1. Field of the Invention
This invention relates to an idler guide unit.
2. Description of the Related Art
As known well, in a crawler type traveling apparatus in a bulldozer, a power shovel and a crawler crane, an axis-to-axis distance of a sprocket and an idler is set so that a crawler normally has a desired degree of slack. This enables a slackened-side portion of the crawler to be rendered free from the reception of the application of a tensile force, though a driving-side portion (a side-portion that is pulled by the sprocket) of the crawler encounters the occurrence of a tensile force. Thus, the reduction of the internal friction of the crawler and the traveling resistance thereof due to the internal friction thereof is attained.
When earth and sand and rocks eat into, for example, meshed portions of the sprocket and crawler during a practical operation of the crawler, a tensile force (which will hereinafter be referred to as shoe tension) occurs over the whole circumference of the crawler. When the shoe tension in such a case is not higher than a predetermined level, the earth and sand and rocks eating into the meshed portions mentioned above are collapsed with the above-mentioned axis-to-axis distance kept unchanged. Thus, the slippage (which will hereinafter be referred to as a jump) of the meshed sprocket and crawler and the dislocation of the crawler are prevented. When the shoe tension becomes not lower than a predetermined level, the idler is reversed (which will hereinafter be referred to as recoiling), and the traveling apparatus is thereby protected. As a means for enabling such inconveniences to be eliminated, an idler guide apparatus supporting bearings for the idler so that the bearing can be slid in the longitudinal direction of the traveling apparatus.
However, in this structure, the idler guide unit is used as it is exposed to dust or the weather, so that the width of a clearance between the crawler and sprocket is liable to increase. In the clearance width-increased condition, the traveling noise increases due to the striking sounds occurring in the clearance during a movement of a crawler type traveling apparatus, and this would give rise to a serious trouble. In order to regulate the width of the clearance, it is necessary to remove the idler of large mass, and repair a worn part by welding or replace such a part. Therefore, the maintenance and repair work for the crawler costs a great deal.
The patent literature 1 [JP-A-5-40090 (pages 6 to 7, FIG. 1 and FIG. 2)] discloses a structure as an example of a means for solving these problems which attains the restraining of an increase in width of a lateral clearance in an idler guide unit by increasing the width of a vertical clearance therein, and the disusing of a lateral-clearance regulating operation.
An example of a related art idler guide unit will be described with reference to FIGS. 5 to 6 by taking this patent literature 1 as an example literature.
FIG. 5 is a side view of a crawler type traveling apparatus to which a related art idler guide unit is applied, and FIG. 6 a sectioned front view, a drawing illustrating the same idler guide unit, taken along the line L—L in FIG. 5.
First, referring to FIG. 5, a traveling apparatus is formed by providing a sprocket at a rear end portion of a track frame 61, an idler 65 at a front end portion thereof, lower rolling wheels 15 at a lower portion thereof, and upper rolling wheels 16 at an upper portion thereof respectively, and by winding a crawler 17 around the sprocket, idler 65, lower rolling wheels 15 and upper rolling wheels 16.
The track frame 61 is provided on an upper portion thereof with a spring box 68, and the idler 65 is rendered able to be recoiled by a spring (not shown) in the spring box 68, the idler 65 being formed so that the idler 65 can be recoiled as the idler is guided by an idler guide unit 70 provided on bearings.
Next, referring to FIG. 6, the idler guide unit 70 has bearings 72 fastened by bolts 76 to left and right end portions of an idler shaft 71 which supports the idler 65 thereon. The bearings 72 are provided with upper guides 73, to which guide plates 75 are fixed, and lower guides 74, and the upper and lower guides are engaged with guide plates 82 on an upper surface of the track frame and guide brackets 84 on inner surfaces of the track frame respectively. A vertical movement of the idler 65 is restricted by this arrangement.
Guide brackets 90, 90 are fastened by bolts 93 to outer end surfaces of the left and right bearings 72, 72 respectively via shims 92, 92. Guide surfaces 91, 91 of the guide brackets 90, 90 are engaged with guide plates 83, 83 on left and right outer side surfaces 81, 81 of the track frames 80 via clearances S1. A lateral movement of the idler 65 is restricted by this arrangement.
The left and right outer side surfaces 81, 81 of the track frame 80 and outer side surfaces of the guide plates 83, 83 are formed into downwardly divergent surfaces, i.e. left and right tapering surfaces.
When the upper guides 73 of the bearings 72 and the guide plates 82 on the upper surfaces of the track frames in the above-described structure shown in FIGS. 5 to 6 are worn, the bearings 72 are moved down. This causes the clearances S1 between the inclined guide plates 83, 83 on the left and right outer side surfaces 81, 81 of the track frames 80 and the guide surfaces 91, 91 of the guide brackets 90, 90 to decrease. As a result, even when the guide plates 83, 83 and guide surfaces 91, 91 are worn, the width of the clearances S1 does not increase, so that operations for regulating the lateral width of the clearances are said to become unnecessary.
However, the construction of the related art idler guide unit 70 shown in FIGS. 5 to 6 has the following problems.
(1) The idler 65 does not always receive a downwardly directed force. For example, when a working vehicle runs on a wasteland, the idler 65 is thrust up due to projecting parts of the ground surface. When the traveling apparatus is moved rearward, shoe tension is applied to an upper portion of the crawler of the apparatus, and the idler 65 is lifted. Consequently, when the width of a vertical clearance of the idler guide unit increases, vertical movements of the idler 65 become large during the running of the working vehicle, and traveling noise increases due to the striking sounds of the clearance-forming parts occurring during such large vertical movements of the idler 65.
(2) In the condition described in (1) above, the lateral clearance reducing effect of the inclined surfaces of the guide plates 83, 83 is not displayed but the lateral vibration of the idler 65 occurs. The striking sounds of the clearance-forming parts also occur during such time.
(3) When a load is imparted to a working machine in a working vehicle, a crawler type traveling apparatus retains the stability of front and rear portions of the vehicle by using the idler and sprocket as front and rear fulcrums. Therefore, in general, the progress of the wear on the vertical guide portions 75, 74, 82, 84 of an idler guide unit is speedier than that of the wear on the lateral guide portions 83, 83, 91, 91 thereof. On the other hand, the above-mentioned structure of the related art idler guide unit does not have clearance regulating means for the vertical guide portions 75, 74, 82, 84, so that the clearances are left in an increased state unless the guide plates 75, 82 are replaced. As a result, the crawler type traveling apparatus is a crawler type traveling apparatus generating a large traveling noise.
(4) As a clearance regulating method, repairing the guide plates 75, 82 by welding, or replacing the same is needed. In order to carry out the repairing or replacing of the guide plates, the idler of large mass has to be removed. Therefore, the crawler type traveling apparatus necessarily becomes a crawler type traveling apparatus of a high maintenance and repair cost.