Machine element or mechanism – Elements – Gear casings
Patent
1980-09-02
1984-03-06
Herrmann, Allan D.
Machine element or mechanism
Elements
Gear casings
74687, 74714, 74705, 74720, 747205, F16H 3706, F16H 142
Patent
active
044346808
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates generally to a differential for a vehicle cross drive or the like, and more particularly to a compact and simplified planetary steering differential.
2. Background Art
A large number of earthmoving tractors have been developed which have incorporated either clutch-and-brake steering mechanisms or geared steering mechanisms. In both of these classifications, however, the drive to the opposite tracks is discontinuous when making turns. This results in poorer operation of the vehicle than is desired during turns in marginal ground conditions.
In some seasons of the year, for example, logging industry tractors with conventional clutch-and-brake steering mechanisms cannot be maneuvered to provide useful work because when one of the steering clutches is disengaged the power to that side of the tractor is interrupted. The other side of the tractor then has to pull the total drawbar load to maintain momentum. Unfortunately, soil strength under only one side is often inadequate to carry the total load so the powered track shears the soil and loses traction. Such a loss is a particular disadvantage when it comes to making relatively small steering corrections. On the other hand, clutch-and-brake steering mechanisms are widely used because they perform well in straight-ahead work applications and are simple in construction.
In geared steering mechanisms, rather than disconnecting one track and/or bringing that track to rest, one track is driven at a lower speed than the other by having additional gear sets in the drive to each track. But these mechanisms are complex and costly in construction because duplicate planetary sets, gears, brakes and/or clutches are typically provided at both sides. Furthermore, since these mechanisms are discontinuous a lower mean track speed is provided during a turn.
Another major group of steering mechanisms includes differential mechanisms in which drive is transmitted continuously to both tracks. The simplest form thereof is a braked differential, but these are rarely used because of relatively large power losses at the steering brake. Many of the disadvantages of the braked differential are obviated by controlled differentials. In such mechanisms engine power is not wasted in the steering brakes since power is merely transferred from the inner track to the outer track. But these also have disadvantages. One major disadvantage is that when the brakes are off these mechanisms act as simple differentials so that they depend on the reaction between the track and the ground to be equal for straightahead operation. Since this is often not true the vehicle tends to drift so that frequent corrections are required. Moreover, if one track loses traction the drive to the opposite track is reduced.
A good many of the above mentioned problems can be overcome by the use of double differentials, triple differentials and equivalent mechanisms which usually can counter rotate the opposite output members for spot turns. Typically, two differentials or their equivalent are arranged in parallel with their output shafts interconnected by gearing. Usually, a main drive power path is provided to one of the differentials and a steering drive power path is provided to the other one of the differentials. In some instances the steering input shaft has been driven by a hydrostatic pump and motor system, with the ability to hold the steering input shaft stationary to prevent differential action and to assure straight ahead operation of the tractor, military tank or the like in an effective manner. One major deficiency thereof is that dual cross shafts and associated gearing are required so that the construction is not only complex and costly, but also an unnecessarily large housing is required for containment of the components. Another related deficiency is that most of these differential mechanisms have a dual power path steering input, which usually involves rotating one gear at one side of the cross drive at the same speed but in the opposite direction to
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Riediger Craig W.
Winzeler James E.
Caterpillar Tractor Co.
Herrmann Allan D.
Lanchantin, Jr. Charles E.
Wright D.
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