This section describes a procedure for mapping axle efficiency through a determination of axle power loss.

(a) You may establish axle power loss maps based on testing any number of axle configurations within an axle family as specified in §1037.232. You may share data across a family of axle configurations, as long as you test the axle configuration with the lowest efficiency from the axle family; this will generally involve testing the axle with the highest axle ratio. For vehicles with tandem drive axles, always test each drive axle separately. For tandem axles that can be disconnected, test both single-drive and tandem axle configurations. Alternatively, you may ask us to approve power loss maps for untested configurations that are analytically derived from tested configurations within the same family (see §1037.235(h)).

(b) Prepare an axle assembly for testing as follows:

(1) Select an axle assembly with less than 500 hours of operation before testing. Assemble the axle in its housing, along with wheel ends and bearings.

(2) If you have a family of axle assemblies with different axle ratios, you may test multiple configurations using a common axle housing, wheel ends, and bearings.

(3) Install the axle on the dynamometer with an input shaft angle perpendicular to the axle.

(i) For axle assemblies with or without a locking main differential, test the axle using one of the following methods:

(A) Lock the main differential and test it with one electric motor on the input shaft and a second electric motor on the output side of the output shaft that has the speed-reduction gear attached to it.

(B) Test with the main differential unlocked and with one electric motor on the input shaft and electric motors on the output sides of each of the output shafts.

(ii) For drive-through tandem-axle setups, lock the longitudinal and inter-wheel differentials.

(4) Add gear oil according to the axle manufacturer's instructions. If the axle manufacturer specifies multiple gear oils, select the one with the highest viscosity at operating temperature. You may use a lower-viscosity gear oil if we approve that as critical emission-related maintenance under §1037.125. Fill the gear oil to a level that represents in-use operation. You may use an external gear oil conditioning system, as long as it does not affect measured values.

(5) Install equipment for measuring the bulk temperature of the gear oil in the oil sump or a similar location.

(6) Break in the axle assembly using good engineering judgment. Maintain gear oil temperature at or below 100 °C throughout the break-in period.

(7) Drain the gear oil following the break-in procedure and repeat the filling procedure described in paragraph (b)(3) of this section.

(c) Measure input and output speed and torque as described in 40 CFR 1065.210(b), except that you may use a magnetic or optical shaft-position detector with only one count per revolution. Use a speed-measurement system that meets an accuracy of ±0.05% of point. Use torque transducers that meet an accuracy requirement of ±0.2% of the maximum axle input torque or output torque tested for loaded test points, and ±1.0 N⋅m for unloaded test points. Calibrate and verify measurement instruments according to 40 CFR part 1065, subpart C. Command speed and torque at a minimum of 10 Hz, and record all data, including bulk oil temperature, as 1 Hz mean values.

(d) The test matrix consists of output torque and wheel speed values meeting the following specifications:

(1) Output torque includes both loaded and unloaded operation. For measurement involving unloaded output torque, also called spin loss testing, the wheel end is not connected to the dynamometer and is left to rotate freely; in this condition the input torque (to maintain constant wheel speed) equals the power loss. Test axles at a range of output torque values, as follows:

(i) 0, 500, 1000, 2000, 3000, and 4000 N⋅m for single drive axle applications for tractors and for vocational Heavy HDV with a single drive axle.

(ii) 0, 250, 500, 1000, 1500, and 2000 N⋅m for tractors, for vocational Heavy HDV with tandem drive axles, and for all vocational Light HDV or vocational Medium HDV.

(iii) You may exclude values that exceed your axle's maximum torque rating.

(2) Determine maximum wheel speed corresponding to a vehicle speed of 65 mi/hr based on the smallest tire (as determined using §1037.520(c)(1)) that will be used with the axle. If you do not know the smallest tire size, you may use a default size of 650 r/mi. Use wheel rotational speeds for testing that include 50 r/min and speeds in 100 r/min increments that encompass the maximum wheel speed (150, 250, etc.).

(3) You may test the axle at additional speed and torque setpoints.

(e) Determine axle efficiency using the following procedure:

(1) Maintain ambient temperature between (15 and 35) °C throughout testing. Measure ambient temperature within 1.0 m of the axle assembly. Verify that critical axle settings (such as bearing preload, backlash, and oil sump level) are within specifications before and after testing.

(2) Maintain gear oil temperature at (81 to 83) °C. Measure gear oil temperature at the drain of the sump. You may use an external gear oil conditioning system, as long as it does not affect measured values.

(3) Use good engineering judgment to warm up the axle by operating it until the gear oil is within the specified temperature range.

(4) Stabilize operation at each point in the test matrix for at least 10 seconds, then measure the input torque, output torque, and wheel speed for at least 10 seconds, recording the mean values for all three parameters. Calculate power loss as described in paragraph (f) of this section based on torque and speed values at each test point.

(5) Perform the map sequence described in paragraph (e)(4) of this section three times. Remove torque from the input shaft and allow the axle to come to a full stop before each repeat measurement.

(6) You may need to perform additional testing based on a calculation of repeatability at a 95% confidence level. Make a separate repeatability calculation for the three data points at each operating condition in the test matrix. If the confidence limit is greater than 0.10% for loaded tests or greater than 0.05% for unloaded tests, perform another repeat of the axle power loss map and recalculate the repeatability for the whole set of test results. Continue testing until the repeatability is at or below the specified values for all operating conditions.

Calculate a confidence limit representing the repeatability in establishing a 95% confidence level using the following equation:

(7) Calculate mean input torque, T̅in mean output torque, T̅out, and mean wheel rotational speed, f̅nwheel, for each point in the test matrix using the results from all the repeat tests.

(f) Calculate the mean power loss, P̅loss, at each operating condition in the test matrix as follows:

(2) For each test calculate the mean power loss, P̅loss, as follows:

(g) Create a table showing the mean power loss,

corresponding to each mean output torque and mean wheel speed for input into GEM. Express wheel speed in r/min to one decimal place; express output torque in N·m to two decimal places; express power loss in kW to four decimal places. Select mean power loss values at or above the corresponding value calculated in paragraph (f) of this section. Use good engineering judgment to select values that will be at or above the mean power loss values for your production axles. For vehicles with tandem drive axles, sum the power losses and output torques of the individual axles when creating your table. For tandem axles with a disconnect, input a separate table into GEM for the single and tandem drive axle configurations. Vehicle manufacturers will use these declared mean power loss values for certification.