Patent Application
20110056192
Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates to hydraulic systems for excavators; and more particularly to controlling a plurality of pumps used in such hydraulic systems.
2. Description of the Related Art
Large excavators, such as power shovels, have a crawler truck on which the cab of the excavator is mounted. A boom is connected to the cab by a pivot joint that enables the boom to move up and down. The boom has a remote end to which one end of an arm is pivotally connected and a bucket is pivotally attached to the other end of the arm in turn has its own remote end to which. The bucket may be a clam-type having two pieces which open and close like a clam shell. The boom, the arm and the bucket are moved with respect to each other by separate hydraulic actuators in the form of cylinder and piston assemblies.
Large excavators have a hydraulic system with multiple pumps that can be selectively activated based on the demand for hydraulic fluid by the actuators. When deactivated, a fixed displacement pump continued was hydraulically “unloaded” by a valve that was opened to route the pump's output flow directly to the fluid reservoir. Alternatively, a variable displacement pumps was deactivated by destroking it. With those deactivation methods, however the pump still contributed to the parasitic losses as it was driven by the prime mover even when unloaded.
The multiple pump systems also typically activated and deactivated the pumps in a fixed order so that one pump always was utilized when hydraulic fluid was needed and the remaining pumps were activated in the same order as the demand for hydraulic fluid rose. Similarly as that demand decreased, the pumps were deactivated in the reverse order. As a result, the pumps were exposed to different amounts of use and thus required maintenance and replacement at different intervals.
Certain types of excavators, such as those used in mining operations, are operated continuously, 24 hours a day, and thus have to be taken out of service in order for maintenance to be performed. As a consequence, it is desirable to minimize the number of times that the excavator is removed from service.
A hydraulic system includes plurality of pumps that provide pressurized fluid to a hydraulic actuator. The plurality of pumps are controlled by a method that measures how much each of the plurality of pumps has been used. For example, that amount of use of a given pump may be determined by measuring an amount of time that the pump operates or by measuring the aggregate amount of work that the performs. When the pump is driven by an electric motor, the amount of work is derived from the voltage and current applied to the electric motor, for example.
The demand for fluid to operate the hydraulic actuator is determined and a number of the plurality of pumps are selectively activated to supply enough fluid to meet that demand. The pumps are selectively activated in sequential order from the pump with a least amount of use to the pump with a greatest amounts of use. That activation tends to operate the pumps that have been used the least so that all the pumps will have approximately the same amount of usage and tend to require maintenance and replacement at about the same time.
Another aspect of the present invention involves a hydraulic system that has a plurality of pumps which provide pressurized fluid to a plurality of hydraulic actuators. With this system, a usage value is produced for each pump indicating an amount that the respective pump has been used. For each of the plurality of hydraulic actuators, one of the pumps is assigned to each hydraulic actuator in response to the usage values for the plurality of pumps. The pumps with lower usage values are assigned to hydraulic actuators which work more, so as to equalize the use of each pump. The assignment of pumps to hydraulic actuators changes with changes in the usage values for the plurality of pumps. When a given one of the plurality of hydraulic actuators is to operate, hydraulic fluid is routed from the assigned pump to that hydraulic actuator.
With initial reference to
With reference to
Each pump 31-34 has a case drain through which fluid leakage flows from the pump to the reservoir 71, as is well known. Each of those case drains is coupled to a reservoir return line 72 by a separate flow meter 35, 36, 37 and 38 connected to the respective variable speed drive 57, 58, 59, and 60. A separate temperature sensor 61, 62, 63 and 64 is mounted on each of the motors 41, 42, 43, and 44 respectively, to sense the temperature and provide a signal back to the associated variable speed drive 57, 58, 59, and 60. Thus in addition to controlling the speed of the associated motor, each variable speed drive also gathers data about the motor temperature and the pump drain flow.
The DMP's 26, 27, 28, and 29 and specifically the variable speed drives 57, 58, 59, and 60 are controlled by a supervisory controller 50 which is a microcomputer based device that responds to control signals from the human operator of the power shovel and other signals to control the hydraulic actuators 22, 23, 24, and 25 to operate the shovel as desired. Those signals are received by the supervisory controller 50 over a conventional control network 51. The supervisory controller responds to those signals by determining the amount of hydraulic fluid necessary to be produced by each pump 31, 32, 33, and 34 and accordingly controls the motor 41, 42, 43, and 44 that drives the respective pump is a manner well known in the art.
The four primary supply lines 45, 46, 47, and 48 feed into a distribution manifold 52 which selectively directs the fluid flow from each pump to different ones of the four hydraulic actuators 22, 23, 24, and 25. Specifically, the manifold 52 has a first actuator supply line 66 which feeds a solenoid operated first control valve 80 for the boom hydraulic actuator 22. The first control valve 80 is a three-position, four-way valve which directs fluid from the first actuator supply line 66 to one of the chambers of the cylinder of the boom hydraulic actuator 22 and drains fluid from the other cylinder chamber into the reservoir return line 72 that leads to the reservoir 71. Depending upon the position of the first control valve 80, the first hydraulic actuator 22 is driven in either of two directions to thereby raise or lower the boom 16. Similarly, the second, third, and fourth actuator supply lines 67, 68, and 69 from the distribution manifold 52 are connected by similar second, third, and fourth control valves 81, 82, and 83 to the arm hydraulic actuator 23, the curl hydraulic actuator 24, and the clam hydraulic actuator 25, respectively. The four actuator control valves 80-83 are independently operated by separate signals from the supervisory controller 50. Although the present hydraulic system 30 utilizes control valves 80-83 between the distribution manifold 52 and the hydraulic actuators 22-25, the control valves could be eliminated by incorporating their functionality into additional valves in the distribution manifold to control flow to and from each cylinder chamber.
The present distribution manifold 52 has a matrix of sixteen distribution valves 84-99. Each distribution valve couples one of the primary supply lines 45, 46, 47, or 48 to one of the actuator supply lines 66, 67, 68, or 69. Therefore, when a given distribution valve 84-99 is electrically operated by a signal from the supervisory controller 50, a path is opened between the associated primary supply line and actuator supply line, thereby applying pressurized fluid from the pump connected to that primary supply line to the control valve 80, 81, 82, or 83 connected to that actuator supply line. For example, when distribution valve 85 is activated fluid from the first pump 31 flows through the first primary supply line 45 into the second actuator supply line 67 and onward to the second control valve 81. By selectively operating one or more of the distribution valves 84-99, the output from each pump 31-34 can be used to operate each of the four hydraulic actuators 22, 23, 24, or 25. This results is a given pump being assigned to a hydraulic actuator. It should be understood that on a particular power shovel, there may be a greater or lesser number of pumps and a greater or lesser number of hydraulic actuators; in which case the distribution manifold 52 will be configured with a corresponding different number of distribution valves. For example, hydraulic motors may independently drive the left and right tracks of the crawler assembly 12 to propel the power shovel.
It also should be understood that the output from two or more pumps can be combined to supply the same hydraulic actuator 22-25. For example, if only the arm hydraulic actuator 23 is active, the output from multiple pumps can be combined so that the arm is driven to dig into the earth with maximum speed and force. When another shovel function is to operate simultaneously with the arm, one or more of the pumps previously connected to the arm function is reassigned to provide fluid to that other shovel function by redirecting the flow through the distribution manifold 52. Also should a DMP 26-29 fail, it is deactivated by shutting off the associated variable speed drive and disconnecting the associated pump by closing all the valves in the distribution manifold 52 that are connected to the respective primary supply line. In this case, fluid from the remaining pumps supplied through the distribution manifold to operate the hydraulic actuators. If, however, the output of a particular pump is not required at a given point in time, its variable speed drive is deactivated so that the motor and thus that pump do not operate.
For very large power shovels, relatively large forces encountered by the arm hydraulic actuator 23 and curl hydraulic actuator 24 during a digging operation. In addition, the arm and curl hydraulic actuators 23 and 24 tend to be operated for longer periods of time than the other hydraulic actuators. The claim hydraulic actuator 25 associated with the bucket 20 typically is significantly smaller and consumes far less hydraulic fluid. In previous power shovels, a given pump often was dedicated to supplying fluid to one of the hydraulic actuators and thus the motor-pumps combinations performed different levels of work. In other words, because the pumps and motors for the arm and the bucket curl functions perform considerably more work than other pumps and motors in the hydraulic system, those heavily worked components tended to require more maintenance and more frequent replacement than the other motors and pumps. Therefore, the different motor/pump combinations required servicing at different times at during which the entire power shovel had to be taken out of service. The resultant downtime adversely affected the power shovel's overall productivity and economy of operation.
The present invention overcomes the problems with such previous systems by dynamically changing the assignment of the DMP's to the hydraulic actuators so that each motor/pump combination is exposed to substantially the same amount of use and work. As a consequence, all the DMP's will require maintenance and possible replacement at about the same point in time. Thus, the service and replacement intervals for the DMP's are synchronized so that the maintenance intervals, mean time to repair, and mean time between failure are optimized and provide a longer mean time between failure for the entire hydraulic system. This reduces the number of service down periods over the life of the excavator and thereby increases productivity.
In order to determine the usage of the DMP's, the supervisory controller 50 gathers data regarding the operation of their motors and pumps, such as electric current and voltage applied to the motor, motor temperature, speed, torque, aggregate operating time, and amount of pump drain flow. The accumulated data is utilized to determine the relative amount of work performed by each DMP 26, 27, 28, and 29. To this end the supervisory controller 50 executes different software routines that gather and analyze the pump and motor data to estimate the remaining anticipated life of those components and the aggregate amount of use that they have provided. The term DMP is being used to refer to performance of the motor/pump combination as well as performance of the individual motor and pump therein.
With reference to
Thereafter at step 114, the DMP life routine 100 enters a section at step 116 in which the present life expectancy of each pump 31-34 is estimated. The supervisory controller 50 initially records the speed and torque of the motors 41-43, which information is derived from the electric voltage and current levels applied by the variable speed drives 57-60. Alternatively, the speed and torque data can be measured by sensors attached to the drive shaft linking a motor to a pump. The supervisory controller 50 also obtains the amounts of fluid flow exhausting from the pump case drains. Those flow rates are sensed by the flow meters 35, 36, 37, and 38 connected to circuitry in the variable speed drives 57, 58, 59, and 60 which relay the case drain flow data to the supervisory controller. Then at step 118, the amounts of fluid flow and pressure at the supply outlet of each pump 31-34 are derived from the respective speed and torque values. Specifically, the flow is the product of the speed and the fixed pump displacement. The torque correlates directly with the pump supply outlet pressure. Alternatively the fluid flow and pressure can be measured directly by sensors at the supply outlet of each pump 31-34.
At step 120, the values for the amounts of supply outlet fluid flow, pump pressure, and the case drain flow are compared with data provided by the manufacturer of the pumps to determine the present point on the life cycle for each pump. Specifically, the leakage of the pump represented by the flow from the pump case drain increases as a pump ages. In other words, the older the pump, the greater the case drain flow, however, the actual case drain flow at any point in time also is a function of the fluid flow and pressure produced at the supply outlet by the pump. That is, the case drain flow increases as the flow and pressure produced by the pump increase. A typical pump manufacturer has correlated the expected pump case drain flow for various pressure and flow amounts at different times during the life cycle of the pump. By comparing the actual fluid flow, pressure, and pump case drain flow to manufacturer specification data, the supervisory controller 50 is able to determine the remaining life of each of the pumps 31-34, at step 122. This determination is stored within the memory of the supervisory controller 50 for display to the pump operator and service personnel, as well as for determining the trends of the pump life cycle to estimate when pump maintenance and replacement will be required.
With reference to
The DMP assignment routine 130 commences at step 132 where a finding is made whether the hydraulic system 30 is currently operating at least one actuator, if so, the routine advances to step 134. At that point, the present assignments of the four DMP's 26, 27, 28 and 29 to the different hydraulic actuators 22, 23, 24, and 25 is recorded as a table in the memory of the supervisory controller 50.
Returning to the DMP assignment routine 130 in
At step 138 the magnitudes of electric voltage and current that the respective variable speed drive 57, 58, 59, and 60 applies to the associated motor 41, 42, 43 and 44 are read by the supervisory controller 50. Each variable speed drive 57, 58, 59, and 60 stores a digitized temperature value resulting from a signal produced by the temperature sensor 61, 62, 63 or 64 attached to the associated motor 41, 42, 43, or 44, respectively. The temperature values also are read from the variable speed drives and stored within the memory of the supervisory controller 50 at step 140.
At step 142, the electrical values read for each motor 41-44 are used to determine the amount of work that the respective DMP performed. Specifically, the current and voltage levels for a particular motor are multiplied to produce a value denoting the amount of electrical power consumed during the time interval between measurements. Not all consumed input electrical power is converted into mechanical power for driving the pump, because energy is lost as heat produced in the motor. The measured temperature of the respective motor is used to calculate the amount of the electrical power that was consumed in heating that motor, i.e., the heat power loss. Therefore, the mechanical power provided by the associated pump 31-34 is calculated by subtracting the heat power loss from the amount of electrical power consumed. The resultant mechanical power value then is integrated over the measurement interval to derive the amount of work that the pump performed. The new amount of work then is added to a sum of similar amount of work calculated previously to provide a measurement of the aggregate amount of work that the pump has performed since its installation. This work computation is performed individually for each of the pumps 31-34 and the resultant aggregate amounts of work are stored in the supervisory controller 50. At step 144, the DMP's 26-29 are ranked in order of the aggregate amount of work that each has performed.
As noted previously, the DMP's supplying the arm and curl hydraulic actuators 23 and 24 perform a greater amount of work over time than the boom and claim hydraulic actuators 22 and 25. Thus the DMP's that control the flow of fluid to the arm and curl hydraulic actuators corresponding perform a greater amount of work. The purpose of the DMP assignment routine 130 is to equalize the aggregate amounts of work that the motor/pump combinations perform so that they are subjected to substantially equal amount of wear and therefore require maintenance and ultimately replacement at approximately the same time. Doing so reduces how often the power shovel 10 must be taken out of operation.
In a standard configuration of the distribution manifold 52, a separate pump 31-34 is connected to feed fluid to a different hydraulic actuator 22-25. Which pump is connected to which hydraulic actuator is determined dynamically in response to the ranking of the DMP's based on the aggregate amount of work that each performed. The DMP to hydraulic actuator assignments are recorded as a table in the memory of the supervisory controller 50 and
For machines in which the different hydraulic actuators are subjected to substantially equal forces, the assignment of DMP's can be based on operating time. For example, the DMP that with the lowest aggregate amount of work is assigned to the hydraulic actuator that operates most often. Similarly the DMP that with the greatest aggregate amount of work is assigned to the hydraulic actuator that operates least often. In another variation of the present control technique, when a hydraulic actuator is operate, the inactive DMP with the lowest aggregate amount of work is assigned to provide fluid that actuator.
In another situation, a given hydraulic actuator may have a varying demand for hydraulic fluid depending on the force acting on that actuator. One DMP alone may not be able to meet all demand levels. Therefore at higher demand levels, multiple pumps are used to provide fluid to that given hydraulic actuator. Here the DMP's are assigned to the given hydraulic actuator in order from the DMP with the lowest aggregate amount of work to the DMP with the greatest aggregate amount of work. Thereafter, when the demand for hydraulic fluid from a hydraulic actuator decreases, the DMP's are unassigned in the reverse order. Specifically, the DMP with the greatest aggregate amount of work is disconnected first and the DMP with the lowest aggregate amount of work remains connected until fluid not longer is needed.
The foregoing description was primarily directed to a preferred embodiment of the invention. Although some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure.
