Abstract:
Disclosed is a steering system which is capable of ensuring that a wheeled excavator travels straight while being driven on a paved road. The steering system for wheeled construction equipment includes: a hydraulic oil pump; a steering motor connected to the hydraulic oil pump; a steering valve controlling the operation of the steering motor; a steering handle operating the steering motor and the steering valve according to steering manipulation by the driver; and a steering cylinder steered by the manipulation of the steering handle. The steering system further includes an idle mode control unit which converts working mode into a steering mode not having straight line driving recovery performance when working mode, in which working and driving are enabled, is selected, and which converts exclusive driving mode into a steering mode having the straight line driving recovery performance through a signal input when the exclusive driving mode, in which only driving is enabled, is selected.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a steering system for a wheel type construction machine. More particularly, the present invention relates to a steering system for a wheel type construction machine, which can ensure driving straightness when a wheeled excavator is driven on a paved road. 
     BACKGROUND OF THE INVENTION 
     In general, a wheel type construction machine can be driven on a paved road, and can perform a work at a construction work site. However, only a steering system suited to the work is applied at the construction work site. In other words, when a steering handle for a wheel type construction machine is manipulated, a driving or traveling direction of the machine is set. On the other hand, when the steering handle is not manipulated, the driving or traveling direction is fixed. 
     For this reason, accuracy of the work is increased and an impact is not transmitted to the steering handle when the construction machine travels on an irregular road surface so that safety of an operator can be ensured. On the contrary, when the wheel type construction machine travels on a paved road due to the absence of a driving straightness restoring force, various driving operations are required to control the traveling direction during the traveling of the machine, and thus an operator suffers from a fatigue sensation. 
     A steering system for a wheel type construction machine in accordance with the prior art as shown in  FIG. 1  includes: 
     a hydraulic pump  1  that is connected to an engine (not shown); 
     a steering motor  2  that is connected to the hydraulic pump  1 ; 
     a steering valve  3  that is installed in a flow path between the hydraulic pump  1  and the steering motor  2  and is shifted to control a start, a stop, and a direction change of the steering motor  2 ; 
     a steering handle  4  that operates the steering motor  2  and the steering valve  3  in response to an operator&#39;s steering manipulation; and 
     a steering cylinder  6  that steers the machine operation by changing a direction of wheels  5  by means of a hydraulic fluid that is supplied from the hydraulic pump  1  through the manipulation of the steering handle  4 . 
     When the steering handle  4  is rotatably manipulated in a clockwise direction or a counter-clockwise direction, the steering valve  3  is shifted and the hydraulic fluid discharged from the hydraulic pump  1  can be supplied to the steering cylinder  6  via the steering motor  2 . 
     In this case, when a spool of the steering valve  3  is shifted to the left on the drawing sheet (i.e., shifted to a first position  3   a ), the hydraulic fluid discharged from the hydraulic pump  1  is supplied to one-side chamber  6   a  of the steering cylinder  6  via the steering valve  3  and the steering motor  2  so that the machine is steered to the right. On the contrary, when the spool of the steering valve  3  is shifted to the right on the drawing sheet (i.e., shifted to a second position  3   b ), the hydraulic fluid discharged from the hydraulic pump  1  is supplied to the other-side chamber  6   b  of the steering cylinder  6  via the steering valve  3  and the steering motor  2  so that the machine is steered to the left. That is, the traveling direction of the machine is controlled by changing a direction of the wheels  5  linkably connected to the steering cylinder  2 . 
     In the meantime, when the steering valve  3  is in a neutral mode (i.e., in a neutral position  3   c ), a flow path between the steering motor  2  and the steering cylinder  6  is blocked in a disconnected fashion. For this reason, since a force from the wheels  5  is not transmitted to the steering motor  2 , the steering system entails a problem in that it does not have a driving straightness restoring force. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Technical Problems 
     Accordingly, the present invention has been made to solve the aforementioned problem occurring in the prior art, and it is an object of the present invention to provide a steering system for a wheel type construction machine, in which when a wheeled excavator or the like is driven on a paved road, the number of manipulations of a steering handle for the machine can be minimized to ensure driving straightness, thereby reducing an operator&#39;s fatigue sensation. 
     Technical Solution 
     To accomplish the above object, in accordance with an embodiment of the present invention, there is provided a steering system for a wheel type construction machine, including a hydraulic pump connected to an engine, a steering motor connected to the hydraulic pump, a steering valve installed in a flow path between the hydraulic pump and the steering motor and configured to control the drive of the steering motor, a steering handle configured to operate the steering motor and the steering valve in response to an operator&#39;s steering manipulation, and a steering cylinder configured to steer the machine by changing a direction of wheels by means of a hydraulic fluid that is supplied from the hydraulic pump through the manipulation of the steering handle, the steering system comprising:
         a neutral mode control means configured to perform the shift of a mode to a steering mode in which a driving straightness restoring force is absent when a working mode is selected in which both a working operation and a traveling operation can be performed, and perform the shift of a mode to a steering mode in which the driving straightness restoring force is present in response to a traveling mode signal applied thereto when a traveling-dedicated mode is selected in which only the traveling operation can be performed.       

     In accordance with a preferred embodiment of the present invention, the steering valve may have a port which is internally provided with a first neutral mode position shifted to block a flow path between the steering cylinder and the steering motor when the working mode is selected in which both the working operation and the traveling operation can be performed, and a second neutral mode position shifted to connect the flow path between the steering cylinder and the steering motor in response to the traveling mode signal applied thereto when the traveling dedicated mode is selected in which only the traveling operation can be performed. 
     The steering valve may be shifted to the first neutral mode position when the steering handle is in a neutral position, and may be shifted to the second neutral mode position when the traveling mode is selected. 
     The steering valve is connected at one side to the other end of a link connected at one end to the steering motor, and is connected at the other side to the neutral mode control means  17 . 
     Advantageous Effect 
     The steering system for a wheel type construction machine in accordance with an embodiment of the present invention as constructed above has the following advantages. 
     When a work is performed using a wheeled excavator at a construction work site, a steering system suited to the work is applied at the construction work site so that accuracy of the work and safety of an operator can be ensured. Meanwhile, when the construction machine is driven on a paved road, the number of manipulations of a steering handle for the machine can be minimized owing to a steering system having a driving straightness restoring force. On the other hand, when the construction machine is driven on a curved surface of the paved road, driving straightness is restored even with a small manipulation force by the driving straightness restoring force after passing through the curved road surface, thereby reducing an operator&#39;s fatigue sensation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above objects, other features and advantages of the present invention will become more apparent by describing the preferred embodiments thereof with reference to the accompanying drawings, in which: 
         FIG. 1  is a hydraulic circuit diagram showing a steering system for a wheel type construction machine in accordance with the prior art; 
         FIG. 2  is a hydraulic circuit diagram showing the steering operation when a working mode is selected in a steering system for a wheel type construction machine in accordance with an embodiment of the present invention; and 
         FIG. 3  is a hydraulic circuit diagram showing the steering operation when a traveling-dedicated mode is selected in a steering system for a wheel type construction machine in accordance with an embodiment of the present invention. 
     
    
    
     EXPLANATION ON REFERENCE NUMERALS OF MAIN ELEMENTS IN THE DRAWINGS 
     
         
         
           
               11 ; hydraulic pump 
               12 ; steering motor 
               13 ; steering valve 
               14 ; steering handle 
               15 ; wheels 
               16 ; steering cylinder 
               17 ; neutral mode control means 
               18 ; link 
           
         
       
    
     Preferred Embodiments of the Invention 
     Now, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The matters defined in the description, such as the detailed construction and elements, are nothing but specific details provided to assist those of ordinary skill in the art in a comprehensive understanding of the invention, and the present invention is not limited to the embodiments disclosed hereinafter. 
     A steering system for a wheel type construction machine in accordance with an embodiment of the present invention as shown in  FIGS. 2 and 3  includes a steering system for a wheel type construction machine, including a hydraulic pump  11  that is connected to an engine (not shown), a steering motor  12  that is connected to the hydraulic pump  11 , a steering valve  13  that is installed in a flow path between the hydraulic pump  11  and the steering motor  12  to control the drive of the steering motor  12 , a steering handle  14  that operates the steering motor  12  and the steering valve  13  in response to an operator&#39;s steering manipulation, and a steering cylinder  16  that steers the machine by changing a direction of wheels  15  by means of a hydraulic fluid that is supplied from the hydraulic pump  11  through the manipulation of the steering handle  14 , the steering system comprising: 
     a neutral mode control means  17  that performs the shift of a mode to a steering mode in which a driving straightness restoring force is absent when a working mode is selected in which both a working operation and a traveling operation can be performed, and performs the shift of a mode to a steering mode in which the driving straightness restoring force is present in response to a traveling mode signal applied thereto when a traveling-dedicated mode is selected in which only the traveling operation can be performed. 
     In this case, the steering valve  13  has a port which is internally provided with a first neutral mode position  13   a  shifted to block a flow path between the steering cylinder  16  and the steering motor  12  when the working mode is selected in which both the working operation and the traveling operation can be performed, and a second neutral mode position  13   b  shifted to connect the flow path between the steering cylinder  16  and the steering motor  12  in response to the traveling mode signal applied thereto when the traveling dedicated mode is selected in which only the traveling operation can be performed. 
     The steering valve  13  is shifted to the first neutral mode position  13   a  when the steering handle  14  is in a neutral position, and is shifted to the second neutral mode position  13   b  when the traveling mode is selected. 
     The steering valve  13  is connected at one side to the other end of a link connected at one end to the steering motor  12 , and is connected at the other side to the neutral mode control means  17 . 
     Hereinafter, the operation of a steering system for a wheel type construction machine in accordance with an embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
     A) In the case where a working mode is selected in which a working operation and a traveling operation can be performed, i.e., no traveling mode signal is applied to the neutral mode control means  17 , the steering operation will be described below. 
     As shown in  FIG. 2 , when an operator selects a working mode in which both the working operation and the traveling operation can be performed (i.e., the working mode is applied to the steering system in which a driving straightness restoring force is absent), the steering valve  13  maintains the first neutral mode position  13   a . Thus, a hydraulic fluid discharged from the hydraulic pump  11  is drained to a hydraulic tank T so that a flow path between the steering motor  12  and the steering cylinder  16  is blocked. In this case, a force from the wheels  15  is not transmitted to the steering motor  12 , and thus the driving straightness restoring force is not present in the steering system. 
     Meanwhile, when the operator manipulates the steering handle  14  to shift the steering valve  13  to a steering position  13   c  or  13   d  through a link  18  linkably connected to the steering handle  14 , the hydraulic fluid from the hydraulic pump  11  can be supplied to the steering cylinder  16  via the steering motor  12 . Thus, the drive of the steering cylinder  16  can change a direction of the wheels  15  linkably connected to the steering cylinder  16  to determine the traveling direction. 
     B) In the case where a traveling dedicated mode is selected in which only the traveling operation can be performed, i.e., a traveling mode signal is applied to the neutral mode control means  17 , the steering operation will be described below. 
     As shown in  FIG. 3 , when the operator selects a traveling-dedicated mode in which only the traveling operation can be performed (i.e., the traveling-dedicated mode is applied to the steering system in which a driving straightness restoring force is present), the steering valve  13  maintains the second neutral mode position  13   b  in response to a control signal outputted from the neutral mode control means  17  in response to a traveling mode signal applied to the neutral mode control means  17 . 
     Thus, although the hydraulic fluid discharged from the hydraulic pump  11  is drained to the hydraulic tank T, the flow path between the steering motor  12  and the steering cylinder  16  is connected. In this case, a force from the wheels  15  is transmitted to the steering motor  12 . Therefore, when the machine travels on a paved road, the steering system has a driving straightness restoring force by virtue of the characteristics in which the wheels  15  positioned at the left and right sides of the steering cylinder  16  are to be aligned in a straight direction. 
     Meanwhile, a configuration in which when the operator manipulates the steering handle  14  to shift the steering valve  13 , the hydraulic fluid from the hydraulic pump  11  is supplied to the steering cylinder  16  to drive the steering cylinder  16  is the same as that in the steering operation as shown in  FIG. 2 . Thus, the detailed description of the configuration will be omitted to avoid redundancy. 
     INDUSTRIAL APPLICABILITY 
     As described above, according to the present invention as constructed above, when a wheeled excavator performs a work, a steering system suited to the work can ensure accuracy of the work and safety of an operator. In addition, when the construction machine is driven on a paved road, the number of manipulations of a steering handle for the machine can be minimized owing to a steering system having a driving straightness restoring force. On the other hand, when the construction machine is driven on a curved surface of the paved road, driving straightness is restored even with a small manipulation force by the driving straightness restoring force after passing through the curved road surface, thereby reducing an operator&#39;s fatigue sensation.