Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Indication or control of braking – acceleration – or deceleration
Reexamination Certificate
2002-05-30
2004-05-25
Nguyen, Tan Q. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Indication or control of braking, acceleration, or deceleration
C701S038000, C340S438000
Reexamination Certificate
active
06741922
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates in general to a rollover prevention system for a heavy duty tractor trailer combination. More specifically, the invention incorporates a rollover prevention algorithm into an antilock braking system (ABS).
Approximately fifty-five percent of all fatalities for operators of tractor-trailer combination vehicles occur in rollover accidents. Rollover can easily occur if the vehicle operator underestimates the speed of the vehicle when entering a corner. In the initial stages of a vehicle rollover condition, one or more wheels of the vehicle lifts off the ground. However, this wheel lift is almost imperceptible to the operator until it is too late (e.g., the vehicle begins to actually rollover) for the operator to reverse the process and prevent an accident.
The main factors which contribute to the rollover of a turning vehicle are vehicle speed, road curvature, position of center of gravity, and tire/road adhesion. Dynamic effects, such as a change in the position of the center of gravity and nonlinear behavior due to a moving load such as a liquid or livestock may also be significant factors. Vehicles with a high center of gravity, such as long haul trucks and tractor-trailer combinations, are particularly susceptible to rollover while cornering at relatively moderate speeds.
FIG. 1
illustrates physical forces that act on a vehicle
10
to cause rollover. The vehicle has a center of gravity (cg), and the height of the center of gravity (h
cg
) is the distance between the point cg and the ground. During steady cornering, lateral or sideways acceleration occurs, and the vehicle is influenced by a downward force (mg) due to gravity and a lateral force (ma
LAT
) due to lateral acceleration. When the vehicle
10
is at rest or traveling in a straight line, the downward force is substantially equally distributed between wheels
12
,
14
at each axle as wheel load, which equals the normal force (F
N1
) (F
N2
). During cornering, however, lateral acceleration causes a sideways imbalance between the wheels
12
(e.g., inner wheels) and the wheels
14
(e.g., outer wheels) due to forces (&Dgr;F
N1
) and (&Dgr;F
N2
) that change the wheel load at each axle. The sideways imbalance force &Dgr;F
N
depends on several parameters such as torsional stiffness and curve radius, which may be approximated as a constant C. Consequently, the sideways imbalance force &Dgr;F
N
may be calculated according to the following equation:
&Dgr;F
N
=C*h
cg
*a
LAT
.
As the lateral acceleration increases, the sideways imbalance force &Dgr;FN reduces the downward wheel load on the inner wheels
12
, and increases the downward wheel load on the outer wheels
14
. If the lateral acceleration exceeds a safe level, the inner wheel load is reduced to zero and the vehicle
10
rolls over. Rollover avoidance measures include reducing speed, lessening lateral force components, and changing vehicle suspension parameters such as damper stiffness or air-bag inflation.
To enhance operator safety, brake system manufacturers offer rollover prevention (ROP) systems. In conventional ROP systems, the determination as to when an unstable condition is imminent is made by monitoring lateral acceleration. If necessary, the brakes are automatically applied to immediately reduce vehicle speed—and thus lateral acceleration—to improve the vehicle's stability. ROP systems are classified as either passive (warning only) or active (automatic intervention) systems.
An ROP system monitors a tractor-trailer combination vehicle from either the tractor or the trailer. A system which observes only the tractor has the advantage of being compatible with virtually any trailer. The drawback, however, is that an impending rollover of the trailer is difficult to detect from the tractor. For example, a flatbed trailer has a flexible frame. In this case, prior to an impending rollover, the wheels of the trailer that leave the ground first are on the inside of the curve (i.e., the inner wheels), while the wheels of the tractor that leave the ground first are on the outside of the curve (i.e., the outer wheels). A box style trailer, on the other hand, has a rigid frame. In this case, prior to an impending rollover, the trailer causes the inner wheels of the tractor's driven axle to also leave the ground first.
Three major directions of ROP system development are: i) tractor-based ROP; ii) trailer-based ROP; and iii) position monitoring ROP. Each of these types of ROP systems is discussed below in greater detail.
In a tractor-based ROP system, one or more sensors are located on the tractor, and output(s) of the tractor mounted sensors are utilized for estimating lateral acceleration of the trailer. If the estimated lateral acceleration exceeds a predetermined level, a test braking pressure is applied to the trailer. The test pressure is a moderate level of braking automatically applied to the trailer through the tractor's trailer brake control proportioning valve. ROP logic determines whether one of more of the trailer's wheels does not have firm contact with the road surface. More specifically, if the application of the test pressure locks the trailer's wheels, it is determined via the ROP logic that the wheel(s) have little or no contact with the road surface, and therefore the trailer's ABS is activated. A current sensor mounted on the tractor detects when wheel-end modulator valves mounted on the trailer are activated as a function of additional electric power consumed by the trailer. In this case, the ROP system triggers an automatic brake application for the tractor-trailer combination.
The tractor-based approach has several disadvantages. For example, the reaction time of such systems is relatively slow, which occurs due to a time lag while air pressure builds on the trailer. Furthermore, tractor-based systems require a current sensor on the tractor to sense the trailer's power consumption, an electronic braking system (EBS) installed on the tractor, and an ABS installed on the trailer. In addition, tractor-based ROP is not a satisfactory solution for box trailers, which have a rigid frame, since, as discussed above, the tractor's driven axle is lifted off the ground by the trailer before the trailer's wheels are lifted off the ground. Thus, by the time the ROP system detects that the trailer's wheels are lifted off the ground, it is too late to prevent the rollover event.
Trailer-based ROP works similar to the tractor-based variant. One or more sensors are located on the trailer. Lateral acceleration of the trailer is estimated as a function of signals output from the sensors. If the estimated lateral acceleration of the trailer exceeds a predetermined level, a test braking pressure is applied to the trailer's inner wheels and ABS activity is monitored. In case of wheel locking, which is a sign of lifted wheels and impending rollover, a full trailer brake application is initiated by the ROP system for preventing a rollover. If an appropriate data link with the tractor exists, the operator may be warned as well.
Although trailer-based ROP systems do not require interaction with the tractor, such systems may not perform acceptably when used with some rigid-body semi-trailers and, furthermore, may require additional hardware to interface with certain EBSs on the trailer.
Position monitoring ROP calculates the trailer's roll angle using a roll rate sensor. Data from such a sensor, when combined with the speed and lateral acceleration, indicate whether any further increases in speed or lateral acceleration could lead to a rollover. This method involves previously known trailer specific structural/dynamic information. The knowledge of exact vertical position as a result of integration of the roll rate sensor is crucial. Once an impending rollover scenario is detected, the ROP system initiates brake application on the trailer or another appropriate counter step(s) (e.g., changing the trailer suspension's characteristics to inhibit ro
Bendix Commercial Vehicle Systems LLC
Calfee Halter & Griswold LLP
Nguyen Tan Q.
Tran Dalena
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