Drivetrain system with lockable differential

Abstract

A drivetrain system (70) for a mobile machine (10), comprising: a power source (34); a plurality of traction devices (28); a differential (32) which operatively connects an output of the power source (34) to the plurality of traction devices (28); a manual input device (38) which can be moved by an operator to generate a first signal indicating a request to lock the differential (32); at least one sensor (74, 76) configured to generate a second signal indicating a parameter of the mobile machine (10); and a control device (72) in conjunction with the at least one sensor, the manual input device (38), and the differential (32), wherein the control device is configured to prevent the differential (32) from locking based on the first signal if the second signal indicates that the parameter deviates from an acceptable range.wherein the mobile machine (10) is a scraper with an attached tractor (12) for pulling a skip (16).

Description

Technical field The present disclosure relates to a drivetrain system and in particular to a drivetrain system with a lockable differential. background Machines such as scrapers, wheel loaders, trucks, and other mobile machinery are used to perform many tasks. To perform these tasks effectively, the machines require an engine that delivers significant torque through a transmission to several traction devices that engage with the ground. Such machines typically have one or more differentials that distribute rotational power from the transmission between tandem pairs of traction devices. These differentials, or differential gears, are used to drive the traction devices simultaneously while allowing them to rotate at different speeds, thus reducing wear on the traction devices, the associated drivetrain, and even the road surface during specific operating maneuvers, such as cornering.However, in some situations a differential can also allow the machine to lose traction by transferring all or a major part of the power from the transmission to just the traction device, which is slipping. One way to reduce traction device slippage is to manually lock the differential when slippage is likely or already occurring. Locking the differential causes both paired traction devices to rotate at the same speed, even if one of them doesn't yet have sufficient traction (i.e., even if the traction device is rotating faster than the machine's ground speed). In this way, the traction device that still has adequate traction receives enough power from the transmission to move the machine through terrain that contributes to slippage. Unfortunately, manually locking a differential can lead to timing and engagement problems associated with the locking and unlocking operations.For example, a machine operator might attempt to lock the differential when high levels of slippage are already occurring (for instance, when one traction device is rotating much faster than the other paired traction device), which can lead to damage to the differential. Similarly, the machine operator might keep the differential locked longer than necessary, which can result in excessive wear on the machine. An attempt to address one or more of the problems described above is disclosed in US Patent 6,174,255 B1, granted to Porter and others on January 16, 2001 (“the '255 patent”). Specifically, the '255 patent discloses a work vehicle with a front axle having a differential and a locking device hydraulically coupled to a solenoid valve. The solenoid valve is further coupled to a microprocessor that has manual and automatic operating modes. In manual mode, the solenoid valve is controlled to activate the locking device and lock the differential when a foot pedal located in an operator's cab is pressed. In automatic mode, the microprocessor automatically determines when the front axle wheels are slipping and, in response, triggers the solenoid valve to activate the locking device and stop the slippage.The microprocessor is further configured to determine when a joint angle or steering angle of the vehicle is greater than a programmed value during operation, either in manual or automatic operating mode, and, responding to this, triggers the solenoid valve to release the locking device and reduce the damage to the differential caused by cornering. Although the system of patent '255 may be suitable for some situations, it may not be entirely optimal. In particular, the system does not prevent an operator from locking the differential under conditions that could damage it. Additionally, the system of patent '255 may have limited applicability because it cannot take into account parameters specific to particular types of machinery during the automatic unlocking of the differential. US patent application US 2007 / 0250236A1, filed by the applicant, describes a method for operating an articulated work machine and includes detecting the articulation angle within the wheel steering angle of the work machine and controlling the locking state of a differential depending on the turning radius of the work machine. An articulated, wheel-driven work machine comprises a front frame unit with a wheel steering device, a rear frame unit, and an articulation device coupled between the front and rear frame units. A first and a second sensor are designed to detect the wheel steering angle and the articulation angle of the work machine. An electronic control system is provided, configured to selectively lock or unlock the differential of the rear frame unit depending on the turning radius of the work machine. The present disclosure is aimed at overcoming one or more of the problems set out above and / or other problems of the prior art. Summary According to one aspect, the present disclosure relates to a drivetrain system for a mobile machine. The drivetrain system may include a power source, a plurality of traction devices, and a differential or differential gear which, in operation, connects an output of the power source to the plurality of traction devices. The drivetrain system may also include a manual input device that can be moved by an operator to generate a first signal indicating a wish to lock the differential, at least one sensor configured to generate a second signal indicating a parameter of the mobile machine, and a control device connected to the at least one sensor, the manual input device, and the differential.The control device can be configured to prevent differential locking based on the first signal if the second signal indicates that the parameter deviates from an acceptable range. The mobile machine is a scraper with an attached tractor for pulling a skip. According to another aspect, the present disclosure relates to a method for operating a mobile machine. The method may include generating a power output and directing the power output through a differential to a plurality of traction devices. The method may also include receiving a manual input indicating a desire to lock the differential, detecting a parameter of the mobile machine, and selectively preventing the locking of the differential based on the manual input if the parameter deviates from an acceptable range. The mobile machine is a scraper with an attached tractor for pulling a dump truck. Brief description of the drawings Fig. 1 is a pictorial representation of an exemplary disclosed mobile machine; Fig. 2 is a schematic representation of an exemplary disclosed drive train system which can be used with the mobile machine of Fig. 1; and Fig. 3 is a flowchart which depicts an exemplary disclosed method which is carried out by the drive train system of Fig. 2. Detailed description Fig. 1 illustrates an exemplary mobile machine 10. In the disclosed example, the machine 10 is an earthmoving machine, such as a scraper, configured to load material at a first location, transport the material from the first location to a second location, and unload the material at the second location. However, it is considered that the machine 10 could represent a different type of mobile machine, if desired, such as a road or off-road truck, a wheel loader, or another machine known in the art. The machine 10 can have a front tractor 12, or hereinafter also tractor section 12, which is operationally connected to a rear tractor 14, or hereinafter also tractor section 14, and a trough 16 arranged between the front and rear tractor sections 12 and 14.The front and rear tractor sections 12, 14 can work together to pull or push the trough 16 against a ground surface. The trough 16 can be rigidly connected to the rear tractor section 14 and operationally connected to the front tractor section via a hinge assembly 18. The front tractor section 12 can have several components that work together to power and control the operation of the tipper 16. In particular, the front tractor section 12 can have a frame 20, a front axle assembly 22, a drive train 24, and an operator station 26. The frame 20 can be rotatably mounted to accommodate the front axle assembly 22 and configured to support the drive train 24. The drive train 24 can be configured to power the front axle assembly 22 and to provide electrical and / or hydraulic power to move the tipper 16. The operator station 26 can, as described in more detail below, enable manual control of the machine 10. The front axle assembly 22 can, among other things, comprise a plurality of traction devices 28, an axle 30 associated with each of the traction devices 28, and a centrally located differential or differential gear 32 connected to the inner ends of the axle 30. In the disclosed exemplary embodiment, the traction devices 28 are wheels attached to the outer ends of the axles 30 opposite the differential 32. It should be noted, however, that traction devices other than wheels could be used if desired, for example, tracks or belts. The differential 32 can be configured to receive a rotational input from the drive train 24 and supply a rotational output to each of the axles 30 to drive the traction devices 28 and thereby propel the machine 10.If one of the traction devices 28 rotates at a considerably different speed than another of the traction devices 28 in the same axis arrangement 22 during a straight-ahead journey of the machine 10, it is said that at least one of the traction devices 28 is slipping. The differential 32 can have a combination of meshing gears and a locking clutch (for example, a conventional dog clutch) which work together to produce two different operating modes, during which the axles 30 are driven either with substantially the same torque or at substantially the same speed. In particular, the differential 32 can deliver substantially the same amount of torque to each axle 30 when the differential 32 is operating in an unlocked mode (i.e., when the dog clutch is disengaged), as is known in the art, regardless of the speeds of the axles 30 (i.e., the speeds of the axles 30 can be different when the differential 32 is operating in the unlocked state).In contrast, it is also known in engineering that the differential 32 can be configured to drive the axles 30 at approximately the same rotational speeds, regardless of the magnitude of the torque supplied to each axle 30, when operating in a locked state (i.e., when the dog clutch is disengaged). Operating with the differential 32 in locked mode can make steering difficult due to the uniform rotational speeds. Because the differential 32 can have a dog clutch, the axles 30 can be coupled to each other by mechanical counteraction when the differential 32 is locked (as opposed to friction, which is common in other types of clutches), so that slippage of the traction devices 28 is not possible without damaging the differential 32.The differential 32 can be made to operate selectively in the locked mode to maintain a traction force of the machine 10, or in the unlocked mode to reduce the wear of the traction devices 28 and / or the drive train 24 during special operating procedures, such as during cornering. The drivetrain 24 can be configured to generate a power output that is directed to the axles 30 via the differential 32. In the published embodiment, the drivetrain 24 includes, among other things, a motor 34 and a transmission 36, which is operationally coupled to the motor 34 and the differential 32. The motor 34 can be any power source known in the art, for example, an internal combustion engine such as a diesel or gasoline engine. The transmission 36 can be a power-shift transmission, a continuously variable transmission, or a hybrid transmission, as desired, and can be configured to transmit a power output generated by the motor 34 to the differential 32 over a range of speed-torque ratios.It should be noted that the drive train 24 may have an alternative power source coupled to the transmission 36 if desired, such as an electric motor, a fuel cell / engine combination or another source known in the art. The operator station 26 can have an interface device 38 located near an operator seat and configured to generate control signals associated with the operation of the machine 10. For example, the interface device 38 can be a foot switch located on the floor of the operator station 26 and selectively actuated by an operator (for example, by stepping on it to manually move the jaw clutch of the differential 32 to lock and unlock). However, it is considered that another type of interface device 38, such as a pedal, push button, or lever, could be used to control the differential 32 if desired. The same or a different interface device can be used to control operations of the trough 16, if desired. The hinge assembly 18 (also known as a damping or folding hinge) can have a curved main beam 40 with a front end 42 and a rear end 44. The front end 42 of the beam 40 can be connected to the frame 20 by a vertical hinge joint 46 and a horizontal hinge joint 48 such that the beam 40 can pivot both horizontally and vertically relative to the frame 20. A pair of steering actuators 50 (only one of which is shown in Fig. 1) can be associated with the vertical hinge joint 46 to provide articulated steering of the machine 10.In particular, the steering actuation devices 50 can be left and right hydraulic cylinders located on each side of the support 40, which extend and retract in opposite directions to cause the support 40 to pivot horizontally at the vertical hinge joint 46. An articulation actuation device 52, for example a hydraulic cylinder, can be associated with the horizontal hinge joint 48 to provide selective isolation of the operator station 26 from vertical movements of the skip 16. The articulation actuation device 52 can be hydraulically locked during certain operating modes (for example, during digging or...unloading), so that the carrier 40 is prevented from moving in the vertical direction relative to the frame, and can be unlocked during other operating modes (for example, during transport) to allow the carrier 40 and the trough 16 to float or hover in the vertical direction relative to the frame 20. The rear end 44 of the support 40 can be connected to the trough 16 via a pair of arms 54 located on opposite sides of the support 40 (only one side is shown in Fig. 1). Each arm 54 can have a first end 56 and a second end 58. The first end 56 can be pivotally connected to the rear end 44 of the support 40, while the second end 58 can be pivotally connected to the trough 16. A pair of trough actuating devices 60 (only one shown in Fig. 1), for example, hydraulic cylinders, can be connected between the support 40 at the rear end 44 and the trough 16 and configured to selectively raise the trough 16 away from the ground surface and lower the trough 16 towards the ground surface by means of retraction and extension movements, respectively. The hopper 16 can be rigidly supported by the rear tractor section 14. During the extension and retraction of the hopper actuation devices 60, the hopper 16 can be caused to pivot vertically about a rear axle assembly 62, so that a front end 64 of the hopper 16 can be raised and lowered relative to the ground. In some embodiments, an additional drive train 66 can be included in the rear tractor section 14 and supported by the rear axle assembly 62. In these embodiments, the drive train 66 can be operated to drive the rear axle assembly 62 and thereby push the machine 10. The drive train 66 of the rear tractor section 14 can be substantially identical to the drive train 24 of the front tractor section 12. The trough 16 can be a tool embodied as a hollow casing with an opening at its front end 64. A horizontal shield 68 can be located at the front end 64 and positioned to selectively engage the ground surface when the front end 64 is lowered by extending the trough actuating devices 60. In this configuration, the extension length of the trough actuating devices 60 can influence the depth or cutting depth of the shield 68 into the ground surface and, in conjunction with the machine's travel speed 10, the rate of material removal from the ground surface. As shown in Fig. 2, the machine 10 can be equipped with a drivetrain system 70, which includes components that work together to control the differential 32 in response to various sensor and operator inputs. In particular, the drivetrain system 70 may include, among other things, a control device 72 in conjunction with the differential 32, the transmission 36, the interface device 38, the articulation device 52, the trough actuating devices 60, and / or one or more sensors arranged around the entire machine 10 and configured to generate signals indicating performance parameters of the machine 10. The control device 72 can be configured, as described in more detail below, to selectively cause the dog clutch of the differential 32 to lock or unlock, thereby changing the operating mode of the differential 32 and the corresponding behavior of the traction devices 28. The control device 72 can be configured to execute instructions stored on a computer-readable medium to perform a control procedure for the differential in response to received signals. The control device 72 can include any component or combination of components to monitor, record, store, index, process, and / or transmit operational aspects of the machine 10 described above. These components can include, for example, a memory, one or more data storage devices, a central processing unit, or any other components used to run an application.Although aspects of the present disclosure may generally be described as being stored in memory, it will nevertheless be clear to the person skilled in the art that these aspects may be stored on or read from types of computer program products or computer-readable media, such as computer chips and secondary storage devices, including hard disks, floppy disks, optical media, CD-ROMs, or other forms of RAM or ROM or read memory. The control device 72 can execute sequences of computer program instructions stored on the computer-readable medium to perform control procedures for the differential, which are explained below. The sensors that can provide an input signal for the control device 72 can include, among others, a speed sensor 74 associated with each of the axes 30 and / or traction devices 28, and a yaw rate sensor 76. The speed and yaw rate sensors 74 and 76 can be any conventional speed and yaw rate sensors known in the art. Based on an input signal from multiple speed sensors 74, the control device 72 can be configured to determine whether slippage (a speed difference between the traction devices 28) occurs or is likely to occur. Based on an input from the yaw rate sensor 76, the control device 72 can be configured to determine whether and at what rate the machine 10 is turning (i.e., steering and / or performing articulating steering). The control device 72 can be configured to determine additional information via communication with the transmission 36, the articulating device 52, and / or the recessed actuating devices 60. For example, the control device 72 can be configured to determine the current speed-torque ratio (i.e., the gear) by communicating with the transmission 36 or with one or more sensors (not shown) associated with the transmission 36. The control device 72 can also be configured to determine the current status of the articulating hinge assembly 18 (i.e., whether the articulating hinge assembly 18 is in a locked or free-floating state) by communicating with the articulating device 52 or with one or more sensors (not shown) associated with the articulating hinge assembly 18.Similarly, the control device 72 can be configured to determine the current position and / or charge level of the hopper 16 by communicating with the hopper actuation devices 60 or by communicating with one or more (not shown) sensors associated with the hopper 16. Fig. 3 illustrates an exemplary method, which is stored as instructions on the computer-readable medium, wherein the instructions can be executed by the control device 72 to perform differential control of the machine 10. Fig. 3 is discussed in more detail in the following section to further illustrate the disclosed concepts. Industrial applicability The disclosed drivetrain system can be applied to any mobile machine where protection of the machine's differential components is desired. The disclosed drivetrain system can help protect the differential by controlling both manual and automatic locking operations based on operator input and measured machine performance parameters. The operation of the drivetrain system 70 will now be explained with reference to Fig. 3. The exemplary method for controlling the drive train system 70 of the machine 10 can begin with the control device 72 receiving a manual input from the operator of the machine 10 regarding a desired locking of the differential 32 (step 300). As described above, the input variable can be a signal generated by the interface device 38 (see Fig. 2). For example, the operator can step on the interface device 38 to indicate a wish to lock the dog clutch of the differential 32 (when the differential 32 is currently unlocked), and the interface device 38 can generate a corresponding signal indicating this wish.The operator can step on the interface device 38 to indicate the wish to lock the differential 32 if the operator becomes aware that the traction devices 28 are slipping, or alternatively, if the operator initiates an operating procedure where slippage is known to commonly occur. Slippage can commonly occur during loading or unloading of the skip 16 when resistance to the forward movement of the machine increases and / or when the machine's ground 10 becomes loose and provides less traction for the traction devices 28.Similarly, the operator can again step onto (or release) the interface device 38 to indicate a wish to unlock the dog clutch of the differential 32 (if the differential is currently locked), and the interface device 38 can generate a corresponding signal indicating this wish. The operator can step onto the interface device 38 to indicate the wish to unlock the differential 32 when completing an operation typically associated with slippage or sliding, and / or when initiating a transport operation where slippage is less likely to occur. Based on the current status of the differential 32 (i.e., whether the differential 32 is currently locked or unlocked) and based on the signal from the interface device 38, the control device 72 can determine whether the operator wants to lock or unlock the differential 32. For example, if the differential 32 is locked when the signal from the interface device 38 is received, the control device 72 can determine that the operator wants to unlock the differential 32 (step 306: Unlock). If the differential 32 is unlocked when the signal from the interface device 38 is received, the control device 72 can similarly determine that the operator wants to lock the differential 32 (step 305: Lock).If the operator wants to unlock the differential 32, the control device 72 can disengage the dog clutch of the differential 32 (step 307) and the control can return to step 300. However, if the operator wants to lock the differential 32, the control can proceed to step 310, where the control device 72 detects various performance parameters of the machine 10 that can influence the successful engagement of the dog clutch. Step 310 can be completed before, during, and / or after the input from the operator of machine 10 regarding the request to lock the differential 32 has been received (step 310). The performance parameters detected by the control device 72 may include, among other things, rotational speeds of the traction devices 28 received by the sensors 74. The control device 72 can then compare the performance parameters with an acceptable range and determine whether the performance parameters have deviated from the range (step 320). For example, the control device 72 can receive signals from the sensors 74 associated with the traction devices 28 and, responding to these signals, can determine whether an actual slip value of the traction devices 28 (i.e.,an actual speed difference between the opposing traction devices 28 or a percentage difference of the machine's travel speed) has deviated from an acceptable range of slip values. If the performance parameters deviate from the acceptable range, locking the differential 32 could damage the dog clutch of the differential 32 (i.e., the increased speed difference could cause the interacting components of the dog clutch to engage violently, resulting in component breakage). Accordingly, in this situation, the control device 72 can prevent locking of the differential 32 in response to the signal received from the interface device 38 (step 330).However, if the performance parameters fall within the acceptable range of values, the control device 72 can instead lock the differential 32 in response to the manual display or instruction provided by the operator of the machine 10 (i.e., in response to the signal from the interface device 38) (step 340). During operation of the differential 32 in locked mode, the axes 30 can be driven to rotate at approximately the same speeds, and improved traction for the machine 10 can be provided, offering improved productivity and / or efficiency. Once the machine 10 has passed through conditions that contribute to slippage, the operator should manually unlock the differential 32 by again actuating the interface device 38. However, in some situations, the operator may be mistaken and might not unlock the differential 32 when the improved traction is no longer necessary or advantageous. Accordingly, the control device 72 can be configured to automatically override the operator.to oversteer and to unlock the differential 32 under certain circumstances, so that the component lifetime of the traction devices 28 and / or the drive train 24 can be increased. After the differential 32 has been locked according to the operator's request (i.e., after completion of step 340), the control device 72 can, for example, detect various other performance parameters of the machine 10. In particular, the control device 72 can detect a position of the trough 16, a load state of the trough 16, a speed-torque ratio (i.e., a gear) of the transmission 36, a state of the joint hinge assembly 18 (locked or floating), a yaw rate (i.e., a cornering rate) of the machine 10, and / or another parameter known in the art (step 350). The control device 72 can then determine whether the detected parameter(s) indicate conditions during which increased traction is no longer desirable.This means that the control device 72 can determine whether the skip 16 is in a transport position (as opposed to a digging or unloading position), whether the skip is unloaded or unloaded, whether the transmission 36 is in a transport gear (a higher gear compared to a lower digging or unloading gear), whether the articulated hinge assembly 18 is in the floating state (as opposed to a locked state, which is required during loading of the skip 16), and / or whether the machine 10 is turning at a significant rate (as opposed to traveling in a straight line) (step 360). If none of these conditions are met (step 360: no), the control device 72 can maintain the locked state of the differential 32 requested by the operator (step 370), and the control can return to step 300.However, if the control device 72 determines that the trough 16 is in a transport position, is not loaded or being unloaded, that the transmission 36 is in a high transport gear, that the joint hinge assembly 18 is unlocked and / or that the machine 10 is turning at a significant rate, the control device 72 may instead unlock the differential 32 (step 380) to help protect the components of the differential 32, and the control may return to step 300. Because the drive system 70 allows the differential 32 to lock in response to manual input, the machine operator is given better control over the machine's operation. Furthermore, because the drive system 70 also functions to override operator commands for locking the differential 32 during conditions that could damage the differential 32, the integrity of the drive system 70 can be preserved. Finally, because the drive system 70 can be operated based on performance parameters specifically designed for a particular application (for example, specifically for a scraper application), additional functions of the machine 10 can be provided.For example, the drivetrain system 70 can allow automatic unlocking of the differential 32 based on the detection of specific performance parameters of a scraper, regardless of the operator's initial command to lock the differential 32 (i.e., regardless of the current position and / or state of the interface device 38). This function can help improve the performance and / or durability of the machine 10 when used in a scraper application. It will be clear to those skilled in the art that various modifications and variations can be made to the disclosed drivetrain system. Other embodiments will become apparent to them from considering the description and a practical implementation of the disclosed drivetrain system. The description and examples are to be regarded as merely illustrative, with the true scope being shown by the following claims and their equivalent embodiments.

Claims

A drivetrain system (70) for a mobile machine (10), comprising: a power source (34); a plurality of traction devices (28); a differential (32) which operatively connects an output of the power source (34) to the plurality of traction devices (28); a manual input device (38) which can be moved by an operator to generate a first signal indicating a request to lock the differential (32); at least one sensor (74, 76) configured to generate a second signal indicating a parameter of the mobile machine (10); and a control device (72) in conjunction with the at least one sensor, the manual input device (38), and the differential (32), wherein the control device is configured to prevent the differential (32) from locking based on the first signal if the second signal indicates that the parameter deviates from an acceptable range.wherein the mobile machine (10) is a scraper with an attached tractor (12) for pulling a skip (16). Powertrain system according to claim 1, wherein the at least one sensor comprises at least one speed sensor (74) associated with at least one of the plurality of traction devices (28); wherein the parameter is a speed difference between the plurality of traction devices (28); and wherein the acceptable range is a range of acceptable speed differences. Powertrain system according to claim 2, wherein the at least one speed sensor comprises a first speed sensor associated with a first of the plurality of traction devices (28) and a second speed sensor associated with a second of the plurality of traction devices (28); and wherein the control device is configured to determine a speed difference between the first and the second of the plurality of traction devices (28) based on signals from the first and second speed sensors. Powertrain system according to claim 1, wherein the at least one sensor is a yaw rate sensor (76); and wherein the acceptable range is a range of acceptable cornering rates of the mobile machine (10). Powertrain system according to claim 1, wherein the powertrain system further comprises a position sensor associated with the recess (16) and configured to generate a third signal associated with the position of the recess (16); and wherein the control device is further configured to unlock the differential (32) based on the third signal, irrespective of the position of the manual input device (38). Drivetrain system according to claim 5, wherein the control device is configured to unlock the differential (32) when the third signal indicates that the trough (16) is in a transport position. Powertrain system according to claim 1, wherein the powertrain system further comprises a load sensor associated with the trough (16) and configured to generate a third signal associated with a load state of the trough (16); and wherein the control device is further connected to the load sensor and configured to unlock the differential (32) based on the third signal, irrespective of the position of the manual input device (38). Drivetrain system according to claim 7 wherein the control device is configured to unlock the differential (32) when the third signal indicates that the trough (16) is not being loaded or unloaded. A method for operating a mobile machine (10) comprising: generating a power output; directing the power output through a differential (32) to a plurality of traction devices (28); receiving a manual input indicating a desire to lock the differential (32); detecting a parameter of the mobile machine (10), wherein the mobile machine (10) is a scraper with an attached tractor (12) for pulling a trough (16); and selectively preventing the locking of the differential (32) based on the manual input when the parameter deviates from an acceptable range. Method according to claim 9, wherein the parameter is a speed difference between the plurality of traction devices (28); and wherein the acceptable range is a range of acceptable speed differences.

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