STAS STAS M, Instructions For Use Manual

Page: 19 / 66

STAS nv – Flanders Fieldweg 45 – 8790 WAREGEM (BELGIUM) Instructions for use, tipper trailer – Version 3.1
Tel. +32 (56) / 60 01 91 – Fax +32 (56) / 60 01 95 – e-mail : sales@stas.be web – - http://www.stas.be Page 16
Anti-locking function (ABS)
The electronics use the signals from the wheel speed sensors to calculate whether one or more wheels
are in danger of locking and decide whether the applied brake pressure should be reduced, maintained
or increased.
For a 2S/2M-configuration, one ABS sensor and pressure control circuit of the trailer modulator have
been combined into one control channel. Any other wheels on that side of the trailer, if present, will be
controlled indirectly. The brake forces are controlled as per the Individual Regulation (IR) principle.
Each side of the trailer can apply a different brake pressure depending upon the conditions of the road
surface and braking characteristics.
For a 4S/2M-configuration (optional) two ABS sensors will be connected for each side of the trailer.
Again, the brake pressure will be regulated per side. All brake cylinders on one side will have the same
pressure. The wheels on one side which are fitted with wheel speed sensors will be adjusted according
to the Modified Side Regulation principle (MSR). The wheel which is most likely to lock on one side of
the trailer determines for that side whether ABS regulation is required. Both modulators are controlled
per side independent of one another. The principle of individual regulation is applied where both sides
of the trailer are concerned.
A 4S/3M-configuration (optional) is used on trailers with a steering axle. The main axle(s) is individually
controlled (IR) as per the 2S/2M-configuration as described previously. On the steering axle,
conversely, there are two sensors and one EBS-relay valve. This provides regulation per axle. The
wheel which is in danger of locking is used for the ABS regulation of the axle. The ABS regulation
occurs as per the Modified Axle Regulation (MAR).
For all configurations listed above, apart from the brake cylinders of ABS sensored wheels, non-
sensored wheels of adjacent axles may also be connected to the modulators. However, these indirectly
regulated wheels will not pass any information to the trailer modulator in the case of potential locking.
The anti-lock brakes on these wheels can therefore not be guaranteed. Figure 3.2.4.b. shows some
examples of sensor locations for the various configurations.
Figure 3.2.4.b. – Placement of the sensors
NEVER pump the brakes. This has possible adverse effects on the braking
behaviour of the trailer.
Roll Stability Support (RSS) (optional)
There are various definitions relating to a vehicle rolling over:
 A vehicle may roll over if the critical lateral acceleration is less than the maximum friction between
the tyres and the road.
 The critical lateral acceleration for rolling over is the limit value of the force which is allowed to
affect a vehicle laterally in the driving direction before the vehicle rolls over.
 The maximum friction between the tyres and the road is the limit value of the force, which is
allowed to affect a vehicle laterally on the driving direction before the vehicle slips.
Trailers often have a relatively high centre of gravity and are therefore extremely likely to roll over when
tight bends are being taken at too high speeds. For trailers, the critical lateral acceleration may be lower
than that of the lorry. In contrast to the rolling over risk of the lorry, the driver often notices this too late
where the trailer is concerned in order to be able to take corrective action (by braking for instance).
With the aid of the RSS function, the imminent risk of the trailer rolling over is recognised and corrected
by automatic braking. This reduces the risk of rolling over.
The RSS function uses the available details of the Trailer EBS:
 wheel speed,
 information on the load,
 information on the required deceleration,
 information from the sensor for lateral acceleration integrated in the EBS modulator.
RSS recognises the risk of rolling over as a result of strong relief in pressure on the wheels in the inside
bend. When the calculated critical lateral acceleration of the trailer is exceeded, a low testing pressure
is temporarily applied. Duration and height of the pressure depend upon the current critical lateral
acceleration. The risk of rolling over is recognised using the wheel reaction during test braking.
When the risk of rolling over is detected, high pressure braking on the wheels of the trailer in the
outside bend will take place in order to prevent rolling over. The brake pressure for the wheels in the
inside bend will remain mainly unchanged, depending upon any ABS regulation.
When braking in accordance with RSS, the brake lights do not illuminate because
the brake light can only be activated by the lorry whereas RSS braking is
controlled by the trailer.
RSS adjustment starts during a driving situation with partial or no braking. If the driver brakes
sufficiently (retardation above the level of the RSS retardation) RSS is not activated. If, during an RSS
adjustment of the trailer which has already started, the lorry indicates a pneumatic or electric braking
value, RSS adjustment will be cancelled as soon as the braking value of the lorry is higher than that of
the RSS. The braking pressure in the trailer is then adjusted to the requirements of the lorry up to the
end of the braking operation.