SYSTEM AND METHOD FOR ESTIMATING A WEIGHT OF A LOAD IN A BUCKET OF A WORK VEHICLE

A method for estimating a weight of a load in a bucket of a work vehicle includes obtaining, via a controller, a speed of an actuator of a lift coupled to the bucket. The method also includes comparing, via the controller, the speed provided to an instantaneous command to a hydraulic valve coupled to the actuator. The method further includes estimating, via the controller, a hydraulic pressure drop across the hydraulic valve based on the comparison of the speed to the instantaneous command to estimate pressures in the cylinder. The method even further includes determining, via the controller, a hydraulic force of the actuator. The method still further includes estimating, via the controller, the weight of the load in the bucket of the work vehicle based on the estimated pressures in the actuator and the hydraulic force.

BACKGROUND

The present disclosure relates generally to work vehicles and, more particularly, to a system or method for estimating a weight of a load in a bucket of a work vehicle.

A loader (e.g., wheel loader, skid-steer loader, excavator loader, etc.) is commonly used to load and move substantial volumes of material (e.g., dirt and similar material) from one location to another. A loader includes a relatively large frame and an implement (e.g., bucket) mounted to one end of the frame. The implement may be selectively elevated and selectively tilted to dump materials therefrom. On certain machines, pressure sensors may not be installed to provide feedback related to a load (e.g., payload) in the bucket or attachment of the machine. Machine performance and operator experience can be improved if feedback is available regarding the load in the bucket or attachment on the machine.

BRIEF DESCRIPTION

In one embodiment, a method for estimating a weight of a load in a bucket of a work vehicle is provided. The method includes obtaining, via a controller, a speed of an actuator of a lift coupled to the bucket. The method also includes comparing, via the controller, the speed to an instantaneous command provided to a hydraulic valve coupled to the actuator. The method further includes estimating, via the controller, a hydraulic pressure drop across the hydraulic valve based on the comparison of the speed to the instantaneous command to estimate pressures in the actuator. The method even further includes determining, via the controller, a hydraulic force of the actuator. The method still further includes estimating, via the controller, the weight of the load in the bucket of the work vehicle based on the estimated pressures in the actuator and the hydraulic force.

In another embodiment, a processor-based system is provided. The processor-based system includes a non-transitory memory configured to store executable routines. The processor-based system also includes a processor configured to execute the routines stored in the non-transitory memory, wherein the routines, when executed, cause acts to be performed. The acts include obtaining a speed of an actuator of a lift coupled to a bucket of a work vehicle. The acts also include comparing the speed to an instantaneous command provided to a hydraulic valve coupled to the actuator. The acts further include estimating a hydraulic pressure drop across the hydraulic valve based on the comparison of the speed to the instantaneous command to estimate pressures in the actuator. The acts even further include determining a hydraulic force of the actuator. The acts still further include estimating a weight of a load in the bucket of the work vehicle based on the estimated pressures in the actuator and the hydraulic force.

In a further embodiment, one or more non-transitory computer-readable media are provided. The computer-readable media encode one or processor-executable routines. The one or more routines, when executed by a processor, cause acts to be performed. The acts include obtaining a speed of an actuator of a lift coupled to a bucket of a work vehicle. The acts also include comparing the speed to an instantaneous command provided to a hydraulic valve coupled to the actuator. The acts further include estimating a hydraulic pressure drop across the hydraulic valve based on the comparison of the speed to the instantaneous command to estimate pressures in the actuator. The acts even further include determining a hydraulic force of the actuator. The acts still further include estimating a weight of a load in the bucket of the work vehicle based on the estimated pressures in the actuator and the hydraulic force.

DETAILED DESCRIPTION

Embodiments of the present disclosure relate generally to estimating a load (e.g. payload) in a bucket of a work vehicle (e.g., wheel loader, skid-steer loader, excavator loader, etc.) where pressure sensors are absent or not installed. In particular, a hydraulic payload system (e.g., having an open center valve control system or non-load sensing hydraulic system) may include a controller that utilizes a controller that executes a control algorithm (which serves as a pressure observer) to monitor a speed (via positions sensors) of an actuator (e.g., hydraulic cylinder) coupled to the bucket and compares it in relation to an instantaneous valve command provided to a hydraulic valve coupled to the actuator. Based on the known kinematics and/or inertial properties of an actuator system including the actuator and the speed of the actuator, the controller is configured to estimate the load in the bucket of the work vehicle. Knowledge of the load may help the performance of the systems (e.g., hydraulic payload system, actuator system, etc.). In addition, knowledge of the load can provide useful feedback to the operator of the work vehicle about their productivity. The disclosed embodiments provide the estimate of the load in the bucket without adding cost, instrumentation, and controller input/output to the system.

FIG.1illustrates a side view of a work vehicle10(e.g., wheel loader) equipped with an implement22(e.g., bucket). In certain embodiments, the work vehicle may be a skid-steer loader, an excavator loader, or any other type of loader having the implement22for handling a load. As shown, the work vehicle10includes a pair of front tires12, (one of which is shown), a pair of rear tires14(one of which is shown) and a frame or chassis16coupled to and supported by the tires12,14. An operator's cab18may be supported by a portion of the chassis16and may house various input devices for permitting an operator to control the operation of the work vehicle10.

Moreover, as shown inFIG.1, the work vehicle10may include a lift assembly20(e.g., actuation system) for raising and lowering a suitable implement22(e.g., a bucket) relative to a driving surface of the vehicle10. In several embodiments, the lift assembly20may include a pair of loader arms24(one of which is shown) pivotally coupled between the chassis16and the implement22. For example, as shown inFIG.1, each loader arm24(e.g., boom) may include a forward end26and an aft end28, with the forward end26being pivotally coupled to the implement22at a forward pivot point30and the aft end28being pivotally coupled to a portion of the chassis16.

In addition, the lift assembly20may also include a pair of hydraulic lift cylinders32(one of which is shown) coupled between the chassis16and the loader arms24and a hydraulic tilt cylinder34coupled between the chassis16and the implement22(e.g., via a pivotally mounted bell crank plate36or other mechanical linkage). It should be readily understood by those of ordinary skill in the art that the lift and tilt cylinders32,34may be utilized to allow the implement22to be raised/lowered and/or pivoted relative to the driving surface of the work vehicle10. For example, the lift cylinders32may be extended and retracted in order to pivot the loader arms24upward and downwards, respectively, thereby at least partially controlling the vertical positioning of the implement22relative to the driving surface. Similarly, the tilt cylinder34(e.g., bucket cylinder) may be extended and retracted in order to pivot the implement22relative to the loader arms24about the forward pivot point30, thereby controlling the tilt angle or orientation of the implement22relative to the driving surface or ground. The number of linkages and/or cylinders of the lift assembly20may vary.

An actuation system (e.g., the lift assembly20) for the implement22of the work vehicle10lacks pressure sensors for providing feedback related to a weight of the load. In certain embodiments, a hydraulic payload system of the work vehicle10utilizes an open center valve control system or non-load sensing hydraulic system where the flow from a pump through a hydraulic valve (or through the hydraulic valve to a tank) is dependent on a valve opening position and the hydraulic pressure (as a result of the load on the system). As described herein, this information can be sued to generate an estimate of a weight of the load in the implement22. In certain embodiments, the hydraulic payload system of the work vehicle10includes a controller that utilizes a control algorithm (which serves as a pressure observer) to monitor a speed (via positions sensors) of an actuator (e.g., hydraulic cylinder) coupled to the implement22and compares it in relation to an instantaneous valve command provided to a hydraulic valve coupled to the actuator. Based on the known kinematics and/or inertial properties of an actuator system including the actuator and the speed of the actuator, the controller is configured to estimate a weight of the load in the implement22(e.g., bucket) of the work vehicle10.

FIG.2is a schematic diagram of a hydraulic payload system38of the work vehicle10inFIG.1. The hydraulic payload system38includes a control system40(e.g., electro-hydraulic control system) coupled to an actuator42(e.g., cylinder such as a bucket cylinder). The actuator42is coupled to an implement (e.g., implement22inFIG.1) such as a bucket and, thus, a load44(e.g., payload) disposed in the implement. As noted above, the actuation system for the implement lacks pressure sensors. Fluid (e.g., hydraulic fluid) flow along conduits46,48controls the operation of the actuator42and, thus, movement (and position) of the implement in a vertical direction relative to the ground (e.g., raising or lowering the implement). In certain embodiments, operation of the actuator involves changing a tilt position of the implement (e.g., bucket) about its horizontal axis. Fluid is provided from a reservoir50(e.g., tank) to the actuator42along the conduit46via a pump52. Fluid is returned to the reservoir50via the conduit48. A control valve54(e.g., electro-hydraulic valve) may be disposed along the conduits46,48. As depicted, the control valve54is a tandem center control valve. In certain embodiments, the control valve54may be an open center control valve. The control valve54is responsive to control signals from a controller56that causes the control valve54to regulate fluid flow to and from the actuator42. For example, u1valve58is a command in a lift direction (relative to the ground) and u2valve60is a command in a lower direction (e.g., relative to the ground). The controller56also receives feedback from one or more position sensors62coupled to the actuator42. The one or more position sensors62may include a linear sensor or a joint angle or tilt sensor using kinematics. For example, the feedback received from the one or more position sensors62includes a position measurement xcyl64(e.g., cylinder position measurement) of the actuator42. In certain embodiments, the controller56also receives feedback from a valve position sensor coupled to the control valve54. For example, the feedback received from the valve position sensor is a valve spool position yvalve66.

The hydraulic payload system38utilizes an open center valve control system or non-load sensing hydraulic system where the flow from the pump52through the control valve54(or through the control valve54to the reservoir50) is dependent on a valve opening position and the hydraulic pressure (as a result of the load on the system). This information can be used to generate an estimate of a weight of the load44. Flow through an orifice is proportional to the square root of delta pressure. Using these known relations or using empirical mapping of valve command and pressure to flow measured on a bench, the controller56is programmed to estimate the pressure in the hydraulic system (e.g., hydraulic pressure drop across the control valve54). In particular, the controller56utilizes a control algorithm (which serves as a pressure observer) to monitor a speed (via positions sensors62) of the actuator42(e.g., hydraulic cylinder) coupled to the implement (e.g., bucket) and compares it in relation to an instantaneous valve command (e.g., u1valve58or u2valve60) provided to the control valve54coupled to the actuator42. Based on the known kinematics and/or inertial properties of an actuator system (including the actuator42and linkages such as a boom) and the speed of the actuator42, the controller56is configured to estimate a weight of the load in the implement (e.g., bucket) of the work vehicle10.

In certain embodiments, the controller56may be coupled to a display or indicator67. The controller56causes feedback on the weight of the load44to be provided to the operator of the work vehicle10.

The controller56contains computer-readable instructions stored in memory68(e.g., non-transitory, tangible, and computer-readable medium/memory circuitry) and a processor70which executes the instructions. More specifically, the memory68may include volatile memory, such as random access memory (RAM), and/or non-volatile memory, such as read-only memory (ROM), optical drives, hard disc drives, or solid-state drives. Additionally, the processor70may include one or more application specific integrated circuits (ASICs), one or more field programmable gate arrays (FPGAs), one or more general purpose processors, or any combination thereof. Furthermore, the term processor is not limited to just those integrated circuits referred to in the art as processors, but broadly refers to computers, processors, microcontrollers, microcomputers, programmable logic controllers, application specific integrated circuits, and other programmable circuits. The processor70and memory68may be used collectively to support an operating system, software applications and systems, and so forth, useful implementing the techniques described herein. For example, the memory68may store instructions for estimating a pressure drop across the control valve54(without feedback from pressure sensors) utilizing a control algorithm as a pressure observer. Also, the memory68may store instructions for estimating a weight of the load44in the implement (e.g., bucket). The memory68may store a variety of maps derived from calibration.

As theoretical calculations relating pressure to weight have the challenge of unknown factors such as friction or inaccuracies in the manufacturing or model properties, calibration of the system (e.g., actuator system) may be done. The calibration could be done by lifting and/or lowering a known load one or more known valve commands and measuring the speed of the actuator42. Because this speed will be load dependent a mapping can be created between the actuator speed and load weight to predict the weight of the load44in the implement (e.g., bucket).

In certain embodiments, a direct calibration is performed to correlate mass to valve flow at different valve commands.FIGS.3and4provide examples of a lift map (e.g., for a lift valve command) and a lower map (e.g., for a lower valve command).FIG.3includes a graph72illustrating the lift map with an x-axis74representing load mass and a y-axis76representing valve flow from the pump to the cylinder.FIG.4includes a graph78illustrating the lower map with an x-axis80representing load mass and a y-axis82representing valve flow from the cylinder (e.g., actuator) to the tank (e.g., reservoir). To generate the maps, a number of known masses (3 known masses inFIGS.3and4) are put in the loader bucket. For each mass, a number of commands (3 commands inFIGS.3and4) are given. For each command, the response velocity/flow of the control valve to the cylinder (e.g., actuator) is measured with the position sensor (e.g., coupled to the cylinder) or other type of sensor from which flow can be derived. Once the data is collected, the mass can be estimated utilizing inverse mapping using the percent valve command and the measured valve flow as inputs to predict the system load. As depicted inFIGS.3and4, this was done for lift and lower directions, respectively. In certain embodiments, for better accuracy, the estimation procedure could require the controller to provide a constant command as one of the calibration points during estimation. For the hydraulic payload system38inFIG.2, at 100 percent lift command, the mass/flow relationship is lost because all flow must go through the control valve regardless of the load, so the lift calibration is only valid for commands below 100 percent.

FIG.5illustrates different actuation positions of a load in a bucket and the effect on a center of gravity (CG).FIG.5depicts the load44disposed in the implement22(e.g. bucket) and the actuator42(e.g., hydraulic cylinder) coupled to the implement22via a linkage84(e.g., boom). The load44in the implement22is shown at a same height but in two different tilt positions (e.g., tilt position86and tilt position88). For a given actuator42used to lift the load44, the hydraulic force89(Fhyd) can be found from the pressures and the cylinder areas. Also, the zero load expected force can found using the known linkage masses and kinematics. Alternatively, the zero load force can be calibrated on the machine doing a lift/lower cycle. Further, forces above the zero load force can be assumed to be the load44in the in the implement22and from this increased load and kinematic knowledge of the vehicle, the mass in the implement22can be estimated. For linkages with more than one link, like a loader and a bucket, the bucket position could move relative to the loader linkage (e.g., linkage84) moving the center of gravity of the load44as depicted in movement between the positions86,88. The different tilts positions86,88result in different centers of gravity and different pressure loads for the same load position. With a sensor measuring the linkage84(e.g., position of the linkage84), this shift in the center of gravity can be anticipated and used to adjust the mass calculation for the observed load. The equations utilized for this relationship are dependent on specific linkage kinematics and any number of kinematics are possible. Since pressure sensors are not present, a method (as described below) to estimate the pressure on both sides of the cylinder is needed.

FIG.6illustrates a flow chart of a method90for estimating a weight of a load in a bucket of a work vehicle. One or more of the steps may be performed by the controller56inFIG.2. One or more of the steps of the method90may be performed in a different order or simultaneously from that depicted inFIG.6. In utilizing the method90, it is assumed that a hydraulic payload system of the work vehicle utilizes an open center valve control system or non-load sensing hydraulic system where the flow from a pump through a hydraulic valve (or through the hydraulic valve to a tank) is dependent on a valve opening position and the hydraulic pressure (as a result of the load on the system). In addition, it is assumed that the actuation system lacks pressure sensors.

In certain embodiments, the method90includes calibrating the actuation system (block92). The calibration may enable the generation of maps correlating mass to valve flow at different valve commands as described herein. Alternatively, in certain embodiments, the method90includes obtaining the calibration data. The method90also includes obtaining a speed of an actuator of the boom or lift (e.g., coupled to the bucket) (block94). The speed is obtained or derived from position measurements provided by one or more position sensors coupled to the actuator. The method90further includes comparing the speed to an instantaneous command provided to a hydraulic valve (e.g., control valve) coupled to the actuator (block96).

The method90still further includes estimating a hydraulic pressure drop across the hydraulic valve based on the comparison of the speed to the instantaneous command to estimate pressures in the actuator (block98). Estimating the hydraulic pressure drop occurs in the absence of pressure measurements from one or more pressure sensors. In addition, estimating the pressures in actuator includes estimating a respective pressure on both sides of the actuator (e.g., hydraulic cylinder). Estimating the respective pressure on both sides of the hydraulic cylinder includes determining a bypass opening area of the hydraulic valve based on the instantaneous command or a spool position (e.g., received from a position sensor coupled to the control valve or from known command versus spool position relationship derived from bench data) of the hydraulic valve.

The pressure (ptcyl) in the actuator (e.g., hydraulic cylinder) on the side connected to tank or reservoir can be determined from the following valve flow equation:

where Q represents valve flow, K represents flow gain, A represents valve opening area, and ptrepresents pressure downstream of the hydraulic valve. Q can be measured based on cylinder area (e.g. annular or piston depending on side) and measured cylinder speed. K is an empirical value considering fluid viscosity and flow geometries. K is determined by a supplier or using bench data. K is typically determined by measuring flow rate at a nominal constant pressure drop across the valve at a nominal valve opening. A is mapped from command or spool position. A is found from a known relationship between valve command/position and valve opening area. The ptcan be assumed to be zero, a constant low pressure drop for a return check valve, or any other method of estimating the tank return line based on flow rate (empirical data) or an equation similar the valve flow equation 1. After obtaining the above parameters, ptcylcan be solved for directly.

Referring toFIG.7, determining pump side pressure (ppcyl, i.e., the pressure in the hydraulic cylinder42on side connected to pump52through valve opening) in the actuator42(e.g., hydraulic cylinder) is a little more complex but is found using similar equations. Both ptcyland ppcylare needed to calculate cylinder force. The tank and pump sides of the hydraulic cylinder will change depending on which direction the hydraulic valve is commanded. The pump side pressure can be determined from the following general valve flow equation:

However, in this case a pressure drop from the pump52to the tank50must be found first, this is from the pump flow (Qp) going through the valve54as depicted inFIG.7. Then a pressure drop from pump52to the cylinder may be determined. A calibration or known mapping would be needed to know the pressure/flow relationships for both the pump/tank bypass channel and the pump/cylinder valve opening. The valve bypass flow from pump52to tank50(Qt) is determined from the following equation:

where Qcylrepresents pump flow to the cylinder42. Qcylis known from cylinder speed and cylinder area. Qpis known from engine speed and pump size. Qtcan be determined with the following equation:

where Atrepresents the bypass opening area, Ktrepresents bypass flow gain, ptrepresents tank pressure, and pprepresents pump pressure. Atis known as a function of command or spool position. Ktis known from bench data (empirical data) of the valve. The ptis assumed to be zero or some pressure as a function of flow for line losses. The ppcan be directly solved having defined the remaining parameters in equation 4. The ppcylis then determined from the following equation:

where Avrepresents the valve opening area, Kvrepresents valve flow gain, and pprepresents pump pressure as solved for in equation 4. Avis known as a function of command or spool position. Kvis known from bench data (empirical data) of the valve. The ppcylcan be directly solved having defined the remaining parameters in equation 5. In certain embodiments, instead of the above equations empirical data and interpolation may be used in place of the equations.

The relationship between the pressure drop across the hydraulic valve and valve flow for a number of valve commands (e.g., 3 commands) is depicted inFIG.8. Graph102inFIG.8includes an x-axis represents hydraulic flow104and the y-axis represents pressure drop106.

Returning toFIG.6, in certain embodiments, the method90further includes obtaining known kinematics and inertial properties of the actuator system configured to move the bucket, wherein the actuator system comprises the actuator (block108). In certain embodiments, this may occur prior to estimating the hydraulic pressure drop across the hydraulic valve as some of these known kinematics or inertial properties may be utilized in algorithms for estimating the hydraulic pressure drop.

The method90includes determining a hydraulic force of the actuator (block109). In certain embodiments, the hydraulic force may be determined based on the known kinematics and inertial properties of the actuator system. In certain embodiments, the hydraulic force may be determined based calibration data.

The method90even further includes estimating the weight of the load in the bucket of the work vehicle based on the estimated pressures in the actuator and the determined hydraulic force (block110). In certain embodiments, the method90still further includes providing an output of the estimated weight of the load (block112). For example, the estimated weight of the load may be provided on a display or indicator to provide feedback to the operator.

FIG.9illustrates a flow chart of a method114for calibrating an actuation system of a bucket on a work vehicle. One or more of the steps may be performed by the controller56inFIG.2. One or more of the steps of the method114may be performed in a different order or simultaneously from that depicted inFIG.9. The method114includes providing a known valve command to move a known load weight in the bucket (block116). The method114also includes obtaining the speed of the actuator of the boom or lift (e.g., coupled to the bucket) (block118). The method114further includes generating a map between the speed of the actuator and a load weight in the bucket (block120). Maps may be generated for different commands (e.g., lift valve command or lower valve command).