Electric drive system for machinery and electric drive control system thereof

Abstract

Electric drive system for machinery and electric drive control system thereof Operating the electric drive machine includes neutralizing a transmission of the electric drive machine for operation in a first range, determining suitability of the electric drive machine for operating the transmission in a second range, and calculating a target transmission input speed based on a speed parameter indicative of the transmission output speed and the determined suitability for operation in the second range. The speed of the electric drive motor is varied based on the target transmission input speed and the changed speed of the electric drive motor, and engaging a second clutch to operate the transmission in the second range. Related apparatus and control logic are also disclosed.

Description

[Technical Field]

[0001] The present disclosure relates generally to electric drive systems for machines, and more particularly to strategies for speed matching rotatable components within an electric drive system during clutch engagement. [Background technology]

[0002] In recent years, there has been increased engineering attention to the electrification of a wide variety of machinery. Electric passenger vehicles and the like are now in widespread use around the world. Certain types of heavy machinery, such as mining machines and passenger trains powered by electric motors, are well known and widely used. However, certain other types of equipment have been slow to adopt power strategies.

[0003] In a typical electric drive machine, a power supply, such as an electric energy storage device or generator, generates electrical power to operate one or more electric traction motors and other onboard equipment. The ground engaging members are driven by the electric traction motors to propel the machine. While electrification offers certain emission reductions, electric propulsion systems present many new challenges.

[0004] Some electric drive systems operate without a transmission, meaning that the speed and torque applied to the ground engaging members depend directly on the power output of one or more electric motors. In other systems, a transmission is coupled between the electric drive motor and the ground engaging members. Shifting gears in a transmission typically requires disengaging a clutch that transfers power from the electric motor to the ground engaging members through a first gear ratio and reengaging another clutch that transfers power to the ground engaging members through a second gear ratio. Transmissions also operate in reverse by shifting into and out of neutral and reversing the direction of rotation of the electric motor. Engineers have identified various sensitivities to the relative speeds of rotating components in electric drive systems and have also identified opportunities for improved performance. An example of a drive system for a non-electric machine that explicitly provides a target transmission-controlled engine speed is known from U.S. Pat. No. 9,855,951 (LISTER). The art leaves ample room for improvement and development of alternative methods. Summary of the Invention

[0005] In one aspect, a method for operating an electric drive machine includes disengaging a first clutch and operating a transmission of the electric drive machine coupled to an electric drive motor in a first range and neutralizing the transmission. The method further includes monitoring a speed parameter of the electric drive machine indicative of a transmission output speed and determining suitability of the electric drive machine for operating the transmission in a second range. The method further includes calculating a target transmission input speed based on the monitored speed parameter and the determined suitability of the machine for operating the transmission in the second range and varying the speed of the electric drive motor based on the target transmission input speed. The method further includes engaging the second clutch and operating the transmission in the second range based on the varied speed of the electric drive motor.

[0006] In another aspect, an electric drive system for an electric drive machine includes an electric drive motor, a transmission including a transmission input coupled to the electric drive motor, a transmission output, and first and second clutches coupled between the transmission input and the transmission output, respectively, for operating the transmission in a first range and a second range. The electric drive system further includes a control system including a sensor configured to monitor a speed parameter of the electric drive machine indicative of the transmission output speed, and an electric drive controller in communication with the sensor. The electric drive controller is configured to determine suitability of the electric drive machine for shifting the transmission from neutral to one of the first range or the second range, and to calculate a target transmission input speed based on the monitored speed parameter and the determined suitability of the electric drive machine for shifting the transmission from neutral to one of the first range or the second range. The electric drive controller is further configured to vary the speed of the electric drive motor based on the target transmission input speed, and to issue a command to engage one of the first clutch or the second clutch corresponding to one of the first range or the second range based on the varied speed of the electric drive motor.

[0007] In yet another aspect, an electric drive control system includes an electric drive controller configured to receive a first speed signal indicative of a transmission output speed of a transmission at an electric drive machine, receive a second speed signal indicative of a transmission input speed of the transmission, and determine suitability of the electric drive machine for shifting the transmission from neutral to one of a first range or a second range of transmissions. The electric drive controller is further configured to output a motor control command to vary the speed of an electric drive motor coupled to a transmission input of the transmission. The electric drive controller is further configured to calculate a transmission input speed error based on a difference between the transmission input speed and a target transmission input speed, and output a clutch engagement command to engage one of a first clutch or a second clutch corresponding to one of the first range or the second range, respectively, at a timing based on the transmission input speed error. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic side view of an electric drive machine according to one embodiment; [Figure 2] 1 is a block diagram of an electric drive system according to one embodiment. [Figure 3] 1 is a schematic diagram of an electric drive system according to one embodiment. [Figure 4] 1 is a block diagram of a logical operation according to one embodiment. [Figure 5] 1 is a flowchart illustrating an exemplary methodology and logic flow according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Referring to FIG. 1 , an electrically driven machine 10 is shown according to one embodiment. The machine 10 includes a frame 12, typically having articulated front and rear frame units (not numbered), supporting a cab 14 and a plurality of ground engaging members 16. The ground engaging members 16 are wheels in the illustrated embodiment, but could be tracks in other implementations, or the machine 10 could even have a semi-tracked configuration. The machine 10 includes a hydraulically driven implement system 18 that includes a boom and bucket (not numbered), although some embodiments could include other types of implement systems, such as a blade, or no implement system at all. While the machine 10 is shown in the context of a wheel loader, it could instead be a motor grader, truck, tractor, scraper, various other types of off-highway machines, on-highway machines, or even a marine vessel.

[0010] The machine 10 includes an electric drive system having an electric drive motor 22, a transmission 24 including a transmission input 26 coupled to the electric drive motor 22, and a transmission output 28. The transmission input 26 may include a transmission input shaft, shaft assembly, or transmission input gear, and the transmission output 28 may include a transmission output shaft, shaft assembly, or output gear, as some examples. The transmission 24 also includes a first clutch 30 and a second clutch 32 coupled between the transmission input 26 and the transmission output 28 and configured to operate the transmission 24 in a first range and a second range, respectively. The transmission 24 may include a mechanical transmission having a finite number of available gear ratios, e.g., a total of two available gear ratios. In other embodiments, a different finite number of gear ratios may be available, or possibly an infinite number of effective gear ratios may be available in a hydrostatic or hydromechanical transmission or a continuously variable mechanical transmission.

[0011] Electric drive system 20 may also include an electrical energy storage device, such as a battery, a capacitor, or a combination thereof. A low-power transmission 36 is coupled to transmission output 28 and may be configured to transmit torque to one or both of front and rear ground engaging members 16 in two-wheel or four-wheel drive applications. Power electronics 38 are coupled between electrical energy storage device 34 and electric drive motor 22. In other embodiments, electric power can be supplied to electric drive system 20 from a generator or fuel cell rather than an electrical energy storage device. Electric drive system 20 also includes an electric drive control system 40.

[0012] The control system 40 includes a sensor 42 (shown as part of the transmission 24 in FIG. 1 , by way of non-limiting example) configured to monitor a speed parameter of the electric drive machine 10 indicative of the transmission output speed, and an electric drive controller 60 in communication with the sensor 42, the electric drive controller 60 having features and functionality as discussed further herein. Referring now also to FIG. 2 , a block diagram illustrating additional features and components of the electric drive system 20 is shown. The electric energy storage device 34 is shown as a battery 34 electrically connected to a traction inverter 39 of the power electronics 38 and electrically connected to a pump inverter 46. The traction inverter 39 is electrically connected to the electric drive motor or traction motor 22, i.e., coupled to the transmission 24. As noted above, the transmission 24 may be, but is not necessarily, a two-speed transmission. The transmission 24 is, in turn, coupled to the low-power transmission 36. The pump inverter 46 is electrically connected to the pump electric motor 48, i.e., operable to rotate a pump divider or gearbox 50. The gearbox 50 is connected to the transmission oil pump 42 , an implement oil pump 54 , a steering oil pump 56 , and a brake oil pump 58 .

[0013] Turning now also to FIG. 3 , still further features of the electric drive system 30 are shown. The electric drive motor 22 includes a motor output shaft 62 that may be directly coupled to the transmission input 26 within the transmission 24. Thus, the transmission input 26 may be fixed to rotate with the motor output shaft 62, although a gearbox, lock-up clutch, or the like may be coupled between the transmission input and the motor output shaft 62 within the scope of the present disclosure. As noted above, the transmission 24 may include a mechanical transmission configured to operate in a first gear range and a second gear range, e.g., a low range and a high range. The transmission 24 also includes a first clutch 30 and a second clutch 32. A first clutch actuator 31 (C1), such as a hydraulic or electric clutch actuator, is coupled to the first clutch 30 and engages and disengages to operate the transmission 24 in the first range according to electronic control commands from the electronic drive controller 60. The second clutch actuator 33 (C2) may similarly be configured to engage and disengage the second clutch 32 to operate the transmission 24 in a second range. When both the first clutch 30 and the second clutch 32 are disengaged, the transmission 24 is in neutral. The first gear set 64 may be coupled between the first clutch 30 and the transmission output 28 and may include at least two meshed gears that rotate the output gear 68. The second gear set 66 is coupled between the transmission input 26 and the transmission output 28 and may also include at least two meshed gears that operate to rotate the output gear 68. The present disclosure is applicable regardless of the specific clutch configuration used. Accordingly, one or both of the first clutch 30 and the second clutch 32 may be either a so-called stationary (or braking) clutch or a rotating clutch.

[0014] It will be recalled that the control system 40 includes a sensor 42 that monitors a speed parameter of the electric drive machine 10 indicative of the transmission output speed. In the illustrated embodiment, the sensor 42 (S1) is coupled to the transmission output 28 and can directly measure the transmission output speed. In other embodiments, the sensor can monitor a different speed parameter, such as the rotational speed of the transmission 24 or other components in the electric drive system 20, which generally has a known or measurable relationship to the transmission output speed. The transmission output speed can also be monitored indirectly by sensing the ground speed of the machine 10. As discussed further herein, it is generally desirable to monitor the transmission output speed directly or indirectly for purposes of measuring the stability of the electric drive machine 10 in order to operate the transmission 24 in a first range, a second range, or possibly other ranges based on the ground speed of the machine 10. The sensor 42 generates a first speed signal indicative of the transmission output speed.

[0015] Another sensor 44 (S2) may be coupled to the transmission input 26 to monitor its rotational speed. It will be appreciated that the sensor 44 may be positioned to monitor the rotational speed of a different portion of the electric drive system 20 that has a known or measurable relationship to the transmission input speed. The sensor 44 generates a second speed signal indicative of the transmission input speed. As will become more apparent below, compared to certain known methods, particularly when shifting from neutral to one of the first range or second range, the transmission input speed may be controlled upon clutch engagement to ensure smoothness of movement and promote the availability of power transfer through the transmission 24.

[0016] Returning to the features and functionality of electronic controller 60, the term "electronic controller" should be understood herein to include a single computerized electronic control unit, such as a microprocessor or microcontroller, or a combination of multiple electronic control units. Electronic controller 60 typically includes, or is in communication with, suitable computer-readable memory that stores computer-executable program instructions that, when executed, cause electric drive controller 60 to perform the logical functions discussed herein. Exemplary suitable computer-readable memory can include RAM, ROM, SDRAM, EPROM, FLASH, etc.

[0017] 4 , the electric drive controller 60 may be configured to determine the suitability of the machine 10 to shift the transmission 24 from neutral to one of the first range or the second range. The electric drive controller 60 may be further configured to calculate a target transmission input speed based on the monitored speed parameter indicative of the transmission output speed and the determined suitability of the machine 10 to shift the transmission 24 from neutral to one of the first range or the second range. The electric drive controller 60 may be further configured to vary the speed of the electric drive motor 22 based on the target transmission input speed, and to command engagement of one of the first clutch 30 or the second clutch 32 corresponding to one of the first range or the second range based on the varied speed of the electric drive motor 22.

[0018] The varied speed of the electric drive motor 22 may prevent the difference between the rotational speed of the rotatable portion of the first clutch 30 or the second clutch 32 and the rotational speed of the transmission output 28 from exceeding a target difference. It is generally desirable for engagement of the first clutch 30 or the second clutch 32 to occur at a relative speed between the engaged components at zero speed or within a relatively small tolerance range. Therefore, the target difference in relative speed between the rotational speed of the rotatable portion of the first clutch 30 or the second clutch 32 and the rotational speed of a rotatable output portion of the transmission 24, such as the transmission output 28, may be limited to the target difference. When the transmission 24 is within the gear speed of the transmission input 26, the transmission output 28 differs to an extent that depends on the torque-transferring activity of the gear mechanisms 64 and 66. Thus, when transmission 24 is engaged in a first range, the transmission input speed may be “X%” greater (or less) than the transmission output speed, and when transmission 24 is engaged in a second range, the transmission input speed may be “Y%” greater (or less) than the transmission output speed. Because the transmission input speed and the transmission output speed may also be equal in the first range or the second range, X% or Y% may equal 0% in some embodiments. When clutch 30 or 32 is engageable, the target difference may be X% or Y%, respectively, plus or minus 0.5%, 1%, 2%, or other tolerance. Similarly, electronic controller 60 may be understood to match the speed of a first engaged clutch portion, which has a constant rotational speed relative to transmission input 26, to a second engaged clutch portion, which has a constant rotational speed relative to transmission output 28. As discussed further herein, the target difference in rotational speed of the first and second on-coming clutch portions within clutches 30 and 32, respectively, during clutch engagement may be zero plus or minus 0.5%, 1%, 2%, etc. The disclosed tolerances are purely exemplary and may be tighter or looser in different applications.

[0019] 4 illustrates calculations 70 including a target input speed calculation 72 and a motor control command calculation 80. Calculation 72 may be performed by receiving a tracking gear logic input 74 and a transmission output speed input 76 (a second speed signal discussed herein). Tracking gear logic input 74 may include, for example, a first input or a first input value when machine 10 is traveling at a ground speed suitable for operation in a first range, and a second input or a second input value when machine 10 is traveling at a ground speed suitable for operation in a second range. In one embodiment, at relatively slow ground speeds indicated by a relatively slow transmission output speed, machine 10 may be suitable for operating transmission 24 in the first range. At relatively high ground speeds indicated by a relatively high transmission output speed, machine 10 may be suitable for operating transmission 24 in the second range. The suitability of additional available gear ratios may be explored in a generally similar manner.

[0020] Thus, the determined suitability may include a determined gear ratio suitability, and electric drive controller 60 may be configured to determine gear ratio suitability by executing tracking gear logic that links the availability of one of the first range or the second range to the transmission output speed. It should be understood that determining that machine 10 is not suitable to operate transmission 24 in the second range may result in suitability for machine 10 to operate transmission 24 in the first range, and vice versa. Execution of tracking gear logic may include determining which ranges are available and unavailable, and other combinations and extensions of these logic functions, including quantitatively or qualitatively measuring range availability based on factors external to machine 10, such as the speed parameters discussed, as well as factors external to machine 10, such as ground grade or load capacity being carried or pushed by mount system 18 or pulled by machine 10.

[0021] Calculation 72 generates (calculates) a target transmission input speed 78 that is sent to calculation 80. Calculation 80 can be implemented by a proportional control, such as a proportional-integral (PI) controller or a proportional-integral-derivative (PID) controller. However, other types of controllers can be used. In one embodiment, electric drive controller 60 is configured to calculate a transmission input speed error and calculate a motor control command 92 for varying the speed of electric drive motor 22 based on the transmission input speed error. In a proportional controller embodiment, a motor maximum speed or motor upper limit input 82 and a motor minimum speed or motor lower limit input 84 can be received to prevent exceeding the limits of electric drive motor 22. Calculation 80 can also be implemented based on a tracking active input 86, an integrator reset logic input 88, and a transmission input speed input 90 (a second speed signal discussed herein). Tracking active input 86 can indicate whether tracking gear logic is activated or not. An integrator reset logic input 88 can reset the integrator in PI or PID control when the electric drive motor 22 is at or near the speed limit of its displacement to avoid excessive overshoot or undershoot.

[0022] Thus, calculation 80 can be understood as calculating a transmission input speed error, e.g., a numerical input speed error, and calculating a motor control command 92 that is output to reduce the transmission input speed error, thereby limiting the relative speed of first clutch 30 or second clutch 32 upon engagement to zero, or a predetermined tolerance of zero as described herein. Motor control command 92 can include one of a motor torque command or a motor speed command. In the case of a motor torque command, the motor torque command can be output to inverter 39.

[0023] Industrial Applicability

[0024] 5, a flowchart 100 illustrating an exemplary methodology and logic flow according to one embodiment is shown. At block 105, the transmission 24 is placed in neutral, meaning that the first clutch 30 or the second clutch 32 is disengaged, placing the transmission 24 in neutral, in a machine 10 operating in one of the first or second ranges. When the transmission 24 is in neutral, the machine 10, if moving, may have a tendency to coast. Depending on ground conditions, such as grade, the load being carried, pushed, or pulled, and whether the operator applies the brakes, the ground speed of the machine 10 may vary after the transmission 24 is placed in neutral. Thus, when the transmission 24 is in neutral, the machine 10 may be operating the transmission 24 in the second range, but after the transmission 24 is in neutral, the machine 10 may be suitable to operate the transmission 24 in the first range depending on the changed ground speed, and vice versa.

[0025] From block 105, the logic proceeds to block 110 to monitor a speed parameter of the machine 10 indicative of the transmission output speed, such as by directly monitoring the transmission output speed, as discussed herein. From block 110, the logic proceeds to block 115 to measure the suitability of the machine 10 to operate the transmission 24 in the first range and / or the second range. It should be understood that in block 115, the suitability of the machine 10 to operate the transmission 24 in the first range may be logically similar to measuring the insuitability of the machine 10 to operate the transmission 24 in the second range. As also discussed herein, the measured suitability may include a measured gear ratio suitability based on the transmission output speed.

[0026] From block 115, the logic may proceed to block 120 to calculate a target transmission input speed as discussed herein, such as by calculating a target input speed corresponding to the measured transmission output speed, taking into account the measured gear ratio compatibility. In other words, in block 120, the electronic controller 60 may be understood to calculate which transmission input speed is appropriate for the given transmission output speed, and whether it is in the first range or the second range.

[0027] From block 120, the logic proceeds to block 125 to calculate a transmission input speed error, such as by calculating the difference between a target transmission input speed and the measured transmission input speed. From block 125, the logic proceeds to block 130 to calculate an appropriate motor control command, including a motor torque command or a motor speed command as discussed herein. From block 130, the logic proceeds to block 135 to command engagement of one of the first clutch 30 and the second clutch 32 corresponding to a suitable available first range or second range. The command to engage the corresponding one of the first clutch 30 or the second clutch 32 may occur at a time based on the transmission input speed error, such as when the transmission input speed error is zero or within a predetermined tolerance of zero.

[0028] This description is for illustrative purposes only and should not be construed to narrow the scope of the present disclosure in any way. Accordingly, those skilled in the art will understand that various modifications can be made to the embodiments of the present disclosure without departing from the full and fair scope and spirit of the present disclosure. Other aspects, features, and advantages will become apparent upon review of the accompanying drawings and the appended claims. As used herein, the articles "A" and "AN" are intended to include one or more items and may be used synonymously with "one or more." When only one item is intended, the term "a" or similar terms are used. Also, as used herein, terms such as "have," "having," and "having" are intended to be open-ended terms. Furthermore, the phrase "based on" is intended to mean "based at least in part on" unless expressly stated otherwise. Similarly, the word "or" as used herein refers to any possible permutation of a set of items. For example, the phrase "A, B, or C" refers to at least one of A, B, and C, or any combination thereof, such as any of a plurality of any items such as A; B; C; A and B; A and C; B and C; A, B, and C; or A and A; B, B, and C; A, A, B, C, and C.

Claims

1. A method of operating an electric drive machine (10), comprising: disengaging and operating a first clutch (30, 32) in a first range to neutralize a transmission of the electric drive machine coupled to the electric drive motor (22); monitoring a speed parameter of the electric drive machine indicative of a transmission output speed; determining suitability of the electric drive machine for operating the transmission in a second range; calculating a target transmission input speed based on the monitored speed parameter and the determined suitability of the machine to operate the transmission in the second range; Varying the speed of the electric drive motor based on the target transmission input speed; and engaging a second clutch (30, 32) and operating the transmission in the second range based on the changed speed of the electric drive motor.

2. 2. The method of claim 1, wherein the changed speed of the electric drive motor limits the difference between the rotational speed of the rotatable portion of the second clutch and the rotational speed of the rotatable output portion (28) of the transmission to a target difference, and the ground speed of the electric drive machine is changed after placing the transmission in neutral.

3. 2. The method of claim 1, wherein determining suitability of the electric drive machine includes determining suitability for operating the transmission in the first range using the first clutch and a first gear ratio between the transmission input (26) and the transmission output (28) or for operating the transmission in the second range using the second clutch and a second gear ratio between the transmission input and the transmission output, the transmission including a finite number of available gear ratios.

4. 4. The method of claim 1, further comprising calculating a motor control command comprising one of a motor torque command or a motor speed command, and wherein varying a speed of the electric drive motor comprises varying a speed of the electric drive motor based on the motor control command.

5. calculating the motor control command includes calculating the motor control command with a proportional controller (80); 5. The method of claim 4, wherein the method further includes receiving the target transmission input speed and a monitored transmission input speed as inputs to the proportional controller, the method further includes calculating a transmission input speed error, wherein calculating the motor control command is based on the transmission input speed error.

6. 6. The method of claim 1, further comprising supplying power to the electric drive motor from an electrical energy storage device by an inverter, and wherein the motor control command comprises a motor torque command output to the inverter.

7. An electric drive system (20) for an electric drive machine (10), comprising: an electric drive motor (22); a transmission (24) including a transmission input (26) coupled to the electric drive motor, a transmission output (28), and first and second clutches (30) and (32) coupled between the transmission input and the transmission output, respectively, for operating the transmission in a first range and a second range, respectively; a control system (40) comprising a sensor (42) configured to monitor a speed parameter of the electric drive machine indicative of a transmission output speed, and an electric drive controller (60) in communication with the sensor, the electric drive controller (60) comprising: determining suitability of the electric drive machine for shifting the transmission from neutral to one of the first range or the second range; calculating a target transmission input speed based on the monitored speed parameter and the determined suitability of the electric drive machine for shifting the transmission from neutral to one of the first range or the second range; Varying the speed of the electric drive motor based on the target transmission input speed; and issuing a command to engage one of the first clutch or the second clutch corresponding to one of the first range or the second range based on the changed speed of the electric drive motor.

8. 8. The electric drive system of claim 7, wherein the electric drive controller is further configured to calculate a transmission input speed error and calculate motor control commands for varying the speed of the electric drive motor based on the transmission input speed error.

9. 9. The electric drive system of claim 7 or 8, wherein the electric drive controller is further configured to calculate the transmission input speed error by a proportional controller configured to receive a motor maximum speed, a motor minimum speed, and an integrator reset as inputs.

10. 10. The electric drive system of claim 7, wherein the determined suitability comprises a determined gear ratio suitability based on the transmission output speed, and the transmission comprises a mechanical transmission having a finite number of available gear ratios.

11. An electric drive control system (40), comprising: In an electric drive machine (10), receiving a first speed signal indicative of a transmission output speed of the transmission (24); receiving a second speed signal indicative of a transmission input speed of the transmission; measuring the suitability of the electric drive machine to shift the transmission from neutral to one of a first range or a second range of transmission; outputting motor control commands to vary the speed of an electric drive motor (22) coupled to a transmission input (26) of the transmission; calculating a transmission input speed error based on a difference between the transmission input speed and a target transmission input speed; an electric drive controller configured to output a clutch engagement command to engage one of a first clutch or a second clutch corresponding to one of the first range or the second range, respectively, at a timing based on the transmission input speed error;

12. 12. The electric drive control system of claim 11, wherein the electric drive controller is further configured to calculate the target transmission input speed based on the first speed signal, and to output the clutch engagement command when a size of the transmission input speed error is zero or within a predetermined tolerance of zero.

13. 13. The electric drive system of claim 11 or 12, wherein the electric drive controller comprises a proportional controller (80), and the motor control command comprises a motor torque command calculated by the proportional controller based on the transmission input speed error.

14. The determined suitability may be adaptability of the determined gear ratio based on the transmission output speed; 14. The electric drive control system of claim 11, wherein the electric drive controller is further configured to determine the suitability of the gear ratio by executing tracking gear logic that links the availability of one of the first range or the second range to the transmission output speed.

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