Method for detecting a lack of driver activity at the steering wheel of a motor vehicle

Abstract

A method detects a lack of driver activity at the steering wheel of a motor vehicle. A moment imparted by hand to the steering wheel by the driver is repeatedly measured, and if in a plurality of successive measurements the magnitude of a value of the moment imparted by hand does not exceed a threshold value, a lack of driver activity is inferred. The magnitude of the threshold value is dependent on the surface condition, in particular on the degree of unevenness, of the roadway being traveled upon. The degree of unevenness of the roadway may be derived from a measured vertical acceleration in the wheel suspension of the vehicle or from deceleration and/or acceleration signals of at least one wheel of the vehicle.

Claims

1. A method of detecting a lack of driver activity at a steering wheel of a motor vehicle, the method comprising the acts of: determining, by an electronic control unit in the motor vehicle based on signals received from a rotational speed sensor of the motor vehicle, a characteristic surface number representing a degree of roughness of a road on which the motor vehicle is traveling; repeatedly measuring, by the electronic control unit based on signals received from a sensor coupled to the steering wheel, a moment imparted by hand to the steering wheel by a driver; and in an event that in several successive measurements a magnitude amount of the moment imparted by hand does not exceed a threshold value, inferring a lack of driver activity and emitting a warning to the driver indicating that the lack of driver activity has been inferred, wherein an amount of the threshold value increases as the degree of roughness of a road being traveled on increases.

2. The method according to claim 1, wherein the degree of roughness of the road is derived from a measured vertical acceleration in a wheel suspension of the vehicle.

3. The method according to claim 1, wherein the degree of roughness of the road is derived from at least one of deceleration and acceleration signals of at least one wheel of the vehicle.

4. The method according to claim 1, wherein: the amount of the measured moment imparted by hand is used as a first magnitude of the moment imparted by hand; a gradient of the moment imparted by hand is taken into account as a further magnitude of the moment imparted by hand; and only in an event that, in several successive measurements, the amount of the first magnitude of the moment imparted by hand does not exceed a first threshold value dependent on the degree of roughness as well as that the further magnitude of the moment imparted by hand does not exceed a second threshold value provided for said magnitude, is the lack of driver activity inferred.

5. The method according to claim 1, wherein a length of a time period within which several successive measurements of the moment imparted by hand are carried out before, in an event of a lasting falling below the threshold value, a lack of driver activity is inferred, is a function of the driving speed of the vehicle.

6. The method according to claim 4, wherein, in an event that at least one of possible considered magnitudes of the moment imparted by hand exceeds an assigned minimal value, a new series of successive measurements of the moment imparted by hand is started, so that preceding measurements are not taken into account for detecting the lack of driver activity.

7. The method according to claim 6, wherein a new series of successive measurements of the moment imparted by hand is started only if one of the magnitudes of the moment imparted by hand continuously exceeds its assigned minimal value during a defined time period.

8. The method according to claim 6, wherein at least one of an amount of the minimal value and an amount of the defined time period is a function of the degree of roughness of the road.

9. The method according to claim 7, wherein at least one of an amount of the minimal value and an amount of the defined time period is a function of the degree of roughness of the road.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a simplified block diagram of a vehicle in which the method according to the invention may be carried out;

(2) FIGS. 2a-2c are exemplary flow charts illustrating the continuous measurement of the moment imparted by a driver on a steering wheel, the measurement of driving speed, and the determination of a characteristic surface number representing wood roughness, respectively; and

(3) FIG. 3 is a flow chart illustrating an exemplary method according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(4) FIG. 1 is a very schematic view of the two steerable front wheels 1a and 1b as well as of the two rear wheels 2a and 2b of a vehicle. A rotational speed sensor 3 is assigned to each wheel 1a, 1b, 2a, 2b. Their sensor signals are fed to an electronic control unit ESP, in which, among others, an electronic vehicle stability program is implemented that is known to a person skilled in the art. The steerable front wheels 1a, 1b can be steered by way of a rack-and-pinion steering system 4, which is also known to a person skilled in the art and whose schematically illustrated steering rack 4a can be transversely displaced according to the direction of the arrow 5 in order to adjust a desired wheel toe at the front wheels 1a and 1b. The driver of the vehicle causes this transverse displacement of the steering rack 4a by way of his steering wheel 4b, which by way of a steering spindle 4c and a steering gear 4d, in which, for example, also an electric-motor-driven power assistance device may be integrated, correspondingly acts upon the steering rack 4a. A torque sensor 6 is integrated in the steering spindle 4c or another suitable element of the steering system 4, by which torque sensor 6, the moment or torque by which the driver holds or rotates the steering wheel 4b can be measured. In the following, this torque will also be called a moment imparted by hand.

(5) As illustrated in FIG. 2a, the amount of the moment imparted by hand to the steering wheel 4b, that is, of that torque by which the driver keeps a firm hold on the steering or rotates it at least slightly, is continuously measured. This measured value is offset-corrected, which results in a first magnitude of the moment imparted by hand M.sub.H used subsequently, and the so-called gradient of the moment imparted by hand is determined from this magnitude of the moment imparted by hand M.sub.H by derivation with respect to time. The high-frequency parts are removed from this last-mentioned signal by low-pass filtering, which results in a second magnitude of the moment imparted by hand G.sub.H used subsequently.

(6) Parallel thereto, according to FIG. 2c, a characteristic surface number representing the roughness of the road and thus the surface condition of the road is determined from the rotational speeds of the vehicle wheels continuously measured by way of the rotational speed sensors 3 by low-pass filtering and further computing steps (in the present case in the control unit ESP), which characteristic surface number is characteristic of the quality of the currently present road section. This information is transmitted to a further electronic control unit ECU, in which the method according to the invention is implemented. By means of the current characteristic surface number, a threshold value M.sub.SW for the moment imparted by hand basically explained above for the first magnitude of the moment imparted by hand M.sub.H or a further (analogously basically already explained) threshold value G.sub.SW for the gradient of the moment imparted by hand or for the second magnitude of the moment imparted by hand G.sub.H are determined in the ECU. These threshold values M.sub.SW and G.sub.SW are stored as tables in the electronic control unit ECU as a function of the characteristic surface number.

(7) Also parallel thereto, as shown in FIG. 2b, it is queried whether the driving speed v of the vehicle is above a minimal value v.sub.min because only above a low speed of, for example, 1.0 km/h does it have to be checked whether the driver is firmly holding the steering wheel or is controlling it. If the answer is in the affirmative, the control unit ECU will operate as illustrated in FIG. 3 and explained in the following.

(8) Referring to FIG. 3, from a point in time t=0, it is first checked in the circle shown on the left-hand side whether the first magnitude of the moment imparted by hand M.sub.H is smaller than the pertaining threshold value M.sub.SW, and it is checked parallel thereto in the circle shown on the right-hand side whether the second magnitude of the moment imparted by hand G.sub.H is smaller than the pertaining threshold value G.sub.SW. This checking may represent a quasi snapshot or may extend over a very brief time period of several fractions of a second. If the answers to these two parallel queries are negative; i.e. either when a moment imparted by hand M.sub.H is present that is greater than the pertaining threshold value M.sub.SW or a gradient of the moment imparted by hand G.sub.H is present that is greater than the pertaining threshold value G.sub.SW, the respective timer t.sub.n (for the left-hand circle) or t.sub.i (for the right-hand circle) remains at the value t=0.

(9) However, should at least one of these parallel queries have been answered or be answered in the affirmative, the respective timer t.sub.n or t.sub.i would be increased by one increment, whereupon it is checked whether the respective timer has already reached a maximal value t.sub.max. If that is not so, it will be newly queried whether the first or second magnitude of a moment imparted by hand M.sub.H or G.sub.H is lower than the respective threshold value M.sub.SW or G.sub.SW.

(10) If a predefined maximal value t.sub.max for the timers was or is exceeded by the above-mentioned increase of one of the two timers t.sub.n or t.sub.i, it will be determined that the pertaining magnitude of the moment imparted by hand (M.sub.H or G.sub.H) is too low. It will then be checked whether the respective other magnitude of the moment imparted by hand (i.e. in that case, G.sub.H or M.sub.H) is also too low. If the answer is in the affirmative, a warning is emitted which indicates that there is a reasonable inference that the driver is not holding the steering wheel 4b in a sufficiently firm manner. However, if the answer to the last-mentioned query is negative, the current monitoring will be continued as described.

(11) Naturally, numerous modifications of the method described so far by way of the attached exemplary figures are contemplated, several possibilities being discussed above as to how these modification may be constructed. The detailed sequence of the method is also not to be incorporated into the claims but, as described in detail, it is claimed that at least one of the above-mentioned threshold values (M.sub.SW or G.sub.SW) for one of the above-mentioned magnitudes of the moment imparted by hand (M.sub.H or G.sub.H) is a function of the surface condition, particularly the degree of unevenness of the road or of the roughness of the road.

(12) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.