Patent Publication Number: US-2015063968-A1

Title: Flywheel excavator

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to a hybrid construction machine and in particular to a hybrid excavator having a swing structure operated by a flywheel. 
     BACKGROUND 
     A construction machine such as a hydraulic excavator uses engine as a prime mover to drive hydraulic actuators. Typically, the engine drives a hydraulic pump that in turn drives the hydraulic actuators such as hydraulic motors, hydraulic cylinders, steering motor, and wheel motors. The term “hydraulic actuator”, as used herein, generically refers to any device, such as a cylinder-piston arrangement or a rotational motor for example, that converts hydraulic fluid flow into mechanical motion. 
     During extension and retraction of a hydraulic cylinder assembly, pressurized fluid from the pump is usually applied by a valve assembly to one cylinder chamber and the fluid exhausting from the other cylinder chamber flows through the valve assembly into a return conduit that leads to the system tank. For example, high pressure fluid from the pump can be applied at a bottom chamber (cap end) of a hydraulic cylinder. Hence, the fluid from the upper chamber (rod end) can simultaneously exit to the tank. Under certain conditions, an external load or force acting on the machine enables extension or retraction of the cylinder assembly without significant fluid pressure from the pump. This is often referred to as an overrunning load. In an excavator for example, when the bucket is filled with heavy material, the boom can be lowered by the force of gravity alone. This external load drives fluid out of one chamber, say bottom chamber, of the boom&#39;s hydraulic cylinder, through the valve assembly, and into the tank. At the same time, an amount of fluid is also drawn from the pump through the valve assembly into the upper chamber which is expanding simultaneously. However because the incoming fluid is not driving the piston, it does not have to be maintained at a significant pressure for the boom motion to occur. In this. situation, the fluid is exhausted from the bottom chamber under relatively high pressure, thereby containing energy that normally is lost when the pressure is metered through the valve assembly. 
     To optimize efficiency and economical operation of the machine, it is desirable to recover the energy of the exhausting fluid. Some existing hydraulic systems store exhausting fluid in an accumulator, where it can be stored under pressure for later use in powering the machine. Other methods of recovering the energy are to drive a hydraulic motor via return fluid which will in turn drive an electric motor/generator. The electric energy thus generated can be stored in a battery for use in electrical system or driving an electric swing motor of an electric hybrid excavator. However, the electric and hydraulic storage and reuse systems are costly and are generally less efficient. 
     The present disclosure presents a solution to one or more of the problems set forth above. 
     SUMMARY 
     In one aspect, a hybrid construction machine is provided. The hybrid construction machine includes a prime mover. Further, the hybrid construction machine includes at least one fluid pump configured to be driven by the prime mover. The hybrid construction machine also includes at least one fluid actuator driven by the at least one fluid pump. Furthermore, the hybrid construction machine includes a swing motor driven by a return fluid from the at least one fluid actuator. Moreover, a first flywheel is included in the hybrid construction machine. The first flywheel can be configured for driving a swing structure. The first flywheel is driven by the swing motor. Additional, the hybrid construction machine includes a second flywheel. The second flywheel is coupled with the prime mover. The second flywheel is configured to store the energy when the prime mover is driven by the at least one fluid pump via the return fluid from the at least one fluid actuator. 
     In another embodiment, a hybrid construction machine having a swing structure, a lower travel structure, and an implement system having at least one work tool is provided. The swing structure can rotate with respect to the lower travel structure to rotate the work tool from a first position to a second position. The hybrid construction machine includes a prime mover. Further, the hybrid construction machine includes at least one fluid pump. The fluid pump is driven by the prime mover. Furthermore, the hybrid construction machine includes at least one fluid actuator. The fluid actuator is driven by the fluid pump. Moreover, the hybrid construction machine includes a swing motor. The swing motor is driven by a return fluid from the at least one fluid actuator. Further, the hybrid construction machine includes a first flywheel for driving a swing structure. The first flywheel is driven by the swing motor. Further, the first flywheel is coupled with the swing motor via a clutch. Additionally, the hybrid construction machine includes, a second flywheel coupled with the prime mover. The second flywheel is configured to store the energy when the prime mover is driven by the fluid pump via the return fluid from the at least one fluid actuator. Also, the second flywheel is configured to assist the prime mover during cold start and/or anti-idle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exemplary hybrid construction machine; and 
         FIG. 2  illustrates is a schematic block diagram of an exemplary powertrain that may be used in conjunction with the hybrid construction machine of  FIG. 1   
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an exemplary hybrid construction machine  100  having multiple systems and components that cooperate to accomplish a task. The hybrid construction machine  100  may embody a fixed or mobile machine that performs various operations associated with an industry such as mining, construction, farming, transportation, or another industry known in the art. For example, the hybrid construction machine  100  may be an earth moving machine such as an excavator (shown in  FIG. 1 ), a shovel, a backhoe, or another earth moving or construction machine. 
     The hybrid construction machine  100  may include a swing structure  102 , a lower travel structure  104 , and an implement system  106 . The swing structure  102  may include a swing frame  108 , a prime mover  110  mounted on the swing frame  108 , and an operator station  112 . The operator station  112  is configured for control of the implement system  106 , the prime mover  110 , the swing structure  102 , and the lower travel structure  104 . The swing structure  102  can be configured to rotate about a vertical axis X-X with respect to the lower travel structure  104 . 
     The lower travel structure  104  includes a pair of tracks  114 L and  114 R. The track  114 L may be driven by a travel motor  116 L and the track  114 R may be driven by a travel motor  116 R. In an alternative embodiment, the lower travel structure  104  may include wheels, belts etc. 
     The implement system  106  may include a linkage structure acted upon by a plurality of fluid actuators  122 ,  126 ,  128  to operate a work tool  118 . The implement system  106  includes a boom  120  configured to be pivoted about an axis by a boom cylinder  122 . Further, the implement system includes a stick  124  configured to be pivoted about an axis by a stick cylinder  126 . Further, the implement system includes a work tool cylinder  128  configured to pivot the work tool  118 . 
     Numerous different work tools  118  may be attached to a single hybrid construction machine  100  and can be operator controllable. Work tool  118  may include any device used to perform a particular task such as, for example, a bucket (shown in  FIG. 1 ), a fork arrangement, a blade, a shovel, a ripper, a broom, a propelling device, a cutting device, a grasping device, or any other task-performing device known in the art. 
     The prime mover  110  may include an engine such as, for example, a diesel engine, a gasoline engine, a gaseous fuel-powered engine, a dual fuel engine, or another type of combustion engine known in the art. The prime mover  110  can produce mechanical output that may then be converted to fluid power for fluid actuators (such as the aforementioned the travel fluid motors  116 L and  116 R, the boom cylinder  122 , the stick cylinder  126  and the work tool cylinder  128 ) of the implement system  106 . 
     The operator station  112  may include devices that receive input from a machine operator indicative of desired maneuvering of the hybrid construction machine  100 . Specifically, the operator station  112  may include one or more operator interface devices for example a joystick, a steering wheel, or a pedal etc (none of which are shown but are well known in the industry). Operator interface devices may initiate movement of hybrid construction machine  100 , for example travel and/or tool movement, swing structure movement by producing displacement signals that are indicative of desired maneuvering. 
       FIG. 2  illustrates a schematic block diagram of an exemplary powertrain  200  that may be used in conjunction with the hybrid construction machine  100 . As shown in  FIG. 2 , the powertrain  200  includes the prime mover  110 , at least one fluid pump  204 , a set of control valves  206 , the boom cylinder  122 , the stick cylinder  126 , and the work tool cylinder  128 . The prime mover  110  can serve as a driving unit for the at least one fluid pump  204 . It can be contemplated that one or more fluid pumps can be driven by the prime mover  110 . It should be understood that the fluid pump  204  can operate as both a pump and a motor as will be further described. In one mode of operation, the at least one fluid pump  204  is powered by the prime mover  110  for pressurizing fluid to be supplied to one or more of the plurality of fluid actuators  122 ,  126 ,  128 . In another mode of operation, the at least one fluid pump  204  can be driven by pressurized fluid returning from one or more of the plurality of fluid actuators  122 ,  126 ,  128  to generate mechanical motion. Thus, herein after, the at least one fluid pump  204  can simply be referred to as the pump motor  204 . The at least one fluid pump  204  can be a variable displacement pump motor or a fixed displacement pump motor. The pressurized fluid, from the at least one fluid pump  204  is directed to the at least one fluid actuator through the control valves  206 . The control valves  206  can be configured to control the quantity and the direction of fluid to the one or more actuators, such as the boom cylinder  122 , the stick cylinder  126 , and the work tool cylinder  128 . For example, the operator may command to lower or raise the boom  120  of the hybrid construction machine  100 . The control valves  206 , accordingly, control the flow of pressurized fluid to the boom cylinder  122 . The control valves  206  may also control the quantity and direction of the fluid to the travel motors  116 L and  116 R. Thus the control valves  206  can also be used for controlling the at least one fluid actuators (such as the aforementioned the travel motors  116 L and  116 R, the boom cylinder  122 , the stick cylinder  126  and the work tool cylinder  128 ). It may be appreciated that there may be one control valve corresponding to each fluid actuator for controlling the quantity and direction of flow of fluid. 
     Each of the boom cylinder  122 , the stick cylinder  126 , and the work tool cylinder  128  includes a rod end chamber and a head end chamber. Consider the boom cylinder  122 , for example, having a cap end chamber  122   a  and a rod end chamber  122   b.  Pressurized fluid can be supplied from the at least one fluid pump  204 , through a fluid path  208  to the cap end chamber  122   a  to extend the boom cylinder  122 . The pressurized fluid causes a piston ‘P’ of the boom cylinder  122  to move towards the rod end chamber  122   b  of the boom cylinder  122 , hence exhausting the fluid from the rod end chamber  122   b  through the fluid path  210 . Similarly, while retracting the boom cylinder  122 , the fluid can be exhausted from the head end chamber  122   a  through the path  208 . This exhausted fluid from the rod end chamber  122   b  or the cap end chamber  122   a  can be referred to as returning fluid or drained fluid, or discharge fluid. 
     In one embodiment, an external force may cause the exhausting fluid to exit at a pressure. In this embodiment, the boom cylinder  122  can be considered to be in an extended state and the work tool  118  of the machine  100  can be assumed be filled with heavy material. Hence, while lowering the boom  120 , the load in the work tool  118  can cause the exhausting of the fluid from the cap end chamber  122   a  through the fluid path  208 . In such a scenario, the returning fluid from the cap end chamber  122   a  can be exhausted in a pressurized state because of effect of gravity due to the load in the work tool  118 . 
     In an embodiment the returning fluid or the drained fluid can be directed towards the at least one fluid pump  204  though fluid path  210  or fluid path  208 . In this embodiment, the at least one fluid pump  204  can act as a motor and the returning fluid can be used to drive the pump motor. 
     It can be contemplated that stick cylinder  126  and the work tool cylinder  128 , or any other fluid actuator, can also function in a similar manner and the returning fluid from the fluid actuator can be directed to drive the fluid pump  204 . 
     The powertrain  200  further includes a swing motor  212 . The swing motor  212  can be a fluid motor which can be driven by pressurized fluid supplied through the fluid path  214 . In one embodiment, the swing motor  212  can be a hydraulic motor configured to be driven by high pressure hydraulic fluid similar to pump motor. In other words, the exhausting fluid or returning fluid can be directed towards the swing motor  212 , through the fluid path  214 . In one embodiment, the swing motor  212  can also be configured to be driven by drained or returned fluid from at least one fluid actuator such as the boom cylinder  122 , the stick cylinder  126 , and the work tool cylinder  128 . 
     Further, the swing motor  212  can be coupled to a first flywheel  218  via a clutch  220 . The clutch  220  can be configured to selectively engage or disengage the first flywheel  218  with the swing motor  212 . Further, the first flywheel  218  can be configured to drive the swing structure  102 . In other words, the swing motor  212  can be driven by the returning fluid from the one or more fluid actuators, such as the boom cylinder  122 . The swing motor  212  in turn rotates the first flywheel  218 . The first flywheel  218  can further rotate the swing structure  102 , when engaged through clutch  220 . Thus, the energy from the returning fluid can be conserved in the first flywheel  218  to drive the swing structure  102 . In an embodiment, a clutch-able flywheel transmission  222  can also be disposed between the swing structure  102  and the first flywheel  218 . The clutch-able flywheel transmission (CFT)  222  can be configured to vary the speed of the swing structure  102 . Also, the swing structure  102  can be rotated in clockwise and anticlockwise direction during operation. The direction of rotation of the swing structure  102  is changed by controlling the CFT  222 . In an embodiment, a reverser  224  can also be positioned between the CFT  222  and the swing structure  102 . The reverser  224  can be configured to change the direction of rotation of the swing structure  102 . In an exemplary embodiment, the reverser  224  can be a gearbox. 
     The powertrain  200  is also shown to include a second flywheel  226 . The second flywheel  226  can be coupled with the prime mover  110 . The second flywheel  226  can be coupled with the prime mover  110  via a gearing  228  for example a gearbox, a clutch, a mechanical coupling, a fluid coupling etc. The second flywheel  226  stores energy as kinetic energy when the prime mover  110  is driven by the at least one fluid pump  204  via the returning fluid from the at least one fluid actuator, such as the boom cylinder  122 , the stick cylinder  126 , and the work tool cylinder  128 . In other words, the returning fluid from the fluid actuators (the boom cylinder  122 , the stick cylinder  126 , and the work tool cylinder  128 ) can drive the fluid pump  204 . The fluid pump  204  acts as a motor thereby driving the prime mover  110 . In an embodiment, when the boom cylinder  122  is operating in an overrunning load condition, the fluid discharged from the boom cylinder  122  may have a pressure elevated above an output pressure of the at least one fluid pump  204 . In this situation, the elevated pressure of the return fluid can be directed through the at least one fluid pump  204  and may be used to drive the fluid pump  204 . In this scenario, the fluid pump  204  drives the prime mover  110  which in turn may drive the second flywheel  226  through the gearing  228 . Thereby, the second flywheel  226  stores the pressure energy of the return fluid of the boom cylinder  122  as kinetic energy. In addition, a speed up or reduction gear box  230  may be connected to the second flywheel  226 . The gear box  230  may also be connected to a motor generator  232 . When the second flywheel  226  is either driven by the prime mover  110  or by the overrunning load condition, the gear box  230  may rotate the motor generator  232  producing electrical energy that can be stored in a battery (not shown) or used to power electrical components of the hybrid construction machine  100 . Alternatively, the motor generator  232  can be used to start the prime mover  110 , to reducing idling of the prime mover  110  after low use time periods, or for cold starting. 
     Further, in an embodiment, the at least one fluid pump  204  can be connected to the swing motor  212  through a fluid path  216 . In this embodiment, the at least one fluid pump  204  can be used to drive the swing motor  212  for the first swing. For example, the swing motor  212  can be driven by the at least one fluid pump  204  to start the rotation of the first flywheel  218 . 
     Hence, the return fluid from the at least one fluid actuator, such as the boom cylinder  122 , the work tool cylinder  128 , and the stick cylinder  126 , can be conserved as kinetic energy in the first flywheel  218  and/or the second flywheel  226 . The energy stored in the first flywheel  218  can be used to drive the swing structure  102 . On the other hand, the energy from the returning fluid can be stored in the second flywheel  226  via the at least one fluid pump  204 , and further used to drive the prime mover  110  during cold start or managing excessive load. Also the at least one fluid pump  204  can be directly connected to the swing motor  212  to drive the first flywheel  218 . 
     Further, the first flywheel  218  can also be configured to store energy as the swing structure  102  slows down during each working cycle. In an embodiment, the working cycle may be referred as a load dump cycle. For example, the hybrid construction machine  100  lifts earth in the work tool  118  and the swing structure  102  is rotated to dump the material in a dump truck. Now as the swing structure  102  is rotated, the brakes need to be applied to slow and eventually stop the swing structure  102  at a position over the dump truck. This braking energy may be stored in the first flywheel  218  as kinetic energy. Hence by operating the clutch  220  (de-clutching) the first flywheel  218  from the swing motor  212  the braking energy can be stored in the first flywheel  218 . The energy stored in the first flywheel  218  can be used to accelerate the swing structure  102  in the next working cycle. Further, the swing motor  212  can be coupled with the first flywheel  218  to provide extra energy to the first flywheel  218  due to losses occurring in the working cycle. This may help in reducing the size of the swing motor  212 . 
     INDUSTRIAL APPLICABILITY 
     The present disclosure applies generally to hybrid construction machine  100 . The hybrid construction machine  100  is configured to perform a digging, loading and unloading during a typical work cycle. The hybrid construction machine  100  includes various actuators to execute their work. For example, the hybrid construction machine  100  can be excavator lifting earth in the bucket. The operator of the hybrid construction machine  100  can actuate a boom to lift the bucket. The boom can be actuated by a boom cylinder such as boom cylinder  122 . The prime mover  110  of the hybrid construction machine  100  provides power to a fluid pump such as the at least one fluid pump  204 . The pressurized fluid from the fluid pump  204  can be direct to the boom cylinder  122  to lift the work tool  118 . While lowering the work tool  118 , the pressurized fluid from the boom cylinder  122  can be direct to a swing motor  212 . Hence, the returning fluid from the boom cylinder  122  can drive the swing motor  212  to rotate the swing structure  102  through the first flywheel  218 . Also the returning fluid from the boom cylinder  122  can be directed to the fluid pump  204 . The fluid pump  204  can act as motor and convert the energy from the returning fluid to rotate the prime mover  110 . The prime mover  110  in turn can rotate the second flywheel  226 . Thus the energy from the returning fluid can be also conserved in the second flywheel  226 . 
     Thus the conserved energy can be used at a later stage to cold start the prime mover  110  or anti idle situation. Also the conserved energy help drive the swing structure  102  thus requiring less energy from the prime mover  110 . Thus the flywheel  226  is configured to primarily support the functions of prime mover  110  hence a smaller prime mover  110  can be utilized. Since energy flow paths exist between all system components, the first flywheel  218  and the second flywheel  226  can be used in concert in a variety of ways. 
     It should be understood that the above description is intended for illustrative purposes only, and is not intended to limit the scope of the present disclosure in any way.