Abstract:
A suspension system for a vehicle includes a wheel carrier for rotatably supporting a wheel, an upper control link having a first end coupled to an upper end of the wheel carrier and a second end proximal to a vehicle body, a lower control link having a second end coupled to a lower end of the wheel carrier and a second end proximal to the vehicle body, a reciprocating hydraulic actuator disposed such that its reciprocating motion becomes perpendicular to a vertical direction of the vehicle body, a converter for converting the reciprocating motion of the reciprocating hydraulic actuator into an up-and-own motion of the upper and lower control links, and an electronic control part for controlling an operation of the reciprocating hydraulic actuator in accordance with a driving condition of the vehicle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of Korean Patent Application No. 97-80121 filed on Dec. 31, 1997, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present invention relates to a suspension system for a vehicle and, more particularly, to an active suspension system for a vehicle which assumes an optimal geometrical shape depending on the driving state. 
     (b) Description of the Related Art 
     Generally, conventional active control suspension systems are designed to control the roll and pitch of a vehicle body by detecting the same and forcing the vehicle body against the directions of the roll and pitch. To apply such force to the vehicle body, the suspension system requires the use of a high level of energy. 
     That is, when using hydraulic force, the mechanical energy W of a hydraulic actuator can be calculated using an equation as shown in the following: 
     
       
           W=F·S=|F||S |Cosθ 
       
     
     where, F is the actuator force, S is an actuator stroke, and θ is an actuating angle of the actuator with respect to a vertical direction of the vehicle. 
     In a conventional active suspension system, as is well known, since the hydraulic actuator is disposed in a vertical direction with respect to the vehicle body, a great amount of mechanical energy needs to be exerted by the actuator to support the vehicle body. Even when the actuator is not mechanically operating in a state where no roll and pitch is applied to the vehicle, mechanical energy for supporting the vehicle against outer force is required. 
     Therefore, to apply such a great amount of mechanical energy, a high capacity hydraulic pump, a highly precise actuator, and various valves are required, complicating the suspension system, enlarging the size of the same as well as increasing manufacturing costs. 
     SUMMARY OF THE INVENTION 
     Therefore, the present invention has been made in an effort to solve the above-described problems. 
     It is an objective of the present invention to provide a suspension system for a vehicle which is simple in structure and can effectively control the height of a roll center, in addition to a camber and a tread using minimized energy, thereby providing optimal driving conditions for the vehicle. 
     To achieve the above objective, the present invention provides a suspension system for a vehicle. The suspension system comprises a wheel carrier for rotatably supporting a wheel, an upper control link having a first end coupled to an upper end of the wheel carrier and a second end proximal to a vehicle body, a lower control link having a second end coupled to a lower end of the wheel carrier and a second end proximal to the vehicle body, a reciprocating hydraulic actuator disposed such that its reciprocating motion becomes perpendicular to a vertical direction of the vehicle body, a converter for converting the reciprocating motion of the reciprocating hydraulic actuator into an up-and-down motion of the upper and lower control links, and an electronic control part for controlling an operation of the reciprocating hydraulic actuator in accordance with a driving condition of the vehicle. 
     According to an embodiment of the present invention, the means for converting comprises an upper bell crank comprising a hinge portion pivotally coupled on an upper stationary hinge shaft supported by an upper bracket fixedly mounted on a vehicle body, a horizontal portion extending from the hinge portion toward the wheel carrier and to which the second end of the upper control link is pivotally coupled, and a vertical portion extending downward from the hinge portion, a lower bell crank comprising a hinge portion pivotally coupled on a upper stationary hinge shaft supported by the lower bracket, a horizontal portion extending from the hinge portion toward the wheel carrier and to which the second end of the lower control link is pivotally coupled, and a vertical portion extending upward from the hinge portion; and a lower end of the vertical portions of the upper bell crank and an upper end of the vertical portion of the lower bell crank being pivotally mounted on a movable hinge shaft to which actuating force of the actuator is applied. 
     Preferably, each length of the vertical portions of the upper and lower bell cranks is longer than that of the horizontal portions of the upper and lower bell cranks. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the present invention, and, together with the description, serve to explain the principles of the invention: 
     FIG. 1 is a perspective view illustrating a suspension system according to a preferred embodiment of the present invention; 
     FIG. 2 is a front view of the suspension system depicted in FIG. 1 illustrating the operation of the same when a roll center ascends; 
     FIG. 3 is a front view of the suspension system depicted in Fig,  1  illustrating the operation of the same when a roll center descends; and 
     FIG. 4 is a schematic view illustrating variations in a roll center achieved by the operation of a suspension system in accordance with a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the presently preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     Referring first to FIG. 1, there is shown a suspension system according to a preferred embodiment of the present invention. 
     The inventive suspension system comprises a wheel carrier  54  for rotatably supporting a wheel (not shown); an upper control link  38  having a first end  50  coupled to an upper end of the wheel carrier  54  by, for example, a ball joint assembly or a bushing assembly and two second ends  42  and  44  branched off from the first end  50  and extending toward a vehicle body (not shown); and a lower control link  40  having a first end  52  coupled to a lower end of the wheel carrier  54  by, for example, a ball joint assembly or a bushing assembly and two second ends  46  and  48  branched off from the first end  52  and extending toward the vehicle body. 
     The two second ends  42  and  44  of the upper control link  38  are respectively connected to first and second upper bell cranks  6  and  8  which are connected to the vehicle body by an upper bracket  30 . 
     The first upper bell crank  6  comprises a hinge portion  60  pivotally coupled on an upper stationary hinge shaft  34  supported by the upper bracket  30  mounted on the vehicle body, a horizontal portion  22  extending from the hinge portion  60  toward the wheel carrier  54  and to which the second end  42  of the upper control link  38  is pivotally coupled by a bushing assembly, and a vertical portion  14  extending downward from the hinge portion  60 . The second upper bell crank  8  comprises a hinge portion  80  pivotally coupled on the upper stationary hinge shaft  34  mounted on the vehicle body, a horizontal portion  24  extending from the hinge portion  60  toward the wheel carrier  54  and to which another second end  44  of the upper control link  38  is pivotally coupled, and a vertical portion  16  extending downward from the hinge portion  80 . 
     In addition, the two second ends  46  and  48  of the lower control link  40  are respectively connected to first and second lower bell cranks  10  and  12  disposed under the first and second upper bell cranks  6  and  8  and connected to the vehicle body by a lower bracket  32  mounted on the vehicle body. 
     The first lower bell crank  10  comprises a hinge portion  100  pivotally coupled on a lower stationary hinge shaft  36  supported by the lower bracket  32 , a horizontal portion  26  extending from the hinge portion  100  toward the wheel carrier  54  and to which the second end  46  of the lower control link  40  is pivotally coupled, and a vertical portion  18  extending upward from the hinge portion  100 . The second lower bell crank  12  comprises a hinge portion  120  pivotally coupled on the lower stationary hinge shaft  36 , a horizontal portion  28  extending from the hinge portion  120  toward the wheel carrier  54  and to which another second end  48  of the lower control link  40  is pivotally coupled, and a vertical portion  20  extending upward from the hinge portion  120 . 
     The lower ends of the vertical portions  14  and  16  of the first and second upper bell cranks  6  and  8  and the upper ends of the vertical portions  18  and  20  of the first and second lower bell cranks  10  and  12  are pivotally coupled on a middle movable hinge shaft  4 . 
     In addition, a hydraulic actuator  2  such as a reciprocating cylinder is horizontally disposed and pivotally coupled at its one end to the middle movable shaft  4  and at its the other end to the vehicle body. 
     In the above, each of the bell cranks  6 ,  8 ,  10  and  12  is designed such that each length of the vertical portions  14 ,  16 ,  18  and  20  is longer than that of the horizontal portions  22 ,  24 ,  26  and  28  so that the hydraulic actuator  2  can easily move the upper and lower control links  38  and  40  upward and downward. 
     The hydraulic actuator  2  is controlled by a hydraulic control part  200  in accordance with driving conditions of a vehicle. 
     The hydraulic control part  200  comprises a sensor part  201  consisting of, for example, a vehicle speed sensor, a steering angle sensor, and a lateral sensor; a control part  203  receiving signals on the driving conditions of the vehicle from the sensor part  201 ; and a fluid pump  205  for feeding fluid from a fluid tank  207  to the hydraulic actuator  2 , the operation of the fluid pump  205  being controlled by the control part  203  in accordance with the signals transmitted from the sensor part  201 . 
     Now the operation of the above described suspension system will be described hereinafter with reference to FIGS. 2 and 3. 
     Referring first to FIG. 2, when the control part  203  determines from the signals received from the sensor part  201  that the roll center requires raising, the control part  203  controls the hydraulic pump  205  such that the hydraulic actuator  2  pulls the movable hinge shaft  4  toward the vehicle body, whereby the upper bell cranks  6  and  8  rotate clockwise while the lower bell cranks  10  and  12  rotate counterclockwise. As a result, the second ends  42  and  44  of the upper control link  38  coupled to the upper bell cranks  6  and  8  descend while the second ends  46  and  48  of the lower control link  38  coupled to the lower bell cranks  10  and  12  ascend. This results in raising the roll center. 
     In addition, with reference to FIG. 3, when a signal for lowering the roll center is transmitted from the sensor part  201  to the control part  203 , the control part  203  controls the hydraulic pump  205  such that the hydraulic actuator  2  pushes the movable hinge shaft  4  toward the wheel  58 , whereby the upper bell cranks  6  and  8  rotate counter-clockwise while the lower bell cranks  10  and  12  rotate clockwise. As a result, the second ends  42  and  44  of the upper control link  38  coupled to the upper bell cranks  6  and  8  ascend while the second ends  46  and  48  of the lower control link  38  coupled to the lower bell cranks  10  and  12  descend. This results in lowering the roll center. 
     FIG. 4 shows a schematic view illustrating variations in the roll center induced by the operation of the inventive suspension system. 
     In a normal driving state, an instantaneous center C 1  of a wheel  58  with respect to the vehicle body is formed at an intersection of a line extending from the upper control link  38  and a line extending from the lower control link  40 . 
     At this point, a roll center RC 1  is formed at an intersection of a line connecting a contact point of the wheel  58  with a road surface to the instantaneous center C 1  and a center line CL of the vehicle body. A distance from the road surface to the roll center RC 1  becomes a height H 1  of the roll center RC 1 . 
     Therefore, the rolling of the vehicle occurs on the basis of the roll center RC 1  unless the roll center is varied. 
     In the above state, if the upper and lower control links  38  and  40  are controlled as shown in FIG. 2, that is, if a distance between the second ends  42  and  44  of the upper control link  38  and the second ends  46  and  48  of the lower control link  40  is lessened, an instantaneous center C 2  of the wheel  58  with respect to the vehicle body is formed at an intersection of a line extending from the upper control link  38  and a line extending from the lower control link  40 . 
     At this point, a roll center RC 2  is formed at an intersection of a line connecting the contact point of the wheel  58  with the road surface to the instantaneous center C 2  and the center line CL of the vehicle body. Therefore, a distance from the road surface to the roll center RC 2  becomes a height H 2  of the roll center RC 2 . 
     In addition, if the upper and lower control links  38  and  40  are controlled as shown in FIG. 3, and if a distance between the second ends  42  and  44  of the upper control link  38  and the second ends  46  and  48  of the lower control link  40  is increased, an instantaneous center C 3  of the wheel  58  with respect to the vehicle body is formed at an intersection of a line extending from the upper control link  38  and a line extending from the lower control link  40 . 
     At this point, a roll center RC 3  is formed at an intersection of a line connecting the contact point of the wheel  58  with the road surface to the instantaneous center C 3  and the center line CL of the vehicle body. Therefore, a distance from the road surface to the roll center RC 3  becomes a height H 3  of the roll center RC 3 , lowering the height of the roll center RC 3 . 
     As described above, the suspension system according to the present invention suppresses the roll of the vehicle by adjusting the height of the roll center in accordance with road conditions. 
     In addition, since the actuator  2  is horizontally disposed such that its reciprocating motion becomes perpendicular to a vertical direction of the vehicle body, the mechanical energy required to be exerted by the actuator  2  is minimized when considering the following equation: 
     
       
           W=F·S=|F||S |Cosθ 
       
     
     where, F is the actuator force, S is an actuator stroke, and θ is an actuating angle of the actuator with respect to a vertical direction of the vehicle. 
     Therefore, there is no need for a high capacity hydraulic pump for operating the actuator of the inventive suspension system, thereby reducing the weight of the vehicle and decreasing the costs for manufacturing the suspension system. 
     While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.