Axle pivoting controller and hydraulic cylinder for industrial vehicles

Abstract: A hydraulic apparatus is used in an industrial vehicle. The apparatus has a hydraulic cylinder (6) interposed between a vehicle frame (1) and an axle (2) swingably coupled to the frame (1). A passage (9a, 9b) connects a first chamber (19) with a second chamber (20) defined by a piston (13) in a cylinder case (12). The piston (13) is movable based on differential pressure in the chambers (19, 20). A cylinder rod (14) selectively extends and retracts in respect with the cylinder case (12) to absorb a swinging motion of the axle (2). The passage (9a, 9b) is selectively open and closed based on at least one of a traveling state and a loading state of the vehicle. The piston (13) has a first surface defining the first chamber (19) and a second surface defining the second chamber (20). The first surface has an area equal to that of the second surface.

Description: The present invention relates to hydraulic apparatus used in an industrial vehicle according to the preamble of claim 1. A forklift is generally provided with a rear axle beam and a body frame. In order to improve the riding comfort and enhance the driving performance of the forklift, the center of the rear axle beam can be supported such that the rear axle beam is pivotal with respect to the body frame. The body frame and the rear axle beam are connected to each other by a hydraulic cylinder. JP-U-56-25609 describes a rear axle beam having ends that are each connected to a body frame by a single action hydraulic cylinder. Each hydraulic cylinder has a piston and an oil chamber. The oil chambers of the hydraulic cylinders are connected with each other by a passage. In accordance with the pivotal movement of the rear axle beam relative to the body frame, each piston is moved axially in its associated cylinder. Hydraulic oil flows between the oil chambers through the passage in accordance with the movement of each piston and restricts the pivotal movement of the rear axle beam. When such a forklift carries a cargo, lifts a cargo to a high position, or changes directions at a high speed, the forklift becomes less stable. In order to increase the driving stability, the pivotal movement of the rear axle beam can be locked by restricting the movement of the pistons. An electromagnetic control valve is arranged in the passage to restrict the movement of the pistons by stopping the flow of hydraulic oil in the passage. A forklift that restricts pivotal movements of the rear axle beam by employing two single action hydraulic cylinders requires a large number of components, which are installed on the forklift. In order to reduce the number of components, the owner of the present application has proposed to arrange a multiple action hydraulic cylinder on just one end of the rear axle beam to connect the rear axle beam with the body frame. The multiple action hydraulic cylinder has a piston, which defines a first oil chamber and a second oil chamber. The first and second oil chambers are connected with each other by a passage. The piston is moved axially in accordance with the pivotal movements of the rear axle beam. This moves the hydraulic oil between the first and second oil chambers and restrains the pivotal movement of the rear axle beam relative to the body frame. In this structure, the electromagnetic control valve restricts the movement of the piston by stopping the flow of the hydraulic oil in the passage between the first and second oil chambers. Thus, the pivotal movements of the rear axle beam are also restricted with this structure. In addition, this type of forklift employs only one cylinder. Therefore, the installation of the hydraulic cylinder is facilitated due to the smaller number of components. However, in the multiple action hydraulic cylinder, one end of the piston is connected to a rod, which extends through one of the hydraulic oil chambers. Thus, the cross sectional area of this chamber, on which pressure is applied, is smaller than that of the other hydraulic oil chamber. Accordingly, the pressure applied to the piston differs when the piston moves in opposite directions. As a result, the velocity of the piston differs according to the moving direction. The difference in the velocity of the piston permits the forklift to tilt to the right and to the left in different manners such that the operator can feel the difference. In addition, the volume of oil that flows outward from one oil chamber is not the same as the volume of oil that enters the other oil chamber. It is thus necessary to eliminate the imbalance between the two oil volumes and permit the forklift to tilt to the right and to the left in the same manner. A generic hydraulic apparatus used in an industrial vehicle is shown in EP-A-0 454 474, which comprises the features mentioned in the preamble of claim 1 of the application. A hydraulic cylinder is interposed between a vehicle frame and an axle swingably coupled to the frame. A hydraulic passage connects a first chamber with a second chamber defined by a piston in a cylinder case. The piston is movable in accordance with differential pressure in the first chamber and the second chamber and has a first surface defining the first chamber and a second surface defining the second chamber. The first surface has an area equal to that of the second surface. A cylinder rod selectively extends and retracts in respect with the cylinder case to absorb a swinging motion of the axle. The hydraulic passage is selectively opened and closed. The piston rod projects from the first surface of the piston, extends through the first chamber and is connected with the axle. A guide rod projects from the second surface of the piston and extends through the second chamber. The piston rod has a cross section area equal to that of the guide rod. A similar hydraulic apparatus used in an industrial vehicle is known from GB-A-1 238 243. Further hydraulic apparatuses used in industrial vehicles are shown in JP-A-06 191 251, JP-A-58 183 307 JP-A-58 214 406 and DE-A-42 35 264. It is an object of the present invention to further develop a hydraulic apparatus used in an industrial vehicle according to the preamble of claim 1. This object is achieved by a hydraulic apparatus used in an industrial vehicle having the features of claim 1. Advantageous further developments are set out in the dependent claims. Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 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 object 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 is a schematic view showing a structure of an axle pivoting controller arranged on a rear axle beam; and Fig. 2 is a cross sectional view showing a hydraulic cylinder. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An axle pivoting controller according to the present invention, which is applied to a pivotal rear axle beam of a forklift, will now be described with reference to Figs. 1 and 2. Fig. 1 shows a schematic rear view of a forklift having a body frame 1 and a rear axle beam 2. The rear axle beam 2 is pivotally supported by a central pin 3, which is arranged in a lower portion of the body frame 1. A shock absorbing elastic body 4 is provided between the body frame 1 and the rear axle beam 2 to absorb shocks produced by the pivotal movement of the rear axle beam 2. A steered wheel 5 is mounted on each end of the rear axle beam 2 and supported such that the wheel 5 can be pivoted to steer the forklift. A multiple action hydraulic cylinder 6 is arranged on one end of the rear axle beam 2. The hydraulic cylinder 6 connects the rear axle beam 2 to the body frame 1. An electromagnetic control valve 7 and an accumulator 8 are arranged on the body frame 1. The hydraulic cylinder 6 is connected to the electromagnetic control valve 7 and the accumulator 8 through passages 9a, 9b, 10a, 10b. Therefore, the passages 9a, 9b, 10a, 10b, the hydraulic cylinder 6, the electromagnetic control valve 7, and the accumulator 8 form a hydraulic circuit. An axle pivoting controller 11 is provided on the body frame 1. Fig. 2 is a cross sectional view showing the hydraulic cylinder 6. The cylinder 6 includes a cylindrical tube 12, a piston 13, a piston rod 14, and a guide rod 15. The upper end of the piston 13 defines a head portion, and the lower end of the piston 13 defines a rod portion. The "upper" and "lower" directions referred to are taken from the upper and lower directions of Fig. 2. The tube 12 includes a body 12a. The upper end of the body 12a is closed by a head piece 16 and a guide piece 17. The lower end of the body 12a is closed by a rod piece 18. The piston 13 defines a rod chamber 19 and a head chamber 20 in the tube 12. The piston rod 14 extends through the rod chamber 19 and is fixed to the piston 13. The guide rod 15 extends through the head chamber 20 and is fixed to the piston 13. The piston rod 14 has a threaded male end 14a, which extends through the piston 13 and into the head chamber 20. The guide rod 15 has a threaded female end 15a, which engages the male end 14a. The other end of the piston rod 14 (the lower end) extends through the rod piece 18 and out of the tube 12. The other end of the guide rod 15 (the upper end) is slidably supported by a bearing 16a in the head piece 16 and is accommodated in a cavity 17a, which is defined in the guide piece 17. The threaded engagement between the male end 14a of the piston rod 14 and the female end 15a of the guide rod 15 forms a single integral rod. The piston 13 is located at the middle of the single rod. The cross sectional area of the guide rod 15 is equal to that of the piston rod 14. Therefore, the cross sectional area (or the piston are) that receives pressure is the same in the head side and in the rod side of the piston 13. The lower end of the piston rod 14 is pivotally supported about a pin 22 on a bracket 21, which is fixed to the rear axle beam 2. The upper end of the guide piece 17 is pivotally supported about a pin 24 on a bracket 23, which is fixed to the body frame 1. The electromagnetic control valve 7 has associated ports a, c, and associated ports b, d. The electromagnetic control valve 7 incorporates an electromagnetic solenoid 25, which shifts the control valve 7 between positions 7a and 7b. At position 7a, the electromagnetic control valve 7 disconnects port a from port c, and it disconnects port b from port d. At position 7b, the control valve 7 connects port a with port c, and port b with port d. A spring 26 is arranged in the control valve 7. When the electromagnetic solenoid 25 is de-excited, the control valve 7 is held at position 7a by the force of the spring 26. When the solenoid 25 is excited, the valve 7 is shifted to position 7b against the force of the spring 26. Therefore, the electromagnetic control valve 7 is normally closed. Port a is connected with the rod chamber 19 by way of the passage 9a. Port b is connected with the head chamber 20 by way of the passage 9b. Port c is connected with the accumulator 8 by way of the passage 10a. Port d is connected with the accumulator 8 by way of the passage 10b. Therefore, when the electromagnetic control valve 7 is shifted to position 7a, the rod chamber 19 is disconnected from the head chamber 20. Thus, the hydraulic cylinder 6 restricts the pivotal movement of the rear axle beam 2 relative to the body frame 1 by stopping the flow of the hydraulic oil between the chambers 19, 20. On the other hand, when the control valve 7 is shifted to position 7b, the rod chamber 19 and the head chamber 20 are connected to each other by way of the passages 9a, 9b and the accumulator 8. The hydraulic cylinder 6 permits the pivotal movement of the rear axle beam 2 relative to the body frame 1 by permitting the hydraulic oil to flow between the chambers 19, 20. When the chambers 19, 20 are connected to each other, the hydraulic cylinder 6 restrains the pivotal movement of the rear axle beam 2 by the resistance generated as hydraulic oil passes through passages 9a and 9b. When predetermined conditions are satisfied, the axle pivoting controller 11 excites the electromagnetic control valve 7. When the predetermined conditions are unsatisfied, the axle pivoting controller 11 de-excites the electromagnetic control valve 7 and restricts the pivotal movement of the rear axle beam 2. The predetermined conditions are unsatisfied when the height to which the cargo is lifted, the angle of the steered wheels 5, and the traveling speed of the vehicle exceed certain values. The height of the cargo is detected by a height sensor H. The angle of the wheels 5 is detected by a steering angle sensor S. The traveling speed of the vehicle is detected by a velocity sensor V. The operation of the axle pivoting controller 11 and the hydraulic cylinder 6 will now be described. When the controller 11 excites the electromagnetic control valve 7, the control valve 7 is shifted to position 7b and the head chamber 20 is communicated with the rod chamber 19. In this state, the hydraulic cylinder 6 is actuated and pivoting of the rear axle beam 2 relative to the body frame 1 is permitted in accordance with driving conditions. Therefore, pivoting of the rear axle beam 2 causes hydraulic oil to enter the rod chamber 19 or the head chamber 20 and move out of the rod chamber 19 or the head chamber 20. When the rear axle beam 2 pivots clockwise relative to the body frame 1, as viewed in Fig. 1, the piston rod 14 retracts into the cylinder 6. The piston 13 thus moves toward the body frame 1 and receives pressure from the hydraulic oil in the head chamber 20. This restrains the axial movement of the piston rod 14 and the pivotal movement of the rear axle beam 2 relative to the body frame 1. As a result, the rear axle beam 2 pivots clockwise at an appropriate velocity. If the rear axle beam 2 pivots counterclockwise relative to the body frame 1, the piston rod 14 projects from the cylinder 6. The piston 13 thus moves toward the rear axle beam 2 and receives pressure from the hydraulic oil in the rod chamber 19. This restrains the axial movement of the piston rod 14 and the pivotal movement of the rear axle beam 2 relative to the body frame 1. As a result, the rear axle beam 2 pivots counterclockwise at an appropriate velocity. Since the cross sectional area of the piston 13 is equal in the head chamber 20 and the rod chamber 19, the piston 13 receives the same pressure in the head chamber 20 and the rod chamber 19 when the piston 13 moves axially. Therefore, the retraction velocity of the piston 13 is equal to the projection velocity of the piston 13. As a result, the pivoting velocity of the rear axle beam 2 relative to the body frame 1 is the same when the rear axle beam 2 tilts clockwise and counterclockwise, as viewed in Fig. 2. In addition, the volume of the hydraulic oil discharged from one of the oil chambers 19, 20 is the same as the volume of the hydraulic oil that enters the other oil chamber 19, 20. The preferred and illustrated embodiment has the advantages described below. (a) In the hydraulic cylinder 6 that connects the body frame 1 and the rear axle beam 2, the volume of the hydraulic oil that flows out of one of the oil chambers 19, 20, is equal to the volume of the hydraulic oil that flows into the other oil chamber 19, 20. As a result, the retraction velocity and the projection velocity of the piston 13 are the same. Thus, the hydraulic cylinder 6 operates in the same manner when the piston rod 14 retracts and projects. Accordingly, the forklift tilts to the right and to the left in the same manner. The volume of the hydraulic oil that flows out of one of the oil chambers 19, 20, and the volume of the hydraulic oil that flows into the other oil chamber 19, 20, are the same. Therefore, it is not necessary to arrange a special structure to compensate for volume differences. As a result, the hydraulic circuit can be constructed in a simpler form. (b) When the rear axle beam 2 pivots relative to the body frame 1, the clockwise pivoting velocity of the rear axle beam 2 is equal to the counterclockwise pivoting velocity of the rear axle beam 2, assuming the same amount of force is applied to each end of the rear axle beam 2. (c) The electromagnetic valve 7 is normally closed. When the controller 11 malfunctions, the valve 7 cannot be controlled. Thus, the hydraulic oil does not flow between the passages 9a, 9b. In such case, the rear axle beam 2 is locked. This stabilizes the forklift even when carrying a cargo. Therefore, the transportation of the cargo can be completed before servicing the controller. (d) The cross sectional area of the head side of the piston 13 and that of the rod side of the piston 13 are equal. Accordingly, the pressure applied to the piston 13 is the same when the piston rod 14 retracts and projects. Then, the velocity of the piston rod 14 is equal regardless of whether the piston rod 14 retracts or projects. As a result, the piston rod 14 operates in the same manner when it projects and retracts. (e) The piston rod 14 and the guide rod 15 form a single rod by fastening the male end 14a of the piston rod 14 to the female end 15a of the guide rod 15. The piston 13 is located at the middle of the single rod. The piston rod 14, the guide rod 15, and the piston 13 are assembled by connecting the piston rod 14 and the guide rod 15. Thus, the rod is assembled with precision in a facilitated manner in comparison with the other assembling methods, such as welding. 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 spirit or scope of the invention. More particularly, the preferred and illustrated embodiment may be modified as described below. The electromagnetic control valve 7 may be normally open. In this case, if the controller 11 malfunctions and the electromagnetic control valve 7 cannot be controlled, the rod chamber 19 and the head chamber 20 are connected. This permits pivoting of the rear axle beam 2. Therefore, the rear axle beam 2 is permitted to pivot, even if the controller 11 malfunctions. Accordingly, traction is maintained by all four wheels of the forklift and the ground as the forklift travels along unpaved roads. Thus, the forklift can be driven even if the road is unpaved before being serviced. The piston rod 14 may be connected to the body frame 1 and the guide rod 15 may be connected to the rear axle beam 2. In other words, the cylinder 6 may be inverted from the orientation shown in Fig. 2. The piston rod 14 and the guide rod 15 may be fixed to the piston 13 by welding, fasteners such as bolts, press fitting, and other appropriate means. The cross sections of the piston rod 14 and the guide rod 15 do not have to be circular and may be polygonal. The head piece 16 and the guide piece 17 may be fixed to each other in an integral manner. 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 scope of the invention defined in the appended claims.

Claims: A hydraulic apparatus used in an industrial vehicle having a hydraulic cylinder (6) interposed between a vehicle frame (1) and an axle (2) swingably coupled to the frame (1), wherein a hydraulic passage (9a, 9b) connects a first chamber (19) with a second chamber (20) defined by a piston (13) in a cylinder case (12), wherein said piston (13) is movable in accordance with differential pressure in the first chamber (19) and the second chamber (20) and has a first surface defining the first chamber (19) and a second surface defining the second chamber (20), said first surface having an area equal to that of the second surface, wherein a cylinder rod (14) selectively extends and retracts in respect with the cylinder case (12) to absorb a swinging motion of the axle (2), wherein said hydraulic passage (9a, 9b) is selectively opened and closed, wherein said piston rod (14) projects from the first surface of the piston (13), extends through the first chamber (19) and is connected with one of the frame (1) and the axle (2), a guide rod (15) projects from the second surface of the piston (13) and extends through the second chamber (20), wherein said piston rod (14) has a cross section area equal to that of the guide rod (15), characterized by a cylindrical guide piece (17) slideably accommodating the guide rod (15), wherein said guide piece (17) is interposed between the guide rod (15) and the other one of the frame (1) and the axle (2), wherein said hydraulic passage (9a, 9b) is selectively opened and closed based on at least one of a traveling state and a loading state of the industrial vehicle, wherein a control valve (7) is disposed in the hydraulic passage (9a, 9b) to be selectively opened and closed so as to permit or prohibit a hydraulic flowage in the passage (9a, 9b), and wherein an accumulator (8) is disposed in the hydraulic passage (9a, 9b). An apparatus as set forth in claim 1, characterized by a controller (11) for controlling the electromagnetic control valve (7) in accordance with at least one of the traveling state and loading state of the industrial vehicle. An apparatus as set forth in claim 1, characterized in that said electromagnetic control valve (7) closes the hydraulic passage (9a, 9b) when the valve (7) is deactivated. An apparatus as set forth in claim 1, characterized in that said industrial vehicle includes a forklift.

Inventors: CHINO KENJI, HYODO MASAYA, MUTO TAKAYUKI, SHIOYA TERUYUKI, CHINO, KENJI, HYODO, MASAYA, MUTO, TAKAYUKI, SHIOYA, TERUYUKI
Applicants: KAYABA INDUSTRY CO LTD, TOYOTA JIDOSHOKKI KK, KABUSHIKI KAISHA TOYOTA JIDOSHOKKI, KAYABA KOGYO KABUSHIKI KAISHA
Application year: 1998
Main classification: B60G17
IPC codes: B60G9, F15B15, B66F9, B60G17, F16F9