Patent Publication Number: US-8538640-B2

Title: Travel damper control device for wheel loader

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Japanese Patent Application No. 2010-288264 filed on Dec. 24, 2010, the disclosure of which is hereby incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present invention relates to a travel damper control device mounted on a wheel loader. 
     BACKGROUND ART 
     In general, wheel loaders are not provided with a suspension system for absorbing vibration of a vehicle body in order to efficiently utilize driving force for works such as digging. Therefore, chances are that a load such as earth and sand, loaded on a work implement (e.g., a bucket) attached to the tips of a pair of booms, drops due to vibration of the vehicle body during travelling. 
     In view of the above, methods of providing a travel damper formed by boom cylinders and an accumulator communicated with the boom cylinders have been proposed (see Japan Laid-open Patent Application Publication Nos. H05-209422 and 2007-186942). In the method described in Japan Laid-open Patent Application Publication No. H05-209422, the accumulator is configured to be coupled to the boom cylinders when the vehicle speed of a wheel loader is greater than or equal to a predetermined value. In the method described in Japan Laid-open Patent Application Publication No. 2007-186942, a control of accumulating pressure in the accumulator is executed depending on at least either of the vehicle speed of the wheel loader and a position of a front/rear travel lever. 
     SUMMARY 
     However, the methods described in Japan Laid-open Patent Application Publication Nos. H05-209422 and 2007-186942 do not take so-called “a rap-out” into consideration, and therefore, have a drawback as described below, it should be noted that “a nip-out” is an action of dropping earth, sand and etc. adhered to a work implement by hitting a cross tube coupling a pair of booms in a vehicle width direction with a bell crank pivotably attached to the cross tube. 
     When a rap-out is executed, an acute peak pressure is generated in the boom cylinder by the shock. Therefore, a drawback is produced that the peak pressure is transmitted to the accumulator from the boom cylinder if the accumulator is coupled to the boom cylinder in executing a rap-out and thereby durability of the accumulator is degraded. 
     The present invention has been produced in view of the aforementioned situation, and it is an object of the present invention to provide a travel damper control device and a travel damper control method whereby degradation in durability of an accumulator can be inhibited. 
     A travel damper control device according to a first aspect of the present invention is mounted on a wheel loader, the wheel loader including a pair of booms, a rotary shaft, a bell crank, a work implement, a boom cylinder and an accumulator, the pair of booms coupled by a cross tube arranged along a vehicle width direction, the rotary shaft arranged along the vehicle width direction and attached to the cross tube, the bell crank attached pivotably about the rotary shaft, the work implement coupled to the bell crank, the boom cylinder coupled to the pair of booms, and the accumulator communicated with the boom cylinder through an open/close valve. The travel damper control device includes a proximity detecting part configured to detect that the bell crank is in proximity to the cross tube and a valve switching part configured to switch the open/close valve into a closed position when the proximity detecting part detects that the bell crank is in proximity to the cross tube. 
     According to the travel damper control device for a wheel loader of the first aspect of the present invention, the open/close valve is configured to be switched into the closed position at a point of time when it is detected that the bell crank is in proximity to the cross tube. In other words, it is possible to quickly block communication between the boom cylinder and the accumulator before the cross tube is hit with the bell crank. It is thereby possible to inhibit an acute peak pressure, generated in the boom cylinder in executing a rap-out, from being transmitted to the accumulator. Therefore, it is possible to inhibit degradation in durability of the accumulator. 
     A travel damper control device according to a second aspect of the present invention relates to the first aspect, the proximity detecting part is configured to detect that the bell crank is in proximity to the cross tube when an inner angle formed by the pair of booms and the bell crank becomes less than or equal to a first angle in a side view of the wheel loader. 
     According to the travel damper control device of the second aspect of the present invention, proximity of the bell crank can be detected based on the inner angle formed by the booms and the bell crank. Therefore, it is possible to further easily and accurately detect proximity of the bell crank compared to cases such as a case that the interval between the bell crank and the cross tube is directly measured. 
     A travel damper control device according to a third aspect of the present invention relates to the second aspect, the proximity detecting part is configured to continuously detect that the bell crank is in proximity to the cross tube while the inner angle is less than or equal to a second angle greater than the first angle after the inner angle becomes less than or equal to the first angle. 
     According to the travel damper control device for a wheel loader of the third aspect of the present invention, the second angle is greater than the first angle, and therefore, the travel damper is configured to be tuned OFF until the bell crank is sufficiently separated away from the cross tube after the bell crank once gets closer to the cross tube. Accordingly, it is possible to inhibit the travel damper from being repeatedly turned ON and OFF uselessly in a short period of time. 
     A travel damper control device according to a fourth aspect of the present invention relates to one of the first to third aspects, the travel damper further includes an angular rate obtaining part configured to configured to obtain an angular rate of the bell crank pivoting about the rotary shaft. The valve switching part is configured to keep the open/close valve in an opened position when the angular rate of the bell crank is less than or equal to a predetermined threshold. According to the travel damper control device for a wheel loader of the fourth aspect of the present invention, it is possible to inhibit the travel damper from being repeatedly turned ON and OFF uselessly when it is less required to block the boom cylinder from communicating with the accumulator. 
     According to the present invention, it is possible to provide a travel damper control device and a travel damper control method whereby degradation in durability of an accumulator can be inhibited. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a wheel loader  1  according to an exemplary embodiment. 
         FIG. 2  is a perspective view illustrating a support structure of a bucket  50  according to the exemplary embodiment. 
         FIG. 3  is a side view illustrating a positional relation between booms  40  and a bell crank  80  according to the exemplary embodiment. 
         FIG. 4  is a circuit diagram representing a configuration of a hydraulic circuit  100  according to the exemplary embodiment. 
         FIG. 5  is a block diagram representing a configuration of a control device  110  according to the exemplary embodiment. 
         FIG. 6  is a flowchart representing actions of the control device  110  according to the exemplary embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Next, an exemplary embodiment of the present invention will be explained using figures. In the following description of the figures, the same or similar reference numeral is given to the same or similar elements. It should be noted that the figures are schematic only and respective dimensional ratios and etc. of the figures may be different from actual ones. Therefore, specific dimensions and etc. should be judged in view of the following explanation. Further, it is apparent that dimensional relations and ratios of corresponding parts/portions/sections are different among the figures. 
     Overall Structure of Wheel Loader  1   
     The structure of a wheel loader  1  according to an exemplary embodiment will be explained with reference to the figures.  FIG. 1  is a perspective view of the wheel loader  1  according to the present exemplary embodiment. 
     The wheel loader  1  includes a vehicle body frame  10 , a cab  20 , four tires  30 , a pair of booms  40  and a bucket  50  (an exemplary “work implement”). 
     The vehicle body frame  10  has so-called an articulate structure. The cab  20  is mounted on the vehicle body frame  10 . The cab  20  accommodates a seat, an operating tool and etc. not illustrated in the figure. The four tires  30  support the vehicle body frame  10 . The booms  40  of the pair are disposed while being opposed to each other in the vehicle width direction. The pair of booms  40  is pivotably supported by the front end of the vehicle body frame  10 . The bucket  50  is pivotably supported by the front ends of the booms  40  of the pair. 
     Now,  FIG. 2  is a perspective view illustrating the support structure of the bucket  50  according to the exemplary embodiment. The wheel loader it includes a cross tube  60 , a rotary shaft  70 , a bell crank  80 , a link  90 , a pair of boom cylinders  40 S and a bucket cylinder  80 S. 
     The cross tube  60  is arranged along the vehicle width direction. The cross tube  60  couples the booms  40  of the pair. The cross tube  60  has a support portion  60   a  for supporting the bell crank  80 . The support portion  60   a  is disposed while being protruded forwardly upwards from the cross tube  60 . 
     The rotary shaft  70  is arranged along the vehicle width direction. The rotary shaft  70  is attached to the support portion  60   a . The rotary shaft  70  is inserted through the center part of the bell crank  80 . 
     The bell crank  80  is supported by the support position  60   a  through the rotary shaft  70 . The bell crank  80  is pivotable about the rotary shaft  70 . The bell crank  80  has a cylinder shaft portion  80   a  disposed at the end thereof in the vehicle width direction. 
     The link  90  is coupled to the bucket  50  and the bell crank  80 . The link  90  transmits vibration of the bell crank  80  to the bucket  50 . Accordingly, the posture (i.e., a tilt/dump angle) of the bucket  50  is controlled. 
     The boom cylinders  40 S of the pair are coupled to the vehicle body frame  10  and the booms  40  of the pair. The pair of boom cylinders  40 S is configured to be extended and contracted by operating oil to be supplied to the inside thereof. Accordingly, the pair of booms  40  is configured to be pivoted up and down. It should be noted that each of the booms  40  of the pair is supported about a first shaft portion  40   a  by the vehicle body frame  10 , while being supported about a second shaft portion  40   b  by the bucket  50 . In the present exemplary embodiment, the pair of boom cylinders is communicated with an accumulator  130  through an open/close valve  120  (see  FIG. 4 ). A hydraulic circuit  100 , fanning a part of a travel damper, will be explained below. 
     The bucket cylinder  80 S is coupled to the vehicle body frame  10  and the bell crank  80 . The front end of the bucket cylinder  80 S is supported about the cylinder shaft portion  80   a  of the bell crank  80 . The bucket cylinder  80 S is configured to be extended and contracted by operating oil to be supplied to the inside thereof. Accordingly, the bucket  50  is configured to be dumped and tilted. 
     Now, as illustrated in  FIG. 2 , the cross tube  60  has a dump stopper  61  while the bell crank  80  has a stopper contact portion  81 . In executing “a rap-out”, an operator hits the dump stopper  61  with the stopper contact portion  81 . “A rap-out” is an action of dropping earth, sand and etc. adhered to the inner surface of the bucket  50  by the shock in hitting the dump stopper  61  with the stopper contact portion  81 . 
     Positional Relation Between Boom  40  and Bell Crank  80   
     The positional relation between the booms  40  and the bell crank  80  according to the present exemplary embodiment will be explained with reference to the figure.  FIG. 3  is a side view illustrating the positional relation between the booms  40  and the bell crank  80 . It should be noted that  FIG. 3  illustrates a state immediately before execution of a rap-out. 
     In executing a rap-out, the dump stopper  61  of the cross tube  60  is hit with the stopper contact portion  81  of the bell crank  80 . In this case, an inner angle R formed by the pair of booms  40  and the bell crank  80  indicates a limit value α in a side view. In other words, when the inner angle R is the limit value α, the stopper contact portion  81  of the bell crank  80  makes contact with the dump stopper  61  of the cross tube  60 . 
     As illustrated in  FIG. 3 , the inner angle R is herein an angle (&lt;90°) formed by a boom baseline A and a bell crank baseline B. The boom baseline A is a straight line connecting the first shaft portion  40   a  and the second shaft portion  40   b  of the booms  40 . The bell crank baseline B is a straight line connecting the cylinder shaft portion  80   a  of the bell crank  80  and the rotary shaft  70 . 
     Further, the inner angle R is detected by a bell crank angle sensor  80 T disposed on the rotary shaft  70 . The bell crank angle sensor  80 T detects an angle of the bell crank  80  rotated about the rotary shaft  70  from a baseline position. 
     Structure of Hydraulic Circuit  100   
     The configuration of the hydraulic circuit  100  according to the present exemplary embodiment will be explained with reference to the figures.  FIG. 4  is a circuit diagram representing the configuration of the hydraulic circuit  100  according to the present exemplary embodiment. The hydraulic circuit  100  forms the travel damper of the wheel loader  1 . 
     The hydraulic circuit  100  includes a control device  110 , the open/close valve  120 , the accumulator  130 , a hydraulic pump  140 , a boom cylinder control valve  150  and an operating oil tank  160 . 
     The control device  110  is configured to switch the position of the open/close valve  120  for executing an on/off control of the travel damper of the wheel loader  1 . The configuration and action of the control device  110  will be described below. 
     The open/close valve  120  is a dual-position switching valve having an opened position X and a closed position Y When located in the opened position X, the open/close valve  120  is communicated with an oil path L 1  and an oil path L 2 . Accordingly, the travel damper of the wheel loader  1  is turned ON. When located in the closed position Y, the open/close valve  120  blocks communication between the oil path L 1  and the oil path L 2 . Accordingly, the travel damper of the wheel loader  1  is turned OFF. 
     The accumulator  130  functions as a damper mechanism for attenuating vibration of the boom cylinders  40 S when communicated with the boom cylinders  40 S through the open/close valve  120 . On the other hand, the accumulator  130  does not function as a damper mechanism when blocked from communicating with the boom cylinders  40 S by the open/close valve  120 . 
     The hydraulic pump  140  is driven by an engine (not illustrated in the figures). The hydraulic pump  140  is configured to supply the operating oil stored in the operating oil tank  160  to the pair of boom cylinders  40 S through the boom cylinder control valve  150 . 
     Structure of Control Device  110   
     The configuration of the control device  110  according to the present exemplary embodiment will be explained with reference to the figures.  FIG. 5  is a block diagram representing the configuration of the control device  110  according to the present exemplary embodiment. 
     The control device  110  includes an inner angle obtaining part  112 , a proximity detecting part  113 , an FNR speed stage obtaining part  114 , a vehicle speed obtaining part  115 , a load state detecting part  116  and a valve switching part  117 . 
     The inner angle obtaining part  112  is configured to obtain the inner angle R formed by the pair of booms  40  and the bell crank  80  from the bell crank angle sensor  80 T on a real-time basis. The inner angle obtaining part  112  is configured to transmit the inner angle R to the proximity detecting part  113 . 
     The proximity detecting part  113  is configured to detect that the bell crank  80  is in proximity to the cross tube  60 . In the present exemplary embodiment, the proximity detecting part  113  is configured to determine whether or not the inner angle R formed by the booms  40  and the bell crank  80  is less than or equal to a first angle R 1  (the limit value α+Δr: Δr is a positive number). The proximity detecting part  113  is configured to output a first OFF signal S OFF1  to the value switching part  117  when the inner angle R is less than or equal to the first angle R 1 . 
     Further, the proximity detecting part  113  is configured to determine whether or not the inner angle R is less than or equal to a second angle R 2  (the limit value α+Δs: Δs is a positive number greater than Δr) greater than the first angle R 1  after once determining that the inner angle R is less than or equal to the first angle R 1 . The proximity detecting part  113  is configured to output the first OFF signal S OFF1  to the valve switching part  117  when the inner angle R is less than or equal to the second angle R 2 . 
     The FNR speed stage obtaining part  114  is configured to obtain an operating position signal indicating the operating position of a shill lever to be operated by an operator. The operating position signal indicates which of the following states the wheel loader  1  is in: a forward travelling state; a rearward travelling state; and a neutral state and indicates which of the first to fourth speed stages a transmission device is in. The FNR speed stage obtaining part  114  is configured to output a second OFF signal S OFF2  to the value switching part  117  when the operating position signal indicates either the neutral state or the first speed stage. 
     The vehicle speed obtaining part  115  is configured to obtain the vehicle speed of the wheel loader  1 , for instance, from a vehicle speed meter. The vehicle speed obtaining part  115  is configured to output a third OFF signal S OFF3  to the value switching part  117  when the vehicle speed is less than or equal to a predetermined speed (e.g., 5 km/h). It should be noted that the vehicle speed obtaining part  115  is configured not to output the third OFF signal S OFF3  to the value switching part  117  when the load state detecting part  116  detects that the bucket  50  contains a load. 
     The load state detecting part  116  is configured to detect whether or not the bucket  50  contains a load based on, for instance, the cylinder bottom pressure of each of the boom cylinders  40 s of the pair. The load state detecting part  116  is configured to output the detection result to the vehicle speed obtaining part  115 . 
     The valve switching part  117  is configured to receive an ON signal S ON  from a travel damper switch DS when an operator turns ON the travel damper switch DS. The valve switching part  117  is configured to switch the open/close valve  120  into the opened position X in response to receipt of the ON signal S ON . It should be noted that the valve switching part  117  is configured to switch the open/close valve  120  into the closed position Y while at least one of the first to firth OFF signals S OFF1  to S OFF3  is being inputted. 
     Actions of Control Device  100   
     Actions of the control device  110  according to the present exemplary embodiment will be explained with reference to the figures.  FIG. 6  is a flowchart representing the actions of the control device  110  according to the present exemplary embodiment. 
     In Step S 10 , the control device  110  determines whether or not the ON signal S ON  is being inputted. The processing repeats Step S 10  when the ON signal S ON  is not being inputted. The processing proceeds to Step S 20  when the ON signal S ON  is being inputted. 
     In Step S 20 , the control device  110  determines whether or not the inner angle R formed by the booms  40  and the bell crank  80  is less than or equal to the first angle R 1  (the limit value α+Δr). The processing proceeds to Step S 30  when the inner angle R is not less than or equal to the first angle R 1 . The processing proceeds to Step S 40  when the inner angle R is less than or equal to the first angle R 1 . 
     In Step S 30 , the control device  110  determines whether or not the second OFF signal S OFF2  and the third OFF Signal S OFF3  are being inputted. The processing proceeds to Step S 60  when the second OFF signal S OFF2  and the third OFF signal S OFF3  are not being inputted. The processing proceeds to Step S 70  when at least either of the second OFF signal S OFF2  and the third OFF signal S OFF3  is being inputted. 
     In Step S 40 , the control device  110  switches the open/close valve  120  into the closed position Y. Accordingly, the travel damper of the wheel loader  1  is turned OFF. 
     In Step S 50 , the control device  110  determines whether or not the inner angle R formed by the booms  40  and the bell crank  80  is less than or equal to the second angle R 2  (&gt;the first angle R 1 ). The processing proceeds to Step S 30  when the inner angle R is not less than or equal to the second angle R 2 . The processing repeats Step S 40  when the inner angle R is less than or equal to the second angle R 2 . 
     In Step S 60 , the control device  110  switches the open/close valve  120  into the opened position X. Accordingly, the travel damper of the wheel loader  1  is turned ON. 
     In Step S 70 , the control device  110  switches the open/close valve  120  into the closed position Y. Accordingly, the travel damper of the wheel loader  1  is turned OFF. 
     Actions and Effects 
     (1) The control device  100  according to the present exemplary embodiment includes the proximity detecting part  113  and the valve switching part  117 . The proximity detecting part  113  is configured to detect that the bell crank  80  is in proximity to the cross tube  60 . The valve switching part  117  configured to switch the open/close valve  120  into the closed position Y when it is detected that the bell crank  80  is in proximity to the cross tube  60 . 
     Thus, the open/close valve  120  is configured to be switched into the closed position Y at a point of time when it is detected that the bell crank  80  is in proximity to the cross tube  60 . In other words, it is possible to quickly block communication between the boom cylinders  80 S and the accumulator  130  before the cross tube  60  is hit with the bell crank  80 . It is thereby possible to inhibit an acute peak pressure, generated in the boom cylinders  80 S in executing a rap-out, from being transmitted to the accumulator  130 . Therefore, it is possible to inhibit degradation in durability of the accumulator  130 . 
     (2) In the control device  100  according to the present exemplary embodiment, the proximity detecting part  113  is configured to detect that the bell crank  80  is in proximity to the cross tube  60  when the inner angle R formed by the pair of booms  40  and the bell crank  80  becomes less than or equal to the first angle R 1 . 
     Thus, it is possible to detect proximity of the bell crank  80  based on the inner angle R formed by the booms  40  and the bell crank  80 . Therefore, it is more simply and accurately detect proximity of the bell crank  80  than cases such as a case that the interval between the bell crank  80  and the cross tube  60  is directly measured. 
     (3) In the control device  100  according to the present exemplary embodiment, the proximity detecting part  113  is configured to continuously detect that the bell brank  80  is in proximity to the cross tube  60  while the inner angle R is less than or equal to the second angle R 2  R 1 ) after the inner angle R becomes less than or equal to the first angle R 1 . 
     Thus, the second angle R 2  is greater than the first angle R 1 , and therefore, the travel damper is turned OFF until the bell crank  80  is sufficiently separated away from the cross tube  60  after the bell crank  80  once gets closer to the cross tube  60 . It is thereby possible to inhibit the travel damper from being repeatedly turned ON and OFF uselessly in a short period of time. 
     Other Exemplary Embodiments 
     The present invention has been described with the aforementioned exemplary embodiment. However, it should not be understood that the description and figures, forming a part of this disclosure, are intended to limit the present invention. A variety of alternative embodiments, examples and operational arts would be apparent for a person skilled in the art from this disclosure. 
     (A) In the aforementioned exemplary embodiment, the proximity detecting part  113  is configured to detect that the bell crank  80  is in proximity to the cross tube  60  based on the inner angle R formed by the pair of booms  40  and the bell crank  80 . However, the present invention is not limited to the above. For example, the proximity detecting part  113  can detect proximity of the bell crank  80  based on the stroke amount of the bucket cylinder  80 S and either the stroke amount of the boom cylinders  40 S or the angle of the booms  40  (which can be detected by for instance, an angle sensor mounted on the first shaft portion  40   a ). Further, the proximity detecting part  113  can also detect proximity of the bell crank  80  based on a detection result of a proximity switch configured to be actuated when the interval between the bell crank  80  and the cross tube  6  (becomes less than or equal to a predetermined value. 
     (B) In the aforementioned exemplary embodiment, the valve switching part  117  is configured to unexceptionally output the first OFF signal S OFF1  when the inner angle R is less than or equal to the first angle R 1 . The present invention is not limited to the above. The valve switching part  117  may be configured to keep the open/close valve  120  in the opened position X when the angular speed of the bell crank  80  is less than or equal to a predetermined threshold. In this case, a small peak pressure is transmitted from the boom cylinders  80 S to the accumulator  130 . Therefore, it is also less required to block the boom cylinders  80  from communicating with the accumulator  130 . Therefore, it is possible to inhibit the travel damper from being repeatedly turned ON and OFF uselessly. In this case, it should be noted that the wheel loader  1  is only required to include an angular speed obtaining part configured to obtain the angular speed of the bell crank  80  pivoting about the rotary shaft  70 . 
     It is thus apparent that the present invention includes a variety of embodiments and etc. not herein described. Therefore, the technical scope of the present invention should be defined only by the matters specifying the invention related to claims that are valid from the aforementioned explanation. 
     According to the illustrated embodiments, it is possible to provide a travel damper control device for a wheel loader whereby degradation in durability of an accumulator can be inhibited. Therefore, the travel damper control device according to the embodiments is useful for the field of construction machines.