GB/T 41607-2022Test method for inertia absorption durability of friction elements in wet automatic transmission (English PDF)

3.1 Friction characteristics

The unique intrinsic properties of friction materials (friction elements) shown in the friction process.

Note: In this document, dynamic and static friction tests are used to evaluate the friction characteristics of friction elements in automatic transmissions.

3.2 Friction coefficient

The ratio of the friction force generated TO the force exerted on the friction element when there is relative movement or relative movement tendency between the friction plate and the dual plate.

Note 1: The friction coefficient is divided into dynamic friction coefficient and static friction coefficient.

Note 2: The dynamic friction coefficient and static friction coefficient shall be calculated according to Formula (1), and the results shall be rounded off to 3 decimal places according to GB/T 8170.

Where: µ - friction coefficient;

T - friction torque, in Newton meter (N·m); n - number of friction plates (n=3); r - average effective friction radius, in millimeters (mm), which shall be 57.4 mm; p - the surface pressure loaded on the friction surface of the friction plate, in kilopascals (kPa), which shall be 785 kPa;

A - the friction area of the friction plate, in square millimeters (mm²), which shall be 4 434 mm².

3.3 Dynamic friction coefficient

The ratio BETWEEN the friction force generated by the relative motion between the friction plate and the dual plate AND the positive pressure, when there is relative motion between the friction plate and the dual plate,

Note: The dynamic friction coefficient (µd, µ0) is calculated according to Formula (2) and Formula (3).

4.2 Test preparation

4.2.1 Friction plate preparation

The size of the friction plate shall meet the requirements of A.1 in Appendix A.

Soak the friction plate which is stored in the desiccator in the test oil for more than 2 h; take it out and wipe the test oil. Then, use a micrometer to measure the thickness of the friction plate at four points every 90°, accurate to 0.001 mm. Mark test points on surfaces that are not rubbed.

4.2.2 Dual plate preparation

The size of the dual plate shall meet the requirements of A.2.

The dual plate used shall be cleaned of oil on the surface using ultrasonic waves in a solvent such as hexane, wiped with lint-free paper, and dried at room temperature.

4.2.3 Testing machine preparation

After each test, the test oil chamber and each oil pipe shall be thoroughly cleaned and dried with a solvent such as hexane. When measuring the oil temperature, the thermocouple shall be fixed at a position 2 mm from the end face and horizontal to the test oil chamber.

4.2.4 Installation of friction components

Install the friction plate and the dual plate one by one; pay attention to adjusting the friction gap at the position of 0.8 mm ± 0.2 mm.

The dual plate and friction plate shall be installed as shown in Figure 5; pay attention to the installation direction (A, B and A', B' in Figure 5); the clearance between the friction components is calculated according to Formula (6) and adjusted to 0.8 mm ± 0.2 mm. As shown in Figure 5, the total thickness of the friction components shall be measured when the pressure is loaded.

Where: CL - clearance, in millimeters (mm);

Ls - total length of the test oil tank, in millimeters (mm); Ld - total thickness of friction components, in millimeters (mm).

6.2.1 Friction plate

After 5 000 times of braking, observe the 6 faces of the friction plate, observe and record the following conditions:

a) Wear and tear of the friction plate;

b) Discoloration or ablation on the surface of the friction plate;

c) Whether there is material peeling on the friction surface;

d) Whether there is blocking on the surface of the friction material.

6.2.2 Dual plate

After 5 000 times of braking, observe the 8 faces of the dual plate, observe and record the following conditions:

a) Wear and tear of the dual plate;

b) Discoloration on the surface of the dual plate, and whether there is a high temperature ablation point.

6.3 Record

6.3.1 Test curve

Curves of torque, revolutions and pressure generated in the 1st, 50th, 200th, 500th, 1 000th, 3 000th, and 5 000th test cycles of the dynamic friction test and the static friction test.

6.3.2 Calculation results

6.3.2.1 Calculate Rd according to Formula (7), round off the result to 2 decimal places according to GB/T 8170.

Where: Rd - the ratio of the friction coefficient at the midpoint TO the initial dynamic friction coefficient; µ0 - the dynamic friction coefficient calculated from T0 in each test cycle; µd - the dynamic friction coefficient calculated from Td in each test cycle.

6.3.2.2 Calculate Ra according to Formula (8), round off the result to an integer according to GB/T 8170.

Where: Ra - change rate of friction coefficient at midpoint, %; µdmax - the maximum value of µd in the test cycle with the number of revolutions of 50 ~ 5 000 times; µdmin - the minimum value of µd in the test cycle with the number of revolutions of 50 ~ 5 000 times.

7.1 Reproducibility

After the last test runs for 3 000 h or 12 months (whichever is shorter), use the same test equipment to conduct one or more tests before starting the next test. The deviation of the average value of µt shown in the last three 5 000-cycle tests (including the above test) shall be within ±5% of the average value of µt of three or more 5 000-cycle tests; the test of the automatic transmission oil, friction plate, and dual plate used in the test shall be judged as a valid test.

7.2 Repeatability

During the last three 5 000-cycle tests, the µt value shall fluctuate within ±2%.