System Description
AUTOMATIC TRANSMISSION - 42RLEDESCRIPTION
The 42RLE (Fig. 1) is a four-speed transmission that is a conventional hydraulic/mechanical assembly controlled with adaptive electronic controls and monitors. The hydraulic system of the transmission consists of the transmission fluid, fluid passages, hydraulic valves, and various line pressure control components. An input clutch assembly which houses the underdrive, overdrive, and reverse clutches is used. It also utilizes separate holding clutches: 2nd/ 4th gear and Low/Reverse. The primary mechanical components of the transmission consist of the following:
- Three multiple disc input clutches
- Two multiple disc holding clutches
- Four hydraulic accumulators
- Two planetary gear sets
- Hydraulic oil pump
- Valve body
- Solenoid/Pressure switch assembly
Control of the transmission is accomplished by fully adaptive electronics. Optimum shift scheduling is accomplished through continuous real-time sensor feedback information provided to the Powertrain Control Module (PCM).
The PCM is the heart of the electronic control system and relies on information from various direct and indirect inputs (sensors, switches, etc.) to determine driver demand and vehicle operating conditions. With this information, the PCM can calculate and perform timely and quality shifts through various output or control devices (solenoid pack, transmission control relay, etc.).
The PCM also performs certain self-diagnostic functions and provides comprehensive information (sensor data, DTC's, etc.) which is helpful in proper diagnosis and repair. This information can be viewed with the DRB6 scan tool.
TRANSMISSION IDENTIFICATION
The 42RLE transmission can be identified by a bar code label that is affixed to the upper left area of the bellhousing.
The label contains a series of digits that can be translated into useful information such as transmission part number, date of manufacture, manufacturing origin, assembly line identifier, build sequence number, etc. Refer to (Fig. 2) for identification label breakdown. If the tag is not legible or is missing, the "PK" number, which is stamped into the left rear flange of the transmission case, can be referred to for identification. The entire part number, build code, and sequence number are stamped into the flange.
OPERATION
The 42RLE transmission ratios are:
FIRST GEAR POWERFLOW
In first gear range, torque input is through the underdrive clutch to the underdrive hub assembly (Fig. 3). The underdrive hub is splined to the rear sun gear. When the underdrive clutch is applied, it rotates the underdrive hub and rear sun gear. The L/R clutch is applied to hold the front carrier/rear annulus assembly. The rear sun gear drives the rear planetary pinion gears. The rear planetary pinion gears are forced to walk around the inside of the stationary rear annulus gear. The pinions are pinned to the rear carrier and cause the rear carrier assembly to rotate as they walk around the annulus gear. This provides the torque output for first gear. The other planetary gearset components are freewheeling. The first gear ratio is 2.84:1.
SECOND GEAR POWERFLOW
Second gear is achieved by having both planetary gear sets contribute to torque multiplication (Fig. 4). As in first gear, torque input is through the underdrive clutch to the rear sun gear. The 2/4 clutch is applied to hold the front sun gear stationary. The rotating rear sun gear turns the rear planetary pinions. The rear pinions rotate the rear annulus/front carrier assembly. The pinions of the front carrier walk around the stationary front sun gear. This transmits torque to the front annulus/rear carrier assembly, which provides output torque and a gear ratio of 1.57:1.
THIRD GEAR POWERFLOW
In third gear, two input clutches are applied to provide torque input: the underdrive clutch and overdrive clutch (Fig. 5). The underdrive clutch rotates the rear sun gear, while the overdrive clutch rotates the front carrier/rear annulus assembly. The result is two components (rear sun gear and rear annulus gear) rotating at the same speed and in the same direction. This effectively locks the entire planetary gearset together and is rotated as one unit. The gear ratio in third is 1:1.
FOURTH GEAR POWERFLOW
In fourth gear input torque is through the overdrive clutch which drives the front carrier (Fig. 6). The 2/4 clutch is applied to hold the front sun gear. As the overdrive clutch rotates the front carrier, it causes the pinions of the front carrier to walk around the stationary front sun gear. This causes the front carrier pinions to turn the front annulus/rear carrier assembly which provides output torque. In fourth gear, transmission output speed is more than engine input speed. This situation is called overdrive and the gear ratio is 0.69:1.
REVERSE GEAR POWERFLOW
In reverse, input power is through the reverse clutch (Fig. 7). When applied, the reverse clutch drives the front sun gear through the overdrive hub and shaft. The L/R clutch is applied to hold the front carrier/rear annulus assembly stationary. The front carrier is being held by the L/R clutch so the pinions are forced to rotate the front annulus/rear carrier assembly in the reverse direction. Output torque is provided, in reverse, with a gear ratio of 2.21:1.