The present invention relates to a tapered roller bearing which is preferably used in an automotive pinion shaft supporting apparatus as in a differential and a transaxle and in a transmission of a vehicle or the like, and an automotive pinion shaft supporting apparatus which uses the tapered roller bearing.
In recent years, there has been increasing a demand for improvement in fuel economy of motor vehicles, and in association with the demand, there is expressed a desire to reduce the running torque of tapered roller bearings which are used to support rotational shafts of transmissions and differentials installed on those motor vehicles.
In these situations, as a method of reducing the running torque of a tapered roller bearing, there is a method of reducing the rolling friction of a tapered roller bearing by crowning rolling contact surfaces of tapered rollers and raceway surfaces of inner and outer rings.
As the method like this, as is described in Patent Document No. 1 below, there is proposed, for example, a method in which raceway surfaces are crowned in an arc-shape fashion so as to realize a reduction in running torque, or, as is described in Patent Document No. 2 below, there is also proposed a method in which rolling contact surfaces of rollers and raceway surfaces which are brought into contact therewith are crowned to a shape which approximates to a logarithmic curve.
In the conventional examples, the performance of the tapered roller bearing was attempted to be enhanced by specifying the shape of the crown imparted to the raceway surface or the rolling contact surface by a numerical value. However, there had been no attempt to grasp the crown as quantity so as to specify the crowning amount so imparted to thereby reduce the running torque of the tapered roller bearing.
Patent Document No. 1: JP-A-2003-130059
Patent Document No. 2: JP-A-2001-65574
Incidentally, when the tapered roller bearing is used in an automotive pinion shaft supporting apparatus in a differential of a motor vehicle, for example, a preload is imparted to the relevant bearing for the purpose of securing rigidity and the like. The extent to which the preload is imparted to the tapered roller bearing is generally determined based on as an indication the value of an assembly torque which is measured as the running torque of the tapered roller bearing when it is assembled onto the automotive pinion shaft supporting apparatus. However, it is often the case that this assembly torque varies. In the even that the assembly torque varies, there may occur in a case where the preloading cannot be imparted accurately, leading to a risk that a preload that is imparted to the relevant bearing varies.
In the event that the preload that is imparted to this bearing varies, leading to a case where the preload is imparted to exceed an extent to which it should be, it constitutes a cause for a shorter life of the tapered roller bearing. On the other hand, in the event that the extent to which the preload is imparted becomes short, as a result, the rigidity of the tapered roller bearing becomes insufficient, and gear noise is generated. Furthermore, there has been caused a risk that the running torque is increased in use of the tapered roller bearing.