Abstract:
Independent wheel suspension for motor vehicles comprising: a wheel support ( 12 ) with a suspension movement and a steering movement, suspension movement guide devices including a steering element ( 16 ), elastic device ( 34 ) and shock absorbing devices ( 16, 26 ), and a control device ( 42, 44, 46, 40 ) of the wheel support steering movement. The wheel support ( 12 ) slides along steering element ( 16 ), which is slanted with respect to a vertical axis, and the steering movement control device comprises an electric actuator ( 42 ) controlled by an electronic control unit ( 50 ) arranged to correct the steering movements induced by the suspension movement.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a continuation-in-part of application Ser. No. 09/892,302, filed Jun. 26, 2001, now abandoned. 

   BACKGROUND OF THE INVENTION 
   This invention relates to an independent wheel suspension for motor vehicles. 
   A common problem for all suspension systems for steering wheels of motor vehicles is that the suspension movement of the wheel induces undesired steering. The kinematic solutions for controlling the variations of the toe-in angle of the wheel induced by the suspension movement are generally rather complex and costly, both in terms of the number of components and the complexity of the vehicle assembly operations. An additional problem consists in that the suspensions permitting a better control of the toe-in variation induced by the suspension movement (for example, transversal quadrilateral suspensions) are often very cumbersome in the transversal direction and cause an increase in transversal dimensions of the vehicle, especially in the case of vehicles with the engine arranged transversally. 
   Purpose of this invention is to provide a suspension for motor vehicles which solves said problems. An additional purpose of this invention is to provide a suspension system which consists of a reduced number of components and which can totally be preassembled off the vehicle assembly line. 
   According to this invention, these purposes are attained by means of a suspension which characteristics are described herein. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     This invention will be better explained by the following detailed descriptions with reference to the accompanying drawings, given as non-limiting example, wherein: 
       FIG. 1  is a schematic perspective view of a suspension according to this invention, 
       FIGS. 2 ,  3  and  4  are schematic views according to arrows II, III and IV in  FIG. 1  respectively, 
       FIG. 5  is a schematic cross-section according to line V—V in  FIG. 1 , and. 
       FIG. 6  is a schematic perspective view of the suspension. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With reference to the figures, numeral  10  indicates an independent wheel suspension for steering wheels of a motor vehicle. Suspension  10  comprises a wheel support  12  on which a wheel  14  turns. 
   As shown in greater detail in  FIG. 5 , suspension  10  comprises a steering arm l 6 , preferably straight, with fastening elements  18 ,  20  connected to the respective extremities destined to be fastened to the body of a motor vehicle (not illustrated). When suspension  10  is fitted on a motor vehicle, the steering arm  16  is fixed with respect to the body of the motor vehicle. In the assembled condition on the motor vehicle, the longitudinal axis A of the steering arm  16  is slanted with respect to a vertical axis. The axis A is slanted both on a longitudinal vertical plane and on a transversal vertical plane. As shown in  FIGS. 2 ,  3  and  4 , the lower extremity  16   a  of the steering arm  16  is moved forward and outwards with respect to the upper extremity  16   b.    
   With reference to  FIG. 5 , a piston  22  is fastened to the steering arm  16  and presents one or more longitudinal apertures  24  for the passage of damping fluid. The wheel support  12  is fastened to a tubular element  26  arranged coaxially with respect to the steering arm  16  and slides with respect to the latter in the longitudinal direction A. The tubular element  26  presents closed extremities  28 , which engage and hold the steering arm  16 . The tubular element  26  defines two chambers  30 , arranged on opposite sides with respect to the piston  22 , and filled with a damping fluid. Consequently, the tubular element  26  forms the external casing of a shock absorber. The wheel support  12 , which is integral with the tubular element  26  is free to undergo suspension movement in the direction of axis A and steering movement consisting of an oscillation around the axis A. According to a particularly advantageous form of embodiment of this invention, the damping characteristics of the shock absorber formed by the steering arm  16 , the piston  22  and the tubular casing  26  can be controlled electronically. This can be obtained, in a way which is known, using a damping fluid with magnetic-rheological qualities or by arranging electronically controlled valves in the fluid passage apertures  24 . In  FIG. 5 , numeral  32  schematically indicates an electric connector for providing electric damping characteristic control signals to the shock absorber. 
   An elastic element  34 , consisting for example of a compressed coil spring, is arranged in coaxial position around the tubular element  26 . The lower extremity of the elastic element  34  rests on a plate  36  fastened to the wheel support  12 . The upper extremity of the elastic element  34  rests on a plate  38  fastened to the upper extremity  16   b  of the steering arm  16 . 
   The wheel support  12  is fastened to a steering lever  40 , which is operated by an electric actuator  42 , destined to be fastened to the body of the motor vehicle. In the form of embodiment illustrated in the figures, the actuator  42  is rotary. A linkage  44 , controlling the steering lever  40  via a connecting rod  46 , is connected to the output shaft of the actuator. The electric actuator  42  is capable of controlling the rotation movement of the wheel support  12  around axis A, which amplitude is correlated to the rotation of the steering wheel of the motor vehicle. Each steering wheel is equipped with an electric actuator  42 , reason for which no mechanical interconnection between the two steering wheels on the two sides of the vehicle is required. 
   The suspension according to this invention is preferably equipped with an electrically controlled braking device  48 , which can be of any known type. As schematically illustrated in  FIG. 1 , an electronic control unit  50  sends electric control signals to the electric actuator  42 , to the shock absorber  16 ,  26  and to the electromechanical brake  48 . 
   The suspension movement of the wheel  14  with respect to the body of the vehicle is a straight movement along the direction of the slanted axis A. Considering that the direction of movement of the suspension is slanted with respect to the suspension of the wheel, if the actuator  42  remained still during the suspension movement of the wheel, the wheel toe-in angle would vary, induced by the suspension movement of the wheel. This toe-in angle variation would produce undesired steering of the wheel. In order to overcome this problem, according to this invention, the electronic control unit  50  is arranged to control the electric actuator  42  so to correct the undesired toe-in angle variations related to the movement of the suspension. Under this arrangement, each position of the wheel support  12  with respect to the shock absorber  16 ,  26  corresponds to a determined steering angle. The memory of the control unit contains tables indicating the correlation between steering angle and wheel support position. For each position of wheel support  12 , the control unit  50  compares the steering due to the configuration of the suspension with a desired value, also residing in the memory of the control unit (for instance, in the form of tables), and controls the steering actuator  42  so as to compensate for the difference between the actual steering angle and the desired steering angle. For this purpose, the electronic control unit  50  receives a signal indicating the position of the wheel support  12  with respect to axis A and, according to this function, computes the correction angle required to compensate for the change in the toe-in angle, whereby controlling the electric actuator  42  so to impose a steering angle equal and opposite to the movement of the wheel support  12  along axis A to the wheel support  12 . The position signal sent to control unit  50  may be provided by conventional sensors that are capable of measuring the displacement of wheel support  12  along axis A. In one embodiment of the invention the position of the wheel is detected by a sensor  53  integrated into the shock absorber  16 . One suitable type of sensor, for example, is a contactless magnetic sensor commercially available under the product name “PLCD” from Tyco Electronics. This particular type of sensor is a linear position sensor which includes a coil  54  inserted into the shaft of the shock absorber  16  and a permanent magnet  52  carried by the body  26  and being moveable therewith. Connector  51  is connected to the coil  54  of the sensor. 
   Furthermore, the electronic control unit  50  can be arranged to receive signals indicating the longitudinal and transversal acceleration of the vehicle and to control the damping characteristics of the shock absorber according to said signals, to control rolling and pitch of the vehicle. Furthermore, the electronic control unit  50  controls the braking device  48  and the steering actuator  42  according to the braking and steering controls of the vehicle driver by means of the brake pedal and the steering wheel. 
   The suspension according to this invention can be used without substantial changes for front and rear wheels and for both driving and idle wheels. The suspension according to this invention permits setting steering control in an individual way on the individual wheels for obtaining ideal steering from a kinematic point of view, without the constraints deriving from the steering mechanism. Also the shock absorber damping and the braking control strategies can be controlled individually on each wheel. In addition to a particularly reduced transversal size, the suspension according to this invention is also characterized by reduced size in the vertical direction, because the vertical size of the suspension depends only on the maximum amplitude of the suspension and is not conditioned by the kinematic structure of the wheel suspension mechanism.