4T65-E Transmission Features & Benefits
OVERVIEW
In developing the 4T65-E, GM engineers benchmarked the transaxle against the very best competitor offerings from around the world, and strived to achieve a balanced package designed for both performance and luxury vehicle applications. The result is an extremely versatile yet competitively priced transaxle that brings world-class electronic controls and outstanding shift smoothness to GM's mid-size product line.
The versatility of the 4T65-E expands yet again in model year 2001 with the introduction of a Power Take Off Unit (PTU) to supply on-demand all-wheel drive in the Pontiac Aztek.
The 4T65-E is mated to GM's 2.5-, 3.0-, 3.1-, 3.4-, 3.5-, 3.8- and supercharged 3.8-liter engines.
NEW OR CHANGED FOR MODEL YEAR 2001
* New Friction Material in 2nd, 3rd And 4th Clutch Packs for Improved Durability
* Pontiac Aztek Application: Power Take Off Unit for On-Demand All-Wheel Drive
CUSTOMER BENEFITS
NEW FRICTION MATERIAL IN 2nd, 3rd AND 4th CLUTCH PACKS
A new friction material has been used in the second, third and fourth clutch packs. The new material withstands higher temperatures and pressures than the previous material, and thus handles higher energy shifts for improved durability. Because of the change to the more resilient material, hydraulic line pressure has been recalibrated to preserve the same shift feel as before (otherwise shifts would have felt more harsh).
AZTEK APPLICATTION: POWER TAKE OFF UNIT FOR ON-DEMAND ALL-WHEEL DRIVE
The most significant update for 2001 is the use of a Power Take Off Unit (PTU) with the 4T65-E in the Aztek application. The PTU works in conjunction with a propeller shaft and a Rear Drive Module (RDM) to supply on-demand all-wheel drive. These three components make up the Versatrak AWD System.
The components are as follows:
Power Take Off Unit (PTU) - The PTU bolts to the right side of the transaxle case barrel with five bolts and is aligned using one dowel pin. Additionally, it is supported with four stiffening braces connecting to the transaxle case, engine block and oil pan.
The PTU replaces the standard case extension that encloses the final drive differential assembly. The PTU consists of a three-piece housing and cover that encloses the differential assembly, a helical gear train consisting of three helical gears, and a 90-degree hypoid gear set. An input helical gear is welded to the right side of the differential carrier. This gear transfers torque from the differential carrier laterally through the other two helical gears, the last of which feeds into the 90-degree hypoid gear set to route the torque to the propeller shaft. The helical gear set in the PTU runs in the same automatic transmission fluid shared with the rest of the transaxle. The 90-degree hypoid gear set runs in a separate synthetic gear lube. A double seal separates the two lubricants.
Propeller Shaft - This shaft simply transfers torque from the PTU in front to the RDM in the rear. The PTU has a reduction ratio of 3.4105, with a corresponding identical step-up ratio in the RDM hypoid gearset.
Rear Differential Module (RDM)- The RDM consists of an aluminum housing, a 90-degree hypoid gear set, a fluid sump, and a differential case assembly, which contains two gerotor pumps, two clutches, and stubshafts for each rear wheel. A gerotor pump consists of a rotor of a specific shape, rotating within an outer race. When the rotor spins, its motion relative to the outer race sucks in and then pumps out hydraulic fluid. In this case, each rotor is splined to an axle stubshaft (which spins at rear wheel speed), while each outer race is splined to the differential housing, which spins at the same speed as the propeller shaft. Relative motion between the two creates hydraulic pressure that draws fluid from the sump and through the internal fluid passages of the differential carrier. The pressurized fluid actuates pistons, which apply the two rear-wheel clutch packs (one on each axle stubshaft). The clutch's outer pressure plates are splined to the differential housing, which rotates at propeller shaft speed, while the inner plates are splined to the axle stubshafts.
The system works as follows: "On-demand" drive is provided at the rear wheels only when slippage is detected at the front wheels. As long as there is no slippage at the front wheels, there is no front-to-rear speed differential and no need for rear-wheel-drive torque.
Under normal circumstances, torque is transferred from the engine through the transaxle to the final drive sun gear, which in turn drives the final-drive planetary gears, which are mounted on pins on the left side of the front differential carrier. The other side of the differential carrier contains a housing with two pinion gears, which drive the axle side gears, thus supplying torque to the front axle stubshafts and the front wheels.
In the event of front-wheel slippage (for example, on ice), the axle side gears in the front differential assembly will hold no torque, causing the differential carrier (and thus the PTU input helical gear) to rotate at a high speed. The input helical gear then drives the PTU gear train and the propeller shaft at that same high speed.
At the rear, the propeller shaft will rotate at a high speed relative to the rear wheels. This speed differential causes relative motion between the gerotor pump rotors and their outer races, which creates hydraulic pressure to actuate the rear wheel clutch packs. When the clutches are applied, they lock the rear differential housing to the axle stubshafts, thus transferring torque from the propeller shaft to the rear wheels.
HISTORY
The Hydra-matic 4T65-E is the third evolution of GM's original four-speed transverse front-wheel-drive automatic. The current version was introduced as a major upgrade of the acclaimed 4T60-E transmission in 1997, with more than 70 percent of its components changed to provide major improvements in cooling, fuel economy and shift smoothness, as well as reduced noise.
The 4T65-E demonstrates GM Powertrain's ability to develop prototypes faster and with improved quality while reducing costs. Powertrain engineers used a 3-D computer database to design the transaxle - including all major castings - in a "paperless" environment. The result was a more lifelike visualization of the product as it was designed, and fast turnaround from prototype to production.
ELECTRONIC CONTROLLED CAPACITY CLUTCH (ECCC)
The 4T65-E's electronic controlled capacity clutch (used instead of a mechanical lock-up clutch) uses sophisticated electronics to maintain very small amounts of slip between the pressure plate and the torque converter housing cover. The ability to precisely control continuously variable amounts of slip leads to reduced torque pulses and allows the clutch to be applied at lower vehicle speeds and with smoother engagement. This results in improved drivability and better fuel economy.
QUIET PERFORMANCE
The 4T65-E features several noise-reducing design measures. Its pump, which pressurizes the hydraulic fluid that drives the actuation of all of the transmission's components, features optimized geometry and timing of the suction and pressure ports in order to provide for maximum fill during the suction cycle and maximum discharge during the pressure cycle. This results in increased pump efficiency and leads to reduced noise throughout the pump's speed range.
The chain design also contributes to quietness. Rather than using one wide chain, the 4T65-E uses a dual-phase sprocket that drives two half-width chains that are rotationally 180 degrees out of phase with one another. The noise from each half-width chain tends to cancel out the noise of the other.
DRIVER CONTROLLED SHIFT PROGRAMMING
Some 4T65-E applications have a feature that allows drivers to select a shift character that is better suited to their personal tastes. Drivers can choose a "normal" mode for imperceptible shift feel, as well as a "performance" mode with quicker shifts that occur at higher RPM for improved acceleration.
ADAPTIVE SHIFT CONTROL FOR SMOOTH, CONSISTENT SHIFTS
The 4T65-E uses sophisticated electronics to modify shift patterns as conditions dictate. The Powertrain Control Module (PCM) monitors factors such as throttle position, vehicle speed, gear range, temperature and engine load.
The PCM also measures changes in the operating condition of the vehicle, which occur naturally over time as components wear. Based on these measurements, shift timing and hydraulic line pressure are adapted to maintain optimum shift feel under different conditions, such as at high altitude, for example, when the engine would normally feel sluggish because of a lack of oxygen. The PCM also allows the system to self-adjust for minor variations in each new unit, ensuring that every customer experiences consistent performance, and it ensures that the transmission will produce a constant high level of performance for the life of the car.
ELECTRONIC SAFEGUARDS
The same powertrain electronics that contribute to smooth, consistent shift quality also help protect the transmission. If a driver manually selects a low range, but then fails to upshift at higher speeds, the PCM protects the engine from over-revving by automatically shifting to a higher gear.
The PCM also reduces engine spark during abusive shifts that occur during "rocking" maneuvers, such as trying to extract the vehicle from a snow bank. The reduced spark cuts engine torque, thus reducing the stress placed on the transmission.
In extreme-high-temperature conditions, the PCM protects from overheating by automatically applying the torque converter clutch to reduce heat build-up. Finally, in the unlikely event that a transmission should fail, the PCM defaults to a "limp home" mode that allows the driver to operate the vehicle at reduced speed.
GARAGE SHIFT PACKAGE
"Garage shifts" refer to shifting from park or neutral into and out of drive and reverse - the shifts used during typical low-speed parking maneuvers. Special attention has been paid to the hydraulic calibrations and mechanical components (for example, the lo/reverse servo assembly and lo/reverse band) that operate during these shifts. The result is reduced noise, vibration and harshness, and optimum shift feel.
LOW MAINTENANCE
The 4T65-E uses long-life DEXRON III transmission fluid, which has a 100,000-mile service interval. Additionally, the PCM monitors operating conditions of the transaxle and alerts the driver with a warning light if there is a deterioration that would cause the vehicle to exceed acceptable emissions levels, in compliance with OBD II regulations.
LEADERSHIP
The 4T65-E earned top honors in the J.D. Power & Associates Initial Quality Surveys (published in spring of 1999). New vehicle owners were asked to fill out surveys that included questions on transmission performance and reliability. The 4T65-E brought home five of the top ten finishes for passenger car transmissions, finishing first (Oldsmobile Aurora), second (Chevrolet Lumina), fourth (Oldsmobile Intrigue), fifth (Buick LeSabre), and eighth (Pontiac Grand Prix).
