Patent Publication Number: US-6339967-B1

Title: Vibration dampening hypoid gear structure

Description:
This application is a divisional of application Ser. No. 09/168,942 filed Oct. 9, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a hypoid gear structure, and more particularly, relates to a hypoid gear structure having an excellent abnormal-sound prevention property. 
     2. Description of the Related Art 
     A technique for using a hypoid gear is a motor-driven power steering device is known. In such a technique, the hypoid gear is disposed as a decelerating mechanism between a rotation axis of an electric motor for providing an auxiliary force for steering and an output axis of a steering system. The rotation axis of the electric motor and the output axis of the steering system are coupled with each other by the hypoid gear structure which functions as a decelerating mechanism. 
     One problem of the above conventional motor-driven power steering device is that it is difficult to appropriately set a backlash produced at the engaging portion of gears in the hypoid gear structure. 
     For example, Japanese Laid-Open Publication No. 7-232651 discloses that such a backlash produced at the engaging portion of the gears can be appropriately controlled by adjusting the position at which a hypoid ring gear is attached in the vertical direction. 
     In the conventional hypoid gear structure described in the above-mentioned publication, the engagement between the hypoid ring gear and a hypoid pinion gear is adjusted so that an appropriate backlash is obtained at a correct meshed position between the hypoid ring gear and the hypoid pinion gear. This allows for smooth engagement therebetween. However, if the hypoid gear structure receives a vibration and the like from the side of the tires (from the road surface), an abnormal sound such as a tooth striking sound may be generated due to a backlash even if the backlash is within an appropriate range. 
     SUMMARY OF THE INVENTION 
     The hypoid gear structure of this invention includes: a hypoid ring gear disposed coaxially with a rotation axis; and hypoid pinion gear provided with a rotation axis of an electric motor and engaging with the hypoid ring gear, wherein the hypoid ring gear includes a first toothed portion disposed on the inner side and a second toothed portion disposed on the outer side, and one of the first toothed portion and the second toothed portion is urged by a spring to press the hypoid pinion gear. 
     In one embodiment of the invention, the one of the first toothed portion and the second toothed portion is shaped so as to be in a correct engagement with the hypoid pinion gear in a state where the one of the first toothed portion and the second toothed portion is meshed with the hypoid pinion gear with the spring being bent. 
     In another embodiment of the invention, the first toothed portion is urged by the spring to press the hypoid pinion gear, and the first toothed portion is coupled with the second toothed portion via the spring. 
     In still another embodiment of the invention, an outer periphery of the first toothed portion is shaped so as to be kept apart from an inner periphery of the second toothed portion. 
     In still another embodiment of the invention, the spring is a plate spring having a ring portion, and a rotation regulating portion for regulating the rotation of the plate spring with respect to the second toothed portion is formed at an inner periphery of the plate spring. 
     In still another embodiment of the invention, the first toothed portion is made of a resin. 
     In still another embodiment of the invention, the first toothed portion is formed on a pedestal disposed on the spring by insert molding. 
     Alternatively, the hypoid gear structure of this invention includes: a hypoid ring gear disposed coaxially with a rotation axis; and a hypoid pinion gear provided with a rotation axis of an electric motor and engaging with the hypoid ring gear, wherein the hypoid ring gear includes a concave portion, and the concave portion is filled with a vibration-absorbing material. 
     Alternatively, the hypoid gear structure of this invention includes: a hypoid ring gear disposed coaxially with a rotation axis; and a hypoid pinion gear provided with a rotation axis of an electric motor and engaging with the hypoid ring gear, wherein the hypoid ring gear includes concave portions formed alternately in a predetermined direction. 
     In one embodiment of the invention, the concave portions are filled with a vibration-absorbing material. 
     In another embodiment of the invention, the tooth flank of the first toothed portion and the tooth flank of the second toothed portion form a continuous tooth flank in a state where the one of the first toothed portion and the second toothed portion is meshed with the hypoid pinion gear with the spring being bent. 
     Thus, the invention described herein makes possible the advantage of providing a hypoid gear structure which can reduce the generation of an abnormal sound such as a tooth striking sound due to a vibration received from the road surface. 
     These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a structural view of a motor-driven power steering device including a hypoid gear structure according to the present invention. 
     FIGS. 2A to  2 C are views illustrating a first example of the hypoid gear structure, where FIG. 2A is a plan view, FIG. 2B is a sectional view, and FIG. 2C is an enlarged partial sectional view of a main portion of the hypoid gear structure. 
     FIG. 3 is a view illustrating a second example of the hypoid gear structure. 
     FIGS. 4A and 4B are views illustrating a third example of the hypoid gear structure, where FIG. 4A is a partial sectional view of a main portion of a hypoid ring gear, and FIG. 4B is a partial sectional view of a main portion of the hypoid gear structure. 
     FIGS. 5A to  5 D are views illustrating a fourth example of the hypoid gear structure, where FIG. 5A is a plan view of a plate spring, FIG. 5B is a plan view of a hypoid ring gear, FIG. 5C is a sectional view of the hypoid ring gear, and FIG. 5D is an enlarged partial sectional view of a main portion of the hypoid ring gear. 
     FIGS. 6A and 6B are view illustrating a fifth example of the hypoid gear structure, where FIG. 6A is a partial plan view of a main portion of a hypoid ring gear, and FIG. 6B is a bottom view of the hypoid ring gear. 
     FIGS. 7A and 7B are view illustrating a sixth example of the hypoid gear structure, where FIG. 7A is a sectional view of a main portion of a hypoid ring gear, and FIG. 7B is a sectional view of a main portion of an alternative hypoid ring gear. 
     FIGS. 8A and 8B are views illustrating the tooth contact of the hypoid gear structure of the second example, where FIG. 8A illustrates the tooth contact of an outer ring gear and an inner ring gear, and FIGS. 8B illustrates the tooth contact of the inner ring gear. 
     FIGS. 9A and 9B are views illustrating the tooth contact of an alternative hypoid gear structure of the second example, where FIG. 9A illustrates the tooth contact of an outer ring gear and an inner ring gear, and FIG. 9B illustrates the tooth contact of the inner ring gear. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinbelow, the present invention will be described by way of example with reference to the accompanying drawings. 
     FIG. 1 illustrates a motor-driven power steering device including a hypoid gear structure according to the present invention. 
     A motor-driven power steering device  2  includes a steering shaft  7  and a rack axis  3 . The rotation of the steering shaft  7  is converted into a movement in the axial direction of the rack axis  3  via the engagement between a pinion gear  4  disposed coaxially with the steering shaft  7  and the rack axis  3 . Wheels (not shown) are coupled with both ends of the rack axis  3  via a shaft coupling (not shown) and a tie-rod (not shown). The wheels are steered rightward and leftward as the rack axis  3  moves in the axial direction. 
     The steering shaft  7  includes an input axis  8  coupled with the side of a steering wheel (not shown) and an output axis  9  coupled with the side of the sheels (not shown). 
     A hypoid ring gear  12  is disposed coaxially with the output axis  9 , and engages with a hypoid pinion gear  15  provided with a rotation axis  14  of an electric motor  13 . 
     FIGS. 2A to  2 C illustrate a first example of the hypoid gear structure according to the present invention. FIGS. 2A and 2B are a plan view and a sectional view, respectively, of the hypoid gear structure, and FIG. 2C is an enlarged partial sectional view of a main portion of the hypoid gear structure. 
     The hypoid ring gear  12  includes an inner ring gear  12   a  on the inner side and an outer ring  12   b  on the outer side. The inner ring gear  12   a  is disposed on the inner periphery of the outer ring gear  12   b  with a plate spring  16 . The inner ring gear  12   a  is disposed so that the tooth flank thereof somewhat projects from the tooth flank of the outer ring gear  12   b  before the hypoid ring gear  12  and the hypoid pinion gear  15  are meshed, as shown in FIG.  2 C. Once the hypoid pinion gear  15  and the inner ring gear  12   a  have engaged with each other, the hypoid pinion gear  15  presses the inner ring gear  12   a  downward. In other words, the inner ring gear  12   a  engages with the hypoid pinion gear  15  while being pressed against the hypoid pinion gear  15  by an urging force of the plate spring  16 . 
     With this arrangement, if a vibration is received from the side of the tires (from the road surface), i.e., from the side of the output axis, the vibration energy is absorbed by bending the plate spring  16  via the inner ring gear  12   a . This reduces the generation of an abnormal sound such as a tooth striking sound due to a vibration and the like received from the side of the tires (from the road surface). Since the spring-urged gear is located on the inner side, the gear can be made small. 
     The inner ring gear  12   a  may be made of a resin, a copper alloy, or a steel, depending on the usages of the hypoid gear structure. 
     FIG. 3 illustrates a second example of the hypoid gear structure according to the present invention. In the engagement with the hypoid pinion gear  15 , when the inner ring gear  12   a  is pressed down and the plate spring  16  is bent, the inner ring gear  12   a  is in a slanted state in the portion thereof engaging with the hypoid pinion gear  15 . That is, the axial angle of the inner ring gear  12   a  shifts by an angle α. In this example, the tooth cutting process of the inner ring gear  12   a  is performed by shifting the axial angle of the inner ring gear  12   a  by the angle α so that the tooth flank of the inner ring gear  12   a  and the tooth flank of the outer ring gear  12   b  form a continuous tooth flank when the hypoid ring gear  12  engages with the hypoid pinion gear  15  with this shifted axial angle. 
     The thus-processed inner ring gear  12   a  and the outer ring gear  12   b  constitute one hypoid ring gear having a shape of continuous teeth in the state where the plate spring  16  is bent. That is, the tooth bottom and the tooth crest of the inner ring gear  12   a  continue with the tooth bottom and the tooth crest of the outer ring gear  12   b , respectively, in the state where the plate spring  16  is bent. 
     Thus, since the tooth flank of the inner ring gear  12   a  is shaped so as to continue with the tooth flank of the outer ring gear  12   b  in the state where the plate spring  16  is bent, the inner ring gear  12   a  engages with the hypoid pinion gear  15  in the state where the tooth flank of the inner ring gear  12   a  is aligned with the tooth flank of the outer ring gear  12   b . This ensures the transmission of the rotation. 
     FIGS. 8a and 8B are views for illustrating the tooth contact of the second example of the hypoid gear structure according to the present invention: FIG. 8A illustrates the tooth contact of the inner ring gear  12   a  and the outer ring gear  12   b , while, FIG. 8B illustrates the tooth contact of the inner ring gear  12   a .    
     The spring-urged inner ring gear  12   a  and the outer ring gear  12   b  correspond to ones which are obtained by dividing an integrated hypoid gear into an inner portion and an outer portion. When engaging with the hypoid pinion gear  15 , therefore, the inner ring gear  12   a  and the outer ring gear  12   b  provide the same tooth contact state as that provided by the integrated hypoid gear. As shown in FIG. 8A, the outer ring gear  12   b  is in contact with the hypoid pinion gear  15  at a contact portion  21 . 
     The portion other than the contact portion  21  is crowned, and is not in contact with the hypoid pinion gear  15 . Especially, the inner ring gear  12   a  which is located farther from the contact portion  21 , has a large grinding undercut due to the crowing. By spring-urging the inner ring gear  12   a  to engage with the hypoid pinion gear  15 , therefore, a contact portion  22  is formed on the outer circumference of the inner ring gear  12   a , i.e., on the side facing the outer ring gear  12   b , causing a tendency for edge contact. 
     FIGS. 9A and 9B are views for illustrating the tooth contact of an alternative hypoid gear structure of the second example according to the present invention: FIG. 9A illustrates the tooth contact of the inner ring gear  12   a  and the outer ring gear  12   b , while FIG. 9B illustrates the tooth contact of the inner ring gear  12   a.    
     The contact portion  22  described above with reference to FIGS. 8A and 8B is formed by spring-urging the inner ring gear  12   a  to engage with the hypoid pinion gear  15 . This is not a contact portion formed by correct tooth contract. 
     In order to provide correct tooth contact, an inner ring gear  12   g  having a shape shown by the one-dot dash line in FIG. 9A may be produced by minutely adjusting the twist angle and the pressure angle in the tooth cutting process. The inner ring gear  12   g  with this shape can form a contact portion  22   a  which realizes correct tooth contact with the hypoid pinion gear  15 , as shown in FIGS. 9A and 9B. Also, by producing an outer ring gear  12   h  having a shape shown by one-dot dash line in FIG. 9A, the contact portion is shifted closer to the outer circumference (farther from the inner ring gear) so that the rotational force is mainly transmitted by the outer ring gear. 
     The shifting of the contact portion of the outer ring gear closer to the outer circumference by changing the shape of the outer ring gear as shown by the one-dot dash line as described above is performed for the purpose of transmitting the rotational force mainly by the outer ring gear. Accordingly, this is applicable to the entirety of the second example of the hypoid gear structure. 
     Thus, the inner ring gear  12   g  is shaped so as to be in the correct engagement with the hypoid pinion gear  15  in the state where the plate spring  16  is bent. Accordingly, the engagement of the inner ring gear  12   g  with the hypoid pinion gear  15  when the inner ring gear  12   g  is slanted is in a correct engagement state. This further ensures the transmission of the rotation. 
     FIGS. 4A and 4B illustrate a third example of the hypoid gear structure according to the present invention: FIG. 4A is a partial sectional view of a main portion of the hypoid ring gear, and FIG. 4B is a partial sectional view of a main portion of the hypoid gear structure. 
     As described above, the inner ring gear  12   a  is slanted when the hypoid ring gear  12  and the hypoid pinion gear  15  engage with each other. In order to avoid the inner ring gear  12   a  and the outer ring gear  12   b  from interfering with each other at the engagement with the hypoid pinion gear  15 , a clearance  12   e  is provided between the outer periphery of the inner ring gear  12   a  and the inner periphery of the outer ring gear  12   b . The inner ring gear  12   a  has a round outer periphery  12   f  so that the clearance  12   e  remains when the inner ring gear  12   a  is pressed down and slanted. 
     Thus, the inner ring gear  12   a  has the outer periphery which is kept apart from the inner periphery of the outer ring gear  12   b . This allows the inner ring gear  12   a  to the spring-urged to press the hypoid pinion gear  15  without interfering with the outer ring gear  12   b . As a result, the inner ring gear  12   a  and the outer ring gear  12   b  will not interfere with each other when the plate spring  16  is bent. 
     FIGS. 5A to  5 D illustrates a fourth example of the hypoid gear structure according to the present invention: FIGS. 5A is a plan view of the spring plate  16 , FIGS. 5B and 5C are a plan view and a sectional view, respectively, of the hypoid ring gear, and FIG. 5D is a partial sectional view of a main portion of the hypoid ring gear. 
     As shown in FIGS. 5A, the plate spring  16  includes a ring portion  16   b  and arms  16   c  extending in the radial direction. The arms  16   c  are bent. The plate spring  16  is fixed to the hypoid ring gear  12  by a fit-in ring  17  which is fitted around an axis  12   c  of the hypoid ring gear by pressure, and held in position by the friction with the fit-in ring  17 . Notches  16   a  are formed at the inner circumference of the plate spring  16 . When the fit-in ring  17  is fit around the axis  12   c  of the hypoid ring gear  12 , the fit-in ring  17  plastically deforms due to the notches  16   a  of the plate spring  16 . This provides the effect of preventing the plate spring  16  from rotating. 
     Thus, the notches  16   a  are formed at the inner circumference of the plate spring  16  to regulate the rotation of the plate spring  16  relative to the hypoid ring gear  12  as described above. Accordingly, the inner ring gear  12   a  which is coupled with the body of the hypoid ring gear  12  via the plate spring  16  is kept stable relative to the body of the hypoid ring gear  12 . This allows the fixing structure of the plate spring  16  to be simplified. 
     FIGS. 6A and 6B illustrate a fifth example of the hypoid gear structure according to the present invention: FIG. 6A is a partial sectional view of a main portion of the hypoid ring gear, and FIG. 6B is a bottom view of the hypoid ring gear. 
     In the case where the inner ring gear is made of a resin, since the plate spring (spider spring) must be thin, it cannot be formed by insert molding. In order to solve this problem, the plate spring  16  is fixed to a ring-shaped steel pedestal  12   i  with a rivet or a screw, and a resin gear  12   d  is formed on the pedestal  12   i  by insert molding. 
     Thus, in this example, the inner ring gear is composed of the resin gear  12   d  which is formed on the pedestal  12   i  disposed on the spring plate  16  by insert molding. This allows for the molding of the resin gear having the plate spring. By using the gear made of a resin, the abnormal-sound reduction effect further improves. 
     In this embodiment, the hypoid gear structure where the inner ring gear on the inner side of the hypoid ring gear is spring-urged to press the hypoid pinion gear has been described. The present invention is not limited to this construction, but the same effect as that described above can also be obtained by a hypoid gear structure where the outer ring gear on the outer side of the hypoid ring gear is spring-urged to press the hypoid pinion gear. 
     FIGS. 7A and 7B illustrate a sixth example of the hypoid gear structure according to the present invention: FIG. 7A is a partial sectional view of a main portion of a hypoid ring gear, and FIG. 7B is a partial sectional view of a main portion of another hypoid ring gear. 
     As shown in FIG. 7A, a hypoid ring gear  112  has a concave portion  112   a  which is filled with a vibration-absorbing material. A resin or rubber, for example, is used as the vibration-absorbing material. This reduces noise from gears, an abnormal sound such as a tooth striking sound due to backlash, and the like. 
     As shown in FIG. 7B, a hypoid ring gear  212  includes concave portions  212   a  which are filled with a vibration-absorbing material, formed alternately in the axial direction. A resin or rubber, for example, is used as the vibration-absorbing material. Rubber should desirably have a large attenuation. With this configuration, the abnormal-sound reduction effect provided by the vibration-absorbing material can be further improved since the sound transmission is prolonged and thus the sound is attenuated during the transmission. This reduces noise from gears, a tooth striking sound due to backlash, and the like. 
     As described above, according to the hypoid gear structure of the present invention, the hypoid ring gear includes the first toothed portion on the inner side and the second toothed portion on the outer side. Either one of the first and second toothed portions is spring-urged to press the hypoid pinion gear. 
     Accordingly, if the hypoid gear structure receives a vibration from the side of the tires (from the road surface), such a vibration energy is absorbed by on of the first and second toothed portions which is spring-urged to press the hypoid pinion gear. This reduces the generation of noise such as a tooth striking sound due to the vibration received from the side of the tires (from the road surface). 
     Various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the scope and spirit of this invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the description as set forth herein, but rather that the claims be broadly construed.