System and method for controlling a motor during clutch shifting in a multi-speed electric drivetrain

Abstract

A system and method (300) for controlling a motor (110) of an electric drivetrain (105) having a multi-speed transmission (115) with at least a first clutch (130) and a second clutch (135), the system and method (300) including initiating a transmission shift requiring engagement of the first clutch (130), applying a synchronous torque command (250) to the motor (110) based on engagement parameters of the first clutch (130) until the shift is complete, and applying a non-shifting torque command (250) to the motor (110) after the shift is complete.

Description

[Technical Field]

[0001] The present disclosure relates generally to systems and methods for controlling a motor in a multi-speed electric drivetrain, and more particularly to systems and methods for generating and applying a synchronous torque command to a motor during clutch shifting in such a multi-speed electric drivetrain. [Background technology]

[0002] The use of electric drivetrains in mobile industrial machinery, such as wheel loaders and motor graders, is increasing due, at least in part, to the reduced drivetrain complexity and the relatively large gear ratio step sizes and improved controllability of electric traction motors compared to internal combustion engines. Thus, such electric drivetrains can offer relatively simple designs with relatively large torque output and controllability. However, during gear shifts in an electric drivetrain's multi-speed transmission, clutch operation and control can be challenging due to the large inertia created by the electric drivetrain's traction motor. While friction clutch elements can be used to absorb some of the high level of inertia of the electric motor during gear shifts, the clutch elements are subject to operational constraints. For example, friction clutch elements and their surrounding components can experience detrimental temperature increases and increased wear when attempting to accelerate or decelerate the traction motor during shifts.

[0003] U.S. Patent No. 8,145,397 (the '397 patent) discusses a hybrid powertrain system with a transmission having four selectively engageable clutches controlled by a hydraulic control circuit. Controlling and managing the transmission's output torque involves outputting a motor torque command to two electric machines in the hybrid powertrain system to deliver a net output torque to the transmission's output members that reacts with the driveline and satisfies the operator's torque demand. To provide driveline damping, the torque offset of the two electric machines can be determined by monitoring the input speed to the transmission and the clutch slip speed, and more specifically, can be based on the difference between the input speed error (the difference between the input speed and the input speed profile) and the clutch slip speed error (the difference between the clutch slip speed and the target clutch slip speed). The target clutch slip speed and the clutch slip profile are used during transitions through the transmission's operating range to synchronize the clutch slip speed before applying the starting clutch. Thus, the system of the '397 patent calculates a motor torque command based on the clutch speed and the slip profile.

[0004] However, there is a need for improved control of multi-speed transmissions in electric drivetrains, particularly with respect to dissipating high levels of motor inertia during gear shifting. The systems and methods of the present disclosure may address or solve one or more of the problems set forth above and / or solve other problems in the art. However, the scope of the present disclosure is defined by the appended claims, not by the ability to solve any particular problem. Summary of the Invention

[0005] In one aspect, a method of controlling a motor of an electric drivetrain having a multi-speed transmission having at least a first clutch and a second clutch is provided, the method including initiating a transmission shift requiring engagement of a first clutch, applying a synchronous torque command to the motor based on an engagement parameter of the first clutch until the shift is complete, and applying a non-shifting torque command to the motor after the shift is complete.

[0006] According to another aspect of the present disclosure, a method of controlling a mobile industrial machine with an electric drivetrain including a traction motor and a multi-speed transmission having at least a first clutch and a second clutch is provided, the method including initiating a transmission shift requiring engagement of a first clutch, applying a motor torque command to a maximum available motor torque during partial engagement of the first clutch, and applying a non-shift torque command to the motor after the shift is completed.

[0007] According to yet another aspect of the present disclosure, a system for controlling a motor of an electric drivetrain having a multi-speed transmission is disclosed. The system includes an electric drivetrain with a multi-speed transmission having at least a first clutch and a second clutch. The system further includes a motor and a motor controller. The motor controller is configured to perform operations including applying a synchronizing torque command to the motor based on an engagement parameter of the first clutch during engagement of the first clutch, and applying a non-shifting torque command to the motor after a shift is completed. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 shows a schematic diagram of a wheel loader as an example of a machine including a multi-speed electric drive train and motor controller with which systems and methods according to the present disclosure can be used. [Figure 2]Figure 2 shows a schematic diagram of a motor controller that can be installed in the wheel loader shown in Figure 1. This controller can be used to store and execute instructions for the methods according to the present disclosure. [Figure 3] FIG. 3 is a flow chart illustrating a method of controlling a motor in an electric drive train of a machine such as the wheel loader shown in FIG. 1 in accordance with the present disclosure. [Figure 4] FIG. 4 is a flow chart illustrating additional steps of the method shown in FIG. 3 according to the present disclosure. [Figure 5] FIG. 5 provides a motor torque command and transmission relative speed chart to illustrate the method of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0009] Both the foregoing general description and the following detailed description are exemplary and explanatory only and do not limit the claimed features. As used herein, "comprises," "comprising," "having," "including," or other variations thereof are intended to cover a non-exclusive inclusion, whereby a process, method, article, or apparatus comprising a list of elements does not include merely those elements, but may include other elements not expressly listed or inherent in such process, method, article, or apparatus. Unless expressly excluded, the use of the singular to describe an element, structure, or operation does not exclude the use of a plurality of such elements, structures, or operations, or equivalents thereof. Use of the terms "a," "an," "the," and "at least one," or "one or more," and similar reference words in the context of describing the invention (particularly in the context of the claims below) should be construed to cover both the singular and the plural unless otherwise indicated herein or clearly contradicted by context. The term "at least one" followed by a list of one or more items (e.g., "at least one of A and B," or "one or more of A and B") shall be construed to mean one item selected from the listed items (A or B), or any combination of two or more of the listed items (A and B; A, A and B; A, B and B), unless otherwise indicated herein or clearly contradicted by context. Similarly, as used herein, the term "or" refers to any possible permutation of a set of items. Furthermore, in this disclosure, relative terms such as "about," "approximately," "substantially," and "nearly" are used to indicate a possible variation of ±10% for the stated value.

[0010] FIG. 1 shows a schematic diagram of a mobile industrial machine in the form of a wheel loader machine 100 with which the systems and methods of the present disclosure can be used. While a wheel loader machine 100 is shown, other types of mobile industrial machines, such as tractors and motor graders, can also use the systems and methods described herein. The machine 100 can be an all-electric drive machine (powered solely by one or more traction motors) or a hybrid-electric machine. The machine 100 can include an electric drive train 105, which includes an electric traction motor 110, a multi-speed transmission 115, ground-engaging elements such as wheels 120, and a drivetrain control system 200. While the electric drive train 105 of the machine 100 is shown with a single electric traction motor 110 and associated multi-speed transmission 115, it is understood that more electric motors and multi-speed transmissions can be used, such as one traction motor and transmission for each wheel 120. As described in more detail below, drivetrain control system 200 may receive various inputs and provide various outputs to electric drivetrain to power machine 100 .

[0011] Electric traction motor 110 is any suitable type of electric motor designed to provide power in the form of torque to the input of multi-speed transmission 115. Electric motor 110 may be powered by a suitable energy source (not shown), such as one or more onboard batteries, a power grid, an onboard engine-driven generator, or a fuel cell. Electric traction motor 110 may have motor capacity limits, including torque and speed limits, defined by continuous, intermittent, and / or peak curves in one or more look-up tables corresponding to the particular electric motor in electric drivetrain system 105.

[0012] The multi-speed transmission 115 can receive input torque from the motor 110 and provide output torque to one or more wheels 120 of the machine 100. The multi-speed transmission can be, for example, a two-speed transmission with appropriate gears (not shown) in a gearbox 140 and two hydraulic clutches 130, 135. The hydraulic clutch 130 can be connected to a pressurized fluid, such as the hydraulic system 140 of the machine 100. While a two-speed transmission is described herein, it is understood that a transmission with more speeds, such as a three- or four-speed transmission, can also be used. Each of the two clutches 130, 135 can be controlled to move between a fully engaged or "on" state, a partially engaged state, and a disengaged or "off" state. In the fully engaged state, the clutch plates of each of the clutches 130, 135 are in mating contact, transmitting all torque from the electric traction motor 110 through the multi-speed transmission 115. In a disengaged or "off" state, the respective clutch plates are separated from one another and that particular clutch does not transmit torque from the electric traction motor 110 through the multi-speed transmission 115. Each clutch 130, 135 is configured to engage for a particular speed range of the motor 110. Additionally, each clutch 130, 135 operates within operating parameters, such as operating temperature limits and operating pressure limits, which may be used to prevent the clutch 130, 135 from overheating, damaging, or malfunctioning. When one of the two or more clutches 130, 135 transitions from fully engaged to disengaged, that clutch 130, 135 is referred to as the "going clutch," and when the clutch 130, 135 transitions from fully engaged to engaged, that clutch is referred to as the "starting clutch."

[0013] 1 and 2, drivetrain control system 200 may include a controller 205 that receives various inputs 210 from and provides various outputs 215 to electric drivetrain 105. For example, controller 205 may receive a desired torque request signal 220 from an operator at operator station 150. This desired torque request signal 220 corresponds to a motive request from the operator, also known as a non-shifting torque request. Controller 205 of drivetrain control system 200 may also receive a transmission input speed signal 230 and a transmission output speed signal 235 that correspond to the speeds of the input and output shafts, respectively, of multi-speed transmission 115. Transmission input speed signal 230 and transmission output speed signal 235 may be provided by suitable real or virtual sensors, such as speed sensors 155 and 160, respectively (FIG. 1).

[0014] Drivetrain control system 200 may provide output from controller 205 in the form of a motor torque command 250 that controls the torque output from electric motor 110. Motor torque command 250 may include a non-shifting motor torque command when no gear shift is required, and may include a synchronous motor torque command during a shift, as described below. Additionally, controller 205 may provide clutch control commands 255 to control one or both clutches 130, 135, as is known in the art.

[0015] The controller 205 may include a memory 240 and one or more processors 245. The memory 240 or secondary storage associated with the controller 205 may store data and / or software routines that may assist the controller 205 in performing its functions, such as the functions of method 300 of FIG. 3 and method 315 of FIG. 4. Additionally, the memory or secondary storage associated with the controller 205 may also store data received from various inputs 210 associated with the electric drivetrain 105. Many commercially available microprocessors may be configured to perform the functions of the controller 205. Of course, the controller 205 could readily embody a general machine controller capable of controlling numerous other machine functions. Alternatively, a dedicated machine controller could be provided. Various other known circuits may be associated with the controller 205, including signal conditioning circuits, communication circuits, hydraulic or other actuation circuits, and other suitable circuits. [Industrial Applicability]

[0016] The systems and methods of the present disclosure are applicable to an electric drivetrain 105 that includes a multi-speed transmission 115. In particular, the present disclosure is applicable to controlling the traction motors 110 of the electric drivetrain 105 to assist in gear changes in the multi-speed transmission 115 and help prevent harmful overheating and wear on the components of the multi-speed transmission 115.

[0017] During operation of machine 100, multi-speed transmission 115 receives gear shift instructions based on desired drive torque request signal 220 from an operator of machine 100, for example, at operator station 150. The gear shift instructions may be determined automatically, as in the case of an automatic transmission, or manually by the operator of machine 100. The gear shift instructions may include an upshift of multi-speed transmission 115 or a downshift of multi-speed transmission 115. Control of electric traction motor 110 may be based on the gear shift instructions, as described below.

[0018] FIG. 3 is a flowchart illustrating a method for controlling a motor of an electric drivetrain 105 including a multi-speed transmission 115 having at least a first clutch 130 and a second clutch 135. The method may include step 305 of applying a standard motor torque (or non-shifting motor torque command) 250 during operation of the multi-speed transmission 115 when the multi-speed transmission 115 is in a particular gear corresponding to a fully engaged or disengaged clutch 130, 135. The method may also include step 310 of initiating a gear shift. As described above, initiating a gear shift may be automatic or manual. The method 300 may also include step 315 of generating and applying a synchronizing shift torque command to the traction motor 110 based on operation or clutch engagement parameters of the multi-speed transmission 115 until the gear shift is completed. Step 315 of generating and applying a synchronizing torque command 250 to the motor 110 is described in more detail below with respect to FIGS. 4 and 5. Method 300 may also include step 320 of applying a standard or non-shifting motor torque command 250 to motor 110 once the gear shift is complete (corresponding to a fully engaged / disengaged clutch 130, 135), similar to step 305. Although method 300 is described as including steps 305-320, the method may include only some of these steps, such as only steps 305-315, only steps 310 and 315, only steps 310-320, or other combinations.

[0019] Steps 310 and 315 of method 300 are performed during the gear shifting process of multi-speed transmission 115 of machine 100 and are therefore integrated with the control of clutches and other components of multi-speed transmission 115 and are performed as part of other methods that may be implemented by one or more control systems of machine 100.

[0020] 4 and 5 show additional details of step 315 of generating and applying a synchronizing torque command 250 to the traction motor 110 based on operating parameters of the multi-speed transmission 115 until the gear shift is complete. In the exemplary operation shown in FIG. 5, an upshift is illustrated. It is understood that a downshift operates in the same manner, but with an opposite sign (positive versus negative) relative to the motor torque command 250. Furthermore, the example of FIG. 5 assumes that the non-shift torque command 250 applied to the motor 110 before the shift and the synchronizing shift torque command 250 applied to the motor 110 during the shift are both positive and of the same sign, as shown in FIG. 5.

[0021] As mentioned above, prior to applying the synchronous shift torque command 250 to the motor 110, a standard non-shifting torque command is applied to the motor 110 (step 305). This standard non-shifting motor torque command 250 is shown as 510 in FIG. 5. Referring again to FIG. 4, applying the synchronous shift torque command 250 to the motor 110 may include step 405 of changing the motor torque command 250 to a maximum available motor torque. The change in motor torque command 250 to the maximum available motor torque may be applied in a stepwise or ramped or linear fashion, shown in FIG. 5 as ramped / linear fashion 515. This ramping to the maximum available motor torque 515 may be characterized as a "ramp on." As mentioned above, the direction (positive or negative) of this "ramp on" depends on whether the shift is an upshift, as indicated, or a downshift (not shown).

[0022] In step 410, the motor torque command 250 is maintained at the maximum available motor torque (520 in FIG. 5) until the particular clutch 130, 135 approaches full engagement. In one example, the drivetrain control system 200 can determine when the clutch 130, 135 is approaching full engagement by monitoring the transmission input speed 230 and the transmission output speed 235 via speed sensors 155 and 160, respectively (FIG. 1). The transmission input speed 230 and the transmission output speed 235 can be used to calculate a clutch relative speed, where the clutch approaches full engagement when the clutch relative speed approaches zero. While other values ​​can be used, the controller 205 can be programmed to identify approaching full clutch engagement when the transmission input speed 230 and the transmission output speed 235 are within 10% of each other, taking ratios into account. This predetermined "approaching" full clutch engagement is shown as a vertical line / time 525 in FIG. 5. It is understood that approaching full clutch engagement may be identified by means other than clutch relative speed. Additionally, although maintenance of maximum available motor torque is depicted in Figure 5 as a straight horizontal line 520, it is understood that the maximum available torque of motor 110 may vary based on system conditions, and thus line 520 may or may not necessarily be a straight horizontal line.

[0023] Once the controller identifies that the clutch is approaching full engagement, the motor torque command is changed toward zero (step 415). Similar to step 405, the change in motor torque command 250 toward zero may be applied in a gradual or ramped manner, depicted in FIG. 5 as ramp or linear formula 530. This slope of the motor torque command 250 toward zero may be characterized as a "ramp off." This change in motor torque command 250 toward zero may continue until the clutch 130, 135 is fully engaged. For example, until the transmission relative speed reaches zero (time 535 in FIG. 5). At this point, a new standard non-shifting torque command 250 corresponding to the new gear of the multi-speed transmission 115 is applied to the motor 110. This corresponds to step 320 in FIG. 3 and is indicated by horizontal line 540 in FIG. 5. However, in some "atypical" shifts, the transmission relative speed may not be zero when motor ramp-off is complete (i.e., when the ramp-off torque command equals the appropriate torque command 250 for the new gear (line 540 in FIG. 5). In this situation, the motor torque command 250 is held stable at the torque command for the new gear 540 until full clutch engagement, e.g., when the transmission relative speed is zero. The standard non-shift torque command 250 may then vary based on the operator's desired torque or other system conditions. Additionally, if the new gear motor torque command (line 450) is negative, the torque command 250 is held stable at zero until full clutch engagement, then moves to the non-shift torque command 250.

[0024] Note that in some instances, the initial standard non-shifting torque command (510 in FIG. 5) may be of opposite sign to the maximum available torque 520. In such instances, an additional control step is included corresponding to adjusting the motor torque command to zero before ramping up to the maximum available torque. This is shown by dashed line 550 in FIG. 5. The adjustment of the motor command may be done in a step manner or a ramp manner or an alternative manner.

[0025] The drivetrain control system 200 described herein may assist in reducing high traction motor inertia loads on the clutches 130, 135 during shifting. This may help reduce high temperatures and wear on the clutches 130, 135 and associated components of the electric multi-speed transmission. The methods and operations performed by the controller 205 may also help reduce the time to dissipate traction motor inertia while changing gears. Furthermore, thanks to the clutch control provided herein, the systems and methods manage the relatively large size of electric motor inertia and, therefore, may implement clutch control in electric drivetrains 105 having multi-speed transmissions 115 to provide relatively large torque outputs by electric motors in machines such as wheel loaders and motor graders.

[0026] It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed system and method without departing from the scope of the disclosure. Other embodiments of the present system and method will become apparent to those skilled in the art from consideration of this specification and the accompanying drawings. The specification, particularly the examples described herein, should be considered exemplary only, with the true scope of the disclosure being indicated by the following claims and their equivalents.

Claims

1. 1. A method (300) for controlling a motor of an electric drivetrain (105) having a multi-speed transmission (115) having at least a first clutch (130) and a second clutch (135), the method (300) comprising: initiating a transmission shift requiring engagement of the first clutch (130); applying a synchronizing torque command (250) to the motor (110) based on engagement parameters of the first clutch (130) until the shift is completed; and applying a non-shifting torque command to the motor after the shift is completed.

2. 2. The method of claim 1, wherein applying the synchronizing torque command to the motor comprises varying a motor torque command to a maximum available motor torque during partial engagement of the first clutch.

3. 3. The method (300) of claim 2, wherein the varying the motor torque command to a maximum available motor torque is performed in a linear fashion.

4. 3. The method (300) of claim 2, wherein the motor torque command is set to zero prior to the varying the motor torque command to the maximum available motor torque.

5. 3. The method of claim 2, wherein applying the synchronizing torque command to the motor further comprises varying a motor torque command toward zero as the first clutch approaches full engagement.

6. 6. The method (300) of claim 5, wherein said varying said motor torque command toward zero is initiated at a predetermined partial engagement of said first clutch (130).

7. 7. The method (300) of claim 6, further comprising holding the synchronizing torque command steady equal to a desired non-shifting torque command until the first clutch (130) is fully engaged.

8. 10. The method of claim 1, wherein the electric drivetrain is used on an all-electric mobile industrial machine, the machine being driven solely by the motor.

9. The method (300) of claim 1, wherein the first and second clutches (130, 135) are hydraulic clutches.

10. 1. A method (300) for controlling a mobile industrial machine (100) having an electric drivetrain (105) including a traction motor (110) and a multi-speed transmission (115) having at least a first clutch (130) and a second clutch (135), the method (300) comprising: initiating a transmission shift requiring engagement of the first clutch (130); applying a motor torque command to a maximum available motor torque during partial engagement of the first clutch (130); and applying a non-shifting torque command to the motor after the shift is completed.

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