Patent Publication Number: US-2023160176-A1

Title: Construction machine with active ride control

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority of U.S. Provisional Patent Application No. 63/281,127, filed Nov. 19, 2021, the entire contents of which are incorporated by reference herein. 
    
    
     BACKGROUND 
     The present invention relates to construction machines, for example, wheel loaders, compact track loaders, etc. and more particularly to ride control in such machines when configured in a designated transport mode. As is often the case, these construction machines do not have shock-absorbing suspension components between the main frame and their drive wheels or tracks. 
     Typical ride control (e.g., U.S. Pat. No. 6,357,230 B1) in construction machines are provided by an accumulator 1 and a valve block 2 to connect the accumulator to boom cylinder 3 as represented in FIG. 1. This valve block 2 is used instead of the main boom control valve 4 during transport mode, usually when the machine is moving above certain speed. For ride control mode, the main boom control valve 4 blocks fluid communication between the boom cylinder 3 and the pump 5. This system provides a dampening to the implement vibration caused by uneven terrain when the machine is driving through it. The pressure fluctuation in the boom cylinder 3 is absorbed by the accumulator 1 to provide a cushioning effect. This conventional system can be referred to as passive ride control as it relies entirely in the accumulator 1, and there is no direct intentional actuation coming from any controller to improve or prevent machine oscillation. In short, the accumulator 1 receives oil at peak pressures on the boom cylinder 3 (e.g., machine is passing through a bump), and the accumulator 1 supplies oil when the pressure is low in the boom cylinder 3, reducing vibrations during drive. 
     Passive ride control requires an additional installation of a large capacity accumulator 1 and a separate valve control valve block 2. Passive ride control cannot prevent fluctuation caused by oil leakage and it has fixed settings, with different performance when the machine is in low speed when compared to high speed. To solve these issues, some active ride control solutions were proposed in the past such as KR20130055302A, an example of which is represented in FIG. 2. Without using an accumulator, these solutions reduce the pressure fluctuations in the boom cylinder 3 by inserting pressure from the pump 5 or relieving the pressure to tank through a directional valve, namely the main boom control valve 4. A pressure sensor 6 is used as feedback for the active ride control, eliminating the need of an accumulator. These active ride control solutions incur a significant delay time caused by command delay and response delay in switching the directional valve 4. In addition, non-linearities in this switching system makes it hard to provide a stable and robust ride control solution. 
     SUMMARY 
     In one aspect, the invention provides a construction machine including a variable displacement pump and a boom cylinder having a rod operable to extend and retract to move a boom of the construction machine. A first chamber of the boom cylinder is configured to be supplied with fluid from the pump during rod extension while fluid is removed from a second chamber of the boom cylinder. The second chamber of the boom cylinder is configured to be supplied with fluid from the pump during rod retraction while fluid is removed from the first chamber of the boom cylinder. The construction machine has an active ride control mode in which a valve between the boom cylinder and the pump remains open, and the pump is configured to actively damp pressure fluctuations in the boom cylinder by variation of a displacement setting. 
     In another aspect, the invention provides a method of actively damping a boom of a construction machine. A boom cylinder is provided having first and second piston-separated variable-volume chambers, a rod of the boom cylinder connected with the boom for moving the boom by selective extension and retraction of the rod. At least one of the first and second chambers of the boom cylinder is connected with the variable displacement pump for fluid exchange in an active ride control mode of the construction machine. Pressure fluctuations in the boom cylinder are actively damped by varying a displacement setting of the pump in the active ride control mode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a passive ride control system for a construction machine, according to the prior art. 
         FIG.  2    illustrates an active ride control system for a construction machine, according to the prior art. 
         FIG.  3    illustrates an active ride control system for a construction machine, according to one embodiment of the present disclosure. 
         FIG.  4    illustrates an active ride control system for a construction machine, according to another embodiment of the present disclosure. 
         FIG.  5    illustrates an exemplary construction machine. 
         FIG.  6    illustrates another exemplary construction machine. 
         FIG.  7    illustrates yet another exemplary construction machine. 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
       FIG.  3    illustrates an active ride control system  20  according to one embodiment of the present disclosure that provides an active ride control mode of a construction machine  100 ,  100 ′,  100 ″ ( FIGS.  5  to  7   ). An electronic controller  24  of the construction machine  100 ,  100 ′,  100 ″ can trigger the active ride control mode in response to travel of the machine above a threshold speed (e.g., as detected by a speed sensor  28  in signal communication with the controller  24 ). Other parameters may also be used in the controller  24  for triggering the active ride control, either in combination with the threshold speed or in lieu thereof. The boom cylinder  32  has a movable rod coupled with a boom  104  such that the pressure in the boom cylinder  32  (i.e., the base or piston-side chamber, opposite the rod side) supports the total boom load F L . The total boom load F L  can be generated by the weight of the boom  104  and also any additional supported external load (e.g., the contents of a bucket at the end of the boom  104 ). Active ride control can provide benefits during driving of the unloaded construction machine, but even greater benefit during driving of the boom-loaded construction machine since there is even more potential for pressure fluctuations and bouncing of the loaded boom due to the bucket load. 
     The two piston-separated chambers of the boom cylinder  32  are coupled via respective lines to the two operational (A and B) ports of the main boom control valve  36 . The other side of the main boom control valve  36  has pressure and tank (P and T) ports, which are coupled, respectively, to the outlet of the pump  40  and to the working fluid reservoir  44 . The main boom control valve  36  can be a conventional directional valve connected to the controller  24  for position switching. The main boom control valve  36  can have a plurality of different positions to establish different connections. In the illustrated construction, the main boom control valve  36  has four positions, which are arbitrarily designated the “first” through “fourth” positions from top to bottom in  FIG.  3   . The first position is a parallel position in which the A port is connected to tank T, and the B port is connected to pressure P. The second position isolates all four connections: A port, B port, pressure P, and tank T. The third position is a cross position in which the A port is connected to pressure P and the B port is connected to tank T. The fourth position is a float position in which the A and B ports are connected together and connected to tank T. 
     The pump  40  is a variable displacement pump (e.g., axial piston pump) connected to the controller  24  for varying the displacement setting (e.g., via swash plate angle). Furthermore, the pump  40  is variable for positive and negative displacement (i.e., reversible flow direction from a flow-producing “Pumping” mode to a flow-receiving “Motoring” mode) and is referred to as having over-center capability as it can switch between positive and negative during operation. The pump  40  may also be referred to as an over-center variable displacement pump. In some constructions, the pump  40  can be a Bosch Rexroth A10VO with eOC control (also called EC4), although other pumps may also be suitable for use. The system  20  utilizes the pump  40  in an open loop hydraulic circuit as shown. In response to movements of a user control (e.g., joystick) of the construction machine, the main boom control valve  36  moves to either the parallel or cross position so that the outlet of the pump  40  supplies fluid to exactly one of the chambers of the boom cylinder  32  while the other chamber is connected through the valve  36  to drain to tank  44 . In other words, the P port is connected through the valve  36  to either the A port or the B port, while the other of the A port and B port is connected through the valve  36  to tank  44  via the T port. In this way, the pump  40  and the main boom control valve  36  are used to control a position (extension/retraction) of the boom  104 . Although not the subject of the present disclosure, the hydraulic controls circuit for the boom  104  can incorporate load sensing so as to manage the speed of boom movements. As shown in  FIG.  3   , the pump  40  can be driven by a prime mover such as an internal combustion engine (ICE) for example. The ICE can be used within the construction machine for powering additional functions, including but not limited to traction drive, and additional pumps for additional boom and/or bucket movements or other implements of the machine. 
     During active ride control, the main boom control valve  36  goes to the bolded position (cross), connecting the A port (base or piston-side chamber of the boom cylinder  32 ) to pressure P, and connecting the B port (rod chamber side of the boom cylinder  32 ) to tank T. All flow dynamics for active ride control are managed through the dynamics of the pump  40 . The valve  36  does not switch position, but rather maintains the single position, during active ride control. Delay from the valve response is avoided since there is no valve position switch requisition during the active ride control. Valve position is not switched during active ride control mode, and the needed additional flow, or needed flow removal, that the system requires to dampen pressure spikes from boom structure inertia is accomplished through pump dynamics—e.g., solely through displacement setting variation within the pump  40 , that can include over-center dynamics of the pump  40 . The controlled pump dynamics can refer to actively changing the Pumping/Motoring mode of the pump  7  and actively changing the variable displacement setting within one of these modes. The pump dynamics are controlled by the electronic controller  24  in accordance with instructions from a pre-programmed algorithm stored in a memory and executed by the controller  24 . The oscillation of the pressure level, measured by pressure transducer(s)  50 ,  52 , is used to counteract the oscillations of the hydraulic system. The electronic controller  24  coupled to the pressure transducer(s)  50 ,  52  and the over-center pump  40  uses the pressure information in order to control the displacement setting of the over-center pump  40 . Although the described formulation provides that pressure transducers  50 ,  52  are utilized as feedback signals, other sensors that can perceive the oscillations in the system can also be utilized in alternative or in addition to the pressure transducers. These sensors, for example, can be but are not limited to an inertial measurement unit  56  mounted on the machine (e.g. on the chassis). As noted further below, an inertial measurement unit  108  can also be provided on the boom  104  for communicating forces and/or orientation to the controller  24 . 
       FIG.  4    illustrates a construction machine active ride control system  120  of another construction as an alternative to that of  FIG.  3   . Features such as the boom, the pump-driving ICE, and electronic controller are not shown with the understanding that they can be applied in the same manner as shown in  FIG.  3   . In the system  120  of  FIG.  4   , the ride control function is provided by a configuration where both chambers of the boom cylinder  32  are connected to pressure P. In other words, the two boom cylinder chambers are connected to each other in parallel. As such, fluid exchange is enabled not only between the boom cylinder  32  and the pump  40 , but also between the two piston-separated chambers of the boom cylinder  32 . A differential mode control for the boom cylinder  32  includes connecting both chambers of the boom cylinder  32  to pressure P, and a delta pressure control is established. The pressure control is set based on the boom cylinder rod and base ratio. Pressure transducer(s)  50 ,  52  give feedback to the system controller for generating a control signal to the over-center pump  40 , similar to the system of  FIG.  3   . 
     The differential pressure control is achieved by a valve  38  that connects both cylinder chambers (ports A and B) to pressure P. As shown, the valve  38  can be a valve separate from the main boom control valve  36 , which remains in the closed position (all ports A, B, P, T isolated from each other) during active ride control. In other embodiments, the function of the separate valve  38  can be integrated into the main boom control valve  36  as an additional position that connects the A and B ports to pressure P while isolating tank T. The position of the valve  38  that is used during active ride control is shown in bold in  FIG.  4   . When active ride control is not active, the valve  38  (if separate from the main boom control valve  36 ) remains closed and the main control valve  36  is used instead. Differential pressure during active ride control makes the load balanced and thus increases the damping effect. In addition, flow required to keep the system balanced is reduced because part of flow composition comes from the boom cylinder chamber-to-chamber exchange. The system pressure increases to balance the load by connecting the two chambers. This means that the maximum load, and therefore the maximum payload of the boom (e.g., inside the bucket), can be limited by the maximum pressure allowed in the hydraulic system. 
     Optional inertia sensors can be used in the system of either  FIG.  3    or  FIG.  4    to increase the system performance. In some constructions orientation of the boom  104  is monitored by a sensor  108  (e.g., an inertial measurement unit, IMU) so that a signal from the sensor  108  can be input to the controller  24 , with the controller  24  operating to control the pump  40  in a way that maintains the orientation of the boom  104  in the orientation set at the time active ride control starts. In addition, based on the sensors reading, when the pressure is low, the need to increase it is met by increasing displacement of the pump  40 . When the pressure is too high, the excess oil volume is discharged through the pump  40 . During active ride control, any additional implements of the construction machine  100 ,  100 ′,  100 ″ controlled by flow from the pump  40  are disabled such that the connections and operation of the pump  40  can be dedicated to the active ride control. Neither embodiment ( FIG.  3    or  FIG.  4   ) relies on directional valve responses during active ride control as the valve used to establish flow to/from the boom cylinder (either the main boom position control valve  36  or the auxiliary ride control valve  38 ) remains open and dormant during the designated active ride control mode of the machine. 
     Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects of the invention as described.