Wheel driving speed reducer

A wheel driving speed reducer includes a parallel shaft gear mechanism that includes a parallel shaft gear, a planetary gear mechanism that is provided on a rear stage of the parallel shaft gear mechanism and includes planetary gears and an internal gear with which the planetary gears internally mesh, and a casing that accommodates the parallel shaft gear mechanism and the planetary gear mechanism. A tooth portion of the parallel shaft gear protrudes and extends into a gap, which is formed between the casing and the internal gear or a member integrated with the internal gear, in an axial direction. The tooth portion of the parallel shaft gear and the internal gear or the member integrated with the internal gear overlap each other when seen in a radial direction.

BACKGROUND

1. Technical Field

The present invention relates to a speed reducer that is used to drive a wheel of a vehicle.

The present application claims priority on Japanese Patent Application No. 2011-227157 filed on Oct. 14, 2011, the entire contents of which are incorporated herein by reference.

2. Description of the Related Art

A speed reducer, which is used to drive a wheel of a vehicle, is disclosed in International Publication WO 00/36317 (FIG. 1).

This speed reducer includes a parallel shaft gear mechanism that includes a parallel shaft gear, and a planetary gear mechanism that is provided on a rear stage of the parallel shaft gear mechanism and includes planetary gears and an internal gear with which the planetary gears internally mesh. Further, apart of the speed reducer is disposed within a wheel.

SUMMARY

According to an embodiment of the present invention, there is provided a wheel driving speed reducer that includes a parallel shaft gear mechanism, a planetary gear mechanism, and a casing. The parallel shaft gear mechanism includes a parallel shaft gear. The planetary gear mechanism is provided on a rear stage of the parallel shaft gear mechanism and includes planetary gears and an internal gear with which the planetary gears internally mesh. The casing accommodates the parallel shaft gear mechanism and the planetary gear mechanism. A tooth portion of the parallel shaft gear protrudes and extends into a gap, which is formed between the casing and the internal gear or a member integrated with the internal gear, in an axial direction. The tooth portion of the parallel shaft gear and the internal gear or the member integrated with the internal gear overlap each other when seen in the radial direction.

Meanwhile, according to another embodiment of the present invention, there is provided a wheel driving speed reducer that includes a parallel shaft gear mechanism, a brake mechanism, and a casing. The parallel shaft gear mechanism includes a parallel shaft gear. The brake mechanism brakes the rotation of a rotating member of the speed reducer. The casing accommodates the parallel shaft gear mechanism and the brake mechanism. A tooth portion of the parallel shaft gear protrudes and extends into a gap, which is formed between one member of the brake mechanism and the casing, in an axial direction. The tooth portion of the parallel shaft gear and the one member of the brake mechanism overlap each other when seen in the radial direction.

DETAILED DESCRIPTION

In the wheel driving speed reducer that is used while a part of the speed reducer is disposed within a wheel as described above, how to ensure a large transmission capacity while the speed reducer is accommodated in a small space is important.

The sizes of the respective members are basically designed larger for the increase in transmission torque in the wheel driving speed reducer. However, in the case of the speed reducer used to drive a wheel, there are many cases where a spatial margin allowing the size of a member to be increased is not formed not only in the radial direction but also in the axial direction.

It is desired to ensure larger transmission capacity of a wheel driving speed reducer while maintaining the compactness of the overall speed reducer.

In the embodiment of the invention, a gap formed between the casing and the internal gear of the planetary gear mechanism (or a member integrated with the internal gear) is effectively used to maintain the compactness of the overall speed reducer.

That is, the tooth portion of the parallel shaft gear is made to protrude and extend into the gap. Accordingly, the protruding and extending tooth portion of the parallel shaft gear and the internal gear or a member integrated with the internal gear overlap each other when seen in the radial direction.

As a result, it is possible to ensure the large tooth width of the parallel shaft gear and to increase transmission torque while preventing an increase of the weight and size of the overall parallel shaft gear mechanism, that is, while maintaining the compactness of the overall speed reducer.

According to the embodiment of the invention, it is possible to ensure larger transmission capacity of a wheel driving speed reducer while maintaining the compactness of the overall speed reducer.

An example of an embodiment of the invention will be described in detail below with reference to the drawings.

FIG. 1is an enlarged cross-sectional view of main parts of a wheel driving speed reducer according to an example of an embodiment of the invention, andFIG. 2is a cross-sectional view of the overall speed reducer.

The speed reducer12is to drive a wheel (not shown) of a forklift (vehicle) (not shown). The speed reducer12includes a parallel shaft gear mechanism14, a planetary gear mechanism16, a brake mechanism18, and a casing20that accommodates these mechanisms, as main elements.

Description will be sequentially made below.

The parallel shaft gear mechanism14mainly includes an input shaft22that receives power from a motor (not shown), a helical pinion24that is formed integrally with the input shaft22, and a helical gear (parallel shaft gear)26that meshes with the helical pinion24.

Both ends of the input shaft22of the parallel shaft gear mechanism14are supported on the casing20by a needle bearing28and a first ball bearing30. An outer ring30A of the first ball bearing30is fixed to a side cover32by being caught between a step32A that is formed on the side cover32forming a part of the casing20and a retaining ring34that is fitted to the side cover32.

Further, an inner ring30B of the first ball bearing30is caught between a step22A that is formed on the input shaft22and a retaining ring35that is fitted to the input shaft22. Accordingly, the inner ring30B restricts the movement of the input shaft22in the axial direction of the input shaft. Accordingly, a thrust load, which is applied to the input shaft22through the helical pinion24, is received by the side cover32through the inner ring30B of the first ball bearing30, the rolling bodies30C, and the outer ring30A.

The helical gear26is rotatably assembled on a protrusion32B of the side cover32with a second ball bearing36interposed therebetween. An inner ring36B of the second ball bearing36comes into contact with a stepped portion32B1of the protrusion32B of the side cover32, and is fixed to the protrusion32B of the side cover32by a retaining ring38. An outer ring36A of the second ball bearing36restricts the movement of the helical gear26toward the side (left side inFIGS. 1 and 2), which is opposite to a vehicle body, by a retaining ring40fitted to the outer ring36A.

The helical gear26is connected to a flange body42by bolts41, and the flange body42is integrated with a planetary input shaft44of the planetary gear mechanism16provided on the rear stage.

The planetary gear mechanism16is formed of a so-called simple planetary gear mechanism. The planetary gear mechanism16includes a sun gear46that is formed integrally with the planetary input shaft44, planetary gears48that revolve around the sun gear46, and an internal gear50with which the planetary gears48internally mesh. A ring body52is fixed to the side of the internal gear50opposite to the vehicle body, and the ring body52is fixed to (a casing main body56of) the casing20by bolts54. Accordingly, the internal gear50is positioned relative to the casing main body56.

The planetary gear mechanism16is adapted to take out power, which is input from the planetary input shaft44, from an output shaft60as the revolution of carrier pins58that support the planetary gears48with the the internal gear50in a fixed state. The output shaft60is rotatably supported on the casing20with a pair of tapered roller bearings66and68interposed therebetween. Since splines62are formed on the outer periphery of the output shaft60, an output flange64can be rotated integrally with the output shaft60by the splines62. Since wheel mounting holes64A are formed in the output flange64, a wheel of a forklift can be mounted on the output flange64by stud bolts (not shown).

Meanwhile, in this embodiment, the brake mechanism18is disposed between the parallel shaft gear mechanism14and the planetary gear mechanism16. The brake mechanism18brakes the rotation of the planetary input shaft (rotating member)44of the planetary gear mechanism16by braking the flange body (a body to be braked)42against a fixed body53that is integrated with the internal gear50.

The brake mechanism18includes a piston72that slides due to oil pressure in a cylinder70formed in the side cover32, a pressing plate (pressing member)74that is driven in the axial direction by the piston72, and a plurality of friction plates80that can generate a friction braking force between the fixed body53and the flange body42by being pressed by the pressing plate74.

The brake mechanism18will be described in more detail. One end of the cylinder70, which is formed in the side cover32, in the axial direction of the cylinder is closed by a plate94that is fixed by bolts92. An end block96is disposed at the end portion of the cylinder70while coming into contact with the plate94. A gap between the end block96and the inner surface of the cylinder70is sealed by an O-ring98.

A hydraulic chamber100is formed between the end block96and the piston72, and oil can flow into and out of the hydraulic chamber100through a tube102. A first spring104is provided between the end block96and the piston72in the hydraulic chamber100, so that a space (into which oil can flow) of the hydraulic chamber100is ensured. The movement of the piston72can be transmitted to the pressing plate74by a pressing pin106.

The pressing plate (pressing member)74is formed in a disc shape, and can be moved in the axial direction by being pressed to the side opposite to the vehicle body by the pressing pin106. Reference numeral108inFIGS. 1 and 2denotes a guide pin. The guide pin108is fitted to a hole32C of the side cover32and a hole75A1of a receiving base75integrated with the pressing plate74, and functions to prevent the rotation of the pressing plate74and guide the pressing plate74when the pressing plate74is moved in the axial direction.

The pressing plate74can press the friction plates80at thin portions74D (to be described below), which are formed at the outer peripheral portion of the pressing plate74, by being moved along the guide pin108in the axial direction. In this embodiment, the friction plates80include first to fifth stationary friction plates81to85and first to fourth movable friction plates86to89. The first to fifth stationary friction plates81to85are fixed to the fixed body53, which is a member integrated with the internal gear50, at predetermined intervals in the axial direction. The first to fourth movable friction plates86to89are inserted and disposed between the first to fifth stationary friction plates81to85. The first to fourth movable friction plates86to89are fixed to the flange body42.

The pressing plate74can press the first stationary friction plate81, which is positioned closest to the vehicle body, of the plurality of friction plates80to the side opposite to the vehicle body. Further, among the first to fifth stationary friction plates81to85, the fifth stationary friction plate85, which is positioned closest to the side opposite to the vehicle body, comes into contact with a stop block112that is assembled with the fixed body53. Accordingly, the movement of the fifth stationary friction plate85toward the side opposite to the vehicle body in the axial direction is restricted.

Meanwhile, a spring pressing plate114is fixed to the surface of the flange body42in the axial direction by the bolts41. The spring pressing plate114includes a plurality of recesses114A on the same circumference, and second springs116are partially accommodated in the recesses114A. The second springs116are provided between the pressing plate74and the recesses114A of the spring pressing plate114. The second springs116cooperate with the above-mentioned first spring104and retaining ring40to position a member group in the axial direction. The member group includes the piston72, the pressing pin106, the receiving base75, the pressing plate74, the spring pressing plate114, the planetary input shaft44(integrated with the flange body42) that is fixed together with the spring pressing plate114by the bolts41, and the helical gear26.

Here, the peripheral configuration of the fixed body53of the brake mechanism18, the internal gear50of the planetary gear mechanism16, and a tooth portion26A of the helical gear26will be described in detail.

The tooth portion26A of the helical gear26protrudes and extends to the side opposite to the vehicle body in the axial direction, and faces a gap S1formed between the casing20and the fixed body53(one member of the brake mechanism18) integrated with the internal gear50. As a result, the tooth width W1of the tooth portion26A of the helical gear26is larger than the thickness W2of a portion of the helical gear26except for the tooth portion26A in the axial direction (W1>W2), and the tooth portion26A and the fixed body53overlap each other by61when seen in the radial direction.

Further, the pressing plate (pressing member)74of the brake mechanism18and the tooth portion26A of the helical gear26also overlap each other when seen in the radial direction (since the pressing plate74is completely accommodated within the tooth portion26A of the helical gear26in this example, the pressing plate74and the tooth portion26A completely overlap each other when seen in the radial direction).

Furthermore, in this embodiment, a first step74B is formed on a part of the surface of the pressing plate74in the axial direction. Accordingly, the surface of the pressing plate74in the axial direction is close (shifted) to the helical gear26by δ2. Further, a second step74C is formed outside the first step74B in the radial direction and the thin portions74D are formed on the outside of the second step74C in the axial direction. Accordingly, the surface of the pressing plate74in the axial direction is closer to the helical gear26by δ3. As a result, three plates, that is, the first stationary friction plate81, the first movable friction plate86, and the second stationary friction plate82(which are a part of the friction plates80of the brake mechanism18) are put in spaces that are ensured on the side of the thin portions74D opposite to the helical gear and corresponds to δ4 (=δ2+δ3), so that the pressing plate74and a part of the friction plates80overlap each other by δ4 when seen in the radial direction. Moreover, as described above, the entire pressing plate74and the tooth portion26A of the helical gear26completely overlap each other when seen in the radial direction.

Next, the operation of the wheel driving speed reducer12will be described.

When the input shaft22is rotated by the driving force of a motor (not shown), the helical pinion24formed integrally with the input shaft22is rotated. When the helical pinion24is rotated, the helical gear26meshing with the helical pinion24is rotated. Accordingly, the flange body42, which is integrated with the helical gear26by the bolts41, is rotated; the planetary input shaft44of the planetary gear mechanism16, which is integrated with the flange body42, is rotated; and the sun gear46formed on the planetary input shaft44is rotated.

Since the internal gear50is integrated with the casing20and is fixed in the planetary gear mechanism16, the planetary gears48revolve around the sun gear46due to the rotation of the sun gear46while internally meshing with the internal gear50. The revolution components of the planetary gears48are taken out from the output shaft60through the carrier pins58. When the output shaft60is rotated, the output flange64is rotated by the splines62and a wheel of a forklift (not shown) connected to the output flange64is rotated.

Here, in this embodiment, the meshing between the helical pinion24and the helical gear26is performed by the tooth portion26A that has a large tooth width W1and protrudes and extends into the gap S1formed between the casing20and the fixed body53(of the brake mechanism18) that is a member integrated with the internal gear50.

Specifically, the tooth portion26A of the helical gear26and the fixed body53in the axial direction overlap each other by δ1 when seen in the radial direction. This overlapping61means that the tooth width W1of the tooth portion26A of the helical gear26can be increased without an increase in the dimensions of the parallel shaft gear mechanism14and the overall speed reducer12in the axial direction. That is, by this configuration, it is possible to further increase transmission torque without increasing the dimensions of the overall speed reducer12in the axial direction (it is possible to reduce the length of the speed reducer in the axial direction by the amount of overlap if transmission torque is the same).

In particular, (not the combination of a spur pinion and a spur gear but) the combination of the helical pinion24and the helical gear26is employed in this embodiment to ensure performance, such as low noise and low vibration. In general, if the helical pinion and the tooth portion (meshing portion) of the helical gear have the same specifications when transmission torque is to be increased, a component force at the meshing portion in the axial direction is increased in proportion to the increase in transmission torque. For this reason, for example, the durability of the first and second ball bearings30and36(particularly, the second ball bearing36) is apt to deteriorate. The reason for this is that there are many cases where it is particularly difficult to ensure a space in the vicinity of a portion where, particularly, the second ball bearing36is disposed and to dispose a bearing having high capacity in the vicinity of the portion where the second ball bearing36is disposed as apparent from the disposition of the respective members of this embodiment.

When a load applied to at least the second ball bearing36is intended to be reduced through the suppression of the generation of an axial component force caused by helices in order to ensure the durability of the second ball bearing36in these circumstances, the helix angle of the helix cannot but be designed small. However, if only the helix angle is designed small without the change of the tooth width, a total meshing ratio is reduced due to the reduction of an overlapping meshing ratio. For this reason, it is not possible to ensure the intended original performance of the helix, such as low noise and low vibration.

However, according to this embodiment, it is possible to maintain the strength of the tooth portion26A high by ensuring a large tooth width W1and to maintain the thickness of a portion of the helical gear26except for the tooth portion26A small in the axial direction. Accordingly, it is possible to effectively utilize a space, which is limited in the axial direction, to ensure the thickness of the flange body42or the pressing plate74in the axial direction, to ensure the dimensions required for the disposition of the second ball bearing36, and the like. As a result, it is possible to ensure the original performance of the helix (having a large helix angle), such as low noise and low vibration, while maintaining a load applied to the assembled second ball bearing36small.

Further, in this embodiment, the shape of the pressing plate (pressing member)74is devised and the pressing plate74is completely accommodated within the tooth portion26A. Accordingly, it is also possible to increase the number of the friction plates80of the brake mechanism18(without increasing the size of a space in the axial direction) according to the increase in transmission torque.

That is, in this embodiment, first, the pressing plate74is disposed so that the pressing plate74and the tooth portion26A overlap each other when the pressing plate74and the tooth portion26A are seen in the radial direction. Accordingly, the inner space of the tooth portion26A in the radial direction is used as a space in which the pressing plate74is disposed.

In addition, the first and second steps74B and74C are formed on a part of the surface of the pressing plate74in the axial direction, so that a part (the first and second stationary friction plates81and82and the first movable friction plate86) of the friction plates80are put in the spaces ensured on the side of the thin portions74D opposite to the helical gear. For this reason, a part of the pressing plate74and a part of the friction plates80overlap each other by δ4 when seen in the radial direction. Accordingly, it is possible to increase the number of the friction plates80without increasing the size of the space in the axial direction. As a result, (even when the same pressing force of the same pressing plate74is used) it is possible to generate a large braking force between the fixed body53and the flange body42by the amount of overlap and to obtain braking performance corresponding to the increase in transmission torque.

Meanwhile, in the above-mentioned embodiment, the parallel shaft gear mechanism has employed the combination of the helical pinion and the helical gear. As described above, it can be said that this combination is a combination by which the merits of the invention are obtained at the minimum limits, in that it is possible to improve the durability of a bearing, which is apt to deteriorate in terms of strength, while maintaining low noise and low vibration in addition to ensuring durability at the meshing portion of the parallel shaft gear.

However, in the invention, the combination of the helical pinion and the helical gear does not need to necessarily be employed and, for example, the combination of a spur pinion and a spur gear may be employed. Even when the combination of a spur pinion and a spur gear is employed, it is possible to invariably obtain a merit caused by durability being ensured at the meshing portion and the dimensions of a portion of the parallel shaft gear except that the tooth portion does not need to be increased (a merit caused by the dimensions of other members, such as the flange body, the pressing plate, the bearing, or the like in the axial direction being able to be ensured without an increase in weight).

Further, a simple planetary gear mechanism has been employed as the planetary gear mechanism in the above-mentioned embodiment, but the planetary gear mechanism of the invention is not limited to a simple planetary gear mechanism. For example, a so-called “eccentrically oscillating” planetary gear mechanism, which is formed so that planetary gears internally mesh with an internal gear while oscillating, may be employed. Even in this case, the invention has a merit in that the durability of a parallel shaft gear mechanism does not often relatively deteriorate (it is possible to further reduce the dimension of the speed reducer in the axial direction if the durability of a parallel shaft gear mechanism does not deteriorate).

Furthermore, in the above-mentioned embodiment, the thin portions have been formed by forming the steps on the pressing plate so that a part of the pressing plate (pressing member) and a part of the friction plates of the brake mechanism overlap each other when seen in the radial direction. However, (thin portions are not formed or the thin portions are formed and) recesses may be formed, and the friction plates may be partially put in the recesses.

Moreover, in the above-mentioned embodiment, the brake mechanism has been disposed between the parallel shaft gear mechanism and the planetary gear mechanism and the tooth portion of the parallel shaft gear has protruded and extended into the gap formed between the casing and the fixed body of the brake mechanism that is a member integrated with the internal gear. However, in the invention, the brake mechanism does not need to be necessarily disposed at this position. If the brake mechanism is not disposed at this position, it is possible to obtain the same effect by making the brake mechanism of the parallel shaft gear into the gap between the casing and the internal gear (or a member except for the brake mechanism integrated with the internal gear, for example, a clutch).

Further, even when the brake mechanism is present in the vicinity of the parallel shaft gear, the fixed body of the brake mechanism does not need to be disposed so as to be necessarily integrated with the internal gear. In this case, the tooth portion of the parallel shaft gear may protrude and extend into a gap formed between the casing and a member that forms a part of a brake mechanism (which is disposed separately from the internal gear). Meanwhile, in this case, the rear stage does not need to be necessarily a planetary gear mechanism.

Furthermore, the parallel shaft gear mechanism and the planetary gear mechanism have formed two stages in the above-mentioned embodiment. However, a speed reduction mechanism may be further disposed on the front stage of the parallel shaft gear mechanism or on the rear stage of the planetary gear mechanism.

Moreover, the internal gear and the fixed body have been formed integrally with each other (as a single member) in the above-mentioned embodiment, but may be formed separately and integrated by being fixed to each other by bolts or the like.

Further, in the above-mentioned embodiment, the invention has been applied to a speed reducer that is used to drive a wheel of a forklift. However, the invention may also be widely applied to a speed reducer that is used to drive a wheel, for example, of a construction vehicle, a passenger vehicle, and the like.