Battery forklift

A battery forklift includes a battery and a motor that includes a rotation shaft and is driven using the battery as a power source. A reduction device reduces the speed of rotation of the rotation shaft and transmits the rotation to an axle. A case accommodates the reduction device. A drive wheel is driven by rotation of the axle. The reduction device includes a helical gear rotated integrally with the rotation shaft and a drive shaft formed integrally with the helical gear and extended in a vertical direction. The reduction device further includes an upper bearing located above the helical gear to support the drive shaft rotatably relative to the case and a lower bearing located below the helical gear to support the drive shaft rotatably relative to the case. The case includes a communication portion that communicates a lower void located below the upper bearing and an upper void located above the upper bearing.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a National Stage of International Application No. PCT/JP2013/057847 filed Mar. 19, 2013, claiming priority based on Japanese Patent Application No. 2012-084907 filed Apr. 3, 2012, the contents of all of which are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to a battery forklift that includes a reduction mechanism, which reduces the rotation speed of a rotation shaft of a motor and transmits the rotation to an axle to drive wheels.

BACKGROUND OF THE INVENTION

In such a battery forklift, it is important that the leakage of lubricating oil from a case that accommodates the reduction device be prevented. Patent document 1 describes an example of a structure that prevents the leakage of lubricating oil from a case.

Patent document 1 describes a reduction device that includes a housing accommodating a differential mechanism, which includes a drive pinion. The housing includes a differential carrier and a rear cover. The differential carrier includes a rotation support that rotatably supports the drive pinion. The drive pinion engages with and rotates a bevel gear that is partially immersed in lubricating oil in an oil reservoir formed in the housing. A restriction plate is arranged above the oil reservoir to limit excessive supply of lubricating oil. The restriction plate limits the amount of lubricating oil that is supplied to the rotation support when the bevel gear rotates. This prevents the leakage of lubricating oil from a gap formed between the rotation support and the housing.

PRIOR ART DOCUMENT

Patent Document

Patent Document 1: Japanese Unexamined Utility Model Publication No. 4-93202

SUMMARY OF THE INVENTION

The reduction device of patent document 1 includes the restriction plate that limits the leakage of lubricating oil from the case. However, the use of such a restriction plate increases the number of components.

Although various structures have been proposed to prevent the leakage of lubricating oil from a case without increasing the number of components, other problems such as enlargement of the reduction device arise in such structures. In this respect, there is a need for further improvements.

It is an object of the present invention to provide an improved battery forklift capable of preventing the leakage of lubricating oil from a case of a reduction mechanism in a preferable manner.

According to one aspect of the present invention, a battery forklift includes a battery and a motor that includes a rotation shaft and is driven using the battery as a power source. A reduction device reduces the speed of rotation of the rotation shaft and transmits the rotation to an axle. A case accommodates the reduction device. A drive wheel is driven by rotation of the axle. The reduction device includes a helical gear rotated integrally with the rotation shaft and a drive shaft formed integrally with the helical gear and extended in a vertical direction. The reduction device further includes an upper bearing located above the helical gear to support the drive shaft rotatably relative to the case and a lower bearing located below the helical gear to support the drive shaft rotatably relative to the case. The case includes a communication portion that communicates a lower void located below the upper bearing and an upper void located above the upper bearing.

When the battery forklift is driven and the lubricating oil is moved by the pumping effect of the helical gear and leaks into the upper void through the gap between the case and the upper bearing, the leakage of the lubricating oil is returned to the lower void through the communication portion. As a result, the lubricating oil sent to the upper void by the pumping effect of the helical gear does not collect in the upper void. This prevents leakage of lubricating oil from the case of the reduction device. Accordingly, the leakage of lubricating oil from the case42is prevented without the need for space between the upper bearing and the helical gear, that is, without enlarging the reduction device. Moreover, the formation of the communication portion in the case prevents leakage of lubricating oil from the case without increasing the number of components.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIGS. 1 to 4, one embodiment of a battery forklift, which is a reach forklift (hereinafter referred to as forklift), will now be described. In the following description, the terms “front”, “rear”, “left”, “right”, “up”, and “down” use a frame of reference taken as viewed from a forklift driver facing toward the front of the forklift (advancing direction). The terms “up” and “down” using the frame of reference taken as viewed from the forklift driver facing toward the front of the forklift conform to “up” and “down” in the vertical direction, respectively.

As shown inFIG. 1, a forklift11includes a vehicle body12and right and left reach legs13extending forward from the vehicle body12. A front wheel14is arranged at the front end of each reach leg13. Rear wheels16, which serve as drive wheels, and caster wheels (not shown) are arranged at the rear side of the vehicle body12. A mast17is arranged in front of the vehicle body12. The mast17is driven by a reach cylinder (not shown) to move back and forth along the reach legs13. A lift bracket21and right and left forks20supported by the lift bracket21are arranged on the front side of the mast17. The forks20are lifted and lowered along the mast17. Further, a standing type operator cab24is located in the rear section of the vehicle body12. The operator cab24includes a steering table25with a steering wheel26used to operate the rear wheels16. In addition, the forklift11includes a battery B.

As shown inFIG. 2, each rear wheel16is driven by a drive unit40. The drive unit40includes a reduction device41including a case42. The case42includes a tubular case body51, an upper case cover52, which is coupled to the upper section of the case body51, and a lower case cover53, which is coupled to the lower section of the case body51. The case42includes an accommodation chamber S.

The upper case cover52includes a tubular projection54that includes a cavity55. The cavity55is in communication with the accommodation chamber S.

A gear wheel43is fixed to the upper surface of the upper case cover52. The gear wheel43allows the drive unit40to be driven in cooperation with the operation of the steering wheel26. In addition, a support44, which is arranged on the upper surface of the gear wheel43, supports a motor M. The motor M is driven using a battery B as a power source. The motor M includes a rotation shaft61that is rotatable in forward and reverse directions.

The rotation shaft61of the motor M is coupled to a drive shaft62that rotates integrally with the rotation shaft61. The drive shaft62is accommodated in the case42and extends in the vertical direction. The drive shaft62is supported by an upper bearing63and a lower bearing64to be rotatable relative to the case42. The upper case cover52includes an upper recess65that receives the upper bearing63. The upper recess65is formed in the inner circumferential surface of upper case cover52at the basal side of the projection54. The case body51includes a lower recess66that receives the lower bearing64. The lower recess66is arranged in a section opposing the upper recess65in the vertical direction. The upper bearing63includes an inner race63a, an outer race63b, and a seal member63cthat seals the space between the inner race63aand the outer race63b. The space between the inner race63aand the outer race63bis filled with lubricating oil.

A first helical gear67is arranged between the upper bearing63and the lower bearing64in the accommodation chamber S. The first helical gear67is formed integrally with the drive shaft62. Thus, the drive shaft62is supported by the two bearings63and64, which are arranged above and below the first helical gear67, to be rotatable relative to the case42. Since the drive shaft62rotates integrally with the rotation shaft61, the first helical gear67rotates integrally with the rotation shaft61. Further, the accommodation chamber S accommodates a second helical gear68, which is a driven gear engaged with the first helical gear67. The second helical gear68is fixed to and rotated integrally with a first support shaft69. The first support shaft69is supported by upper and lower bearings70and71to be rotatable relative to the case42. A third helical gear72is arranged below the second helical gear68and fixed to and rotated integrally with the first support shaft69. Rotation of the first helical gear67integrally rotates the second helical gear68, the third helical gear72, and the first support shaft69.

The accommodation chamber S also accommodates a fourth helical gear74that is engaged with the third helical gear72. The fourth helical gear74is fixed to and rotated integrally with a second support shaft75. The second support shaft75is supported by upper and lower bearings76and77to be rotatable relative to the case42. A drive bevel gear78is fixed to the lower end of the second support shaft75. Rotation of the third helical gear72integrally rotates the fourth helical gear74and the drive bevel gear78.

The lower case cover53rotatably supports an axle80of the rear wheels16. The axle80is integrated with a driven bevel gear70that is engaged with the drive bevel gear78. The first helical gear67, the second helical gear68, the third helical gear72, and the fourth helical gear74are all accommodated in the accommodation chamber S. The area in the accommodation chamber S excluding the cavity55forms a gear accommodation chamber56. When the rotation shaft61of the motor M rotates, the first to fourth gears67,68,72and74transmit the rotation of the rotation shaft61to the axle80while reducing the rotation speed. This drives the rear wheels16. In addition, the accommodation chamber S is filled with lubricating oil that lubricates the engaged parts of the gears67,68,72,74,78and79and the bearings63,64,70,71,76and77.

Referring toFIG. 5, technology on which the present embodiment is based will now be described. InFIG. 5that shows a drive unit102, same reference numerals are given to those components that are the same as the corresponding components of the drive unit40shown inFIG. 2. In the drive unit102, when the forklift is moved in reverse, the pumping effect of the first helical gear67moves lubricating oil upward in the vertical direction. In the drive unit102ofFIG. 5, the upper bearing63is arranged above and spaced apart from the first helical gear67to create space between the first helical gear67and the upper bearing63. The space prevents lubricating oil from reaching the upper bearing63. Thus, even when lubricating oil is sent to the upper side of the helical gear67, the lubricating oil does not reach the upper bearing63. This prevents the lubricating oil from leaking through the gap between the upper bearing63and the case42into the cavity55, which is located above the upper bearing63. Consequently, the leakage of lubricating oil from the case42is prevented.

However, since the upper bearing63is arranged above and spaced apart from the first helical gear67to create space between the upper bearing63and the first helical gear67, the distance between the upper bearing63and the lower bearing64is relatively long. This lowers the support rigidity of the drive shaft62and enlarges the reduction device41and, consequently, the drive unit102.

Thus, to avoid enlargement of the drive unit40, the present embodiment includes the following structures.

As shown inFIGS. 3A and 3B, the circumferential surface of the upper recess65includes a communication recess59, which functions as a communication portion. The communication recess59extends continuously in the vertical direction from the lower end of the upper recess65to a position slightly above the upper end of the upper recess65. The communication recess59has a cross-section perpendicular to the vertical direction having an arcuate shape.

As shown inFIG. 2, the communication recess59communicates the cavity55and the gear accommodation chamber56, which are separated from each other by the upper bearing63. In the present embodiment, the cavity55functions as an upper void that is located above the upper bearing63, and the gear accommodation chamber56functions as a lower void that is located below the upper bearing63.

Specifically, the communication recess59communicates the cavity55and a region in the gear accommodation chamber56that is located at the side of the first helical gear67opposite to the second helical gear68. Consequently, the lubricating oil returned to the gear accommodation chamber56through the communication recess59is supplied to a region located at the side of the first helical gear67opposite to the second helical gear68. Thus, the lower void may be considered to be the region in the gear accommodation chamber56that is located at the side of the first helical gear67opposite to the second helical gear68. In other words, the communication recess59opens in the region that is located at the side of the first helical gear67opposite to the second helical gear68.

The operation of the forklift11of the present embodiment will now be described.

As shown inFIG. 4, when the forklift11is driven (moved in reverse) and the drive shaft62and the first support shaft69rotate, the pumping effect of the third helical gear72moves lubricating oil to the upper side of the third helical gear72. Then, the lubricating oil is further moved upward by the pumping effect of the first helical gear67and scattered at the upper side of the gear accommodation chamber56. Some of the lubricating oil scattered to the upper side of the gear accommodation chamber56leaks into the cavity55through the narrow gap between the bearing63and the upper recess65(the wall surface of the case42) as indicated by arrow Y1. The lubricating oil that leaks into the cavity55is returned to the gear accommodation chamber56through the communication recess59by its own weight.

The advantages of the present embodiment will now be described.

(1) The upper case cover52includes the communication recess59that communicates the cavity55and the gear accommodation chamber56, which are located above and below the communication recess59. Thus, even when lubricating oil leaks into the cavity55due to the pumping effect of the first helical gear67, the leakage of the lubricating oil is returned to the gear accommodation chamber56through the communication recess59by its own weight. As a result, the lubricating oil sent to the cavity55by the pumping effect of the first helical gear67does not collect in the cavity55. This prevents leakage of lubricating oil from the case42. Accordingly, the leakage of lubricating oil from the case42is prevented without the need for space between the upper bearing63and the first helical gear67, that is, without enlarging the reduction device41. Thus, the present embodiment does not increase the distance between the upper bearing63and the lower bearing64, lower the support rigidity of the drive shaft62, or enlarge the drive unit40. Moreover, the formation of the communication recess59in the case42prevents leakage of lubricating oil from the case42without increasing the number of components.

(2) The cross-section of the communication recess59perpendicular to the vertical direction has the shape of an arc. That is, the cross-section of the communication recess59perpendicular to the vertical direction is curved. If the cross-section of the communication recess59were to include a corner, stress would be concentrated at the corner. The curved cross-section inhibits the concentration of stress in one section. Thus, decreases are limited in the strength of the case42that may be caused by the formation of the communication recess59.

(3) The lubricating oil returned to the gear accommodation chamber56through the communication recess59is delivered to the region located at the side of the first helical gear67opposite to the second helical gear68. Thus, the lubricating oil returned to the gear accommodation chamber56from the cavity55is prevented from being immediately sent to the upper side of the gear accommodation chamber56by the pumping effect of the first helical gear67. This reduces the amount of lubricating oil scattered to the upper side of the gear accommodation chamber56and, consequently, the amount of lubricating oil leaking to the cavity55.

The above embodiment may be modified as described below.

The case42may include a communication hole that functions as a communication portion that communicates a region above a bearing and a region below the bearing. In this case, the cavity55may be in communication with a region where lubricating oil tends to become insufficient so that lubricating oil is supplied to that region. For example, as indicated by the double-dashed lines inFIG. 2, a communication hole91may communicate the cavity55and a region in the gear accommodation chamber56that is located above the bearing70.

The communication portion may be arranged at any location as long as it communicates the region above the upper bearing63(hollow55) and the region below the upper bearing63(gear accommodation chamber56).

The shape of the communication recess may be modified. For example, the communication recess may have a cross-section that is polygonal like a tetragon or a pentagon.

In the present embodiment, lubricating oil leaks to the region above the upper bearing63(hollow55) when driving the forklift11in reverse. However, depending on the directions of the teeth of helical gears67,68,72and74, lubricating oil may leak to the region above the upper bearing63(hollow55) when driving the forklift11forward. Nevertheless, the lubricating oil leaking to the region above the upper bearing63(hollow55) is returned to the gear accommodation chamber56through the communication recess59by its own weight. Thus, the operation and advantages of the present embodiment are present in both backward driving and forward driving.

In addition to a battery forklift, the prevent invention may be embodied in an order picking truck, for example.