SUSPENSION SYSTEM FOR WORK VEHICLE

Abstract: A suspension system comprising buffer springs (21L, 21R) interposed between an axle (1) and a chassis frame (7), a pair of double-acting cylinders (22L, 22R) provided a preset distance apart in the lateral direction of the vehicle and each pivotally supported on the tube (22a) side and rod (22b) side by the chassis frame (7) and the axle (1), respectively, and a link (24) coupled to the chassis frame (7) at one end and to the axle (1) at the other end thereof in such a manner that horizontal displacements in left and right, and forward and rearward directions relative to the vehicle are restricted, while displacement in the vertical direction are allowed, wherein the double-acting cylinders (22L, 22R) are kept free while running, and are locked while digging work is performed.

Description: The present invention relates to a vehicle suspension system connected between the vehicle chassis and a rigid axle supporting left and right wheels said vehicle suspension system comprising: a pair of shock absorbing springs connected between said axle and said vehicle chassis at a fixed distance apart in the lateral direction of the vehicle; a pair of double acting cylinders which are provided at a fixed distance apart in the lateral direction of said vehicle, and whose tube sides and rod sides are pivotally connected to said chassis and said axle respectively, about axes parallel to the longitudinal axis of the vehicle; and changeover means which by locking said double acting cylinders obstructs the action of said springs, and by freeing said double acting cylinders permits the action of said springs. Such suspension system is known from DE-U-1,922,852, the vehicle being a lifting vehicle. Apart from the suspension system there is no connection between the vehicle chassis and the rigid axle for restraining the relative horizontal movement between the axle and the chassis in the stationary working position of the vehicle. It is the object of the invention to provide a vehicle suspension system of the above described type, which in the horizontal plane completely immobiles the connection between the vehicle chassis and the suspended axle, in the working position of the vehicle. This object is achieved by a vehicle suspension system which is characterized in that said suspension system comprises a lateral link whose two ends are pivotally connected to a central portion of said axle and a side portion of said vehicle chassis respectively, about axes extending in the longitudinal direction of the vehicle, whereby said lateral link substantially restrains horizontal displacement of said axle relative to said chassis and in that said double acting cylinders are each pivotally connected, at an intermediate portion of their respective cylinder tubes, to bracket means extending outwardly from said chassis. From US-A-3,406,983 and corresponding DE-U-1,978,099 an air spring suspension system for commercial vehicles is known, comprising a wishbone shaped combined torque rod and track bar arranged between the vehicle chassis and the suspended axle to improve the lateral stability of the suspension system during vehicle propulsion. No means are provided to lock or immobilise the air springs or the hydraulic shock absorbers of the suspension system. Further developed embodiments of the suspension system according to the invention are defined in the subclaims. An embodiment of the vehicle suspension system according to the invention will now be described with reference to the drawings, in which: Fig. 1A shows schematically the construction of the suspension system. Fig. 1B shows a hydraulic circuit which switches over to lock or to unlock the double acting cylinders shown in Fig. 1A. Fig. 2 is a side view of a wheel type hydraulic shovel on which a suspension system according to this embodiment has been provided for the front wheels. Fig. 3 is an enlarged view of a portion of Fig. 2, showing the details of the attachment portions of a shock absorbing spring. Fig. 4 is an enlarged plan view partly in section of a portion of Fig. 2, showing the details of the attachment portions of a link. Fig. 5 is a front view, partly in section, showing the details of the attachment portions of a double acting cylinder. Fig. 6 is a right side view of Fig. 5. Best Mode for Carrying Out the Invention An embodiment of the present invention will be described with reference to Fig. 1A through Fig. 6, showing the present invention applied to a suspension system for a wheel type hydraulic shovel. Fig. 1A shows schematically the construction of a suspension system according to the present invention. Shock absorbing springs 21L and 21R are interposed between an axle 1 and a vehicle chassis 7, and tube portions 22a and rod portions 22b of a pair of double acting cylinders 22L and 22R, which are provided a fixed distance apart in the lateral direction of the vehicle, are respectively connected to the chassis 7 and to the axle 1 by pins 23a and 23b. Further, one end of a link 24, which restrains horizontal displacement in the longitudinal and the lateral directions between the chassis 7 and the axle 1 while allowing displacement in the vertical direction, is connected to the chassis 7 by a pin 25a, while its other end is connected by a pin 25b to the portion of the axle 1 which is central with respect to the vehicle. As shown in Fig. 1B, the rod chambers 22c and the bottom chambers 22d of the double acting cylinders 22L and 22R are connected to a tank 42 via pilot operated check valves 41L and 41R respectively. The respective pilot ports of the pilot operated check valves 41L and 41R are connected to a hydraulic pressure source 44 via a solenoid controlled valve 43, and a solenoid portion 43S of this solenoid controlled valve 43 is connected to a battery 46 via a switch 45. During excavation the switch 45 is open, while during vehicle propulsion the switch 45 is closed. When the switch 45 is closed, the solenoid controlled valve 43 is shifted to its "a" position, and hydraulic pressure from the hydraulic pressure source 44 acts upon the respective pilot ports of the pilot operated check valves 41L and 41R and the pilot operated check valves 41L and 41R are opened, so that the double acting cylinders 22L and 22R become free. When the switch 45 is opened, the solenoid controlled valve 43 is shifted to its "b" position, and the respective pilot ports of the pilot operated check valves 41L and 41R are connected to the tank 42 and the rod chambers 22c and the bottom chambers 22d are respectively shut off by the pilot operated check valves 41L and 41R from the tank 42, so that the double acting cylinders 22L and 22R become locked. Moreover, it would also be acceptable to provide restrictors in the lines 47L and 47R, so that during vehicle propulsion the double acting cylinders 22L and 22R are made to function as hydraulic dampers. As is clearly shown in Fig. 3, the shock absorbing spring 21 comprises a leaf spring which is fixed by a fixing member 31 to the bottom surface of the axle 1, and spring receiving portions 7a and 7b which are projecting in the downward direction from the chassis 7 are contacted against the upper surfaces of both the end portions of the leaf spring 21 in the longitudinal direction of the vehicle; and shocks from the tires 11 are absorbed by the leaf spring 21. Referring to Figs. 3 and 4, the link 24 is provided with a cylindrical connecting portion 24a which is linked by a pin 25a to the chassis 7, flange shaped pin connecting portions 24b which are linked to the axle 1 by a pin 25b, a pair of side plates 24c which connect the pin connection portions 24a and 24b, and a pair of upper and lower cover plates 24d. By connecting the chassis 7 and the axle 1 by this type of link 24, horizontal displacement in the longitudinal and in the lateral direction between the chassis 7 and the axle 1 is restrained, while displacement in the vertical direction is allowed. Fig. 5 and Fig. 6 show the details of the attachment portions of the double acting cylinder 22. A block 7c having projecting load bearing portions 7d is welded on the right side surface of the chassis 7, and on this block 7c there are screwed by bolts 33 a pair of brackets 32 provided with load bearing portions 32a which engage with the load bearing portions 7d. Pins 23a are provided as projecting respectively in the forward and the rearward direction of the vehicle from two opposing side surfaces of the tube 22a of the double acting cylinder 22, and the pins 23a are inserted into the brackets 32 and thereby the double acting cylinder 22 is linked to the chassis 7. On the other hand, a pair of brackets 1b are provided on the upper surface of the axle 1, and the piston rod 22b of the double acting cylinder 22 is linked to the axle 1 by a pin 23b. Now the operation of the suspension system as described above will be explained. During vehicle propulsion the switch 45 is closed, and both the rod chambers 22c and the bottom chambers 22d of the double acting cylinders 22L and 22R are connected to the tank and are kept free. When the tire on the right side rides up and over a bump, the leaf spring 21R is deflected, and the axle 1 is swivelled in the clockwise direction as seen in Fig. 1 around the pin 25b as a center. At this time, the piston rods 22b of the left and right pair of double acting cylinders 22L and 22R extend and retract according to the swivelling motion of the axle 1. At this time, although a hydraulic pressure resistance force is generated by the extending and retracting motion of the double acting cylinders 22L and 22R, the shocks from the road surface are mainly absorbed by the deflecting of the leaf springs 21. When a shock is received from the tire on the left side, only the direction of swivelling of the axle 1 is opposite, and the shock absorbing operation for the shock force by the leaf springs 21 is identical. Further, when both the left and the right tires ride up and over a bump at the same time, the left and right lamellar springs 21L and 21R are deflected at the same time, and the shock is absorbed. At this time, the leaf springs 21 are able to deflect until the double acting cylinders 22 are retracted to their retracting limits. When both the tires fall off from the bump, the leaf springs 21 are able to deflect until the double acting cylinders 22 are extended to their extending limits. The reason why both the ends of the leaf springs 21R and 21L are not fixed to the chassis 7 is as follows. The chassis 7 can be displaced leftwards and rightwards with respect to the axle 1, because they are both connected by the link 24. Accordingly, the construction is such that, without the leaf springs 21R and 21L being fixed to the chassis frame 7, their movement in the leftward and rightward direction of the chassis frame 7 is permitted. Moreover, in the case that the double acting cylinders 22 are provided with a hydraulic damping function, the moment load around the pin 25b acting upon the chassis 7 due to the rolling load is absorbed by the spring force of the leaf springs 21R and 21L and by the hydraulic pressure force of the double acting cylinders 22L and 22R. On the other hand, during excavation, the switch 45 is opened, and the rod chambers 22c and the bottom chambers 22d of the double acting cylinders 22 are shut off from the tank 42 by the pilot operated check valves 41L and 41R, so that the double acting cylinders 22L and 22R are locked, and the action of the leaf springs 21L and 21R is prevented. By doing this, swivelling of the chassis 7 around the pin 25b is restrained by the double acting cylinders 22, and movement of the vehicle in the forward, backward, leftward, and rightward directions is restrained by the link 24. Accordingly, although the riding quality using the lamellar springs 21L and 21R has been maintained, the stability of the vehicle during excavation is improved. Further, since the pins 23a are provided as protruding from central portions of the tubes 22a of the double acting cylinders 22, and the double acting cylinders 22 are linked to the chassis 7 by these pins 23a, the total length in the vertical direction of the suspension system is reduced, compared with the case in which the base end portions of the tubes are linked to the chassis frame 7. Yet further, because the load bearing portions 32a of the brackets 32 to which the double acting cylinders 22 are attached are engaged to the load bearing portions 7d of the chassis 7, no shearing force due to the load during excavation or the load input from the road surface acts upon the bolts 33 for fixing on the brackets 32, so that no problem arises regarding the strength thereof. Moreover, the present invention is not limited to the above embodiment, and variations are possible like the following: (1) Coil springs can also be used for the shock absorbing springs. In this case, it is desirable for the double acting cylinders to be provided with a hydraulic damping function. (2) Any construction for the double acting cylinders will be acceptable, as long as it allows them to be locked during excavation and unlocked during vehicle propulsion. (3) Although with the above described link a displacement of the chassis in the lateral direction of the vehicle is not absolutely prevented because the chassis swivels with respect to the axle, it would also be acceptable to prevent any displacement in the horizontal direction by a link, and various forms of link could be used. (4) Although the explanation has been made for the case in which the suspension system is provided for the front wheels, it would also be acceptable to provide it for the rear wheels only, or for both the front and the rear wheels.

Claims: A vehicle suspension system connected between the vehicle chassis (7) and a rigid axle (1) supporting left and right wheels (11) said vehicle suspension system comprising: a pair of shock absorbing springs (21) connected between said axle (1) and said vehicle chassis (7) at a fixed distance apart in the lateral direction of the vehicle; a pair of double acting cylinders (22) which are provided at a fixed distance apart in the lateral direction of said vehicle, and whose tube sides (22a) and rod sides (22b) are pivotally connected to said chassis (7) and said axle (1) respectively, about axes (23a; 23b) parallel to the longitudinal axis of the vehicle; and changeover means (43) which by locking said double acting cylinders (22) obstructs the action of said springs (21), and by freeing said double acting cylinders (22) permits the action of said springs (21), characterized in that said suspension system comprises a lateral link (24) whose two ends (24a, 24b) are pivotally connected to a central portion of said axle (1) and a side portion of said vehicle chassis (7) respectively, about axes (25b, 25a) extending in the longitudinal direction of the vehicle, whereby said lateral link (24) substantially restrains horizontal displacement of said axle (1) relative to said chassis (7) and in that said double acting cylinders (22) are each pivotally connected, at an intermediate portion of their respective cylinder tubes (22a), to bracket means (32) extending outwardly from said chassis (7). A vehicle suspension system according to claim 1, characterized in that the bracket means (32) for receiving the upper pivot pin (23a) of a double acting cylinder (22) is connected to the vehicle chassis (7) by bolts (33), the bracket means (32) and the vehicle chassis (7) being provided with cooperating load supporting portions (32a; 7d) in order to inhibit shearing forces to act on said bolts (33). A vehicle suspension system according to claims 1 and 2, characterized in that the shock absorbing springs (21) are leaf springs, extending in the longitudinal direction of the vehicle, the vehicle chassis (7) being provided with downwardly projecting spring receiving portions (7a, 7b), the lower ends of which rest on the upper surface of the end portions of a corresponding leaf spring (21).

Inventors: TAHARA KOUJI, TAMURA SEIJI, TAHARA, KOUJI, TAMURA, SEIJI, TAHARA, KOUJI, 9-301 CHIYODAHAUSU
Applicants: HITACHI CONSTRUCTION MACHINERY, HITACHI CONSTRUCTION MACHINERY CO., LTD.
Application year: 1992
Main classification: B60G9
IPC codes: B60G9, B60G17