Patent Publication Number: US-2021172141-A1

Title: Hydraulic Power Shovel with Tamping Function

Description:
This application claims priority under 35 U.S.C. § 119 to patent application no. FR 1913948, filed on Dec. 9, 2019 in France, the disclosure of which is incorporated herein by reference in its entirety. 
     The subject of the disclosure is a hydraulic power shovel that, in addition to its normal use as excavation shovel, also allows it to operate for tamping with the shovel equipment. 
     BACKGROUND 
     It is known practice to use power shovels for the compacting of terrains, as is also known from the document US 2011/0013982. 
     This known shovel uses tamping equipment installed at the end of the rocking arm in addition or instead of the bucket. The movement of the boom with the rocking arm and the equipment at the end makes it possible to tamp the ground in front of the power shovel. 
     However, this operating mode of the hydraulic power shovel has a certain number of drawbacks. Since the weight of the equipment is used to drop the boom with its tamping equipment, this operation creates a depression with a cavitation effect in the power cylinder which actuates the boom. In addition, the reversing movement between the descent by gravity of the boom, of the rocking arm and of the bucket or of the tamping equipment and then the reverse movement or raising of this equipment is delayed, specifically because of the dead times at the moment of reversal. 
     SUMMARY 
     The aim of the disclosure is to develop a hydraulic power shovel that ensures not only the normal function of a shovel but also the tamping function while avoiding the delays at the moment of the reversal of the movement between the descent of the tamping equipment and the raising of the boom for a new tamping phase. 
     To this end, the subject of the disclosure is a hydraulic power shovel including a frame bearing a turret equipped with an arm (boom, rocking arm) terminated by a tool such as a bucket having a tamping surface, a power cylinder linked to the arm and pressing on the turret, a hydraulic installation with an adjustable flow pump supplying the power cylinder via a slide valve and a hydraulic liquid tank, a control unit linked to a control member actuated by the operator and generating a control signal and a sensor of pressure and of temperature of the hydraulic liquid in the power cylinder generating a signal S (P-T), the vapour pressure diagram of the hydraulic liquid (pressure and temperature) available in the control unit, a comparator receiving the signal from the sensor to compare it to the vapour pressure curve and to generate a control signal for the pump, a control member activated by the operator to supply a signal controlling the operating mode to the control unit, the control unit controlling the operation of the shovel: in normal operating mode according to which the valve and the flow rate of the pump are set as a function of the signal from the control member, in tamping mode according to which, for the free descent of the arm under the effect of its weight, requested by the control member, the valve fully opens the output of the power cylinder to the tank, the pump supplies the input of the power cylinder to maintain the pressure therein above the vapor pressure of the hydraulic liquid but below the atmospheric pressure at the temperature of the hydraulic liquid in the power cylinder. 
     The hydraulic power shovel according to the disclosure has the advantage of operating very efficiently in the tamping mode. The hydraulic circuit avoids the development of the cavitation effect in the rapid descent of the arm and of the tamping tool under the effect of the weight of this assembly. 
     This allows the shovel to devote all of its effectiveness to both normal operation and tamping. The return after descent to high position is ensured efficiently since the absence of cavitation and the return of hydraulic liquid in the power cylinder during the descent shortens the time between the end of this movement of descent and the start of the raising of the arm. 
     In no circumstances does this operation limit the amplitude of the movement of the arm. Depending on the work to be performed, the arm can be raised to any position within the limits of the possible movement of the power cylinder while retaining its effectiveness against the cavitation effect. 
     According to an advantageous feature, the electronic control unit is a computer applying a program managing the operation in normal mode and in tamping mode. 
     This electronic control unit can be the unit managing the overall operation of the power shovel and in which the normal and tamping operating modes are program modules. 
     According to another advantageous feature, the power shovel comprises a manual control device linked to the control unit to switch the control unit to the first or the second operating mode making it possible to activate the movement of descent and of lifting of the arm with the first control device. The second control device is a switch or a pushbutton. 
     Although the power shovel according to the disclosure advantageously uses the bucket as tamping tool, that does not exclude replacing the bucket with a specific tamping tool installed in place of the bucket. 
     However, this replacement requires the dismantling of the bucket and the fitting of the tool which blocks the operation of the shovel during this intervention and does not allow the power shovel to be used alternately with its bucket as excavation tool and in parallel, or in the interval, as tamping tool. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be described hereinbelow, using an exemplary embodiment represented in the attached drawings in which: 
         FIG. 1  is a diagram of a hydraulic power shovel according to the disclosure; 
         FIG. 2A  is a graph of the movement of the control handle; and 
         FIG. 2B  is a graph of the response to the movement of the handle for the control of the hydraulic circuit pump. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically shows a hydraulic power shovel  100  having a mobile frame  110  for example with tracks and supporting a turret  120  with the driving position, the motor  1 , the arm  2  with its equipment and the hydraulic installation  3 . The arm  2  is formed by a boom  21  linked to the turret  120  by an articulation A 1  and a power cylinder V 1  controlling the pivoting about this articulation A 1 . The boom  21  is continued by a rocking arm  22  linked to the boom  21  by an articulation A 2  and a power cylinder V 2  controlling the pivoting of the rocking arm  22  about the articulation A 2 . 
     The end of the rocking arm  22  is linked to a tool  23  such as a bucket by an articulation A 3  and a power cylinder V 3 . The bucket  23  can be tilted to use its outer surface  231  as surface or tamping tool. 
     The power cylinder V 3  controls the movement of the bucket  23 ; the power cylinder V 2  controls the movement of the rocking arm  22  with its bucket  23  and the power cylinder V 1  controls the movement of the boom  21  and of the components ( 22 ,  23 ) that it supports, that is to say all of the arm  2 . 
     The power cylinders V 1 , V 2 , V 3  are supplied in a controlled manner with hydraulic fluid by the hydraulic installation  3  equipped with a pump  31  and valves such as a slide valve  32  according to the movements to be executed. The power cylinders V 1 -V 3  or each group of power cylinders are controlled with associated handles, that are not detailed, for example forming part of a hydraulic control block linked to slide valves such as the valve  32  controlling the hydraulic liquid supplying the power cylinders and possibly other accessories of the power shovel  100 . 
     According to the disclosure, the power shovel  100  can execute not only its normal excavation function (mf 1 ) with its bucket  23 , but also the tamping function mf 2  with the bucket  23 . This tamping function mf 2  uses the rigid arm  2  formed by the boom  21 , the rocking arm  22  and the bucket  23 . This arm  2  pivots, controlled by the power cylinder V 1 , about the articulation Al for movements of descent using the force of gravity and of raising of the bucket  23  by supplying the power cylinder V 1 . 
     The description of the hydraulic installation  3  will be limited to the means necessary to this operating mode mf 2  with the power cylinder V 1 . 
     The power cylinder V 1  is divided by the piston P into a chamber C 1  on the bottom side and a chamber C 2  on the power cylinder rod T side. Schematically, the hydraulic liquid in the chamber C 1  pushes the rod T and, in the chamber C 2 , it retracts the rod T. 
     The chambers C 1 , C 2  are each linked by a respective duct CC 1 , CC 2  ensuring both the intake and the return of the hydraulic liquid, from and to a slide valve  32  which is itself linked to a duct CP coming from the pump  31  and a return duct CR to the tank  33  from which the pump  31  is supplied. 
     To facilitate and simplify the description, since the role of the chambers C 1 , C 2  is reversed for the lifting of the arm  2  (or of the boom  21 ) and for the descent thereof, the link between a chamber C 1 , C 2  and its respective duct CC 1 , CC 2  will be designated according to the active direction of passage of the hydraulic liquid: 
     for lifting:
         input EC 1  of the chamber C 1     output SC 2  of the chamber C 2         

     for descent
         output SC 1  of the chamber C 1     input EC 2  of the chamber C 2         

     in other words:
         in lifting, the pump  31  supplies the power cylinder through its chamber C 1  (input EC 1 )   in descent, the pump  31  supplies the power cylinder V 1  through its chamber C 2  (input EC 2 ).       

     The hydraulic installation  3  is managed by a control unit  6  linked to a first control member  4  in the form of a handle and to a second control member  5  to switch between the functions mf 1  and mf 2 . This control member  5  is in the form of a handle or of a pushbutton. The switching can also be done on the basis of the repeated actuation according to a certain pattern, of the control member  4  which is interpreted as a signal for switching between the two functions mf 1 , mf 2  by the control unit  6 . 
     The first control member  4  manages the operating mode mf 1  or mf 2  of the power cylinder V 1  out of the two operating modes selected by the second control member  5 , namely: 
     normal operation mf 1   
     tamping mf 2 . 
     The tamping mf 2  is the operating mode that is more particularly the concern of the disclosure. 
     Tamping consists in packing the ground with the bucket  23  pivoted about the articulation A 3  with the rocking arm  22  to present the outer surface  231  of the bucket  23  as compacting surface. The repeated movement of raising and of descent of the arm  2  is controlled by the operator with the handle  4 . This movement must be repeated as rapidly as is permitted by the operation of the hydraulic circuit  3  and the kinematics of the arm  2 . 
     According to the disclosure, the valve  32  has three switching ranges Po, P 1 , P 2  on its slide  321  for cutting the two ducts CC 1 , CC 2  of the power cylinder V 1  or linking them to the two ducts CP, CR corresponding respectively to the intake from the pump  31  and to the return to the tank  33 . 
     The range Po of the valve closes the two ducts CC 1 , CC 2  and thus blocks the power cylinder V 1  in its position, that is to say the position of the piston P of the power cylinder V 1  at that moment. 
     This range Po also ensures the closure of the ducts CP, CR or, as a variant, the return of the duct CP to the duct CR and the tank  33  which allows the pump  31  to continue to operate while the power cylinder V 1  is cut from the circuit. 
     The range P 1  links the chamber C 1  to the pump  31  and the chamber C 2  to the tank  33 . 
     The range P 2  links the chamber C 2  to the pump  31  and the chamber P 1  to the tank  33 . 
     The ranges P 1 , P 2  reverse the operation of the power cylinder V 1  and between them, the range Po blocks the operation of the power cylinder V 1 . 
     To simplify the language, this range P 1  corresponds to the active supplying of the power cylinder V 1  by the pump  31  while the range P 2  corresponds to the passive operation of the power cylinder V 1  whose chamber C 1  is emptied under the effect of the piston P pushed by the weight of the arm  2 . 
     The unit  6  controls the valve  32  by displacing the slide  321  by its two actuators AC 1 , AC 2  at the two ends of the slide  321  which push and pull the latter into the chosen position, opposite the ducts C 1 , C 2  or CP, CR. In mode mf 2 , the ranges P 1 , P 2  are not proportional; they fully open or close the passage of the hydraulic liquid and the switching between the ranges P 1  and P 2  goes through the range Po regardless of the switching direction. 
     The control unit  6  manages the operation of the pump  31  (flow rate Q of the pump) based on instructions from the handle  4  and information supplied by sensors that are not represented, monitoring the operation of the hydraulic installation  3 . 
     The control unit  6  is linked to a pressure sensor  34  which detects the pressure in the chamber C 2  of the power cylinder V 1  and associated with the duct CC 2  linked to the chamber C 2  or to the output duct CP of the pump  31 . The sensor  34  or another associated sensor measures the temperature of the hydraulic liquid in the chamber C 2  of the power cylinder or at the input of this chamber. It supplies the signal of pressure SP and of temperature ST to the control unit  6 . 
     This signal is also represented in the combined form of pressure and temperature signal S(P-T) whether supplied by itself or two sensors. 
     The control unit  6  comprises, in memory, the vapour pressure curve of the hydraulic liquid  61  and a comparator  62  for comparing the pressure signal S(P-T) supplied by the sensor  34  to the vapour pressure curve of the hydraulic liquid to control the operation of the pump  31 . 
     The vapour pressure diagram of the hydraulic liquid is a known curve, not represented, with coordinates (T, P) separating the liquid state and the gaseous state. The cavitation occurs schematically when the pressure of the liquid drops below the constant temperature vaporization curve while the transition of the constant pressure and increasing temperature curve is reflected by the boiling of the liquid. 
     The operation according to the first mode mf 1  consists in controlling the upward and downward pivoting of the arm  2  or of the boom  21  by supplying the chamber C 1  or the chamber C 2 . 
     The operation according to the second mode mf 2  is different in that it uses the weight of the arm  2  (boom, rocking arm and bucket) to lower the arm  2  and strike the surface of the ground to be tamped S under the bucket  23 . 
     The manoeuvring of the handle  4  is reflected by the sending, to the unit  6 , of a control signal SC 1 , SC 2  for the raising or lowering manoeuvring of the arm  2 . 
     It is assumed that, initially, the arm  2  is lowered, for example bearing on the ground or even in any position between its raised position (depending on the maximum travel of the power cylinder V 1 ) or in an intermediate position depending on the stop at the end of the manoeuvre. The slide  321  is, by definition, in its neutral position Po blocking the power cylinder V 1 . 
     The manoeuvre to be performed is that of tamping (in the operating mode mf 2 ). 
     The unit  6  detects the start of the movement of the handle  4  and interprets it as a request to supply the power cylinder V 1  in the direction of lifting of the arm  2 . The unit  6  pushes the slide  321  to set up the range P 1  and supply the chamber C 1  (active supply) and at the same time link the chamber C 2  to the return CR to the tank  33 . 
     The operator manoeuvres the handle  4  into an intermediate position or to the end of travel. 
     The manoeuvre continues as long as the handle is actuated and the power cylinder V 1  can operate in this direction, that is to say until the chamber C 1  is totally filled. A travel or pressure sensor associated with the chamber C 1  stops the pump  31  or switches the slide  321  to switch over to the range Po. 
     At the end of this operation, the operation of the arm  2  is stopped and, if the handle  4  is not placed in its rest position, it must be returned thereto; it can also be released by the operator and revert automatically to that position. 
     The manoeuvre which should follow the raising of the arm  2  is detected by the control unit  6  which controls the slide  321  to set its range P 2  in active position and link the duct CR to the duct CC 1  and the duct CP to the duct CC 2 . 
     The communication through the slide  321  is fully open for the two ducts CC 1 , CC 2 , that is to say without the flow rate leaving the chamber C 1  in return to the liquid tank  33  (also called tank), or the flow rate Q from the pump  31  to the chamber C 2 , being laminated. 
     The pump  31  supplies output under the control of the unit  6  and supplies the chamber C 2  for the pressure therein to remain slightly above the vapour pressure of the hydraulic liquid at that temperature and below atmospheric pressure, so as to avoid the cavitation or the onset of cavitation, without loading the chamber C 2  beyond what is necessary, and not delay the subsequent manoeuvre of lifting of the arm  2 . 
     To control the pump  31  and its flow rate/pressure Q, the control unit  6  compares the pressure of the hydraulic liquid in the chamber C 2  supplied by the pump  31  to the vapour pressure at the temperature of the hydraulic liquid in the chamber C 2  to servocontrol the flow rate Q from the pump  31 , so that, when the movement of descent of the bucket  23  is stopped, not necessarily at the end-of-travel position of the piston P in the cylinder, the reverse movement can begin immediately. 
     This state is detected by the detection of the change of pressure gradient in the chamber C 2  of the boom power cylinder V 1 , provoked by the impact on the ground. That is reflected by a pressure peak. Normally, the operator instinctively reverses the control  4  at the moment when he or she hears the noise provoked by the noise of the impact of the bucket on the ground. The slide  321  is thus automatically set in the position Po to block the arm  2  and avoid any movement before the arm  2  can be raised as required, controlled by the operator. 
     Upon this automatic stop at end of descent travel under the effect of the weight, the handle  4  may still be in its end of descent phase of the arm  2  position. 
     For the next phase of lifting of the arm  2 , the handle  4  must go back through its rest position. Then, when the handle  4  is actuated, the control unit  6  detects the start of control and sets the slide  321  of the valve in position P 1  to supply the chamber C 1  and lift the arm  2  to the end of the travel of the power cylinder V 1  or to a heightwise position, chosen by the operator, depending on the work to be performed. The tamping cycle then recommences. 
     The handle  4  controls the pump  31  as is illustrated by the curves of  FIGS. 2A, 2B . 
       FIG. 2A  represents the diagram of operation of the handle  4  with, on the x axis, the time T, and on the y axis, the travel of the handle  4 . 
     The travel is represented on a scale of between 0% and 100% of the total travel. 
     Starting from the origin 0 (0%, to), the movement of the handle  4  is, for example, linear. The travel can be stopped at any level, for example X % of the total travel. When this point chosen by the operator is reached (instant t 1 ), he or she maintains the handle  4  until the instant t 2  then raises or lowers or releases the handle. It then reverts automatically to the 0% x axis position in a relatively short return time. 
       FIG. 2B  shows the control function applied by the control unit  6  to the pump  31  to control the flow rate Q thereof. This function is assumed linear. It is represented in relation to time with the curve of  FIG. 2A . The y axis here represents the flow rate Q as a percentage relative to the maximum flow rate (100%) of the pump  31 . The degree of actuation (X %) of the handle  4  corresponds to a flow rate Q (X %). 
     The operation of the pump  31  is the image of the actuation of the handle  4  as long as the request represented by the signal from the handle  4  is compatible with the known operating capabilities of the power cylinder V 1  and applied by the control unit  6 . 
     According to the disclosure, the flow rate Q of the pump  31  supplying the chamber C 2  is set so that the descent of the bucket  3  by gravity does not create, in the chamber C 2 , a depression lower than the vapour pressure of the hydraulic liquid or that the pressure of the hydraulic liquid does not create a thrust on the piston that is added to that of the weight exerted by the arm  2 , so as to avoid the cavitation in the power cylinder or not to increase the time of reversal of the movement of the boom for its future lift. 
     The delay on the lifting of the arm  2  after its descent would be created by the time needed to first fill the chamber C 2  from empty on stopping or, in the reverse direction, to discharge the hydraulic liquid under pressure from the chamber C 2 , delaying the intake of the hydraulic liquid into the chamber Cl. 
     The repetition of the working tamping cycles comprises, for each cycle:
         a phase of lifting of the arm  2  to the necessary height which is that corresponding to the end of travel of the power cylinder V 1  or to an intermediate position   a phase of descent, releasing the arm  2  and its load to the action of the weight until the bucket  23  (or the tamping tool) strikes the ground S.       

     The control unit  6  is preferably a computer applied to a program to manage the operation of the power shovel  100  and the observance of safety conditions in normal mode (mf 1 ) and in tamping mode (mf 2 ). 
     PARTS LIST OF MAIN ELEMENTS 
       100  Hydraulic power shovel 
       110  Frame 
       120  Turret 
       1  Motor 
       2  Arm 
       21  Boom 
       22  Rocking arm 
       23  Tool/bucket 
       231  Tamping surface 
       3  Hydraulic installation 
       31  Adjustable pump 
       32  Slide valve 
       321  Slide 
       33  Hydraulic liquid tank, tank 
       34  Pressure/temperature sensor 
       4  Handle 
       5  Other control member 
       6  Control unit UC 
       61  Diagram (P-T) of the hydraulic liquid 
       62  Comparator 
     A 1 , A 2 , A 3  Articulations 
     V 1 , V 2 , V 3  Power cylinders 
     P Piston of the power cylinder V 1   
     T Rod of the power cylinder V 1   
     C 1 , C 2  Chambers of the power cylinder V 1   
     CC 1 , CC 2  Ducts linked to the chambers of the power cylinder 
     CP Output duct from the pump 
     CR Return duct to the tank 
     S Ground 
     SC Signal from the control member  4   
     S (P-T) Pressure-temperature signal of the hydraulic liquid in the power cylinder V 1   
     SP Pump  31  control signal 
     SCmf Control signal for switching between the operating modes 
     mf 1  Normal mode 
     mf 2  Tamping mode