Patent Application
20090003927
The present invention pertains to a ball pin of a ball-and-socket joint for a motor vehicle suspension and more particularly pertains to a ball pin (ball stud) with a joint ball provided with a molded surface.
Ball joints have been produced where the ball pin is a single-piece ball pin. These ball pins are prepared by cold forming steel material. Typically, machining and burnishing steps are required to achieve the final form of the ball pins. The production of such single-piece ball pins involves several manufacturing steps. The overall cost is significant including the steel. Further the manufacturing steps produce waste. This becomes more significant as material costs rise.
A two-piece ball pin has already being used in stabilizer applications. With such two-piece stabilizer ball pins the joint balls are press-fitted onto the ball stud creating a low load-bearing capacity. Such two-piece stabilizer ball pins would not be effective for automotive suspension ball joint applications due to the high pull-out requirements for a suspension ball joint.
A ball joint with a molded ball is known from German Offenlegungsschrift No. DE-A1 102 17 149. The ball joint ball is injection molded using plastic. The resulting structure that is metal and plastic can only carrying low loads. Further, problems are encountered based on the different rates of thermal expansion of the metal and plastic.
It is the object of the present invention to provide a ball pin for ball joints with high load-bearing capacity, so as to particularly be useful in the suspension of a motor vehicle, which ball pin can be manufactured at low cost and which makes possible a high level of joint ball customization.
According to the invention, a metallic ball pin is provided for use in a ball joint in the suspension of motor vehicles. The ball pin has a pin member with a joint ball core portion on one end of the pin member and a pin end on the other. The pin member has a pin outer surface and a longitudinal axis. The joint ball core portion has a surface portion that extends radially outwardly with respect to the longitudinal axis of the pin member and with respect to an adjacent surface portion to create a core contour. The joint ball core portion is the region that receives and supports a ball surface part. The ball surface part is molded and formed around the joint ball core portion using an injection molding process. The injection molding process allows for material optimization in terms of strengths, machine-ability, and other material properties since a greater array of materials are available. The design of the ball pin using the injection molding process allows for two different distinct parts (the joint ball core portion and the ball surface part) to permanently attach making it possible to combine ball surface parts with different shaped pin members to create a modular system. Furthermore, this design results in considerably reducing manufacturing costs since machining of the ball pin is simplified and makes it possible to use variable pin diameters, which leads to longer service of the ball pin.
Metal or any other suitable material, particularly a zinc alloy, is injected into a mold release burr creating a joint ball surface that forms around the contour of the joint ball core portion of the pin member. When the material of the ball surface part is cooled, the ball surface part is nonrotatably attached to the joint ball core portion. The ball surface is inserted into a bearing shell of a housing of a ball and socket joint, which can be connected to another motor vehicle part or suspension part. The pin member may be prepared by cold forming and is formed of a metal or any other suitable material, particularly steel, that is different from the material used to form the joint ball surface. As the pin member is formed of a metal material, preferably steel, and the ball surface part is made of another material, preferably zinc, the thermal expansion is advantageously similar. The pin member is shaped for connection to a suspension part or a motor vehicle part.
The pin member advantageously includes a backing surface at the joint core portion. The backing surface may be a knurled surface or a similar holding function of a joint ball core region of the pin member providing a positive locking between the pin member and ball surface part material. The knurled surface includes surface portions that extend radially outwardly with respect to the longitudinal axis of the pin member and radially outwardly with respect to an adjacent core surface region. The joint ball core region may have a top surface portion perpendicular to a longitudinal axis of the pin member. Optionally, the ball surface part may or may not be in contact with the top surface of the joint ball core region. The joint ball core region may be mushroom shaped providing good positive locking. The joint ball core region may also be somewhat ball shaped with the molded or deposited outer material forming the ball bearing surface. Furthermore, the joint ball core region may have concave shaped side surfaces that transition to a flange edge for better positive locking. The joint ball core region may also have a circumferential side edge surface that extends substantially perpendicular to a longitudinal axis of the pin member to provide better positive locking.
By forming the ball as a molded surface, the various shape aspects of the outer surface may be controlled based on the mold used. The molded joint ball surface allows joint ball surfaces to be created with constant ball dimensions. Constant ball dimensions make it possible to considerably reduce the expense of machining and to improve the quality of the joint ball surface shape since secondary operations can be performed, such as induction hardening, prior to formation of the ball to help avoid heat distortion of the ball shape. Numerous features can also be incorporated into the injected areas, such as support rings for boots, seal grooves, and customized ball shapes, which can include equator clearances for torque control and grease grooves. Furthermore, both the ball surface part and the pin member are formed of a metallic metal and are therefore capable of being used in joints with high loading-bearing capacity. The joint ball may also be molded so that the outer surface has grooves for receiving lubricant. This allows for complicated lubricating grooves to be better prepared in the ball. The lubricant grooves may be straight, curved or extend helically over the shape of the joint ball.
According to the invention, a heat-shrinkable sleeve may be applied to the joint ball surface to form a ball shell. The heat-shrinkable sleeve is placed around the joint ball surface. The joint ball core portion is then subjected to heat causing the joint ball core portion to expand and to come in contact with the heat-shrinkable sleeve. The heat-shrinkable sleeve conforms to the shape of the joint ball surface and attaches to the joint surface. The flat areas of the heat-shrinkable sleeve attach to the top portion and the bottom portion of the joint ball surface. The heat-shrinkable sleeve being applied to the joint ball surface is advantageous as it avoids integrating the joint ball into a geometrically complicated ball shell. (We need more information on how this works so we can better describe it). Furthermore, the heat-shrinkable sleeve advantageously prevents rotation between the joint ball surface and the heat-shrinkable sleeve. The heat-shrinkable sleeve also reduces cost as it eliminates a ball shell that is normally found in such ball pins.
According to the invention, a method is contemplated for forming a pin member having a longitudinal axis and a pin end on one end of the pin member and a joint ball core portion on the other. The pin member is formed out of a metal material, preferably steel, and has a pin outer surface. The joint ball core portion has a core surface portion that extends radially outwardly with respect to the longitudinal axis and with respect to an adjacent surface portion to provide a core contour. The method further includes injection molding a second metal material, which is different from the metal material used to form the pin member, on the joint ball core portion to create a molded ball surface part. The ball surface part is in contact with the joint ball core and follows the core contour and the metal material of the ball surface part is on each axial side of the core surface portion.
According to the invention, the method further includes applying a heat-shrinkable sleeve to an outer metal surface of a joint ball core portion to create a ball shell. The heat-shrinkable sleeve is placed around the joint ball outer surface. The joint ball core region is then heated and expands as a result of the heating. As a result, the outer joint ball surface comes in contact with the heat-shrinkable sleeve and the heat-shrinkable sleeve conforms to the shape of the joint ball outer surface and attaches to the joint ball outer surface. Flattened areas of the heat-shrinkable sleeve attach parallel to the joint ball outer surface and advantageously act to prevent rotation between the heat-shrinkable sleeve and the joint ball core portion. The heat-shrinkable sleeve may be any suitable material, preferably plastic.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.
In the drawings:
Referring to the drawings in particular,
The joint ball core portion 16 is the region that receives and supports the ball surface part 22. The ball surface part 22 is formed around the core portion using an injection molding process. When the material of the ball surface part 22 is cooled, the ball surface part 22 is nonrotatably attached to the joint ball core portion 16. As the pin member 12 is made of a metal material, preferably steel, and the ball surface part 22 is made of another metal material, preferably zinc, the thermal expansion is similar.
The joint ball core portion 16 has a top surface at the end 20 and a circumferential surface with a contour with an edge 24 that extends radially outwardly with respect to the longitudinal axis 15 of the pin member 12 and also radially outwardly of the adjacent core surface regions 26 and 28. The pin end side surface 23 of the edge surface 24 is almost perpendicular to the longitudinal axis 15 of the pin member 12. The ball surface part 22 contacts the joint ball core portion 16 and follows the contour based on the ball surface part 22 being molded thereto. With this construction, the core contour with side 23 of the edge surface 24 forms a positive lock with the ball surface part 22. A good connection is provided between the ball surface part 22 and the pin member 12 while also providing a desired shape for the ball joint surface 25.
The pin member 12 is manufactured with accurate dimensions according to the cold forming process. Constant ball dimensions make it possible to considerably reduce the expense of machining and to improve the quality of the ball surface part 22. Both the ball surface part 22 and the pin member 12 consist of a metallic material and are therefore particularly suitable for joints with high load-bearing capacity.
