Reach type fork lift

Abstract: A reach forklift (1) comprises: a forklift body (2); left and right straddle arms (10L,10R); a pair of load wheels (12L,12R) supported in a steerable manner in the vicinity of front ends of the left and right straddle arms (10L,10R), respectively; driving means (34,33,31,32,30,29,25,35,18,17) for steering the load wheels (12L,12R), the load wheels and the driving means being housed in the straddle arms; a drive wheel (11) disposed in a rear portion of the forklift body; and a steering wheel (6) for steering the drive wheel (11); steering angle detecting means (26,27,28) for detecting steering angles of the left and right load wheels (12L,12R) and the drive wheel (11). Each of the left and right straddle arms (10L,10R) comprises: a bracket (13) which rotatably supports a steering shaft (16), the center of the steering shaft (16) being positioned at an outer position in the width direction of the forklift body (2), the bracket (13) being fixed to a lower face of the steering shaft (16), supporting the load wheels (12L,12R) at an outer position of the forklift body (2), and rotatably supporting the center of the load wheel in the width direction of the load wheel, the center of the load wheel (12) being separated from the center of the steering shaft (16) by a predetermined distance (S); a gear (20) which is fixed to the bracket (13) and formed into a sector shape, the arc portion of the sector gear (20) being directed to the center of the forklift (1); and a driving gear (19) which engages with the sector gear (20) and is driven by the driving means (29-35,25,18,17), the driving gear being positioned in the side of the center of the forklift.

Description: This invention relates to a reach forklift according to the preamble part of claim 1, and more particularly to a reach forklift which has steerable load wheels and is mainly intended to attain an improvement in the efficiency of cargo work. Examined patent publications JP-B-5815342, 5815343, 5815344 and unexamined patent publication JP-A-57121599 relate to a multi-directional vehicle as shown in Figs. 12 and 13. When the vehicle travels in the directions indicated by arrow A, caster wheels p and m are turned and then fixed in these directions so that they cannot make a turn, and a caster wheel n is allowed to turn, by hydraulically controlling cylinders provided for these wheels. In this state, a steered and driving wheel l is turned toward a desired direction, so that Ackerman steering can be effected. When the vehicle travels in the directions indicated by arrow B, the caster wheels p and n are turned and then fixed in these directions so that they cannot make a turn, and the caster wheel m is allowed to turn, by hydraulically controlling the cylinders. In this state, the steered and driving wheel l is turned toward a desired direction, so that Ackerman steering can be effected in the same manner as described above. In the above-described vehicle, however, the cylinders s1 and s2, link levers and the like are housed in straddle arms, so that the left and right straddle arms become larger in width. The large width of straddle arms is quite inconvenient because such a forklift is required to travel along very narrow pathways in a warehouse. When the travel direction is to be changed from A to B or vice versa, the vehicle a is first stopped, and then a button switch or the like is pressed. The necessity of individually performing such mode switching operations makes it impossible to continuously change the travel direction. When the vehicle is steered according to the theory of Ackerman-Jeantaud, the travel direction is limited to those indicated by A or B, and the attitude of the vehicle cannot be changed with respect to other directions (for example, directions inclined at 45 degrees away from the directions of arrow A). Furthermore, the steering of the vehicle cannot be controlled in such a manner that the turning center thereof is continuously changed and located on the approximate center of the body of the vehicle. Thus, the vehicle cannot make a small turn. FR-2 201 66 relates to a forklift having two steerable wheels and a lead wheel, whose center axis coincides with the center axis of a steering shaft. The object of the present invention is to provide a reach fork-lift with an improved steerability which at the same time is simple in structure and thus reliable. This object is solved by a reach forklift comprising the features of claim 1. Preferred embodiments of the invention are subject to dependent claims 2 to 4. Fig. 1 is a side elevation view of a reach forklift according to the invention; Fig. 2 is a sectional view taken along the line A-A shown in Fig. 4; Fig. 3 is a side elevation view of a left load wheel; Fig. 4 is a front view of the left load wheel; Fig. 5 is a front view of the left load wheel; Fig. 6 is a plan view illustrating a wheelbase for a lateral travel in the case where an offset of load wheels is not provided; Fig. 7 is a plan view illustrating a wheelbase for a lateral travel in the case where an offset of load wheels is provided; Fig. 8 is a front view of the left load wheel; Fig. 9 is a perspective view of a straddle arm; Fig. 10 is a side elevation view of the straddle arm; Fig. 11 is a side elevation view of the straddle arm; Fig. 12 is a diagram illustrating a conventional multi-directional vehicle; and Fig. 13 is a diagram illustrating a conventional multi-directional vehicle. Embodiments of the invention will be described with reference to the attached drawings. First, a reach forklift according to one embodiment of the invention will be described with reference to Figs. 1 to 5. Fig. 2 is a sectional view taken along the line A-A shown in Fig. 4. According to the invention, in a reach forklift having left and right load wheels which can be steered, the width of left and right straddle arms housing these load wheels can be reduced. As shown in Fig. 1, a reach forklift (hereinafter, referred to as "forklift") 1 comprises a body 2, left and right straddle arms 10L and 10R protruding from the body 2, and load wheels 12L and 12R respectively supported by the straddle arms 10L and 10R in such a manner that they can be steered. The body 2 has a drive wheel 11 which can be steered by a steering wheel 6. Between the straddle arms 10L and 10R, mounted is a carriage 36 which can be slid back and forth by a reach cylinder 38. On the carriage 36, a mast 3 is mounted. Load-carrying means 4 such as a fork or one of various other attachments is engaged with the mast 3 so that the loadcarrying means 4 can be moved up and down by a lift cylinder 5. To the carriage 36, rollers 24A and 24B are attached in such a manner that they can roll along a rail formed on the inner side wall of the straddle arm 10L. Reference numeral 7 designates a loading operation lever for operating the load-carrying means 4, 8 designates a driving operation lever for instructing the acceleration of the drive wheel, and 9 designates a battery. Next, the mechanism of the load wheels will be described in detail. The left load wheel 12L is attached to a wheel 15 which is rotatably supported on a supporting shaft 14 by means of bearings. The supporting shaft 14 is welded to a vertical downward portion 13a of a bracket 13 which is approximately L-shaped in its front view. The outer side walls of the vertical portion 13a and straddle arm 10L are substantially on the same vertical plane. On a horizontal portion 13b of the bracket 13, an upwardly-protruding steering shaft 16 is rotatably supported by a pair of tapered roller bearings 21. The tapered roller bearings 21 are so disposed that their rear sides face each other. Thus, they can support a moment load generated in the steering shaft 16. The steering shaft 16 is located as close to the outer side of the body of the forklift as possible. To the inner end of the horizontal portion 13b of the bracket 13, a sector gear 20 is secured by means of a bolt 23. The sector gear 20 engages with a pinion 19 into which a shaft 17 is fitted. Since the gear 20 has the shape of a sector of a circle, a sufficient reduction gear ratio can be obtained and the width of the straddle arm 10L can be made small. The sector gear 20 has an arc portion corresponding to an angle of about 230 degrees, and allows the load wheel 12L to turn toward the left and right each at an angle of about 115 degrees. The horizontal portion 13b of the bracket 13 is not in contact with the straddle arm 10L, so that the entire load imposed on the steering shaft 16 is applied to the tapered roller bearings 21. The shaft 17 and the steering shaft 16 are juxtaposed, and the shaft 17 is rotatably supported by a boss 22. A timing pulley 18 is fixed to the upper end portion of the shaft 17. As seen from Fig. 3, a steering motor 34L is securely mounted inside the straddle arm 10L so as to rotate a drive shaft 29 via a pinion 33 attached to the shaft of the motor, a single reduction gear 31, an idle gear 32 attached to the shaft of the single reduction gear 31, and a double reduction gear 30. These gears are housed in a gear case 39 filled with gear oil. Furthermore, to the upper end of the drive shaft 29, attached is a timing pulley 25 which is smaller in diameter than the timing pulley 18 attached to the shaft 17. A timing belt 35 is wound around both the timing pulleys 18 and 25, so that the torque of the steering motor 34L is reduced by the gears and transmitted to the timing pulley 18 of the shaft 17, thereby enabling the load wheel 12L to be steered. The reference numeral 28 in Figs. 3 and 4 designates an encoder. The end of a detection shaft of the encoder 28 is provided with a gear 27 which engages with a gear 26 fixed to the drive shaft 29 so that the steering angle of the load wheel 12L can be detected. The above-described components such as the steering motor 34L, timing pulleys 18 and 25, and steering shaft 16 are all housed in the straddle arm 10L. The configuration of the right load wheel is substantially the same as that of the left load wheel described above. That is, the left and right load wheels are so constructed as to be symmetric with respect to the center line of the body of the forklift 1. When the steering motor 34L is so driven as to rotate the timing belt 35 in the direction shown in Fig. 5, therefore, the torque of the steering motor 34L is transmitted through the driving gear 19 to the sector gear 20. This results in that the bracket 13 on which the load wheel 12L is rotatably supported can turn about its steering axis. This steering axis of the bracket 13 is the axis of the steering shaft 16. Fig. 5 shows the load wheel 12L in the state of its maximum steering angle. When this state of the load wheel 12L is detected by the encoder 28, the steering motor 34L may be stopped. Alternatively, other devices such as a mechanical stopper may be provided in order to limit the steering angle. It is needless to say that, when the steering motor 34L is driven to rotate in the direction opposite to that shown in Fig. 5, the load wheel 12L is also turned in the opposite direction. Furthermore, as seen from Fig. 2, the center line of the load wheel 12L is displaced from the turning center of the steering shaft 16 by a distance s which is a so-called king pin offset. This offset is extremely important for the following reasons: In the case where the forklift travels in a lateral direction without changing the direction of the body as shown in Figs. 6 and 7, if the steering center coincides with the center line of the load wheel 12L, the wheelbase is L, and, in contrast, if the offset distance s is provided as described above, it is possible to obtain a longer wheelbase of L + 2s. Moreover, when the load wheels are steered with the forklift 1 kept stationary, i.e., in the case of so-called stationary swing, the provision of the offset reduces the friction between the load wheel and the ground, so that the load wheel can easily roll toward a desired direction, resulting in a reduction in the steering torque. Furthermore, even when the load wheel 12L is turned by an angle of 90 degrees from the position shown in Fig. 2, the steering of the load wheel 12L can be ensured because a clearance r is provided between the load wheel 12L and the side wall of the rail 40 of the straddle arm 10L. Next, a forklift according to another embodiment of the invention will be described with reference to Figs. 8 to 11. In Figs. 8 to 11, the components identical with those of the above-described embodiment are designated by the same reference numerals, and their detailed description is omitted. According to this invention, the width of the straddle arms can be further reduced as compared with the above-described invention. As shown in Fig. 9, in this embodiment, upper and lower grooves 38 and 39 are formed on one side wall of the straddle arm 10L which side wall faces the center of the body of the forklift. The structure of the grooves 38 and 39 will be described. To the inner wall of the straddle arm 10L, an inner plate 44 is welded. An upper rail 45 and a middle rail 46 are fixed to the upper and lower ends of the inner plate 44, thereby constituting the upper groove 38. In this embodiment, the upper rail 45 does not extend to the front end of the straddle arm 40. However, this configuration of the upper rail 45 should not be construed as restricting the scope of the invention. To the lower end of the inner plate 44, welded is a lower plate 49 provided with a lower rail 47 so as to have a substantially "L"-shaped section. The middle rail 46 and the lower rail 47 constitute the lower groove 39. In order to prevent wear of the rails, liners 48 are attached to the sliding faces of the rails. The front end of the lower plate 49 is positioned behind that of the upper plate 44 to form a space 50, so that the lower plate 49 does not interfere with the load wheel 12L under steering. Therefore, even when the load wheel 12L turns toward the inside of the truck body as shown by the two-dot chain line in Fig. 8, the rails will not interfere with the load wheel 12L. In this manner, as shown in Fig. 8, the width W2 of the straddle arm 40 can be made smaller as compared with the above-described embodiment. Next, the carriage 36 supporting the mast 3 thereon will be described with reference to Figs. 10 and 11. On both the side walls of the carriage 36, a front roller 42 and rear roller 43 are rotatably supported. Each of the front rollers 42 is supported on the upper portion of the carriage 36 so that it rolls along the upper groove 38. Each of the rear rollers 43 is supported on the lower portion of the carriage 36 so that it rolls along the lower groove 39. Fig. 10 shows the state where the mast 3 has been retracted toward the body 2, or a so-called reach-in state, and Fig. 11 shows the state where the mast 3 has been moved forward toward the load wheel 12L, or a so-called reach-out state. Thus, although the front end of the lower groove 39 is positioned behind that of the upper groove 38, the essential operations of a reach forklift, i.e., the reach-in and reach-out operations can be ensured. The reason why the upper rail 45 does not extend to the front end of the straddle arm 40 is as follows: As shown in Fig. 11, the weight of a load imposed on the mast 3 applies a downward force to the front roller 42 and an upward force to the rear roller 43. Accordingly, it is not necessary to provide a rail on the upper side of the front end portion of the upper plate 44.

Claims: A reach forklift comprising: a forklift body (2); left and right straddle arms (10L, 10R); a pair of load wheels (12L, 12R) provided in the vicinity of the front ends of said left and right straddle arms, respectively; a drive wheel (11) disposed in a rear portion of said forklift body (2); a steering wheel (6) for steering said drive wheel (11); characterised by said pair of load wheels (12L, 12R) being mounted in a steerable manner in said straddle arms (10L, 10R); steering means (17, 18, 25-33, 34L, 34R. 35) for steering said load wheels (12L, 12R), said steering means being housed in said straddle arms (10L, 10R); steering angle detection means (28) for detecting steering angles of said left and right load wheels (12L, 12R) and said drive wheel (11); each of said left and right straddle arms (10L, 10R) comprising: a bracket (13) which rotatably supports a steering shaft (16), the centre of said steering shaft being positioned at an outer position in the width direction of said forklift body (2), said bracket (13) being fixed to a lower end of said steering shaft (16) to support said load wheels (12L 12R) at an outer position of said forklift body (2), and rotatably supporting the centre of said load wheel in the width direction of said load wheel, said centre of said load wheel being separated from said centre of said steering shaft (16) by a predetermined distance; a gear (20) which is fixed to said bracket and formed into a sector shape, the arc portion of said sector gear being directed to the centre of said forklift (11); and a driving gear (19) which engages with said sector gear (20) and is driven by said driving means (17, 18, 25-33,34L, 34R, 35), said driving gear being positioned in the side of the centre of said forklift. A reach forklift according to claim 1, wherein upper and lower grooves (38, 39) are formed inside each of said left and right straddle arms (10L, 10R), the front end of said lower groove is positioned behind that of said upper groove in a range where said lower groove does not interfere with the steering of each of said load wheels, a front roller (42) rolls in said upper groove, and a rear roller (43) rolls in said lower groove, said front and rear rollers being rotatably attached to a carriage for supporting a mast (3) which can move back and forth. A reach forklift according to claim 1 or 2, wherein said steering means for each of said load wheels (12L, 12R) comprises: a shaft (17) provided to support said driving gear (19); a first pulley (18) fixed to said shaft (17); a steering motor (34L, 34R) mounted inside said straddle arms (10L, 10R), said steering motor being adapted to rotate a drive shaft (29) through a plurality of gears (33, 31, 32, 30); a second pulley (25) fixed to said drive shaft (29); and a belt (35) connecting said first pulley (18) to said second pulley (25), such that torque generated by said steering motor (34L, 35R) is reduced by the plurality of gears (33, 31, 32, 30) and transmitted to the load wheels (12L, 12R) from said gears through said drive shaft (29), said second pulley (25), said belt (35), said first pulley (18), said shaft (17), said driving gear (19), said gear (20) and said bracket (13) in order to turn said load wheels (12L, 12R).

Inventors: HIROOKA SHIGERU, KATANAYA IKUYA, ORITA KOJI, TANAKA SHINOBU, HIROOKA, SHIGERU, KATANAYA, IKUYA, ORITA, KOJI, TANAKA, SHINOBU
Applicants: NIPPON YUSOKI CO LTD, NIPPON YUSOKI CO.,LTD
Application year: 1993
Main classification: B66F9
IPC codes: B66F9, B62D7