Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Construction or agricultural-type vehicle
Reexamination Certificate
1999-12-16
2001-11-20
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Construction or agricultural-type vehicle
C060S422000, C060S430000
Reexamination Certificate
active
06321152
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to control of hydraulic valve systems and, more particularly, to a system and method for monitoring margin pressure in a hydraulic system to detect an impending saturation condition and for implementing measures to control the system so as to limit further saturation thereof.
BACKGROUND ART
In the operation of a fluid system serving a plurality of work elements, the work elements often demand large volumes of fluid from their associated hydraulic fluid pumps. Situations arise where the work elements demand fluid at a rate greater than the capacity of the hydraulic pump, thus flow limitation or “saturation” occurs. Full saturation occurs at the point at which the pump pressure is substantially the same as the pressure at the work element.
Depending upon the specific machine application, the flow demands of the work element may exceed the flow capacity of the pump or pumps if the hydraulic system remains in a fixed element priority. In this state, control of the work elements is severely limited. Attempts by the operator to adjust the inputs correctly to avoid or overcome this state often lead to poor production. For example, as an agricultural tractor using a seed spreading implement approaches the end of a row and prepares to turn, the seed spreading implement is raised as the implement continues to spread the seed. If the demand on the electro-hydraulic pump is greater than what it can produce, other valves will be “starved” as pump flow is rerouted to the valve controlling the lifting of the seed spreading implement. An area of unseeded land is produced if one of the valves being starved is the valve controlling the spreading of the seed. The process of starving some more heavily loaded valves to supply pump flow to a valve under a lower load demand is a result of a saturation condition. In addition, automatic functions, such as an auto dig cycle for an excavator, cannot be implemented on such a machine. When saturation occurs during an automatic function cycle, the machine stalls or incorrectly performs the function.
Known attempts to address the problem of flow saturation include a priority system and a pressure compensation system. The former solution gives priority to one valve over all other valves in a given system. One of the valves receives pump flow while the other valves are starved. For example, a plurality of control valves can pass fluid from a pump to a plurality of respective work elements. A preprogrammed controller responsively determines the priority in which fluid is distributed from the pump to the respective control valves and then the controller delivers control signals to the respective control valves in response to the determination to control the amount of flow through each valve, for example, by selectively positioning the stem of the respective control valves. In the latter solution, the pressure compensation system, there is proportional scaling back of flow to all control valves in the system when the load demand exceeds what the hydraulic pump can supply.
Other known systems of dealing with saturation include simply increasing pump speed in an attempt to provide more output flow to the valves. None of the known methods for addressing the problem of saturation has confronted the saturation problem before the situation has fully occurred, that is, previous methods have not attempted to predict a saturation condition and limit fluid flow to prevent valve starvation. Rather, the problem of saturation has conventionally been addressed only after the condition has completely developed and valves are being starved, either fully or in part.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
DISCLOSURE OF THE INVENTION
The present system and method for implementing some type of valve prioritization scheme permits monitoring of a hydraulic system having multiple fluid valves in order to predict a saturation condition before system control is degraded. The present system then initiates system adaptations to inhibit further progression of a decrease in actual margin pressure and to inhibit the saturation condition thereby preventing a more severe reduction in work element performance level which would otherwise be caused by such saturation. The present system is, in effect, an early warning system to prevent valve starvation by noting a decrease in margin pressure and, before any valve is adversely affected, limiting fluid flow to prevent unintentional starving of the valves.
More specifically, the present system and method provides constant monitoring of the actual margin pressure and a comparison of the actual margin pressure with a preset, e.g., predetermined, established margin pressure allows detection of initiation of a saturation condition when it is determined that the actual margin pressure has just begun to fall below the established margin pressure. It is understood that “margin pressure” is the difference between the maximum supply pressure of which the pump is capable and the current highest load pressure which is demanded by the operator. The established margin pressure is set at a level intended to provide a buffer region between the pressure level which will be commanded by the operator and that which is available based upon the maximum capabilities of the system pump. If, during the constantly repeating monitoring cycle of the present system, a slight margin pressure deficit is detected, immediate correction is implemented according to a predetermined scheme such as implementing priority flow or proportional scaled-down flow to the various valves of the system.
In one aspect of the present invention, a control system and method for detecting and inhibiting an impending saturation condition in a hydraulic system of a work machine is disclosed, the hydraulic system including a hydraulic pump for supplying fluid under pressure to the system and a plurality of control valves for controlling fluid flow from the pump to a plurality of work elements. The present control system includes at least one operator input device actuatable to control the operation of the work elements and an electronic controller coupled to both the operator input device and the respective control valves, the controller being operable to receive signals from the operator input device indicative of the commanded fluid flow to at least one of the respective work elements, and being further operable to output signals to the respective control valves to control the fluid flow to the respective work elements based upon the signals received from the operator input device. In accordance with the teachings of the present invention, the controller is also operable to determine the actual margin pressure of the hydraulic pump in response to the total commanded fluid flow requested through actuation of the operator input device, and the controller is further operable to compare the actual margin pressure of the pump to an established margin pressure and to output appropriate signals to the control valves to implement a predetermined fluid flow to the respective work elements when the actual margin pressure of the pump is less than the established margin pressure.
In another aspect of the present invention, besides monitoring the margin pressure of the system, the controller is still further operable to determine the total commanded fluid flow to the respective work elements in response to actuation of the operator input device; to determine the maximum pump flow based upon the current pump speed; to compare the total commanded fluid flow to the maximum pump flow capacity; and to output appropriate signals to the control valves to establish a predetermined fluid flow to the respective work elements when the total commanded fluid flow is greater than the maximum pump flow.
REFERENCES:
patent: 4070857 (1978-01-01), Wible
patent: 4437307 (1984-03-01), Budzich
patent: 4712376 (1987-12-01), Hadank et al.
patent: 5083430 (1992-01-01), Hirata et al.
patent: 5155996 (1992-10-01), Tats
Amborski Stephen P.
Krone John J.
Ufheil Steven T.
Caterpillar Inc.
Cuchlinski Jr. William A.
Marc-Coleman Marthe Y.
LandOfFree
System and method for inhibiting saturation of a hydraulic... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with System and method for inhibiting saturation of a hydraulic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System and method for inhibiting saturation of a hydraulic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2608028