CONTROL SYSTEM FOR COOLING FAN, WORK MACHINE, AND METHOD OF CONTROLLING COOLING FAN

TECHNICAL FIELD

The present disclosure relates to a control system for a cooling fan, a work machine, and a method of controlling a cooling fan.

BACKGROUND ART

For example, WO2007/026627 (PTL 1) describes a control system for a cooling fan, the cooling fan sending air for cooling of working fluid. This literature discloses adjustment of a rotating speed of the cooling fan in the case that a stopped state of a working mechanism is detected on the basis of an operation state of a working machine lever.

CITATION LIST
Patent Literature

PTL 1: WO2007/026627

SUMMARY OF INVENTION
Technical Problem

When a hydraulically driven cooling fan is rotated at a high speed when an apparatus to be cooled does not have to be cooled so much even during rotation of an engine at a high speed, engine output is uselessly consumed, and hence the cooling fan is controlled to decrease in number of rotations. In spite of the fact that an advantage of the hydraulically driven cooling fan resides in control of the number of rotations thereof during rotation of the engine at a relatively high speed, resonance may disadvantageously occur between the cooling fan and the engine.

The present disclosure proposes a control system for a cooling fan, a work machine, and a method of controlling a cooling fan that can achieve suppression of resonance and ensured cooling capability of the cooling fan.

Solution to Problem

According to the present disclosure, a control system for a cooling fan is proposed, the control system including an engine, a work implement driven by the engine, a cooling fan configured such that the number of rotations thereof is controllable independently of the number of rotations of the engine, and a controller that controls the cooling fan. The controller obtains a frequency of the engine and a frequency of the cooling fan. The controller controls the cooling fan to make a difference in frequency between the cooling fan and the engine larger than the difference at a time point when the controller obtains the frequency of the cooling fan, by changing the frequency of the cooling fan when the number of rotations of the engine is larger than a threshold value and the frequency of the cooling fan is within a prescribed range from the frequency of the engine while the work implement is in a standstill.

Advantageous Effects of Invention

According to the present disclosure, resonance can be suppressed and cooling capability of the cooling fan can be ensured.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view schematically showing a construction of a work machine based on an embodiment.

FIG. 2 is a block diagram showing a schematic configuration of a system of the work machine shown in FIG. 1.

FIG. 3 is a block diagram illustrating a functional configuration of a controller.

FIG. 4 is a flowchart showing a flow of processing involved with control of a frequency of a cooling fan.

FIG. 5 shows a graph of relation between an operation onto a control lever and the number of rotations of the cooling fan.

FIG. 6 shows a graph of relation between the number of rotations of the engine and execution or cancellation of control of the number of rotations of the cooling fan in the embodiment.

FIG. 7 shows a graph of relation between the number of rotations of the engine and frequencies of the engine and the cooling fan.

DESCRIPTION OF EMBODIMENTS

An embodiment will be described below with reference to the drawings. In the description below, the same components have the same reference characters allotted and their labels and functions are also identical. Therefore, detailed description thereof will not be repeated.

FIG. 1 is a side view schematically showing a construction of a hydraulic excavator 100 as an exemplary work machine based on an embodiment of the present disclosure. As shown in FIG. 1, hydraulic excavator 100 in the present embodiment mainly includes a traveling unit 1, a revolving unit 2, and a work implement 3. A vehicular body of hydraulic excavator 100 is constituted of traveling unit 1 and revolving unit 2.

Traveling unit 1 includes a pair of left and right crawler belt apparatuses 1a. Each of the pair of left and right crawler belt apparatuses 1a includes a crawler belt. As a pair of left and right crawler belts is rotationally driven, hydraulic excavator 100 travels.

Revolving unit 2 is provided as being revolvable with respect to traveling unit 1. Revolving unit 2 mainly includes an operator's cab (cab) 2a, an operator's seat 2b, an engine compartment 2c, and a counterweight 2d. Operator's cab 2a is arranged, for example, on the forward left (on a front side of a vehicle) of revolving unit 2. Operator's seat 2b where an operator takes a seat is arranged in an internal space in operator's cab 2a.

Each of engine compartment 2c and counterweight 2d is arranged on a rear side (on a rear side of the vehicle) of revolving unit 2 with respect to operator's cab 2a. An engine unit (an engine, an exhaust treatment structure, and the like) is accommodated in engine compartment 2c. An engine hood covers the top of engine compartment 2c. Counterweight 2d is arranged in the rear of engine compartment 2c.

Work implement 3 is pivotably supported on the front side of revolving unit 2, and for example, on the right of operator's cab 2a. Work implement 3 includes, for example, a boom 3a, an arm 3b, a bucket 3c, a boom cylinder 4a, an arm cylinder 4b, and a bucket cylinder 4c. Boom 3a has a base end (one end) rotatably coupled to revolving unit 2 by a boom bottom pin 5a. Arm 3b has a base end (one end) rotatably coupled to a tip end (the other end) of boom 3a by a boom top pin 5b. (One end of) bucket 3c is rotatably coupled to a tip end (the other end) of arm 3b by an arm top pin 5c.

In the present embodiment, positional relation of portions of hydraulic excavator 100 will be described with work implement 3 being defined as the reference.

Boom 3a of work implement 3 rotationally moves around boom bottom pin 5a with respect to revolving unit 2. A trace of movement of a specific portion of boom 3a, for example, the tip end of boom 3a, that pivots with respect to revolving unit 2 is in an arc shape, and a plane including the arc is identified. When hydraulic excavator 100 is two-dimensionally viewed, the plane is shown as a straight line. A direction of extension of this straight line is defined as a forward/rearward direction of the vehicular body of hydraulic excavator 100 or the forward/rearward direction of revolving unit 2, and it is also simply referred to as the forward/rearward direction below. A lateral direction (direction of a vehicle width) of the vehicular body of hydraulic excavator 100 or the lateral direction of revolving unit 2 is a direction orthogonal to the forward/rearward direction in a plan view and it is also simply referred to as the lateral direction below. An upward/downward direction of the vehicular body of hydraulic excavator 100 or the upward/downward direction of revolving unit 2 is a direction orthogonal to the plane defined by the forward/rearward direction and the lateral direction and it is also simply referred to as the upward/downward direction below.

In the forward/rearward direction, a side where work implement 3 protrudes from the vehicular body is defined as the forward direction and a direction opposite to the forward direction is the rearward direction. A right side and a left side in the lateral direction when one faces the forward direction are defined as a right direction and a left direction, respectively. A side where the ground is located and a side where the sky is located in the upward/downward direction are defined as a lower side and an upper side, respectively.

The forward/rearward direction refers to the forward/rearward direction of an operator who sits in operator's seat 2b in operator's cab 2a. The lateral direction refers to the lateral direction of the operator who sits in operator's seat 2b. The upward/downward direction refers to the upward/downward direction of the operator who sits in operator's seat 2b. A direction in which the operator sitting in operator's seat 2b faces is defined as the forward direction and a direction behind the operator sitting in operator's seat 2b is defined as the rearward direction. A right side and a left side at the time when the operator sitting in operator's seat 2b faces front are defined as the right direction and the left direction, respectively. A foot side of the operator who sits in operator's seat 2b is defined as the lower side and a head side is defined as the upper side.

Boom 3a can be driven by boom cylinder (boom hydraulic cylinder) 4a. As a result of this drive, boom 3a can pivot around boom bottom pin 5a in the upward/downward direction with respect to revolving unit 2. Arm 3b can be driven by arm cylinder (arm hydraulic cylinder) 4b. As a result of this drive, arm 3b can pivot around boom top pin 5b in the upward/downward direction with respect to boom 3a. Bucket (attachment) 3c can be driven by bucket cylinder (attachment hydraulic cylinder) 4c. As a result of this drive, bucket 3c can pivot around arm top pin 5c in the upward/downward direction with respect to arm 3b. Work implement 3 can thus be driven.

Boom bottom pin 5a is supported by the vehicular body of hydraulic excavator 100. Boom bottom pin 5a is supported by a pair of vertical plates (not shown) of a frame of revolving unit 2. Boom top pin 5b is attached to the tip end of boom 3a. Arm top pin 5c is attached to the tip end of arm 3b. Each of boom bottom pin 5a, boom top pin 5b, and arm top pin 5c extends in the lateral direction. Boom bottom pin 5a is also called a boom foot pin.

Work implement 3 includes a bucket link 3d. Bucket link 3d includes a first link member 3da and a second link member 3db. A tip end of first link member 3da and a tip end of second link member 3db are coupled to each other as being rotatable relative to each other with a bucket cylinder top pin 3dc being interposed. Bucket cylinder top pin 3dc is coupled to a tip end of bucket cylinder 4c. Therefore, first link member 3da and second link member 3db are coupled to bucket cylinder 4c with the pin being interposed.

First link member 3da has a base end rotatably coupled to arm 3b with a first link pin 3dd being interposed. Second link member 3db has a base end rotatably coupled to a bracket at a root of bucket 3c with a second link pin 3de being interposed.

A pressure sensor 6a may be attached to a head side of boom cylinder 4a. Pressure sensor 6a can detect a pressure (a head pressure) of hydraulic oil within a cylinder-head-side oil chamber 40A of boom cylinder 4a. A pressure sensor 6b may be attached to a bottom side of boom cylinder 4a. Pressure sensor 6b can detect a pressure (a bottom pressure) of hydraulic oil within a cylinder-bottom-side oil chamber 40B of boom cylinder 4a. Pressure sensors 6a and 6b output hydraulic oil pressure information defined by the head pressure and the bottom pressure to a controller 30 which will be described later.

A pressure sensor 6c may be attached to a head side of arm cylinder 4b. Pressure sensor 6c can detect a pressure (a head pressure) of hydraulic oil within a cylinder-head-side oil chamber of arm cylinder 4b. A pressure sensor 6d may be attached to a bottom side of arm cylinder 4b. Pressure sensor 6d can detect a pressure (a bottom pressure) of hydraulic oil within a cylinder-bottom-side oil chamber of arm cylinder 4b. Pressure sensors 6c and 6d output hydraulic oil pressure information defined by the head pressure and the bottom pressure to controller 30 which will be described later.

A pressure sensor 6e may be attached to a head side of bucket cylinder 4c. Pressure sensor 6e can detect a pressure (a head pressure) of hydraulic oil within a cylinder-head-side oil chamber of bucket cylinder 4c. A pressure sensor 6f may be attached to a bottom side of bucket cylinder 4c. Pressure sensor 6f can detect a pressure (a bottom pressure) of hydraulic oil within a cylinder-bottom-side oil chamber of bucket cylinder 4c. Pressure sensors 6e and 6f output hydraulic oil pressure information defined by the head pressure and the bottom pressure to controller 30 which will be described later.

Boom 3a, arm 3b, and bucket 3c may be provided with respective position sensors for obtaining information on positions and attitudes thereof. The position sensors output boom information, arm information, and attachment information for obtaining the respective positions of boom 3a, arm 3b, and bucket 3c to controller 30 which will be described later.

A stroke sensor 7a may be attached to boom cylinder 4a as a position sensor. Stroke sensor 7a detects an amount of displacement of a cylinder rod 4ab with respect to a cylinder 4aa in boom cylinder 4a as boom information. A stroke sensor 7b may be attached to arm cylinder 4b as a position sensor. Stroke sensor 7b detects an amount of displacement of a cylinder rod in arm cylinder 4b as arm information. A stroke sensor 7c may be attached to bucket cylinder 4c as a position sensor. Stroke sensor 7c detects an amount of displacement of a cylinder rod in bucket cylinder 4c as attachment information.

An angle sensor may be employed as the position sensor. An angle sensor 9a may be attached around boom bottom pin 5a. An angle sensor 9b may be attached around boom top pin 5b. An angle sensor 9c may be attached around arm top pin 5c. Angle sensors 9a, 9b, and 9c may each be implemented by a potentiometer or a rotary encoder. Angle sensors 9a, 9b, and 9c output information on an angle of rotation of boom 3a and the like (boom information, arm information, and attachment information) to controller 30 which will be described later.

As shown in FIG. 1, in a side view, an angle formed between a straight line (shown with a chain double dotted line in FIG. 1) that passes through boom bottom pin 5a and boom top pin 5b and a straight line (shown with a dashed line in FIG. 1) that extends in the upward/downward direction is defined as a boom angle θb. Boom angle θb is normally an acute angle. Boom angle θb represents an angle of boom 3a with respect to revolving unit 2. Boom angle θb can be calculated from a result of detection by stroke sensor 7a or a measurement value from angle sensor 9a.

In a side view, an angle formed between the straight line that passes through boom bottom pin 5a and boom top pin 5b and a straight line (shown with a chain double dotted line in FIG. 1) that passes through boom top pin 5b and arm top pin 5c is defined as an arm angle θa. Arm angle θa represents an angle of arm 3b with respect to boom 3a in an area where arm 3b pivots in the side view. Arm angle θa can be calculated from a result of detection by stroke sensor 7b or a measurement value from angle sensor 9b.

In a side view, an angle formed between the straight line that passes through boom top pin 5b and arm top pin 5c and a straight line (shown with a chain double dotted line in FIG. 1) that passes through arm top pin 5c and a cutting edge of bucket 3c is defined as a bucket angle θk. Bucket angle θk represents an angle of bucket 3c with respect to arm 3b in an area where bucket 3c pivots in the side view. Bucket angle θk can be calculated from a result of detection by stroke sensor 7c or a measurement value from angle sensor 9c.

A schematic configuration of a system of the work machine will now be described with reference to FIG. 2. FIG. 2 is a block diagram showing a schematic configuration of the system of the work machine shown in FIG. 1.

The system in the present embodiment is a system for controlling a cooling fan 21. The system in the embodiment includes hydraulic excavator 100 representing an exemplary work machine shown in FIG. 1 and controller 30 shown in FIG. 2. Controller 30 may be mounted on hydraulic excavator 100. Controller 30 may be provided outside hydraulic excavator 100. Controller 30 may be arranged at a worksite of hydraulic excavator 100 or at a remote location distant from the worksite of hydraulic excavator 100.

An engine 15 is mounted on revolving unit 2. Engine 15 is accommodated in engine compartment 2c. Engine 15 is, for example, a diesel engine. Output from engine 15 is controlled by control of an amount of injection of fuel into engine 15. Engine 15 is a drive source of operations of hydraulic excavator 100. Drive force generated by engine 15 allows traveling unit 1 to travel, revolving unit 2 to revolve with respect to traveling unit 1, and work implement 3 to operate. In the embodiment, engine 15 is an in-line six-cylinder engine.

A hydraulic pump 23 is coupled to engine 15. As engine 15 rotates, hydraulic pump 23 is rotationally activated. As hydraulic pump 23 is activated, hydraulic oil is supplied from hydraulic pump 23 through an electromagnetic proportional control valve 24 to a hydraulic motor 22 and hydraulic motor 22 rotates. Hydraulic motor 22 is a motor to rotate cooling fan 21. In the embodiment, cooling fan 21 includes six blades. Cooling fan 21, hydraulic motor 22, and hydraulic pump 23 are mounted on revolving unit 2.

Cooling fan 21 is rotationally driven by hydraulic motor 22. Cooling fan 21 is a hydraulically driven fan driven by hydraulic oil serving as a motive power transmission medium. Since cooling fan 21 is not directly connected to an output shaft of engine 15, it is configured such that the number of rotations thereof is freely controllable independently of the number of rotations of engine 15. Specifically, the number of rotations of cooling fan 21 is controlled in accordance with a flow rate of hydraulic oil supplied from hydraulic pump 23 to hydraulic motor 22.

An intake air cooler 25 cools air suctioned into engine 15. An oil cooler 26 cools hydraulic oil that circulates through hydraulic motor 22 and hydraulic pump 23. A radiator 27 cools cooling water for engine 15. Intake air cooler 25, oil cooler 26, and radiator 27 are arranged as being opposed to cooling fan 21. As hydraulic motor 22 rotates cooling fan 21, air for cooling is sent to intake air cooler 25, oil cooler 26, and radiator 27.

Hydraulic oil for operations of hydraulic motor 22, cooling water for cooling of engine 15, and air supplied to engine 15 are exemplary working fluid involved with activation of engine 15. Cooling fan 21 sends air for cooling of working fluid.

A water temperature sensor 28 is provided in a path for cooling water. An oil temperature sensor 29 is provided in a path for hydraulic oil. An engine rotation number sensor 31 is attached to engine 15. During rotation of engine 15, water temperature sensor 28 detects a temperature of cooling water, oil temperature sensor 29 detects a temperature of hydraulic oil, and engine rotation number sensor 31 detects the number of rotations of engine 15. These results of detection are outputted to controller 30.

A fan rotation number sensor 32 is attached to cooling fan 21. During rotation of cooling fan 21, fan rotation number sensor 32 detects the number of rotations of cooling fan 21. This result of detection is outputted to controller 30.

Hydraulic excavator 100 includes an operation apparatus 33 to be operated by an operator. Operation apparatus 33 is arranged, for example, in operator's cab 2a. Operation apparatus 33 includes a work implement operation apparatus to be operated for operations of work implement 3, a revolution operation apparatus to be operated for revolution operations of revolving unit 2, and a travel operation apparatus to be operated for operations of traveling unit 1. The work implement operation apparatus and the revolution operation apparatus are, for example, control levers. The travel operation apparatus is, for example, a control pedal.

An operation detector 33A detects an amount of operation onto operation apparatus 33. When operation apparatus 33 is the control lever, operation detector 33A detects a direction and an angle of inclination from a neutral position of the control lever. When operation apparatus 33 is the control pedal, operation detector 33A detects an amount of pressing down on the control pedal. This result of detection is outputted to controller 30.

Operation detector 33A may be, for example, a displacement sensor such as a potentiometer. Operation apparatus 33 is not limited to an electrical operation apparatus, but may be a pilot hydraulic operation apparatus. In this case, operation detector 33A may be a hydraulic sensor that detects a pressure of pilot oil.

Controller 30 includes a not-shown central processing unit (CPU) and a storage 34. A program for control of operations of cooling fan 21 and various types of data necessary for execution of the program are stored in storage 34. Working data generated as works are done is temporarily stored in storage 34.

FIG. 3 is a block diagram illustrating a functional configuration of controller 30. As shown in FIG. 3, controller 30 based on the embodiment includes a work implement state distinction unit 30A, an engine frequency obtaining unit 30B, a fan frequency obtaining unit 30C, a resonance frequency setting unit 30D, a computing processing unit 30E, a fan control command unit 30F, and a timer 30T.

Work implement state distinction unit 30A distinguishes between operation and standstill of work implement 3. Engine frequency obtaining unit 30B obtains a frequency of engine 15 based on the number of rotations of engine 15 detected by engine rotation number sensor 31. Fan frequency obtaining unit 30C obtains a frequency of cooling fan 21 based on the number of rotations of cooling fan 21 detected by fan rotation number sensor 32. Resonance frequency setting unit 30D sets a range of frequencies within which resonance with the frequency of engine 15 may occur.

Computing processing unit 30E carries out various types of computation involved with control of the frequency of cooling fan 21. Fan control command unit 30F outputs a control signal to cooling fan 21. Timer 30T counts time. Computing processing unit 30E can read current time from timer 30T.

Control of cooling fan 21 by controller 30 in hydraulic excavator 100 in the embodiment configured above will be described below. FIG. 4 is a flowchart showing a flow of processing involved with control of the frequency of cooling fan 21.

As shown in FIG. 4, in step S1, whether or not the control lever to be operated for operations of work implement 3 is in a neutral state is determined. An inclination from the neutral positon of the control lever detected by operation detector 33A is inputted to controller 30. Work implement state distinction unit 30A distinguishes the state of work implement 3 based on a result of detection by operation detector 33A. Specifically, work implement state distinction unit 30A determines that the control lever has been operated, a command from the operator for activation of work implement 3 has been provided, and hence work implement 3 is operating, based on the result of detection that the control lever has been tilted from the neutral state. Work implement state distinction unit 30A determines that the operation onto the control lever has not been performed and hence work implement 3 is in a standstill, based on the result of detection that the control lever is in the neutral state.

When the control lever is determined as being in the neutral state (YES in step S1), then in step S2, whether or not a prescribed time period has elapsed. FIG. 5 shows a graph of relation between an operation onto the control lever and the number of rotations of cooling fan 21. The abscissa in FIG. 5 represents time and the ordinate in FIG. 5 represents a target number of rotations of cooling fan 21.

Computing processing unit 30E reads time from timer 30T. Computing processing unit 30E calculates time elapsed since the time of determination made for the first time that the control lever is in the neutral state in step S1 until the current time. Computing processing unit 30E reads a threshold value (a prescribed time period T1) in connection with lapse of time. Computing processing unit 30E determines whether or not a duration for which the control lever is in the neutral state has exceeded prescribed time period T1. Prescribed time period T1 is set, for example, to four seconds.

When the duration for which the control lever is neutral and work implement 3 is in a standstill is determined as not having exceeded prescribed time period T1 (NO in step S2), the process returns to step S1. Determination in step S1 as to whether or not the control lever is in the neutral state and determination in step S2 as to whether or not prescribed time period T1 has elapsed are repeated.

When it is determined that prescribed time period T1 has elapsed with the control lever being neutral and with work implement 3 being in a standstill and hence it is determined that a state that work implement 3 is in a standstill has continued for the prescribed time period (YES in step S2), then in step S3, the frequency of engine 15 is obtained. The number of rotations of engine 15 detected by engine rotation number sensor 31 is inputted to controller 30. Engine frequency obtaining unit 30B calculates the frequency of engine 15 based on the number of rotations of engine 15. This calculation is performed based on a mathematical expression below, where Fe represents the frequency of engine 15, Ne represents the number of rotations of engine 15, and C represents the number of cylinders of engine 15.

$Fe = Ne \times C / 2 \times 60$

Then, in step S4, whether or not the number of rotations Ne of engine 15 is larger than a first threshold value is determined. FIG. 6 shows a graph of relation between the number of rotations of engine 15 and execution or cancellation of control of the frequency of cooling fan 21 in the embodiment. The abscissa in FIG. 6 represents the number of rotations of engine 15. ON of a logic when the lever is neutral represented on the ordinate in FIG. 6 indicates setting to execute control of the frequency of cooling fan 21 in the embodiment. OFF of the logic when the lever is neutral represented on the ordinate in FIG. 6 shows setting to cancel control of the frequency of cooling fan 21 in the embodiment.

Computing processing unit 30E reads a first threshold value TH1 in connection with the number of rotations Ne of engine 15 from storage 34. Computing processing unit 30E compares the number of rotations Ne of engine 15 detected by engine rotation number sensor 31 with first threshold value TH1, and determines whether or not the number of rotations Ne of engine 15 is larger than first threshold value TH1. First threshold value TH1 is set, for example, to 1400 rpm.

When the number of rotations Ne of engine 15 is determined as being larger than first threshold value TH1 (YES in step S4), then in step S5, the frequency of cooling fan 21 is obtained. Fan frequency obtaining unit 30C calculates the frequency of cooling fan 21 based on the number of rotations of cooling fan 21. This calculation is performed based on a mathematical expression below, where Ff represents the frequency of cooling fan 21, Nf represents the number of rotations of cooling fan 21, and B represents the number of blades of cooling fan 21.

$Ff = Nf \times B / 60$

Cooling fan 21 sends air for cooling to intake air cooler 25, oil cooler 26, and radiator 27. A target number of rotations Nf of cooling fan 21 is set in accordance with the temperature of air which is working fluid for intake air cooler 25, the temperature of hydraulic oil which is working fluid for oil cooler 26, or the temperature of cooling water which is working fluid for radiator 27. Fan frequency obtaining unit 30C calculates a target frequency Ff of cooling fan 21 corresponding to the target number of rotations Nf of cooling fan 21 with the mathematical expression above.

FIG. 7 shows a graph of relation between the number of rotations Ne of engine 15 and frequency Fe of engine 15 and frequency Ff of cooling fan 21. The abscissa in FIG. 7 represents the number of rotations Ne of engine 15 and the ordinate in FIG. 7 represents frequency Fe of engine 15 and frequency Ff of cooling fan 21.

According to the mathematical expression described above, since the number of cylinders of engine 15 is fixed, frequency Fe of engine 15 is in proportion to the number of rotations Ne of engine 15. Frequency Ff of cooling fan 21 can be set to a value equal to or smaller than a maximum value shown in FIG. 7, independently of frequency Fe of engine 15. When a difference between frequency Ff of cooling fan 21 and frequency Fe of engine 15 is small, resonance may occur between cooling fan 21 and engine 15.

Resonance frequency setting unit 30D sets a prescribed range of frequencies within which resonance with frequency Fe of engine 15 may occur. Resonance frequency setting unit 30D sets an upper limit value and a lower limit value of frequency Ff of cooling fan 21 between which resonance may occur, as shown in FIG. 7. Resonance frequency setting unit 30D may set a range within +10 Hz of frequency Fe of engine 15 as the range within which resonance may occur. In other words, an upper limit of the range within which resonance may occur, as shown with a dashed line in FIG. 7, may be +10 Hz of frequency Fe of engine 15. A lower limit of the range within which resonance may occur, as shown with a chain dotted line in FIG. 7, may be −10 Hz of frequency Fe of engine 15.

In step S6, computing processing unit 30E determines whether or not frequency Ff of cooling fan 21 is higher than the upper limit value of the range of frequencies within which resonance with frequency Fe of engine 15 may occur. In step S7, computing processing unit 30E determines whether or not frequency Ff of cooling fan 21 is higher than the lower limit value of the range of frequencies within which resonance with frequency Fe of engine 15 may occur. In other words, in steps S6 and S7, whether or not frequency Ff of cooling fan 21 is within the range within which resonance with frequency Fe of engine 15 may occur is determined.

When frequency Ff of cooling fan 21 is determined as being equal to or lower than the upper limit value (NO in step S6) and as being higher than the lower limit value (YES in step S7), that is, when frequency Ff of cooling fan 21 is determined as being within the prescribed range within which resonance with frequency Fe of engine 15 may occur, in step S8, frequency Ff of cooling fan 21 is changed. Computing processing unit 30E makes the difference between frequency Ff of cooling fan 21 and frequency Fe of engine 15 larger than the difference at the time point when the computing processing unit obtains frequency Ff of cooling fan 21 in step S5 to suppress resonance between cooling fan 21 and engine 15, so that frequency Ff of cooling fan 21 is out of the range within which resonance may occur.

For example, computing processing unit 30E can change frequency Ff of cooling fan 21 to a frequency equal to or lower than the lower limit of the range within which resonance may occur, as shown with the chain dotted line in FIG. 7. Typically, computing processing unit 30E may change frequency Ff of cooling fan 21 to the lower limit of the range within which resonance may occur.

When frequency Ff of cooling fan 21 is higher than the upper limit value (YES in step S6) or when frequency Ff of cooling fan 21 is equal to or lower than the lower limit value (NO in step S7), frequency Ff of cooling fan 21 is not changed. Frequency Ff of cooling fan 21 calculated in step S5 is used as it is.

In step S9, cooling fan 21 is controlled in accordance with frequency Ff calculated in step S5 or frequency Ff changed in step S8. When frequency Ff of cooling fan 21 is changed in step S8, the target number of rotations Nf of cooling fan 21 is calculated from changed frequency Ff in accordance with the mathematical expression above. A control signal is transmitted from fan control command unit 30F to electromagnetic proportional control valve 24 to change the flow rate of hydraulic oil supplied from hydraulic pump 23 to hydraulic motor 22. Supplied hydraulic oil rotationally operates hydraulic motor 22. Cooling fan 21 is thus controlled to rotationally operate at the target number of rotations Nf.

Then in step S10, whether or not the number of rotations Ne of engine 15 is larger than a second threshold value is determined. As shown in FIG. 6, a second threshold value TH2 is smaller than first threshold value TH1. Second threshold value TH2 is set, for example, to 1350 rpm. When the number of rotations Ne of engine 15 is larger than first threshold value TH1, control to change frequency Ff of cooling fan 21 according to the embodiment is carried out. Even when the number of rotations Ne of engine 15 decreases to first threshold value TH1 or smaller, so long as the number of rotations Ne of engine 15 is larger than second threshold value TH2, control to change frequency Ff of cooling fan 21 is continued. When the number of rotations Ne of engine 15 decreases to second threshold value TH2 or smaller, control to change frequency Ff of cooling fan 21 is canceled.

Computing processing unit 30E reads second threshold value TH2 in connection with the number of rotations Ne of engine 15 from storage 34. Computing processing unit 30E compares the target number of rotations Ne of engine 15 set in accordance with the temperature of working fluid with second threshold value TH2 to determine whether or not the number of rotations Ne of engine 15 is larger than second threshold value TH2.

When the number of rotations Ne of engine 15 is determined as being larger than second threshold value TH2 (YES in step S10), then in step S11, whether or not the control lever is in the neutral state is determined. This determination is made as in step S1.

When the control lever is determined as being in the neutral state (YES in step S11), the process returns to step S3. When the control lever is determined as being no longer in the neutral state as a result of operation by the operator onto operation apparatus 33 for moving hydraulic excavator 100 (NO in step S11), control to change frequency Ff of cooling fan 21 is canceled and the process ends (end).

In determination in step S1, when it is determined that the control lever has been tilted from the neutral state, the operation onto the control lever has been performed, and hence work implement 3 is operating (NO in step S1), control to change frequency Ff of cooling fan 21 is not carried out. In determination in step S4, when the number of rotations Ne of engine 15 is determined as being equal to or smaller than first threshold value TH1 (NO in step S4), control to change frequency Ff of cooling fan 21 is not carried out. In step S10 after the number of rotations Ne of engine 15 is determined as being larger than first threshold value TH1 in step S4, when the number of rotations Ne of engine 15 is determined as having decreased to second threshold value TH2 or smaller (NO in step S10), control to change frequency Ff of cooling fan 21 is canceled.

In the absence of control to change frequency Ff of cooling fan 21, cooling fan 21 is controlled to rotate at the target number of rotations Nf set in accordance with the temperature of working fluid.

FIG. 5 shows such a behavior that the target number of rotations of cooling fan 21 is decreased at the time point of lapse of prescribed time period T1 with the control lever being in the neutral state, control to change frequency Ff of cooling fan 21 is canceled as a result of subsequent operation onto the control lever, and the target number of rotations of cooling fan 21 returns to the number of rotations before it is decreased. At this time, the target number of rotations of cooling fan 21 gradually increases with a prescribed time period T2 being spent. Prescribed time period T2 is set, for example, to two to three seconds. Sudden increase in pressure of hydraulic oil supplied to hydraulic motor 22 and resultant malfunction in a flow path of hydraulic oil and each hydraulic apparatus are thus suppressed.

Characteristic features and functions and effects of the embodiment will be summarized as below, although some description may overlap with the description above.

As shown in FIG. 4, controller 30 controls cooling fan 21 to make the difference in frequency between cooling fan 21 and engine 15 larger than the difference at the time point when the controller obtains the frequency of cooling fan 21, by changing frequency Ff of cooling fan 21 when the number of rotations Ne of engine 15 is larger than first threshold value TH1 and frequency Ff of cooling fan 21 is within the prescribed range from frequency Fe of the engine while work implement 3 is in a standstill.

While work implement 3 is operating, cooling capability for cooling of working fluid (hydraulic oil) by cooling fan 21 should be prioritized, and resonance between engine 15 and cooling fan 21 is less likely due to fluctuation of frequency Fe of engine 15. When the number of rotations Ne of engine 15 is equal to or smaller than first threshold value TH1, resonance between engine 15 and cooling fan 21 is less likely. Unless frequency Ff of cooling fan 21 is within the range within which resonance with frequency Fe of engine 15 may occur, control for suppression of resonance does not have to be carried out. Therefore, control to change frequency Ff of cooling fan 21 is not carried out. Since a time period for operations during which the number of rotations Nf of cooling fan 21 is decreased to lower cooling capability is shorter, cooling capability of cooling fan 21 can be ensured.

When work implement 3 is in a standstill, the number of rotations Ne of engine 15 is larger than first threshold value TH1, and frequency Ff of cooling fan 21 is within the range within which resonance with frequency Fe of engine 15 may occur, control to change frequency Ff of cooling fan 21 is carried out. Resonance between engine 15 and cooling fan 21 can thus be avoided and generation of vibration and noise can be prevented.

As shown in FIG. 4, controller 30 may change frequency Ff of cooling fan 21 to be equal to or lower than the lower limit of the prescribed range. By setting frequency Ff of cooling fan 21 to be equal to or lower than the lower limit of the range within which resonance with frequency Fe of engine 15 may occur, resonance between engine 15 and cooling fan 21 can reliably be avoided. Fuel efficiency can be improved by setting the number of rotations Nf of cooling fan 21 to be small to reduce motive power to be used for rotational drive of cooling fan 21.

As shown in FIG. 4, controller 30 may change frequency Ff of cooling fan 21 to the lower limit of the prescribed range. By rotating cooling fan 21 at the maximum number of rotations Nf within the range within which resonance between engine 15 and cooling fan 21 can reliably be avoided, lowering in cooling capability of cooling fan 21 can be suppressed.

As shown in FIGS. 4 and 6, controller 30 may cancel control to change frequency Ff of cooling fan 21 when the number of rotations Ne of engine 15 becomes equal to or smaller than second threshold value TH2 smaller than first threshold value TH1. First threshold value TH1 for execution of control to change frequency Ff of cooling fan 21 and second threshold value TH2 for cancellation of control to change frequency Ff of cooling fan 21 are set to be different from each other to exhibit hysteresis characteristics that first threshold value TH1 and second threshold value TH2 are different from each other. Since frequent switching between execution and cancellation of control to change frequency Ff of cooling fan 21 due to variation in number of rotations Ne of engine 15 can thus be avoided, undesired occurrence of an error can be prevented.

As shown in FIGS. 1 and 2, cooling fan 21 is mounted on hydraulic excavator 100. As shown in FIG. 4, controller 30 may cancel control to change frequency Ff of cooling fan 21 when it receives a command from the operator to activate hydraulic excavator 100. While work implement 3 is operating, control for suppression of resonance is not necessary. By decreasing a time period for operations during which the number of rotations Nf of cooling fan 21 is decreased to lower cooling capability, cooling capability of cooling fan 21 can be ensured.

In the embodiment, an example in which control to change frequency Ff of cooling fan 21 is carried out when it is determined in steps S1 and S2 that a standstill state of work implement 3 has continued for prescribed time period T1 is described. Determination that a state in which the number of rotations Ne of engine 15 detected by engine rotation number sensor 31 is constant has continued for a prescribed time period may be added as a condition for execution of control to change frequency Ff of cooling fan 21. While the number of rotations Ne of engine 15 fluctuates, resonance between engine 15 and cooling fan 21 is less likely, and even if resonance occurs, it will stop in a short period of time. Therefore, resonance is less likely to give rise to a problem. The number of rotations Ne of engine 15 is estimated as being constant based on determination that work implement 3 is in a standstill. Determination that the number of rotations Ne of engine 15 is constant, however, can more accurately be made based on determination based on a result of detection by engine rotation number sensor 31.

Control may be such that, when hydraulic excavator 100 is self-propelled by drive of traveling unit 1 although work implement 3 is relatively in a standstill with respect to revolving unit 2, control to change frequency Ff of cooling fan 21 is not carried out. Even when resonance between engine 15 and cooling fan 21 occurs in hydraulic excavator 100 while hydraulic excavator 100 is self-propelled, self-propelling is less frequent and resonance is less likely to give rise to a problem. Alternatively, control may be such that, when revolving unit 2 is revolving with respect to traveling unit 1 although work implement 3 is relatively in a standstill with respect to revolving unit 2, control to change frequency Ff of cooling fan 21 is not carried out. Even when resonance between engine 15 and cooling fan 21 occurs in hydraulic excavator 100 while revolving unit 2 is revolving, an angle of revolution is often 90° and revolution ends in a short period of time. Therefore, resonance is less likely to give rise to a problem. By decreasing a time period for operations during which the number of rotations Nf of cooling fan 21 is decreased to lower cooling capability, cooling capability of cooling fan 21 can be ensured.

In the embodiment, an example in which control to change frequency Ff of cooling fan 21 is canceled when it is determined in step S11 that the control lever has been operated to operate work implement 3 is described. In addition to this determination, control to change frequency Ff of cooling fan 21 may be canceled also when the revolution operation apparatus for revolution operations of revolving unit 2 or the travel operation apparatus for operations of traveling unit 1 is operated. Resonance between engine 15 and cooling fan 21 during revolution or travel is less likely to give rise to a problem. Therefore, by decreasing a time period for operations during which the number of rotations Nf of cooling fan 21 is decreased to lower cooling capability, cooling capability of cooling fan 21 can be ensured.

In the embodiment, whether work implement 3 is operating or in a standstill is determined based on detection as to whether or not the control lever to be operated for operations of work implement 3 is in the neutral state. Without being limited to this example, the operation or the standstill of work implement 3 may be determined based on results of detection by position sensors for obtaining information on positions and attitudes of boom 3a, arm 3b, and bucket 3c. The position sensor may be, for example, one or combination of stroke sensors 7a, 7b, and 7c and angle sensors 9a, 9b, and 9c described with reference to FIG. 1. When the attitudes of work implement 3 are different based on comparison of the attitudes of work implement 3 detected at different times by the position sensor, work implement 3 may be determined as being operating.

Alternatively, work implement 3 may be determined as being operating based on fluctuation over time in information on a hydraulic oil pressure detected by pressure sensors 6a, 6b, 6c, 6d, 6e, and 6f described with reference to FIG. 1. When fluctuation in delivery pressure of the hydraulic pump that supplies hydraulic oil to boom cylinder 4a, arm cylinder 4b, and bucket cylinder 4c is sensed, work implement 3 may be determined as being operating. Hydraulic excavator 100 may include an image pick-up apparatus that picks up an image of work implement 3. In this case, whether work implement 3 is operating or in a standstill may be determined based on analysis of the image picked up by the image pick-up apparatus.

Though cooling fan 21 is a hydraulically driven fan in the embodiment, without being limited as such, the cooling fan should only be such that the number of rotations Nf thereof is freely controllable with respect to the number of rotations Ne of engine 15. For example, cooling fan 21 may be an electric fan. An alternator coupled to the output shaft of engine 15 may generate electric power with drive force generated by engine 15, and an electric motor may be driven by electric power generated by the alternator to rotate cooling fan 21.

A work machine to which the concept of the present disclosure is applicable is not limited to hydraulic excavator 100, and a work machine of another type including an engine and a cooling fan, such as a crawler dozer, a wheel loader, a motor grader, or an engine-driven forklift, may be applicable.

Though embodiments have been described as above, it should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims rather than the description above and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

REFERENCE SIGNS LIST

1 traveling unit; 2 revolving unit; 3 work implement; 3a boom; 3b arm; 3c bucket; 4a, boom cylinder; 4b arm cylinder; 4c bucket cylinder; 6a, 6b, 6c, 6d, 6e, 6f pressure sensor; 7a, 7b, 7c stroke sensor; 9a, 9b, 9c angle sensor; 15 engine; 21 cooling fan; 22 hydraulic motor; 23 hydraulic pump; 24 electromagnetic proportional control valve; 25 intake air cooler; 26 oil cooler; 27 radiator; 28 water temperature sensor; 29 oil temperature sensor; 30 controller; 30A work implement state distinction unit; 30B engine frequency obtaining unit; 30C fan frequency obtaining unit; 30D resonance frequency setting unit; 30E computing processing unit; 30F fan control command unit; 30T timer; 31 engine rotation number sensor; 32 fan rotation number sensor; 33 operation apparatus; 33A operation detector; 34 storage; 100 hydraulic excavator; T1, T2 prescribed time period; TH1 first threshold value; TH2 second threshold value

CONTROL SYSTEM FOR COOLING FAN, WORK MACHINE, AND METHOD OF CONTROLLING COOLING FAN

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