System and method for controlling an engine torque load

Abstract

Machine (10) comprising: an internal combustion engine (20); a plurality of ground-engaging elements (16); a plurality of torque-consuming devices (46) drivingly coupled to the internal combustion engine (20), the plurality of torque-consuming devices (46) comprising a continuously variable transmission (14) coupling the internal combustion engine (20) and the ground-engaging elements (16); and an electronic control device (52) in communication with the internal combustion engine (20) and the plurality of torque consuming devices (46), the electronic control device (52) being configured to execute a torque load control algorithm to generate a torque load limit (58, 59) based at least in part on an engine underspeed value (57, 62, 114, 124, 134, 144, 154, 164); to identify a potential engine stall event during which a current engine speed (55, 60) of the internal combustion engine (20) falls below the engine underspeed value (57, 62, 114, 124, 134, 144, 154, 164) by a predetermined amount; and execute a transient torque load control algorithm to adjust the torque load limit (58, 59, 63, 64) in response to the identification of the potential engine stall event.

Description

Technical field

[0001] The present disclosure relates generally to a system and method for controlling engine torque load in a machine having a continuously variable transmission, and more particularly to a control system and method for setting torque load limits during a potential engine stall event. background

[0002] Many machines, including off-road equipment such as loaders, graders, excavators, and dozers, employ numerous devices and / or systems that receive power from a primary power source, such as an internal combustion engine. For example, many machines typically include engine-driven pumps that deliver high-pressure fluid to operate an implement system of the machine. In particular, a loader may use high-pressure fluid to move actuators associated with a bucket of the loader. Additionally, many machines employ continuously variable transmissions that utilize engine-driven pumps to deliver high-pressure fluid to drive ground-engaging elements of the machine, such as wheels.As the power demanded by these engine-driven systems increases, the engine's speed may begin to drop. If the engine speed drops below a threshold, the engine may stall.

[0003] By setting limits on machine operation so that the engine speed does not fall below the threshold speed, engine stalling may be avoided and / or reduced. For example, US 2009 / 0 319 136 A1 by Anderson et al. teaches a system and method for calculating torque load limits and controlling the distribution of engine torque to maintain the engine speed above the underspeed value and thus reduce stalling. Although the cited document by Anderson et al. may sufficiently reduce engine stalling during the majority of machine operation, there may be certain operating scenarios or conditions during which engine stalling may still occur, including severe transient load conditions.

[0004] Furthermore, WO 2009 / 145 706 A1 discloses a method and a system for controlling a hydraulic device of a motorized vehicle, wherein a safety margin is invoked when controlling the hydraulic device. The current maximum torque of the engine is continuously monitored along with the current torque demand. The control signal for the hydraulic device is then controlled depending on the difference between the maximum torque and the torque demand.

[0005] US 7,810,323 B2 discloses a load control device for the engine of a work vehicle. When the engine speed detected by the engine speed sensor has dropped to or below the threshold value, the control unit performs a control to reduce the absorption torque of the variable displacement hydraulic pump. The hydraulic load is shifted to a low hydraulic load line.

[0006] The present invention is directed to overcoming one or more problems or disadvantages associated with the prior art. Summary of Revelation

[0007] The object of the present invention is achieved by a machine and by a method for controlling an engine torque load on an internal combustion engine of a machine according to the main claims. Advantageous developments of the invention are described in the subclaims.

[0008] In one aspect, a machine includes a plurality of torque-consuming devices drivingly coupled to an internal combustion engine. The plurality of torque-consuming devices includes a continuously variable transmission coupling the internal combustion engine to a plurality of ground-engaging members. An electronic controller is in communication with the internal combustion engine and the plurality of torque-consuming devices and is configured to execute a torque load control algorithm to generate a torque load limit based at least in part on an engine underspeed value.The electronic controller identifies a potential engine stall event during which a current engine speed of the internal combustion engine drops below the engine underspeed value by a predetermined amount and executes a transient torque load control algorithm to adjust the torque load limit in response to the identification of the potential engine stall event.

[0009] According to another aspect, a computer-readable medium for use by a control system for a machine has executable instructions for performing a method for controlling an engine torque load. The method includes executing a torque load control algorithm to generate a torque load limit based at least in part on an engine underspeed value. The method also includes identifying a potential engine stall event during which a current engine speed of the internal combustion engine drops below the engine underspeed value by a predetermined amount and executing a transient torque load control algorithm to adjust the torque load limit in response to identifying the potential engine stall event.

[0010] According to yet another aspect, a method for controlling the engine torque load of an internal combustion engine comprises the steps of generating a torque load limit signal based at least in part on an engine underspeed value, and controlling the internal combustion engine and / or a plurality of torque-consuming devices drivingly connected to the internal combustion engine based on the torque load limit signal to regulate the engine torque load on the internal combustion engine. The method also includes sensing a current engine speed of the internal combustion engine and identifying a potential engine stall event during which the current engine speed of the internal combustion engine drops below the engine underspeed value by a predetermined amount.The torque load limit signal is adjusted in response to the identification of the potential engine stall event to generate an adjusted torque load limit signal, and the internal combustion engine and / or the plurality of torque consuming devices are controlled based on the adjusted torque load limit signal to regulate the engine torque load on the internal combustion engine. Short description of the drawings Fig. 1 is a schematic side view of a machine having a continuously variable transmission according to the present disclosure; Fig. 2 is a control system schematic diagram of the machine of Fig. 1, including exemplary torque-generating devices and torque-consuming devices, according to an exemplary embodiment of the present disclosure; Fig. 3 is exemplary control system logic corresponding to an exemplary torque load control algorithm in accordance with one aspect of the present disclosure; Fig. 4 is exemplary control system logic according to an exemplary transient torque load control algorithm in accordance with another aspect of the present disclosure; Fig. 5 is a logic flow diagram of one embodiment of a method for controlling an engine torque load according to the exemplary transient torque load control algorithm in accordance with another aspect of the present disclosure; Fig. 6 is an exemplary trigger speed map relating trigger speed thresholds to engine underspeed values and actual transmission ratios, according to another aspect of the present disclosure; Fig. 7 is an exemplary step speed map relating step speed thresholds to engine underspeed values and actual transmission ratios, according to another aspect of the present disclosure; Fig. 8 is an exemplary recovery speed map relating recovery speed thresholds to engine underspeed values and actual transmission ratios, according to another aspect of the present disclosure; Fig. 9 is an exemplary rate limit table relating maximum rate limits to engine underspeed values according to another aspect of the present disclosure; Fig. 10 is an exemplary rate limit table relating increasing rate limits for a drive system torque load limit to engine underspeed values, according to another aspect of the present disclosure; and Fig. 11 is an exemplary rate limit table relating increasing rate limit values for a tool system load limit to engine underspeed values, according to another aspect of the present disclosure; Detailed description

[0011] An exemplary embodiment of the machine 10 is generally shown in Fig. 1. The machine 10 may be a wheel loader, as shown, or any other off-road or on-road vehicle having a continuously variable transmission. Although the application is broadly applicable to any machine having a continuously variable transmission, a machine having a hydrostatic drive system is shown. As such, the machine 10 may also be referred to herein as a hydrostatically driven machine, or more specifically, as a hydrostatic drive wheel loader. In the illustrated embodiment, the machine 10 generally includes a frame 12 with a hydrostatic drive system 14 suspended therefrom for driving ground-engaging elements 16 of the machine 10, such as wheels (shown) or tracks.A strategy for controlling an engine torque load presented here may be widely applicable to a machine having a continuously variable transmission, and therefore, it should be noted that the specific embodiments provided are provided for exemplary purposes only.

[0012] The hydrostatic drive system 14 may generally include at least one pump 18, such as a hydraulic pump, driven by a prime mover, such as a compression-ignition or spark-ignition internal combustion engine 20 or an electric motor, of the machine 10. The pump 18 may be configured to have at least one motor 22, such as one or more sets of hydraulic motors, which in turn drive the ground-engaging elements 16 of the machine 10. Both the pump 18 and the motor 22 may provide variable displacement so that fluid flow between the components of the hydrostatic drive system 14 can be adjusted while the machine 10 is running. As a result, the direction, speed, and torque of the ground-engaging elements 16 or wheels can be continuously varied.

[0013] The machine 10 may also include an implement system 24 that includes at least one pump 26, such as a hydraulic pump, which is also driven by the internal combustion engine 20. As should be understood, the pump 26 may generate pressurized fluid that is circulated along a fluid circuit having control cylinders 28 to effect desired movement of an implement 30, such as a bucket, of the machine 10. It should be noted that the implement system 24 may include additional components known in the art, such as fluid reservoirs, additional pumps, electronically actuated valves, filters, sensors, etc., to enable the desired operation. The engine torque load control strategy presented herein is widely applicable to machines having a variety of engine loads, and thus, the implement system 24 is provided for exemplary purposes only.

[0014] An operator control station 32 may also be supported on the frame 12 and may include various controls and devices that may be used by an operator of the machine 10. For example, the operator control station 32 may include known devices such as a seat assembly 34, a steering device 36, and one or more machine operation controls 38. According to a specific example, a first machine operation control 38 may be provided to control directional movement of the machine 10, while a second machine operation control 38 may be provided to control operation of the implement 30. The operator control station 32 may include additional machine controls, such as controls for controlling engine speed, transmission ratio, rim pull, etc.

[0015] It should be noted that the internal combustion engine 20 is configured to combust fuel in one or more combustion chambers to reciprocate pistons within the respective chambers. Each piston is connected to a common crankshaft by a connecting rod, such that the reciprocating motion of the pistons rotates the crankshaft. Thus, the linear motion of the pistons is converted into a rotational motion, which can be delivered to an output 40, which can include a rotating shaft. In addition to the internal combustion engine 20, the machine 10 can include a variety of additional torque-generating devices 42 or systems configured to rotate the output 40, as shown in Fig. 2. For example, a secondary internal combustion engine 44 and / or any other suitable power source may also be configured to generate, store, accumulate, and / or distribute torque. The one or more devices, as well as the internal combustion engine 20, may be operatively coupled to the output 40 to assist in rotating the output 40.

[0016] Still referring to Fig. 2, the machine 10 may also include one or more torque-consuming devices 46. The torque-consuming devices 46 may include any device or system of the machine 10 configured to convert an input, such as torque from the output 40, into an output, such as movement of the ground-engaging elements 16, the tool 30, and / or any other change in the state of the machine 10. For example, the torque-consuming devices 46 may specifically include the drive system 14 and the tool system 24, which were described above with reference to Fig. 1. In particular, the internal combustion engine 20 may provide an output torque used to operate the pump 18 of the drive system 14 and the pump 26 of the tool system 24. Additionally and / or alternatively, torque-consuming devices 46 drivingly coupled to the internal combustion engine 20 are also applicable to the engine torque load control strategy provided herein.

[0017] A control system 50 may include at least one electronic control device 52 configured to control the operation of the machine 10. Although a single electronic control device 52 will be described, it should be appreciated that the control system 50 may include a plurality of electronic control devices. For example, additional electronic control devices may be provided to control different subsystems of the machine 10. As such, each electronic control device of the control system 50 may be configured to communicate laterally and / or in a hierarchical manner. Therefore, it should be appreciated that a variety of control systems, ranging from simple to complex, are contemplated for use with the present disclosure.

[0018] The electronic control device 52 may be of standard construction and may include a processor 52a, such as a central processing unit, a memory 52b, and input / output circuitry that enables communication within and outside the electronic control device 52. The processor 52a may control the operation of the electronic control device 52 by executing operating instructions, such as computer-readable program code, stored in the memory 52b, wherein operations may be initiated within or outside the electronic control device 52.A control scheme, the example of which is set out below, can be used which monitors outputs from systems or devices, such as sensors, actuators, or control units, via the input / output circuitry to control inputs to various other systems or devices.

[0019] The memory 52b may include temporary storage areas, such as a cache, virtual memory, or RAM, or permanent storage areas, such as ROM, removable drives, network / internet storage, hard drives, flash memory, memory sticks, or any other known volatile or non-volatile data storage devices. Such devices may be located internally or externally of the electronic control device 52. Those skilled in the art will recognize that any computer-based system or device employing similar components to control the components or subsystems of the machine 10 is suitable for use with the present disclosure.

[0020] As shown, the electronic controller 52 may be in communication with both the torque-generating devices 42 and the output 40, as well as the torque-consuming devices 46, via communication lines 53. For example, the electronic controller 52 may be in communication with the internal combustion engine 20 to control its speed, such as by issuing control commands via communication lines 53 to control a fuel supply to the internal combustion engine 20. The engine speed may be adjusted based at least in part on a position of one or more engine operating controls 38. As should be appreciated, the electronic controller 52 may also receive input from various sensors or devices that monitor operating conditions of the internal combustion engine 20.Such devices and means for controlling the operation of the internal combustion engine 20 are known and will therefore not be discussed in detail here.

[0021] The electronic controller 52 may also be in communication with the variable displacement pump 18 and the variable displacement motors 22. In particular, for example, the electronic controller 52 may be in communication with the variable displacement pump 18 to adjust its swashplate angle, resulting in the variable displacement described above. According to one embodiment, a pump displacement solenoid, such as a proportional solenoid, may be provided to vary the swashplate angle and control the direction of fluid flow. However, various means for adjusting displacement and fluid flow are known and may be provided in the present disclosure.Accordingly, the electronic controller 52 may issue pump displacement commands and / or additional commands to the variable displacement pump 18 via wired or wireless communication lines 53 to efficiently control the displacement and direction of fluid flow of the variable displacement pump 18. Similarly, the electronic controller 52 may communicate with the variable displacement motors 22 to adjust the angles of the swash plates of the motors 22. As noted above, the displacement and fluid flow control devices are generally known and therefore will not be discussed in detail here.

[0022] The electronic controller 52 may also be in communication with additional torque-consuming devices 46, including the tool system 24, to similarly monitor and control their operation. For example, the electronic controller 52 may be in communication with the tool pump 26, which may include a variable displacement or fixed displacement pump, to monitor and control the operation of the tool system 24 in a known manner. As should be appreciated, the tool 30 may be controlled based at least in part on a position of one or more of the machine operation control devices 38.

[0023] The torque-consuming devices 46, including the drive system 14 and the tool system 24, may receive torque from the output 40 when rotated by the one or more torque-generating devices 42, such as the internal combustion engine 20, and thus may act as a torque load on the internal combustion engine 20. The torque demands of the torque-consuming devices 46 may be relatively constant or may vary over time depending on the operations being performed. When the torque-consuming devices 46 receive or use torque from the output 40, they may have an effect on the internal combustion engine 20. For example, as the torque demanded by the torque-consuming devices 46 increases, the torque load on the output 40 increases.The increase in torque load may slow the angular velocity of the output 40 and thus the speed of the internal combustion engine 20 may decrease.

[0024] The internal combustion engine 20 may have an engine underspeed value that may be lower than a desired engine speed value selected by the operator. According to some embodiments, it may be desirable to maintain the speed of the internal combustion engine 20 at or above the engine underspeed value to provide the operator with desired performance characteristics, including the perception of consistent and adequate engine power. The engine underspeed value may also represent an engine speed threshold below which excessive engine speed stuttering may be a problem. Further, if the engine speed drops below the engine underspeed value by a predetermined amount, engine stalling may also be a problem. Thus, it may be desirable to maintain the internal combustion engine 20 at speeds equal to or above the engine underspeed value for a number of reasons.

[0025] According to the exemplary embodiment, the engine underspeed value may be used in determining a torque load limit for the internal combustion engine 20. The torque load limit may indicate a torque load that can be applied to the internal combustion engine 20 without causing the speed of the engine 20 to drop below its engine underspeed value. Adjusting the operating parameters of the machine 10 and / or the torque load on the output 40 based on the torque load limit may make the internal combustion engine 20 less susceptible to stalling.

[0026] An exemplary torque load control strategy is taught by U.S. Patent Application Publication No. 2009 / 0319136 to Anderson et al., which is incorporated herein by reference. Specifically, the torque load control strategy provided in Anderson et al. teaches the use of a calculated torque load limit to allocate or distribute engine torque between torque-consuming devices, such as torque-consuming devices 46. In particular, the operation of the torque-consuming devices may be controlled or adjusted in response to the torque load limits.For example, if the torque load limit for a torque consuming device is less than the torque requested by the torque consuming device, the operation of the torque consuming device may be delayed or limited until additional torque becomes available.

[0027] According to a torque load control strategy similar to the strategy taught in the reference by Anderson et al., the control system 50 may thus execute a torque load control algorithm to generate a torque load limit. For example, as in Fig. As shown in Figure 3, the electronic controller 52 may have as inputs an available torque 54, an engine speed 55, an engine rotational inertia 56, and an engine underspeed value 57, and may perform calculations to arrive at a drive system torque limit 58 or torque load limit signal and an implement system torque limit 59 or torque load limit signal. It should be noted that additional and / or alternative inputs may be provided by the electronic controller 52 and used to obtain one or more torque load limits.The example torque limits 58 and 59 may be used by the control system 50 to control the operation of the machine 10 such that the internal combustion engine 20 operates at or above a particular threshold, such as the engine underspeed value 57, to avoid excessive engine speed stuttering and to provide the desired operator feedback, as described above.

[0028] Again with reference to Fig. 4, the control system 50 may also be configured to execute a transient torque load control algorithm to set a torque load limit during potential engine stall events, such as the torque load limits 58 and 59 generated above. In particular, the electronic controller 52 may have as inputs the drive system torque limit 58, the implement system torque limit 59, a current engine speed 60, an actual gear ratio 61 of the drive system 14, and an engine underspeed value 62. The electronic controller 52 then performs operations, such as according to the exemplary method described below, to obtain a set drive system torque limit 63 or torque load limit signal and a set implement system torque limit 64 or torque load limit signal.The set torque limits 63 and 64 may be used by the control system 50 to control operation of the machine 10 in a manner described above to reduce engine stall during potential engine stall events.

[0029] With reference to Fig. 5, a flowchart 70 is shown illustrating an exemplary method for controlling the engine torque load in the machine 10 according to the present disclosure. In particular, the method may illustrate a strategy for setting the torque load limits 58 and 59 that are dynamic and based at least in part on the engine underspeed value 57 and may be generated by the torque load control algorithm described above. The method may be performed by the control system 50 of the machine 10. According to one example, the steps implementing the disclosed method may be in the form of computer-readable program code stored in the memory 52 and executed by the processor 52a of the electronic control device 52 or on another computer-usable medium. The method may run continuously or may be initiated in response to a predetermined event.For example, the transient torque load control algorithm can be initialized in response to the identification of a possible engine stall event.

[0030] The method begins at START, box 72. From box 72, the method proceeds to box 74, which includes the electronic controller 52 comparing the current engine speed 60 to a dynamic step speed threshold, which is described below with reference to Fig. 7. If the current engine speed 60 has fallen below the dynamic step speed threshold, the method proceeds to box 76. Otherwise, if the current engine speed 60 is greater than the dynamic step speed threshold, the method proceeds to box 78. At box 78, the electronic controller 52 compares the current engine speed 60 to a dynamic trigger speed threshold, which is discussed below with reference to Fig. 6. If the current engine speed 60 has fallen below the dynamic trigger speed threshold, the method proceeds to box 80. Otherwise, if the current engine speed 60 is above the dynamic trigger speed threshold, the method proceeds to END, at box 82.

[0031] At box 80, the electronic controller 52 will reduce the drive system torque limit 58 and the tool system torque limit 59, such as based on a configurable rate, to reduce the torque limits 63 and 64. For example, the torque limits 58 and 59 may be reduced at a constant rate, such as 5% or less of the reference torque per processor loop, when the current engine speed 60 falls below the dynamic trigger speed threshold. After reducing the torque limits 58 and 59, the method next proceeds to box 84, which provides that the electronic controller 52 again compares the current engine speed 60 to the dynamic step speed threshold. If the current engine speed 60 has fallen below the dynamic step speed threshold, the method proceeds to box 76.Otherwise, if the current engine speed 60 is greater than the dynamic step speed threshold, the method proceeds to box 86. At box 86, the electronic controller 52 compares the current engine speed 60 to a dynamic recovery speed threshold, which is described below with reference to FIG. Fig. 8. If the current engine speed 60 has risen above the dynamic recovery speed threshold, the method advances to box 88. Otherwise, if the current engine speed 60 remains below the dynamic trigger speed threshold, the method advances to box 90.

[0032] In box 90, the electronic controller 52 determines whether the reduced torque load limits 63 and 64 have reached a lower torque limit, which may be a non-zero torque limit. The lower torque limit may be a configurable parameter selected to provide a desired minimum torque limit magnitude. For example, the lower torque limit may be selected to greatly reduce the torque loads on the internal combustion engine 20 without completely removing all torque loads. If the reduced torque load limits 63 and 64 have been reduced to the lower torque limit, the method proceeds to box 92.Otherwise, the method will return to box 80, where the electronic controller 52 will continue to decrease the reduced torque limits 63 and 64 until the lower torque limit is reached, the current engine speed 60 falls below the dynamic step speed threshold, or the current engine speed 60 rises above the dynamic recovery speed threshold. In box 92, the reduced torque limits 63 and 64 are maintained at the lower torque limit while the current engine speed 60 remains between the dynamic trigger speed threshold and the dynamic step speed threshold.

[0033] If the current engine speed 60 drops below the dynamic step speed threshold at box 94, the method proceeds to box 76. Alternatively, if the current engine speed 60 increases above the dynamic recovery speed threshold, as compared at box 96, the method proceeds to box 88. At box 88, the electronic controller increases reduced torque limits 63 and 64 in response to the current engine speed 60 increasing above the dynamic recovery speed threshold, such as based on a configurable rate, which is discussed below. The method will continue to increase the torque limits 58 and 59 or the reduced torque limits 63 and 64 until a certain monitored condition occurs.

[0034] Specifically, if the current engine speed 60 falls below the dynamic step speed threshold, as compared in box 98, the method returns to box 76. If the current engine speed 60 falls below the dynamic trigger speed threshold, as compared in box 100, the method returns to box 80. The current engine speed 60 is again compared to the dynamic recovery speed threshold at box 102, and if the current engine speed 60 remains below the dynamic recovery speed threshold, the electronic controller 52 continues recovery at box 88. Once the current engine speed 60 increases above the dynamic recovery speed threshold, the reduced torque limits 63 and 64 are compared to the current dynamic torque load limits 58 and 59 at box 104.If the reduced torque load limits 63 and 64 have not yet returned to the current dynamic torque load limits 58 and 59, the method returns to box 88. Otherwise, if the reduced torque load limits 63 and 64 have returned to the current dynamic load limits 58 and 59, the method proceeds to the END in box 82.

[0035] If the current engine speed 60 drops below the dynamic step speed threshold at any point, the method advances to box 76, where the torque load limits 58 and 59, or the reduced torque load limits 63 and 64, are reduced to zero or a negative value. Alternatively, however, the reduced torque load limits 63 and 64 may be reduced to relatively low positive values less than the torque floor. The torque load limits 58 and 59, or reduced torque load limits 63 and 64, will remain at the value of zero or a negative value, or at a relatively low positive value, until the current engine speed 60 increases above the dynamic recovery speed threshold. Once the current engine speed 60 increases above the dynamic recovery speed threshold, as compared in box 106, the reduced torque load limits 63 and 64 are increased in box 88.As noted above, the reduced torque load limits 63 and 64 are increased until the limits 63 and 64 have returned to the current dynamic torque load limits 58 and 59.

[0036] Dynamic trigger speed thresholds, dynamic step speed thresholds, and dynamic recovery speed thresholds, as mentioned above, may be stored in memory 52b and may be provided for specific engine underspeed values and actual gear ratios of machine 10. For example, Fig. 6 depicts an electronically stored trigger speed map 110 that relates dynamic trigger speed threshold values 112 to engine underspeed values 114 and actual transmission ratios 116. Thus, the electronic controller 52 may receive as an input the current engine speed 60 and the actual transmission ratio 61, which may represent the current ground speed of the machine 10 and may be calculated as a function of a pump displacement divided by an engine displacement, and may select a dynamic trigger speed threshold according to the input values 60 and 61. As shown, the dynamic trigger speed threshold values 112 in the electronically stored trigger speed map 110 may deviate less from a corresponding engine underspeed value 114 as the engine underspeed value 114 decreases.Furthermore, the dynamic trigger speed thresholds 112 in the electronically stored trigger speed map 110 may deviate less from a corresponding engine underspeed value 114 as the actual transmission ratio 116 increases. As such, the transient torque load control algorithm may be more active at lower engine underspeed values and higher transmission ratios.

[0037] Fig. 7 depicts an electronically stored step speed map 120 relating dynamic step speed thresholds 122 to engine underspeed values 124 and actual transmission ratios 126, while Fig. 8 depicts an electronically stored recovery speed map 130 relating dynamic recovery speed thresholds 132 to engine underspeed values 134 and actual transmission ratios 136. It should be noted that the values reflected in tables 110, 120, and 130 are provided for exemplary purposes only. The values are configurable and can be obtained through testing to provide desired response of the transient torque load control algorithm provided therein.

[0038] According to some embodiments, it may be desirable to apply a rate limit value to each of the values provided in maps 110, 120, and 130. With reference to Fig. 9, for example, a rate limit table 140 may be provided having maximum rate limits 142 provided in revolutions per minute (RPM) per processor loop, corresponding to specific engine underspeed values 144. The maximum rate limits 142 may be applied to any of the electronically stored maps 110, 120, and 130 described above and, as shown, may require slower rate limit increases at higher engine underspeed values 144 so that the speeds reflected or represented in the maps 110, 120, and 130 are not increased too rapidly during acceleration. As should be understood, a minimum rate limit may also be provided, such as a minimum rate limit of -50 RPM per processor loop.

[0039] As mentioned above, the torque limits 58 and 59 may be decreased at a constant rate, such as 5% or less of the reference torque per processor loop, when the current engine speed 60 falls below the dynamic trigger speed threshold. However, it may be desirable to increase the decreased torque limits 63 and 64 at a rate dependent on specific engine underspeed values. For example, with reference to Fig. 10, a table 150 may be provided which has rate of increase limits 152 corresponding to specific engine underspeed values 154 for the drive system 14. Similarly, a Fig. 11, which includes ramp rate limits 162 corresponding to specific motor underspeed values 164 for the tool system 24. For example, it may be desirable to prevent the torque loads from returning too quickly.

[0040] The transient torque load control strategy provided herein may include additional features to adjust the torque limits 58 and 59 during a potential engine stall event, characterized by the engine speed dropping a predetermined amount below an engine underspeed value. According to one example, the strategy may also include logic to ensure that the dynamic recovery speed threshold is greater than the dynamic trigger speed threshold, which is greater than the dynamic step speed threshold. Further, the exemplary data provided herein may be modified based on a desired performance of the machine 10. Industrial applicability

[0041] The present disclosure has potential application to any machine having one or more torque-generating devices configured to generate torque for one or more torque-consuming devices, including a continuously variable transmission. Furthermore, the present disclosure may be particularly applicable to machines that utilize torque load limits to control operation of the torque-generating devices and / or the torque-consuming devices. Still further, the disclosure may be applicable to control strategies for further limiting the torque load limits in response to identification of a potential engine stall event.

[0042] Generally with reference to the Fig. 1-11, a machine 10 may include one or more torque-generating systems 42, including an internal combustion engine 20 that generates or delivers torque through an output 40 to one or more torque-consuming devices 46, including a drive system 14 and an implement system 24. A control system 50, including at least one electronic controller 52, may be provided to control an engine torque load of the machine 10. In particular, the control system 50 may execute a torque load control algorithm to generate torque load limits 58 and 59 based at least in part on an engine underspeed value 57. The torque load limits 58 and 59 indicate a torque load that can be applied to the internal combustion engine 20 without causing the speed of the engine 20 to fall below the engine underspeed value 57.It should be noted that such a control strategy may be executed during the majority of operation of machine 10 to generate one or more torque load signals to regulate the engine torque load. For example, the internal combustion engine 20 and / or the torque-consuming devices 46 may be controlled based on the torque load limit signals 58 and 59 to regulate the engine torque load.

[0043] However, under certain operating conditions, the motor 20 may still potentially stall. For example, during highly transient load conditions, such as when the machine 10 runs into a pile of material and the tool 30 comes into contact with the material, the torque load limits 58 and 59 may not be adjusted quickly enough to prevent a motor stall from occurring. In particular, torque may be relayed from the torque output at the wheels 16 back through the torque-generating device output 40. This input torque, caused by an increase in drive pressure, is applied to the motor shaft, causing the motor speed to drop rapidly. Such a scenario may represent a potential engine stall event.

[0044] When such a potential engine stall event is identified, such as by determining that the current engine speed 60 has dropped below the engine underspeed value 62 by a predetermined amount, the transient torque load control strategy provided herein may be executed. Specifically, the method may monitor the current engine speed 60 and, if the current engine speed 60 drops below a corresponding dynamic trigger speed threshold selected from the electronically stored trigger speed map 110 or below a corresponding dynamic step speed threshold selected from the electronically stored step speed map 120, the torque load limits 58 and 59 may be reduced to reduced torque limits 63 and 64.In particular, the torque load limits 58 and 59 may be reduced at a constant rate, such as by 5% or less of the reference torque per processor loop, when the current engine speed 60 falls below the dynamic trigger speed threshold. The electronic controller 52 will continue to decrease the reduced torque limits 63 and 64 until the torque floor is reached, the current engine speed 60 falls below the dynamic step speed threshold, or the current engine speed 60 rises above the dynamic recovery speed threshold. The reduced torque limits 63 and 64 are maintained at the torque floor while the current engine speed 60 remains between the dynamic trigger speed threshold and the dynamic step speed threshold.

[0045] If the current engine speed 60 falls below the dynamic step speed threshold at any point, the torque load limits 58 and 59 or the reduced torque load limits 63 and 64 are reduced to zero or a negative value. The torque load limits 58 and 59 or the reduced torque load limits 63 and 64 will remain at zero or the negative value until the current engine speed 60 increases above the dynamic recovery speed threshold. If the current engine speed 60 increases above the dynamic recovery speed threshold, the electronic controller 52 increases the reduced torque limits 63 and 64 until the reduced torque limits 63 and 64 are returned to the current dynamic torque load limits 58 and 59 calculated according to the torque load control algorithm described with reference to Fig.3. It should be understood that the internal combustion engine 20 and / or the plurality of torque consuming devices 46 are controlled based on the adjusted torque load limit signals 63 and 64 to regulate the engine torque load.

[0046] The engine torque control strategy provided herein includes executing a torque load control algorithm during a major portion of machine operation to generate torque load limits that help maintain an appropriate torque distribution that can mitigate engine stall. The control strategy monitors engine speed to identify potential engine stall events and, when such an event is identified, executes a transient torque load control algorithm in place of the torque load control algorithm to adjust the torque load limits. For example, the torque load limits can be decreased at a configurable rate or dropped to zero to effectively reduce torque loads during a potential engine stall event and return the engine speed to the engine underspeed level.Such a strategy may be particularly applicable to machines using continuously variable transmissions, where direct connections between the engine and the transmission can generate high transient loads on the engine.

Claims

[1] Machine (10) comprising: an internal combustion engine (20); a plurality of ground-engaging elements (16); a plurality of torque-consuming devices (46) drivingly coupled to the internal combustion engine (20), the plurality of torque-consuming devices (46) comprising a continuously variable transmission (14) coupling the internal combustion engine (20) and the ground-engaging elements (16); and an electronic control device (52) in communication with the internal combustion engine (20) and the plurality of torque consuming devices (46), the electronic control device (52) being configured to execute a torque load control algorithm to generate a torque load limit (58, 59) based at least in part on an engine underspeed value (57, 62, 114, 124, 134, 144, 154, 164); to identify a potential engine stall event during which a current engine speed (55, 60) of the internal combustion engine (20) falls below the engine underspeed value (57, 62, 114, 124, 134, 144, 154, 164) by a predetermined amount; and execute a transient torque load control algorithm to adjust the torque load limit (58, 59, 63, 64) in response to the identification of the potential engine stall event. [2] The machine (10) of claim 1, wherein the electronic control device (52) is further configured to determine a dynamic trigger speed threshold (112) based on the engine underspeed value (57, 62, 114, 124, 134, 144, 154, 164) and an actual gear ratio (61, 116, 126, 136) of the continuously variable transmission (14); to compare the current engine speed (55, 60) with the dynamic trigger speed threshold (112); and to execute the transient torque load control algorithm when the engine speed (55, 60) is less than the dynamic trip speed threshold (112). [3] The machine (10) of claim 2, wherein the electronic control device (52) is further configured to to determine a dynamic step speed threshold (122) based on the engine underspeed value (57, 62, 114, 124, 134, 144, 154, 164) and the actual transmission ratio (61, 116, 126, 136), wherein the dynamic step speed threshold (122) is less than the dynamic trigger speed threshold (112); and to compare the current engine speed (55, 60) with the dynamic step speed threshold (122); wherein the transient torque load control algorithm reduces the torque load limit (58, 59, 63, 64) to zero or a negative value when the current engine speed (55, 60) is less than the dynamic step speed threshold (122). [4] The machine (10) of claim 3, wherein the electronic control device (52) is further configured to determine a dynamic recovery speed threshold (132) based on the engine underspeed value (57, 62, 114, 124, 134, 144, 154, 164) and the actual transmission ratio (61, 116, 126, 136) if the dynamic recovery speed threshold (132) is greater than both the dynamic trigger speed threshold (112) and the dynamic step speed threshold (122); and comparing the current engine speed (55, 60) with the dynamic recovery speed threshold (132); wherein the transient torque load control algorithm increases the torque load limit (58, 59, 63, 64) when the current engine speed (55, 60) is greater than the dynamic recovery speed threshold (132). [5] The machine (10) of claim 2, wherein the electronic controller (52) is further configured to select the dynamic trigger speed threshold (112) from an electronically stored trigger speed map (110), the electronically stored trigger speed map (110) having dynamic trigger speed threshold values (112) plotted against engine underspeed values (57, 62, 114, 124, 134, 144, 154, 164) and actual transmission ratio values (61, 116, 126, 136), the dynamic trigger speed threshold values (112) in the electronically stored trigger speed map (110) deviating less from a corresponding engine underspeed value (57, 62, 114, 124, 134, 144, 154, 164) when the engine underspeed values (57, 62, 114, 124, 134, 144, 154, 164) decrease and the actual gear ratio values (61, 116, 126, 136) increase. [6] A method for controlling an engine torque load on an internal combustion engine (20) of a machine (10), the machine (10) having a plurality of torque consuming devices (46) drivingly coupled to the internal combustion engine (20), the plurality of torque consuming devices (46) comprising a continuously variable transmission (14) coupling the internal combustion engine (20) and ground engaging elements (16) of the machine (10), the method comprising: Generating a torque load limit signal (58, 59) based at least in part on an engine underspeed value (57, 62, 114, 124, 134, 144, 154, 164); Controlling the internal combustion engine (20) and / or the plurality of torque consuming devices (46) based on the torque load limit signal (58, 59) to regulate the engine torque load on the internal combustion engine (20); Sensing a current engine speed (55, 60) of the internal combustion engine (20); Identifying a potential engine stall event during which the current engine speed (55, 60) of the internal combustion engine (20) drops below the engine underspeed value (57, 62, 114, 124, 134, 144, 154, 164) by a predetermined amount; Adjusting the torque load limit signal (58, 59) in response to the identification of the potential engine stall event to generate an adjusted torque load limit signal (63, 64); and Controlling the internal combustion engine (20) and / or the plurality of torque consuming devices (46) based on the adjusted torque load limit signal (63, 64) to regulate the engine torque load on the internal combustion engine (20). [7] The method of claim 6, wherein the potential engine stall event is identified when the current engine speed (55, 60) drops below a dynamic trigger speed threshold (112), the dynamic trigger speed threshold (112) being based on the engine underspeed value (57, 62, 114, 124, 134, 144, 154, 164) and an actual gear ratio (61, 116, 126, 136) of the continuously variable transmission (14). [8] The method of claim 7, wherein the adjusted torque load limit signal (63, 64) corresponds to zero or a negative value when the current engine speed (55, 60) falls below a dynamic step speed threshold (122), the dynamic step speed threshold (122) being based on the engine underspeed value (57, 62, 114, 124, 134, 144, 154, 164) and the actual transmission ratio (61, 116, 126, 136), the dynamic step speed threshold (122) being less than the dynamic trigger speed threshold (112). [9] The method of claim 8, wherein the adjusted torque load limit signal (63, 64) is increased when the current engine speed (55, 60) increases above a dynamic recovery speed threshold (132), the dynamic recovery speed threshold (132) being based on the engine underspeed value (57, 62, 114, 124, 134, 144, 154, 164) and the actual transmission ratio (61, 116, 126, 136), the dynamic recovery speed threshold (132) being greater than both the dynamic trigger speed threshold (112) and the dynamic step speed threshold (122). [10] The method of claim 9, wherein the adjusted torque load limit signal (63, 64) is increased at a rate that increases as the engine underspeed value (57, 62, 114, 124, 134, 144, 154, 164) increases.

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