Abstract:
A displacement-controlled hydraulic system for installation on a multi-function machine, and multi-function machines equipped with the hydraulic system and having devices for propelling the machine, at least a first implement, and multiple actuators that perform multiple functions of the machine. The multiple actuators include first actuators that control the first implement and second actuators that control the propelling devices. The hydraulic system comprises multiple pumps for controlling the first actuators and optionally the second actuators, and valves that enable at least one of the pumps to sequentially control two of the multiple actuators and a corresponding two functions of the multiple functions performed thereby. None of the pumps sequentially controls the second actuators in combination with any of the first actuators.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/111,752, filed Nov. 6, 2008, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to machines having multiple functions performed by hydraulic circuits. More particularly, this invention relates to a displacement-controlled (DC) hydraulic system for use on multi-function machines with earthmoving implements whose movements are performed by rotary and linear actuators. 
     Compact excavators, wheel loaders and skid-steer loaders are examples of multi-function machines whose operations involve controlling movements of various implements of the machines.  FIG. 1  illustrates a compact excavator  100  as having a cab  101  mounted on top of an undercarriage  102  via a swing bearing (not shown) or other suitable device. The undercarriage  102  includes tracks  103  and associated drive components, such as drive sprockets, rollers, idlers, etc. The excavator  100  is further equipped with a blade  104  and an articulating mechanical arm  105  comprising a boom  106 , a stick  107 , and an attachment  108  represented as a bucket, though it should be understood that a variety of different attachments could be mounted to the arm  105 . The functions of the excavator  100  include the motions of the boom  106 , stick  107  and bucket  108 , the offset of the arm  105  during excavation operations with the bucket  108 , the motion of the blade  104  during grading operations, the swing motion for rotating the cab  101 , and the left and right travel motions of the tracks  103  during movement of the excavator  100 . In the case of a compact excavator  100  of the type represented in  FIG. 1 , the blade  104 , boom  106 , stick  107 , bucket  108  and offset functions are typically powered with linear actuators  20 - 25  (represented as hydraulic cylinders in  FIG. 1 ), while the travel and swing functions are typically powered with rotary hydraulic motors (not shown in  FIG. 1 ). 
     On conventional excavators, the control of these functions is accomplished by means of directional control valves. However, throttling flow through control valves is known to waste energy. In some current machines, the rotary functions (rotary hydraulic drive motors for the tracks  103  and rotary hydraulic swing motor for the cabin  101 ) are realized using displacement control (DC) systems, which notably exhibit lower power losses and allow energy recovery. In contrast, the position and velocity of the linear actuators  20 - 25  for the blade  104 , boom  106 , stick  107 , bucket  108 , and offset functions typically remain controlled with directional control valves. It is also possible to control linear hydraulic actuators directly with hydraulic pumps. Several pump-controlled configurations are known, using both constant and variable displacement pumps. Displacement control of linear actuators with single rod cylinders has been described in U.S. Pat. No. 5,329,767 and German Patents DE000010303360A1, EP000001588057A1 and WO002004067969, and offers the possibility of large reductions in energy requirements for hydraulic actuation systems. Other aspects of using displacement control systems can be better appreciated from further reference to Zimmerman et al., “The Effect of System Pressure Level on the Energy Consumption of Displacement Controlled Actuator Systems,” Proc. of the 5th FPNI PhD Symposium, Cracow, Poland, 77-92 (2008), and Williamson et al., “Efficiency Study of an Excavator Hydraulic System Based on Displacement-Controlled Actuators,” Bath ASME Symposium on Fluid Power and Motion Control (FPMC2008), 291-307 (2008), whose contents are incorporated herein by reference. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention provides a displacement-controlled hydraulic system for installation on a multi-function machine, and multi-function machines equipped with the hydraulic system. 
     According to a first aspect of the invention, a displacement-controlled hydraulic system is installed on a multi-function machine having means for propelling the machine, at least a first implement, and multiple actuators that perform multiple functions of the machine. The multiple actuators comprise first actuators that control the first implement and second actuators that control the propelling means of the machine. The hydraulic system comprises multiple pumps for controlling the first actuators and optionally for controlling the second actuators, and valve means for enabling at least one of the pumps to sequentially control two of the multiple actuators and a corresponding two functions of the multiple functions performed thereby, wherein none of the pumps sequentially controls the second actuators in combination with any of the first actuators. 
     According to a second aspect of the invention, a displacement-controlled hydraulic system adapted for installation on a multi-function machine comprises first and second travel actuators for propelling the machine, a plurality of function actuators for performing other functions of the machine, and a plurality of pumps. The first and second travel actuators are associated with oppositely-disposed first and second sides, respectively, of the machine. The plurality of pumps includes a first pump dedicated for powering the first travel actuator, a second pump dedicated for powering the second travel actuator, and multiple pumps for powering the function actuators. At least one of the multiple pumps for powering the function actuators is controllable for powering two or more of the function actuators. 
     Another aspect of the invention is a multi-function machine, and particularly an excavator, equipped with a displacement-controlled hydraulic system. The excavator comprises means for propelling the excavator, at least a first earthmoving implement, multiple actuators that perform multiple functions of the excavator, a system for controlling and actuating the multiple actuators. The multiple actuators comprise first actuators that control the first earthmoving implement and second actuators that control the propelling means of the excavator. The system comprises multiple pumps for controlling the first actuators and optionally for controlling the second actuators. The excavator further comprises valve means for enabling at least one of the pumps to sequentially control two of the multiple actuators and a corresponding two functions of the multiple functions performed thereby, wherein none of the pumps sequentially controls the second actuators in combination with any of the first actuators. 
     In view of the above, it can be seen that a significant advantage of this invention is the capability of switching between outputs of individual pumps to sequentially control multiple different machine functions of a multi-function machine, with the result that the machine is capable of using pumps in numbers less than the number of multiple functions of the machine. 
     Other aspects and advantages of this invention will be better appreciated from the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically represents a compact excavator of a type known in the prior art. 
         FIG. 2  represents a hydraulic actuation system for controlling functions of the excavator represented in  FIG. 1  in accordance with an embodiment of this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides a displacement-controlled (DC) hydraulic system for use on multi-function machines with implements whose movements are performed by rotary and linear actuators. An example is the excavator  100  represented in  FIG. 1 , which was previously described as equipped multiple actuators that perform multiple functions of the excavator  100 , including propulsion of the excavator  100  and movement of its multiple earthmoving implements  104 - 108 . A nonlimiting commercial example of the excavator  100  is the Bobcat® 435 compact excavator manufactured by the Bobcat Company. While the invention will be discussed with specific reference to the excavator  100  of  FIG. 1 , it should be understood that the invention is generally applicable to multi-function machines, including other types of excavators as well as wheel loaders and skid-steer loaders. 
     In conventional displacement-controlled circuits, a separate pump is required to individually control each actuator (which may be a rotary or linear hydraulic motor or actuator), and each actuator would perform a single function of the excavator  100 . The invention provides “switching” the output of individual pumps to sequentially control two different machine functions, with the result that the excavator  100  is able to use pumps in numbers less than the number of multiple functions of the excavator  100 . In a particular example illustrated in  FIG. 2 , six pumps can be installed and used to control rotary and/or linear actuators that perform eight different functions, including drive motors for the excavator  100 . 
       FIG. 2  shows a hydraulic actuation system equipped with six pumps  14  through  19  with power sharing capabilities that enable control of eight functions of the excavator  100  represented in  FIG. 1 , while maintaining independent control of rotary hydraulic drive/travel motors  26  and  27  of the excavator  100  regardless of simultaneous operation of the remaining functions. The pumps  14 - 19  are represented as variable displacement pumps powered through mechanical connections  2  through  13  from a primary power source  1 , for example, an internal combustion engine. The mechanical connections  2 - 13  can be of any suitable type, for example, drive shafts  2 - 10  and  13  and gear boxes  11  and  12  that transfer and distribute rotary power from the power source  1  to the pumps  14 - 19 . Controls  49  through  54  of any suitable type are used to control the displacements of the variable displacement pumps  14 - 19 . The flows produced by the pumps  14 - 19  directly control the operations of the linear actuators (hydraulic cylinders)  20 - 25  previously identified in reference to  FIG. 1 , as well as rotary hydraulic drive/travel motors  26  and  27  for the tracks  103  and a rotary hydraulic swing motor  28  for the cabin  101 . These linear and rotary actuators  20 - 28  perform the several functions of the excavator  100 , including the operation of the two earthmoving implements of the excavator  100 , namely, the blade  104  and the articulating arm  105  (which, as represented in  FIG. 1 , comprises the boom  106 , stick  107  and bucket  108 ). Pumps  14  and  19  are each represented as controlling one of two different machine functions at any given time, with valves  29  through  32  provided to allow the output of each pump  14  and  19  to be switched between the two different machine functions controlled by that particular pump  14  or  19 . As such, the valves  29 - 32  enable the pumps  14  and  19  to sequentially control multiple different machine functions assigned to them. The hydraulic system of  FIG. 2  is represented as further including a hydraulic return system that includes a charge pump  33 , accumulator  34 , pressure control valve  35 , reservoir  36 , check valves  37 - 48 , and control valves  49 - 54 , whose functions within the system can be readily appreciated from  FIG. 2 . 
     In the configuration shown in  FIG. 2 , the pump  19  controls the rotary swing motor  28  that performs the swing function of the excavator cab  101 , and controls the linear actuators  24  and  25  that operate the excavator blade  104 . The valves  29  and  30  enable switching of the pump  19  between control of the swing motor  28  (swing function) and control of the blade actuators (hydraulic cylinders)  24  and  24  (blade function) at any given time. As such, the swing function and the blade function cannot be performed simultaneously. Similarly, the valves  31  and  32  enable switching of the pump  14  between control of the actuator (hydraulic cylinder)  23  that operates the bucket  108  and control of the actuator (hydraulic cylinder)  22  that controls the offset function of the articulating arm  105 . As such, motion of the bucket  108  (with the actuator  23 ) and offset adjustments (with the actuator  22 ) cannot be simultaneously performed. 
     In contrast to the pumps  14  and  19 , the pumps  15  and  16  are dedicated to controlling the boom actuator (hydraulic cylinder)  21  and stick actuator (hydraulic cylinder)  20 , respectively, and the pumps  17  and  18  as dedicated to controlling the drive/travel motors  26  and  27 , respectively (travel function). As such, motion of the boom  106  and stick  107  and travel of the excavator  100  can be performed simultaneously. 
     As summarized in Table I, alternate configurations to that of  FIG. 2  are also possible, where other pairs of functions that do not require simultaneous operation can be performed by one of the pumps  14 - 16 , 19 , as may be permitted or practical. Analysis of the system of  FIG. 2  reveals that for full functionality of the excavator  100 , the number of pumps  14 - 19  should not be reduced below six, because there are six functions that should be capable of being operated simultaneously, namely, the motions of the boom  106 , stick  107 , bucket  108 , cab  101  (swing function), and the left and right tracks  103  (travel function). More particularly the left and right travel functions should be capable of simultaneous operation with the remainder of the functions, and therefore separate and dedicated pumps ( 17  and  18 ) are provided for the left and right travel functions. 
     
       
         
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Boom 
                 Stick 
                 Bucket 
                 Swing 
                 Offset 
                 Blade 
                 Travel L 
                 Travel R 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Option 1 
                   
                   
                 ◯ 
                 X 
                 ◯ 
                 X 
                   
                   
               
               
                 Option 2 
                   
                 ◯ 
                   
                 X 
                 ◯ 
                 X 
               
               
                 Option 3 
                 ◯ 
                   
                   
                 X 
                 ◯ 
                 X 
               
               
                 Option 4 
                   
                   
                 X 
                 ◯ 
                 ◯ 
                 X 
               
               
                 Option 5 
                   
                 ◯ 
                 X 
                   
                 ◯ 
                 X 
               
               
                 Option 6 
                 ◯ 
                   
                 X 
                   
                 ◯ 
                 X 
               
               
                 Option 7 
                   
                 X 
                   
                 ◯ 
                 ◯ 
                 X 
               
               
                 Option 8 
                   
                 X 
                 ◯ 
                   
                 ◯ 
                 X 
               
               
                 Option 9 
                 ◯ 
                 X 
                   
                   
                 ◯ 
                 X 
               
               
                 Option 10 
                 X 
                   
                   
                 ◯ 
                 ◯ 
                 X 
               
               
                 Option 11 
                 X 
                   
                 ◯ 
                   
                 ◯ 
                 X 
               
               
                 Option 12 
                 X 
                 ◯ 
                   
                   
                 ◯ 
                 X 
               
               
                   
               
             
          
         
       
     
     Possible arrangements for implementing switching functions for two of six pumps while maintaining independent control of the travel functions are shown in Table 1, in which functions with an “o” represent two functions controlled by a single pump and those labeled with an “x” represent two functions sharing a different single pump, while those with no label do not share a pump but have one pump for its function. Option 1 is believed to represent the preferred solution for the excavator  100  for the following reasons. The swing function (performed by the swing motor  28 ) often, though not necessarily, has lower flow rate requirements than the boom, stick, or bucket functions (performed by the actuators  21 ,  20  and  23 , respectively). Thus, the flow losses introduced by the switching valves ( 29  and  30 ) will be lower in the swing function than in the boom, stick or bucket functions. Sharing the bucket and the offset functions (performed by the actuators  23  and  22 , respectively) allows control of the boom  106  and stick  107  during the operation of the offset function, giving the most control possible of the excavator mechanical arm  105  during operation of the offset function. It is not desirable that the swing and offset functions (performed by the swing motor  28  and actuator  22 , respectively) share a pump because they both control the angular orientation of the mechanical arm  105 , and simultaneous operation of these functions is often desirable. 
     In all arrangements, the left and right travel functions (performed by the motors  26  and  27 ) are always independent of the other six (they never share a pump) to allow the excavator  100  full control while driving. While displacement control of the travel functions as shown in  FIG. 2  is desirable, other control methods could be used, such as control valves, and the motors  26  and  27  could be electric motors or other types of motors that can be or must be controlled by other than variable displacement pumps. It should also be noted that the invention can be applied to wheeled excavators as well as the track-type excavator represented in  FIG. 1 . 
     A pump-controlled (displacement-controlled) hydraulic system as described above eliminates the need for control valves and the large energy losses existing with throttle-based control methods. This consequently reduces the heat generated by the system and thus reduces the cooling requirements of the system. The pump-controlled system also allows energy saving through the recovery of energy through any of the variable displacement pumps  14 - 19  and redistributing the recovered energy to power simultaneous operations of other functions. Furthermore, the system architecture is simplified, requiring fewer components, generating fewer potential leak points in the system, and minimizing the number of pumps required to have full control of the system using pump-controlled actuation. Finally, the system minimizes the number of pumps required for a pump-controlled multi-function machine while maintaining independent control of the travel motors, for example, a hydrostatic drive. 
     Other aspects and advantages of this invention will be better appreciated from further reference to  FIG. 2 . 
     While the invention has been described in terms of a specific embodiment, it is apparent that other forms could be adopted by one skilled in the art. For example, the invention is applicable to a wide variety of multi-function machines with one or more implements whose movements are controlled by multiple actuators. Furthermore, the functions of individual components of the system could be performed by components of different construction but capable of a similar (though not necessarily equivalent) function. Accordingly, it should be understood that the invention is not limited to the specific embodiment illustrated in  FIGS. 1 and 2 . Instead, the scope of the invention is to be limited only by the following claims.