Differential gear

Abstract: When a casing (1) and a retainer (4) are rotated around their axis, torque is transmitted to the groove (3b) of each rotary member (3) via the rolling elements (5) and the pair of rotary members rotate together with the casing. When a revolution difference occurs between said pair of rotary members, rolling elements retained in the guide slots (4c) of said retainer rolls along the grooves of said pair of rotary members to make reciprocal movement within the range of said guide slots. At this time, when a force which causes revolution difference between said pair of rotary members is applied from the side of only one of said pair of rotary members, since the rolling elements which come to the following side when revolution difference is occurring work to let trail the groove which comes to the leading side when revolution difference is occurring to their own movements, the reaction force occurring here works as a resistance to restrict the revolution difference between said pair of rotary members. This invention can therefore provide reliable torque-sensitive revolution difference restricting effects without need for addition of a special mechanism to obtain the revolution difference restricting effect.

Description: FIELD OF THE INVENTION This invention is of a differential gear that allows revolution difference between the left-hand and right-hand driving wheels or between the front and rear driving wheels of a vehicle and, in particular, of a differential gear equipped with a revolution difference limiting function, according to the preamble of claim 1. The generic US-A-2 220 432 discloses a differential driving mechanism having a pair of coaxially positioned rotary members facing each other in the axial direction, the rotary members being housed by a casing. Axial slots are provided on the inner surface of the casing opposite to the periphery of the rotary members, and grooves are provided on the rotary members in peripheral direction. Retainers are positioned between the peripheral surface of the rotary members and the inner periphery of the casing, the retainers extending in axial direction inside the guide slots and having a pair of teeth engaged with the grooves of the rotary members, respectively. The grooves of the rotary members are so designed that, when revolution difference occurs between the rotary members, the retainers make reciprocal movement along the axial guide slots of the inner periphery of the casing. The DE-C 391583 and the DE-C 801 421 disclose differential gears having two rotary members provided with grooves on the surfaces facing each other and rolling elements inserted into these grooves and being held in a retainer. A differential gear of a vehicle is a mechanism permitting revolution difference between the left-hand and right-hand driving wheels or between the front and rear driving wheels for four-wheel drive vehicles and it is a gear train consisting of a pinion gear being engaged between a pair of bevel gears connecting to the output shaft and when a torque is transmit to the pinion gear shaft from outside, said pinion gear starts autorotation when revolution difference occurs thus permitting one output shaft to revolve faster than the other. Nevertheless, when one of the driving wheels only enters a surface area where the friction factor is extraordinarily small, such as on the snowy ground or sandy surface, said driving wheel only slips by the function of the differential gear losing the overall driving force and the vehicle more probably gets trapped at said spot. When a vehicle travels on a curve at a high speed, if the load on the inner wheel is substantially reduced by centrifugal force, the driving force to negotiate the curve at a high speed tends to be lost by idling of said inner wheel. To make up for such a drawback, some vehicles are being equipped with a revolution difference restricting mechanism such as of the clutch disk engaging type. However, with this mechanism, pre-pressure is usually being applied to the clutch discs to acquire necessary driving force even when one of the driving wheels is not catching the ground and, consequently, with this type, the two driving wheels become bound each other even during engine idling period when driving force is not being transmitted from the engine or when a vehicle speed is being decelerated, thus making it difficult to make a combined application with a device demanding independence for revolution of respective wheels such as the anti-lock brake system. Also, recently, revolution-sensitive revolution difference restricting mechanisms using viscous coupling are being widely used. The viscous coupling is a kind of viscous clutch which transmits torque by means of the shear resistance of a viscous fluid (such as silicone oil). Therefore, with this type, smoother revolution difference restricting effect can be obtained corresponding to the extent of occurring revolution difference. However, since the viscous fluid provides initial resistance, binding between the two driving wheels becomes inevitable although not as prominent as with the case of the clutch disc engaging type. Being known as a differential gear capable to restrict the rotation difference during driving period only, with lesser restriction of respective driving wheels during engine idling period or when activating the brake, include the torque reacting type differential gear incorporating combinations of worm gears like the one having been disclosed by the Japanese Patent Laid-Open Publication No. 271926/1992. With this type, a pair of screw-shaped worms that can coaxially rotate independently are being engaged with multiple worm wheels with the axis of rotation perpendicular to that of said pair of worms and when the worms are driven to rotate, the worm wheels rotate smoothly, while if they are let driven from the worm wheel side, they resist to rotate. This property characteristic with worm gears is being made use of with the aforesaid type, thus providing revolution biasing effect or revolution difference restricting effect to meet the requirements. The revolution difference restricting mechanism of revolution sensitive type, being represented by ones using the viscous coupling, however, has a disadvantage to the effect that its torque transmissibility relies only on the viscosity of the fluid, when the viscosity of said fluid changes by variation in the temperature, the torque transmissibility itself changes making it difficult to acquire always stable revolution difference restricting effects. Another problem with this type is that time lag occurs between the occurrence of revolution difference and the implementation of revolution difference restriction, thereby making it difficult to instantly react to changes in the vehicle movements. While with the differential gears using worm gears, although the revolution difference restricting effect is stable with a differential gear using worm gears wherewith revolution difference restriction is being performed mechanically, its structure becomes complex because of its requirement for larger number of parts and extraordinarily high precision is necessary for machining and assembly of these parts and, moreover, the overall size of the mechanism becomes too large for its allowable torque level. This invention intends, in view of the aforesaid issues, to provide a differential gear of a simpler construction whereby more stable revolution difference restricting effects can be obtained. To comply with this aim, the differential gear according to the invention is characterized by the features if claim 1. Fig. 1 is a side sectional view of the differential gear of the eighth exemplary embodiment of this invention. Fig. 2 shows the cross-section A-A of the drawing in Fig. 1. Fig. 3 is an exploded perspective view of the differential gear. Fig. 4 is an explanatory exploded view of the grooves on a plain surface. Fig. 1 through Fig. 4 show an exemplary embodiment, Fig. 1 being a side sectional view of the differential gear of this exemplary embodiment, Fig. 2 showing cross-section A-A in the drawing of Fig. 1 and Fig. 3 being an exploded perspective view of the differential gear. The differential gear of this exemplary embodiment consists of a gear case 70, a gear case cover 71 which covers one end of said gear case 70, a pair of coaxially positioned ball discs 72, a ball holder inserted between said pair of ball discs 72, multiple number of ball holders 73 spanning across the two ball discs 72 and multiple number of balls retained by said ball holders 73 for free rolling, the space where said balls 74 moves about inside the gear case 70 being filled by a viscous fluid 75. Namely, said pair of ball discs 72 constitute the rotary member, said ball holders 73 constitute the retainer and said balls 74 constitute the rolling elements, respectively. Said gear case 70 is of a cylindrical shape with its one end opened and a bearing 70a to support one of said ball discs 72 is being provided around the axial center thereof. A flange 70b is provided around the periphery of said gear case 70 wherein multiple number of bolting holes 70c are being opened. In the bore surface of said gear case 70, multiple number of grooves 70d into which said balls 74 engage are being provided, the longitude of said grooves 70d being directed toward the axial direction of said gear case 70 and being provided at equal intervals around the peripheral direction. Namely, said grooves 70d constitute the guide. Also, in said grooves 70d, into their bottoms, fluid conduits 70e are being formed which allow passage of the viscous fluid 75. Said gear case cover 71 is of a disc shape and a bearing 71a to support the other ball disc 72 is being provided around the axial center of said gear case cover. A flange 71b is provided around the periphery of said gear case cover 71 wherein multiple number of bolting holes 71c are being opened. Namely, said gear case cover 71 is being attached to the gear case 70 by the bolts clamping said flanges 70b and 71b together via a sealing O-ring 71d. Also said gear case cover 71 is being provided with filling ports 71e through which the viscous fluid 75 is to be supplied, each filling port 71e being sealed by a ball after the viscous fluid 75 has been filled and said ball being clamped by smashing in the surrounding of said filling port 71e. Meanwhile, said filling ports 71e are being provided at total two places or more for fluid supply and for air bleeding. Also, around the internal surface of said gear case cover 71, a circular groove 71g is provided which works to disperse the supplied viscous fluid throughout the periphery of the bore of said gear case 70, said circular groove 71g connecting to said filling ports 71e. The two ball discs 72 are of a hollow structure and one side of said ball disc is being formed into a coupler structure 72a for connection with the drive shaft to the wheel. The two ball discs 72 are of equal outer diameter being put together on their mating surfaces for free individual rotations. On the peripheral surface of each ball disc 72, a groove 72b into which balls 74 engage for free rolling is provided in continuation in the peripheral direction. Fig. 30 shows exploded views of said ball discs 72 on a flat plane wherein angle scales 0° through 360° represent the peripheral coordinates. Namely, each groove 72b consists of first guide zones 72b-1 which work to move the balls 74 to one side in the axial direction of said ball disc 72 toward the other side and second guide zones 72b-2 which work to move balls from said other side of said ball disc 72 toward the opposite side in the axial direction of said ball disc 72 in an alternate continuation, said first guide zones 72b-1 being made longer than said second guide zones 72b-2 with one of the two ball discs 72 and said second guide zones 72b-2 being made longer than said first guide zones 72b-1 with the other ball disc 72. Namely, when the direction changing points at one end in the axial direction of the two grooves 72b meet in the peripheral direction, the direction changing points at the other ends of respective grooves 72b are so designed to deviate between the two grooves 72b. Also, in said grooves 72b, into their bottoms, fluid conduits 72c are being formed which allow passage of the viscous fluid 75. The mutually facing surfaces of the two ball discs 72 are provided with disc caps 72d which work to close the hollow space thereof and sealing O-rings 72a are being inserted between the peripheral surfaces of said disc caps 72d and said ball disc 72. Also, thrust washers 72f are being provided between the end surface of one of the two ball discs 72 and the gear case 70 and between the end surface and the gear case cover 71, while oil seals 72g are inserted between the coupler structures 72a of the two ball discs and bearings 70a and 71a for sealing. Moreover, plural numbers of fluid conduits 72h are provided in the peripheral surface of each ball disc 72 which connects the groove 72b and open at both ends of said ball disc 72 to let the viscous fluid 75 having been supplied through the filling ports 71e provided in the gear case cover 71 fed into and fill the space of said groove 72b. The ball holders 73 are being positioned between each ball disc 72 and the gear case 70 spanning across the peripheral surfaces of the two ball discs 72. Each ball holder 73 is provided with two holes 73a to sustain one ball 74 each for one of the two ball discs 72 and for the other ball disc 72 to let two balls 74 engaging with the two grooves 72b of the two ball discs 72 move reciprocally in the axial direction of each ball holder 73 maintaining the prescribed distance between said two balls 74. Also, a spacer 73b is being provided between every two ball holders 73 and the grooves 70d in said gear case 70 and the grooves 72b of said two ball discs are being covered by said ball holders 73 and said spacers 73b, all around. Balls 74 are being housed in said holes 73a of said ball holders 73 and engaging with the grooves 70d of said gear case 70 and the grooves 72b of the two ball discs 72. Said viscous fluid 75 consists of silicon oil or a similar substance and filling the space inside said gear case 70, including the space of said grooves 72b of the two ball discs 72, namely space being enclosed by oil seals 72g. With a differential gear of the aforesaid structure, when revolution difference occurs between the two ball discs 72, balls 74 rolls about along said grooves 72b of said ball discs 72 to make reciprocating movement together with their ball holders 73 in the axial direction of said ball discs 72. At this time, when on one the two ball discs 72 only is driven to rotate from the drive shaft side, the reaction force which balls 74 receive from said grooves 72b works to restrict the revolution difference. Also, when the revolution difference between the two ball discs 72 expands larger, resistance of said viscous fluid 75 against said balls 74 increases and said resistance also works to restrict the revolution difference. Namely, when balls 74 roll along said grooves 70d and 72b being enclosed by all the ball holders 73 and spacers 73b, said viscous fluid 75 flows through the fluid conduits 70e and 72c provided in said grooves 70d and 72b, the flowing resistance at the time of said viscous fluid 75 also works to restrict the revolution difference. In this case, the revolution difference restricting effect becomes larger corresponding to the revolution difference between the two ball discs 72. Consequently, with the differential gear of this exemplary embodiment, revolution-sensitive revolution difference restricting effect occurring from the resistance of the viscous fluid 75 against balls 74 can be obtained in addition to the torque-sensitive revolution difference restricting effect being derived from the reaction force the balls 74 receive from the grooves 72b, always reliable revolution difference restriction can be expected for all the travelling modes of a vehicle.

Claims: A differential gear, comprising: a pair of coaxially positioned rotary members (72, 72) facing each other in the axial direction and each having a peripheral surface, a casing (70, 71) to house said rotary members (72), multiple number of elements (74) inserted between the respective surface of said rotary members and a bore surface of said casing facing said peripheral surfaces in the radial direction, and multiple number of retainers (73), whereby one retainer (73) works to retain one of said elements (74) on one rotary member (72) and another of said elements (74) on the other rotary member simultaneously in position said bore surface of said casing being provided with multiple number of guide grooves (70d) with their longitudes directed in the axial direction of said rotary members (72) and said guide grooves (70d) being engaged with said elements, said rotary members (72) being provided with grooves (72b, 72b), which engage with said elements, on their peripheral surfaces facing the bore surface of said casing (70,71) in continuation in the peripheral direction of said rotary members and said grooves so designed that, when revolution difference occurs between said pair of rotary members (72), said retainers and said elements (74) make reciprocal movement along said guide grooves provided in the bore surface of said casing, characterized in that said elements are rolling elements separated from said multiple number of retainers (73), whereby said one retainer (73) works to retain one of said rolling elements on one rotary member and another of said rolling elements on the other rotary member simultaneously in position and for simultaneous free rolling, and whereby said guide grooves (70d) in said bore surface being engaged with said rolling elements (74) for free rolling. A differential gear according to claim 1, characterized in that said guide grooves (72b) of said rotary members (72) consist of first guide zones (72b-1) which work to move said rolling elements (74) from one side thereof toward the other side thereof and second guide zones (72b-2) which work to move said rolling elements from said other side thereof toward the opposite side thereof in an alternate continuation in the peripheral direction, said first guide zones (72b-1) of one rotary member are made longer than said second guide zones thereof and said second guide zones (72b-2) of the other rotary member are made longer than said first guide zones thereof. A differential gear according to claim 2, characterized in that the contact angle between said guide grooves (72b) and said rolling elements (74) in the radial directions of said rotary members (72) being so determined that, even if the distances between the axis of respective rotary member (72) and respective rolling elements (74) change, the magnitude of the reaction force which said guide grooves receive from said rolling elements remains always constant. A differential gear according to claim 2, characterized in that the contact angle between said guide grooves (72b) and said rolling elements (74) in the axial direction of said rotary members (72) being so determined that, even if the distances between the axis of respective rotary member (72) and respective rolling elements (74) change, the magnitude of the reaction force which guide said grooves receive from said rolling elements remains always constant. A differential gear according to claim 1, characterized in that said guide grooves (72b) of said rotary members (72) consist of first guide zones (72b-1) which work to move said rolling elements (74) from one side thereof toward the other side thereof and second guide zones (72b-2) which work to move said rolling elements from said other side toward the opposite side thereof in an alternate continuation in the peripheral direction, whereby the number of the first guide zones or second guide zones of one rotary member differs from the number of the first guide zones or second guide zones of the other rotary member. A differential gear according to claim 5, characterized in that the total sum of the number of the first guide zones or second guide zones of one rotary member and the number of the first guide zones or second guide zones of the other rotary member coincides with the total number of rolling elements. A differential gear according to one of the claims 1 to 6, characterized in that the space inside said casing (70,71) or at least the space where said rolling elements roll about is filled by a viscous fluid (75). A differential gear according to claim 7, characterized in that at least either one of said guide grooves (72b) are provided with a clearance allowing flow of said viscous fluid beyond said rolling elements (74).

Inventors: MIMURA KENJI, MIMURA, KENJI
Applicants: MIMURA KENJI, MIMURA, KENJI
Application year: 1995
Main classification: F16H48
IPC codes: B60K17, F16H13, F16H48