# Title 40

## SECTION 1066.265

### 1066.265 Acceleration and deceleration verification.

§ 1066.265 Acceleration and deceleration verification.(a) *Overview.* This section describes how to verify the
dynamometer's ability to achieve targeted acceleration and
deceleration rates. Paragraph (c) of this section describes how
this verification applies when the dynamometer is programmed
directly for a specific acceleration or deceleration rate.
Paragraph (d) of this section describes how this verification
applies when the dynamometer is programmed with a calculated force
to achieve a targeted acceleration or deceleration rate.

(b) *Scope and frequency.* Perform this verification or an
equivalent procedure upon initial installation and after major
maintenance that could affect acceleration and deceleration
accuracy. Note that this procedure relies on proper verification of
speed as described in § 1066.235.

(c) *Verification of acceleration and deceleration rates.*
Activate the dynamometer's function generator for measuring roll
revolution frequency. If the dynamometer has no such function
generator, set up a properly calibrated external function generator
consistent with the verification described in this paragraph (c).
Use the function generator to determine actual acceleration and
deceleration rates as the dynamometer traverses speeds between 10
and 40 mi/hr at various nominal acceleration and deceleration
rates. Verify the dynamometer's acceleration and deceleration rates
as follows:

(1) Set up start and stop frequencies specific to your
dynamometer by identifying the roll-revolution frequency, *f*,
in revolutions per second (or Hz) corresponding to 10 mi/hr and 40
mi/hr vehicle speeds, accurate to at least four significant
figures, using the following equation:

*v*= the target roll speed, in inches per second (corresponding to drive speeds of 10 mi/hr or 40 mi/hr).

*n*= the number of pulses from the dynamometer's roll-speed sensor per roll revolution.

*d*roll = roll diameter, in inches.

(2) Program the dynamometer to accelerate the roll at a nominal
rate of 1 mi/hr/s from 10 mi/hr to 40 mi/hr. Measure the elapsed
time to reach the target speed, to the nearest 0.01 s. Repeat this
measurement for a total of five runs. Determine the actual
acceleration rate for each run, *a*act, using the following
equation:

*a*act = acceleration rate (decelerations have negative values).

*v*final = the target value for the final roll speed.

*v*init = the setpoint value for the initial roll speed.

*t*= time to accelerate from

*v*init to

*v*final. Example:

*v*final = 40 mi/hr

*v*init = 10 mi/hr

*t*= 30.003 s

*a*act = 0.999 (mi/hr)/s

(3) Program the dynamometer to decelerate the roll at a nominal
rate of 1 (mi/hr)/s from 40 mi/hr to 10 mi/hr. Measure the elapsed
time to reach the target speed, to the nearest 0.01 s. Repeat this
measurement for a total of five runs. Determine the actual
acceleration rate, *a*act, using Eq. 1066.265-2.

(4) Repeat the steps in paragraphs (c)(2) and (3) of this section for additional acceleration and deceleration rates in 1 (mi/hr)/s increments up to and including one increment above the maximum acceleration rate expected during testing. Average the five repeat runs to calculate a mean acceleration rate, aact, at each setting.

(5) Compare each mean acceleration rate, aact, to the
corresponding nominal acceleration rate, *a*ref, to determine
values for acceleration error, *a*error, using the following
equation:

*a*ref = 1 (mi/hr)/s

*a*error = −0.100%

(d) *Verification of forces for controlling acceleration and
deceleration.* Program the dynamometer with a calculated force
value and determine actual acceleration and deceleration rates as
the dynamometer traverses speeds between 10 and 40 mi/hr at various
nominal acceleration and deceleration rates. Verify the
dynamometer's ability to achieve certain acceleration and
deceleration rates with a given force as follows:

(1) Calculate the force setting, *F*, using the following
equation:

*I*b = the dynamometer manufacturer's stated base inertia, in lbf·s 2/ft.

*a*= nominal acceleration rate, in ft/s 2. Example:

*I*b = 2967 lbm = 92.217 lbf·s 2/ft

*a*= 1 (mi/hr)/s = 1.4667 ft/s 2

*F*= 92.217 − 1.4667

*F*= 135.25 lbf

(2) Set the dynamometer to road-load mode and program it with a
calculated force to accelerate the roll at a nominal rate of 1
(mi/hr)/s from 10 mi/hr to 40 mi/hr. Measure the elapsed time to
reach the target speed, to the nearest 0.01 s. Repeat this
measurement for a total of five runs. Determine the actual
acceleration rate, *a*act, for each run using Eq. 1066.265-2.
Repeat this step to determine measured “negative acceleration”
rates using a calculated force to decelerate the roll at a nominal
rate of 1 (mi/hr)/s from 40 mi/hr to 10 mi/hr. Average the five
repeat runs to calculate a mean acceleration rate, aact, at each
setting.

(3) Repeat the steps in paragraph (d)(2) of this section for additional acceleration and deceleration rates as specified in paragraph (c)(4) of this section.

(4) Compare each mean acceleration rate, aact, to the corresponding nominal acceleration rate, aref, to determine values for acceleration error, aerror, using Eq. 1066.265-3.

(e) *Performance evaluation.* The acceleration error from
paragraphs (c)(5) and (d)(4) of this section may not exceed
±1.0%.