PMP – Particle Measurement Program UNECE Informal Group
Non-exhaust particle emissions
Working Item 1
Investigation of typical driving patterns and in particular of typical
accelerations/decelerations
Questions related to the present document
Q1. Does the content of the document cover the main aspects discussed during the last
face-to-face meeting?
Q2. Does the table cover the most important aspects regarding driving conditions?
Please provide comments/suggestion
This document is the result of discussion regarding the parameters that need to be taken
into consideration in order to derive a solid definition of typical driving patterns for the
purpose of investigating wear particles.
1. Introduction
Driving conditions have a large influence on particle generation for brake and tyre wear
processes. From the survey of the available literature it appears that different driving
conditions in experimental investigation of particle emissions from brake and tyre wear is
one of the reasons why different - or even sometimes- contradictory conclusions are
reported. In particular, during hard accelerations or decelerations ultrafine particles can be
generated due to the high temperatures reached in brakes and tyres. The question is
whether these conditions are within the range of the driving conditions that can be
considered “normal/typical” or should be considered as “extreme” with a low occurrence
frequency.
In addition, there are already standardized test conditions used by the industry in designing
brake systems as well as tyres.
In order to harmonize future studies on particles from brake and tyre wear and improve the
comparability of the relative results, the definition of “normal” or “typical” driving patterns
and in particular of typical accelerations/decelerations has been identified by PMP group
as an important working item.
The proposed approach is to use activity data collected in the framework of other projects
in order to investigate typical acceleration / deceleration frequency distributions. The main
objectives of this activity are to compare “typical/normal driving conditions” derived by
existing datasets like the WLTP vehicle activity database with the industry standards, as well
as to reach, if possible, a shared definition of normal, severe, extreme or infrequent
conditions. This will narrow down the range of driving conditions to be taken into
consideration as far as non-exhaust particle emissions are concerned and will improve the
comparability of future studies.
In the 33d PMP Meeting held in Brussels on the 1st-2nd October 2014 Mr. Heinz Steven, who
was in charge of the statistical analysis of the vehicle activity data collected in the
framework of the WLTP project, illustrated the data available and gave an overview on what
specific information can be distilled from this data set. As next step, it was decided to
prepare a document, which will be circulated and commented by the members of the PMP
group, describing what parameters related to driving conditions are important, as far
particle from brake and tyre wear are concerned. This document which will provide the
basis for further processing of the WLTP (or others) data set to extract the relevant
information was presented and discussed in the 35th PMP Meeting held in Brussels on the
4th-5th March 2015.
It was also decided that working item 1 should be completed by June 2015 (71st GRPE
Meeting) with a proposal on a definition of typical/normal driving conditions.
2. List of parameters to be taken into consideration
Non-exhaust traffic related wear particles content, properties and generation rates depend,
among other, on parameters such as the brake system temperature (pad and disc) and the
tyre surface temperature. These parameters are largely influenced by driving conditions
such as those listed in the table below. Grey shadowed cells refer to parameters already
calculated from previous work done for the WLTP database:
Parameter
Brake Wear
Particles
Tyre (and road)
Wear Particles
1
Trip length distribution
Relevant
Relevant
2
Speed distribution in urban and
extra-urban areas/highways
Relevant
Relevant
3
Acceleration rate distribution in urban
and extra-urban areas/highways
Relevant
Relevant
4
Deceleration rate distribution in urban
and extra-urban areas/highways
Relevant
Relevant
5*
Braking frequency
as a function of the trip length
Relevant
Relevant
Not relevant
Relevant
Relevant
Relevant
Relevant
Relevant
Relevant
Relevant
6
7
8
9
Acceleration frequency
(Time and distance based distribution
of acceleration phases per vehicle and
in relation to the trip and “short trip”)
Deceleration frequency
(Time and distance based distribution
of deceleration phases per vehicle and
in relation to the trip and “short trip”)
Braking severity (deceleration x
vehicle speed distribution – indicates
energy dissipated by brakes and tyres)
Definition of a short journey
*Determination of the use of the brakes during deceleration phases by using expert guess based thresholds
for v*a and calculation of the distributions described in 7 and 8 but restricted to brake use only
1
Brake pressure in urban and extra-urban areas/highways and Brake pressure distribution while stopping:
Attention should be paid in distinguishing brake line and friction pressure, they are not the same. Since these
parameters cannot be derived by the WLTP database some data will be provided by brake manufacturers - and
possibly OEMs - in order to test the suitability of this parameter.
2
Amount of creeping situations next to standstill (traffic jam): There should be information related to this
parameter when the “typical short journey” is defined. It should be relevant to the temperature of brakes and
thus brake wear but not for tyres. The idea is not just define the “typical short journey” but calculate other
parameters as a function of the “typical short journey”.
3
Parameters like brake recuperation profile (relevant for hybrids and EVs), intervention of ESC / ACC / and
other systems, number of EPB / Mechanical PB application (influencing factor regarding residual drag and offbrake-wear) could be relevant but these cannot be derived by available datasets and ii. They have minor
influence compared to parameters like speed and acceleration profile.
4
Slope/descent during braking and state of the vehicle before usage (i.e. long parking) and vehicle load
condition could be relevant and Heinz Steven will be consulted for these parameters. The above mentioned
parameters could be relevant for both tyres and brakes.
5
Lateral acceleration profile (influencing factor regarding residual drag - pad/disc clearance) is probably
relevant for both brakes and tyres but cannot be derived by currently available datasets.
3. Approach
One of the open issues on working item 1 is whether it makes sense to investigate
“normal/typical driving conditions” at global level or extend the analysis at regional level. As
agreed at the 33d and 35th PMP IG face-to-face meetings, both approaches will be followed
in order to compare the “normal/typical driving conditions” of different regions. One
important reason behind this decision is that different regions have today different brake
friction couple technologies (like NAO and ECE), as well as different driving styles as already
taken into account in the definition of the harmonized test cycle for emissions (WLT).
4. Data available
The WLTP database represents an important source of data that can be analysed to derive
the parameters listed above. Besides the WLTP database there are several other databases
that could be used (i.e. FIAT eco-drive which contains 1 Hz data for about 2 Million km
distance), but at this point it was decided to proceed with WLTP database.