the front and rear axles. However, AWD is intended primarily to enhance a vehicle s on-road, all-weather capability, as opposed to its ability to traverse difficult terrain off-road. AWD systems are generally appropriate for light off-road use (such as gravel or dirt roads), but they lack low-range gearing, which limits off-road capability. Nissan and Infiniti offer AWD systems for vehicles based on either rear-wheel-drive or front-wheel-drive platforms. For front-wheel-drive vehicles with a transverse-mounted engine, such as Murano, the transfer case requires a coupling to redirect power to the rear wheels when needed. Certain Nissan and Infiniti vehicles offer a sophisticated intelligent all-wheel-drive system that uses microprocessors to deliver optimum power to each axle. Under normal road conditions, the system operates in 2-wheel drive for improved fuel efficiency. As necessary, the all-wheel-drive system automatically engages all-wheel drive for stable, no-slip start-ups and optimizes power distribution for improved driving stability. Advantages The design benefits of the Automatic 4WD and AWD systems are threefold: When operating in 4-wheel drive, they provide optimum control on snow, slippery surfaces, and rough terrain. Because both systems operate in 2-wheel drive on dry road surfaces, they provide good fuel economy with less steering effort and wear. Switching from 2-wheel drive to 4-wheel drive is automatic. It happens when it s needed. ATTESA E-TS (Advanced Total Traction Engineering System for All Electronic Torque Split) ATTESA E-TS is an advanced AWD system that automatically distributes engine power among the four wheels depending on driving conditions. It is derived from the same system used on the legendary Skyline GT-R in Japan. The system automatically directs power to the front axle for stable, no-slip start-ups. The amount of power directed to the front varies according to the vehicle. If no wheel slips, power is quickly adjusted to up to 100% rear-wheel delivery. The system varies power distribution for improved driving stability under various road conditions. Advantages The design benefits of the ATTESA E-TS system are fourfold: When starting from a full stop in slippery conditions, it provides sure traction and stable, smooth acceleration. It provides sporty cornering and handling even in snowy or slippery conditions. 6 I Encyclopedia
Yet, it provides good fuel economy and smooth handling on normal, dry road surfaces. Finally, snow mode can be engaged to increase control when accelerating in snow or other slippery conditions. Snow mode slows the rate of throttle opening at all speeds for optimum control of wheel slippage. Dana axles when driving in snow, on slippery roads, or off-road. That s why all Nissan and Infiniti vehicles are available with a variety of advanced traction and stability control systems that enhance drivetrain characteristics. Limited-slip differential A limited-slip differential increases traction and vehicle stability by automatically distributing engine power to the drive-wheel that has the most traction. On a vehicle without a limited-slip differential, once a drive-wheel begins to spin, power continues to be directed to the spinning wheel. A limited-slip differential helps provide good traction for driving on slippery roads as well as dry, smooth road surfaces, which increases driver confidence and enjoyment. The limited-slip rear differential available on the previousgeneration Pathfinder, Xterra, and Frontier is pressuresensitive. The thrust from the spinning wheel forces the gears to turn the opposite wheel. A brand-name Dana front axle is standard on all Nissan and Infiniti 4x4 full-size vehicles (also applied on selected Xterra and Frontier models). This axle is built to handle the heavy-duty requirements of both towing and off-road driving. In addition, Nissan Titan features a standard Dana rear axle with a 2.94 gear ratio for fuel-efficient highway driving. With the towing and off-road packages, however, Titan gets a special axle based on the Dana-44. It has a 3.36 axle ratio that provides enhanced low-speed response in off-road and towing conditions. Nissan and Infiniti full-size SUVs have an independent rear suspension instead of a solid rear axle. However, they use Dana rear driveshafts ( half shafts ) that offer a 3.36 axle ratio for enhanced towing capability (see illustration). (Note: Combined with the lower 1st gear ratio of the 5-speed automatic transmission, the 3.36 axle ratio is equivalent to a 4.10 axle ratio on a vehicle with a 4-speed automatic transmission.) Front Standard rear Optional rear axle axle/ratio axle/ratio Titan Dana Dana axle/2.94 Dana axle/3.36 Armada Dana Dana half Dana half shafts/2.94 shafts/3.36 QX56 Dana Dana half shafts/3.36 TRACTION AND STABILITY CONTROL Transferring power smoothly and effectively to the drivewheels is an important consideration in any vehicle, especially Viscous Limited-Slip Differential (VLSD) If a vehicle has a Viscous Limited-Slip Differential (VLSD), the sealed differential housing is filled with temperaturesensitive silicone-based fluid that expands rapidly when heated. Inside the differential housing are a series of interlacing plates. One set is connected to the left drivewheel and one set to the right drive-wheel. Under normal driving conditions, when both drive-wheels are traveling at the same speed, the plates are all rotating together at the same speed. But if one wheel begins to spin, one set of plates within the differential will begin to turn much faster than the other set. Because the plates are very close together, this motion of the plates relative to each other causes the fluid to heat and expand. The expanding fluid forces the plates together, so that the slower-turning set of plates absorbs torque from the faster set. The result is that the wheel with better traction receives power from the wheel that is spinning faster so that overall traction is improved. Helical Limited-Slip Differential (HLSD) The Helical Limited-Slip Differential (HLSD) uses a set of gears inside the differential to control power flow. Helical is the name for the angle at which the gears are cut. This gear-driven system is more sensitive to torque and responds more quickly than a viscous, or liquid-based, system. A helical gear system generally has the following advantages over other limited-slip differential designs: Its function is not affected by ambient temperature or vehicle operating temperature. It can provide different traction management characteristics for acceleration versus deceleration. DRIVETRAINS Encyclopedia I 7
To left axle Direction of rotation To right axle It does not depend on internal friction material or components that can wear. It will not interfere with ABS, which can happen with other limited-slip differential designs under extreme conditions. Locking rear differential A locking differential literally locks the right and left axles together so both rear wheels turn at the same speed, sending an equal amount of power to each drive-wheel at all times. In severe off-road, low-traction situations, it s important to keep both wheels turning, not slipping, so the vehicle can crawl out of mud, sand, gravel, or other difficult conditions. The sophisticated electronically controlled switch-ondemand system gives drivers more control than a mechanical locking differential. The system operates only in 4LO at speeds up to 12 mph. It disengages if 4H is selected. Limited Slip (ABLS) Active brake limited slip (ABLS) is not a differential, but like a limited-slip differential it redirects power to the drive-wheel or drive-wheels that have better traction. It applies braking force to any wheels that are slipping to help slow them down so they can maintain grip and/or transfer power to the wheel(s) that have better traction. 2-Wheel Limited Slip (ABLS) applies braking force to either drive-wheel of 2-wheel-drive vehicles. 4-Wheel Limited Slip (ABLS) applies braking force to any of the drive-wheels of 4-wheel-drive vehicles. Hill Descent Control (HDC) Hill Descent Control (HDC) helps drivers maintain a controlled speed on downhill slopes without having to use the brakes. The driver is free to concentrate on steering. It is available on selected Frontier, Xterra, and Pathfinder models equipped with automatic transmission and 4-wheel drive. HDC works below 15 mph on steeper slopes where engine braking alone is not enough to control vehicle speed. It operates in forward and reverse gears, but only in 4-wheel drive (4H or 4LO) with the HDC switch in the ON position. HDC is temporarily deactivated when the driver presses the brake or accelerator pedals. For best results, HDC should be used in 1st or 2nd gear. Hill Start Assist (HSA) When the vehicle is stopped on an incline, Hill Start Assist (HSA) automatically keeps the brakes applied to help prevent the vehicle from rolling downhill during the interval between the time the driver releases the brake pedal and applies the throttle. It works when the vehicle is in 2-wheel or 4-wheel drive and in forward or reverse gears. No driver input is needed to turn the system on, but the driver must apply the brake pedal to activate HSA and has two seconds to apply the throttle before HSA deactivates. It is available on selected Frontier, Xterra, and Pathfinder models equipped with automatic transmission and 4-wheel drive. Clutch start cancel switch A clutch start cancel switch allows the driver to start the vehicle without depressing the clutch. It is useful if the vehicle s engine stalls on a steep hill and the driver does not want the vehicle to roll downhill when restarting. The ignition must be in the ON position to activate the clutch start cancel switch. Clutch start deactivates after the vehicle has been started, so the driver must either depress the clutch pedal or reactivate the switch to start the vehicle again. This feature is available on selected Frontier and Xterra models equipped with manual transmission and 4-wheel drive. Traction Control System (TCS) Traction control limits drive-wheel slippage (wheel spin) under most conditions. It does so by sensing impending traction loss and correcting it to maximize vehicle stability and driver control. Loss of traction (wheel spin) occurs when acceleration forces exceed the friction capability of one or more tires. TCS uses the four wheel sensors of the Anti-lock Braking System (ABS) to detect a loss of traction. The TCS computer averages the speed of the two driven wheels and compares that speed to the average speed of the nondriven wheels. If the average speed of the driven wheels exceeds the average speed of the non-driven wheels by a predetermined amount, slip is indicated and TCS goes into operation. The system controls the engine throttle, momentarily shuts off one or several fuel injectors, and/or upshifts the transmission to reduce power to the rear wheels. Note: The Traction Control System on the firstgeneration Q45 operates differently than the system on the current Q45. The system on first-generation Q45 operates by first closing a secondary engine throttle to 8 I Encyclopedia
reduce power. Second, but almost simultaneously if wheel spin persists, the rear brakes are applied to slow the spinning wheel or wheels. An important feature of this system is that it can independently control the left rear or right rear wheel. There are many scenarios especially in winter driving in which TCS excels: To provide traction on slippery surfaces, TCS automatically controls drive-wheel traction and power delivery. Applicable conditions include ice, snow, sand, dirt, water, and gravel. For cornering performance, TCS minimizes wheel slip due to over-acceleration or a change in road surfaces. To provide stability during fluctuating side winds, TCS eliminates the need for the driver to modulate the throttle to maintain directional stability during high winds or sudden lane changes. The system works automatically, but can be switched off by the driver. The system automatically re-engages every time the engine is started. Vehicle Dynamic Control (VDC) VDC takes stability control a step further. It helps enhance performance in emergency avoidance maneuvers, helps improve vehicle stability, and helps provide improved control on slippery surfaces. VDC works in conjunction with the ABS, TCS, and 2-Wheel or 4-Wheel Limited Slip (ABLS) to improve traction and directional stability. Based on input from various sensors, VDC controls the amount of engine power and/or applies brake pressure to individual wheels as needed. How VDC works Seven sensors determine the vehicle s operating characteristics at any given instant. Front wheel speed sensors VDC/TCS/ABS actuator VDC controller VDC off switch Rear wheel speed sensors Four wheel-speed sensors monitor the speed of each wheel individually, and compare wheel speed to actual vehicle speed. The brake pressure sensor monitors the amount of brake pressure being applied to the wheels. The steering angle sensor monitors the angle of the steering wheel to help determine if the vehicle is going in the intended direction. The yaw rate/lateral g-sensor is located in the center of the vehicle and monitors the vehicle s position in relation to the road. Yaw refers to how much the vehicle rotates around its center axis. Lateral g s refer to forces exerted on the vehicle from the side. The sensors help determine if the vehicle is moving in a direction it s not supposed to for example, if it s sliding through a curve. Together, all seven sensors provide the VDC control unit with information about the vehicle s behavior at any instant. Based on this information, the VDC control unit sends a signal to actuate the ABS, traction control, and throttle as necessary to help maintain vehicle stability. Compensating for oversteer and understeer Without VDC With VDC VDC applies brake pressure to the outside wheels to reduce oversteer. Target Line Target Line If a vehicle oversteers when driving through a slippery curve, the back of the vehicle will tend to slide outward. With VDC on, the system senses the beginning of the slide and reacts by braking the outside wheels and reducing engine power to generate force in the opposite direction of the spin. This helps hold the vehicle to the intended line of travel. DRIVETRAINS Relay box Precharge pump VDC buzzer Steering angle sensor Yaw rate/lateral G-sensor Encyclopedia I 9
If a vehicle understeers on a similar curve, the front wheels lose traction and push out beyond the intended line of travel. In this situation, VDC applies brake force to the inside wheels and reduces engine power. The front wheels regain their grip, and the driver can maintain the intended line of travel. In both cases, full power becomes available again as soon as VDC has helped stabilize the vehicle. (This immediate return of power is a distinct advantage over the systems in some competitors.) Benefits of VDC Without VDC With VDC Target Line Target Line VDC applies brake pressure to the inside wheels to reduce understeer. Vehicle Dynamic Control is an important control safety feature. It helps compensate for oversteer and understeer by controlling brake pressure in one or more wheels and by controlling engine power output. It even counteracts driver input, if necessary. It enhances performance in emergency avoidance maneuvers and helps provide improved control even on slippery road surfaces. And it works automatically and seamlessly in fractions of a second. FOR ADDITIONAL INFORMATION Every vehicle product guide lists the applicable drivetrain features described in this chapter. Be sure to study each product guide to determine which features are available on each vehicle, and to review the advantage and benefit for each feature. Resource materials that provide additional information about Nissan and Infiniti drivetrains include the following: NPLS/Sales Encyclopedia Video Library on DVD Nissan Engine, Drivetrain, and Electrical Systems Advanced Technologies (Traction Control System) All-Mode 4WD Selling the Benefits of Vehicle Dynamic Control ILS/Sales Encyclopedia Video Library on DVD Advanced Technologies (Traction Control System) All-Mode 4WD (Revised) Selling the Benefits of Vehicle Dynamic Control Note: The VDC system is designed to help improve driving stability. It does not prevent accidents due to abrupt steering at high speeds or by careless or dangerous driving techniques. 10 I Encyclopedia