Abstract:
In manufacturing a knuckle body forged or cast from light alloy of a suspension device, a large vertical height of a pair of bosses protruding downward from front and rear ends in a lower portion of the knuckle body may cause degradation in forgeability or castability of the knuckle body to hinder manufacturing, and also cause reduction in rigidity of the bosses to reduce mounting strength of a lower arm support bracket made of ferrous metal. A vertical height of the pair of bosses of the knuckle body is set to be smaller than a vertical height of the lower arm support bracket, thereby improving forgeability or castability of the knuckle body and increasing rigidity of the bosses.

Description:
RELATED APPLICATION DATA 
   The Japanese priority application Nos. 2004-57450 and 2004-57453 upon which the present application is based are hereby incorporated in their entirety herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a suspension device in which a knuckle is supported by an upper arm and a lower arm. More particularly, the present invention relates to a suspension device in which a knuckle is formed by connecting a knuckle body forged or cast from light alloy and a lower arm support bracket made of ferrous metal, and a suspension device in which an outer end of a lower arm in a vehicle width direction is supported on a lower arm support bracket connected to a lower surface of an upper arm body via a ball joint. 
   2. Description of the Related Art 
     FIG. 5  shows a knuckle  01  of a suspension device according to a first conventional example (Prior Art 1). The knuckle  01  is formed by connecting a lower arm support bracket  03  made of ferrous metal to a lower end of a knuckle body  02  forged from light alloy with two bolts  04  and  05 , an outer end of an upper arm  06  in a vehicle width direction is connected to an upper end of the knuckle  01 , and an outer end of a lower arm  07  in the vehicle width direction is connected to the lower arm support bracket  03 . A pair of bosses  02   a  and  02   b  protruding downward are integrally formed at front and rear ends in a lower portion of the knuckle body  02  to which the lower arm  07  is connected. Front and rear ends of the lower arm support bracket  03  are fastened to lower surfaces of the bosses  02   a  and  02   b  with the bolts  04  and  05 . 
     FIG. 6  shows a knuckle  01  of a suspension device according to a second conventional example (Prior Art 2). A space  08  is formed between a recess  02   c  interposed between a pair of bosses  02   a  and  02   b  of a knuckle body  02  and an upper surface of a lower arm support bracket  03 , and an outer end of a lower arm  07  in a vehicle width direction is secured with a nut  09  to an upper end of a ball joint  010  oscillably supported on the lower arm support bracket  03  and extending into the space  08 . 
   In the knuckle  01  of the suspension device according to Prior Art 1, the pair of bosses  02   a  and  02   b  significantly protrude from the lower portion of the knuckle body  02 , thus the elongated bosses  02   a  and  02   b  may cause degradation in forgeability to increase manufacturing costs, and strength of the bosses  02   a  and  02   b  may be insufficient to which a heavy load from the lower arm  07  is transferred. Also when the knuckle body  02  is cast from light alloy, the elongated bosses  02   a  and  02   b  may interfere with flowing molten metal to cause degradation in castability, and cavities may be created in the bosses  02   a  and  02   b  to reduce quality. 
   In the knuckle  01  of the suspension device according to Prior Art 2, when the nut  09  loosens from vibration caused by driving of a vehicle, the lower arm  07  may fall off from the ball joint  010  leading to separation of the lower arm  07  from the knuckle  01 . 
   SUMMARY OF THE INVENTION 
   The present invention has been achieved in view of the above-mentioned circumstances, and has a first object to improve forgeability or castability and increase rigidity of a pair of bosses formed in a lower portion of a knuckle body forged or cast from light alloy and secured to a lower arm support bracket made of ferrous metal. 
   The invention has a second object to prevent a ball joint that supports an outer end of a lower arm in a vehicle width direction from falling off from a knuckle even if a nut for securing the ball joint to the knuckle loosens. 
   In order to achieve the first object, according to a first feature of the present invention, there is proposed a suspension device including: a knuckle formed by connecting a knuckle body forged or cast from light alloy and a lower arm support bracket made of ferrous metal; an upper arm having an inner end in a vehicle width direction connected to a vehicle body, and an outer end in the vehicle width direction connected to an upper portion of the knuckle body; and a lower arm having an inner end in the vehicle width direction connected to the vehicle body, and an outer end in the vehicle width direction connected to the lower arm support bracket, the lower arm support bracket being secured to lower surfaces of a pair of bosses protruding downward from front and rear ends in a lower portion of the knuckle body, wherein a vertical height of the pair of bosses is smaller than a vertical height of the lower arm support bracket. 
   In manufacturing the knuckle body forged or cast from light alloy, a large vertical height of the pair of bosses protruding downward from the front and rear ends in the lower portion of the knuckle body may cause degradation in forgeability or castability of the knuckle body to hinder manufacturing, and also cause reduction in rigidity of the bosses to reduce mounting strength of the lower arm support bracket. With the above described configuration, however, the vertical height of the pair of bosses is smaller than the vertical height of the lower arm support bracket, thereby improving forgeability or castability of the knuckle body and increasing rigidity of the bosses to increase mounting strength of the lower arm support bracket. 
   In order to achieve the second object, according to a second feature of the present invention, there is proposed a suspension device including: a knuckle formed by connecting a lower arm support bracket to a lower surface of a knuckle body so as to form a space; an upper arm having an inner end in a vehicle width direction connected to a vehicle body, and an outer end in the vehicle width direction connected to an upper portion of the knuckle body; and a lower arm having an inner end in the vehicle width direction connected to the vehicle body, and an outer end in the vehicle width direction connected to the lower arm support bracket via a ball joint, the ball joint having a head connected to the lower arm in the space, a shaft extending downward from the head to pass through a mounting hole of the lower arm support bracket, and an external thread extending downward from the shaft and onto which a nut is screwed, wherein a distance between the lower surface of the knuckle body facing the space and an upper surface of the outer end of the lower arm in the vehicle width direction is smaller than a distance between a lower end of the external thread of the ball joint and an upper end of the mounting hole of the lower arm support bracket. 
   With the above described configuration, the ball joint that supports the outer end of the lower arm in the vehicle width direction on the lower arm support bracket of the knuckle includes the head connected to the lower arm in the space between the knuckle body and the lower arm support bracket, the shaft extending downward from the head to pass through the mounting hole of the lower arm support bracket, and the external thread extending downward from the shaft and onto which the nut is screwed; and the distance between the lower surface of the knuckle body facing the space and the upper surface of the outer end of the lower arm in the vehicle width direction is smaller than the distance between the lower end of the external thread of the ball joint and the upper end of the mounting hole of the lower arm support bracket. Thus, even if the nut loosens and falls off from the external thread, the upper surface of the lower arm interferes with the lower surface of the knuckle body to prevent upward movement the lower arm, thereby preventing the ball joint from falling off from the lower arm support bracket to prevent the lower arm from being separated from the knuckle. 
   The above-mentioned object, other objects, characteristics, and advantages of the present invention will become apparent from an explanation of preferred embodiments, which will be described in detail below by reference to the attached drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a double wishbone type suspension of a left rear wheel, according to a first embodiment of the present invention. 
       FIG. 2  is an enlarged view on arrow in a direction  2  in  FIG. 1 . 
       FIG. 3  is an enlarged sectional view of essential portions of  FIG. 2 . 
       FIG. 4  is a view corresponding to  FIG. 3  according to a second embodiment of the present invention. 
       FIG. 5  is a view corresponding to  FIG. 2  according to a first conventional example. 
       FIG. 6  is a view corresponding to  FIG. 2  according to a second conventional example. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Now, a first embodiment of the invention will be described with reference to  FIGS. 1 to 3 . 
   As shown in  FIGS. 1 and 2 , a double wishbone type suspension device S includes a knuckle  13  supported on a vehicle body by an upper arm  11  and a lower arm  12 . The knuckle  13  includes a knuckle body  14  forged from light alloy and a lower arm support bracket  15  made of ferrous material and fastened to a lower portion of the knuckle body  14 . The knuckle body  14  includes an axle support portion  14   a  that rotatably supports an axle of a wheel W and an upper arm support portion  14   b  extending upward from the axle support portion  14   a . An outer end of the upper arm  11  in a vehicle width direction is pivotably supported on an upper end of the upper arm support portion  14   b  via a ball joint  16 . 
   As is apparent from  FIG. 3 , a pair of bosses  14   c  and  14   d  protrude downward from front and rear ends in a lower surface of the axle support portion  14   a  of the knuckle body  14 . A recess  14   e  bowed upward is formed between the bosses  14   c  and  14   d . The lower arm support bracket  15  includes mounting portions  15   a  and  15   b  at front and rear ends, a lower arm support portion  15   c  in the middle, and a pair of inclined connecting portions  15   d  and  15   e  connecting the mounting portions  15   a  and  15   b  and the lower arm support portion  15   c . The front mounting portion  15   a  is secured to a lower end of the front boss  14   c  with a stud bolt  17  and a nut  18 , and the rear mounting portion  15   b  is secured to a lower end of the rear boss  14   d  with a bolt  19 . The lower arm support portion  15   c  of the lower arm support bracket  15  is placed in a position lower than the mounting portions  15   a  and  15   b . An outer end of the lower arm  12  in the vehicle width direction is placed in a space  20  formed between the recess  14   e  of the knuckle body  14  and the lower arm support portion  15   c  of the lower arm support bracket  15 . 
   A ball joint  21  that pivotably supports the outer end of the lower arm  12  in the vehicle width direction on the lower arm support bracket  15  has a ball stud  22  including a spherical head  22   a , a conical shaft  22   b  connecting to the head  22   a , and an external thread  22   c  connecting to the shaft  22   b . The shaft  22   b  of the ball stud  22  passes from above to down through a mounting hole  15   f  provided in the lower arm support portion  15   c  of the lower arm support bracket  15 , and is secured by screwing a nut  23  onto the external thread  22   c  protruding downward from the lower arm support portion  15   c . The ball joint  21  includes a cup-shaped housing  12   a  provided at an end of the lower arm  12 . A bearing  25  made of synthetic resin and in slide contact with the head  22   a  of the ball stud  22  is housed in the housing  12   a  along an inner peripheral surface thereof, and held by a retainer  26  secured so as to cover an opening of the housing  12   a . A boot  27  is fitted between the opening of the housing  12   a  and the lower arm support portion  15   c  of the lower arm support bracket  15  so as to prevent dust from entering a slide surface between the head  22   a  of the ball stud  22  and the bearing  25 . 
   A height h 1  from a bottom surface of the recess  14   e  of the knuckle body  14  to lower ends of the bosses  14   c  and  14   d  is smaller than a height h 2  from the lower ends of the bosses  14   c  and  14   d  to the lower arm support portion  15   c  of the lower arm support bracket  15 , that is, an input point of a load from the lower arm  12  to the lower arm support bracket  15 . Thus, the protruding height h 1  of the pair of bosses  14   c  and  14   d  provided at the lower end of the knuckle body  14  is decreased to facilitate machining for the bosses  14   c  and  14   d  to protrude in forging the knuckle body  14  to thereby reduce machining costs, and also increase rigidity of the bosses  14   c  and  14   d  to which the load from the lower arm  12  is transferred via the lower arm support bracket  15 . 
   A distance d 1  from the bottom surface of the recess  14   e  of the knuckle body  14  to an upper end of the ball joint  21  is smaller than a distance d 2  from an upper end of the mounting hole  15   f  in the lower arm support portion  15   c  to a lower end of the external thread  22   c  of the ball stud  22 . Therefore, even if the nut  23  for securing the ball stud  22  of the ball joint  21  to the lower arm support bracket  15  loosens and falls off due to vibration caused by driving of a vehicle, and the shaft  22   b  of the ball stud  22  is about to slip upward out of the mounting hole  15   f  in the lower arm support bracket  15 , the housing  12   a  of the ball joint  21  abuts against the bottom surface of the recess  14   e  of the knuckle body  14  to prevent falling of the ball joint  21  and reliably prevent the lower arm  12  from being separated from the knuckle  13 . 
   Because the ball joint  21  cannot be mounted after the lower arm support bracket  15  is connected to the knuckle body  14 , the lower arm support bracket  15  to which the ball joint  21  is previously mounted needs to be connected to the knuckle body  14 . 
   Next a second embodiment of the invention will be described with reference to  FIG. 4 . 
   In the first embodiment, the ball stud  22  of the ball joint  21  is secured to the lower arm support bracket  15 , while in the second embodiment, a housing  24  of a ball joint  21  is secured to a lower arm support bracket  15 . Specifically, the housing  24  of the ball joint  21  is pressed from above to down into a mounting hole  15   f  formed in a lower arm support portion  15   c  of the lower arm support bracket  15 . An outer end of a lower arm  12  in a vehicle width direction fits to a ball stud  22  protruding downward from the housing  24  and is fastened with a nut  28 . 
   Also in the second embodiment, a height h 1  from a bottom surface of a recess  14   e  of a knuckle body  14  to lower ends of bosses  14   c  and  14   d  is smaller than a height h 2  from the lower ends of the bosses  14   c  and  14   d  to the lower arm support portion  15   c  of the lower arm support bracket  15 , that is, an input point of a load from the lower arm  12  to the lower arm support bracket  15 . This facilitates machining for the bosses  14   c  and  14   d  to protrude in forging the knuckle body  14  to reduce machining costs, and also increases rigidity of the bosses  14   c  and  14   d.    
   The embodiments of the invention have been described, but the invention is not limited to the above described embodiments, and various changes in design may be made without departing from the subject matter of the invention described in the claims. 
   For example, the double wishbone type suspension device S is described as an example in the embodiments, but the invention is applicable to any other types of suspension devices. 
   The knuckle body may be cast from light alloy rather than forged from light alloy.