Toe angle adjustment mechanism for vehicle wheels

Abstract: A vehicle having a toe angle adjustment mechanism. The vehicle has a frame member (1), a steerable wheel (2), a steering knuckle (3) pivotally connecting the wheel to the frame member about a substantially vertical axis, a steering mechanism for steering the vehicle, and a steering actuator (5) included as part of the steering mechanism for moving in a predetermined direction to cause a steering change. A transfer member (18) is connected to the wheel for transferring a force applied by the actuator to the wheel to effect the steering change. The adjustment mechanism pivotally couples the distal end of the transfer member to distal end of the steering actuator about an adjustable pivot axis. The adjustment mechanism permits adjustment of the toe angle of the wheel and varies the position of the adjustable pivot axis with respect to one of the distal end portions to vary the toe angle.

Description: The present invention relates to toe angle adjustment mechanisms that facilitate toe-in and toe-out adjustment of vehicle wheels. There are industrial vehicles that employ a full hydraulic pressure system (FHPS) type rear axle. As shown in Figs. 5(a) and 5(b), a typical FHPS type rear axle includes a rear axle beam 1. A wheel 2 is coupled to each end of the axle beam 1. A cylinder 5 is fixed longitudinally to the middle of the axle beam 1. A piston rod 4 extends outward from each end of the cylinder 5. The projection and retraction of the piston rod 4 turns each wheel 2 about an axis extending in a substantially vertical direction. This steers the vehicle. Each wheel 2 is coupled to the axle beam 1 by means of a steering knuckle 3. When the wheel 2 is turned, the steering knuckle 3 is turned accordingly. The steering knuckle 3 is connected to the piston rod 4 by means of a rod end 7, which is secured to the distal end of the piston rod 4, a tie rod 18, and a ball joint. The cylinder 5 is actuated by hydraulic pressure. The hydraulic pressure is applied by a steering valve, or ORBITROL, located below a steering wheel (not shown), which is arranged in front of the driver's seat. A nut portion 7a is provided on each rod end 7. The rod end 7 is threaded into the piston rod 4. The length of the piston rod 4 is adjusted by rotating the nut portion 7a. When the steering wheel is at a neutral position, the vehicle moves straight. However, dimensional tolerances that are allowed when assembling the rear axle may cause the left and right wheels to aim in a direction that is not straight forward. This may result in side slipping. To maintain the amount of side slipping within an allowable range, the nut portion 7a of each rod end 7 is turned to adjust the length of the piston rod 4. However, each rod end 7 must be rotated independently when turning the nut portion 7a. Thus, the rod end 7 must be disconnected from the associated tie rod 18 for adjustment. The rod end 7 and the tie rod 18 are reconnected after adjustment. Furthermore, exclusive tools are required to rotate the rod end 7. Thus, adjustment of the length of the piston rod 4 has been costly and inefficient. Furthermore, the employment of a threaded adjusting mechanism together with a ball joint increases the size of the rod ends 7. This also results in cost increases. Further, from DE-OS 42 21 169 a steering device is known which has a steering mechanism for a vehicle, the steering mechanism having a steerable wheel with a steering knuckle coupled to an actuator via a transfer member. The movable connections between these elements are ball joints. Moreover, document US 4,162,859, shows an adjustable pivot axis which is arranged at the distal end of the steering knuckle so that the steering actuator is directly connected to the steering knuckle. The adjustable pivot axis is embodied as an adjustable ball joint having a frustoconical portion arranged eccentrically with respect to the turning axis of the ball joint. Finally, the US 5,213,435 shows an adjustable fastening of a ball joint to a tie rod for steering linkages having a mechanism for pivoting the axis of the ball joint relatively to a centre axis. The adjustment movement is generated with a screw using the threaded portion thereof as a drive co-operating with a suitable gearing provided on a fastening plate. The fastening plate is fixed in the adjusted position by means of clamping screws. It is the object of the invention to provide a vehicle having a toe angle adjustment device which is quick and easy to operate and securely maintains the adjusted toe angle. This object is solved with a vehicle having the features of claim 1. Advantageous modifications are depicted in the dependent claims. The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: Fig. 1(a) is a plan view showing a rear axle provided with a toe angle adjustment mechanism according to the present invention; Fig. 1(b) is a front view showing the rear axle of Fig. 1(a); Fig. 2 is an exploded view showing the portion connecting the rod end and the tie rod; Fig. 3 is a cross-sectional view showing the joint between the rod end and the tie rod; Fig. 4 is an explanatory drawing showing the movement of the toe angle adjustment mechanism; Fig. 5(a) is a plan view showing the prior art rear axle; and Fig. 5(b) is a front view showing the rear axle of Fig. 5(a). A toe angle adjustment mechanism according to an embodiment of the present invention will now be described with reference to the drawings. Figs. 1(a) and 1(b) show a rear axle of a forklift. The rear axle includes a laterally extending rear axle beam 1, or frame member, which is fixed to the rear portion of the vehicle body. A wheel 2 is coupled to each end of the axle beam 1 by means of a steering knuckle 3. Each wheel 2 rotates about a horizontal axis and pivots about a vertical axis. A cylinder 5, which serves as an actuator, is fastened to the middle of the axle beam 1 by bolts 6 and is arranged extending longitudinally along the beam 1. A single piston rod 4 extends outward from each end of the cylinder 5. A rod end 7 is integrally fixed to each end of the piston rod 4. The cylinder 5 is actuated by hydraulic pressure. The hydraulic pressure is applied by a steering valve, or ORBITROL, located below a steering wheel (not shown), which is arranged in front of the driver's seat. The rear axle is symmetrical about a central vertical plane. Therefore, only one side of the rear axle will be described with reference to Fig. 2. A connecting portion 8, which is bifurcated into a first connecting piece 8a and a second connecting piece 8c, is provided at the distal end of the rod end 7. A slot 8b, which is slightly wider than the thickness of a tie rod 18, is defined between the first and second connecting pieces 8a, 8c. A first bore 9 extends through the first connecting piece 8a, while a second bore 10 extends through the second connecting piece 8c. A lock plate 12 having a hexagonal hole 11, which constitutes part of a rotation restricting mechanism, is fastened to the outer surface of the first connecting piece 8a by a bolt 12a. The first bore 9, the second bore 10, and the hexagonal hole 11 are aligned coaxially. The diameter of the first bore 9 is greater than that of the second bore 10. A coupling pin 13 has first and second sections 14, 15 that correspond to the bores 9, 10, respectively, and a head 16 corresponding to the hexagonal hole 11. An eccentric section 17 extends between the first and second sections 14, 15. The outer surface of the eccentric section 17 is spherical. The tie rod 18 connects the steering knuckle 3 to the piston rod 4. A pin bore 18a is provided on the end of the tie rod 18. The tie rod 18 and the steering knuckle 3 are rotatably coupled to each other by a known coupling device. The rod end 7 is connected to the tie rod 18 in the following manner. As shown in Fig. 3, the distal end of the tie rod 18 is fit into the slot 8b. The pin bore 18a is located between the first bore 9 and the second bore 10. The coupling pin 13 is then inserted through the first bore 9, the pin bore 18a, and the second bore 10. When the head 16 is fit into the hexagonal hole 11, a lock pin 19 is used to lock the projecting lower end of the coupling pin 13. Since the slot 8b is slightly wider than the thickness of the tie rod 18, a slight clearance is formed between the tie rod 18 and the walls of the slot 8b. A sleeve 20 is arranged between the eccentric section 17 of the coupling pin 13 and the wall of the pin bore 18a. However, the sleeve 20 is not necessary if the eccentric section 17 can easily slide against the pin bore 18a without undue wear. At the joint between the rod end 7 and the tie rod 18, the spherical surface of the eccentric section 17 contacts the wall of the pin bore 18a by means of the sleeve 20. Thus, the movement of the rod end 7 is positively transmitted to the tie rod 18 by the coupling pin 13. The tie rod 18 pivots about the eccentric section 17 of the connecting pin 13 in accordance with the movement of the rod end 7. The eccentric shaft portion 17 functions in the same manner as a ball joint. The center of the eccentric section 17 is offset from the axis of the coupling pin 13 by a predetermined distance. Thus, when the coupling pin 13 is rotated about its axis, the center of the eccentric section 17 orbits the axis of the pin 13. The locus of the center of the eccentric section 17 defines a circle, the radius of which is equal to the offset distance. Hence, the rotation of the coupling pin 13 alters the relative position of the tie rod 18 and the rod end 7 (Fig. 4). This facilitates toe adjustment. In addition, since this structure is compact and simple, costs are reduced. The head 16 of the coupling pin 13 is fitted into the hexagonal hole 11 so as to restrict rotation of the pin 13. By removing the lock pin 19, the coupling pin 13 may be moved upward until the head 16 comes out of the hexagonal hole 11. This enables the head 16 to be turned in increments of 60 degrees. The angular interval of 60 degrees allows alignment between the outer surface of the head 16 and the wall of the hexagonal hole 11. The turning of the coupling pin 13 changes the position at which the tie rod 18 is connected to the rod end 7 in the axial direction of the cylinder 5. This adjusts the toe angle of the wheel. In the above embodiment, the hexagonal head of the coupling pin is aligned with and fit into the hexagonal hole that is provided in the lock plate so as to restrict rotation of the coupling pin. However, the portion of engagement between the coupling pin and the lock plate need not be hexagonal as long as it is polygonal. Furthermore, the lock plate may be eliminated by providing a polygonal hole in the rod end. Furthermore, the rotation restricting means is not limited to a polygonal engagement mechanism and may employ other restricting mechanisms. When using polygonal engagement mechanisms, it is preferable that the number of sides be as high as possible to allow fine adjustment. In the above embodiment, a slot is provided in the rod end. However, the slot may instead be provided in the tie rod. In this case, the lock plate is also arranged on the tie rod. The eccentric section does not necessarily have to be provided at the middle of the coupling pin and may be provided at any position on the pin. The outer surface of the eccentric section need not be spherical and may be cylindrical. However, in this case, a separate ball joint will be necessary. Thus, such structure may not be cost efficient. The lock plate 12 and the coupling pin 13 do not necessarily have to be arranged on the upper surface of the rod end 7 and may be arranged on the lower surface instead. The toe angle adjustment mechanism may be employed anywhere as long as it defines a rotatable joint with a member that is mechanically connected to the steering knuckle. This enables the advantageous effects of the above embodiment to be obtained. The application of the present invention is not limited to FHPS type axles and may be applied to vehicles that employ separate type linkage power steering systems. In such a system, the present invention may be applied to portions connecting a pitman arm to a steering connecting rod or to portions connecting a knuckle arm and a tie rod. It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the scope of the invention. Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope of the appended claims.

Claims: A vehicle having a frame member (1), a steerable wheel (2), a steering knuckle (3) pivotally connecting the wheel (2) to the frame member (1) about a substantially vertical axis, a steering mechanism for steering the vehicle, a steering actuator (5) included as a part of the steering mechanism for moving in a predetermined direction to cause a steering change, the steering actuator (5) having a distal end portion, and a transfer member (18) connected to the wheel for transferring a force applied by the steering actuator (5) to the wheel (2) to effect the steering change, the transfer member (18) having a distal end portion connected to a distal end portion of the steering actuator (5), characterized by an adjustment mechanism (13, 17) pivotally connecting the distal end portion of the transfer member (18) to the distal end portion of the steering actuator (5) about an adjustable pivot axis, wherein the adjustment mechanism permits adjustment of the toe angle of the wheel (2) by varying the position of the adjustable pivot axis with respect to one of the distal end portions, and wherein the adjustment mechanism includes: a coupling pin (13) having an axis and passing through the distal end portions of the actuator (5) and the transfer member (18), wherein the coupling pin (13) has an eccentric section (17), the center of which orbits the coupling pin axis when the coupling pin (13) rotates, and wherein the eccentric section (17) defines the adjustable pivot axis, and a locking device (12, 12a) for preventing the coupling pin (13) from rotating with respect to one of the distal end portions, said locking device including a plate (12) that is secured to one of the distal ends, wherein the plate (12) has a polygonal hole (11) formed therein for engagement with the polygonal shaped head (16) of the coupling pin (13). The vehicle according to claim 1, wherein the actuator includes a hydraulic cylinder (5) having a rod (4). The vehicle according to claim 1 or 2, wherein the transfer member is a tie rod (18), and wherein the tie rod (18) is connected to the steering knuckle (3). The vehicle according to claim 1, wherein the eccentric section (17) is spherical.

Inventors: IWANAGA YOSHIHISA, IWANAGA, YOSHIHISA
Applicants: TOYOTA JIDOSHOKKI KK, KABUSHIKI KAISHA TOYOTA JIDOSHOKKI
Application year: 1997
Main classification: B62D17
IPC codes: B62D7, B60G7, B62D17