The present invention is directed to a method of optimizing the steering assistance of a motorized vehicle, using angle sensors instead of a torque detector. The method of the present invention also provides an improved steering power in case of failure. The present invention also encompasses a vehicle comprising two angle sensors used to optimize the steering assistance.
For utility vehicles, a steering assistance is necessary. It is usually provided through a torsion bar, which opens a hydraulic valve, according to the torque applied by the driver to the steering wheel. In case of failure of the hydraulic pump, or another part of the steering system, the effort to steer the steered axle considerably increases. In case such a failure occurs on an heavy truck, the driver becomes unable to steer the steerable wheels. It is therefore necessary to provide a backup steering system, which allows at least partial steering power. A back up steering system usually requires a second torsion bar, which is costly, heavy and space consuming. It is sometime not possible to implement such a second torsion bar on the steering column. DE102004049038 describes the use of two angle sensors to record the data resulting from the torsion of the torsion bar. However, DE102004049038 is not directed to backup steering systems.
It is therefore desirable to provide a method of optimizing the steering assistance with a costly efficient and space saving solution.
The steering system of an aspect of the present invention comprises one torsion bar and two angle sensors. The first angle sensor is positioned upstream the torsion bar and the second angle sensor is positioned downstream the torsion bar, in such a way that the torsion angle of the torsion bar can be monitored by the means of the two angle sensors. The portion of the steering column which is upstream the torsion bar comprises all the mechanical elements between the steering wheel and the part just above the torsion bar. It encompasses for example the upper shaft, the lower shaft, with inner shaft and outer shaft, a steering wheel adjustment device. The portion of the steering column which is downstream the torsion bar encompasses all the elements between the torsion bar and the steered wheels. This part comprises for example the drop arm, ball joints, drag link, the upper steering arm, the track rod. In case of twin steered axles, the portion which is downstream the torsion bar also encompasses the elements involved in the steering of the second steered axle. In particular, the second steering pump, the steering actuator of the second steered axle, and the secondary steering rod are downstream the torsion bar.
In a first embodiment, the angle sensors are used to detect an abnormal increase of angle between the first and the second angle sensor.
The method of the present invention comprises the steps of
a) Monitoring the steering angle of the steering wheel, by the means of a first angle sensor;
b) Monitoring the steering angle of the steered wheels, by the means of a second angle sensor;
c) Comparing the difference between the steering angle of the steering wheel, monitored is step a), and the steering angle of the steered wheels, monitored in step b), with a first reference value and/or comparing the steering angle of the steered wheels, monitored in step b), with a second reference value;
d) Detecting whether the difference between the steering angle of the steering wheel monitored in step a) and the steering angle of the steered wheels monitored in step b) reaches the first reference value of step c) and/or whether;
e) If the difference between the steering angle of the steeling wheel monitored in step a) and the steering angle of the steered wheels monitored in step b) reaches the first reference value of step c) and/or the steering angle of the steered wheels, monitored in step b) differs from the second reference value of step c), then activating a failure mode.
In step a), the angle to which the driver steers the steering wheel is determined by the means of the first angle sensor, positioned upstream the torsion bar. Each angle of rotation of the steering wheel may be associated or not associated to a theoretical angle of rotation of the steered wheels. The theoretical angle of rotation of the steered wheel is the angle expected for a given steering angle of the steering wheel. It may be for example a linear function of the steering angle of the steering wheel. Alternatively, the theoretical angle of the steered wheels may be a non-linear function of the angle of rotation of the steering wheel. The first angle sensor is preferably an angle sensor already present on the vehicle and involved in other functions. For example, the first angle sensor may be the angle sensor already used for the ESP functions.
In step b), the effective steering angle of the steerable wheels is determined by the means of a second angle sensor, positioned downstream the torsion bar. This second angle sensor is preferably positioned close to the torsion bar, on the output shaft of the steering gear, in order to provide a direct measurement. However, the second angle sensor may be positioned anywhere else downstream the torsion bar. In case of twin steered axles, the second angle sensor is preferably positioned on the first steered axle. The second angle sensor is preferably an angle sensor already present in the vehicle and involved in other functions. Indeed, an angle sensor may already be present for the steering management of the second steered axle. In this case, there is no need for additional specific sensors.
Step a) is concomitant with step b). This means that the steering angle of the steering wheel, is determined in step a) at the same time the steering angle of the steered wheels is determined in step b). Monitoring the steering angles in steps a) and b), or the difference of angles, has to be understood as repeating the operation of determining the steering angles, either permanently or as soon as one of the steering angles is modified. Permanently determining the steering angles means that a regular measurement is performed, for example at a predetermined frequency. Preferably, the steering angle is determined each few milliseconds, most preferably between 1 and 10 milliseconds.
In step c), the difference between the steering angle of the steering wheel and the steering angle of the steered wheels is monitored and compared to a predetermined value, which is a first reference value, or a warning threshold value, under which should remain the difference of steering angles. If a theoretical value is associated to the steering angle of the steering wheel in step a), the effective steering angle of the steered wheels, measured in step b), may also be monitored and compared to this theoretical value, which is a second reference value. Under normal conditions, the effective steering angle of the steered wheels should correspond to the second reference value. Also, under normal conditions, the difference of the steering angles determined in steps a and b) should remain under the first reference value. Under these circumstances, it is considered that the suitable steering assistance is delivered, allowing effective steering of the steered wheels. No additional steering power is triggered.
In step d), it is identified that the difference of the steering angles, reaches the first reference value or the effective steering angle of the steering wheels departs from the second reference value. Under these conditions, it is considered that the steering system is in fault and step e) is initiated. Alternatively, step e) may be initiated if the two conditions of step b) are reached. In this case, step e) is initiated only when the difference of the steering angles reaches the first reference value and the effective steering angle of the steering wheels departs from the second reference value.
Step e) triggers a failure mode, wherein additional power steering is delivered to compensate the efforts of the driver. The failure mode may be the activation of an auxiliary steering power. In case of more than one steered axle, the failure mode may be a special mode of the steering system of the second steered axle. For example, under failure mode, the steering system of the second steered axle may be activated in a way to provide an oversteering of the second steered axle. The failure mode may encompass any other action which aims at improving the steering assistance.