METHOD FOR CONTROLLING A GEAR RANGE AS A RESPONSE TO A LOSS OF COMMUNICATION WITH AN ENGINE AND SYSTEM FOR THIS PURPOSE

Abstract

Method for controlling a multi-speed transmission, comprising: Providing a transmission control system, a plurality of gears of the transmission, at least one of which is defined as a limiting gear, and a communication link, each of which includes a torque limit from the plurality of switchable gears; Defining each gear from the plurality of switchable gears as either a limiting gear or a non-limiting gear based on its respective torque limit, each limiting gear having a lower torque limit than one or more non-limiting gears; Operating the transmission in a first gear from a plurality of gears; Detecting a loss of communication via the communication link between the transmission control unit and another control unit; Determine whether the first gear is a limiting gear; Commands by the transmission control unit to shift from first gear to a second gear from the plurality of gears, when first gear is a limiting gear and second gear is a non-limiting gear; and Shifting the transmission from first gear to second gear.

Description

RELATED APPLICATIONS

[0001] This application claims priority from U.S. patent application Ser. No. 16 / 168,191, filed October 23, 2018, the disclosure of which is hereby incorporated by reference in its entirety. AREA OF REVELATION

[0002] The present disclosure relates to the control of a transmission, and more particularly to a method for controlling a transmission gear in response to a loss of communication with an engine or other power generating device. BACKGROUND

[0003] In a conventional vehicle or work machine, an engine control unit communicates with a transmission control unit and other controllers via a communication link, such as an SAE J-1939 communication protocol (SAE = Society of Automotive Engineers). The communication can include information such as torque, speed, power, and the like. Communication over the link enables the controllers to optimally control the engine, transmission, and any other device.

[0004] However, if communication is lost or interrupted, the controllers will be unable to communicate with each other. This can be particularly problematic if the vehicle or machine is operating at high torque or high speed and an operator wants to change the operation of the vehicle or machine, for example, shift into a different gear. To protect the transmission and its internal components, the transmission controller may relay certain torque level requests to the engine controller, for example, to maintain the engine torque at a certain level. If communication between the controllers is either lost or intermittently interrupted, the controllers may be unable to communicate with each other. As a result, high or fluctuating engine output torque can pose problems for the transmission.US 2003 / 0186782 A1 describes a method for controlling an automatic transmission system. In the method, after an abnormal operating condition is detected, the output torque of an engine is reduced by interrupting the transmission of an ignition signal.

[0005] There is therefore a need for a method and system to protect the transmission in the event of a loss of communication, whether temporary or over a longer period. SUMMARY

[0006] In one embodiment of the present disclosure, a method for controlling a multi-speed transmission includes: providing a transmission controller, a plurality of gears of the transmission, at least one of the plurality of gears being defined as a limiting gear, and a communication link; operating the transmission in a first gear of the plurality of gears; detecting a loss of communication over the communication link between the transmission controller and another controller; determining whether the first gear is a limiting gear; commanding a shift from the first gear to a second gear of the plurality of gears by the transmission controller if the first gear is a limiting gear and the second gear is a non-limiting gear; and shifting the transmission from the first gear to the second gear.

[0007] In one non-limiting example of the present disclosure, the method includes preventing, by the transmission controller, a shift from any one of the plurality of gears not defined as a limiting gear to the at least one of the plurality of gears defined as a limiting gear. In a second example, the method may include maintaining the transmission in first gear when the first gear is not a limiting gear. In a third example, the method may include performing a jump shift by shifting from second gear to a third gear, wherein the first gear is between the second and third gears.

[0008] In a fourth example of this embodiment, the method may include determining whether there is a lower gear to which a downshift may be made that is not a limiting gear. In a fifth example, the method may include upshifting to a higher, non-limiting gear if the first gear is a limiting gear and there is no lower, non-limiting gear. In a sixth example, the method may also include upshifting or downshifting from first gear to a non-limiting gear based on a shift schedule if a lower, non-limiting gear is available to shift. In a seventh example, the method may further include avoiding over-revving an engine by upshifting based on the shift schedule.

[0009] In an eighth non-limiting example of this embodiment, the method includes maintaining the transmission in a non-limiting gear after the shifting step until communication is restored. In a ninth example, the method may include detecting that communication between the transmission controller and the other controller via the communication link has been restored; and resuming normal operation of the transmission.

[0010] In another example of this embodiment, the method includes shifting from second gear to first gear once normal operation has resumed. In yet another example, the method may include: detecting, by the transmission controller, a timeout condition upon receiving a message over the communication link from the other controller; implementing a counter upon detecting the timeout condition; and triggering a diagnostic code if a number of samples detected via the implementing step exceeds a sampling threshold.

[0011] In another non-limiting example, the method may include activating an algorithm to perform the determining step, the commanding step, and the switching step if the number of samples exceeds the sampling threshold. In another example, the method may include, after the detecting step, determining whether a lock-up clutch of the transmission is engaged. Furthermore, the method may include: shifting out of first gear if the lock-up clutch is not engaged; and shifting the transmission into first gear or one of the plurality of gears if the lock-up clutch is engaged.

[0012] In another embodiment of the present disclosure, a method for controlling a multi-speed transmission of a vehicle having an engine comprises: providing the transmission with a transmission controller for controlling the transmission, a lock-up clutch, and a plurality of shiftable gears, each of the plurality of shiftable gears including a torque limit; defining each of the plurality of shiftable gears as either a limiting gear or a non-limiting gear based on its respective torque limit, each limiting gear having a lower torque limit than the non-limiting gears; operating the transmission according to a shift schedule in a first of the plurality of gears, the first gear being defined as the limiting gear; detecting a loss of communication via a communication link between the transmission controller and another controller;Determining whether the lock-up clutch is engaged or disengaged; commanding a shift from first gear to a second gear by the transmission controller, wherein the second gear is defined as a non-limiting gear; and controlling the transmission by the transmission controller to shift from first gear to second gear.

[0013] In one example of this embodiment, the method may include the transmission controller preventing a shift from one of the non-limiting gears to one of the limiting gears until communication is restored. In another example, the method may include determining if there is a lower, non-limiting gear to downshift the transmission; and upshifting from first gear to a higher, non-limiting gear if there is no lower, non-limiting gear. In another example, the method may include upshifting or downshifting from first gear to a non-limiting gear based on the shift schedule if a lower, non-limiting gear is available to downshift to.

[0014] In another embodiment of the present disclosure, a multi-speed transmission comprises a transmission having an input and an output, the input configured to be operatively coupled to an engine; a plurality of shiftable gears of the transmission, each of the plurality of shiftable gears including its own torque limit; and a transmission controller comprising a memory unit and a processor, the memory unit storing a shift map for operatively controlling the transmission; wherein each of the plurality of shiftable gears is defined as either a limiting gear or a non-limiting gear based on its torque limit, the torque limit of the limiting gear being less than the torque limit of the non-limiting gear;wherein the transmission controller is configured to be in electrical communication with an engine controller via a communication link; further wherein a set of instructions is executable by the processor of the transmission controller to detect a loss of communication with the engine controller via the communication link; determine whether a current operative gear of the transmission is a limiting gear; command a shift from the current operative gear to a non-limiting gear; and operatively shift the transmission from the current operative gear to the non-limiting gear. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The above-mentioned aspects of the present disclosure and the manner of obtaining them will become clearer, and the disclosure itself will be better understood, by reference to the following description of embodiments of the disclosure taken in conjunction with the accompanying drawings. In the drawings: Fig. 1 is a block diagram and schematic view of an illustrative embodiment of a powered vehicle system; Fig. 2 is a flowchart of a first method for controlling transmission gear in response to a loss of communication with an engine; and Fig. 3 is a flowchart of a second method for controlling transmission gear in response to a loss of communication with an engine.

[0016] Corresponding reference numbers are used to identify corresponding parts throughout the various views. DETAILED DESCRIPTION

[0017] The embodiments of the present disclosure described below are not intended to be exhaustive or to limit the disclosure to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art can understand and appreciate the principles and practices of the present disclosure.

[0018] The terminology used herein is for the purpose of describing particular illustrative embodiments only and is not intended to be limiting. As used herein, the singular forms "a," "an," and "the" include the plural forms unless the context clearly indicates otherwise. Likewise, plural forms may be used to describe particular illustrative embodiments when singular forms would also be applicable. The terms "comprises," "comprising," "including," and "having" are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.The procedural steps, processes, and operations described herein should not be construed as requiring their performance in the order discussed or illustrated unless specifically identified as such. It should also be understood that additional or alternative steps may be used.

[0019] If you now turn Fig. 1, there is shown a block diagram and schematic view of an illustrative embodiment of a vehicle system 100 having a drive unit 102 and a transmission 118. In the illustrated embodiment, the drive unit 102 may include an internal combustion engine, a diesel engine, an electric motor, or other power-producing device. The drive unit 102 is configured to rotatably drive an output shaft 104 that is coupled to an input or pump shaft 106 of a conventional torque converter 108. The input or pump shaft 106 is coupled to an impeller or pump 110 that is rotatably driven by the output shaft 104 of the drive unit 102. The torque converter 108 further includes a turbine 112 coupled to a turbine shaft 114, and the turbine shaft 114 is coupled to or integral with a rotatable input shaft 124 of the transmission 118.The transmission 118 may also include an internal pump 120 for building pressure in various flow circuits (e.g., main circuit, lubrication circuit, etc.) of the transmission 118. The pump 120 may be driven by a shaft 116 coupled to the output shaft 104 of the drive unit 102. In this arrangement, the drive unit 102 may deliver torque to the shaft 116 to drive the pump 120 and build pressure in the various circuits of the transmission 118.

[0020] The transmission 118 may include a planetary gear system 122 with a number of automatically selected gear ratios. An output shaft 126 of the transmission 118 is coupled or integral with and rotatably drives a propeller shaft 128, which in turn is coupled to a conventional universal joint 130. The universal joint 130 is coupled to and rotatably drives an axle 132, to which wheels 134A and 134B are mounted at each end. The output shaft 126 of the transmission 118 drives the wheels 134A and 134B in a conventional manner via the propeller shaft 128, the universal joint 130, and the axle 132.

[0021] A conventional lock-up clutch 136 is connected between the pump 110 and the turbine 112 of the torque converter 108. The operation of the torque converter 108 is conventional in that the torque converter 108 can be operated in a so-called "torque converter" mode during certain operating conditions, such as vehicle launch, low speed, and certain shift conditions. In torque converter mode, the lock-up clutch 136 is disengaged, and the pump 110 rotates at the rotational speed of the drive unit output shaft 104, while the turbine 112 is rotationally driven by the pump 110 through a fluid (not shown) located between the pump 110 and the turbine 112.In this mode, torque multiplication occurs through the fluid coupling, so that the turbine shaft 114 is subjected to a higher torque than that supplied by the drive unit 102, as is known in the art. The torque converter 108 is alternatively operable in a so-called "lock-up mode" during other operating conditions, for example, when torque multiplication is not required. In the lock-up mode, the lock-up clutch 136 is engaged, and the pump 110 is thereby directly connected to the turbine 112, so that the drive unit output shaft 104 is directly coupled to the input shaft 124 of the transmission 118, as is also known in the art.

[0022] The transmission 118 further comprises an electro-hydraulic system 138 which has a number J of fluid paths 1401-140 Jis fluidly coupled to the planetary gear system 122, where J can be any positive integer. The electro-hydraulic system 138 responds to control signals to selectively cause fluid to flow through one or more of the fluid paths 1401-140 Jflows to thereby control the operation, ie, the engagement and disengagement, of a plurality of corresponding friction devices in planetary gear system 122. The plurality of friction devices may include, but are not limited to, one or more conventional braking devices, one or more torque-transmitting devices, and the like. Generally, the operation, ie, the engagement and disengagement, of the plurality of friction devices is controlled by selectively controlling the friction exerted by each of the plurality of friction devices, such as by controlling the fluid pressure at each of the friction devices.In one embodiment, which is not intended to be limiting in any way, the plurality of friction devices includes a plurality of braking and torque-transmitting devices in the form of conventional clutches, each of which can be controllably engaged and disengaged via the fluid pressure supplied by the electro-hydraulic system 138. In any event, shifting or changing between the various gears of the transmission 118 is accomplished in a conventional manner by selectively controlling the plurality of friction devices via controlling the fluid pressure within the number of fluid paths 1401-140. J reached.

[0023] The system 100 further includes a transmission control circuit 142, which may include a memory unit 144. The transmission control circuit 142 is illustrated as microprocessor-based, and the memory unit 144 generally contains instructions stored therein that are executable by a processor of the transmission control circuit 142 to control the operation of the torque converter 108 and the operation of the transmission 118, i.e., switching between the various gear ratios of the planetary gear system 122. However, it should be understood that this disclosure contemplates other embodiments in which the transmission control circuit 142 is not microprocessor-based, but is configured to control the operation of the torque converter 108 and / or the transmission 118 based on one or more sets of hard-wired instructions and / or software instructions stored in the memory unit 144.

[0024] In the Fig. 1, the torque converter 108 and the transmission 118 include a number of sensors configured to generate sensor signals indicative of one or more operating conditions of the torque converter 108 and the transmission 118, respectively. For example, the torque converter 108 is shown including a conventional speed sensor 146 positioned and configured to generate a speed signal corresponding to the rotational speed of the pump shaft 106, which corresponds to the rotational speed of the output shaft 104 of the drive unit 102. The speed sensor 146 is electrically connected to a pump speed input PS of the transmission control circuit 142 via a signal path 152, and the transmission control circuit 142 may process the speed signal generated by the speed sensor 146 in a conventional manner to determine the speed of the pump shaft 106 / drive unit output shaft 104.

[0025] The transmission 118 is shown to include another conventional speed sensor 148 positioned and configured to generate a speed signal corresponding to the rotational speed of the transmission input shaft 124, which is equal to the rotational speed of the turbine shaft 114. The input shaft 124 of the transmission 118 is directly coupled to or integral with the turbine shaft 114, and the speed sensor 148 may alternatively be positioned and configured to generate a speed signal corresponding to the rotational speed of the turbine shaft 114. In any event, the speed sensor 148 is electrically connected to a transmission input shaft speed input TIS of the transmission control circuit 142 via a signal path 154, and the transmission control circuit 142 may process the speed signal generated by the speed sensor 148 in a conventional manner to determine the rotational speed of the turbine shaft 114 / transmission input shaft 124.

[0026] The transmission 118 further includes another speed sensor 150 arranged and configured to generate a speed signal corresponding to the rotational speed and direction of the output shaft 126 of the transmission 118. The speed sensor 150 may be of a conventional type and is electrically connected to a transmission output shaft speed input TOS of the transmission control circuit 142 via a signal path 156. The transmission control circuit 142 is configured to process the speed signal generated by the speed sensor 150 in a conventional manner to determine the rotational speed of the transmission output shaft 126.

[0027] In the illustrated embodiment, the transmission 118 further includes one or more actuators configured to control various operations within the transmission 118. The electro-hydraulic system 138 described herein is shown to include, for example, a number of actuators, e.g., conventional solenoids or other conventional actuators, connected via a corresponding number J of signal paths 721-72 J electrically with a number J of control outputs CP1 - CP J the transmission control circuit 142, where J can be any positive integer, as described above. The actuators within the electro-hydraulic system 138 each respond to a corresponding one of the control signals CP1 - CP J , which are transmitted by the transmission control circuit 142 on one of the corresponding signal paths 721 - 72 Jgenerated to control the friction exerted by each of the plurality of friction devices by controlling the pressure of a fluid in one or more corresponding fluid passages 1401 - 140 J and thus control the operation, ie the engagement and disengagement, of one or more corresponding friction devices based on information provided by the various speed sensors 146, 148 and / or 150.

[0028] The friction devices of the planetary gear system 122 are shown controlled by a hydraulic fluid that is distributed by the electro-hydraulic system 138 in a conventional manner. The electro-hydraulic system 138 is shown to include, for example, a conventional hydraulic positive displacement pump 120 that distributes fluid to the one or more friction devices via the control of the one or more actuators within the electro-hydraulic system 138. In this embodiment, the control signals CP1 - CP Jare illustrated as analog friction device pressure commands to which the one or more actuators respond to control the hydraulic pressure to the one or more friction devices. However, it should be understood that the friction exerted by each of the plurality of friction devices may alternatively be controlled according to other conventional friction device control structures and techniques, and such other conventional friction device control structures and techniques are contemplated by this disclosure. In any event, however, the analog operation of each of the friction devices is controlled by the control circuit 142 in accordance with instructions stored in the memory unit 144.

[0029] In the illustrated embodiment, the system 100 further includes a drive unit control circuit 160 having an input / output (I / O) port electrically coupled to the drive unit 102 via a number K of signal paths 162, where K can be any positive integer. The drive unit control circuit 160 can be conventional and is capable of controlling and managing the overall operation of the drive unit 102. The drive unit control circuit 160 further includes a communication port COM electrically connected to a similar communication port COM of the transmission control circuit 142 via a number L of signal paths 164, where L can be any positive integer. The one or more signal paths 164 are typically collectively referred to as a data link.In general, the powertrain control circuit 160 and the transmission control circuit 142 are capable of exchanging information over the one or more signal paths 164 in a conventional manner. For example, in one embodiment, the powertrain control circuit 160 and the transmission control circuit 142 are operable to exchange information over the one or more signal paths 164 in the form of one or more messages according to a Society of Automotive Engineers (SAE) J-1939 communication protocol, although this disclosure also contemplates other embodiments in which the powertrain control circuit 160 and the transmission control circuit 142 are operable to exchange information over the one or more signal paths 164 according to one or more other conventional communication protocols (e.g.,from a conventional data bus such as a J1587 data bus, J1939 data bus, IESCAN data bus, GMLAN, Mercedes PT-CAN).

[0030] In many conventional control systems, a transmission control circuit 142 (i.e., the transmission controller) can communicate with the powertrain control circuit 160 (often referred to as the engine controller) and send default torque limits for the engine controller to remember in the event of a loss of communication. For example, in the event of a stall condition, the transmission controller can send a torque limit to the engine controller to control the output torque. However, if the communication link fails, the transmission controller can no longer send these messages.

[0031] At least in some transmissions, each gear has the same turbine torque limit. In other words, due to the architecture of the transmission and the hardware that comprise it, the transmission control unit can pass a single torque limit to the engine in the event of a loss of communication between them. In some cases, the engine control unit can be programmed to automatically reduce engine torque in the event of a loss of communication with the transmission control unit.

[0032] However, in at least one case, a transmission may be designed such that not every gear is designed to have the same turbine torque limit. In this case, at least one gear may have a turbine torque limit that is lower than the other gears. This may be due to hardware limitations and the like. In any case, the transmission controller communicates the turbine torque limit of each gear to the engine controller, but not all engines may be able to integrate with the transmission controller to support the lower turbine torque limit. In this case, a problem may arise if the transmission is in a particular gear that requires a lower turbine torque and the engine is unable to meet that requirement.Therefore, it is desirable to avoid these aforementioned cases and instead to be able to control the effects on the transmission without resorting to communication between the transmission and engine control units.

[0033] Referring to Fig. 2, several blocks or steps are provided for the execution of a control process or method 200 by the transmission controller to control gear shifting in the event of a loss of communication over the data link. Data link communication may be interrupted or lost due to several problems. For example, if the wires between the transmission controller and the engine controller malfunction, are cut, or there is another wiring problem, communication may be lost. Additionally, communication may be compromised if, for example, water enters a connector and shorts the connection. Furthermore, one of the controllers may become damaged or malfunction, causing it to send incorrect messages over the data link, and then it may be determined that communication has been lost.This can primarily affect the transmission and engine controls, but other controls that communicate via the data link can also be affected by a loss of communication.

[0034] In method 200, the controller (i.e., transmission control circuit 142) may execute a first block 202 in which it determines a loss of communication with the engine controller (i.e., powertrain control circuit 160). The manner in which this block is executed may depend on the type of messages being sent or received. For example, if a message is indeterminate, the transmission controller may determine that communication has been lost.

[0035] In another example, the transmission controller may attempt to receive one or more messages over the data connection. If the controller detects a timeout condition for a particular message it is attempting to receive, the controller may implement an error counter. If a certain number of samples (e.g., 500 samples) out of a threshold number of samples (e.g., 600 samples) fail, a diagnostic may be triggered.

[0036] In another example, an additional intermittent diagnostic check may be implemented where, if a number of samples (e.g., 15 samples) out of a threshold number of samples (e.g., 600 samples) fail, an intermittent error counter is incremented. If the counter exceeds a further threshold number (e.g., 18 counts) in a key cycle, an intermittent error may be set.

[0037] Each of the above examples is not intended to be limiting, but rather presents different ways a transmission control system can detect whether communication has been lost. Other conventional methods may also be used.

[0038] If the loss of communication is detected by the controller in block 202, a controller-executable algorithm may be activated or triggered to control the transmission gear. The algorithm may be activated to allow the transmission controller to monitor the gear the transmission is currently operating in and to limit or prevent the transmission from shifting to one or more gears. To do so, the transmission controller may execute a first block 204 in which it is determined whether the lock-up clutch 136 is engaged. The lock-up clutch 136 may only be engaged in a certain number of gears. In any case, if the lock-up clutch 136 is determined to be engaged, the process 200 may proceed to block 206, where the controller performs no immediate action.

[0039] Additionally, after block 206, process 200 may proceed to block 220. At this time, if lock-up clutch 136 is engaged, the controller may be programmed to use one or more gears.

[0040] If the lock-up clutch is not engaged, the process 200 may proceed from block 204 to block 208. In block 208, the controller may detect whether the vehicle is moving or stationary, and if moving, the controller may detect which gear the transmission is currently operating in. The algorithm may define one or more gears as operable gears and one or more gears as limiting gears. In one example, the transmission may include nine or more forward gears, and only first and third gears are predefined as limiting gears. The other seven forward gears may be predefined as operable gears. In block 208, the controller determines whether the transmission is currently in an operable gear or a limiting gear. If the transmission is determined to be operating in an operable gear and not a limiting gear in block 208, the process 200 may proceed to block 210.On the other hand, if the transmission is operating in a limiting gear, process 200 proceeds to block 212.

[0041] In block 210, the transmission controller has determined that the transmission is not currently operating in a limiting gear and thus is not operating in a gear requiring lower turbine torque. As such, the transmission controller may continue to allow the transmission to operate in its current gear without taking any action.

[0042] If it is determined in block 210 that the transmission is operating in a limiting gear, then the transmission controller executes block 212 by determining if there is a lower gear to which the transmission can be shifted. In the above example, if the transmission is operating in third gear and it is possible to downshift to second gear, which is an operable gear, then the process 200 proceeds to block 214. However, if it is determined in block 212 that there is no lower gear to which to shift, then the process 200 proceeds to block 216, where the controller commands an upshift to the next available gear. For example, if the transmission is operating in first gear, the transmission controller may command an upshift to second gear, which in this example is not a limiting gear.

[0043] If the transmission is operating in a limiting gear and a lower gear is available to shift to that is not another limiting gear, the transmission controller may command a downshift or an upshift in block 214 based on a shift map stored in the controller's memory unit. For example, the controller may determine whether a downshift will result in engine overspeed. An overspeed threshold may, for example, be stored in the controller or communicated to the controller in software, an algorithm, or the like. In addition, the controller may prevent an upshift if doing so would cause the engine speed to fall below a minimum threshold for a particular gear. Thus, whether the transmission controller decides whether to upshift or downshift may depend on the engine speed and the output speed.

[0044] Once the transmission is operating in an operative gear and not in a limiting gear, the controller can control gear shifts to avoid the limiting gear(s). To do this, the controller can initiate an upshift or downshift that skips all limiting gears. So, in the previous example, if the vehicle is traveling in second gear and the operator wishes to upshift, the transmission controller can command a shift from second to fourth gear to avoid the limiting gear of third gear. Similarly, if the vehicle is traveling in fourth gear and the operator wishes to downshift, the transmission controller can operatively command the transmission to skip third gear and shift into second gear.

[0045] Although first and third gears are described as limiting gears in this example, it is understood throughout this disclosure that any gear or gears may be a limiting gear. For the purposes of this disclosure, a limiting gear may be defined as a gear that has a lower torque capacity or torque rating compared to the other gears. As noted above, the lower torque capacity or torque rating may be due to hardware limitations related to the transmission in the particular limiting gear. In some cases, the torque capacity of a limiting gear may be one or two times lower than the torque capacity of the operational gears. Additionally, the transmission controller may be programmed with limiting gears. This may be done at the factory or after it leaves the factory.

[0046] In another embodiment, the transmission control may simply lock the transmission to an operational gear and not allow it to shift to another gear. In other words, the transmission control may not perform jump shifts or the like to avoid limiting gears. However, this is less desirable than the control logic of Fig. 2.

[0047] Another embodiment may include requesting the engine controller to reduce the engine torque to a value below the torque limits in a particular gear. This is, of course, not as desirable as the process 200 of Fig. 2, since a lack of communication between the transmission control and the engine control via the data connection makes the implementation of this embodiment difficult.

[0048] If you turn Fig. 3, another embodiment of a control method or process for controlling transmission gear in the event of a loss of communication with the engine controller is illustrated. In this process 300, the transmission controller may detect whether there is a loss of communication with the engine controller at block 302. If a loss is detected at block 302, the control process 300 may proceed to block 304, where the transmission controller determines whether the transmission is operating in a limiting gear or an operative gear. For the purposes of this example, it is assumed that the transmission has at least nine forward gears, with first gear and third gear being limiting gears and the other forward gears being operative gears.

[0049] In block 304, control determines the current gear based on a current gear ratio, which may be calculated in any known manner (i.e., comparing the transmission output speed to the transmission input speed). If the current gear is a limiting gear, then control process 300 proceeds to block 308. However, if the current gear is not a limiting gear but an operational gear, then control process proceeds to block 306, where no immediate action is required.

[0050] However, when the control process 300 proceeds to block 308, the transmission controller determines whether there is a lower gear to which the transmission can be shifted without shifting into a limiting gear. For example, in our present example, if the transmission is operating in third gear, the transmission controller may determine that it is safe to downshift to second gear, which is an operable gear. Thus, the controller may command a downshift to second gear. Alternatively, in block 310, the transmission controller may also determine whether it is better to upshift to another operable gear, i.e., fourth gear in this example. In the previous embodiment of Fig.2, a list of criteria, including engine speed and output speed, may be used in conjunction with a shift schedule to guide control in deciding whether to upshift or downshift. Once the transmission has upshifted or downshifted in block 310, process 300 proceeds to block 314, where the transmission may operate in a non-limiting gear.

[0051] If it is determined at block 308 that the transmission cannot be downshifted to an inoperative gear, the process 300 proceeds to block 312, where the transmission controller commands an upshift from a limiting gear to a non-limiting gear. For example, if the transmission is operating in first gear, which is a limiting gear, then the controller may command an upshift to second gear. The upshift command may be communicated at block 312, causing the transmission to operate in a non-limiting gear at block 314.

[0052] At block 316, the transmission controller may lock or prevent the transmission from shifting to a limiting gear while communication is lost. The controller may initiate jump shifts and the like to prevent a shift to a limiting gear. Alternatively, the controller may lock the transmission to a non-limiting gear and prevent further shifts until communication is restored.

[0053] It is worth noting that control processes 200, 300, which are executed during a loss of communication between the transmission control and the engine control, differ from fail-safe or limp-home modes, which involve a complete loss of electrical power. In the latter case, a complete loss of electrical power results in the transmission control no longer being able to energize any solenoids, and the entire electrical control system is deactivated. When designing control systems for a complete power loss, the control system may include conventional normally closed or normally open solenoids that specify predefined default gears to which the transmission shifts in the event of a power loss. These predefined default gears allow the transmission to continue operating in an limp-home or fail-safe mode.

[0054] However, in the present disclosure, the electrical power is not completely lost. Instead, the data link communication between the transmission controller and the engine controller is interrupted or disabled, but other components on the J-1939 link can still communicate with each other. Furthermore, the transmission controller can still turn solenoids on and off to cause the transmission to shift to a desired gear. In other words, the transmission controller can still operationally control the transmission to shift into different gears even if there is a loss of communication over the data link, but communication between the transmission controller and the engine controller is interrupted.

[0055] If communication is restored or regained while control process 200 or 300 is executing, the respective control process may be exited. The transmission control logic may determine whether a shift out of a limiting gear was a result of the loss of communication. Once communication is restored, the transmission control may shift back to the limiting gear.

[0056] Alternatively, the transmission control may consider the shift map and determine whether the transmission should remain in its current gear or shift to another gear once communication is restored. For example, if the shift lines in the shift map dictate shifting from fourth gear to third gear, the control may follow the shift map's dictate. Additionally, normal control logic based on shift speeds and the like may determine whether to downshift to a limiting gear. Other control logic may consider engine torque, other algorithms, the most effective transmission mode, etc., when determining which gear the transmission should operate in once communication is restored.

[0057] In most cases, once communication is restored and the algorithm is exited, the transmission control can return to normal operation and control the transmission shift based on a current shift schedule.

[0058] Although exemplary embodiments incorporating the principles of the present disclosure have been disclosed herein, the present disclosure is not limited to the disclosed embodiments. Instead, this application is intended to cover all variations, applications, or adaptations of the disclosure using its general principles. Furthermore, this application is intended to cover such departures from the present disclosure as are known or customary in the technical field to which this disclosure relates and which fall within the scope of the appended claims.

Claims

[1] A method for controlling a multi-speed transmission, comprising: Providing a transmission controller, a plurality of gears of the transmission, at least one of the plurality of gears being defined as a limiting gear, and a communication link, each of the plurality of shiftable gears including a torque limit; defining each gear of the plurality of shiftable gears as either a limiting gear or a non-limiting gear based on its respective torque limit, wherein each limiting gear has a lower torque limit than one or more non-limiting gears; Operating the transmission in a first gear of the plurality of gears; Detecting a loss of communication via the communication link between the transmission control and another control; Determine whether the first gear is a limiting gear; Commanding a shift from the first gear to a second gear of the plurality of gears by the transmission control when the first gear is a limiting gear and the second gear is a non-limiting gear; and Shifting the transmission from first gear to second gear. [2] The method of claim 1, further comprising preventing, by the transmission controller, a shift from any one of the plurality of gears not defined as a limiting gear to the at least one of the plurality of gears defined as a limiting gear. [3] The method of claim 1, further comprising maintaining the transmission in first gear when the first gear is not a limiting gear. [4] The method of claim 1, further comprising performing a jump shift by shifting from second gear to a third gear, the first gear being intermediate between the second and third gears. [5] The method of claim 1, further comprising determining whether there is a lower gear to which a downshift may be made that is not a limiting gear. [6] The method of claim 5, further comprising upshifting to a higher non-limiting gear when the first gear is a limiting gear and there is no lower non-limiting gear. [7] The method of claim 5, further comprising upshifting or downshifting from first gear to a non-limiting gear based on a shift schedule when a lower non-limiting gear is available to shift. [8] The method of claim 7, further comprising avoiding overspeeding of an engine by upshifting based on the shift schedule. [9] The method of claim 1, further comprising maintaining the transmission in a non-limiting gear after shifting the transmission from first gear to second gear until communication is restored. [10] The method of claim 1, further comprising: Detecting that communication between the transmission controller and the other controller via the communication link has been restored; and Resumption of normal operation of the transmission. [11] The method of claim 10, wherein resuming normal operation of the transmission comprises shifting from second gear to first gear. [12] The method of claim 1, wherein detecting a loss of communication over the communication link between the transmission controller and another controller comprises: Detection of a timeout condition by the transmission controller upon receipt of a message via the communication link from the other controller; Implementing a counter upon detection of the timeout condition; and Trigger a diagnostic code when a number of samples detected by implementing a counter upon detection of the timeout condition exceeds a sample threshold. [13] The method of claim 12, further comprising activating an algorithm to perform the following when the number of samples exceeds the sampling threshold: Determine whether the first gear is a restricting gear; Commanding a shift from the first gear to a second gear of the plurality of gears by the transmission control; and Shifting the transmission from first gear to second gear. [14] The method of claim 1, further comprising, after detecting a loss of communication over the communication link between the transmission controller and another controller, determining whether a lock-up clutch of the transmission is engaged. [15] The method of claim 14, further comprising: Shifting out of first gear when the lock-up clutch is not engaged; and Engaging the transmission into first gear or one of a plurality of gears when the lock-up clutch is engaged. [16] A method for controlling a multi-speed transmission of a vehicle having an engine, comprising: Providing the transmission with a transmission controller for controlling the transmission, a lock-up clutch, and a plurality of shiftable gears, each of the plurality of shiftable gears including a torque limit; defining each gear of the plurality of shiftable gears as either a limiting gear or a non-limiting gear based on its respective torque limit, wherein each limiting gear has a lower torque limit than one or more non-limiting gears; Operating the transmission according to a shift schedule in a first gear of the plurality of shiftable gears, the first gear being defined as the limiting gear; Detecting a loss of communication via a communication link between the transmission controller and another controller; Determine whether the lock-up clutch is engaged or disengaged; Commanding a shift from first gear to a second gear by the transmission control, wherein the second gear is defined as a non-limiting gear; and Controlling the transmission through the transmission control to shift from first gear to second gear. [17] The method of claim 16, further comprising preventing the transmission controller from shifting from one of the non-limiting gears to one of the limiting gears until communication is restored. [18] The method of claim 16, further comprising: Determine whether there is a lower, non-limiting gear to downshift the transmission; and Upshifting to a higher, non-limiting gear from first gear when there is no lower, non-limiting gear. [19] The method of claim 18, further comprising upshifting or downshifting from first gear to a non-limiting gear based on the shift schedule when a lower non-limiting gear is available for downshifting. [20] Multi-speed gearbox, comprising: a transmission having an input and an output, the input configured to be operatively coupled to an engine; a plurality of shiftable gears of the transmission, each of the plurality of shiftable gears including its own torque limit; and a transmission control comprising a memory unit and a processor, the memory unit storing a shift map for operational control of the transmission; wherein each of the plurality of shiftable gears is defined as either a limiting gear or a non-limiting gear based on its torque limit, wherein the torque limit of each limiting gear is less than the torque limit of one or more non-limiting gears; wherein the transmission controller is configured to be in electrical communication with an engine controller via a communication link; further comprising a set of instructions executable by the transmission control processor to: detect a loss of communication with the engine control unit via the communication link; to determine whether a currently operable gear of the transmission is a limiting gear; to command a shift from the current operational gear to a non-limiting gear; and to operatively switch the transmission from the current operational gear to the non-limiting gear.

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