Steering compensation with grip sensing

A system for grip-based handwheel compensation includes a net handwheel torque moment determination module that determines a net handwheel torque moment between a left grip and a right grip on a handwheel. The system also includes a filter transition compensation module that applies a filter to smooth transitions in the net handwheel torque moment as a bias compensation. The system further includes a handwheel torque compensation module that determines a grip compensated handwheel torque based on a difference between a sensed handwheel torque and the bias compensation.

BACKGROUND OF THE INVENTION

Steering systems are typically tuned by engineers holding a steering wheel (also referred to as a handwheel) with two hands in a symmetric grip pattern (e.g., 9/3 o'clock or 10/2 o'clock hand positions). However, in operation, drivers often adapt the grip patterns for comfort which can result in asymmetric grip patterns. Such an asymmetric grip pattern often results in a bias torque on the handwheel due to the weight of the driver's arm acting on the rim of the handwheel with unbalanced moment arms. This bias torque is very similar to the steering pull due to chassis/tire imbalances. The unbalance has to be compensated by the arm muscles of the driver and can result in driver fatigue over longer times/distances.

Another situation occurs when a driver shifts from two-handed to one-handed driving. This can take place either due to arm fatigue or because the driver is performing another task with the free hand, e.g., holding a beverage cup, operating an infotainment system, etc. A steering system tuned for two-handed driving can be significantly more fatiguing to drive with one hand, as the force required in a single hand has to be doubled to produce the same input shaft torque.

SUMMARY OF THE INVENTION

A system for grip-based handwheel compensation includes a net handwheel torque moment determination module that determines a net handwheel torque moment between a left grip and a right grip on a handwheel. The system also includes a filter transition compensation module that applies a filter to smooth transitions in the net handwheel torque moment as a bias compensation. The system further includes a handwheel torque compensation module that determines a grip compensated handwheel torque based on a difference between a sensed handwheel torque and the bias compensation. Grip force or pressure can be determined with respect to a grip area on the handwheel.

A steering system includes a handwheel torque sensor operable to produce a sensed handwheel torque, a steering actuator motor, and a control module. The control module is operable to determine a net handwheel torque moment between a left grip and a right grip on a handwheel, apply a filter to smooth transitions in the net handwheel torque moment as a bias compensation, determine a grip compensated handwheel torque based on a difference between the sensed handwheel torque and the bias compensation, and control the steering actuator motor based on the grip compensated handwheel torque.

A method for grip-based handwheel compensation includes determining, by a control module of a steering system, a net handwheel torque moment between a left grip and a right grip on a handwheel. A filter is applied to smooth transitions in the net handwheel torque moment as a bias compensation. A grip compensated handwheel torque is determined based on a difference between a sensed handwheel torque and the bias compensation.

DETAILED DESCRIPTION

Referring now to the Figures, where the invention will be described with reference to specific embodiments, without limiting same, an exemplary embodiment of a vehicle10including a steering system12is illustrated. In various embodiments, the steering system12includes a handwheel14coupled to a steering shaft16. In the exemplary embodiment shown, the steering system12is an electric power steering (EPS) system that further includes a steering assist unit18that couples to the steering shaft16of the steering system12and to a left tie rod20and a right tie rod22of the vehicle10. The steering assist unit18includes, for example, a rack and pinion steering mechanism (not shown) that may be coupled through the steering shaft16to a steering actuator motor19and gearing. During operation, as the handwheel14is turned by a vehicle operator, the steering actuator motor19provides the assistance to move the left tie rod20and the right tie rod22which in turn moves left and right steering knuckles24,26, respectively. The left knuckle24is coupled to a left roadway wheel28, and the right knuckle26is coupled to a right roadway wheel30of the vehicle10.

As shown inFIG. 1, the vehicle10further includes various sensors31-35that detect and measure signals of the steering system12and/or of the vehicle10. The sensors31-35generate sensor signals based on the measured signals. In one embodiment, a handwheel torque sensor31is provided for sensing a torque placed on the handwheel14. In the exemplary embodiment as shown, the handwheel torque sensor31is placed on the handwheel14, however it is to be understood that the handwheel torque sensor31may not always be placed near or on the handwheel14. In one embodiment, a motor position/velocity sensor32senses motor position and/or velocity, and a handwheel position/velocity sensor33senses handwheel position and/or velocity. In addition, the vehicle10may include a wheel speed sensor34to assist in measuring vehicle speed. In some embodiments, one or more grip sensors35measure a grip force or pressure on the handwheel14at various locations, such as a left grip15A and a right grip15B defined in reference to a straight ahead position of the handwheel14. In alternate embodiments, the grip sensors35are omitted, and grip magnitude and/or angular position values are computed using other parameters of the steering system12.

A control module40controls the operation of the steering system12based on one or more of the sensor signals and further based on the steering control systems and methods of the present disclosure. The control module40generates a command signal to control the steering actuator motor19of the steering system12based on one or more of the inputs and further based on the steering control systems and methods of the present disclosure. The steering control systems and methods of the present disclosure adapt and compensate for a moment created by the grip style of a driver operating the handwheel14.

FIG. 2illustrates a system100for grip-based handwheel compensation according to an embodiment. The system100includes control module40and may include one or more of the sensors31-35ofFIG. 1. In various embodiments, the control module40can include one or more sub-modules and datastores, such as a net handwheel torque moment determination module102, a filter transition compensation module104, a scale one-handed module106, and a handwheel torque compensation module108. As used herein the terms module and sub-module refer to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, or other suitable components that provide the described functionality. As can be appreciated, the control module40shown inFIG. 2may be further partitioned and include additional control elements known in the art of steering control systems.

Inputs to the control module40may be generated from the sensors31-35(FIG. 1) of the vehicle10(FIG. 1) as well as other sensors (not depicted). In addition, the inputs may be received from other control modules (not shown) within the vehicle10(FIG. 1), and may be modeled or predefined. For example, a sensed handwheel torque110can be received at the control module40from the handwheel torque sensor31(FIG. 1). A left grip magnitude112of the left grip115A (FIG. 1) can be received from a grip sensor35(FIG. 1) or be derived from other values. A right grip magnitude114of the right grip115B (FIG. 1) can be received from a grip sensor35(FIG. 1) or be derived from other values. Alternatively, motor position/velocity signals from the motor position/velocity sensor32(FIG. 1), handwheel position/velocity signals from the handwheel position/velocity sensor33(FIG. 1), and/or the sensed handwheel torque110can be used to estimate the left grip magnitude112and the right grip magnitude114in combination with system configuration information, for instance, using a system model of mass/inertia components in the steering system12(FIG. 1). Force or pressure sensor readings can be used to estimate the left grip magnitude112and the right grip magnitude114based on a surface area of contact on the handwheel14(FIG. 1).

As a further example, a driver's hands can be considered to be on the handwheel14(FIG. 1) when the sensed handwheel torque110remains above a tunable threshold value for a tunable period of time. Various driver grip levels can be estimated based on the level of the sensed handwheel torque110over a period of time. High values of sensed handwheel torque110for a short duration of time (with respect to torque level and time thresholds) can be considered as a high level of grip, while lower values of sensed handwheel torque110for a longer period of time can indicate a weak grip. Various such tunable levels of grip can be obtained through analysis and developmental testing for particular system configurations.

As depicted in the example ofFIG. 2and with continued reference toFIG. 1, the net handwheel torque moment determination module102can determine a net handwheel torque moment116between the left grip115A and the right grip115B on handwheel14based on the left grip magnitude112and the right grip magnitude114. The filter transition compensation module104can apply a filter to smooth transitions in the net handwheel torque moment116as a bias compensation118based on the left grip magnitude112and the right grip magnitude114. The handwheel torque compensation module108can determine a grip compensated handwheel torque120(FIG. 4) based on a difference between the sensed handwheel torque110and the bias compensation118.

The scale one-handed module106can determine a gain compensation122to adjust a scaling of the grip compensated handwheel torque120between a one-handed grip and a two-handed grip handwheel steering mode. The scale one-handed module106can determine that the one-handed grip handwheel steering mode is active based on the left grip magnitude112or the right grip magnitude114falling below a grip magnitude threshold. In some embodiments, a detected change between the one-handed grip and the two-handed grip handwheel steering mode results in a gain change by the scale one-handed module106. The gain compensation122can be a function of a lower value of the left grip magnitude112and the right grip magnitude114. The gain compensation122can be filtered, for instance, by the scale one-handed module106, to smooth transitions in the scaling of the grip compensated handwheel torque120between one and two-handed operation. The handwheel torque compensation module108can multiply the gain compensation122by the grip compensated handwheel torque120to produce a grip and one-handed compensated handwheel torque124as depicted inFIG. 4. The steering actuator motor19(FIG. 1) can be controlled based on the grip compensated handwheel torque120and/or the grip and one-handed compensated handwheel torque124.

FIG. 3depicts an example of the net handwheel torque moment determination module102in greater detail. In the example ofFIG. 3, the net handwheel torque moment116is determined based on a left grip angular position113of the left grip15A (FIG. 1) and a right grip angular position115of the right grip15B (FIG. 1) of the handwheel14(FIG. 1) in reference to a straight ahead position. The left grip angular position113and the right grip angular position115can be determined based on readings from the grip sensors35(FIG. 1) and the handwheel position/velocity sensor33(FIG. 1). The net handwheel torque moment116is further determined based on a left moment126and a right moment128in response to a nominal measure of arm weight and geometry of the left grip angular position113, the right grip angular position115, and the handwheel14. A scale and calculate left moment module202can produce the left moment126by scaling the left grip angular position113with respect to the left grip magnitude112, for instance, as a product of the left grip magnitude112and an offset based on the left grip angular position113. A scale and calculate right moment module204can produce the right moment128by scaling the right grip angular position115with respect to the right grip magnitude114, for instance, as a product of the right grip magnitude114and an offset based on the right grip angular position115. Left and right grip angular positions113,115(as angles from vertical) and the radius of the handwheel14enable computation of the left moment126and right moment128respectively. The left grip magnitude112and right grip magnitude114can be applied for scaling depending on whether the grip is full or weak, which may indicate whether or not the full weight of an arm is transferred to the rim of the handwheel14. The net handwheel torque moment116can be calculated as a difference between the left moment126and the right moment128.

FIG. 5illustrates a process300for grip-based handwheel compensation. Process300is described in further reference toFIGS. 1-4. At block302, net handwheel torque moment module102of control module40determines a net handwheel torque moment116between a left grip15A and a right grip15B on a handwheel14. At block304, a filter is applied (e.g., by filter transition compensation module104) to smooth transitions in the net handwheel torque moment116as a bias compensation118. At block306, a grip compensated handwheel torque120is determined (e.g., by handwheel torque compensation module108) based on a difference between a sensed handwheel torque110and the bias compensation118. At block308, a one-handed scaling is applied (e.g., by handwheel torque compensation module108) as gain compensation122(e.g., from scale one-handed module106) to the grip compensated handwheel torque120to adjust scaling of the grip compensated handwheel torque120between a one-handed grip and a two-handed grip handwheel steering mode and produce the grip and one-handed compensated handwheel torque124. The one-handed scaling can be a gain compensation122that is filtered to smooth transitions in the scaling of the grip compensated handwheel torque120, for instance, when switching between one-handed and two-handed grips. The grip and one-handed compensated handwheel torque124can be used in place of the sensed handwheel torque110as a compensated value in control algorithms of the control module40used to command the steering actuator motor19of the steering system12, thereby compensating for various grip patterns and one/two handed operation as opposed to an expected two-handed grip pattern at 10/2 or 9/3 o'clock on the handwheel14.