Research and Development of Automotive Frame Prestressed Surveyors

From the pre-tightening torque to the axial pre-tightening force, as shown, the outer ring of the bearing is press-fitted into the bearing seat, the inner ring is mounted on the main cone, and the inner ring is an elastic spacer sleeve. By tightening the locking nut, The lock nut presses against the flange and the flange presses against the inner ring of the upper bearing.

F is the axial force generated by the tightening nut under the tightening torque T. It acts on the inner ring of the upper bearing through the flange, and then the positive pressure is transmitted to the inner ring of the lower bearing through the deformation of the elastic spacer. Under the action of F, the upper and lower bearings respectively generate an axial preload, Fao, and an axial displacement, δao. The mechanical analysis yields: Fao = FF′ (2) where F′ is the pressure of the elastic spacer in the elastic region. The relationship between F′ and axial displacement δao is: F′=EAδao/H (3) where E is the elastic modulus; A is the spacer cross-sectional area; H is the spacer height.

The relation between F and the tightening torque T of the lock nut is: F=2Td2tan(θ+β)+23μ(D3-d3)(D2-d2)d2(4) where T is the tightening torque and d is the outside diameter of the thread. D2 is the average thread diameter; θ is the thread angle, tanθ=s/πd2, where s is the pitch; β is the thread friction angle, tanβ=f, where f is the friction coefficient between the bolt and the nut; μ is the nut Friction coefficient with its support surface; D is the diameter of the bottom circle of the bolt.

Substituting Equations (3) and (4) into Equation (2), we get: Fao=2Td2tan(θ+β)+23μ(D3-d3)(D2-d2)d2-2EAδaoH(5) Substituting Equation (1) After formula (5), it is calculated approximately: Fao=2Td-12-1×-1=K1T(6)K1=2d-12-1×-1.

After the preload, the axial relative displacement of the inner and outer rings of the two bearings is under the axial preload force Fao. The axial relative displacement of the inner and outer rings of the bearing is δao. If an axial load is exerted on the inner ring of the bearing, Fa, and set the relative axial displacement of the inner and outer rings generated by Fa as δa, and due to the influence of δao, make the preload on both sides of the bearing become Fa+ and Fa-, respectively. The relationship between axial displacement and force balance is shown.

Fa=F left-F right=171368zl8/9esin19/9×α. It can be seen that the relative displacement of the inner and outer rings of the right side bearing becomes δao+δa, and the axial and relative displacements of the inner and outer rings of the left side bearing are relative. Change to δao-δa. If δao≤δa, there will be a gap between the roller and the inner and outer rings.

In the running of the car, the magnitude and direction of the axial force Fa change, so that δa also changes every moment. To make δa≤δao, we must find the maximum axial force Famax. When Famax produces δamax≤δao, The roller will always contact the inner and outer rings, and the main cone will not produce axial turbulence.

The maximum axial relative displacement of the main cone in the inner and outer rings is related to the axial force of the main cone helical gear and the direction of rotation of the main cone. When the direction of the axial force is away from the top of the cone, the axial force acts on the inner ring of the lower bearing 7; otherwise, the axial force is transmitted from the main cone to the lock nut 1 and then transmitted from the lock nut to the inner ring of the upper bearing 5. . When the gear ratio of the transmission is maximum imax, the maximum torque Tmax acting on the main cone is: Tmax=ηMmaximax.

Among them, Mmax is the maximum torque of the engine; η is the transmission efficiency. The main cone is a concave spiral bevel gear. Calculate the maximum tangential force Ftmax on the index circle at the midpoint of the main taper width as: Ftmax=2000Tmax/d. Among them, d is the main cone index circle diameter.

The measurement and preload of the main cone pre-tightening torque (1) The axial relative displacement of the inner and outer rings of the bearing is the pre-tightening amount, the measurement of the pre-tightening amount is difficult, and the measurement of the pre-tightening torque is relatively easy, according to the actual measurement Tight torque is used to calculate the preload, see (1) and (6).

Concluding remarks The automobile main reducer pretightening force measuring machine is a typical electromechanical integration product. The equipment was put into use for a year in Hefei Axle Co., Ltd., its working time is less than 3 min, the lock nut tightening torque accuracy is less than 3%, and the starting friction torque Less than 1%, the primary cone assembly of the main reducer assembly once the success rate of about 90%, much higher than the manual operation of the 20% to 30% success rate.