Wheeled type working vehicle

Details Wheeled type working vehicle Wheeled type working vehicle

2001-08-07

2004-11-23

Culbreth, Eric (Department: 3616)

Land vehicles

Body elevation or tilt

Establishing riding or trim height

C180S089130, C280S124159, C280S124161

Reexamination Certificate

active

06820877

ABSTRACT:

INCORPORATION BY REFERENCE
The disclosures of the following priority applications are herein incorporated by reference:
Japanese Patent Application No. H11-031732
Japanese Patent Application No. H11-036047
Japanese Patent Application No. H11-036048
Japanese Patent Application No. H11-036049
Japanese Patent Application No. H11-036050
Japanese Patent Application No. H11-031733
Japanese Patent Application No. H11-040164
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a wheeled work vehicle that travels on tires.
2. Description of Related Art
In order to improve the comfort of the operator driving a work vehicle travelling on tires such as a wheeled hydraulic excavator, which has come to run at an increasingly high speed in recent years, Japanese Laid-Open Patent Publication No.S 62-110509, Japanese Laid-Open Patent Publication No. H 6-278438, Japanese Laid-Open Patent Publication No. H 7-125523 and Japanese Laid-Open Patent Publication No. H 7-132723, for instance, each disclose a work vehicle having a suspension mechanism provided between the body and an axle.
In the work vehicle disclosed in Japanese Laid-Open Patent Publication No. S62-110509 (hereafter referred to as prior art 1), two sets of hydraulic cylinders are provided at the two sides, i.e., on the left side and the right side of the body, the upper ends of the cylinder tubes and the lower ends of the cylinder rods are respectively linked to the body and the beam provided over the axle by using pins, and a long hole extending along the vertical direction is formed at the center of the body to link the upper center of the beam and the center of the body with a pin inserted at the long hole. The head chambers of the left hydraulic cylinder and the right hydraulic cylinder are made to communicate with each other via a restrictor, the head chambers of the left and right hydraulic cylinders are also connected to an accumulator via a pressure control valve. The line between the pressure control valve and the accumulator is connected to a hydraulic pump via a check valve which allows hydraulic oil to flow toward the accumulator. As a result, while the body moves vertically due to the contraction of the hydraulic cylinders when the wheels are subject to strong impact during travelling, the load is damped since the pressure control valve opens to communicate the hydraulic cylinders to the accumulator. If either of the left wheel or the right wheel is subject to an impact, the pressure oil from one of the hydraulic cylinders flows into the other hydraulic cylinder to rock the body.
In the work vehicle disclosed in Japanese Laid-Open Patent Publication No. H 6-278438 or Japanese Laid-Open Patent Publication No. H 7-132723 (hereafter referred to as prior art 2), double-acting hydraulic cylinders are mounted at the right side surface and the left side surface of the body with head chambers of the hydraulic cylinders connected with each other via a piping. A restrictor and an accumulator are provided in the middle of the piping and the lower ends of the cylinder rods of the hydraulic cylinders are individually linked to the axle of the work vehicle with pins. Thus, the vibration of the axle occurring during travelling is absorbed and damped to improve the comfort of the operator while travelling the vehicle.
Japanese Laid-Open Patent Publication No. H 7-125523 discloses a work vehicle (hereafter referred to as prior art 3) achieved by linking the upper ends of the cylinder tubes of one set of hydraulic cylinders and the lower ends of the cylinder rods respectively to the center of the body and the center of the axle with pins and linking the center of the axle and either the left side or the right side of the body with a link. In this vehicle, the bottom chamber of the hydraulic cylinder is connected to an accumulator via a restrictor. As a result, while the body moves in the vertical direction due to the contraction of the hydraulic cylinders if the wheels are subject to a strong impact during travelling, the load on the hydraulic cylinder communicating with the accumulator is attenuated.
SUMMARY OF THE INVENTION
The work vehicles disclosed in the publications above present the following problems. Namely, in the work vehicle in prior art 1 having the body and the axle linked with each other through a pin, a load applied to the body and the axle along the forward/backward direction during an excavating operation or due to brakes applied on the travelling vehicle must be borne by the pin and, therefore, it is necessary to use a large pin having a large pin diameter to assure a sufficient degree of pin strength. In addition, the pin used to restrict the movement of the axle relative to the body slides along the vertical direction as the axle moves up and down, hastening the process in which the sliding area becomes worn. As a result, the play of the pin in the long hole increases, which causes a displacement of the axle relative to the body along the horizontal direction as well as along the vertical direction, thereby making it difficult to smoothly absorb an impact. Furthermore, since single-acting hydraulic cylinders are utilized, which are engaged only when they contract, an impact cannot be hydraulically absorbed while they are extended, allowing the impact to be applied to the component members.
Since the body and the axle are linked to each other by the left hydraulic cylinder and the right hydraulic cylinder in the work vehicle in prior art 2, an excessive load is applied to the hydraulic cylinders in the forward/backward direction and the lateral direction as well as along the vertical direction while the vehicle is engaged in an excavating operation or if the vehicle is rocked.
In the work vehicle in prior art 3, since the body and the axle are linked to each other through the central hydraulic cylinder and the link, there is no means for limiting the rocking movement of the body, and thus, a shock related to the rocking movement cannot be absorbed. Thus, the work vehicle disclosed in the publication, in which the frame is not allowed to move vertically or to rock in a smooth manner while absorbing any impact from the axle, is not suited for practical use.
The work vehicles in prior art 2 and prior art 3 also present a problem in that while a fixed restrictor is provided in the passage between the hydraulic cylinder and the accumulator, the bottom chamber and the rod chamber of the hydraulic cylinder are not made to communicate with each other, which allows the attenuating force of the suspension to entirely depend upon the size of the sectional area of the variable constriction, thereby presenting difficulty in satisfying the personal preferences of individual operators.
Furthermore, since the movement of the left hydraulic cylinder and the right hydraulic cylinder are adjusted by a single accumulator in the work vehicles in prior art 1 through prior art 3, the capacity of the accumulator is bound to be large, which necessitates the scale of the accumulator to be large as well. It is difficult to fit such a large accumulator within the limited space inside the body through efficient space utilization, which places limits on the degree of flexibility with regard to wheeled hydraulic excavator design. In particular, if a bladder-type hydro-pneumatic accumulator is to be utilized, its structure necessitates that it be installed vertically, placing further restrictions on the installation arrangement. As a result, the accumulator may need to be installed with a part thereof projecting out from the body and, in such a case, a falling object or the like may collide with the projecting portion to damage the accumulator.
The work vehicle in prior art 2 is provided with a spool-type three ports/three positions solenoid control valve for leveling the height of the vehicle. By switching this solenoid control valve, the pressures in the hydraulic cylinders are controlled so as to set the distance between the axle and the body while the vehicle travels or it is engaged in operation to a predetermined

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