BRIEF DESCRIPTION OF THE DRAWING
FIG. 1A is a torque-torsional diagram showing an embodiment of the invention;
FIG. 1B is a torque-torsion diagram showing a comparative example;
FIG. 2A is a plan view of a steering device;
FIG. 2B is a side view of the steering device;
FIG. 2C is a perspective view of the steering device;
FIG. 3 is a longitudinal sectional view of a fixed type constant velocity joint;
FIG. 4 is a principal enlarged view of FIG. 3;
FIG. 5 is a principal enlarged view of FIG. 3;
FIG. 6 is a longitudinal sectional view showing the joint taking a bending angle;
FIG. 7 is a schematic view of a steering-purpose fixed type constant velocity joint;
FIG. 8 is a torque-torsional angle diagram for the joint of FIG. 7;
FIG. 9 is a schematic view of a steering-purpose fixed type constant velocity joint;
FIG. 10 is a torque-torsional angle diagram for the joint of FIG. 9; and
FIGS. 11A to 11D show torque-torsional angle diagrams made by changing the phase in increments of 10°.
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the invention will now be described.
First, a brief description of a steering device will be given. As shown in FIGS. 2A through 2C, a steering device is so designed that rotational motion of a steering wheel 6 is transmitted to a steering gear 8 through a steering column consisting of one or a plurality of steering shafts 2, thereby converting it into the reciprocating motion of a tie rod 9. In the case where the steering shafts 2 cannot be disposed in a straight line in consideration of the vehicle space or the like, one or a plurality universal joints 1 will be disposed between the steering shafts 2 to ensure that accurate rotational motion is transmitted to the steering gear 8 even with the steering shafts 2 being bent. A fixed type constant velocity joint is used in place of the universal joint 1. The character α in FIG. 2B denotes the bending angle of the joint, and a large angle exceeding 30° can be set as the bending angle α.
Next, a fixed type constant velocity joint will be described. FIGS. 3 through 6 show by way of example a Rzeppa type joint (BJ), which is a kind of fixed type constant velocity joint. As shown in FIG. 3, this type of constant velocity joint 1 comprises an outer joint member 10, an inner joint member 20, torque transmitting balls 30, and a cage 40, as main components. The outer joint member 10 is connected to an input shaft or an output shaft, while the inner joint member 20 is connected to an input shaft or an output shaft. Here, the inner joint member 20 is serration-joined to the shaft 2.
The outer joint member 10 is the form of a cup opened at one end and having axially extending ball grooves 14 formed at circumferentially equispaced positions on an inner spherical surface 12. The inner joint member 20 has axially extending ball grooves 24 formed at circumferentially equispaced positions on an outer spherical surface 22. the ball grooves 14 of the outer joint member 10 and the ball grooves 24 of the inner joint member 20 are paired to form ball tracks which wedge-wise contract or expand from one to the other of the axial direction, with a single torque transmitting ball 30 incorporated in each ball track. The cage 40 is slidably interposed between the inner spherical surface 12 of the outer joint member 10 and the outer spherical surface 22 of the inner joint member 20, and each torque transmitting ball 30 is received in respective one of the pockets 46 of the cage 40.
The outer spherical surface 42 of the cage 40 makes spherical contact with the inner spherical surface 12 of the outer joint member 10, while the inner spherical surface 44 of the cage 40 makes spherical contact with the outer spherical surface 22 of the inner joint member 20. And, the center of curvature of the inner spherical surface 12 of the outer joint member 10 and the center of curvature of the outer spherical surface 22 of the inner joint member 20 coincide with the joint center O. The center of curvature O1 of the ball grooves 14 of the outer joint member 10 and the center of curvature O2 of the ball grooves 24 of the inner joint member 20 are offset axially by an equal distance in opposite directions. For this reason, a ball track defined by a pair of ball grooves 14, 24 take a wedge shape contracting from the opening side to the innermost side of the outer joint member 10.
In this fixed type constant velocity joint, as shown in FIG. 6, irrespective of what working angle, namely a bending angle θ, the outer and inner joint members 10 and 20 may take, the torque transmitting balls 30 are always maintained in a plane perpendicular to the bisector of the bending angle θ, so that the constant velocity property of the joint is secured.
As shown in FIG. 3, the shaft end of the shaft 2 is provided with a pressing member 50. The pressing member 50, as shown in FIG. 4, is composed of a ball serving as a pressing section 52, a compression coil spring serving as an elastic member 54, and a case 55 for assembling the pressing section 52 and elastic member 54. The elastic member 54 acts as an elastic force through the pressing section 52. Further, the pressing section 52 may be in the form of a hemisphere or in the form of a column formed at the top with a convex spherical surface. The case 55 is fixed to the front end of the shaft 2 integrally serration-joined to the inner joint member 20, by a suitable means such as press fitting or adhesive agent.
The end of the innermost side of the outer joint member 10 of the cage 40 has a receiving member 56 attached thereto. This receiving member 56 is in the form of a lid covering the end opening in the cage 40 (see FIG. 3) and is composed of a spherical section 56a in the form of a partial sphere and an attaching section 56b annularly formed in the outer periphery thereof. The inner surface of the spherical section 56a (the surface opposed to the shaft 2) is a concave spherical surface, and this concave spherical surface functions as the receiving section 58 for receiving the pressing force from the pressing section 52. The attaching section 56b is fixed to the end of the cage 40 by a suitable means such as press fitting or welding.
In order to allow the pressing member 50 and receiving member 56 to smoothly slide when the joint takes a bending angle, as shown in FIG. 5, the inner diameter dimension Ro of the concave spherical surface-like receiving section 58 is made larger than the radius r (FIG. 4) of the pressing section 52 (Ro>r). Further, in order to prevent interference between the receiving member 56 and the inner joint member 20 when a bending angle θ is taken as shown in FIG. 6, the inner diameter dimension Ro of the receiving section 58 is made larger than the radius dimension Ri of the inner spherical surface 44 of the cage 40 (Ro>Ri).
In the above arrangement, when the serration shaft section of the shaft 2 and the inner joint member 20 are serration-joined to each other and a snap ring 4 is mounted to completely join the two (see FIG. 3 or 4), the pressing section 52 of the pressing member 50 and the receiving section 58 of the receiving member 56 abut against each other, whereby the elastic member 54 is compressed. Thereby, the inner joint member 20 integrated with the shaft 2 is axially displaced to the opening side of the outer joint member by elastic force, which displacement, since the ball grooves 24 of the inner ring 20 are shaped to expand to the innermost side of the outer ring 10, reduces the axial clearance stemming from the track clearance, thus preventing rotational backlash.
Elimination of the rotational backlash requires that the elastic force of the elastic member 54 be set in consideration of various conditions acting on the joint-mounted state of the vehicle. For example, in the case where the self-weight of the shaft 2 acts on the elastic member 54, the self-weight and plunging force must be taken into consideration. Further, it is desirable that vibrations in the steering system be taken into consideration. By optimizing the setting of the spring force in this manner, the play can always be reduced, making it possible to avoid abnormal sound due to a clearance produced by axial or radial input.
In addition, the description given above has shown examples in which BJs are used as fixed type constant velocity joints; however, the invention is not limited thereto and can be likewise applicable to undercut free joints having a straight section in portions of the ball grooves 14 and 24 or to other fixed type constant velocity joints, achieving the same effects.
In attaching the fixed type constant velocity joint 1 to a vehicle to serve as a steering-purpose shaft joint, it is preferable that the bend phase of the steering shaft 2 in the straight travel state of the vehicle be adjusted to be the ball groove 14, 24 direction of the constant velocity joint 1. In other words, the rotational direction phase in which the bending direction of the steering shaft 2 is the ball groove 14, 24 direction is placed in coincidence with the steering wheel rotational phase when in the straight travel state of the vehicle. Thereby, degradation of the steering stability accompanying an increase in hysteresis can be avoided. More specifically, as shown in FIG. 7, the joint is attached so that the bend phase of the steering shaft 2 in the straight travel state of the vehicle coincides with the ball groove 14, 24 direction of the constant velocity joint 1. FIG. 9 shows a comparative example in which the bending direction of the steering shaft 2 extends between the ball groove 14, 24 directions of the constant velocity joint 1. The torque-torsional angle diagrams for FIGS. 7 and 10 are shown in FIGS. 8 and 10, respectively. As is clear from these figures, the hysteresis is small (FIG. 8) when the bending direction of the steering shaft 2 is the ball groove 14, 24 direction (FIG. 7) and is large (FIG. 10) when it extends between the ball groove 14, 24 directions (FIG. 9). Such tendency is pronounced particularly when the set joint angle (α: FIG. 2B) exceeds 30°.
In the straight travel state of the vehicle, an increase in the hysteresis in the torque-torsional angle diagram for the joint influences steering wheel operability (direct feeling); therefore, it is desirable that this hysteresis be small. For this reason, by adjusting the bend phase of the steering shaft 2 in the straight travel state of the vehicle to be the ball groove direction, degradation of the steering stability accompanying an increase in hysteresis can be avoided.
FIGS. 11A to 11D show play diagrams made by changing the bend phase of the steering shaft in increments of 10° from the ball groove direction to the between-ball-grooves direction. Phase 0° (FIG. 11A) refers to the case of the ball groove direction, while phase 30° (Fig. 11D) refers to the case of extending between the ball groove directions. Comparing FIGS. 11A through 11D with each other shows that the change in hysteresis increases with 20° phase from the ball groove direction. Therefore, making the direction of the steering shaft to be not more than ±20° on a ball groove basis makes it possible to avid or mitigate the degradation of operability accompanying an increase in hysteresis.
Next, FIGS. 1A and 1B are schematic forms of torque-torsional angle diagrams shown in FIGS. 8, 10, and 11A to 11D, in which likewise the vertical axis indicates torque (Nm) and the horizontal axis indicates torsional angle (deg). In the case of the fixed type constant velocity joint used for steering devices, the torque in the vertical axis corresponds to the force for turning the steering wheel, while the torsional angle in the horizontal axis corresponds to the rotational angle of the steering wheel, though the torque in the torque-torsional angle diagrams is a value measured for the constant velocity joint itself, differing from the so-called steering force in a steering device mounted in an automobile. As shown in FIG. 1A, the torque-torsional angle curve is decreased in slope in the vicinity of torque 0. Specifically, it is preferable that it be set in the range from 1.5 to 6.0 Nm/deg. FIG. 1B shows a comparative example in which there is a region where the slope is 0 over a given torsional angle in the vicinity of torque 0. In this region, the steering wheel turns with torque 0. In other words, the steering wheels turns with no resistance, a fact which is recognized as a circumferential play which degrades the feeling characteristics.
In the above description, the outer joint member and the inner joint member are substantially the same as the outer ring and the inner ring, respectively.
Patent Application
20080051203
