Working machine

Abstract

A working machine includes a pump actuated by power from a prime mover to deliver hydraulic fluid, a working unit including a working device and an attachment to perform work upon actuation, by hydraulic fluid, of actuator(s) included in the working device and/or the attachment, a solenoid valve to change a flow rate of hydraulic fluid to the actuator(s) based on a control signal, a controller to input the control signal into the valve, an accelerator to input a target rotation speed of the prime mover, and a rotation speed sensor to detect an actual rotation speed of the prime mover. The controller is configured or programmed to, during high-load work, if a decrease in actual rotation speed relative to the target rotation speed reaches a threshold or greater, change the control signal based on the actual rotation speed to limit the flow rate of hydraulic fluid to the actuator(s).

What is claimed is: 
     
         1 . A working machine comprising:
 a main pump to be actuated by power from a prime mover in or on a machine body to deliver hydraulic fluid;   a working unit including a working device and an attachment attached to the working device and operable to perform work via the working device and the attachment upon actuation, by the hydraulic fluid, of at least one actuator included in at least one of the working device or the attachment;   a solenoid valve to change a flow rate of the hydraulic fluid to the at least one actuator based on a control signal inputted thereto;   a controller configured or programmed to input the control signal into the solenoid valve;   an accelerator to be used to input a target rotation speed of the prime mover; and   a rotation speed sensor to detect an actual rotation speed of the prime mover; wherein   the controller is configured or programmed to, while the working unit is performing specific work that imposes a load of a predetermined amount or higher on the prime mover, if a drop which is a decrease in the actual rotation speed of the prime mover relative to the target rotation speed reaches a first threshold or greater, change the control signal based on the actual rotation speed to limit the flow rate of the hydraulic fluid to the at least one actuator.   
     
     
         2 . The working machine according to  claim 1 , further comprising:
 an auxiliary (AUX) port to allow the hydraulic fluid to flow to and from an auxiliary actuator which is the at least one actuator included in the attachment;   a pilot pump to be actuated by power from the prime mover to deliver pilot fluid; and   an AUX control valve including at least one AUX pressure receiver and operable to control the flow rate of the hydraulic fluid supplied via the AUX port to the auxiliary actuator based on a pilot pressure which is a pressure of the pilot fluid acting on the at least one AUX pressure receiver; wherein   the solenoid valve includes an AUX solenoid valve to, based on the control signal inputted thereto from the controller, change the pilot pressure acting on the at least one AUX pressure receiver to change the flow rate of the hydraulic fluid from the AUX control valve to the auxiliary actuator; and   the controller is configured or programmed to, while the specific work is being performed by the attachment which is a specific attachment including the auxiliary actuator, when the drop reaches the first threshold or greater, change the control signal based on the actual rotation speed of the prime mover to reduce the pilot pressure acting on the at least one AUX pressure receiver to limit the flow rate of the hydraulic fluid from the AUX control valve to the auxiliary actuator.   
     
     
         3 . The working machine according to  claim 2 , wherein the controller is configured or programmed to:
 control an electric current value of the control signal to the AUX solenoid valve at a predetermined value when another work differing from the specific work is being performed by the attachment which is another attachment differing from the specific attachment and when the specific work is being performed by the specific attachment but the drop is not equal to or greater than the first threshold; and   while the specific work is being performed by the specific attachment, if the drop reaches the first threshold or greater, reduce the electric current value of the control signal to the AUX solenoid valve such that the electric current value is smaller than when the other work is being performed by the other attachment and than when the drop during the specific work is not equal to or greater than the first threshold, to reduce the flow rate of the hydraulic fluid to the auxiliary actuator.   
     
     
         4 . The working machine according to  claim 1 , further comprising:
 a pilot pump to be actuated by power from the prime mover to deliver pilot fluid; and   a work control valve including at least one work pressure receiver and operable to control the flow rate of the hydraulic fluid supplied to at least one work actuator included in the working device based on a pilot pressure which is a pressure of the pilot fluid acting on the at least one work pressure receiver; wherein   the solenoid valve includes a work solenoid valve to, based on the control signal inputted thereto from the controller, change the pilot pressure acting on the at least one work pressure receiver to change the flow rate of the hydraulic fluid from the work control valve to the at least one work actuator; and   the controller is configured or programmed to, while the specific work is being performed by the working device and the attachment, if the drop reaches the first threshold or greater, change the control signal based on the actual rotation speed of the prime mover to reduce the pilot pressure acting on the at least one work pressure receiver to limit the flow rate of the hydraulic fluid from the work control valve to the at least one work actuator.   
     
     
         5 . The working machine according to  claim 4 , wherein the controller is configured or programmed to:
 control an electric current value of the control signal to the work solenoid valve at a predetermined value when another work differing from the specific work that does not impose a load of a predetermined amount or higher is being performed and when the specific work is being performed but the drop is not equal to or greater than the first threshold; and   while the specific work is being performed, if the drop reaches the first threshold or greater, reduce the electric current value of the control signal to the work solenoid valve such that the electric current value is smaller than when the other work is being performed and than when the drop during the specific work is not equal to or greater than the first threshold, to reduce the flow rate of the hydraulic fluid to the at least one work actuator.   
     
     
         6 . The working machine according to  claim 1 , further comprising an input interface to receive input of information indicating the attachment attached to the working device; wherein
 the controller is configured or programmed to, based on the information indicating the attachment, determine whether or not work to be performed by the working unit is the specific work that imposes a load of a predetermined amount or higher.   
     
     
         7 . The working machine according to  claim 2 , wherein the controller is configured or programmed to, until a predetermined period of time has passed since a start of the specific work, change the control signal inputted into the solenoid valve based on the actual rotation speed of the prime mover to limit the flow rate of the hydraulic fluid to the actuator if the drop reaches a second threshold greater than the first threshold. 
     
     
         8 . The working machine according to  claim 1 , further comprising:
 a variable displacement travel pump to be actuated by power from the prime mover, the travel pump including at least one pump pressure receiver and operable to vary a delivery flow rate of the hydraulic fluid based on a pilot pressure which is a pressure of pilot fluid acting on the at least one pump pressure receiver;   a travel motor to be actuated by the hydraulic fluid delivered by the travel pump;   a traveling device to be actuated by power from the travel motor to cause the machine body to travel; and   a travel solenoid valve to change the pilot pressure acting on the at least one pump pressure receiver based on a control signal inputted thereto from the controller; wherein   the controller is configured or programmed to, while the traveling device is causing the machine body to travel, if the drop reaches a third threshold or greater, change the control signal inputted into the travel solenoid valve based on the actual rotation speed of the prime mover to limit the delivery flow rate of the hydraulic fluid from the travel pump, the third threshold differing from the first threshold.   
     
     
         9 . The working machine according to  claim 1 , further comprising a memory and/or a storage to store a control-under-high-load graph indicating an electric current value of the control signal to the solenoid valve for use when the drop reaches the first threshold or greater during the specific work; wherein
 the control-under-high-load graph indicates that the electric current value of the control signal decreases in proportion to a decrease in rotation speed of the prime mover; and   the controller is configured or programmed to determine the electric current value of the control signal based on the control-under-high-load graph and the actual rotation speed of the prime mover, and input the control signal having the determined electric current value into the solenoid valve to limit the flow rate of the hydraulic fluid to the at least one actuator such that the flow rate decreases.   
     
     
         10 . The working machine according to  claim 9 , wherein the controller is configured or programmed to change, gradually at a predetermined rate, the electric current value of the control signal inputted into the solenoid valve such that the electric current value matches the electric current value determined based on the control-under-high-load graph and the actual rotation speed of the prime mover. 
     
     
         11 . The working machine according to  claim 9 , wherein
 the control-under-high-load graph indicates that a slope is steeper in a second range of the electric current value of the control signal than in a first range of the electric current value of the control signal, the slope being a ratio of an increase in electric current value of the control signal to an increase in rotation speed of the prime mover, the second range being below the first range; and   the controller is configured or programmed to, if the drop during the specific work reaches the first threshold or greater, change, based on the control-under-high-load graph, the electric current value of the control signal based on the actual rotation speed to a greater extent when the electric current value of the control signal is in the second range than when the electric current value of the control signal is in the first range.   
     
     
         12 . The working machine according to  claim 9 , further comprising an input interface to receive input of an instruction to change the flow rate of the hydraulic fluid to the at least one actuator; wherein
 the memory and/or the storage stores at least one control-not-under-high-load graph indicating a constant electric current value of the control signal to the solenoid valve; and   the controller is configured or programmed to, when another work differing from the specific work is being performed and when the specific work is being performed but the drop is not equal to or greater than the first threshold, input the control signal having the constant electric current value indicated by one of the at least one control-not-under-high-load graph that corresponds to the at least one actuator into the solenoid valve, and, based on the instruction inputted via the input interface, shift the corresponding control-not-under-high-load graph in a direction in which the electric current value of the control signal changes.   
     
     
         13 . The working machine according to  claim 9 , wherein
 the memory and/or the storage is operable to store a control-during-normal-time graph indicating a constant electric current value of the control signal to the solenoid valve for use when the drop is not equal to or greater than the first threshold during the specific work;   the control-under-high-load graph indicates that the electric current value of the control signal decreases in proportion to a decrease in rotation speed of the prime mover;   the control-under-high-load graph and the control-during-normal-time graph have a common point indicating the same electric current value of the control signal at the same rotation speed of the prime mover; and   the controller is configured or programmed to, if the drop reaches the first threshold or greater during the specific work, shift the control-under-high-load graph in a direction in which the rotation speed of the prime mover changes such that the rotation speed at the common point matches the actual rotation speed of the prime mover.   
     
     
         14 . The working machine according to  claim 9 , wherein the controller is configured or programmed to correct the control-under-high-load graph based on at least one of a state of the working machine, a state of the working device, a state of the hydraulic fluid, the attachment, or input information. 
     
     
         15 . The working machine according to  claim 14 , wherein the controller is configured or programmed to, if the at least one of the state of the working machine, the state of the working device, the state of the hydraulic fluid, the attachment, or the input information matches a predetermined condition a satisfaction of which leads to a further increase in the load of a predetermined amount or higher on the prime mover, correct the control-under-high-load graph such that the flow rate of the hydraulic fluid to the at least one actuator is reduced to a greater extent than when the control-under-high-load graph is not corrected. 
     
     
         16 . The working machine according to  claim 14 , wherein the controller is configured or programmed to, if the at least one of the state of the working machine, the state of the working device, the state of the hydraulic fluid, the attachment, or the input information matches a predetermined condition a satisfaction of which necessitates ensuring work performance of the working machine, correct the control-under-high-load graph such that the flow rate of the hydraulic fluid to the at least one actuator is reduced to a lesser extent than when the control-under-high-load graph is not corrected. 
     
     
         17 . The working machine according to  claim 14 , further comprising:
 a swash plate angle sensor to detect an angle of a swash plate of the main pump which is a variable displacement pump;   an AUX port to allow the hydraulic fluid to flow to and from an auxiliary actuator which is the at least one actuator included in the attachment; and   an AUX pressure sensor to detect a pressure of the hydraulic fluid acting on the AUX port; wherein   the controller is configured or programmed to calculate a horsepower consumed by the auxiliary actuator based on a detected value detected by the swash plate angle sensor and a detected value detected by the AUX pressure sensor, and correct the control-under-high-load graph based on the calculated horsepower.   
     
     
         18 . The working machine according to  claim 14 , further comprising:
 an AUX port to allow the hydraulic fluid to flow to and from an auxiliary actuator which is the at least one actuator included in the attachment; and   an AUX pressure sensor to detect a pressure of the hydraulic fluid acting on the AUX port; wherein   the controller is configured or programmed to correct the control-under-high-load graph based on the pressure of the hydraulic fluid flowing between the AUX port and the auxiliary actuator detected by the AUX pressure sensor.   
     
     
         19 . The working machine according to  claim 14 , further comprising an AUX port to allow the hydraulic fluid to flow to and from an auxiliary actuator which is the at least one actuator included in the attachment; wherein
 the controller is configured or programmed to detect a flow rate of the hydraulic fluid flowing between the AUX port and the auxiliary actuator and correct the control-under-high-load graph based on the detected flow rate.   
     
     
         20 . The working machine according to  claim 14 , further comprising an input interface to receive input of information indicating the attachment attached to the working device; wherein
 the controller is configured or programmed to correct the control-under-high-load graph based on the information indicating the attachment.   
     
     
         21 . The working machine according to  claim 14 , further comprising:
 a variable displacement travel pump to be actuated by power from the prime mover, the travel pump including at least one pump pressure receiver and operable to vary a delivery flow rate of the hydraulic fluid based on a pilot pressure which is a pressure of pilot fluid acting on the at least one pump pressure receiver;   a travel motor to be actuated by the hydraulic fluid delivered by the travel pump;   a traveling device to be actuated by power from the travel motor to cause the machine body to travel;   a travel solenoid valve to change the pilot pressure acting on the at least one pump pressure receiver based on a control signal inputted thereto from the controller to limit the delivery flow rate of the hydraulic fluid from the travel pump; and   an input interface to receive input of priority information indicating that one of (i) limiting the delivery flow rate of the travel pump using the travel solenoid valve and (ii) limiting the flow rate of the hydraulic fluid to the at least one actuator using the solenoid valve is prioritized over the other; wherein   the controller is configured or programmed to correct the control-under-high-load graph based on the priority information.   
     
     
         22 . The working machine according to  claim 14 , further comprising:
 an AUX port to allow the hydraulic fluid to flow to and from an auxiliary actuator which is the actuator included in the attachment;   a pilot pump to be actuated by power from the prime mover to deliver pilot fluid; and   an AUX control valve including at least one AUX pressure receiver and operable to control the flow rate of the hydraulic fluid supplied via the AUX port to the auxiliary actuator based on a pilot pressure which is a pressure of the pilot fluid acting on the at least one AUX pressure receiver;   a work control valve including at least one work pressure receiver and operable to control the flow rate of the hydraulic fluid supplied to a work actuator included in the working device based on a pilot pressure which is a pressure of the pilot fluid acting on the at least one work pressure receiver; and   an input interface; wherein   a plurality of the solenoid valves include:
 an AUX solenoid valve to, based on the control signal inputted thereto from the controller, change the pilot pressure acting on the at least one AUX pressure receiver of the AUX control valve to limit the flow rate of the hydraulic fluid from the AUX control valve to the auxiliary actuator; and 
 a work solenoid valve to, based on the control signal inputted thereto from the controller, change the pilot pressure acting on the at least one work pressure receiver of the work control valve to limit the flow rate of the hydraulic fluid from the work control valve to the work actuator; 
   the input interface is operable to receive input of priority information indicating that one of (i) limiting the flow rate of the hydraulic fluid using the AUX solenoid valve and (ii) limiting the flow rate of the hydraulic fluid using the work solenoid valve is prioritized over the other; and   the controller is configured or programmed to correct the control-under-high-load graph based on the priority information.   
     
     
         23 . The working machine according to  claim 14 , further comprising:
 a travel pump to be actuated by power from the prime mover to deliver hydraulic fluid;   a travel motor including an output shaft to be actuated by the hydraulic fluid delivered by the travel pump to rotate the output shaft; and   a travel switching valve to switch between a first state in which a rotation speed of the output shaft of the travel motor is brought into a first speed stage and a second state in which the rotation speed of the output shaft of the travel motor is brought into a second speed stage which is higher than the first speed stage; wherein   the controller is configured or programmed to correct the control-under-high-load graph based on whether the travel switching valve is in the first state or the second state.   
     
     
         24 . The working machine according to  claim 14 , further comprising a temperature sensor to detect a temperature of the hydraulic fluid; wherein
 the controller is configured or programmed to correct the control-under-high-load graph based on the temperature detected by the temperature sensor.   
     
     
         25 . The working machine according to  claim 14 , further comprising:
 a pair of traveling devices at a left side and a right side of the machine body; and   a travel operator including a position for forward travel, a position for rearward travel, and a turning position to be operated to any of the positions to cause the pair of traveling devices to cause the machine body to travel forward, travel rearward, or turn; wherein   the controller is configured or programmed to correct the control-under-high-load graph based on an operation state of the travel operator.   
     
     
         26 . The working machine according to  claim 14 , further comprising a work operator to be operated to actuate the working device; wherein
 the controller is configured or programmed to correct the control-under-high-load graph based on an operation state of the work operator.   
     
     
         27 . The working machine according to  claim 1 , wherein the controller is configured or programmed to produce a quasi accelerator signal which changes at a predetermined rate based on an accelerator signal inputted thereto via the accelerator, determine a quasi rotation speed of the prime mover based on the quasi accelerator signal, and change the control signal based on the quasi rotation speed instead of the actual rotation speed. 
     
     
         28 . The working machine according to  claim 1 , wherein the controller is configured or programmed to, while the specific work is being performed by the working unit, if the target rotation speed is suddenly changed by the accelerator by a predetermined value or more, calculate a decrease in the actual rotation speed relative to the target rotation speed a plurality of times within a predetermined period of time to obtain a plurality of the decreases and calculate, as the drop, an average of the plurality of calculated decreases.