SECTION 12: BRAKE AND AIR SYSTEM
30
DOB 2490-2789 | X3-45 Commuter PA1605 Maintenance Manual (Final Version – Rev.2 April 2016)
FIGURE 44: M-40QR PRESSURE MODULATOR VALVE
Maintenance
NOTE
On older vehicles, when replacing for the first
time the older modulator valve M-32QR by the
newer M-40QR modulator valve, it is important
to replace both left and right valves on the
vehicles drive axle or front suspension.
Modulator valve model can be easily identified
by their different side cover and exhaust
section.
Mixing valve type on the left and right sides of
the vehicle may result in slight pull to one side
when braking.
Maintenance, removal and installation
information of this valve is supplied in Bendix
booklet, reference number SD-13-4958.
30.3
ADVANCED ABS WITH ELECTRONIC
STABILITY CONTROL (ESC)
Overview
Bendix ESC stability system reduces the risk of
rollovers, jackknifing and other loss of control.
ESC features include Roll Stability Program
(RSP) and Yaw Control. During operation, the
ECU of the Bendix Advanced ABS system
constantly compares performance models to the
vehicle’s actual movement, using the wheel
speed sensors of the ABS system, as well as
lateral, yaw, and steering angle sensors. If the
vehicle shows a tendency to leave an appropri-
ate travel path, or if critical threshold values are
approached, the system will intervene to assist
the driver.
Roll Stability Program
Bendix RSP, an element of the overall ESC
system, addresses rollover conditions. In the
case of a potential roll event, the ECU will
override the throttle and quickly apply pressure
at all wheel ends to slow the vehicle combina-
tion. The level of braking application during an
RSP event will be proportional to roll risk.
Yaw Stability
Yaw stability counteracts the tendency of a
vehicle to spin about its vertical axis. During
operation, if the friction between the road
surface and the tires is not sufficient to oppose
lateral (side) forces, one or more of the tires can
slide, causing the vehicle to spin. These events
are referred to as either an “under-steer”
situation (where there is a lack of vehicle
response to steering input due to the slide on
the front axle) or an “over-steer” (where the
vehicle’s rear end slides out due to tire slide on
the rear axle) situation. Factors that influence
yaw stability are: wheelbase, suspension,
steering geometry, weight distribution front to
rear, and vehicle track width.
Yaw Control
Yaw Control corresponds to a wide range of low
to high friction surface scenarios including
rollover, jackknife and loss of control. It is the
recommended system for all power vehicles and
especially critical for vehicles pulling trailers. In
the case of vehicle slide (over-steer or under-
steer situations), the system will reduce the
throttle and then brake one or more of the “four
corners” of the vehicle (in addition to potentially
applying the trailer brakes), thus applying a
counter-force to better align the vehicle with an
appropriate path of travel.
For example, in an over-steer situation, the
system applies the “outside” front brake; while in
an under-steer condition, the “inside” rear brake
is applied.
