_{1}

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In the present paper; two models of the input shaft for a Longitudinal Mounted four Speed Automotive Automatic Transmission for the first time were introduced to describe the input shaft critical loads. In the first model; the DC (Direct Clutch) connects two gears together. This gives no change in the set torque (the set output torque equal to the set input torque). In the second model; the ODB (Over Drive Brake) fixes one element of the planetary set. This is resulting, the gear set gives reduction ratio (the set output torque is not equal to the set input torque). So, the transmission input shaft is worked under two different working operating conditions of torque. Also, it is loaded by a two vertical loads which are coming from the turbine and planetary set loads respectively. They are shown that there are three critical combinations of forces (contact force, shear force, and normal force) applied on the input shaft. The critical forces can be possibility exist three types of cracks for the input shaft cross section they are: transverse (torsion stress), longitudinal (bending stress), and vertical (shear stress). The three cracks are studied in this article. The article considers three stress factors: shearing torsion stress, shear stress, and bending stress.

In study of stress sources and critical stress combinations of the input shaft for the present longitudinally mounted four speed automotive automatic transmissions, which they are resulting in failure. It is common to focus on the main loads acting on the spline part of the input shaft which are forces due to the turbine torque and turbine weight, and also focus on the loads acting on the solid part of the input shaft which are forces due to the planetary set torque (the maximum set torque is occurred at the brake set is applied) and the planetary set weight respectively [

Turbine forces are transmitted to the input shaft through the spline part. For the simplest calculations it is assumed that the turbine transmits force and torque to the spline part of the shaft at the middle of its width, and study the stressed-strained is based on the corresponding cross-section. Although, actually, turbine force of interaction between the turbine hub and the spline shaft part is distributed along the length of the turbine hub. Also, the planetary set force is distributed along the bearing of the set.

Forces on the input shaft for the mentioned longitudinal mounted four speed automatic transmission induce stresses which are of torsional, bending, shearing, and axial nature. In studies of stressed-strained states of the input shaft resulting in fatigue failure, it is common to forces on the input shaft induce stresses which are of a torsional, bending, shearing, and axial nature. focus primarily on torsion phenomena. In so doing, torsional shear stresses are considered for the most part. The effect of axial forces is usually not significant and can be omitted.

The longitudinally four speed automatic transmission

The second stage is occurred when the torque converter lock-up clutch is activated (at the design point), the turbine and pump are connected to the engine output. The angular velocity and torque of turbine are expressed as follows [

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The resistant torque of the planetary gear set for the turbine torque has two values. One value occurs when the DC clutch is applied

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The other value is occurred when the ODB brake is applied

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The turbine torque (T_{T}) transmits through a spline part on the input shaft

Diagrams of bending moment M_{b}, caused by turbine weight (W_{1}) and first planetary gear set (W_{2}), and shear force (F_{s}), are shown in

Hence, the diagrams of contact forces from torsion are shown in

B.M.D