Patent Application
20060184299
The present invention relates generally to a control apparatus for controlling a safety system of an automotive vehicle in response to sensed rollover, and more specifically, to a method and apparatus for determining rollover.
Occupant restraint systems and, in particular, inflatable occupant restraint systems, are increasingly being used in automotive vehicles. Nearly every vehicle now produced has driver and passenger front airbags. Side airbags are also increasingly being used in automotive vehicles. Side airbags use lateral acceleration sensors to detect the lateral acceleration of the vehicle and thus the presence of a side impact. In response to lateral acceleration, the side airbags are deployed in side impacts.
Another newer type of inflatable occupant restraint system is a side curtain airbag. The side curtain airbag deploys from the ceiling or near the roof header and extends downward in front of the side windows of the vehicle. This system is designed to protect occupants in rollover conditions.
Another type of non-inflatable system is a pretensioner system coupled to the seatbelt. A pretensioner system reduces the amount of spool-out in the seatbelts upon a sensed condition.
Each of the above systems may potentially be employed during rollover of a vehicle. Commonly, an energy-based model is used to determine when rollover occurs.
Dynamic control systems such as yaw stability control systems and roll stability control systems have been to control vehicle dynamics. Vehicle roll stability control (RSC) schemes, i.e., U.S. Pat. No. 6,324,446, have been proposed to address the issue of friction-induced rollovers. RSC system includes a variety of sensors sensing vehicle states and a controller that controls a distributed brake pressure to reduce a tire force so the net moment of the vehicle is counter to the roll direction.
During an event causing the vehicle to roll, the vehicle body is subject to a roll moment due to the coupling of the lateral tire force and the lateral acceleration applied to the center of gravity of vehicle body. This roll moment causes suspension height variation, which in turn results in a vehicle relative roll angle (also called chassis roll angle or suspension roll angle). The relative roll angle is an important variable that is used as an input to the activation criteria and to construct the feedback pressure command, since it captures the relative roll between the vehicle body and the axle. The sum of the chassis roll angle and the roll angle between wheel axle and the road surface (called wheel departure angle) provides the roll angle between the vehicle body and the average road surface, which is one of the important variables feeding back to the roll stability control module.
Vehicle dynamic control systems such as roll control systems and occupant restraint devices are independent systems, thus not working together. Roll stability control systems may ultimately prevent the vehicle from rolling over even though the energy rate threshold has been reached or exceeded. It would therefore be desirable to provide a system for activating an occupant restraint that utilizes the information available from a dynamic control system in the determination for the activation of the occupant restraint.
The present invention takes into consideration a vehicle instability control signal that may be generated from the activation of a roll stability control system or other dynamic control system and/or an energy threshold.
In one aspect of the invention, a method of operating a vehicle having a safety device includes generating a vehicle instability signal indicative of an unstable vehicle in response to the vehicle instability signal, generating an accumulative directional indicator. The method further includes a step of activating the safety device when the accumulative directional indicator and the vehicle instability signal are indicative of a rollover condition.
In a further aspect of the invention, a method of operating a safety device includes sensing a plurality of dynamic conditions of the vehicle, activating a dynamic control system in response to at least some of the plurality of dynamic conditions and generating a dynamic control system status signal in response to activating. After the step of generating a dynamic control system status signal a rollover trend is determined in response to the roll rate signal. The safety device is activated when the roll trend is indicative of a rollover condition in the dynamic control system status signal.
One advantage of the invention is that the presence of an uncorrectable rollover is determined and activation of a device is prevented during a correctable rollover condition.
Other advantages and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.
In the following figures, the same reference numerals will be used to identify the same components. The present invention may be used in conjunction with a rollover control system or other dynamic control systems for a vehicle. The present invention may also be used with a deployment device such as airbag or active roll bar or pre-tensioning belts. The present invention will be discussed below in terms of preferred embodiments relating to an automotive vehicle moving in a three-dimensional road terrain.
Referring to
As mentioned above, the system may also be used with safety systems including active/semi-active suspension systems, anti-roll bar, or airbags or other safety devices deployed or activated upon sensing predetermined dynamic conditions of the vehicle.
The sensing system 16 is coupled to a control system 18. The sensing system 16 may comprise many different sensors including the sensor set typically found in a roll stability control or a rollover control system (including lateral accelerometer, yaw rate sensor, steering angle sensor and wheel speed sensor which are equipped for a traditional yaw stability control system) together with a roll rate sensor and a longitudinal accelerometer. The various sensors will be further described below. The sensors may also be used by the control system in various determinations such as to determine a lifting event. The wheel speed sensors 20 are mounted at each corner of the vehicle and generate signals corresponding to the rotational speed of each wheel. The rest of the sensors of sensing system 16 may be mounted directly on the center of gravity of the vehicle body, along the directions x, y and z shown in
The angular rate sensors and the accelerometers may be mounted on the vehicle car body along the body frame directions b1, b2 and b3 which are the x-y-z axes of the sprung mass of the vehicle.
The longitudinal acceleration sensor is mounted on the car body located at the center of gravity, with its sensing direction along b1-axis, whose output is denoted as ax. The lateral acceleration sensor is mounted on the car body located at the center of gravity, with its sensing direction along b2-axis, whose output is denoted as aY.
The other frame used in the following discussion includes the road frame, as depicted in
In the following discussion, the Euler angles of the body frame b1b2b3 with respect to the road frame r1r2r3 are denoted as θxbr and θybr, which are also called the relative Euler angles (i.e., relative roll and relative pitch angles, respectively).
Referring now to
Speed sensor 20 may be one of a variety of speed sensors known to those skilled in the art. For example, a suitable speed sensor may include a sensor at every wheel that is averaged by controller 26. The controller 26 may translate the wheel speeds into the speed of the vehicle. Yaw rate, steering angle, wheel speed and possibly a slip angle estimate at each wheel may be translated back to the speed of the vehicle at the center of gravity. Various other algorithms are known to those skilled in the art. Speed may also be obtained from a transmission sensor. For example, if speed is determined while speeding up or braking around a corner, the lowest or highest wheel speed may not be used because of its error. Also, a transmission sensor may be used to determine vehicle speed.
By identifying wheel lift, a roll condition, a yaw condition, activation of the roll stability control system, activation of a yaw control system, a determination as to the vehicle stability and the generation of a vehicle instability signal may be generated.
Roll angular rate sensor 34 and pitch rate sensor 37 may sense the roll condition or lifting of the vehicle based on sensing the height of one or more points on the vehicle relative to the road surface. Sensors that may be used to achieve this include but are not limited to a radar-based proximity sensor, a laser-based proximity sensor and a sonar-based proximity sensor. The roll rate sensor 34 may also use a combination of sensors such as proximity sensors to make a roll rate determination.
Roll rate sensor 34 and pitch rate sensor 37 may also sense the roll condition or lifting based on sensing the linear or rotational relative displacement or velocity of one or more of the suspension chassis components. This may be in addition to or in combination with suspension position sensor 42. The position sensor 42, roll rate sensor 34 and/or the pitch rate sensor 37 may include a linear height or travel sensor, a rotary height or travel sensor, a wheel speed sensor used to look for a change in velocity, a steering wheel position sensor, a steering wheel velocity sensor and a driver heading command input from an electronic component that may include steer by wire using a hand wheel or joy stick.
The roll condition or lifting may also be sensed by sensing directly or estimating the force or torque associated with the loading condition of one or more suspension or chassis components including a pressure transducer in an act of air suspension, a shock absorber sensor such as a load sensor 40, a strain gauge, the steering system absolute or relative motor load, the steering system pressure of the hydraulic lines, a tire laterally force sensor or sensors, a longitudinal tire force sensor, a vertical tire force sensor or a tire sidewall torsion sensor. The yaw rate sensor 28, the roll rate sensor 34, the lateral acceleration sensor 32, and the longitudinal acceleration sensor 36 may be used together to determine that the wheel has lifted. Such sensors may be used to determine wheel lift or estimate normal loading associated with wheel lift. These are passive methods as well.
The roll condition of the vehicle may also be established by one or more of the following translational or rotational positions, velocities or accelerations of the vehicle including a roll gyro, the roll rate sensor 34, the yaw rate sensor 28, the lateral acceleration sensor 32, the vertical acceleration sensor 33, a vehicle longitudinal acceleration sensor 36, lateral or vertical speed sensor including a wheel-based speed sensor 20, a radar-based speed sensor, a sonar-based speed sensor, a laser-based speed sensor or an optical-based speed sensor.
In the preferred embodiment, the sensors are located at the center of gravity of the vehicle. Those skilled in the art will recognize that the sensor may also be located off the center of gravity and translated equivalently thereto.
Lateral acceleration, roll orientation and speed may be obtained using a global positioning system (GPS). Based upon inputs from the sensors, controller 26 may control a safety device 44. Depending on the desired sensitivity of the system and various other factors, not all the sensors 28-42 may be used in a commercial embodiment.
Load sensor 40 may be a load cell coupled to one or more suspension components. By measuring the stress, strain or weight on the load sensor a shifting of the load can be determined.
Controller 26 may include a signal multiplexer 50 that is used to receive the signals from the sensors 20 and 28-42. The signal multiplexer 50 provides the signals to a wheel lift detector 52, a vehicle roll angle calculator 54, and to a roll stability control (RSC) feedback control command 56. Also, wheel lift detector 52 may be coupled to the vehicle roll angle calculator 54. The vehicle roll angle calculator 54 may also be coupled to the RSC feedback command 56. The RSC feedback command 56 may include a torque controller 57. Vehicle roll angle calculator 54 is described in U.S. Provisional Applications 60/400,376 and 60/400,172, and in U.S. patent application Ser. No. 10/459,697, the disclosures of which are incorporated herein by reference.
Safety device 44 may control an airbag 45 or a steering actuator 46a-46d at one or more of the wheels 12a, 12b, 13a, 13b of the vehicle. Also, other vehicle components such as a suspension control 48 may be used to adjust the suspension to prevent rollover.
Safety device 44 may control the position of the front right wheel actuator 46a, the front left wheel actuator 46b, the rear left wheel actuator 46c, and the right rear wheel actuator 46d. Although as described above, two or more of the actuators may be simultaneously controlled. For example, in a rack-and-pinion system, the two wheels coupled thereto are simultaneously controlled. Based on the inputs from sensors 20 and 28 through 42, controller 26 determines a roll condition and/or wheel lift and controls the steering position, braking of the wheels and/or activation of a safety device.
Safety device 44 may be coupled to a brake controller 60. Brake controller 60 controls the amount of brake torque at a front right brake 62a, front left brake 62b, rear left brake 62c and a rear right brake 62d.
The roll condition of a vehicle can be characterized by rolling radius-based wheel departure roll angle, which captures the angle between the wheel axle and the average road surface through the dynamic rolling radii of the left and right wheels when both of the wheels are grounded. Since the computation of the rolling radius is related to the wheel speed and the linear velocity of the wheel, such rolling-radius based wheel departure angle will assume abnormal values when there are large wheel slips. This happens when a wheel is lifted and there is torque applied to the wheel. Therefore, if this rolling radius-based wheel departure angle is increasing rapidly, the vehicle might have lifted wheels. Small magnitude of this angle indicates the wheels are all grounded.
The roll condition of the vehicle can be seen indirectly from the wheel longitudinal slip. If during a normal braking or driving torque the wheels at one side of the vehicle experience increased magnitude of slip, then the wheels of that side are losing longitudinal road torque. This implies that the wheels are either driven on a low mu surface or lifted up. The low mu surface condition and wheel-lifted-up condition can be further differentiated based on the chassis roll angle computation, i.e., in low mu surface, the chassis roll angle is usually very small. Hence, an accurate determination of chassis roll is desired.
The roll condition of the vehicle can be characterized by the normal loading sustained at each wheel. Theoretically, when a normal loading at a wheel decreases to zero, the wheel is no longer contacting the road surface. In this case a potential rollover is underway. Large magnitude of this loading indicates that the wheel is grounded. Normal loading is a function of the calculated chassis roll and pitch angles. Hence, an accurate determination of chassis roll and pitch angles is desired.
The roll condition can be identified by checking the actual road torques applied to the wheels and the road torques, which are needed to sustain the wheels when they are grounded. The actual road torques can be obtained through torque balancing for each wheel using wheel acceleration, driving torque and braking torque. If the wheel is contacting the road surface, the calculated actual road torques must match or be larger than the torques determined from the nonlinear torques calculated from the normal loading and the longitudinal slip at each wheel.
The roll condition of a vehicle can be characterized by the chassis roll angle itself, i.e., the relative roll angle θxr between the vehicle body and the wheel axle. If this chassis roll angle is increasing rapidly, the vehicle might be on the edge of wheel lifting or rollover. Small magnitude of this angle indicates the wheels are not lifted or are all grounded. Hence, an accurate determination of the chassis roll angle is beneficial for determining if the vehicle is in non-rollover events.
The roll condition of a vehicle can also be characterized by the roll angle between the wheel axle and the average road surface, this is called wheel departure angle. If the roll angle is increasing rapidly, the vehicle has lifted wheel or wheels and aggressive control action needs to be taken in order to prevent the vehicle from rolling over. Small magnitude of this angle indicates the wheels are not lifted.
The center of gravity C is also illustrated with nominal mass m. A roll axis is also illustrated at a distance D from the center of gravity. ay is the lateral acceleration.
Referring now to
Another angle of importance is the linear bank angle. The linear bank angle is a bank angle that is calculated more frequently (perhaps in every loop) by subtracting the relative roll angle generated from a linear roll dynamics of a vehicle (see U.S. Pat. No. 6,556,908 which is incorporated by reference herein), from the calculated global roll and pitch angles (as the one in U.S. patent application Ser. No. 09/789,656, which is incorporated by reference herein). If all things were slowly changing without drifts, errors or the like, the linear bank angle and reference road bank angle terms would be equivalent.
Referring now to
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ADI=k1ΣΔω+k2ΣΔθ,
where k1 and k2 are weighting factors for the roll rate and the roll angle. The roll rate is w and the roll angle is θ. In an implementation, the change in roll rate Δω and/or the change in roll angle Δθ term will be monitored for a certain time (5 msec to 100 msec). This is expressed using the Σ in the above equation. When the roll trend is continuing, which means the ADI is positive or non-negative, passive rollover protection system may be needed. In a digital implementation, the above formula may be set forth as ADIk+1=ADIk+k1Δωk+1+k2Δθk+1. Such an implementation is illustrated in block 126. The ADI provides an input to the rollover detection block 110 illustrated in
The gains k1 and k2 may be determined experimentally during testing of the vehicle. A chart or table may be used to adjust the gains based on various vehicle conditions. These conditions may be performed on the test track and may be set for each individual type of vehicle based on the current operating conditions. For example, the gains may change based upon the vehicle forward speed, the yaw rate, the slip angle of the vehicle, the lateral acceleration, and the steering wheel input of the vehicle. Thresholds may be set for the yaw rate, slip rate, forward speed, roll angle/rate to allow the gains k1 and k2 to change.
Referring now to
The energy threshold may be used to determine a roll trend. Also, other variables may be compared to a threshold to determine a roll trend. A combination of comparisons may also be used. For example, comparing lateral velocity, forward velocity, roll rate, roll angle, and yaw rate to respective thresholds may be performed. The thresholds are set during vehicle testing and development.
Referring now to
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In step 148 a roll trend has been indicated in step 146 and a safety device is activated. As mentioned above, various safety devices may be activated including a side curtain airbag, seatbelt pretensioners, external airbags, side impact airbags, and the like.
As is evident to those skilled in the art, the present invention allows a more accurate determination of the vehicle rolling over when vehicle instability is initially indicated. Therefore, unnecessary deployments of airbags when a correction of rollover may be provided by the vehicle is prevented.
While particular embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited only in terms of the appended claims.
