Rubber track assembly

Abstract: A rubber track assembly comprising a driving wheel (1), an idler wheel (2), an endless rubber track (3) extending around the driving wheel and the idler wheel and having a plurality of rubber lugs (6) formed on its outer circumference (7) and a plurality of rubber guide projections (8) formed on its inner surface (5), and a plurality of roller wheels (4) arranged in contact with the inner surface of the rubber track in a ground contact region thereof, wherein each of the wheels (1,2,4) has a pair of wheel portions (11) formed at is opposite sides and spaced apart to be disposed at opposite sides of the guide projection (8) for engaging the inner surface (5) of the rubber track (3) at the opposite sides of the guide projection. The rubber guide projection (8) is provided with at least one low friction surface having a coefficient of friction lower than that of the rubber material of the rubber guide projection.

Description: This invention relates to a rubber track assembly for use in construction equipment, agriculture machinery, civil engineering machinery and the like. There is known a conventional rubber track assembly as shown in Fig. 1 of the accompanying drawings. Such a rubber track assembly comprises a driving sprocket wheel 1, an idler wheel 2, an endless rubber track 3 which extends around the driving sprocket wheel 1 and the idler wheel 2, and a plurality of roller wheels 4 arranged in contact with the inner surface 5 of a ground contact region of the rubber track 3 between the driving sprocket wheel 1 and the idler wheel 2. Furthermore, the conventional rubber track 3 has a plurality of rubber lugs 6 formed on its outer circumference 7, a plurality of rubber guide projections 8 formed on the inner surface 5 to protrude at the central region thereof and spaced from each other by a predetermined distance in the longitudinal direction of the rubber track 3, and steel cords 9 embedded in the rubber material 10 thereof and extended in the longitudinal direction of the rubber track 3 as shown in Fig. 2 of the accompanying drawings. Each of the wheels 1, 2 and 4 has a pair of wheel portions 11 spaced from each other in a direction of the width of the rubber track 3 to contact the inner surface 5 of the rubber track at opposite sides of the rubber guide projection 8 as shown in Fig. 2. In particular, the driving sprocket wheel 1 includes a pair of wheel portions 11 spaced apart to be disposed at opposite sides of the guide projection 8 for engaging the inner surface 5 of the rubber track 3 at the opposite sides of the guide projections 8, and a plurality of driving members 12 such as drive pins, teeth or the like disposed between the wheel portions 11 and adapted for engaging the guide projections 8 to drive the rubber track 3. Such a conventional rubber track assembly has a disadvantage that when the rubber track assembly is cornering along a curve, the wheel portion 11 is forcedly moved toward a lateral direction shown by an arrow A in Fig. 3 of the accompanying drawings, and then the wheel portion 11 laterally pushes an inclined side surface 8a of the rubber guide projection 8 on the rubber track 3 so that the rubber track is subjected to a side force f which consists of a horizontal component fx and a vertical component fy as illustrated in Fig. 4 of the accompanying drawings. Since the side surface 8a of the rubber guide projection of a conventional rubber track assembly is made of rubber having a high coefficient of static friction such as µ=0.5, the vertical component fy cannot cause a horizontal component fx sufficient to overcome a friction F between the rubber track 3 and the ground G, and therefore the wheel 1, 2 or 4 climbs on the inclined side surface 8a to ride over the guide projection 8 and as a result the wheel is detracked from the rubber track 3 or the guide projection 8 is damaged by the wheel and also an energy loss is caused by substantial travelling resistance. Attention is also drawn to the disclosures of DE-A-3319 067 and US-A-3118709. DE-A-3319067 discloses a rubber track assembly comprising a driving wheel, an idler wheel, an endless rubber track extending around the driving wheel and the idler wheel and having a plurality of rubber lugs formed on its outer circumference and a plurality of rubber guide projections formed on its inner surface, and a plurality of roller wheels arranged in contact with the inner surface of the rubber track in a ground contact region thereof, said rubber guide projections being provided with a low friction surface having a coefficient of friction lower than that of the rubber material of the rubber guide projection. US-A-3118709 discloses a rubber track assembly comprising a driving wheel 3, an idler wheel 4, an endless rubber track 1 extending around the driving wheel and the idler wheel and having a plurality of rubber lugs formed on its outer circumference 13 and a plurality of rubber guide projections 10 formed on the inner surface 12 of the rubber track to protrude at the central region thereof, and a plurality of roller wheels 5 arranged in contact with the inner surface of the rubber track in a ground contact region thereof; wherein each of said wheels has wheel portions engaging the inner surface of the rubber track at the opposite sides 14a, 14b of the rubber guide projections, and wherein said rubber guide projections 10 have nylon surfaces 16 situated at longitudinal end surfaces thereof. It is an aim of the present invention to provide an improved rubber track assembly having a superior tracking faculty and also a long effective life. In order to achieve this aim, the present invention provides a low friction surface at a portion on the rubber guide projection which is engaged with the wheel to prevent the wheel from detracking from the rubber track and also prevent the guide projections from being worn or damaged by the wheel. The present invention provides a rubber track assembly comprising a driving wheel, an idler wheel, an endless rubber track extending around the driving wheel and the idler wheel and having a plurality of rubber lugs formed on its outer circumference and a plurality of rubber guide projections formed on the inner surface of the rubber track to protrude at the central region thereof, and a plurality of roller wheels arranged in contact with the inner surface of the rubber track in a ground contact region thereof; wherein said rubber guide projections have low friction surfaces situated at widthwise end surfaces thereof, said low friction surfaces having a coefficient of friction lower than that of the rubber material of the rubber guide projection, and wherein said low friction surfaces of the rubber guide projections are disposed to be in contact with a said wheel; and wherein each of said wheels has wheel portions on opposite sides of the rubber guide projections for engaging the inner surface of the rubber track at the opposite sides of the rubber guide projections. The low friction surface may be provided by a low friction member made of low friction material such as ultra-high-molecular polyethylene having a low friction coefficient of µ=0.05-0.20 depending on the partner material and moisture condition. Thus, when the wheel portion pushes such a low friction side surface of the guide projection, the horizontal component fx of the side force f applied to the rubber track by the wheel portion is greater than the vertical component fy as shown in Fig. 4, and is greater than a friction F between the rubber track 3 and the ground G so that the rubber track is laterally shifted to prevent the wheel from climbing on the side surface 8a and thereby preventing the wheel from detracking from the rubber track. Accordingly, the rubber track is effectively driven by the wheel during the cornering of a vehicle without loss of driving energy. In a rubber track assembly comprising a driving sprocket wheel including a pair of wheel portions and driving members such as drive pins, teeth or the like disposed between the wheel portions and adapted for engaging with rubber guide projections to drive the rubber track, the rubber guide projection may be provided at four side surfaces thereof with the low friction surfaces having a friction coefficient lower than that of the rubber material of the rubber guide projection. The rubber guide projections of the rubber track may be provided with the low friction surfaces by inserting low friction members made of material having a low friction coefficient. Such low friction members may be inserted into a metal mold adapted for molding the rubber track so as to expose surfaces of the low friction members at wheel contacting regions of the rubber guide projections and then filling rubber material into the metal mold to form the rubber guide projections integrally with the low friction members. The low friction member having a low friction coefficient applicable for the rubber guide projection may be made of for example ceramics, synthetic resin such as nylon, and ultra-high-molecular-weight polyethylene having a molecular weight of at least five hundred thousand. Among others, the ultra-high-molecular-weight polyethylene is preferable in view of light weight, low cost and high adhesion with rubber. Some ultra-high-molecular-weight polyethylene has an average molecular weight of three million to five million and has superior characteristics such as high impact resistance, self-lubricating properties, and extremely low friction coefficient. The material is available in the form of powder and therefore able to be easily formed into a desired shape by press forming or injecting in a metal mold. In a preferred embodiment of the invention, a plate shaped low friction member having a low friction coefficient may be embedded in the central portion of the rubber guide projection and extended through the guide projection in a direction of width of the rubber track to expose opposite end surfaces of the plate shaped member on the inclined opposite side surfaces of the guide projection. In another preferred embodiment of the invention, a cross shaped low friction member having a low friction coefficient may be embedded in the central portion of the rubber guide projection to expose four end surfaces of the cross shaped member on the four side surfaces of the rubber guide projection, respectively. Alternatively an angle shaped member having a low friction coefficient may be arranged on the rubber guide projection to cover the inclined opposite side surfaces with the angle shaped members or a cap shaped member having a low friction coefficient may be arranged on the rubber guide projection to cap the rubber guide projection. Furthermore, two plate members having a low friction coefficient may be arranged on the inclined opposite side surfaces of the rubber guide projection, respectively, to cover the opposite side surfaces of the rubber guide projection with the plate members. The plate member or plate members covering the side surfaces of the rubber guide projection may be extended to the inner tracking surface of the rubber track at the opposite sides of the guide projection. Furthermore, in a preferred embodiment of the invention, in order to improve transmission of driving force from the driving sprocket wheel to the rubber track, the driving sprocket wheel may be provided with a plurality of driving members in the form of elongate drive pins arranged at a constant interval on the peripheries of the wheel portions and extended transversally over the full width of the driving wheel and/or a range of 1/2-4/5 width of the rubber track, while the rubber track is provided with grooves transversely formed on the inner surface of the rubber track between the guide projections for engaging with the drive pins. In still another embodiment of the invention, the rubber track may have a plurality of protrusions formed in a wave shape on the inner tracking surfaces at the opposite sides of the guide projections, while the driving sprocket wheel having a pair of wheel portions integrally formed with drum portions is provided with a plurality of recesses formed on the outer peripheries of the drum portions for receiving the wave shaped protrusions. The protrusions preferably protrude on the inner surface of the rubber track at positions corresponding to regions between the rubber lugs on the outer circumference of the rubber track. Moreover, the wheel portions of the wheel preferably have openings for permitting discharge of earth and sand out of space between wheel portions. Each of the wheel portions preferably has a rounded corner at its inner side formed with a radius of curvature of 1/20-1/5 distance between the pair of wheel portions so as to be smoothly contacted with the low friction side surface of the guide projection. The invention will be further described, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a side view illustrating a conventional rubber track assembly; Fig. 2 is a front view illustrating a driving sprocket wheel shown in Fig. 1; Fig. 3 illustrates a roller wheel contacting a side inclined surface of a rubber guide projection during cornering of a vehicle; Fig. 4 is an explanatory view of a side force applied to a rubber track by a roller wheel; Fig. 5 is a cross sectional view illustrating a preferred first embodiment of a rubber track according to the invention; Fig. 6 is a sectional view taken along a line VI-VI in Fig. 5; Fig. 7 is a plan view illustrating a modification of the embodiment of the rubber track shown in Fig. 5; Fig. 8 is a sectional view taken along a line VIII-VIII in Fig. 7; Fig. 9 is a plan view illustrating another modification of the embodiment shown in Fig. 5; Fig. 10 is a fragmental plan view of a rubber track illustrating another embodiment of the invention; Fig. 11 is a sectional view taken along a line XI-XI in Fig. 10; Fig. 12 is a sectional view taken along a line XII-XII in Fig. 10; Fig. 13 is a vertical sectional view of a rubber guide projection illustrating another embodiment of the invention; Fig. 14 is a fragmental plan view of a rubber track of another embodiment of the invention; Fig. 15 is a sectional view taken along a line XV-XV in Fig. 14; Fig. 16 is a sectional view taken along a line XVI-XVI in Fig. 14; Fig. 17 is a plan view of another embodiment of the invention; Fig. 18 is a sectional view taken along a line XVIII-XVIII in Fig. 17; Fig. 19 is a perspective view of another preferred embodiment of a rubber track according to the invention; Fig. 20 is a plan view of the rubber track shown in Fig. 19; Fig. 21 is a side view of the rubber track shown in Fig. 20; Fig. 22 is a front view illustrating a preferred embodiment of a driving sprocket wheel adapted to the embodiment shown in Fig. 19; Fig. 23 is a side view of the driving sprocket wheel shown in Fig. 22; Fig. 24 is a vertical sectional view of the driving sprocket wheel shown in Fig. 23; Fig. 25 illustrates another embodiment of a rubber track assembly of the invention; Fig. 26 is a cross sectional view of the rubber track shown in Fig. 25; Fig. 27 is a sectional view of the rubber track contacting the driving wheel shown in Fig. 25; Fig. 28 is a sectional view of the rubber track contacting the roller wheel shown in Fig. 25; Fig. 29 is a sectional view illustrating an embodiment of a driving wheel of friction drive type; Fig. 30 is a side view illustrating an embodiment of a wheel portion of friction drive type; and Fig. 31 is a sectional view illustrating an embodiment of a driving wheel of pin drive type. Referring to Figs. 5 and 6 illustrating a first embodiment of the invention, a rubber guide projection 8 protrudes at the central portion of the inner surface 5 of the rubber track 3. A plate shaped low friction member 15 having a low friction coefficient is embedded in the central portion of the rubber guide projection 8 and extended through the guide projection to expose opposite ends surfaces 15a and 15b and a top surface 15c of the plate shaped member 15 on central portions of inclined opposite side surfaces 8a and 8b and the top surface 8c of the rubber guide projection 8. The plate shaped low friction member 15 is made of ultra-high-molecular-weight polyethylene having a molecular weight of three million and is inserted in a metal mold for molding the rubber track 3 at a recessed portion corresponding to the guide projection to be molded integrally with the rubber guide projection. The plate shaped low friction member 15 is exposed on surfaces of the opposite sides 8a and 8b and the top portion 8c of the guide projection 8 as mentioned above so as to contact the driving sprocket wheel 1, idler wheel 2 and roller wheels 4 to prevent the rubber track from detracking from the rubber track assembly. Figs. 7 and 8 illustrate a modification of the embodiment shown in Fig. 5. In this modification, the plate shaped low friction member 15 is exposed only on the opposite side surfaces 8a and 8b in the width direction of the rubber guide projection 8. Fig. 9 illustrates still other modification of the embodiment shown in Fig. 5. In this modification, the plate shaped low friction member 15 is exposed on the opposite side surfaces 8a and 8b in the width direction and top surface 8c of the rubber guide projection 8. Figs. 10 to 12 illustrate another embodiment of the rubber track 3 according to the invention. In this embodiment, a cross shaped low friction member 15 having a low friction coefficient is embedded in the central portion of the rubber guide projection 8 to expose four end surfaces 15a, 15b, 15d and 15e of the cross shaped member 15 on the four side surfaces 8a, 8b, 8d and 8e of the rubber guide projection 8, respectively. It should be noted that the cross shaped low friction member 15 may be set in the metal mold to expose the upper surface of the cross shaped member 15 on the top surface 8c of the rubber guide projection 8. Such a rubber track 3 having the low friction surfaces 15d and 15e on the front and rear surface of the rubber guide projection in the longitudinal direction of the rubber track 3 is preferably driven by driving members such as drive pins or teeth of the driving sprocket wheel of the rubber track assembly without damage or wear of the rubber guide projection. The cross shaped low friction member may be formed by a unitary body or four divided pieces. Fig. 13 illustrates another embodiment of the invention, in which the rubber guide projection 8 is capped with a cap shaped low friction member 15. Figs. 14-16 illustrate still another embodiment of the invention, in which the rubber guide projection 8 is covered with an angle shaped low friction member 15 to provide inclined side low friction surfaces 15a, 15b, 15d and 15e and a top low friction surface 15c. Figs. 17 and 18 illustrate another embodiment of the invention, in which the rubber guide projection 8 is capped with a cap shaped low friction member 15 having extensions 16 which extend onto the inner tracking surface 5 of the rubber track 3 at the opposite sides of the guide projection 8 and terminate at grooves 17, respectively, which are formed in the inner tracking surface 5. Figs. 19-24 illustrate another embodiment of the invention. Referring to Figs. 19-21, the rubber track 3 is provided with grooves 21 which extend transversely of the inner tracking surface 5 between the guide projections 8. Referring to Figs. 22-24, the driving sprocket wheel 1 is provided with a plurality of driving members in the form of elongate drive pins 22 arranged at a constant interval on the peripheries of the wheel portions 11 and extended transversely over the full width of the driving sprocket wheel and/or a range of 1/2-4/5 width of the rubber track 3. Thus, in this embodiment, the drive pins 22 of the driving sprocket wheel 1 engage the groove 21 in the rubber track 3 to positively transmit driving force from the driving sprocket wheel 1 to the rubber track 3 when the sprocket wheel 1 is driven by a driving shaft 23 of a vehicle. One of the wheel portions 11 of the driving sprocket wheel 1 has an opening 24 for permitting discharge of earth and sand out of space between the wheel portions 11. Figs. 25-28 illustrate another embodiment, in which the rubber track 3 has a plurality of protrusions 25 formed in a wave shape on the inner track surface 5 at the opposite sides of the guide projections 8, and the driving sprocket wheel 1 has a plurality of recesses 26 formed in outer peripheries 13 of the wheel portions 11 for receiving the wave shaped protrusions 25. The protrusions protrude on the inner track surface 5 of the rubber track 3 at positions corresponding to regions 27 between the rubber lugs 6 on the outer circumference 7 of the rubber track 3. Each of the wave shaped protrusions 25 has a height of 5-20% of the lug pitch of the rubber lugs 6 formed on the outer circumference 7 of the rubber track. In Figs. 5, 24, 27 and 28, the reference numeral 28 designates a rounded corner having a radius of corvature R of 1/20-1/5 distance (d) between the pair of wheel portions 11. Referring to Fig. 29 illustrating an embodiment of the rubber track assembly including a driving wheel 1 of friction drive type, the rubber guide projection 8 has low friction surfaces 8a and 8b provided by a plate shaped member 15 having a low friction coefficient and each of the wheel portions 11 of the driving wheel 1 also has a rounded corner 28 having a radius of curvature R of 1/20-1/5 distance (d) between the pair of wheel portions 11. Fig. 30 illustrates a modification of a driving wheel 1 of friction drive type which is provided with a plurality of steel rods 29 welded to the peripheral surface 30 of the wheel portion 11 and spaced at intervals in the circumferential direction. Each steel rod 29 preferably has a diameter of 1/10-1/2 thickness of the inner rubber layer 10a (Fig. 29) of the rubber track 3. Fig. 31 illustrates a modification of a driving wheel 1 of pin drive type which is provided with a low friction surface 31 formed by a low friction material 32 such as nylon adhered on the peripheral surface of the wheel portion 11 which contacts the inner surface 5 of the rubber track 3.

Claims: A rubber track assembly comprising a driving wheel (1), an idler wheel (2), an endless rubber track (3) extending around the driving wheel and the idler wheel and having a plurality of rubber lugs (6) formed on its outer circumference (7) and a plurality of rubber guide projections (8) formed on the inner surface (5) of the rubber track (3) to protrude at the central region thereof, and a plurality of roller wheels (4) arranged in contact with the inner surface of the rubber track in a ground contact region thereof; wherein said rubber guide projections (8) have low friction surfaces situated at widthwise end surfaces thereof, said low friction surfaces having a coefficient of friction lower than that of the rubber material of the rubber guide projection, and wherein said low friction surfaces of the rubber guide projections (8) are disposed to be in contact with a said wheel (1, 2, 4); and wherein each of said wheels (1, 2, 4) has wheel portions (11) on opposite sides of the rubber guide projections (8) for engaging the inner surface (5) of the rubber track (3) at the opposite sides of the rubber guide projections (8). A rubber track assembly as claimed in claim 1, characterized in that said low friction surface is provided by at least one low friction member (15) made of low friction material such as nylon or ultra-high-molecular polyethylene having a molecular weight of at least 500,000. A rubber track assembly as claimed in claim 1 or 2, characterized in that said low friction member is a plate shaped low friction member (15) having a low friction coefficient embedded in the central portion of the rubber guide projection (8) and extended through the guide projection in a direction of width of the rubber track (3) to expose opposite end surfaces (15a, 15b) of the plate shaped member on opposite side surfaces (8a, 8b) of the guide projection. A rubber track assembly as claimed in claim 1 or 2, characterized in that said low friction members are two plate members (15) having a low friction coefficient and arranged on inclined opposite side surfaces of the rubber guide projection (8), respectively, to cover the opposite side surfaces of the rubber guide projection. A rubber track assembly as claimed in claim 1 or 2, characterized in that said low friction member is an angle shaped member (15) having a low friction coefficient and arranged on the rubber guide projection (8) to cover inclined opposite side surfaces. A rubber track assembly as claimed in claim 1 or 2, characterized in that said low friction member is a cap shaped member (15) having a low friction coefficient and capped on the rubber guide projection (8). A rubber track assembly as claimed in claim 1 or 2, characterized in that said low friction member is at least one plate member (15) covering opposite side surfaces of the rubber guide projection (8) and extending on the inner surface (5) of the rubber track (3) at the opposite sides of the guide projection. A rubber track assembly as claimed in claim 1 or 2, characterized in that said low friction member is a cross shaped low friction member (15) having a low friction coefficient and embedded in the central portion of the rubber guide projection (8) to expose four end surfaces (15a, 15b, 15d, 15e) of the cross shaped member on four side surfaces (8a, 8b, 8d, 8e) of the rubber guide projection, respectively. A rubber track assembly as claimed in any of claims 1 to 8, characterized in that each of said wheel portions (11) has a rounded corner (28) at its inner side formed with a radius of curvature of 1/20-1/5 distance (d) between the pair of wheel portions (11). A rubber track assembly as claimed in any of claims 1 to 9, characterized in that at least one of the pair of wheel portions (11) has at least one opening (24) for permitting discharge of earth and sand out of space between wheel portions (11). A rubber track assembly as claimed in any of claims 1 to 10, characterized in that said driving wheel (1) has a plurality of driving members (12) such as drive pins, teeth or the like which are disposed between the wheel portions (11) and adapted for engaging the guide projections (8) to positively drive the rubber track (3). A rubber track assembly as claimed in claim 11, characterized in that said wheel portions (11) are covered at their peripheries with a low friction material. A rubber track assembly as claimed in any of claims 1 to 12, characterized in that said driving wheel (1) is provided at peripheries (30) of its wheel portions (11) with a plurality of metallic rods (29) spaced with respect to each other and having a diameter of 1/10-1/2 thickness of an inner rubber layer (10a) of the rubber track (3). A rubber track assembly as claimed in any of claims 1 to 13, characterized in that the driving wheel (1) including a pair of wheel portions (11) is provided with a plurality of elongate drive pins (22) arranged at a constant interval on peripheries of the wheel portions and extended transversally over the full width of the driving wheel and/or a range of 1/2-4/5 width of the rubber track (3), and the rubber track is provided with grooves (21) transversely formed on the inner surface (5) of the rubber track between the guide projections (8) for engaging with the drive pins (22). A rubber track assembly as claimed in claim 14, characterized in that at least one of the wheel portions (11) has an opening (24) for permitting discharge of earth and sand out of space between wheel portions (11). A rubber track assembly as claimed in any of claims 1 to 15, characterized in that said rubber track (3) has plurality of protrusions (25) formed in a wave shape on the inner surface (5) at the opposite sides of the guide projections (8), and the driving wheel (1) has a pair of wheel portions (11) formed with a plurality of recesses (26) on their outer peripheries (13) for receiving the wave shaped protrusions (25). A rubber track assembly as claimed in claim 16, characterized in that said protrusions (25) protrude on the inner surface (5) of the rubber track (3) at positions corresponding to regions (27) between the rubber lugs (6) on the outer circumference (7) of the rubber track. A rubber track assembly as claimed in claim 15 or 16, characterized in that each of the protrusions (25) has a height of 5-20% lug pitch of the rubber lugs (6).

Inventors: ISHIBASHI MASARU, MURAMATSU TATEO, YAMAZAKI HARUMICHI, ISHIBASHI, MASARU, MURAMATSU, TATEO, YAMAZAKI, HARUMICHI
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1993
Main classification: B62D55
IPC codes: C09K19, B62D55