Patent Description:
Construction machines such as an excavator includes a self-propelled undercarriage, a slewable upper structure provided on top of the undercarriage. The upper structure includes a cab where an operator boards. One end of an operating unit is rotatably (swingably) coupled to the slewable upper structure. The operating unit includes, for example, a boom, an arm rotatably coupled to the boom, and a bucket rotatably coupled to the arm. One end of the arm is coupled to the other end of the boom facing away from the slewable upper structure. The bucket is rotatably coupled to the other end of the arm facing away from the boom.

In many cases, a hydraulic actuator having a linear motion mechanism is provided as a drive transmission device in the coupling portion between the slewable upper structure and the boom, the coupling portion between the boom and the arm, and the coupling portion between the arm and the bucket. The slewable upper structure is rotated relative to the undercarriage, and the boom, arm, and bucket are swingably moved by driving the hydraulic actuators. In recent years, electrification of construction machinery is desired from the viewpoint of structural simplification. It has been proposed to use electric actuators as the drive transmission devices. For example, instead of a hydraulic actuator, use of an electric cylinder of a linear motion mechanism having a ball-screw type speed changer (speed reducer) provided therein is disclosed.

Patent Literature <NUM>: Japanese Patent Application Publication No. <CIT>.

Document <CIT> relates to a speed reducer capable of precisely and reliably maintaining a rotational force of the output shaft and of maximizing its efficiency by allowing the rotational force of the driving shaft to transmit and to slow down via a plurality of bevel gears and by preventing the fluctuation of the output shaft so as to prevent uneven wear due to the long working and to prevent the damage due to the fluctuation. The speed reducer comprises a pair of driving gears installed at one end of respective driving shafts driven by a driving means, a pair of driven gears meshed with the driving gear and different rotational members for outputting the rotational force to slow down. The driven gears comprise a bevel gear, respectively and the rotational members are coupled to the driven gears. The driving shafts are connected to the different rotation members and output rotations to the different members.

Document <CIT> discloses, in the opinion of the Examining Division of the European Patent Office, a drive transmission device falling within the wording of the precharacterizing portion of claim <NUM>. It relates to a land leveler transmission system. The system comprises a power source, a hydraulic pump, a hydraulic motor, an axle, a left and a right wheel, which are respectively mounted on respective sides of the axle. The power source is connected with the hydraulic pump. The hydraulic pump is connected with the hydraulic motor through a hydraulic oil way. The hydraulic motor is connected with the axle. The axle comprises a left half and a right half axle. The left half axle is connected with a left planetary reducer and the right half axle is connected with a right planetary reducer. The left wheel is mounted on the left planetary reducer and the right wheel is mounted on the right planetary reducer such that the planetary reducers are respectively connected to different wheels and respectively output rotations to the different wheels.

Each coupling portion of construction machines tends to be heavily loaded due to its usage environment. For this reason, the speed changer in particular needs to have sufficient mechanical strength to withstand the heavy load. To address this, the speed change unit has become large and the drive transmission device as a whole has become large in size.

The present invention provides a drive transmission device and a construction machine with a sufficient mechanical strength while accomplishing a reduced size.

The above mentioned problems are solved by the invention as claimed in claim <NUM>. The latter defines a drive transmission device for which protection is sought. The dependent claims concern particular embodiments of the invention as claimed in claim <NUM>.

The above drive transmission device and construction machine can secure sufficient mechanical strength while their sizes can be reduced.

The following describes embodiments with reference to the drawings, whereby only the second embodiment falls within the wording of claim <NUM>.

<FIG> schematically illustrates an excavator <NUM>, which is an embodiment of a construction machine according to one aspect of the invention, viewed from the side. In the following description, a front direction to which an operator of the excavator <NUM> faces is simply referred to as the front. The opposite side to the front in the horizontal direction is referred to as the rear. The upper and lower directions with the excavator <NUM> placed on a road surface is simply referred to as the vertical direction. A direction orthogonal to the front-rear direction and the vertical direction is referred to as a vehicle width direction. <FIG> shows the excavator <NUM> as viewed from the vehicle width direction.

As shown in <FIG>, the excavator <NUM> includes a self-propelled undercarriage <NUM>, a slewable upper structure <NUM> that is provided on top of the undercarriage <NUM> via a slewing mechanism <NUM> and slews or rotates relative to the undercarriage <NUM>, and an operating unit <NUM> provided on the slewable upper structure <NUM>. The undercarriage <NUM> and the slewing mechanism <NUM> are driven, for example, by an unshown electric motor with a reducer. The traveling body <NUM> includes, for example, two continuous tracks <NUM> arranged side by side in the vehicle width direction. The configurations are not limited to this, and wheels or the like may be used instead of the continuous tracks <NUM>.

The operating unit <NUM> includes a boom <NUM> and arm <NUM> extending in the front-rear direction, and a bucket <NUM>. The boom <NUM>, the arm <NUM>, and the bucket <NUM> are rotatably connected to each other via drive transmission devices <NUM>. Specifically, one end of the boom <NUM> (this end of the boom <NUM> in the longitudinal direction and the drive transmission device <NUM> provided at this end are not shown in <FIG>) in the longitudinal direction is rotatably coupled to the slewable upper structure <NUM> via the drive transmission device <NUM>. One end 109a of the arm <NUM> in the longitudinal direction is rotatably coupled to the other end 108a of the boom <NUM> in the longitudinal direction via the drive transmission device <NUM>. The bucket <NUM> is rotatably coupled to the other end 109b of the arm <NUM> in the longitudinal direction via the drive transmission device <NUM>. The drive transmission devices <NUM> provided in the above sections all have the same configuration. Therefore, in the following description, only the drive transmission device <NUM> that couples the bucket <NUM> to the other end 109b in the longitudinal direction of the arm <NUM> will be described. Description of the other drive transmission devices <NUM> will be hereunder omitted.

<FIG> schematically illustrates the coupling portion between the arm <NUM> and the bucket <NUM> in detail. In <FIG>, the arm <NUM> and the bucket <NUM> are shown by a dashed-two dotted line for the sake of clarity. As shown in <FIG>, the arm <NUM> includes a motor <NUM> (an example of the drive source or motor in the claims) installed therein. The rotational force of the motor <NUM> is transmitted to the bucket <NUM> via the drive transmission device <NUM>. That is, the arm <NUM> is an example of the first member in independent claim <NUM>. The bucket <NUM> is an example of the second member in the claims.

The motor <NUM> is, for example, a so-called electric motor driven by electric power of an external power source (battery) provided in the slewable upper structure <NUM>. As the motor <NUM>, various electric motors such as a so-called brushed motor and a brushless motor can be adopted. The motor <NUM> is disposed such that a motor shaft 120a rotatable about a first rotation axis C1 faces the bucket <NUM>. The first rotation axis C1 of the motor shaft 120a and the longitudinal direction of the arm <NUM> coincide with each other.

The drive transmission device <NUM> is disposed on the second rotation axis C2 (an example of the rotation axis in the claims) of the bucket <NUM> relative to the arm <NUM>. On the second rotation axis C2, an attachment bracket 110a of the bucket <NUM> is arranged on each side of the drive transmission device <NUM>. By fixing these attachment brackets 110a to the drive transmission device <NUM>, the bucket <NUM> becomes rotatable about the second rotation axis C2 relative to the arm <NUM>.

The drive transmission device <NUM> includes a differential unit <NUM> housed in a housing <NUM> fixed to the other end 109b in the longitudinal direction of the arm <NUM>, and two speed reducers 3A and 3B (first speed reducer 3A and second speed reducer 3B) arranged on each side of the differential unit <NUM> and coupled to the differential unit <NUM>. Rotation axes of the two speed reducers 3A and 3B are coaxial to the second rotation axis C2. In the following description, the direction parallel to the second rotation axis C2 may be referred to as an axial direction. The rotational direction about the second rotation axis C2 may be referred to as a circumferential direction. The direction orthogonal to the axial direction and the circumferential direction may be referred to as a radial direction.

<FIG> schematically shows the configuration of the differential unit <NUM>. The differential unit <NUM> is coupled to the motor shaft 120a via a transmission shaft <NUM>. The differential unit <NUM> includes a first bevel gear <NUM> that is provided at an end of the transmission shaft <NUM> opposite to the motor <NUM> and rotates about the first rotation axis C1, a second bevel gear <NUM> (an example of the ring gear in claim <NUM>) meshed with the first bevel gear <NUM>, a differential case <NUM> fixed to the second bevel gear <NUM>, a pinion gear <NUM> rotatably supported by the differential case <NUM> such that it protrudes from the differential case <NUM>, and a pair of side gears 75a and 75b (first side gear 75a, second side gear 75b) meshed with the pinion gear <NUM>.

The second bevel gear <NUM> rotates about the second rotation axis C2. An insertion hole 72a through which a first operation output shaft 76a, which will be described later, penetrates is formed in the radial center of the second bevel gear <NUM>. The differential case <NUM> is fixed to an end surface 72b of the second bevel gear <NUM> situated closer to the first bevel gear <NUM>. The differential case <NUM> is formed in a square frame shape. The differential case <NUM> includes two side surfaces 73a and 73b (first side surface 73a and second side surface 73b) opposed to each other in the axial direction, and two side surfaces 73c and 73d (third side surface 73c and fourth side surface 73d) opposed to each other and their planar direction are orthogonal to the planar direction of the side surfaces 73a and <NUM>. Of the four side surfaces 73a to 73d, the outer side of the first side surface 73a is fixed to the end surface 72b situated closer to the first bevel gear <NUM>.

A pinion gear <NUM> is respectively provided on the third side surface 73c and the fourth side surface 73d. The pinion gear <NUM> is supported by the side surfaces 73c and 73d rotatably about the third rotation axis C3 that extends orthogonal to the axial direction. The pinion gear <NUM> is also rotatable together with the differential case <NUM> about the second rotation axis C2.

The pair of side gears 75a and 75b are arranged on each side of the pinion gear <NUM>. That is, of the pair of side gears 75a and 75b, the first side gear 75a is disposed coaxially with the second rotation axis C2 and on inner side of the first side surface 73a of the differential case <NUM>. Of the pair of side gears 75a and 75b, the second side gear 75b is disposed coaxially with the second rotation axis C2 and on inner side of the second side surface 73b of the differential case <NUM>.

One end of the first operation output shaft 76a is provided on the end surface 75c of the first side gear 75a situated closer to the first side surface 73a. The first operation output shaft 76a is arranged coaxially with the second rotation axis C2. The other end of the first operation output shaft 76a extends through the insertion hole 73e formed in the first side surface 73a and the insertion hole 72a of the second bevel gear <NUM> and protrudes out. That is, the first side gear 75a is rotatably supported by the first side surface 73a of the differential case <NUM>. At the other end of the first operation output shaft 76a, a teeth portion 76c that meshes with the first speed reducer 3A of the two speed reducers 3A and 3B is formed on the outer peripheral surface.

One end of the second operation output shaft 76b is provided on the end surface 75d of the second side gear 75b situated closer to the second side surface 73b. The second operation output shaft 76b is arranged coaxially with the second rotation axis C2. The other end of the second operation output shaft 76b extends through the insertion hole 73e formed in the second side surface 73b and protrudes out. That is, the second side gear 75b is rotatably supported by the second side surface 73b of the differential case <NUM>. At the other end of the second operation output shaft 76b, a teeth portion 76d that meshes with the second speed reducer 3B of the two speed reducers 3A and 3B is formed on the outer peripheral surface. As described above, the operation output shafts 76a and 76b form a part of the speed reducers 3A and 3B respectively connected to the differential unit <NUM>.

<FIG> schematically shows the configuration of the first speed reducer 3A. The two speed reducers 3A and 3B have the same configuration, and are arranged symmetrically with respect to the third rotation axis C3. Therefore, in the following description, only the first speed reducer 3A will be described, and description of the second speed reducer 3B will be hereunder omitted. As shown in <FIG>, the first speed reducer 3A includes a cylindrical casing <NUM>, a carrier <NUM> disposed radially inside the casing <NUM>, and a speed reducer output portion <NUM> that rotates the carrier <NUM> at a rotation speed reduced at a predetermined ratio with respect to the rotation speed of the first operation output shaft 76a.

An outer flange portion 11a projecting outward in the radial direction is integrally formed with the outer circumferential surface of the casing <NUM>. The outer flange portion 11a has a rectangular section along the axial direction. The housing <NUM> is disposed on the end surface 11b of the outer flange portion 11a situated closer to the differential unit <NUM> (left side in <FIG>). The housing <NUM> is fastened and fixed to the outer flange portion 11a by bolts <NUM>. Internal teeth <NUM> are provided on an inner circumferential surface of the casing <NUM>. The internal teeth <NUM> are pin-shaped (cylindrical) teeth provided on an inner peripheral surface of the case <NUM>. Two or more internal teeth <NUM> are arranged at equal intervals in the circumferential direction.

More specifically, the carrier <NUM> is rotatably supported by the casing <NUM> via a pair of main bearings <NUM> (one example of the bearing in claim <NUM>) disposed at a distance from each other in the axial direction of the casing <NUM>. The main bearing <NUM> is, for example, an angular contact ball bearing. The carrier <NUM> is situated on the same axis as the casing <NUM> and the second rotation axis C2.

The carrier <NUM> includes a base plate portion <NUM> situated on the differential unit <NUM> side in the axial direction, and an end plate portion <NUM> disposed on a side of the base plate portion <NUM> away from the differential unit <NUM>, and three cylindrical column portions <NUM> that are integrally molded with the base plate portion <NUM> and protrude out from the base plate portion <NUM> toward the end plate portion <NUM>. The pillar portions <NUM> are arranged at equal intervals in the circumferential direction. The end plate portion <NUM> is disposed at tips 33a of the pillar portions <NUM>. The attachment bracket 110a of the bucket <NUM> is arranged on one surface 30a of the end plate portion <NUM> facing away from the base plate portion <NUM>. The end plate portion <NUM> and the attachment bracket 110a are fastened and fixed to the pillar portions <NUM> by bolts <NUM>. In this state, a space having a predetermined width in the axial direction is formed between the base plate portion <NUM> and the end plate portion <NUM>.

A pin <NUM> for positioning the end plate portion <NUM> with respect to the base plate portion <NUM> is provided slightly inner in the radial direction than the bolt <NUM> in the pillar portion <NUM>. The pin <NUM> is disposed such that it spans the pillar portion <NUM> and the end plate portion <NUM>. The pillar portion <NUM> and the base plate portion <NUM> are not necessary formed integrally with each other. In this case, the pillar portion <NUM> is fastened to the base plate portion <NUM>. The configuration of the pillar portions <NUM> is not limited to such a columnar shape. The pillar portions <NUM> may be formed in any shape or configuration provided that they form a space having a certain width in the axial direction between the base portion <NUM> and the end plate portion <NUM>.

The end plate portion <NUM> and the base portion <NUM> are formed with a plurality of through holes 30c and 32b (for example, three in this embodiment) into which a crankshaft <NUM> described later of the speed reducer output portion <NUM> is inserted. The through holes 30c and 32b are arranged at equal intervals in the circumferential direction.

The speed reducer output portion <NUM> includes two or more transmission gears <NUM> (for example, three in this embodiment) that mesh with the teeth portion 76c of the first operation output shaft 76a, two or more crankshafts <NUM> (three in this embodiment) having one end fixed to the transmission gear <NUM>, a first external gear 48a (an example of the external teeth member in claim <NUM>) and a second external gear 48b (an example of the external teeth member in claim <NUM>) that oscillatory rotate with the rotation of the crankshaft <NUM>.

Since the transmission gears <NUM> are fixed to one end of the crankshafts <NUM>, the rotation of the first operation output shaft 76a is transmitted to the crankshaft <NUM> via the transmission gear <NUM>. The crankshafts <NUM> are arranged extending along the axial direction. In other words, the crankshaft <NUM> rotates on a crank rotation axis C4 (an example of the rotation axis parallel to a rotation axis direction of the input shaft in claim <NUM>) parallel to the second rotation axis C2. The crankshaft <NUM> is rotatably supported by the end plate portion <NUM> via a first crank bearing <NUM>. The crankshaft <NUM> is rotatably supported on the base plate portion <NUM> via a second crank bearing <NUM>. The first crank bearing <NUM> and the second crank bearing <NUM> are, for example, tapered roller bearings.

At the center of the crankshaft <NUM> in the axial direction, a first eccentric portion 46a and a second eccentric portion 46b disposed eccentrically from the axial center of the crankshaft <NUM> are provided. The first and second eccentric portions 46a, 46b are disposed adjacent to each other in the axial direction between the first crank bearing <NUM> and the second crank bearing <NUM>. The first eccentric portion 46a is disposed adjacent to the first crank bearing <NUM>. The second eccentric portion 46b is disposed adjacent to the second crank bearing <NUM>. The first eccentric portion 46a and the second eccentric portion 46b are out of phase with each other. These crankshafts <NUM> are inserted into the through holes 30c and 32b in the end plate portion <NUM> and the base plate portion <NUM>, respectively. That is, the crankshafts <NUM> are also arranged at equal intervals in the circumferential direction like the through holes 30c and 32b.

A first roller bearing 55a is attached to the first eccentric portion 46a of the crankshaft <NUM>. A second roller bearing 55b is attached to the second eccentric portion 46b. The first roller bearing 55a is, for example, a cylindrical roller bearing. The first roller bearing 55a includes a plurality of rollers <NUM> and a cage <NUM> for holding the plurality of rollers <NUM>. Since the second roller bearing 55b has the same configuration as the first roller bearing 55a, detailed description thereof will be omitted. The first external gear 48a and the second external gear 48b are oscillatory rotated in conjunction with the rotation of the crankshaft <NUM> via the roller bearings 55a and 55b.

The first and second external gears 48a, 48b are disposed in a space between the base plate portion <NUM> of the carrier <NUM> and the end plate portion <NUM>. The first external gear 48a and the second external gear 48b have external teeth 49a and 49b respectively that mesh with the internal teeth <NUM> of the casing <NUM>. In the first external gear 48a and the second external gear 48b, formed are a first through hole 48c into which the pillar portion <NUM> is inserted, and second through holes 48d into which the eccentric portions 46a and 46b of the crankshaft <NUM> are inserted.

The first eccentric portion 48a of the crankshaft <NUM> and the first roller bearing 55a are inserted into the second through hole 48d of the first external gear 48a. The second eccentric portion 46b of the crankshaft <NUM> and the second roller bearing 55b are inserted into the second through hole 48d of the second external gear 48b. The first eccentric portion 46a and the second eccentric portion 46b are oscillatory rotated by the rotation of the crankshaft <NUM>, and thus the first external gear 48a and the second external gear 48b are oscillatory rotated while they mesh with the internal teeth <NUM> of the casing <NUM>.

Next, a description is given of an operation of the drive transmission device <NUM>. When the motor <NUM> provided in the arm <NUM> is driven, the rotation of the motor shaft 120a is transmitted to the first bevel gear <NUM> in the drive transmission device <NUM> via the transmission shaft <NUM>. The second bevel gear <NUM> that meshes with the first bevel gear <NUM> is then rotated. The differential case <NUM> fixed to the second bevel gear <NUM> is thus rotated. Then, the pinion gear <NUM> is rotated about the second rotation axis C2. As a result, the pair of side gears 75a, 75b meshing with the pinion gear <NUM> are rotated.

Of the pair of side gears 75a, 75b, the rotation of the first side gear 75a is transmitted to the first speed reducer 3A via the first operation output shaft 76a. Of the pair of side gears 75a, 75b, the rotation of the second side gear 75b is transmitted to the second speed reducer 3B via the second operation output shaft 76b. The operation of the first speed reducer 3A among the two speed reducers 3A and 3B will be now described.

In the first speed reducer 3A, the transmission gear <NUM> that meshes with the first operation output shaft 76a is rotated by the rotation of the first operation output shaft 76a. Thus, the crankshaft <NUM> is integrally rotated with the transmission gear <NUM> about the crank rotation axis C4. When the crankshaft <NUM> is rotated, the first external gear 48a is rotated while meshing with the internal teeth <NUM> as the first eccentric portion 46a oscillatory moves. As the second eccentric portion 46b oscillatory moves, the second external gear 48b is rotated while meshing with the internal teeth <NUM>. That is, the crankshaft <NUM> rotates on the crank rotation axis C4 and revolves around the second rotation axis C2.

In the present embodiment, the pillar portion <NUM> penetrating the first through hole 48c of the external gears 48a and 48b is fixed in a predetermined position together with the base plate portion <NUM>. As a result, the carrier <NUM> is rotated about the second rotation axis C2 relative to the casing <NUM> at a rotation speed slower than that of the first operation output shaft 76a. The other end 109b of the arm <NUM> in the longitudinal direction is fixed to the casing <NUM> via the housing <NUM>. The attachment bracket 110a for the bucket <NUM> is fixed to the end plate <NUM> of the carrier <NUM>. Thus, by driving the motor <NUM> provided in the arm <NUM>, the bucket <NUM> is rotationally moved about the second rotation axis C2 relative to the arm <NUM>.

That is, the operation output shafts 76a, 76b of the speed reducers 3A, 3B are input shafts to which the rotation of the motor shaft 120a is inputted via the differential unit <NUM>. In other words, the operation output shafts 76a, 76b are connected to the drive shaft of the differential unit <NUM>. The carrier <NUM> is the output shaft that decelerates the rotation of the operation output shaft 76a, 76b and outputs the decelerated rotation to the bucket <NUM>.

Here, the rotation of the motor shaft 120a of the motor <NUM> is transmitted to the two speed reducers 3A, 3B via the transmission shaft <NUM> and the differential unit <NUM>. The outputs of these two speed reducers 3A, 3B are transmitted to the bucket <NUM>. Meshing timings of the components in the two speed reducers 3A, 3B may differ due to a slight formation error of the components and an assembly error. Therefore, at the time of an initial operation of the differential device <NUM> (at the time of an initial operation of the drive transmission device <NUM>), loads applied to the operation output shafts 76a, 76b connected to the speed reducers 3A, 3B respectively may be different. In such a case, there is a high possibility that the speed reducers 3A, 3B continue to be driven with the load difference therebetween.

The pinion gear <NUM> of the differential device <NUM> is supported by the differential case <NUM> such that it is rotatable about the third rotation axis C3. Thus, even when the loads applied to the operation output shafts 76a, 76b are different, the pinion gear <NUM> is rotated about the third rotation axis C3 and the difference in the loads to the operation output shafts 76a, 76b is absorbed. Thereafter loads are equally applied to the two operation output shafts 76a and 76b, and the rotation of the transmission shaft <NUM> is transmitted to the speed reducers 3A and 3B in this state.

As described above, in the above first embodiment, the drive transmission device <NUM> includes the differential unit <NUM> to which the rotation of the motor <NUM> is transmitted, and the two speed reducers 3A and 3B that decelerate the rotations of the operation output shafts 76a and 76b of the differential device <NUM>. In the two speed reducers 3A and 3B, the rotation axis (second rotation axis C2) of the operation output shafts 76a, 76b respectively that serve as the input shaft and the rotation axis (second rotation axis C2) of the carrier <NUM> that serves as the output shaft are parallel to each other (extend in the same rotation axis direction). The two speed reducers 3A, 3B are arranged such that they oppose each other in the axial direction (direction parallel to the second rotation axis C2). Therefore, for the single differential unit <NUM>, the two speed reducers 3A and 3B to which the rotation of the differential unit <NUM> is transmitted can be arranged in a space-saving manner. In this way, the size of the drive transmission device <NUM> can be reduced. Moreover, by providing the two speed reducers 3A and 3B, load can be distributed to these two speed reducers 3A and 3B. Therefore, it is possible to obtain a sufficient mechanical strength for the drive transmission device <NUM>.

The differential unit <NUM> is disposed between the two speed reducers 3A and 3B. In this way, a limited space is effectively used for arranging the differential unit <NUM> and the two speed reducers 3A and 3B so that the drive transmission device <NUM> can be further reduced in size. As a result, the drive transmission device <NUM> can be arranged even in a narrow space such as the coupling portion between the arm <NUM> and the bucket <NUM>. The differential unit <NUM> is used as a means for transmitting the rotation of the motor <NUM> to the two speed reducers 3A and 3B. Thus, loads are equally applied to the two operation output shafts 76a and 76b, and the rotation of the transmission shaft <NUM> is transmitted to the speed reducers 3A and 3B. Therefore, it is possible to prevent the speed reducers 3A and 3B from continuing to be driven with the load imbalance. As a result, the product life of the drive transmission device <NUM> can be extended.

The speed reducers 3A, 3B each include the cylindrical casing <NUM>, the carrier <NUM> disposed radially inside the casing <NUM>, and the speed reducer output portion <NUM> that rotates the carrier <NUM> at a rotation speed reduced at a predetermined ratio with respect to the rotation speed of the operation output shafts 76a, 76b that serve as the input shaft. The speed reducer output portion <NUM> includes the two or more crankshafts <NUM>, and the first external gear 48a and second external gear 48b that oscillatory rotate in conjunction with the rotation of the crankshaft <NUM>. With such two speed reduces 3A and 3B, a high output can be obtained at a high reduction ratio. Therefore, the boom <NUM>, the arm <NUM>, and the bucket <NUM> can be operated appropriately while reducing the size of the drive transmission device <NUM>. In the speed reducers 3A, 3B, the internal gear <NUM> and the external gears 48a, 48b have a high contact ratio to each other, which improves the resistance of the drive transmission device <NUM> against overloads and impact loads. Consequently, it is possible to improve the resistance against overloads and impact loads on the coupling portion between the slewable upper structure <NUM> and the boom <NUM>, the coupling portion between the boom <NUM> and the arm <NUM>, and the coupling portion between the arm <NUM> and the bucket <NUM>.

The second embodiment will now be described with reference to <FIG>. Elements and components similar to those of the first embodiment are referred to using the same labels or referral numerals and description thereof will be omitted. <FIG> schematically illustrates a configuration of a differential unit <NUM> in a drive transmission device <NUM> according to a second embodiment of the invention. <FIG> corresponds to <FIG> referred above. As shown in <FIG>, the drive transmission device <NUM> includes a clutch mechanism <NUM> (an example of the overload protection device in the claims) disposed in the differential unit <NUM>. This is different from the above first embodiment.

The clutch mechanism <NUM> is disposed in the differential case <NUM>. The clutch mechanism <NUM> is provided such that it connects the two side gears 75a and 75b. The side gears 75a and 75b rotate integrally with the corresponding operation output shafts 76a and 76b. Thus, the clutch mechanism <NUM> connecting the two side gears 75a and 75b means the same as the clutch mechanism <NUM> connecting the operation output shafts 76a and 76b. The clutch mechanism <NUM> includes a clutch plate <NUM> and a pusher plate <NUM> facing each other in the second rotation axis C2 direction, and a spring <NUM> that presses the pusher plate <NUM> toward the clutch plate <NUM>. In the second embodiment, for example, the clutch plate <NUM> is connected to the second side gear 75b, and the pusher plate <NUM> is arranged on the first side gear 75a side.

In this configuration, when a difference between loads applied to the two side gears 75a and 75b (operation output shafts 76a and 76b) is equal to or less than a predetermined value, the pusher plate <NUM> remains being pressed toward the clutch plate <NUM> by the spring <NUM>. In this state, the clutch plate <NUM> and the pusher plate <NUM> are connected, and the two side gears 75a and 75b (operation output shafts 76a and 76b) are integrally rotated. Therefore, without operating the differential unit <NUM> (the pinion gear <NUM> is not rotated about the third rotation axis C3), the rotation of the motor shaft 120a is transmitted to the speed reducers 3A and 3B via the operation output shafts 76a and 76b.

Whereas when the difference in the load between the two side gears 75a and 75b (operation output shafts 76a and 76b) exceeds a predetermined value, the pusher plate <NUM> is separated from the clutch plate <NUM> against the spring force of the spring <NUM>. As a result, the connection between the clutch plate <NUM> and the pusher plate <NUM> is released, and the two side gears 75a and 75b (operation output shafts 76a and 76b) are relatively rotated. In this case, the differential unit <NUM> is operated to absorb the difference in load applied to the operation output shaft 76a and the operation output shaft 76b. After that, the rotation of the motor shaft 120a is transmitted to the speed reducers 3A and 3B via the operation output shafts 76a and 76b respectively.

As described above, in the above second embodiment, the two side gears 75a and 75b (operation output shafts 76a and 76b) are connected via the clutch mechanism <NUM>. Therefore, in addition to the same advantageous effects as those of the first embodiment described above, for example, when the two speed reducers 3A and 3B are driven with almost no load difference, it is possible to prevent the differential unit <NUM> from operating unnecessarily. If the differential unit <NUM> works all the time, drive noise and slight vibration of the differential unit <NUM> increase, and the product life of the drive transmission device <NUM> is shortened. Therefore, the drive transmission device <NUM> provided with the clutch mechanism <NUM> can extend the product life as compared with the above first embodiment.

The present invention is not limited to the above embodiments. For example, in the above-described embodiment, the drive transmission devices <NUM>, <NUM> for driving the bucket <NUM> relative to the arm <NUM> have been described with the case where the motor <NUM> is provided in the arm <NUM>. Whereas when the boom <NUM> is driven relative to the slewable upper structure <NUM>, the motor <NUM> may be provided in either the slewable upper structure <NUM> or the boom <NUM>. When driving the arm <NUM> relative to the boom <NUM>, the motor <NUM> may be provided in either the boom <NUM> or the arm <NUM>.

In the above embodiments, described was the case where the excavator <NUM> is provided with the drive transmission devices <NUM>, <NUM> for driving the boom <NUM>, the arm <NUM>, and the bucket <NUM> of the excavator <NUM>, which is a construction machine. However, the drive transmission devices <NUM>, <NUM> can be used for various devices without limitation. For example, when the drive transmission devices <NUM>, <NUM> are provided to any other machines or devices other than the construction machine, various types of drive source can be adopted instead of the motor <NUM>. For example, although the motor <NUM> is an electric motor, it may be a hydraulic motor driven by hydraulic oil. An engine or the like can be adopted instead of the motor.

In the above-described embodiments, the case where the drive transmission device <NUM>, <NUM> includes the two speed reducers 3A, 3B that reduce the rotation speed of the operation output shafts 76a, 76b and outputs the reduced rotation has been described. However, the invention is not limited to this, and instead of the speed reducers 3A, 3B, speed increasers that increase the rotation speed of the operation output shafts 76a, 76b respectively may be provided. Anything may be used provided that it changes the rotation speeds of the operation output shafts 76a, 76b, and the speed reducers are configured such that the input shaft and the output shaft are aligned in the same rotation axis direction, and the speed reducers are disposed such that they are opposed each other in the axial direction.

In the above embodiments, the speed reducers 3A, 3B each includes the cylindrical casing <NUM>, the carrier disposed radially inside the casing <NUM>, and the speed reducer output portion <NUM> that rotates the carrier <NUM> at a rotation speed reduced at a predetermined ratio with respect to the rotation speed of the motor shaft 120a. The deceleration output unit <NUM> has been described as a so-called eccentric oscillating speed reducer that includes the two or more crankshafts <NUM>, and the first external gear 48a and second external gear 48b that oscillatory rotate in conjunction with the rotation of the crankshaft <NUM>. The speed reducer output portion <NUM> may be an eccentric oscillating speed reducer that reduces the rotation speed of the crankshaft and transmits it to the second member to rotate the second member relative to the first member at a reduced rotation speed.

For example, an eccentric oscillating speed reducer having a single crankshaft will be specifically described. The speed reducer in this case has a so-called center crankshaft coaxial with the second rotation axis C2 as the crankshaft. In conjunction with the rotation of the center crankshaft, the first external gear 48a and the second external gear 48b are oscillatory rotated.

The foregoing embodiments disclosed herein describe a plurality of physically separate constituent parts. They may be combined into a single part, and any one of them may be divided into a plurality of physically separate constituent parts. Irrespective of whether or not the constituent parts are integrated, they are acceptable as long as they are configured to solve the problems.

Claim 1:
A drive transmission device (<NUM>, <NUM>) comprising:
a single transmission portion (<NUM>, <NUM>) to which rotation of a drive source (<NUM>) generating a rotational force is transmitted; and
two speed changers (3A, 3B) each having an input shaft (76a, 76b) and an output shaft (<NUM>), each input shaft (76a, 76b) being coupled to the single transmission portion (<NUM>, <NUM>), each of the two speed changers (3A, 3B) changing a speed of rotation of each input shaft (76a, 76b) and each output shaft (<NUM>) outputting a speed-changed rotation,
wherein each input shaft (76a, 76b) and each output shaft (<NUM>) are aligned in a same rotation axis (C2) direction and the two speed changers (3A, 3B) are opposed to each other in the rotation axis (C2) direction,
wherein the single transmission portion (<NUM>, <NUM>) is disposed between the two speed changers (3A, 3B),
wherein the transmission portion (<NUM>, <NUM>) includes a differential unit (<NUM>) that includes a ring gear (<NUM>) to which the rotation of the drive source (<NUM>) is transmitted, and
wherein each input shaft (76a, 76b) is coupled to a drive shaft (2a) of the differential unit (<NUM>),
characterized in that
the drive transmission device (<NUM>, <NUM>) further comprises an overload protection device (<NUM>-Fig.<NUM>) connecting the input shafts (76a, 76b) of the two speed changers (3A, 3B), and
the overload protection device (<NUM>-Fig.<NUM>) is configured such that the input shafts (76a, 76b) rotate relatively to each other when a difference in torque between the input shafts (76a, 76b) exceeds a predetermined value.