AN INVESTIGATION OF ANTI-LOCK BRAKING SYSTEMS FOR HEAVY GOODS VEHICLES
#1

AN INVESTIGATION OF ANTI-LOCK BRAKING SYSTEMS FOR HEAVY GOODS VEHICLES

ABSTRACT
An articulated lorry was instrumented in order to measure its performance in straight-line
braking. The trailer was fitted with two interchangeable tandem axle sub–chassis, one with
an air suspension and the other with a steel monoleaf 4–spring suspension. The brakes were
only applied to the trailer axles, which were fitted with anti–lock braking systems (ABS),
with the brake torque controlled in response to anticpated locking of the leading axle of the
tandem. The vehicle with the air suspension was observed to have significantly better
braking performance than the steel suspension, and to generate smaller inter–axle load
transfer and smaller vertical dynamic tyre forces.
Computer models of the two suspensions were developed, including their brakes and anti–
lock systems. The models were found to reproduce most of the important features of the
experimental results. It was concluded that the poor braking performance of the steel 4–
spring suspension was mainly due to interaction between the ABS and inter–axle load
transfer effects. The effect of road roughness was investigated, and it was found that vehicle
stopping distances can increase significantly with increasing road roughness.
Two alternative anti–lock braking control strategies were simulated. It was found that
independent sensing and actuation of the ABS system on each wheel greatly reduced the
difference in stopping distances between the air and steel suspensions. A control strategy
based on limiting wheel slip was least susceptible to the effects of road roughness.
INTRODUCTION
Over the last few years, there has been a trend towards use of air suspensions on heavy vehicles,
replacing traditional steel leaf–spring suspensions. The Commission of the European Community
has actively encouraged this trend in the belief that softer suspensions, such as air, produce less
road wear [1]. The differences between these suspensions in braking has not been considered in
detail. It has also become mandatory, since October 1989, to fit anti-lock braking systems (ABS)
to all heavy goods vehicles in the UK, and this legislation is likely to be extended following the
drafting of new legislation in the EEC [2].
Robinson [3] measured the stopping distances of heavy vehicles, with and without ABS, and
showed that under certain conditions the action of the ABS can extend stopping distances.
However, his overall conclusion was that these small increases in stopping distance are a small
cost compared with the benefit of improved controllability, and the elimination of jack-knifing.
Robinson also found that using independent ABS systems on each axle in multiple–axle
suspensions always gave shorter stopping distances than controlling all of the brakes with the
output of an ABS sensor on a single axle.
A computer simulation study of an ABS system fitted to a ‘walking-beam’ suspension was
performed by Fancher et al [4]. The researchers found that the ABS could cycle at 3Hz which
would ‘tune-in’ to one of the pitch modes of vibration of the vehicle, causing large oscillations,
and increasing stopping distances. The simulation agreed well with the experimental results.
The main objectives of the study described in this paper were:
(i) To measure and analyse the differences in straight-line braking performance of two
conventional UK suspensions, one with steel springs and one with air springs, both fitted
with ABS;
(ii) To investigate the performance of various ABS control strategies: (a) a standard commercial
system with wheel-speed sensors on a single axle; (b) the same system but with a sensor on
each wheel; and © an unconventional system controlling the longitudinal slip of each
wheel.
EXPERIMENTAL PROGRAMME
The experiments were conducted on a long, straight section of the Transport Research Laboratory
(TRL) test track during a period of three weeks in August and September 1992 (see [5] for details).
The test vehicle was a four axle articulated tractor/semi–trailer combination. The tractor had two
axles with steel suspensions on each, and the trailer had a detachable subchassis to which
instrumented tandem axle air and steel suspensions were fitted in turn. The vehicle was tested with
each subchassis to assess its straight–line braking performance under a variety of different
operating conditions. The instrumentation measured the vertical and longitudinal (braking) forces
applied to the braked axles, as well as the longitudinal acceleration and speed of the vehicle. The
trailer was a compartmentalised fuel-oil tanker, and the unladen gross weight of the combination
was approximately 13 tonnes. For the laden tests, a gross weight of 31 tonnes was achieved by
completely filling four of the seven compartments in the tanker with water.
The trailer suspensions were: (i) a Crane Fruehauf air suspension with Rubery Owen–Rockwell
axles, and (ii) a Crane Fruehauf monoleaf wide spread 4–spring suspension, with Crane Fruehauf
axles. Both suspensions were tested with the same set of Dual 11R22.5 tyres, and both
subchassis were equipped with identical ‘Skidchek MGX’ anti–lock braking systems manufactured
by Grau Limited. The brakes on the two suspensions were made by different manufacturers, but
all brakes were fitted with new Duron P2001 linings immediately before the tests. The ABS
systems measured wheel rotation on the leading axle of the tandem suspensions, and controlled the
brake torque applied to both axles with the same output air pressure signal.
The pneumatic system of the vehicle was modified so that the trailer brakes could be applied
independently of the tractor brakes, by a test engineer in the driver’s cab. The system was
designed so that normal braking action by the driver would over-ride the test and cause all brakes
to be applied if necessary. The brakes were only applied to the trailer axles, so as to
emphasise any suspension differences that would otherwise be masked by the behaviour of
the tractor. The instrumentation and experimental procedure are described in [6].
All of the braking tests presented in this paper were conducted from an initial vehicle speed of
18 m/s (40 mph). This speed was chosen so that the trailer brakes would dissipate approximately
the same amount of energy as they would under normal operation, with all vehicle brakes
operating, when stopping from 27 m/s (60 mph). (This assumes the trailer contributes
2
approximately half of the braking force under normal operation.) Tests were also conducted from
9 m/s and these results are presented in [5]. All tests were carried out when the track was dry.
1 2 3 4 5 6 7 8 9
Nominal Brake Pressure (bar)
0
50
100
150
200
Stopping Distance (m)
Steel laden
Air unladen
Steel unladen
Air laden
Fig. 1 Measured stopping distances from 15 m/s.
Figure 1 shows stopping distances as a function of brake pressure for both suspensions, for the
laden and unladen tests. To reduce errors due to variations in the initial speed (nominally 18 m/s),
all braking distances were measured from the point at which the speed reached 15 m/s.
For low brake pressures, none of the wheels of the laden vehicles were observed to skid, and the
ABS system did not intervene in the brake operation. In these cases, the stopping distance is most
strongly affected by the relationship between brake pressure and brake torque, which is a
characteristic of the brake actuation system. The two trailer subchassis had different axles, with
slightly different brake actuation systems, which accounts for the (unimportant) differences
between stopping distances of the laden vehicles at low pressures.
Of much more significance are the results for the laden vehicles at higher brake pressures, above 6
bar, and for the unladen vehicles. It can be seen that in both of these situations, the air suspended
vehicle stops considerably more quickly than the leaf–sprung vehicle. It can also be seen that
increasing the brake pressure further has little or no beneficial effect. This is because the brake
pressure is sufficient to cause the wheels to lock–up and the stopping distance is governed by the
action of the ABS.
At high pressures the stopping distances of the unladen vehicles are greater than for the same
vehicles when laden. This is again attributable to the action of the ABS. When there is only a
small mean vertical load on the trailer suspension, skidding is more likely under the action of the
brakes. Therefore the ABS spends more time switching the brakes off when the vehicle is
unladen. This effect is most dramatic for the air suspension. Note, however, that this effect
would be much less exaggerated if all the brakes on the vehicle were applied, because the heavily
laden tractor axles would make a significant contribution to the overall braking effort.
It is useful to examine the measured longitudinal (braking) forces and vertical tyre forces generated
by the suspensions during braking. The tyre forces from tests on the unladen steel suspension at a
nominal pressure of 4 bar are shown in figures 2a, b. The longitudinal force trace, Fig. 2a,
shows the time at which the brakes are activated (at approximately 1 second); when the ABS
switches off, the tyres begin to skid and the oscillations stop (at approximately 11 s); and when
the vehicle stops skidding and finally comes to rest, rocking gently on its tyres (at 13 s). For this
suspension the mean value of the longitudinal force whilst the ABS is active is less than the
3
skidding value, between 11 and 13s. This is due to a combination of vertical load transfer between
the two steel–suspended axles and the action of the ABS, and will be explained in detail later.
Once the vehicle has stopped (after 13s), the difference between longitudinal forces generated by
the two axles is due to static tyre/road friction forces.
The vertical tyre forces generated during the same test run are shown in figure 2b. The mean
vertical force on the leading axle of the steel suspension (7 kN) is considerably less than for the
trailing axle (13 kN). This is due to ‘static’ load transfer from the leading to the trailing axle,
through the load levelling linkage. This phenomenon is not exhibited by the air suspension. For a
more detailed discussion of the experimental results see [6].
0 2 4 6 8 10 12 14
-10
0
10
20
Longitudinal force (kN)
Leading axle
Trailing axle
(a) Time (s)
0 2 4 6 8 10 12 14
Vertical force (kN)
0
10
20
Leading axle
Trailing axle
(b) Time (s)
Fig. 2 Measured tyre forces generated by the steel suspension for an unladen test
at 4 bar brake pressure. (a) Longitudinal force, (b) Vertical force.
COMPUTER SIMULATION
The main aim of the simulation study was to develop the simplest possible models of the
suspensions, tyres and braking systems, which explained the main features of system behaviour.
Vehicle Models
The model used to analyse the behaviour of the vehicle with the leaf–spring suspension is shown
in figure 3. It had seven degrees of freedom (shown as arrows on the figure): vertical motion of
the sprung mass; bouncing motion of the two axles constrained by the radius arms; load leveller
pitch; rotation of the two wheels; and longitudinal motion of the whole vehicle. The tractor unit
(which did not have its brakes applied during the tests) was modelled as a mass, constrained to
move horizontally, but not resting on the braked axles.
The geometry of the wide spaced 4–spring suspension was simplified and linearised, but still
retained the features that are important in braking. The leaf–springs were replaced with equivalent
linear springs and viscous dampers which gave appropriate energy dissipation. The levelling beam
was enlarged so that it connected the springs, and maintained its vertical load levelling action. The
inclined ‘radius arms’ in the suspension model were necessary, because horizontal forces at the
tyre/road interface cause some vertical movement of the axles. The angles of the two radius arms
were different, and were not equal to the angles of the ‘real’ radius arms on the test suspension.
4
This is because axle wind-up and rotation of the leaf–springs during braking cause the axles to
rotate about an instantaneous centre that is not located at the attachment point of the real radius
arms.
The tyres were modelled as linear springs with light damping and the ability to lose contact with the
road surface if necessary. The reactions generated by the tyre springs and dampers at the road
acted perpendicularly to the road surface. The generation of braking forces by the tyres is
described in the next section.
Trailer
Tractor
Radius arm
Levelling
beam
Degrees of freedom
Fig. 3 Vehicle model.
The air suspension was simulated using the same vehicle model, but with the levelling arm fixed in
the horizontal position. In this case, the angles of the radius arms were set equal to the angles of
the trailing arms on the real suspension. (The axles of the air suspension are less susceptible to
wind-up, and therefore rotate about the trailing arm attachment points.)
The parameters chosen for the simulation came from various sources. Vehicle suspension
parameters were mostly measured values, taken from a previous experimental study on the vertical
vibration of the same vehicle [7]. The angles of inclination of the radius arms of the steel
suspension were fitted to the experimental results for one of the test runs.
Reply
#2

to get information about the topic "anti lock braking system ppt " full report ppt and related topic refer the page link bellow

http://studentbank.in/report-anti-lock-b...e=threaded


http://studentbank.in/report-anti-lock-b...e=threaded

http://studentbank.in/report-an-investig...s-vehicles

http://studentbank.in/report-anti-lock-b...e=threaded

http://studentbank.in/report-anti-lock-b...e=threaded
Reply

Important Note..!

If you are not satisfied with above reply ,..Please

ASK HERE

So that we will collect data for you and will made reply to the request....OR try below "QUICK REPLY" box to add a reply to this page
Popular Searches: fabrica arms 7mm mauser, anti lock brake problems, questionnaire of durable goods, goods in rural market latest project ppt, electrical goods, anti lock braking system seminar project docs file download, air braking systems,

[-]
Quick Reply
Message
Type your reply to this message here.

Image Verification
Please enter the text contained within the image into the text box below it. This process is used to prevent automated spam bots.
Image Verification
(case insensitive)

Possibly Related Threads...
Thread Author Replies Views Last Post
  AUTOMATED CAR BRAKING SYSTEM USING FUZZY LOGIC CONTROLLER project uploader 3 3,756 15-05-2013, 09:52 AM
Last Post: computer topic
  SLOT VIEW SIMULATION OF WIND ELECTRICAL SYSTEMS seminar paper 1 1,354 26-11-2012, 01:49 PM
Last Post: seminar details
  INTRODUCTION TO DATABASE MANAGEMENT SYSTEMS seminar paper 1 2,194 13-11-2012, 12:18 PM
Last Post: seminar details
  AUTO BRAKING SYSTEM seminar paper 1 1,198 09-11-2012, 11:46 AM
Last Post: seminar details
  BUG TRACKING SYSTEMS project uploader 1 1,767 20-10-2012, 12:37 PM
Last Post: seminar details
  SIMULATION OF AN ANTI-COLLISION SYSTEM ON SAME TRACK FOR RAILWAYS full report seminar details 0 1,119 08-06-2012, 04:43 PM
Last Post: seminar details
  An Open Source Laboratory for Operating Systems Projects full report seminar details 0 939 08-06-2012, 04:21 PM
Last Post: seminar details
  Mobile Radio Systems Historical Milestones to 1995 seminar details 0 764 08-06-2012, 11:55 AM
Last Post: seminar details
  An Open Source Laboratory for Operating Systems Projects seminar details 0 879 08-06-2012, 11:31 AM
Last Post: seminar details
  Vision for Beyond 4G Broadband Radio Systems seminar details 0 1,017 07-06-2012, 12:07 PM
Last Post: seminar details

Forum Jump: