Motors: expansible chamber type – With motive fluid valve – Inlet fluid supplemented by controlled fluid pressurized in...
Reexamination Certificate
2001-09-26
2003-01-07
Ryznic, John E. (Department: 3745)
Motors: expansible chamber type
With motive fluid valve
Inlet fluid supplemented by controlled fluid pressurized in...
C091S444000
Reexamination Certificate
active
06502499
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hydraulic recovery apparatus for use in a construction machine such as a hydraulic excavator, and a construction machine using the hydraulic recovery apparatus.
2. Description of the Related Art
For example, a hydraulic excavator usually comprises a lower travel structure; an upper swing structure rotatably mounted on the lower travel structure; a multi-articulated front mechanism rotatably coupled to the upper swing structure and including a boom, an arm and a bucket; and a plurality of actuators including a boom hydraulic cylinder, an arm hydraulic cylinder and a bucket hydraulic cylinder for driving the boom, the arm and the bucket, respectively.
For some of among the plurality of actuators, a higher actuator speed has recently been required, as operators have become skillful in operation of a hydraulic excavator. When performing an arm crowding operation, for example, the arm is preferably operated at a higher speed from the standpoint of work efficiency during a stroke until the bucket reaches the ground surface. In such a case, therefore, associated mechanisms are required to operate at higher speeds.
As a means for meeting that demand for speed-up, there is known a hydraulic recovery apparatus including a recovery circuit which returns a hydraulic fluid on the rod side of a hydraulic cylinder to the bottom side with a selector valve or the like for increasing the speed at which a cylinder rod is extended at the same pump delivery rate, thereby recovering energy (or keeping the same speed at a smaller pump delivery rate). Such a conventional hydraulic recovery apparatus is disclosed in, e.g., JP,A 3-117704.
The disclosed hydraulic recovery apparatus is equipped in a hydraulic drive system for a construction machine in which a plurality of actuators, such as a boom hydraulic cylinder, an arm hydraulic cylinder and a bucket hydraulic cylinder, are driven by a hydraulic fluid supplied from a hydraulic pump that is driven by a prime mover such as an engine. Then, the disclosed hydraulic recovery apparatus comprises a first line for supplying the hydraulic fluid to the bottom side of the arm hydraulic cylinder; a second line for draining the hydraulic fluid from the rod side of the arm hydraulic cylinder; and a hydraulic selector valve including a recovery line for supplying at least a part of the hydraulic fluid from the second line to the first line, and a drain line for returning the remaining part of the hydraulic fluid, which is not recovered, from the second line to a hydraulic reservoir through restricting means.
In that hydraulic recovery apparatus, during the arm crowding operation where the hydraulic selector valve is shifted to one side and the hydraulic fluid is supplied to a bottom side hydraulic chamber of the arm hydraulic cylinder, when the load imposed on the arm hydraulic cylinder is relatively small and the pressure in the bottom side hydraulic chamber is relatively low, most of the hydraulic fluid drained from the rod side of the arm hydraulic cylinder to the second line is introduced to the first line via the recovery line rather than to the drain line in which the restricting means is disposed, and is returned to the bottom side of the arm hydraulic cylinder (joined recovery state). As the load imposed on the arm hydraulic cylinder increases and the pressure in the bottom side hydraulic chamber rises, the amount of the hydraulic fluid introduced to the recovery line is reduced and a larger amount of the hydraulic fluid is introduced to the drain line in which the restricting means is disposed. Finally, the hydraulic fluid is all introduced to only the drain line and then drained to the hydraulic reservoir (end of recovery joining).
In addition, the relationship between the load of the arm hydraulic cylinder and the end of recovery joining can be optionally set by constructing the throttling means as a variable throttle driven with a pilot pressure.
SUMMARY OF THE INVENTION
The above-mentioned related art, however, has the following problems.
In the related-art hydraulic recovery apparatus, as described above, the recovery operation is basically performed by simple control, namely, just by switching over the start of recovery joining and the end of recovery joining depending on the load pressure of the arm hydraulic cylinder.
When the operating mode of a hydraulic excavator is changed, for example, from the arm-crowding sole operation to the arm-crowding and bucket-crowding combined operation, a part of the delivery rate from a hydraulic pump is introduced not to the side of the arm hydraulic cylinder, but to the side of the bucket hydraulic cylinder. Even in the case where the load pressure of the arm hydraulic cylinder is relatively low and the system is in the joined recovery state, therefore, the above situation may often result in that the hydraulic fluid cannot be supplied at a sufficient flow rate to the bottom side of the arm hydraulic cylinder in spite of a recovery flow rate being added, and the arm hydraulic cylinder cannot follow the arm crowding operation in a satisfactory manner. Such a deficiency of the supply flow rate causes the occurrence of bubbles (cavitation) in the bottom side hydraulic chamber of the arm hydraulic cylinder and hydraulic circuits connected to it, thus resulting in deterioration of operability and durability.
While the above description is made, by way of example, in connection with a deficiency of the supply flow rate caused upon a shift from the sole operation to the combined operation, the occurrence of a deficiency of the supply flow rate is not limited to such a case. A similar situation also occurs, for example, when the revolution speed of a prime mover for driving the hydraulic pump is reduced, and a similar problem arises in that case as well.
Accordingly, it is an object of the present invention to provide a hydraulic recovery apparatus for a construction machine and a construction machine using the hydraulic recovery apparatus, which can prevent the occurrence of cavitation upon, e.g., a shift to the combined operation and a decrease in revolution speed of a prime mover, and which can improve operability and durability.
(1) To achieve the above object, a hydraulic recovery apparatus for a construction machine, according to the present invention, is provided in a hydraulic drive system for driving a plurality of actuators by a hydraulic fluid supplied from at least one hydraulic pump in the construction machine, and comprises a first line for supplying the hydraulic fluid to the bottom side of at least one particular hydraulic cylinder among the plurality of actuators; a second line for draining the hydraulic fluid from the rod side of the particular hydraulic cylinder; a recovery valve means for supplying at least a part of the hydraulic fluid from the second line to the first line; a second variable throttle provided in the recovery valve means and supplying at least the part of the hydraulic fluid from the second line to the first line at a desired opening; a throttle valve means for returning the remaining part of the hydraulic fluid, which is not recovered, from the second line to a hydraulic reservoir; a first variable throttle provided in the throttle valve means and returning the remaining part of the hydraulic fluid, which is not recovered, to the hydraulic reservoir at a desired opening; and a control means for controlling respective opening areas of the first variable throttle and the second variable throttle depending on an actuator flow rate supplied from the hydraulic pump to the particular hydraulic cylinder.
With the present invention, the second variable throttle is provided in the recovery valve means for supplying a part of the hydraulic fluid from the second line to the first line, and the first variable throttle is provided in the throttle valve means for returning the remaining part of the hydraulic fluid, which is not recovered, from the second line to the hydraulic reservoir. By properly controll
Sannomiya Naoto
Tanaka Sotaro
Hitachi Construction Machinery Co. Ltd.
Mattingly Stanger & Malur, P.C.
Ryznic John E.
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