ISO 7401:2011 pdf free download – Road vehicles一Lateral transient response test methods一Open-loop test methods.
If optional lateral acceleration levels are measured, it is useful to present data as functions of lateral acceleration.
11.3.5 Asymmetry factors
The justification for making two initial turn directions is that an asymmetry can exist. This asymmetry can be presented in terms of asymmetry factors (see ISO/TR 8725).
12 Random input (see ISO/TR 8726)
12.1 Test procedure
Make the test runs by driving the vehicle at the required test speed (see 9.4) while making continuous inputs to the steering-wheel, up to predetermined limits of steering-wheel angle.
The test shall cover a minimum frequency range of 0,2 Hz to 2 Hz. Optionally, the frequency range may also be extended above and below these limits.
Do not use mechanical limiters of the steering-wheel angle, if existing, because of their effect on the harmonic content of the input. It is also important that the input be continuous, as periods of relative inactivity will seriously reduce the signal-to-noise ratio.
To ensure adequate high-frequency content, the input should be energetic (see 12.2.2 and 12.2.3).
To ensure enough total data, capture at least 12 mm of data, unless confidence limits indicate that a shorter time is sufficient. Ideally, all data should be accomplished in a continuous run, but practical considerations can prevent this for two reasons. Firstly, the test track could be insufficiently long to permit a continuous run of such a length at the required test speed. Secondly, the computer used to analyse the data might not be large enough to handle all the data at once. In either case, data may be captured using a number of shorter runs of at least 30 s duration.
For each test run, maintain the longitudinal velocity within a tolerance of ± 3 km/h of the desired test speed.
Determine the steering-wheel angle limits by steady-state driving on a circle, the radius of which gives the preselected steady-state lateral acceleration at the required test speed. The standard steady-state lateral acceleration level is 3 m/s2 or less, as necessary to remain within the range in which the vehicle exhibits linear properties (see “IMPORTANT” in 5.1, and ISO/TR 8726). Optionally, higher lateral acceleration levels may also be used, provided the vehicle remains in the linear range.
13 Pulse input
13.1 Test procedure
Drive the vehicle at the test speed (see 9.4) in a straight line. The initial speed shall not deviate by more than 2 km/h from the test speed. Starting from a 0 0/s ± 0,5 0/s yaw velocity equilibrium condition, apply a triangular waveform steering-wheel input, followed by 3 s to 5 s neutral steering-wheel position. No change in throttle position shall be made, although speed may decrease.
Use a pulse width of 0,3 s to 0,5 s. Make efforts to minimize the overshoot of the steering-wheel angle and the differences between zero references before and after the steering-wheel input to values 5 % of the peak input level. The zero reference is the steady-state value before and after the steering-wheel input.
Determine the amplitude of the steering-wheel input by steady-state driving on a circle, the radius of which gives the preselected steady-state lateral acceleration at the required test speed. The standard steady-state lateral acceleration level is 4 m/s2 or less as necessary to remain within the range in which the vehicle exhibits linear properties (see “IMPORTANT” in 5.1). Optionally, higher lateral acceleration levels may also be used, provided the vehicle remains in the linear range.
Perform all test runs at least three times.