EP0712805B1 - Chariot élévateur à longue portée - Google Patents

Chariot élévateur à longue portée Download PDF

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Publication number
EP0712805B1
EP0712805B1 EP95119390A EP95119390A EP0712805B1 EP 0712805 B1 EP0712805 B1 EP 0712805B1 EP 95119390 A EP95119390 A EP 95119390A EP 95119390 A EP95119390 A EP 95119390A EP 0712805 B1 EP0712805 B1 EP 0712805B1
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EP
European Patent Office
Prior art keywords
steering
angle
drive wheel
wheel
forklift
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP95119390A
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German (de)
English (en)
Other versions
EP0712805A2 (fr
EP0712805A3 (fr
Inventor
Shigeru Hirooka
Ikuya Katanaya
Koji Orita
Shinobu Tanaka
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nippon Yusoki Co Ltd
Original Assignee
Nippon Yusoki Co Ltd
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Priority claimed from EP93108095A external-priority patent/EP0625478B1/fr
Priority to US08/063,189 priority Critical patent/US5325935A/en
Priority to EP93108095A priority patent/EP0625478B1/fr
Priority to DE1993629156 priority patent/DE69329156T2/de
Priority to EP95119390A priority patent/EP0712805B1/fr
Application filed by Nippon Yusoki Co Ltd filed Critical Nippon Yusoki Co Ltd
Publication of EP0712805A2 publication Critical patent/EP0712805A2/fr
Publication of EP0712805A3 publication Critical patent/EP0712805A3/xx
Publication of EP0712805B1 publication Critical patent/EP0712805B1/fr
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B66—HOISTING; LIFTING; HAULING
    • B66F—HOISTING, LIFTING, HAULING OR PUSHING, NOT OTHERWISE PROVIDED FOR, e.g. DEVICES WHICH APPLY A LIFTING OR PUSHING FORCE DIRECTLY TO THE SURFACE OF A LOAD
    • B66F9/00—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes
    • B66F9/06—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes movable, with their loads, on wheels or the like, e.g. fork-lift trucks
    • B66F9/075—Constructional features or details
    • B66F9/08—Masts; Guides; Chains
    • B66F9/10—Masts; Guides; Chains movable in a horizontal direction relative to truck
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B66—HOISTING; LIFTING; HAULING
    • B66F—HOISTING, LIFTING, HAULING OR PUSHING, NOT OTHERWISE PROVIDED FOR, e.g. DEVICES WHICH APPLY A LIFTING OR PUSHING FORCE DIRECTLY TO THE SURFACE OF A LOAD
    • B66F9/00—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes
    • B66F9/06—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes movable, with their loads, on wheels or the like, e.g. fork-lift trucks
    • B66F9/075—Constructional features or details
    • B66F9/07568—Steering arrangements

Definitions

  • This invention relates to a reach forklift, 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.
  • a multi-directional vehicle shown in Figs. 57 and 58 is proposed.
  • Such a vehicle is known for example from JP-A- 57 121 599.
  • 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.
  • a steered and driving wheel 1 is turned toward a desired direction, so that Ackerman steering can be effected.
  • 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.
  • the vehicle a 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.
  • 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).
  • 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.
  • the invention has been conducted in view of the above-mentioned problems, and has an object of providing a reach forklift which can be operated based on the driverbility of an ordinary reach forklift and in which the steering of load wheels supported by straddle arms can be realized without increasing the width of the straddle arms or with an extremely reduced width of the straddle arms.
  • Another object of the invention is to provide a reach forklift in which the steering of left and right load wheels can be controlled in such a manner that the forklift can smoothly turn in accordance with the theory of Ackerman-Jeantaud and also can make a small turn, thereby improving the efficiency of cargo work.
  • a further object of the invention is to provide a reach forklift which allows its travel direction to be freely changed, and which can change the attitude angle with respect to the changed directions and travel with an extremely high degree of freedom, thereby improving the efficiency of cargo work.
  • Fig. 2 is a sectional view taken along the line A-A shown in Fig. 4.
  • the width of left and right straddle arms housing these load wheels can be reduced.
  • 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.
  • a carriage 36 which can be slid back and forth by a reach cylinder 38.
  • a mast 3 is mounted on the carriage 36.
  • Load-carrying means 4 such as a fork or one of various other attachments is engaged with the mast 3 so that the load-carrying means 4 can be moved up and down by a lift cylinder 5.
  • 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
  • 9 designates a battery.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • Fig. 5 shows the load wheel 12L in the state of its maximum steering angle.
  • the steering motor 34L may be stopped.
  • 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.
  • 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.
  • 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.
  • 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.
  • a forklift according to another embodiment of the invention will be described with reference to 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.
  • the width of the straddle arms can be further reduced as compared with the above-described invention.
  • 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.
  • an inner plate 44 is welded to the inner wall of the straddle arm 10L.
  • 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.
  • the upper rail 45 does not extend to the front end of the straddle arm 40.
  • this configuration of the upper rail 45 should not be construed as restricting the scope of the invention.
  • a lower plate 49 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.
  • 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.
  • a front roller 42 and rear roller 43 are rotatably supported on both the side walls of the carriage 36.
  • 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
  • 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.
  • 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.
  • This invention has been accomplished with objects of: enabling a natural steering operation of a reach forklift with steerable left and right load wheels; achieving a steering control which enables the forklift to make a small turn in response to the operation of its steering wheel; and fully satisfying the theory of Ackerman-Jeantaud to maintain a smooth steering operation.
  • Fig. 12 illustrates an example of the configuration of a reach forklift with steerable left and right load wheels (hereinafter, referred to as "forklift") of this embodiment.
  • the forklift 101 comprises a body 102, left and right straddle arms 120 protruding from the body 102, and load wheels 106 and 105 respectively supported by the left and right straddle arms 120 in such a manner that they can be steered.
  • the body 102 has a drive wheel 104 which can be steered by a steering wheel 103.
  • the drive wheel 104 is mounted on the body 102, or more specifically, supported on a rotary gear 117 which is rotatable and mechanically linked to the steering wheel 103.
  • the rotary gear 117 is provided with a potentiometer 118 which can detect the degree of rotation of the rotary gear 117 by measuring a voltage corresponding to the rotation degree. On the basis of the thus detected degree of rotation, the steering angle of the drive wheel 104 can be determined.
  • a caster wheel (not shown) is provided in the side of the drive wheel 104, in order to ensure the travel stability.
  • load- carrying means 107 which can slide back and forth and can be vertically moved by a lift cylinder (not shown).
  • the drive wheel 104 can be steered by the steering wheel 103 in the following manner: As shown in Fig. 13, steering torque applied to the steering wheel 103 is transmitted from a sprocket 305 to another sprocket 307 through a chain 306, and further transmitted through an input shaft 308 fixed to the sprocket 307, a steering torque detection device 309, an output shaft 310, a universal joint 311 and a drive shaft 314, to a driving gear 315, thereby rotating the rotary gear 117.
  • a rotary gear case 317 on which the drive wheel 104 is rotatably supported is fixed to the rotary gear 117.
  • the steering torque detection device 309 electrically detects the relative torsion between the input shaft 308 and the output shaft 310 to generate a steering torque signal.
  • the power steering motor 312 is driven to provide assist torque to the drive shaft 314 through a gear case 313 containing a reduction gear mechanism. In this manner, the steering torque is reduced.
  • a detection gear 319 of a steering angle detection device 118 comprising a potentiometer and the like engages with the rotary gear 117, so that the steering angle of the drive wheel 104 can be detected.
  • the drive wheel 104 is further provided with a well-known brake device which is not shown.
  • the brake device is a so-called deadman brake which is released when a brake pedal 222 provided in an operator cab 221 is pressed down and which is actuated when the operator's foot is removed from the brake pedal 222.
  • the brake pedal 222 is provided with a limit switch 223 which functions as brake operation detecting means for detecting the pressing state of the brake pedal 222. The function of the limit switch will be described later.
  • the steerable load wheels 105 and 106 are respectively supported on rotary brackets 108 and 109 in such a manner that they can be turned with respect to the straddle arms 120.
  • steering motors 111 and 112 are respectively linked by transmission means 110 such as chains, belts or the like.
  • transmission means 110 such as chains, belts or the like.
  • the left and right load wheels 105 and 106 can be turned about steering centers L and R, respectively.
  • the centers L and R of the load wheels 105 and 106 serve as their respective steering centers.
  • the steering centers may be located at other positions so that a so-called king pin offset of a predetermined length is provided as described above.
  • Potentiometers 113 and 114 are respectively attached to the output shafts of the steering motors 111 and 112 to detect their degree of rotation, so that the steering angles of the load wheels 105 and 106 can be determined.
  • the body 102 is provided with a control device 116, a travel mode select switch (hereinafter, referred to as "select switch") 400, and a travel angle input device 215.
  • the travel angle input device 215 comprises a rotary-type potentiometer or the like, and is preferably located in the vicinity of the operator cab 221 so that the operator can set a desired travel angle. The operator can arbitrarily select one of plural travel modes through the select switch 400.
  • the travel angle input device 215 has an arrow marked on the operation panel.
  • the arrow indicates the travel direction so that the operator can easily recognize the current travel direction of the forklift 101. This will be described in detail later.
  • the control device 116 comprises, as shown in Fig. 14, a master control section 116A and a steering control section 116B which are connected in such a manner that they can communicate with each other.
  • the master control section 116A comprises an A/D converter 130, a ROM1 131 for storing programs or the like, a RAM1 132 serving as a working storage, a master CPU 133 which is a microprocessor, and a serial I/O port (SIO) 134 for performing a serial transmission with the steering control section 116B.
  • A/D converter 130 for storing programs or the like
  • RAM1 132 serving as a working storage
  • a master CPU 133 which is a microprocessor
  • SIO serial I/O port
  • the A/D converter 130 receives a travel angle signal ⁇ O from the travel angle input device 215 and converts it into digital data.
  • the master CPU receives through its I/O port a brake detection signal B K from the limit switch 223 functioning as brake operation detecting means, and also travel mode signals md1 to md5 from the select switch 400.
  • the SIO 134 receives a steering angle signal ⁇ D of the drive wheel 104 from the steering control section 116B, and sends target steering angle signals ⁇ L and ⁇ R for the left and right load wheels and left and right steering end signals ⁇ DL and ⁇ DR , to the steering control section 116B.
  • the target steering angle signals ⁇ L and ⁇ R are calculated by the master CPU 133 on the basis of the steering angle signal ⁇ D , the travel mode signals md1 to md5 from the select switch 400, the brake detection signal B K , and the travel angle signal ⁇ O .
  • the steering control section 116B includes an A/D converter 136, a ROM2 137, a RAM2 138, a slave CPU 139, an SIO 140, D/A converters 141 to 143, and logic circuits 144 to 146.
  • the A/D converter 136 receives a steering angle signal ⁇ D of the drive wheel from the potentiometer 118, actual steering angle signals ⁇ R ' and ⁇ L ' of the left and right load wheels respectively from the potentiometers 114 and 113, and a steering torque signal T from the steering torque detection device 309.
  • the SIO 140 sends the steering angle signal ⁇ D to the master control section 116A, and receives the target steering angle signals ⁇ L and ⁇ R for the left and right load wheels which are calculated by the master CPU 133 on the basis of the steering angle signal ⁇ D , and also receives the left and right steering end signals ⁇ DL and ⁇ DR .
  • the slave CPU 139 Based on the signals sent from the master control section 116A, the slave CPU 139 performs a well-known feedback control to control the power steering motor 312 and the steering motors 112 and 111 for the left and right load wheels so as to achieve the target values.
  • the slave CPU 139 sends control signals through its I/O to the logic circuits 144, 145 and 146 which respectively control the steering motors so that they are, for example, rotated in a normal or reverse direction, or forced to be locked.
  • the process of the master CPU 133 will be described by illustrating each STEP with reference to the flowchart of Fig. 15.
  • the RAM1 132 and hardware components such as the I/0 devices are initialized (STEPs 1 and 2), and a travel mode signal is input (STEP 3).
  • the master CPU 133 receives a steering angle signal ⁇ D of the drive wheel from the steering control section 116B (STEP 4).
  • branching is effected so that the process proceeds to one of the branch procedures (STEP 5).
  • a program corresponding to the selected travel mode is read out from the above-mentioned ROM1 131, and target steering angles ⁇ L and ⁇ R for the left and right load wheels and the like based on the travel mode signal md1, md2, md3, md4 or md5 are calculated (STEPs 6 to 19), and then sent to the steering control section 116B (STEP 20).
  • the procedures for travel modes 1 to 5 will be described below in that order.
  • the process for travel mode 1 is effected when the travel mode signal md1 is selected through the select switch 400 (STEP 7).
  • first, variable steering end signals ⁇ DL and ⁇ DR are sent to the steering control section 116B (STEP 6).
  • the reason of this is as follows: According to the invention, a desired travel mode can be selected from a plurality of travel modes, and therefore the positions of the steering ends which define the range of the steering angle of the drive wheel are required to be changed depending on the selected travel mode. This process will be specifically described later in the description of the operation of the slave CPU 139.
  • the calculation procedure for travel mode 1 is programmed in the form of a subroutine. In this travel mode, the forklift can make extremely small turns. The procedure is shown in Fig. 16.
  • the steering angles ⁇ L and ⁇ R of the left and right load wheels 105 and 106 are angles formed by an axis G and an extension line H L , and by the axis G and an extension line H R , respectively.
  • the axis G passes both the steering centers L and R of the left and right load wheels 105 and 106.
  • the extension lines H L and H R are virtual lines respectively elongating from the rotation axes of the left and right load wheels (hereinafter, these lines are referred to as "extension lines H L and H R ").
  • the steering angle ⁇ D of the drive wheel is an angle formed by an extension line H F of the rotation axis of the drive wheel 104 (hereinafter, referred to as "extension line H F ”) and an axis which is perpendicular to the center line of the forklift in a plan view. It is supposed that these steering angles are positive in the counterclockwise direction. Hence, when the steering angle ⁇ D of the drive wheel is positive, the forklift 101 turns toward the right. When it is negative, the forklift 101 turns toward the left.
  • the master CPU 133 checks the steering angle ⁇ D of the drive wheel to judge whether it is zero or not, or whether the forklift travels straight or makes a turn (STEP 100). When the steering angle ⁇ D is zero (Yes in STEP 100), the target steering angles ⁇ L and ⁇ R for the left and right load wheels are both set to zero (STEPS 101 and 102). Then, the process returns to the main routine.
  • the steering control section 116B carries out a feedback control so that the steering angles ⁇ L and ⁇ R of the left and right load wheels are zero, i.e., coincide with their target value.
  • the required direction is detected (STEP 103).
  • the target steering angle ⁇ R for the right load wheel is determined by multiplying the steering angle ⁇ D of the drive wheel by a predetermined steering angle gain G R .
  • the target steering angle ⁇ L for the left load wheel is determined by multiplying the steering angle ⁇ D of the drive wheel by a predetermined steering angle gain G L (STEP 106).
  • the steering angle ⁇ D of the drive wheel 104 is always kept proportional to the target steering angle ⁇ L or ⁇ R for the left or right load wheel.
  • the constant of this proportion is referred to as a steering angle gain.
  • the steering angle gain can be determined depending on the size and use of a forklift, the environment where it is used, etc. In this embodiment, a few preferred examples of the steering angle gain will be described below.
  • a minimum turning center S about which the forklift 101 carrying a load thereon can turn with its minimum turning radius is previously set.
  • a steering angle ⁇ DR of the drive wheel is so determined that the extension line H F of the drive wheel passes the minimum turning center S
  • a steering angle ⁇ RE of the right load wheel is so determined that the extension line H R of the right load wheel passes the minimum turning center S.
  • the steering angle gain is determined on the basis of the ratio of the steering angle ⁇ RE to the steering angle ⁇ DR .
  • a steering angle ⁇ DL of the drive wheel is so determined that the extension line HF of the drive wheel passes the minimum turning center S
  • a steering angle ⁇ LE of the left load wheel is so determined that the extension line H L of the left load wheel passes the minimum turning center S.
  • the steering angle gain is determined.
  • the minimum turning center S is designated as the origin of an x-y rectangular coordinate system
  • the steering centers L and R of the left and right load wheels 105 and 106 are represented by (x L , y L ) and (x R , y R ), respectively
  • the steering center D of the drive wheel is represented by (x D , y D ).
  • the steering angle gain GR for the right load wheel can be obtained by Ex. 1 below
  • the steering angle gain G L for the left load wheel can be obtained by Ex. 2 below.
  • G R tan -1 (y R /x R ) tan -1 (y D /x D )
  • G L tan -1 (y L /x L ) tan -1 (y D /x D ) - ⁇
  • a turning center P (x P , y P ) of the forklift is calculated on the basis of the geometric relationship between the steering angle ⁇ D of the drive wheel and the target steering angle ⁇ R for the right load wheel which has been obtained by multiplying the steering angle ⁇ D by the steering angle gain G R .
  • a target steering angle ⁇ L for the left load wheel is determined through calculation so that the extension line H L of the left load wheel can pass the thus calculated turning center P (STEP 105).
  • the turning center P of the forklift can be given by obtaining the intersection of the extension line H F of the drive wheel and the extension line H R of the right load wheel.
  • the extension -line H F of the drive wheel and the extension line H R of the right load wheel can be expressed by the linear equations of Exs. 3 and 4, respectively.
  • y tan ⁇ D x + y D - x D tan ⁇ D
  • y tan ⁇ R x + y R - x R tan ⁇ R
  • the target steering angle ⁇ L for the left load wheel is so determined that the extension line H L of the left load wheel can pass the turning center P.
  • the forklift 101 is kept to perform an extremely smooth turning operation while fully satisfying the theory of Ackerman-Jeantaud.
  • the turning center P (x P , y P ) of the forklift is calculated on the basis of the geometric relationship between the steering angle ⁇ D of the drive wheel and the target steering angle ⁇ L for the left load wheel which has been obtained by multiplying the steering angle ⁇ D by the steering angle gain G L .
  • the target steering angle ⁇ R for the right load wheel 106 is so determined that the extension line H R of the right load wheel can pass the turning center P.
  • the steering angles of the left and right load wheels 105 and 106 with respect to that of the drive wheel 104 are calculated by the above-described procedure. The results are shown in the angle diagram of Fig. 29. The locus of the turning center P of the forklift 101 is shown in Fig. 30.
  • the steering angle gains G R and G L obtained by the above- described procedure are approximately +0.57 and about +0.36, respectively.
  • the target steering angle ⁇ R for the right load wheel can be linearly changed in proportion to the steering angle ⁇ D of the drive wheel 104, thereby achieving an extremely stable and excellent steering control.
  • the turning center P coincides with the steering center R of the right load wheel 106.
  • the phases of both the left and right load wheels 105 and 106 start to be reversed.
  • the turning center P can be continuously changed eventually to the above-described minimum turning center S, in accordance with the steering angle of the drive wheel 104 provided by operating the steering wheel. This means that the forklift 101 is turned with an extremely small turning radius R2.
  • the ratio of the minimum turning radius R2 of the forklift 101 of the invention to a minimum turning radius R1 of a conventional forklift is approximately 0.7 in the case where the forklifts are of the size shown in this example.
  • the ratio of the area occupied by the forklift 101 of the invention to that occupied by the conventional forklift is approximately 0.5 in the case where the forklifts turn with their bodies kept at their respective positions. In this manner, according to the invention, the minimum turning radius and the occupied area of the forklift can be significantly reduced.
  • Fig. 31 shows the forklift 101 which is turning with its minimum turning radius.
  • the steering angles ⁇ DR and ⁇ DL of the drive wheel 104 respectively shown in Figs. 24 and 25 are the angles for the left and right steering ends.
  • the drive wheel 104 is so controlled that it cannot be turned beyond the steering ends. This will be described later.
  • the minimum turning center S R about which the forklift turns toward the right is displaced from the steering center R of the right load wheel by 300 mm in the vertically downward direction (as viewed in the figure).
  • the steering angle gain G R is determined.
  • the minimum turning center S L is displaced from the steering center L of the left load wheel by 300 mm in the vertically under direction (as viewed in the figure).
  • the steering angle gain G L is determined.
  • the steering angle gains G R and G L are approximately -1.79 and -1.19, respectively, when calculated by Exs. 1 and 2 above using the above specific values.
  • the turning center follows a locus designated by P R as the forklift turns to the right, while it follows a locus designated by P L as the forklift turns to the left.
  • P R the forklift turns to the right
  • P L a locus designated by P L
  • the, turning center can be continuously changed in either direction while being kept below (as viewed in the figure) the axis G passing the steering centers L and R of the left and right load wheels.
  • the left and right load wheels 105 and 106 are steered with a phase opposite to that of the drive wheel 104, so that the forklift can make a small turn.
  • the left and right load wheels 105 and 106 are controlled with the same phase.
  • angles ⁇ DL and ⁇ DR shown in Fig. 32 are the angles for the left and right steering ends, respectively, which define the range of the steering angles of the drive wheel.
  • travel mode 2 will be described with reference to the flowchart of Fig. 17.
  • a travel mode signal md2 is selected by the select switch 400, the process for travel mode 2 is effected (STEP 9).
  • This mode is characterized in that, only when the steering angle ⁇ D is within a certain range, it is multiplied by the above-mentioned steering angle gain and the steering control of the left and right load wheels 105 and 106 is performed using thus obtained value.
  • the above mentioned range of angles is set to a range K where the extension line H F of the drive wheel can exist on or between the steering centers L and R of the left and right load wheels.
  • the steering angle ⁇ D of the drive wheel 104 is multiplied by the steering angle gain when it is ⁇ GR or more.
  • the steering angle ⁇ D is multiplied by the steering angle gain when it is ⁇ GL or less ( ⁇ GL or more in terms of absolute value).
  • Fig. 17 is a flowchart composed of the flowchart for the above-described travel mode 1 (shown in Fig. 16) and additional STEPs 200 and 201.
  • the target steering angles for the left and right load wheels 105 and 106 are set to zero in the same manner as in travel mode 1.
  • the steering angle ⁇ D of the drive wheel 104 becomes outside an arbitrarily determined range of angles, the left and right load wheels 105 and 106 are so steered that the forklift can make a small turn.
  • the steering angle gains are obtained by setting the minimum turning center S to the same point as that of the first example presented for travel mode 1.
  • the target steering angles ⁇ L and ⁇ R for the left and right load wheels 105 and 106 obtained in this example with respect to the steering angle ⁇ D of the drive wheel 104 are shown in the angle diagram of Fig. 36.
  • the locus of the turning center P obtained in this example is shown in Fig. 37.
  • the right load wheel 106 can be linearly controlled, and the left load wheel 105 can also be controlled in an approximately linear manner. This means that the rates of change in the steering angles of the left and right load wheels 105 and 106 are always kept constant. This enables the steering of both the left and right load wheels 105 and 106 to be controlled in an extremely stable manner. In the leftward turning of the drive wheel 104, the same effect can also be attained.
  • the steering ends of the drive wheel 104 are determined in the same manner as in the first example presented for travel mode 1.
  • the invention should not be construed as being limited by the above embodiments. Particularly, according to the invention, it is possible to use a variety of steering angle gains depending on the user's demands and the like. It is needless to say that the range of the steering angles of the drive wheel in which they are to be multiplied by the steering angle gains may be set in various manners within the scope of the invention.
  • the process for travel mode 3 is effected when the travel mode signal md3 is selected through the select switch 400 (STEP 10).
  • this travel mode the forklift can make a small turn even when the steering angle of the drive wheel is relatively small.
  • the basic concept for this mode is the same as those for travel modes 1 and 2, but a technological concept is introduced into this travel mode, that is, the wheelbase is made shorter in order to allow the forklift to make a small turn even when the steering angle of the drive wheel is in the range of relatively small angles.
  • ROM1 131 As shown in Fig. 38, functional data on the target steering angles ⁇ R for the right load wheel 106 are stored when the steering angles ⁇ D of the drive wheel is positive, and functional data on the target steering angles ⁇ L for the left load wheel 105 are stored when the steering angles ⁇ D of the drive wheel 104 is negative.
  • Fig. 39 shows the locus of the turning center P of the forklift 101.
  • the locus passes through at least the above-mentioned minimum turning center S and the steering centers L and R of the left and right load wheels.
  • the locus further extends outward from the steering center R of the right load wheel and from the steering center L of the left load wheel, while gradually approaching an arbitrary straight line K elongating along the width direction of the forklift 101 toward the outside thereof.
  • the locus is an ideal one which is set by smoothly connecting these points.
  • the straight line K functions as a reference axis which is used in the case where the steering angle ⁇ D of the drive wheel 104 is relatively small, and can be regarded as a reference for a virtual wheelbase. While the straight line K passes the minimum turning center S in this embodiment, this is not intended to limit the scope of the invention.
  • the target steering angles ⁇ L and ⁇ R for the left and right load wheels are determined as follows:
  • the steering angle ⁇ D of the drive wheel 104 is gradually changed by a minute increment, and at each of the different steering angles ⁇ D of the drive wheel, the intersection Pn of the locus P of the turning center and the extension line H F of the drive wheel 104 is obtained.
  • the target steering angle of the right or left load wheel is obtained as an angle obtained when the extension line H R or H L of the right or left load wheel passes the intersection Pn. This is illustrated in the angle diagram of Fig. 38.
  • the master CPU 133 checks the steering angle ⁇ D of the drive wheel to judge whether it is zero or not (STEP 300). When it is zero (Yes in STEP 300), the target steering angles ⁇ L and ⁇ R for the left and right load wheels are both set to zero (STEPs 301 and 302).
  • the turning center P is obtained through calculation in a geometrical manner from the steering angle ⁇ D of the drive wheel and the target steering angle ⁇ R for the right load wheel which has been read out from the ROM1 131.
  • the target steering angle ⁇ L for the left load wheel 105 is determined through calculation so that the extension line H L of the left load wheel can pass the calculated turning center P.
  • the target steering angle ⁇ L for the left load wheel corresponding to this steering angle ⁇ D is read out (STEP 306).
  • the turning center P is calculated, and then the target steering angle ⁇ R for the right load wheel 106 is determined through calculation so that the extension line H R of the right load wheel can pass the calculated turning center P.
  • the target steering angles ⁇ L and ⁇ R for the left and right load wheels with respect to the steering angle ⁇ D of the drive wheel obtained in this embodiment are shown in the angle diagram of Fig. 40.
  • the steering angle ⁇ D of the drive wheel is relatively small (in this example, approximately +57 degrees or less in the case of rightward steering, and approximately -78 degrees or more in the case of leftward steering)
  • the turning center is continuously changed while being kept below (as viewed in Fig. 39) the axis G passing the steering centers L and R of the left and right load wheels, thereby attaining excellent feeling of turning operation.
  • the turning radius is decreased by the length DR, so that the forklift of the invention can make small turns.
  • the steering ends of the drive wheel 104 are set in the same manner as in the first example for travel mode 1.
  • the process for travel mode 4 is effected when the travel mode signal md4 is selected through the select switch 400 (STEP 14).
  • the travel direction of the forklift can be changed freely without causing the body of the forklift to turn.
  • the attitude of the truck body can be changed with respect to the changed travel direction, thereby attaining an extremely high degree of extendibility.
  • the direction in which the forklift 101 travels is herein referred to as a travel direction.
  • the travel direction S serves as the reference direction for the steering of the forklift 101.
  • the operator usually faces toward the travel direction, and changes the attitude angle of the truck body with respect to the travel direction S by turning the steering wheel to the right or left from the neutral position.
  • the travel direction S is taken as the reference direction and the steering angle ⁇ D of the drive wheel is zero, the forklift 101 travels straight in the travel direction S.
  • a travel angle is the angle formed by the center line C and the travel direction S.
  • the travel direction S can be set to any direction by operating the travel angle input device 215.
  • the operator can steer the forklift 101 on the assumption that the center line C coincides with the arbitrarily determined travel direction. Therefore, the operator can steer the forklift by using, as the reference direction, the direction of the arrow indicated on the travel angle input device 215.
  • Fig. 41 shows the forklift 101 traveling while both the travel angle and steering angle ⁇ D of the drive wheel 104 are set to zero.
  • the steering angles of the left and right load wheels 105 and 106 are both set to zero.
  • the turning center P of the forklift is geometrically determined by the above-mentioned axis G and the steering angle ⁇ D of the drive wheel.
  • the forklift 101 is turning about this turning center (which is a point at infinity on the axis G in this case).
  • Fig. 42 shows the forklift 101 traveling with the travel angle set to ⁇ O in the counterclockwise direction by the travel direction input device 215, and with the steering angle of the drive wheel set to ⁇ D .
  • the target steering angle ⁇ L for the left load wheel 105 is made equal to the travel angle ⁇ O .
  • the intersection of the extension line H L of the left load wheel 105 and the extension line H F of the drive wheel 104 is obtained as the turning center P.
  • the right load wheel 106 is steered so that the extension line H R thereof can pass the above-mentioned turning center P.
  • Fig. 43 shows the forklift 101 traveling while the travel angle is set to ⁇ O in the counterclockwise direction by the travel direction input device 215, and the drive wheel is steered so that the steering angle ⁇ D thereof is made equal to the travel angle ⁇ O .
  • the target steering angle ⁇ L for the left load wheel 105 is made equal to the travel angle ⁇ O
  • the intersection of the extension line H L of the left load wheel 105 and the extension line H F of the drive wheel 104 is obtained as the turning center P.
  • the extension lines H L and H F are parallel to each other, so that the turning center P is a point at infinity on the extension line H L (or H F ).
  • the target steering angle ⁇ R for the right load wheel 106 is determined through calculation so that the extension line H R thereof passes the turning center P.
  • the extension line H R also is parallel to both the extension lines H L and H F , so that the forklift 101 travels diagonally along the travel direction S without causing its body to make a turn. This is because the steering angle ⁇ O of the drive wheel 104 becomes zero when the travel direction S is regarded as the reference direction for the steering of the forklift 101.
  • Fig. 44 shows the forklift 101 traveling while the travel angle ⁇ O is set to ⁇ /2 in the counterclockwise direction by the travel angle input device 215 and with the steering angle of the drive wheel is set to ⁇ D .
  • the target steering angle ⁇ L for the left load wheel 105 is set to ⁇ /2.
  • the intersection of the extension line H L of the left load wheel 105 and the extension line H F of the drive wheel 104 is obtained as the turning center P.
  • the steering of the right load wheel 106 is so controlled that the extension line H R thereof can pass the turning center P.
  • the actual wheelbase can be significantly decreased to the length L1, so that the forklift 101 can change its attitude in an extremely severe manner.
  • the travel angle is set to a negative angle, i.e., - ⁇ O .
  • the target steering angle ⁇ R for the right load wheel 106 is made equal to the travel angle - ⁇ O , and the intersection of the extension line H R of the right load wheel 106 and the extension line H F is obtained as the turning center P.
  • the left load wheel 105 is steered so that the extension line H L thereof can pass the turning center P.
  • the travel angle ⁇ O is - ⁇ /2.
  • the wheelbase is L2. This means that the wheelbase can be made slightly longer than that in the previous case shown in Fig. 42.
  • both the travel angle ⁇ O and the steering angle ⁇ D of the drive wheel 104 are - ⁇ /2.
  • an arbitrary travel direction S is provided so that the attitude of the body of the forklift 101 can be corrected using the travel direction S as the reference direction.
  • reference coordinate axes (which will be described later) are subjected to a coordinate transformation to be rotated by the travel angle ⁇ O (STEP 400). Then, when the travel angle is zero (Yes in STEP 401), both the target steering angles ⁇ L and ⁇ R for the left and right load wheels are set to zero (STEPs 402 and 403).
  • the master CPU 133 checks the travel angle ⁇ O to judge whether it is positive or not (STEP 404).
  • the target steering angle ⁇ L for the left load wheel is made equal to the travel angle ⁇ O (STEP 405), and then the target steering angle ⁇ R for the right load wheel is calculated (STEP 406).
  • the target steering angle ⁇ R for the right load wheel is made equal to the travel angle ⁇ O (STEP 407), and then the target steering angle ⁇ L for the left load wheel is calculated (STEP 408).
  • An arbitrarily determined representative point E on the center line of the forklift body is herein designated as the origin of an x-y rectangular coordinate system in which the y-axis coincides with the center line.
  • this x-y rectangular coordinate system it is supposed that the steering center L of the left load wheel 105 is indicated by (x L , y L ), the steering center R of the right load wheel 106 by (x R , y R ), and the steering center D of the drive wheel 104 by (x D , y D ).
  • the coordinates of the turning center P in the transformed X-Y coordinate system i.e., (Xp, Yp) are calculated.
  • the intersection of the extension line H L of the left load wheel and the extension line HF of the drive wheel 104 is obtained as the turning center P.
  • Fig. 49 shows the forklift 101 in which the travel angle is - ⁇ O (i.e., No in STEP 404 of the flowchart of Fig. 19) and the steering angle of the drive wheel 104 is + ⁇ D .
  • the target steering angle ⁇ L for the left load wheel 105 can be obtained by Ex. 23.
  • ⁇ L tan -1 (Y R - Y L )tan( ⁇ D - ⁇ O ) (X D - X L )tan( ⁇ D - ⁇ O ) + Y R - Y D + ⁇ O
  • the coordinates of the steering centers L, R and D of the load wheels 105 and 106 and drive wheel 104 i.e., (x L , y L ), (x R , y R ) and (x D , y D ), etc., are previously stored in the ROM1 131.
  • the origin E of the x-y rectangular coordinate system can be located at a point other than that shown in the above embodiment, and it can be located at various points, including those which are not on the center line of the truck body.
  • the process for travel mode 5 is effected when the travel mode signal md5 is selected through the select switch 400 (STEP 18).
  • travel mode 5 the advantages that the travel direction of the forklift can be changed freely, and that the attitude of the body of the forklift can be changed with respect to the changed travel directions can be attained in the same manner as travel mode 4, but the steering sense in travel mode 5 is somewhat different from that of travel mode 4.
  • the axis G is rotated about an arbitrarily determined representative point of the truck body by an angle input from the travel angle input device 215, and the intersection of the rotated axis G' and the extension line H F of the drive wheel is set as the turning center P.
  • the travel angle input device 215 the intersection of the rotated axis G' and the extension line H F of the drive wheel is set as the turning center P.
  • the center of a circle U which is tangent to the axis G and to axes J and W that respectively elongate from the steering centers L and R of the left and right load wheels 105 and 106 is set as the body representative point V.
  • Fig. 50 shows the initial state in which the steering angles of the left and right load wheels 105 and 106 and drive wheel 104 are zero and the travel angle of the forklift 101 also is zero. Under this state, the axis G is rotated by the travel angle about the body representative point V. Since the travel angle is zero in the embodiment, however, the axis G is not rotated.
  • the intersection of the axis G and the extension line H F of the drive wheel elongating from the steering center D of the drive wheel is set as the turning center P (not shown in Fig. 50).
  • the theoretical turning center P is a point at infinity on the axis G.
  • the extension lines H L and H R of the left and right load wheels are formed so as to pass the turning center P.
  • the steering is performed while setting the angles respectively formed by the axis G and the extension lines H L and H R as the target steering angles for the left and right load wheels 105 and 106. In this case, however, both the target steering angles ⁇ L and ⁇ R for the left and right load wheels 105 and 106 are zero.
  • both the left and right load wheels 105 and 106 are not steered so that the forklift is kept to advance straight, resulting in that the steering operation is the same as that of a conventional reach forklift in which the left and right load wheels 105 and 106 are not turned.
  • the extension lines H L and H R of the left and right load wheels are formed so as to pass the turning center P.
  • the steering control is performed while setting the angles ⁇ L and ⁇ R respectively formed by the unrotated axis G and the extension lines H L and H R as the target steering angles for the left and right load wheels 105 and 106.
  • the axis G is rotated by the travel angle ⁇ O about the body representative point V to obtain the rotated axis G' in the same manner as the above example, and the intersection of the axis G' and the extension line H F of the drive wheel serves as the turning center P. Since the axis G' is parallel to the extension line H F of the drive wheel in this example, the theoretical turning center P (not shown) is a point at infinity on the axis G'.
  • the steering of the left and right load wheels 105 and 106 is controlled so that the extension lines H L and H R of the left and right load wheels pass the turning center P.
  • both the angles formed by the axis G and the extension lines H L and H R of the left and right load wheels, i.e., the target steering angles ⁇ L and ⁇ R are equal to the travel angle ⁇ O and the steering angle ⁇ D of the drive wheel 104.
  • the body attitude of the forklift 101 is not changed so that the forklift 101 travels diagonally in the direction of the travel angle ⁇ O while maintaining its body direction.
  • the RAM2 138 and hardware components such as the I/0 devices are initialized (STEPS 600 and 601), and the steering end process for the drive wheel 104 which is enclosed by broken lines in the figure is conducted. This process will be described later.
  • the chopper rate of the steering motor 111 for steering the left load wheel 105 is calculated and then converted to a corresponding analog value.
  • the analog chopper rate is sent to the D/A converter 142 (STEP 613).
  • the chopper rate of the steering motor 112 for steering the right load wheel 106 is calculated and then converted to a corresponding analog value.
  • the analog chopper rate is sent to the D/A converter 143 (STEP 614).
  • the signal transmitted from the steering control section 116B to the master control section 116A is the steering angle ⁇ D for the drive wheel
  • the signals transmitted from the master control section 116A to the steering control section 116B include the target steering angles ⁇ L and ⁇ R for the left and right load wheels, and the left and right steering ends ⁇ DR and ⁇ DL for the drive wheel.
  • the steering end of the drive wheel 104 can be freely changed using the power steering motor 312 mounted in the forklift 101.
  • the steering angle of the drive wheel In each of the travel modes, the steering angle of the drive wheel must be restricted within a predetermined range.
  • the steering end signals ⁇ DL and ⁇ DR for the drive wheel 104 are read out from ROM1 131, and the readout signals are transmitted from the SIO 134 of the master control section 116A to the SIO 140 of the steering control section 116B.
  • Fig. 23 The portion of Fig. 23 enclosed by the broken lines shows the process procedure of the invention. Initially, the steering torque signal T indicative of the torque applied to the steering wheel 103 is input (STEP 602), and the chopper rate D1 of the power steering motor 312 is calculated (STEP 603).
  • the chopper rate D1 which can be derived from Fig. 53, is set so that, when the steering torque signal T or the rotational direction of the steering wheel 103 indicates the rightward turning, the power steering motor 312 rotates in the same direction or rightward, and in proportion to the steering torque.
  • a dead zone is provided so that, when the absolute value of the steering torque is greater than a predetermined value, the absolute value of the chopper rate D1 is set to 100 % at the maximum, and that, when the absolute value of the steering torque is smaller than a predetermined value, the chopper rate D1 is set to zero in order to prevent the hunting of the power steering motor 312 from occurring. It is assumed that the chopper rate for the rightward rotation of the power steering motor 312 has the positive sign and that for the leftward rotation has the negative sign.
  • the slave CPU 139 receives the current steering angle ⁇ D of the drive wheel 104 from the A/D converter (STEP 604), and calculates chopper rates D2 and D3 of the power steering motor 312 which are determined from the current steering angle ⁇ D (STEPs 605 and 606).
  • the chopper rates D2 and D3 are respectively used to restrict the left and right steering ends within the allowable output range of a chopper rate for driving the power steering motor 312.
  • the chopper rates D2 and D3 will be described with reference to Fig. 54.
  • the abscissa indicates the steering angle ⁇ D of the drive wheel 104
  • the ordinate indicates the chopper rate for driving the power steering motor 312.
  • the left and right ends of the abscissa correspond to the steering ends for the drive wheel 104 which are mechanically formed.
  • variable steering ends are set inside the mechanical steering ends and within the range of the steering ends ⁇ DL to ⁇ DR , in accordance with the selected travel mode.
  • the mechanical steering ends should be considered as illustrative, and are not necessary to be always formed.
  • the chopper rate D2 is zero at the right steering end ⁇ DR of the drive wheel, and gradually increases when the steering angle increases from this point toward the left end, so that the chopper rate can be 100 % or the output can be increased to full power until the steering angle reaches the mechanical left steering end.
  • the chopper rate opposite to this direction i.e., the negative chopper rate for rotating the power steering motor 312 leftward is output.
  • the chopper rate of -80 % is output at the mechanical right steering end.
  • the chopper rate D3 restricts the left steering end ⁇ DL of the allowable output range of a chopper rate for driving the power steering motor 312.
  • the chopper rate D3 is zero at the left steering end ⁇ DL for the drive wheel 104, and linearly increases when the steering angle increases from this point toward the right end, so that the power steering motor can be driven to rotate leftward at 100 % output.
  • the chopper rate opposite to this direction i.e., the chopper rate for rotating the power steering motor 312 rightward is output.
  • the chopper rate of 80 % is output at the mechanical left steering end.
  • the chopper rate D1 obtained in relation to the steering torque signal T indicative of the torque applied to the steering wheel 103 is compared with the chopper rate D2 obtained in relation to the steering angle ⁇ D of the drive wheel (STEP 607).
  • the chopper rate D1 is greater than the chopper rate D2 (Yes in STEP 607), the chopper rate D2 is determined as the chopper rate for driving the power steering motor 312 (STEP 609).
  • the chopper rate D1 is further compared with the chopper rate D3 (STEP 608).
  • the chopper rate D1 is smaller than the chopper rate D3 (Yes in STEP 608), it is finally determined that the chopper rate D3 is used (STEP 611).
  • the chopper rate D1 is greater than the chopper rate D3 (No in STEP 608), the chopper rate D1 is used (STEP 610).
  • the area enclosed by the curves defining the chopper rates D2 and D3 indicates the allowable output range of the chopper rate for driving the power steering motor according to the steering angle ⁇ D of the drive wheel.
  • a state is supposed where the steering wheel 103 is rotated rightward from the neutral position and the drive wheel is gradually approaching the right steering end ⁇ DR .
  • the chopper rate D1 corresponding to the steering torque signal can be output as far as that the steering angle ⁇ D is smaller than ⁇ S .
  • the chopper rate at the steering angle of ⁇ DR of the drive wheel has the value indicated by D2 or is zero even in the case where the chopper rate D1 indicates +100 % in the same manner as described above. This results in that any assist torque is not applied to the steering wheel 103.
  • a positive value is calculated as the chopper rate D1 as described above, and the steering angle momentarily tries to exceed ⁇ DR .
  • the chopper rate is finally determined as D2 or a negative value, resulting in that the power steering motor 312 is driven to rotate leftward.
  • the invention is not limited to the embodiment described above, and can be variously modified within the spirit of the invention.
  • the chopper rate is linearly changed. It is needless to say that the chopper rate may be changed in various manners, for example, in the manner of a quadratic function or a cubic function.
  • the invention relates to a braking process which is conducted when travel mode 4 or 5 is selected (STEP 15 or 19 in Fig. 15), and prevents the change of attitude of the truck body which often occurs during the braking in the prior art, from occurring.
  • the left and right load wheels 105 and 106 are constructed so as to be freely turned or constituted as a free wheel or caster. Therefore, particularly when the forklift brakes hard during the truck travels with the travel angle of the lateral direction as shown in Fig. 44, the left and right load wheels 105 and 106 turn about the contact point between the drive wheel 104 and the road surface, thereby arising a problem that the attitude angle of the forklift 101 is largely changed.
  • Fig. 55 shows the relationship between the pressing amount of the brake pedal 222 and the output of the limit switch 223. In Fig. 55, when the pressing amount of the brake pedal 222 is at "max" or the brake pedal 222 is fully pressed down, the brake is released as described above.
  • the brake device When the operator's foot is gradually raised so that the pressing amount k of the brake pedal 222 is reduced from the "max" state to its lower level, the brake device produces in accordance with the level the braking action between the drive wheel 104 and the road surface, as described above.
  • the range of the pressing amount k of the brake pedal 222 from "max" to k2 (or k2 ⁇ k) corresponds to a so-called mechanical play stroke.
  • the brake device applies to the drive wheel 104 the braking operation the level of which is inversely proportional to the pressing amount.
  • the braking operation of the brake device applied to the drive wheel 104 is increased in level, and the limit switch 223 is turned ON to exert the braking operation according to the invention as described below.
  • Fig. 22 The procedure of the braking operation is shown in Fig. 22. Initially, the state of the limit switch 223 for detecting the pressing state of the brake pedal 222 is checked to judge whether the limit switch 223 is ON or not (STEP 701).
  • the target steering angles ⁇ L and ⁇ R for the left and right load wheels 105 and 106 are set to arbitrarily determined fixed angles ⁇ GL and ⁇ GR , respectively (STEPs 702 and 703).
  • the fixed angles ⁇ GL and ⁇ GR which are set as the target steering angles of the left and right load wheels 105 and 106 are those shown in Fig. 56. That is, the fixed angles may be selected as angles by which the travel directions of the left and right load wheels (indicated by broken lines in Fig. 56) can pass the steering center D of the drive wheel.
  • the fixed angles for the target steering angles of the left and right load wheels 105 and 106 which are employed in a braking state are limited to those of the above-described embodiment. This is because that, for the suppression of the change of the attitude of the body of the forklift 101 during a braking operation, it is sufficient to inhibit Ackerman steering from being conducted at that instance.
  • the case described above is an example in which the maximum braking effect can be attained.
  • the fixed angles for the steering angles of the left and right load wheels can be arbitrarily selected as far as they are not based on Ackerman steering.
  • a reach forklift in which the steering of load wheels supported at ends of straddle arms can be realized without increasing the width of the straddle arms or with an extremely reduced width of the straddle arms.
  • the configuration in which components such as steering motors, timing pulleys, and steering shafts can be housed in the straddle arms prevents a foreign material from entering the inside of the truck body, thereby preventing the gears and timing belts from being damaged.
  • the load wheels are disposed inside the truck body without being restricted by guide rail members of load-carrying means. Therefore, the width of the straddle arms can be reduced. This leads to the reduction of the body size of a reach forklift in which load wheels can be steered.
  • the offset distance can be set to a substantially same value as that of a conventional forklift in spite of the reduced width of the width of the straddle arms. Therefore, a sufficient wheelbase can be obtained even when the forklift moves laterally, thereby attaining an excellent travel stability and improving the riding comfortableness.
  • the turning center while operating a reach forklift on the basis of the driverbility of an ordinary reach forklift, the turning center can be gradually moved to the center of the body of the forklift, in accordance with the operation of the steering wheel, whereby the forklift can turn with a very smaller turning radius than that required in the prior art. Accordingly, the area of pathways in a warehouse can be reduced, and this reduced area produces an effect that the space for storing cargoes can be made large.
  • either of the left and right load wheels can be surely controlled in proportion to the steering angle of the drive wheel, the steering angle of one of the left and right load wheels is prevented from being abruptly changed, so that the steering control is stably performed. Furthermore, since the theory of Ackerman-Jeantaud can be satisfied in any travel condition, the load wheels are prevented to the utmost from slipping, so that the steering can be done smoothly.
  • the minimum turning center can be easily changed in various manners so that the driverbility in accordance with the use of a forklift, thereby providing a forklift with an extremely high degree of extendibility.
  • the steering angle of both the left and right load wheels can be controlled so as to be substantially proportional to the steering angle of the drive wheel. This prevents the load wheels from being abruptly steered, and reduces the power consumption of the steering motors for driving the load wheels.
  • the turning center in accordance with the steering operation of the steering wheel, can be gradually moved to the center of the body of the reach forklift.
  • the steering angle of the drive wheel is relatively small, the turning center is kept below the axis passing the steering centers of the left and right load wheels, whereby feeling of steering operation is improved and the turning radius is made small so that the forklift can make a small turn.
  • discontinuous operations such as an operation of changing the mode are not required and the travel direction can be continuously changed to any direction. Accordingly, irrespective of the actual direction of the body of the forklift, the direction of the body of the forklift can be corrected while using an arbitrary travel direction as the reference. Therefore, the area necessary for the forklift to travel can be minimized so as to reduce the space for pathways in a warehouse.
  • the steering position can be restricted without using any mechanical contact. Therefore, stoppers and butting members to be contacted therewith which are used in a prior art are entirely unnecessary, thereby providing a power steering device which is very advantageous also in the economical view point.
  • the steering reaction of the steering wheel is gradually increased before the steering end, and, when the steering is tried to exceed the steering end, the power steering motor generates torque which corresponds in level and is opposite in direction to the steering torque. Accordingly, the invention can achieve the further effects that the steering position can be restricted without producing a feeling of artificiality, and that the level of a shock produced at the steering ends can be reduced.
  • the change in the attitude angle of a forklift which often occurs during the braking in the prior art can be prevented from occurring by a friction force generated through the left and right load wheels.
  • the forklift can be correctly positioned with respect to a load, which contributes to the improvement in the efficiency of cargo work. Since not only the drive wheel but also load wheels are subjected to the braking operation, the braking distance can be shortened so as to ensure safety cargo work.
  • the theory of Ackerman-Jeantaud can be satisfied in any travel condition. Accordingly, the load wheels can be prevented to the utmost from slipping, so that the steering can be done smoothly.

Landscapes

  • Engineering & Computer Science (AREA)
  • Transportation (AREA)
  • Structural Engineering (AREA)
  • Civil Engineering (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • Mechanical Engineering (AREA)
  • Forklifts And Lifting Vehicles (AREA)
  • Steering Control In Accordance With Driving Conditions (AREA)
  • Steering-Linkage Mechanisms And Four-Wheel Steering (AREA)

Claims (7)

  1. Chariot élévateur (101) à longue portée comprenant :
    un corps de chariot élévateur (102) ;
    des bras de fourche gauche et droit (120) ;
    des roues de charge (105, 106) prévues respectivement au voisinage des extrémités frontales desdits bras de fourche gauche et droit (12),
    lesdites roues de charge (105, 106) étant montées d'une manière orientable dans lesdits bras de fourche (120) ;
    des moyens d'entraínement (110, 111, 112) pour diriger lesdites roues de charge (105, 106), lesdits moyens d'entraínement étant logés dans lesdits bras de fourche (120) ;
    une roue motrice (104) qui est dirigée par un volant (103) et disposée dans une portion arrière dudit corps de chariot élévateur (102) ;
       caractérisé par
    des moyens de détection d'angle de direction (113, 114, 118) pour détecter des angles de direction desdites roues de charge gauche et droite (105, 106) et de ladite roue motrice (104) ; et
    un dispositif de commande (116) pour, dans un premier mode, déterminer un angle de direction (L, R) de l'une desdites roues de charge (105, 106) en multipliant l'angle de direction (D) de ladite roue motrice (104) par un gain d'angle de direction prédéterminé (GL, GR) pour calculer un centre de rotation d'après une relation géométrique entre ladite roue motrice (104) et ladite roue de charge, et pour commander la direction de façon qu'une ligne d'extension (HR, HL) de l'axe de rotation de l'autre roue de charge passe par ledit centre de rotation.
  2. Chariot élévateur à longue portée selon la revendication 1, dans lequel ledit dispositif de commande (116), dans un deuxième mode, effectue la multiplication uniquement lorsqu'une ligne d'extension (HF) de l'axe de rotation de ladite roue motrice (104) peut exister sur ou entre les centres de direction desdites roues de charge gauche et droite (105, 106).
  3. Chariot élévateur à longue portée selon la revendication 1 ou 2, dans lequel ledit dispositif de commande (116) est adapté pour commander, dans un troisième mode, lesdites roues de charge gauche et droite (105, 106) de façon qu'un lieu du centre de rotation dudit chariot élévateur passe au moins par un centre de rotation minimum déterminé arbitrairement et des centres de direction desdites roues de charge gauche et droite (105, 106) s'approchent progressivement d'une ligne droite qui s'étend à partir desdits centres de direction desdites roues de charge gauche et droite vers l'extérieur dudit corps de chariot élévateur (102) et forment une courbe raccordant régulièrement lesdits centres.
  4. Chariot élévateur à longue portée selon la revendication 1, 2 ou 3, comprenant en outre :
    des moyens d'entrée d'angle de parcours (215) pour indiquer un angle de parcours qui est formé par une direction de référence s'étendant le long de la ligne centrale du corps (102) et d'une direction de parcours déterminée arbitrairement ; et
    dans lequel ledit dispositif de commande (116) est adapté de façon que, dans un quatrième mode, lorsque ledit angle de parcours se trouve du côté droit de ladite direction de référence, l'angle de direction de ladite roue de charge droite (106) est rendu coïncident avec ledit angle de parcours, lorsque ledit angle de parcours se trouve du côté gauche de ladite direction de référence, l'angle de direction de ladite roue de charge gauche (105) est rendu coïncident avec ledit angle de parcours, un centre de rotation du corps (102) est calculé d'après une relation géométrique entre ladite roue déterminée desdites roues de charge gauche et droite (105, 106) et ladite roue motrice (104) et les directions desdites roues de charge gauche et droite (105, 106) sont commandées de façon que la ligne d'extension de l'axe de rotation de l'autre roue de charge passe par ledit centre de rotation.
  5. Chariot élévateur à longue portée selon l'une quelconque des revendications précédentes, comprenant en outre :
    des moyens d'entrée d'angle de parcours (215) pour indiquer un angle de parcours dudit corps de chariot élévateur (102) ; et
    dans lequel ledit dispositif de commande (116) est adapté de façon que, dans un cinquième mode, un axe imaginaire passant par les centres de direction desdites roues de charge gauche et droite (105, 106) et sur lequel existe un centre de rotation, tourne de l'angle de parcours indiqué par lesdits moyens d'entrée d'angle de parcours (215) autour d'un point de corps représentatif déterminé arbitrairement, une intersection dudit axe ayant tourné sur lequel existe ledit centre de rotation et d'un axe s'étendant depuis le centre de direction de ladite roue motrice et le long de l'angle de direction de ladite roue motrice est déterminée comme centre de rotation, un axe qui raccorde ledit centre de rotation aux centres de direction desdites roues de charge gauche et droite est déterminé et la direction s'effectue en utilisant un angle formé par ledit axe qui raccorde ledit centre de rotation aux centres de direction desdites roues de charge gauche et droite (105, 106) et ledit axe sur lequel ledit centre de rotation existe avant la rotation, comme l'angle de direction desdites roues de charge gauche et droite (105, 106).
  6. Chariot élévateur à longue portée selon l'une quelconque des revendications précédentes, comprenant en outre un dispositif de direction assistée comprenant :
    un dispositif de détection de couple de direction (309) pour détecter le degré et la direction de couple de direction (T) appliqué à ladite roue de direction (103) ;
    un moteur de direction assistée (312) qui est disposé de façon à fournir un couple assisté à ladite roue motrice (104) ;
    un dispositif de commande de direction assistée (116B) pour entraíner ledit moteur de direction assistée (312) pour tourner, ledit dispositif de commande de direction assistée comprenant une portion de mémorisation (131) pour mémoriser des limites de direction gauche et droite (DL, DR) de ladite roue motrice (104) qui sont déterminées arbitrairement ;
    des moyens pour calculer un premier rythme de découpage (D1) qui coïncide avec la direction d'un signal de couple obtenu par ledit dispositif de détection de couple de direction et qui est sensiblement proportionnel au degré dudit signal de couple ;
    des moyens (13a) pour calculer un deuxième et un troisième rythmes de découpage (D2, D3) par lesquels, lorsqu'un signal d'angle de direction (D) obtenu par lesdits moyens de détection d'angle de direction (118) s'approche de l'une desdites limites de direction gauche et droite (DL, DR), ledit moteur de direction assistée (312) est entraíné pour tourner dans la direction opposée à la direction allant vers l'une desdites limites de direction gauche et droite ; et
    des moyens pour comparer ledit premier rythme de découpage (D1) auxdits deuxième et troisième rythmes de découpage (D2, D3) pour déterminer un rythme de découpage,
    ledit moteur de direction assistée (312) étant entraíné par ledit rythme de découpage déterminé.
  7. Chariot élévateur à longue portée selon au moins l'une des revendications 1 à 6 précédentes, comprenant en outre :
    des moyens de détection d'opération de freinage (223) pour détecter une opération de freinage dudit chariot élévateur (101) ; et
    un dispositif de commande (133) pour, pendant un parcours normal, commander les roues de charge gauche et droite (105, 106) de façon à effectuer une direction d'Ackerman et pour, lorsque lesdits moyens de détection d'opération de freinage (223) détectent une opération de freinage, commander au moins l'une desdites roues de charge gauche et droite (105, 106) de façon à ne pas effectuer de direction d'Ackerman.
EP95119390A 1993-05-18 1993-05-18 Chariot élévateur à longue portée Expired - Lifetime EP0712805B1 (fr)

Priority Applications (4)

Application Number Priority Date Filing Date Title
US08/063,189 US5325935A (en) 1993-05-18 1993-05-18 Reach forklift
EP93108095A EP0625478B1 (fr) 1993-05-18 1993-05-18 Chariot élévateur à longue portée
DE1993629156 DE69329156T2 (de) 1993-05-18 1993-05-18 Schubgabelstapler
EP95119390A EP0712805B1 (fr) 1993-05-18 1993-05-18 Chariot élévateur à longue portée

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP93108095A EP0625478B1 (fr) 1993-05-18 1993-05-18 Chariot élévateur à longue portée
EP95119390A EP0712805B1 (fr) 1993-05-18 1993-05-18 Chariot élévateur à longue portée

Related Parent Applications (2)

Application Number Title Priority Date Filing Date
EP93108095A Division EP0625478B1 (fr) 1993-05-18 1993-05-18 Chariot élévateur à longue portée
EP93108095.6 Division 1993-05-18

Publications (3)

Publication Number Publication Date
EP0712805A2 EP0712805A2 (fr) 1996-05-22
EP0712805A3 EP0712805A3 (fr) 1996-06-05
EP0712805B1 true EP0712805B1 (fr) 2000-08-02

Family

ID=8212917

Family Applications (1)

Application Number Title Priority Date Filing Date
EP95119390A Expired - Lifetime EP0712805B1 (fr) 1993-05-18 1993-05-18 Chariot élévateur à longue portée

Country Status (2)

Country Link
EP (1) EP0712805B1 (fr)
DE (1) DE69315198T2 (fr)

Cited By (1)

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US8930082B2 (en) 2010-04-16 2015-01-06 Hubtex Maschinenbau Gmbh & Co. Kg Steering method and steering system for an industrial truck

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Publication number Priority date Publication date Assignee Title
DE19960946C2 (de) * 1999-12-17 2002-01-10 Jungheinrich Ag Lenkung für Gegengewichtsstapler
ES2186491B1 (es) * 2000-10-23 2004-09-01 Tecna 2000 Carretillas, S.L. Sistema de seguridad antivuelco para carretillas elevadoras.
US6901323B2 (en) 2000-11-28 2005-05-31 Nippon Yusoki Co., Ltd. Cargo handling vehicle
FR2826353B1 (fr) * 2001-06-22 2003-09-26 Michel Amiand Engin de manipulation de charges tel que gerbeur
CN103754284A (zh) * 2014-01-28 2014-04-30 浙江诺力机械股份有限公司 一种可以四向行驶的工业车辆及该种工业车辆的行走机构
DE102020128489A1 (de) * 2020-10-29 2022-05-05 Hubtex Maschinenbau Gmbh & Co. Kg Flurförderzeug mit Rotations-Lenkantrieb
GB202101426D0 (en) * 2021-02-02 2021-03-17 Combilift Steering systems for lift trucks
CN117602538B (zh) * 2024-01-23 2024-04-19 合肥搬易通科技发展有限公司 一种双驱四支点agv叉车转向死区的控制方法及系统

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US5018594A (en) * 1988-12-22 1991-05-28 Fuji Jukogyo Kabushiki Kaisha Rear-wheel steering system for four-wheel steering vehicle
JPH035680U (fr) * 1989-06-06 1991-01-21
JPH03295768A (ja) * 1990-04-13 1991-12-26 Nippon Yusoki Co Ltd フオークリフトの安全装置
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JPS57121599A (en) * 1981-01-17 1982-07-29 Shinko Electric Co Ltd Forklift, attitude of steering thereof can be selected

Cited By (1)

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Publication number Priority date Publication date Assignee Title
US8930082B2 (en) 2010-04-16 2015-01-06 Hubtex Maschinenbau Gmbh & Co. Kg Steering method and steering system for an industrial truck

Also Published As

Publication number Publication date
EP0712805A2 (fr) 1996-05-22
DE69315198T2 (de) 1998-03-05
EP0712805A3 (fr) 1996-06-05
DE69315198D1 (de) 1997-12-18

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