Power plants – Pressure fluid source and motor – Having condition responsive control in a system of distinct...
Patent
1990-08-28
1992-01-14
Look, Edward K.
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of distinct...
60427, 60450, 60484, 91517, 91531, F16D 3102
Patent
active
050799193
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a hydraulic drive system for crawler mounted vehicles such as hydraulic excavators, and more particularly to a hydraulic drive system in which hydraulic fluid is distributed and supplied from a hydraulic pump via a plurality of pressure compensating valves to a plurality of associated actuators, including a pair of left and right travel motors, for performing the combined operation of traveling and any other at least one kind of operation.
BACKGROUND ART
A hydraulic excavator is known as one example of a crawler mounted vehicle in which a plurality of actuators including a pair of left and right travel motors are simultaneously driven to perform the combined operation of traveling and any other at least one kind of operation. Such a hydraulic excavator comprises a lower travel body including a pair of left and right crawler belts to move the hydraulic excavator, an upper swing which is swingably mounted on the lower travel body, and a front mechanism consisting of a boom, an arm and a bucket. Various equipment such as a cab, a prime mover and a hydraulic pump are mounted on the upper swing to which is also attached the front mechanism.
A hydraulic drive system for use in that type crawler mounted vehicle may be constituted as a load sensing system which includes a pump regulator for controlling the pump delivery rate such that a delivery pressure of the hydraulic pump is held higher a fixed value than a maximum load pressure among the plurality of actuators, causing the hydraulic pump to deliver a hydraulic fluid at a flow rate necessary for driving the actuators, as disclosed in JP, A, 60-11706 by way of example. In the load sensing system, a pressure compensating valve is generally disposed upstream of each flow control valve. This permits a differential pressure across the flow control valve to be held at a predetermined value decided by a spring of the pressure compensating valve. By thus arranging the pressure compensating valve to hold the differential pressure across the flow control valve at the predetermined value, when plural actuators are simultaneously driven, the differential pressures across the flow control valves associated with all the actuators can be held at the predetermined value. It is therefore possible to precisely perform flow rate control for all the flow control valves irrespective of fluctuations in load pressures, allowing the plural actuators to be simultaneously driven at desired drive speeds in a stable manner.
In the load sensing system disclosed in JP, A, 60-11706, means for applying the pump delivery pressure and the maximum load pressure in directions opposite to each other is provided in place of the spring of each pressure compensating valve, so as to set the above predetermined value in accordance with the differential pressure therebetween. As mentioned above, the differential pressure between the pump delivery pressure and the maximum load pressure is held at the predetermined value by the pump regulator. Accordingly, the differential pressure between the pump delivery pressure and the maximum load pressure can be used, in place of the spring, to set the predetermined value of the differential pressure across each flow control valve. This also permits the plural actuators to be simultaneously driven in a stable manner as with the above case.
In the case of using the differential pressure between the pump delivery pressure and the maximum load pressure in place of the spring, when the hydraulic pump is saturated and the delivery rate runs short to supply the demanded flow rate, that differential pressure is lowered and the resulting lowered differential pressure is applied to all the pressure compensating valves, whereby the differential pressures across the flow control valves are now all held at a value smaller than the predetermined value during a normal mode. As a result, under such shortage of the pump delivery rate, the hydraulic fluid is prevented from being preferentially supplied to the actuator on the low
REFERENCES:
patent: 3623322 (1971-11-01), Hancock
patent: 3720059 (1973-03-01), Schuwarski et al.
patent: 3987623 (1976-10-01), Bianchetta
patent: 4011721 (1977-03-01), Yip
patent: 4354797 (1982-10-01), Hirose et al.
patent: 4617854 (1986-10-01), Kropp
patent: 4617854 (1986-10-01), Kropp
patent: 4716728 (1988-01-01), Kakeya
patent: 4788820 (1988-12-01), Sakai et al.
patent: 4850191 (1989-07-01), Kreth et al.
patent: 4920748 (1990-05-01), Kordak et al.
patent: 4945723 (1990-08-01), Izumi et al.
patent: 4967557 (1990-11-01), Izumi et al.
Hirata Toichi
Nakamura Kazunori
Hitachi Construction Machinery Co. Ltd.
Look Edward K.
Mattingly Todd
LandOfFree
Hydraulic drive system for crawler mounted vehicle does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Hydraulic drive system for crawler mounted vehicle, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hydraulic drive system for crawler mounted vehicle will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-532819