The Aisin 55-51LE is a fully automatic, five speed, electronically controlled, transaxle. It consists primarily of a four-element torque converter, three planetary gear sets, friction and mechanical clutches and a hydraulic pressurization and control system.
The TCM commands shift solenoids, within the transmission, ON and OFF to control shift timing. The TCM controls shift feel through the line pressure control solenoid valve. The TCM also controls the apply and release of the torque converter clutch which allows the engine to deliver the maximum fuel efficiency without sacrificing vehicle performance. The hydraulic system primarily consists of a gear type pump, four control valve bodies, case cover, converter housing and case. The pump maintains the working pressures needed to stroke the servo and clutch pistons that apply or release the friction components. These friction components, when applied or released, support the automatic shifting qualities of the transmission. The friction components used in this transmission consist of seven multiple disc clutches and one band. The multiple disc clutches combine with two mechanical sprag clutches, to deliver six different gear ratios through the gear sets. The gear sets then transfers torque through the front differential assembly and out to the drive axles.
The transmission can be operated in any one of the 6 different ranges.
| • | P - Park position enables the engine to be started while preventing the vehicle from rolling either forward or backward. For safety reasons, the vehicle parking brake should be used in addition to the transmission Park position. Since the front differential assembly and drive axles are mechanically locked to the case through the park pawl and front differential transfer drive gear assembly, Park position should not be selected until the vehicle has come to a complete stop. |
| • | R - Reverse enables the vehicle to be operated in a rearward direction. |
| • | N - Neutral position enables the engine to start and operate without driving the vehicle. If necessary, this position should be selected to restart the engine while the vehicle is moving. |
| • | D - Drive range should be used for all normal driving conditions for maximum efficiency and fuel economy. Drive range allows the transmission to operate in each of the five forward gear ratios. Downshifts to a lower gear, or higher gear ratio are available for safe passing by depressing the accelerator or by manually selecting a lower gear with the shift selector. |
| • | L4 - Low Four range can be used for conditions where it may be desirable to use only three gear ratios. These conditions include towing a trailer and driving on hilly terrain as described above. This range is also helpful for engine braking when descending slight grades. Upshifts and downshifts are the same as in Drive range for first, second and third gears except that the transmission is prevented from shifting above third gear. Low Four can be selected at any vehicle speed but will downshift into third gear only if vehicle speed is low enough not to overrev the engine, calibratable in TCM. |
| • | L2 - Low Two range adds more performance for congested traffic and hilly terrain. It has the same starting ratio, first gear, as Drive and Low Two ranges but prevents the transmission from shifting above second gear. Thus, Low Two can be used to retain second gear for acceleration and engine braking as desired. Low Two can be selected at any vehicle speed but the transmission will downshift into second gear only if vehicle speed is low enough not to overrev the engine, calibratable in TCM. This range is particularly beneficial for maintaining maximum engine braking when descending steep grades. |
