Patent Publication Number: US-2019168803-A1

Title: Method of controlling a vehicle in case of steering system failure

Description:
FIELD OF THE INVENTION 
     The present invention relates to autonomously driven vehicles and, in particular, to a method of controlling an autonomously driven vehicle in case of steering system failure. 
     BACKGROUND TO THE INVENTION 
     The prevalence of vehicles having autonomous driving capabilities is rapidly increasing, if the steering system of a vehicle fails, it is desirable for there to be a backup mechanism that allows the vehicle to maintain a desired course. To this end, autonomously driven vehicles have been provided with a secondary steering system that steers the rear wheels if the primary steering system that steers the front wheels fails. 
     When the secondary steering system is tasked with maintaining the vehicle on the desired course, it is desirable to lock out the primary steering system (i.e., prevent the front wheels from turning). One way of accomplishing lock out of the primary steering system is by providing a clamping system that, for example, damps a steering shaft associated with the primary steering system. However, it has been found that an autonomously driven vehicle may deviate from a desired course in instances of primary steering system failure during high-g situations (e.g., when the vehicle is navigating a curve) due to lag associated with the damping system. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, a method of operating a vehicle to maintain the vehicle along a desired course is disclosed. The vehicle has a first steering system for turning left and right wheels at a first end of the vehicle, a second steering system for turning left and right wheels at a second end of the vehicle, brakes for slowing rotation of the wheels, and a steering lock mechanism. The method includes determining that the first steering system is malfunctioning. The steering lock mechanism is operated to lock out turning of the left and right wheels at the first end of the vehicle. The brakes are operated to maintain the vehicle along the desired course The second steering system is operated to maintain the vehicle along the desired course. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic of a vehicle; and 
         FIG. 2  is a flow chart depicting a method of operating the vehicle of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     A vehicle  10  having autonomous driving capabilities is shown in  FIG. 1 . The vehicle  10  has a front  15 , a rear  20 , a left side  23 , and a right side  25 . As used in this specification, the front  15  refers to the leading side of the vehicle  10  when the vehicle is traveling in a forward gear. The rear  20  refers to the leading side of the vehicle  10  when the vehicle is traveling in a reverse gear. The left side  23  and the right side  25  are defined with respect to an occupant seated in the vehicle  10  facing the front  15 . 
     The vehicle  10  includes a front left wheel  30 , a front right wheel  35 , a rear left wheel  40 , and a rear right wheel  45 . A first steering system  50  is provided for turning the front wheels  30 ,  35 . As used in this specification, turning the wheels refers to adjusting the direction of the wheels so as to effect the direction of travel of the vehicle  10  when the vehicle is traveling in a forward or reverse gear. The first steering system  50  can be controlled by an input device  55  (e.g., steering wheel) that can be manipulated by an operator of the vehicle  10 . 
     A second steering system  60  is provided for turning the rear wheels  40 , 45 . It is contemplated that the second steering system  60  may also be controlled by the Input device  55 . A steering controller  65  is in communication with the first steering system  50 , the second steering system  60 , and the input device  55 . The steering controller  65  can monitor operation of the first and second steering systems  50 ,  60 , control operation of the first and second steering systems, and monitor operation of the input device  55 . The steering controller  65  is also in communication with a steering lock mechanism  70 . The steering lock mechanism  70  is operable to lock out operation of the first steering system  50 , thereby preventing turning of the front wheels  40 ,  45 . 
     A front left brake  75 , a front right brake  80 , a rear left brake  85 , and a rear right brake  90  are provided for slowing rotation of the front left wheel  30 , the front right wheel  35 , the rear left wheel  40 , and the rear right wheel  45 , respectively. A brake controller  95  is in communication with the brakes  75 ,  80 ,  85 ,  90 . The brake controller  95  can operate the brakes  75 ,  80 ,  85 ,  90  in a vehicle slowing mode and a vehicle turning mode. In the vehicle slowing mode, the brakes  75 ,  80 ,  85 ,  90  are operated primarily to slow forward or reverse travel of the vehicle  10 . In vehicle turning mode, the brakes  75 ,  80 ,  85 ,  90  are operated primarily to turn the vehicle  10  to the left or to the right. It is contemplated that the brakes  75 ,  80 ,  85 ,  90  may simultaneously be operated in vehicle slowing mode and vehicle turning mode (i.e., slow forward or reverse travel of the vehicle  10  while also turning the vehicle to the left or the right). 
     As known by those skilled in the automotive art, the vehicle turning mode of operating the brakes can be referred to as “differential braking”. In differential braking, the front and rear left brakes  75 ,  85  can be operated to slow rotation of the front and rear left wheels  30 ,  40 , respectively, thereby causing the vehicle  10  to turn to the left. Similarly, the front and rear right brakes  80 ,  90  can be operated to slow rotation of the front and rear right wheels  35 ,  45 , respectively, thereby causing the vehicle  10  to turn the right, it is contemplated that all the brakes  75 ,  80 ,  85 ,  90  may be operated while still employing differential braking. For example, the front and rear left brakes  75 , 85  can be applied at a greater level than the front and rear right brakes  80 ,  90 , thereby slowing rotation of the front and rear left wheels  30 ,  40  more rapidly than rotation of the front and rear right wheels  35 ,  45 , thus causing the vehicle  10  to turn left. As another example, the front and rear right brakes  80 ,  90  can be applied at a greater level than the front and rear left brakes  75 ,  85 , thereby slowing rotation of the front and rear right wheels  35 , 45  more rapidly than rotation of the front and rear left wheels  30 ,  40 , thus causing the vehicle  10  to turn right. 
     The steering controller  65  and the brake controller  95  can be part of an electronic control unit (ECU)  105 . The ECU  105  can facilitate communication between, and monitor, the steering controller  65  and the brake controller  95 . The ECU  105  can also monitor and/or control other operational aspects of the vehicle  10 . For example, the ECU  105  can control the autonomous driving capabilities of the vehicle  10 . It is contemplated that the ECU  105  may be omitted and the steering controller  65  and the brake controller  95  be in direct communication with one another. 
     A method of controlling the vehicle is shown in  FIG. 2 . The method is directed at maintaining the vehicle along a desired course in the event that the first steering system  50  malfunctions. 
     At  400 , the first steering system  50  maintains the vehicle  10  along the desired course in an autonomous driving mode. At  500  a determination is made as to whether the first steering system  50  is malfunctioning. The determination can be made, for example, by the ECU  105 . As used in this specification, malfunctioning of the first steering system  50  refers to instances where the first steering system fails to maintain the vehicle  10  along the desired course. If the first steering system  50  is not malfunctioning, the method loops back to  500  to make another determination as to whether the first steering system is malfunctioning. 
     If the first steering system  50  is malfunctioning, the method moves to  510  and the steering lock mechanism  70  is operated to lock out the first steering system  50  to prevent turning of the front wheels  30 ,  35 . Then, at  520  the brake controller  95  operates the brakes  75 ,  80 ,  85 ,  90  in the vehicle turning mode to maintain the vehicle  10  along a desired course. It is contemplated that operation of the steering lock mechanism  70  to lock out the first steering system  50  and operation of the brakes  75 ,  80 ,  85 ,  90  in vehicle turning mode occurs simultaneously. 
     Next, at  530 , a determination is made as to whether the steering lock mechanism  70  has completed the process of locking out the first steering system  50 . As understood by those skilled in the automotive art, it can be desirable to delay turning of the rear wheels  40 ,  45  until turning of the front wheels  30 ,  35  is prevented (i.e., the process of locking out the first steering system  50  is completed), if the process of locking out the first steering system  50  is not completed, the method loops back to  530  to make another determination as to whether the process of locking out the first steering system is completed. 
     If the process of locking out the first steering system  50  is completed, the method moves to  540  and the second steering system  60  is operated to maintain the vehicle  10  along a desired course. It is contemplated that the determination of whether the steering lock mechanism  70  has completed the process of locking out the first steering system  50  may be omitted, in this case, simultaneous operation of the second steering system  60  and operation of the brakes  75 ,  80 ,  85 ,  90  in vehicle turning mode would occur immediately after operation of the steering locking mechanism  70  to lock out the first steering system  50  simultaneously with regardless of whether the process of locking out the first steering system is completed 
     At  550 , a determination is made as to whether operation of the second steering system  60  alone can maintain the vehicle  10  along the desired course. If the second steering system  60  alone cannot maintain the vehicle  10  along the desired course, the method loops back to  550  to make another determination as to whether operation of the second steering system alone can maintain the vehicle along the desired course. Thus, operation of the second steering system  60  and operation of the brakes  75 ,  80 ,  85 ,  90  in the vehicle turning mode are both responsible for maintaining the vehicle  10  along the desired course. 
     If the second steering system  60  alone can maintain the vehicle  10  along the desired course, the method moves to  560  and operation of the brakes  75 ,  80 ,  85 ,  90  in the vehicle turning mode is terminated. Thus, operation of the second steering system  60  is solely responsible for maintaining the vehicle  10  along the desired course. The method ends at  570 . At  580  the vehicle  10  continuous to operate in the autonomous driving mode while the second steering system  60  maintains the vehicle along the desired course. It is contemplated that the determination as to whether operation of the second steering system  60  alone can maintain the vehicle  10  along the desired course may be omitted. In this case, in the event of first steering system  50  malfunction, maintenance of the vehicle  10  along the desired course in the autonomous driving mode after the method ending at  570  would continue by way of tandem operation of the second steering system  60  and the brakes  75 ,  80 ,  85 ,  90  in the vehicle turning mode. 
     From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. For example, an alert may be provided to an operator of the vehicle  10  that vehicle maintenance is required upon a determination that the first steering system  50  is malfunctioning. As another example, the vehicle  10  may be programmed to pull off the road and stop upon a determination that the first steering system  50  is malfunctioning. As yet another example, the autonomous driving mode may be interrupted upon a determination that the operator of the vehicle  10  has attempted to control the vehicle through the input device  55 . Such improvements, changes, and modifications as those enumerated above and further improvements, changes, and modifications not specifically enumerated are within the skill of the art and are intended to be covered by the appended claims.