Patent Publication Number: US-11027770-B2

Title: Steer by wire road vehicle steering system provided with a telescopic support element for the steering wheel

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application claims priority from Italian Patent Application No. 102017000121876 filed on Oct. 26, 2017, the disclosure of which is incorporated by reference. 
     TECHNICAL FIELD 
     The invention relates to a “steer by wire” road vehicle steering system. 
     PRIOR ART 
     In a road vehicle, a steering system is provided, which fulfils the function of controlling the steering angle, namely the angle existing between the direction of the front wheels (i.e. the plane of rotation of the front wheels and the longitudinal axis of the road vehicle. The steering system comprises a control shaft, which is arranged crosswise, is mechanically connected, at its opposite ends, to the hubs of the front wheels, and is mounted in an axially sliding manner in order to change the steering angle. Furthermore, the steering system comprises a steering wheel, which is mounted in a rotary manner inside the passenger compartment and is mechanically connected to the control shaft by means of a transmission device so that the rotation of the steering wheel determines an axial translation of the control shaft and, hence, a corresponding variation of the steering angle. 
     In the automotive industry there is a tendency towards an increasing use of “drive by wire” systems, in which the direct mechanical connection between the controls of the vehicle (steering wheel, accelerator, brake clutch, gear stick) and the actuators of the vehicle (steering tie rod, throttle valve, brake pump . . . ) is replaced by a (virtual) electronic connection, which involves the use of a position sensor, which reads the position of a control of the vehicle and communicates it to an electronic control unit, which controls an (electric or hydraulic) motor, which operates the corresponding actuator of the vehicle. 
     In modern vehicles, “drive by wire” systems are regularly used to control the accelerator as well as the gearbox controls and are currently spreading for the control of the brake and, in the near future, they should also be implemented in relation to the control of the steering wheel. Patent applications WO2017115411A1, US2017158222A1, US2016068182A1, WO2017097662A1 describe “steer by wire” road vehicle steering systems, i.e. systems with no mechanical connection between the steering control (i.e. the steering wheel) and the steering tie rod. 
     Patent application DE102015224602A1 describes a steering system of a road vehicle comprising a support element, which, on one side, can be rigidly fixed on the inside of the vehicle and, on the other side, is connected to a steering wheel so as to support the steering wheel; the support element is telescopic so as to vary its axial size along to rotation axis of the steering wheel in order to change the axial position of the steering wheel. 
     DESCRIPTION OF THE INVENTION 
     The object of the invention is to provide a “steer by wire” road vehicle steering system, which can be manufactured in a simple and economic fashion and, at the same time, is compact, effective and efficient. 
     According to the invention, there is provided a “steer by wire” road vehicle steering system according to the appended claims. 
     The appended claims describe preferred embodiments of the invention and form an integral part of the description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described with reference to the accompanying drawings, showing a non-limiting embodiment thereof, wherein: 
         FIG. 1  is a schematic plan view of a road vehicle provided with a “steer by wire” steering system according to the invention; 
         FIG. 2  is a schematic, partially sectional view of a transmission device of the steering system of  FIG. 1 ; 
         FIGS. 3-10  are schematic, partially sectional views of corresponding variants of the transmission device shown in  FIG. 2 ; 
         FIG. 11  is a perspective view of a mechanical limit stop device of the transmission device shown in  FIGS. 3, 6 and 9 ; 
         FIG. 12  is a side view of the limit stop mechanism of  FIG. 11 ; 
         FIG. 13  is a side view, with a longitudinal section, of the limit stop mechanism of  FIG. 11 ; and 
         FIG. 14  is a side view, with a longitudinal section, of a variant of the limit stop mechanism of  FIG. 11 . 
     
    
    
     PREFERRED EMBODIMENTS OF THE INVENTION 
     In  FIG. 1 , number  1  indicates, as a whole, a road vehicle provided with two front steering wheels  2  and two rear drive wheels  3 , which receive the torque from a powertrain system. 
     The road vehicle  1  comprises a steering system  4 , which fulfils the function of controlling the steering angle, namely the angle existing between the direction of the front wheels  2  (i.e. the plane of rotation of the front wheels  2 ) and the longitudinal axis of the road vehicle  1 . 
     The steering system  4  comprises a steering mechanism  5 , which can be operated so as to change the steering angle, is arranged crosswise and consists of a central rod, which can axially slide and is mechanically connected to the fork ends of the front wheels  2  through articulated tie rods. Furthermore, the steering system  4  comprises a steering wheel  6 , which is mounted in a rotary manner inside a passenger compartment and is electronically (virtually) connected to the steering mechanism  5  by means of an electronic transmission device  7  (without mechanical connection) so that the rotation of the steering wheel  6  determines an axial translation of the steering mechanism  5  and, hence, a corresponding variation of the steering angle. In other words, there is no mechanical connection between the steering mechanism  5  and the steering wheel  6  and the transmission device  7  only creates a functional (not mechanical) connection between the steering mechanism  5  and the steering wheel  6 . 
     The transmission device  7  comprises a sensor  8 , which detects in real time the angular position of the steering wheel  6  and the torque applied by the driver to the steering wheel  6 ; obviously, the sensor  8  is capable of determining the angular position of the steering wheel  6  in an extremely safe manner by carrying out different independent and redundant reading operations aimed at reading the angular position of the steering wheel  6 . It should be pointed out that the sensor  8  can be directly coupled, in a mechanical manner, to the steering wheel  6  or to any other part that is angularly integral to the steering wheel  6 . 
     Furthermore, the transmission device  7  comprises an actuator device  9 , which operates the steering mechanism  5  so as to control the steering of the front steering wheels  2  of the road vehicle  1  and comprises an electric motor  10  and a transmission  11 , which mechanically connects the electric motor  10  to the steering mechanism  5 . As already mentioned above, the electric motor  10  (namely, the actuator device  9 ) is mechanically completely independent of and separate from the steering wheel  6  and is designed to control the steering of the front steering wheels  2  of the road vehicle  1  without any type of mechanical force/torque coming from the steering wheel  6 . 
     Finally, the transmission device  7  comprises an electronic control unit (“ECU”)  12 , which is connected to the position sensor  8  so as to receive the reading of the angular position of the steering wheel  6  and is designed to control the electric motor  10  of the actuator device  9  so as to adjust the steering of the front steering wheels  2  of the road vehicle  1  based on the angular position of the steering wheel  6 . The control unit  12  can physically consist of one single device or of different devices separated from one another and communicating with one another through the CAN network of the road vehicle  1 . 
     According to  FIG. 2 , the steering wheel  6  is mounted so as to rotate around a rotation axis  13 . According to a possible embodiment (shown by way of example in  FIGS. 2-4 and 8-10 ), the entire steering wheel  6  (i.e. both the central hub  14  and an outer ring  15 ) is mounted so as to rotate around the rotation axis  13 ; according to an alternative embodiment (shown by way of example in  FIGS. 5-7 ), the central hub  14  of the steering wheel  6  is fixed (i.e. it does not rotate around the rotation axis  13 ), whereas the outer ring  15  of the steering wheel  6  is mounted so as to rotate around the rotation axis  13 . 
     The transmission device  7  of the steering system  4  comprises an electric motor  16 , which is directly connected to the steering wheel  6  so as to apply a variable feedback torque to the steering wheel  6  (to the outer ring  15  of the steering wheel  6 ); in other words, the function of the electric motor  16  is that of applying to the steering wheel  6  (to the outer ring  15  of the steering wheel  6 ) a variable torque that transmits to the driver torque sensations that are similar to the torque sensations of a traditional steering wheel mechanically connected to the steering wheels. In the absence of the electric motor  16 , the steering wheel  6  (the outer ring  15  of the steering wheel  6 ) would rotate around the rotation axis  13  always with the same type of effort, thus preventing the driver from receiving any type of feedback from the steering wheel  6  (in other words, the steering wheel  6  would behave like the steering wheel of a video game instead of like the steering wheel of the an actual vehicle). The electric motor  16  comprises a stator  17 , which does not rotate, and a rotor  18 , which can rotate relative to the stator  17  around the rotation axis  13  (namely, is coaxial to the steering wheel  6 ) and is mechanically connected to the steering wheel  6  (to the outer ring  15  of the steering wheel  6 ) so as to apply a variable feedback torque to the steering wheel  6 . Furthermore, the electric motor  16  supports the steering wheel  6 , i.e. the steering wheel  6  is mounted on the electric motor  16 ; as a consequence, the steering wheel  6  (the outer ring  15  of the steering wheel  6 ) is rigidly integral to the rotor  18  of the electric motor  16  and is supported by the rotor  18  of the electric motor  16 . 
     In the embodiment shown in  FIGS. 2 and 3 , in the electric motor  16 , the rotor  18  is internal and, therefore, it is radially arranged on the inside of the stator  17 . In this embodiment, the rotor  18  of the electric motor  16  comprises a shaft  19 , which supports the steering wheel  6 ; in particular, the bearings  20 , which support the rotor  18  and are interposed between the rotor  18  and the stator  17 , are preferably coupled to the shaft  19  of the rotor  18 . 
     In the alternative embodiment shown in  FIGS. 4-8 , in the electric motor  16 , the rotor  18  is external and, therefore, it is radially arranged on the outside of the stator  17 . In this embodiment, the rotor  18  of the electric motor  16  generally (though, not necessarily) is without shaft. This embodiment is particularly advantageous when the central hub  14  of the steering wheel  6  is fixed (i.e. does not rotate around the rotation axis  13 ) and the sole outer ring  15  of the steering wheel  6  can rotate around the rotation axis  13 ; indeed, in this embodiment, the central hub  14  of the steering wheel  6  can be directly connected to the stator  17  of the electric motor  16  (i.e. the central hub  14  of the steering wheel  6  can be rigidly constrained to the stator  17  of the electric motor  16 ), whereas the outer ring  15  of the steering wheel  6  can be directly connected to the rotor  18  of the electric motor  16  (i.e. the outer ring  15  of the steering wheel  6  can be rigidly constrained to the rotor  18  of the electric motor  16 ). 
     In all the embodiments shown in the accompanying figures, the transmission device  7  of the steering system  4  comprises a support element  21 , which, on one side can be rigidly fixed on the inside of the road vehicle  1  (in particular, to the dashboard of the road vehicle  1 ) and, on the other side, is rigidly connected to the stator  17  of the electric motor  16  so as to support the electric motor  16 . In other words, the support element  21  is the mounting means through which the electric motor  16  (and, hence, the steering wheel  6  supported by the electric motor  16 ) is installed and fixed on board the road vehicle  1 . 
     According to a preferred embodiment, the support element  21  is telescopic so as to vary its axial size along the rotation axis  13  in order to change the axial position of the electric motor  16  and, hence, of the steering wheel  6 . In particular, the support element  21  comprises an outer tubular body  22 , which can be rigidly fixed on the inside of the vehicle  1  and is internally hollow, namely has, on the inside, a chamber  23 , which is open on one side (facing the electric motor  16 ); furthermore, the support element  21  comprises an inner body  24 , which is rigidly connected to the stator  17  of the electric motor  16  (i.e. supports the stator  17  of the electric motor  16 ), is partially arranged inside the outer body  22  (i.e. in the chamber  23  of the outer body  22 ), and can axially slide relative to the outer body  22 . It should be pointed out that the inner body  24  can only slide axially relative to the outer body  22  and, therefore, cannot make any rotation relative to the outer body  22 . 
     In the embodiment shown in the accompanying figures, the outer body  22  is provided with a bracket  25 , which is used to fix the outer body  22  (hence, the support element  21 ) to the dashboard of the road vehicle  1 . 
     The support element  21  comprises an actuator device  26 , which is arranged on the inside of the outer body  22  (i.e. is housed in the chamber  23  of the outer body  22 ) and is designed to axially translate the inner body  24  relative to the outer body  22 . The actuator device  26  always has the function of stopping (forbidding) the axial translation between the two bodies  22  and  24 , so as to make sure that, in use, the steering wheel  6  remains still in a predefined axial position; furthermore, the actuator device  26  can be active, i.e. have an (electric) motor, which causes an axial translation movement of the inner body  24  relative to the outer body  22 , or it can be passive, i.e. need the manual intervention of the driver in order to cause an axial translation movement of the inner body  24  relative to the outer body  22 . In the non-limiting embodiments shown in the accompanying figures, the actuator device  26  is active and comprises an electric motor, which is integral to the outer body  22  and causes the rotation of a worm screw, on which an abutment is screwed, which is integral to the inner body  24 . 
     According to  FIG. 7 , the stator  17  of the electric motor  16  has, at the centre, a cable-leading through duct  27 , which is coaxial to the rotation axis  13 ; similarly, the inner body  24  of the support element  21  also has a cable-leading through duct  28 , which is elbow-shaped (i.e. “L”-shaped) and has an opening, which is obtained through a base wall of the inner body  24 , faces and is coaxial to the cable-leading duct  27 , and another opposite opening, which is obtained through a side wall of the inner body  24 . A cabling  29  (i.e. a set of electrical cables grouped together to form one single bundle) is provided, which originates from the central hub  14  of the steering wheel  6  and is arranged through the cable-leading ducts  27  and  28  so as to electrically connect the steering wheel  6  to the rest of the road vehicle  1 . In this embodiment, it is possible to establish an electrical connection between the steering wheel  6  and the rest of the road vehicle  1  without using rotary (i.e. sliding) electrical contacts or spiral cabling (which enables a certain degree of twisting). The presence of the cable-leading duct  27  inside the stator  17  of the electric motor  16  is particularly advantageous when, in the electric motor  16 , the rotor  18  is external (according to  FIG. 7 ), but it is also possible when, in the electric motor  16 , the rotor  18  is internal. 
     In the embodiments shown in  FIGS. 2-8 and 10 , the transmission device  7  of the steering system  4  comprises the electric motor  16 , which applies the feedback torque to the steering wheel  6 ; in the alternative embodiment shown in  FIG. 9 , the transmission device  7  of the steering system  4  has no electric motor  16  and, therefore, the steering wheel  6  is directly connected to the inner body  24  of the support element  21 ; in particular, there is a shaft that, on one side, is rigidly connected to the steering wheel  6  and, on the opposite side, is connected to the inner body  24  of the support element  21  through bearings. 
     In the embodiments shown in  FIGS. 2-9 , the support element  21  is coaxial to the electric motor  16  and to the steering wheel  6 ; in the alternative embodiment shown in  FIG. 10 , the support element  21  is not aligned with the electric motor  16  and with the steering wheel  6  and is mounted lower than the electric motor  16  and the steering wheel  6 ; the lack of alignment between the support element  21  and the electric motor  16  as well as the steering wheel  6  increases the space available in the part of dashboard above the support element  21  (since the bracket  25  can be placed lower), thus creating a larger space for information devices (control panel, screens) or other devices to be installed in the upper part of the dashboard in front of the driver. 
     In the embodiments shown in  FIGS. 3, 6 and 9 , the transmission device  7  of the steering system  4  comprises a mechanical limit stop device  30 , which is coupled to the steering wheel  6  and limits, in both directions, the maximum angular width of the rotation of the steering wheel  6  around the rotation axis  13 , so that the steering wheel  6  can make, on the whole, a rotation around the rotation axis  13  that is greater than 360°. It should be pointed out that the fact that the steering wheel  6  is allowed to rotate, on the whole, over more than 360° ensures (when desired) a high steering “reduction”, namely in order to avoid (when desired) a too direct steering (which is ideal when driving on a race track, but is not suitable for everyday driving in traffic). In the absence of the mechanical limit stop device  30 , it would be necessary to create “virtual” limit stops using the electric motor  16  to generate a very high braking torque, which simulates the presence of a mechanical limits stop; however, this solution, despite being very elegant, requires an oversized electric motor  16  (in order to allow the electric motor  16  to generate a braking torque that is high enough to stop the rotation of the steering wheel  6 ) and, hence, leads to an increase in size, mass and costs. 
     According to  FIGS. 11-14 , the limit stop device  30  comprises a groove  31 , which is wound in a spiral around the rotation axis  13  over more than 360° and has, at the two opposite ends, two abutments  32 , which define respective stop strikers; in other words, the groove  31  extends in a spiral around the rotation axis  13  over more than 360° from an abutment  32  to the opposite abutment  32 . By way of example, the groove  31  could extend around the rotation axis  13  over approximately 720° (i.e. two complete rotations of the steering wheel  6 ) or over approximately 1080° (i.e. three complete rotations of the steering wheel  6 ). Furthermore, the limit stop device  30  comprises a pin  33 , which is arranged inside the groove  31  so as to engage and follow the groove  31  from an abutment  32  up to the opposite abutment  32 ; in other words, the pin  33  is inside the groove  31  and is forced to remain inside the groove  31 , thus covering the entire extension of the groove  31  from an abutment  32  to the opposite abutment  32 . 
     Furthermore, one between the groove  31  and the pin  33  is angularly integral to the steering wheel  6  (hence, rotates in an angularly integral manner with the steering wheel  6 ), whereas the other one between the groove  31  and the pin  33  is angularly integral to a part that does not rotate together with the steering wheel  6  (in particular, is angularly integral to the inner body  24  of the support element  21 ). In other words, according to a possible embodiment, the groove  31  is angularly integral to the steering wheel  6 , whereas the pin  33  is angularly integral to a part that does not rotate with the steering wheel  6  (i.e. is angularly integral to the inner body  24  of the support element  21 ); alternatively, the pin  33  is angularly integral to the steering wheel  6 , whereas the groove  31  is angularly integral to a part that does not rotate with the steering wheel  6  (i.e. is angularly integral to the inner body  24  of the support element  21 ). 
     Finally, one between the groove  31  and the pin  33  can axially slide relative to the steering wheel  6 . In other words, the groove  31  can axially slide relative to the steering wheel  6  or the pin  33  can axially slide relative to the steering wheel  6 . 
     In the embodiment shown in  FIGS. 11, 12 and 13 , the groove  31  is angularly integral to the steering wheel  6  (in particular, to a shaft  34  coaxial to the rotation axis  13  which rigidly supports at least the outer ring  15  of the steering wheel  6 ) and can also axially slide relative to the steering wheel  6  (in particular, relative to the shaft  34 ); as a consequence, the pin  33  is rigidly connected to a part that does not rotate with the steering wheel  6  (i.e. is angularly integral to the inner body  24  of the support element  21 ). In this embodiment, the groove  31  is coupled to the steering wheel  6  (in particular, to the shaft  34 ) through a splined coupling, which constrains in an angular manner, enabling, at the same time, an axial sliding. It should be pointed out that the groove  31  can be mounted on any part that is angularly integral to the steering wheel  6  (i.e. that rotates around the rotation axis  13  together with the steering wheel  6 ), for example the shaft  34  coaxial to the rotation axis  13  which rigidly supports at least the outer ring  15  of the steering wheel  6 , the rotor  18  of the electric motor  16  or the steering wheel  6  itself. 
     In the embodiment shown in  FIG. 14 , the groove  31  is angularly integral to the steering wheel  6  (in particular, to a shaft  34  coaxial to the rotation axis  13  which rigidly supports at least the outer ring  15  of the steering wheel  6 ) and is also rigidly constrained to the steering wheel  6  (in particular, to the shaft  34 ); as a consequence, the pin  33  is angularly integral and can axially slide relative to a part that does not rotate with the steering wheel  6  (i.e. is angularly integral and can axially slide relative to the inner body  24  of the support element  21 ). In other words, the pin  33  can axially slide, but cannot rotate relative to a part that does not rotate together with the steering wheel  6  (i.e. relative to the inner body  24  of the support element  21 ). 
     The embodiments described herein can be combined with one another, without for this reason going beyond the scope of protection of the invention. 
     The steering system  4  described above has numerous advantages. 
     First of all, the steering system  4  described above is particularly compact, effective and efficient, since the total number of components of the transmission device  7  is reduced to a minimum. In particular, the steering wheel  6  is directly supported by the electric motor  16 , which, hence, applies the feedback torque to the steering wheel  6  without intermediate elements. Furthermore, the support element  21  is extremely simple, functional and compact, as it has a tubular shape housing, on the inside, the actuator device  26 , which regulates the axial movements of the steering wheel  6 . 
     Moreover, the support element  21  allows the steering wheel  6  to cover a much wider axial stroke, which can get up to 250 mm, without particular constructive complications (also thanks to the absence of a connection shaft towards the steering mechanism  5 ). 
     LIST OF THE REFERENCE NUMBERS OF THE FIGURES 
     
         
         
           
               1  road vehicle 
               2  front wheels 
               3  rear wheels 
               4  steering system 
               5  steering mechanism 
               6  steering wheel 
               7  transmission device 
               8  sensor 
               9  actuator device 
               10  electric motor 
               11  transmission 
               12  control unit 
               13  rotation axis 
               14  central hub 
               15  outer ring 
               16  electric motor 
               17  stator 
               18  rotor 
               19  shaft 
               20  bearings 
               21  support element 
               22  outer body 
               23  chamber 
               24  inner body 
               25  bracket 
               26  actuator device 
               27  cable-leading duct 
               28  cable-leading duct 
               29  cabling 
               30  limit stop device 
               31  groove 
               32  abutment 
               33  pin 
               34  shaft