ELECTRIC DRIVE SYSTEM FOR A MACHINE AND ELECTRIC DRIVE CONTROL SYSTEM FOR THE SAME

Abstract

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

Description

Technical field

[0001] The present disclosure relates generally to an electric drive system for a machine, and more particularly to a strategy for adjusting the speed of rotatable components in an electric drive system during clutch engagement. background

[0002] The technology for electrifying various types of machinery has increasingly attracted the attention of engineers in recent years. Electric passenger cars and the like are now widespread throughout the world. Certain types of heavier equipment, including mining equipment and passenger trains powered by electric motors, are well-known and widely used. However, for other types of equipment, the transition to electric propulsion has been slower.

[0003] In a typical electric-powered machine, a power source, such as an electrical energy storage device or a generator, generates electricity to operate one or more electric traction motors and other onboard equipment. The floor elements are driven by the electric traction motor to propel the machine. While electrification promises to reduce certain emissions, electric drive systems have also brought with them many new challenges.

[0004] Some electric drive systems operate without a gearbox, meaning that the speed and torque applied to the ground elements depend directly on the output of one or more electric motors. In other systems, a gearbox is coupled between an electric drive motor and the ground elements. Shifting a gearbox typically requires disengaging one clutch, which transmits power from the electric motor to the ground elements through a first gear ratio, and re-engaging another clutch to drive the ground elements through a second gear ratio. Gearboxes are also shifted in and out of neutral and operated in reverse by reversing the direction of rotation of the electric motor. Engineers have observed various sensitivities to the relative speeds of rotating components in electric drive systems, as well as opportunities to increase performance.An example of a drive system in a non-electric prime mover that appears to provide a target speed for transmission control is known from Patent No. US 9,855,951 to Lister. The technique offers ample scope for improvement and the development of alternative strategies. Brief description

[0005] In one aspect, a method of operating an electric drive machine includes disengaging a first clutch to neutralize a transmission in the electric drive machine operating in a first range and coupled to an electric drive motor. 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 operation of 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 operation of the transmission in the second range, and varying a speed of the electric drive motor based on the target transmission input speed.The method further includes engaging a second clutch to operate 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 and a transmission having a transmission input coupled to the electric drive motor, a transmission output, a first clutch, and a second clutch, each coupled between the transmission input and the transmission output, for operating the transmission in a first and second range, respectively. The electric drive system further includes a control system having a sensor configured to monitor a speed parameter of the electric drive machine indicative of a transmission output speed, and an electric drive controller in communication with the sensor.The electric drive controller is configured to determine the suitability of the electric drive machine to shift the transmission from neutral to a gear in the first or 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 to shift the transmission from neutral to one of the first or second ranges. 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 command engagement of one of the first or second clutches corresponding to the first or second range based on the varied speed of the electric drive motor.

[0007] In 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 in an electric drive machine, receive a second speed signal indicative of a transient input speed of the transmission, and determine the suitability of the electric drive machine for shifting the transmission from neutral to a first or second range of the transmission. The electric drive controller is further configured to output a motor control command that varies 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 for engaging a first or a second clutch corresponding to the first or second range, respectively, at a timing based on the transient speed error. Short description of the drawings Fig. 1 is a side schematic view of an electric drive machine according to an embodiment; Fig. 2 is a block diagram of an electric drive system according to an embodiment; Fig. 3 is a schematic view of an electric drive system according to an embodiment; Fig. 4 is a block diagram of logical calculations according to one embodiment; and Fig. 5 is a flowchart illustrating an example methodology and logic flow according to one embodiment. Detailed description

[0008] In Fig. 1, an electric prime mover 10 is illustrated according to one embodiment. The machine 10 includes a frame 12, typically having articulated front and rear frame units (unnumbered) supporting an operator's cab 14 and a plurality of ground engaging elements 16. The ground engaging elements 16 are wheels in the illustrated embodiment, but could be tracks in other embodiments, or the machine 10 could even have a half-track configuration. The machine 10 includes a hydraulically actuated attachment system 18 having a boom and bucket (unnumbered), but in some embodiments could include other types of work tool systems, such as a dozer blade, or no work tool system.Machine 10 is shown in the context of a wheel loader, but could instead be a motor grader, a truck, a tractor, a dragline, a variety of other types of off-road equipment, a road machine, or even a watercraft.

[0009] Machine 10 includes an electric drive system 20 having an electric drive motor 22 and a transmission 24 with a transmission input 26 coupled to the electric drive motor 22 and a transmission output 28. The transition input 26 may comprise a transmission input shaft, a shaft assembly, or a transmission input gear, and the transmission output 28 may comprise a transmission output shaft, a shaft assembly, or an output gear, to name a few examples. The transmission 24 also includes a first clutch 30 and a second clutch 32, each coupled between the transition input 26 and the transmission output 28 to operate the transmission 24 in first and second ranges, respectively. The transmission 24 may comprise a mechanical transmission with a finite number of available gear ratios, for example, a total of two available gear ratios.In other embodiments, a different finite number of gear ratios could be available, or possibly an infinite number of effective gear ratios, such as might be available in a hydrostatic or hydromechanical transmission or a continuously variable mechanical transmission.

[0010] The electric drive system 20 may also include an electrical energy storage device such as a battery, a capacitor, or combinations thereof. A lower driveline 36 is coupled to the transmission output 28 and may be configured to transfer torque to one or both of the front ground contact elements 16 and the rear ground contact elements 16 in a two-wheel or four-wheel drive application. Power electronics 38 are coupled between the electrical energy storage device 34 and the electric drive motor 22. In other embodiments, electrical energy in the electric drive system 20 could be provided by a generator or a fuel cell instead of an electrical energy storage device. The electric drive system 20 also includes an electric drive control system 40.

[0011] The control system 40 comprises a sensor 42 (for example, but not exclusively, in Fig. 1 as part of the transmission 24) configured to monitor a speed parameter of the electric drive machine 10 indicative of a transmission output speed, and an electric drive controller 60 in communication with the sensor 42 and having features and functions further explained herein. Referring to Fig. 2, a block diagram illustrating additional features and components of the electric drive system 20 is shown. The electrical energy storage device 34 is shown as a battery 34, which is electrically connected to a traction inverter 39 of the power electronics system 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, which in turn is coupled to the transmission 24. As mentioned above, the transmission 24 may or may not be a two-speed transmission. The transmission 24 is in turn coupled to the lower driveline 36. The pump inverter 46 is electrically connected to a pump electric motor 48, which in turn may rotate a pump splitter or gearbox 50. The transmission 50 is connected to a transmission oil pump 42, an implement oil pump 54, a steering oil pump 56, and a brake oil pump 58.

[0012] In Fig. 3, yet further features of the electric drive system 30 are illustrated. The electric drive motor 22 includes a motor output shaft 62 that can be directly coupled to the transmission input 26 in the transmission 24. Thus, the transmission input 26 can be mounted to rotate with the motor output shaft 62, although a gear box or lock-up clutch, or the like, could be coupled between the transmission input 26 and the motor output shaft 62 within the scope of the present disclosure. As mentioned above, the transmission 24 can include a mechanical transmission configured to operate in a first gear range and a second gear range, such as 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 is actuated via electronic control commands from the electric drive controller 60 to engage and disengage the transmission 24 in the first range. A second clutch actuator 33 (C2) is similarly constructed and can engage and disengage the second clutch 32 to operate the transmission 24 in the second range. When neither the first clutch 30 nor the second clutch 32 is engaged, the transmission 24 is neutral. A first gear combination 64 is coupled between the first clutch 30 and the transmission output 28 and can include at least two intermeshing gears that rotate an output gear 68.A second gear combination 66 is coupled between the transmission input 26 and the transmission output 28 and also includes at least two intermeshing gears that rotate the output gear 68. The present disclosure is applicable regardless of the specific clutch configuration used. Therefore, 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.

[0013] Recall that control system 40 includes a sensor 42 for monitoring a speed parameter of electric drive machine 10 indicative of transmission output speed. In the illustrated embodiment, sensor 42 (S1) may be coupled to transmission output 28 to directly measure transmission output speed. In other embodiments, a sensor could monitor another speed parameter, such as the speed of another component in transmission 24 or in electric drive system 20, which generally has a known or determinable relationship to transmission output speed. Transmission output speed could also be monitored indirectly by sensing a ground speed of machine 10.It is generally desirable to directly or indirectly monitor the transmission output speed to determine the suitability of the electric drive machine 10 for operating the transmission 24 in the first range, the second range, or possibly other ranges based on a ground speed of the machine 10, as further explained herein. The sensor 42 generates a first speed signal indicative of the transmission output speed.

[0014] Another sensor 44 (S2) is coupled to the transmission input 26 and can monitor its speed. It should be understood that the sensor 44 can be arranged to monitor the speed of another part of the electric drive system 20 that has a known or determinable relationship to the transmission input speed. The sensor 44 generates a second speed signal indicative of the transmission input speed. As will be further understood from the following description, the transmission input speed can be controlled upon clutch engagement to ensure smooth shifting and to expedite the availability of power delivery through the transmission 24, particularly when shifting from neutral to one of the first or second ranges, compared to certain known strategies.

[0015] Returning to the features and functions of the electronic controller 60, the term "electronic controller" should be understood herein to include a single computer-based electronic control unit, such as a microprocessor or microcontroller, or a combination of multiple electronic control units. The electronic controller 60 typically includes or is coupled to a suitable computer-readable memory storing executable computer program instructions that, when executed, cause the electric drive controller 60 to perform the logical functions described herein. Suitable computer-readable memory may be, for example, RAM, ROM, SDRAM, EPROM, FLASH, or other.

[0016] With reference to Fig. 4, the electric drive controller 60 may be configured to determine the suitability of the machine 10 for shifting the transmission 24 from neutral to one of the first or second ranges. 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 for shifting the transmission 24 from neutral to the first or second range. The electric drive controller 60 may be further configured to vary a 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 second clutch 32 corresponding to the first or second range based on the varied speed of the electric drive motor 22.

[0017] The varied speed of the electric drive motor 22 may be such that a difference between a rotational speed of a rotatable portion of the first clutch 30 or the second clutch 32 and a rotational speed of the transmission output 28 does not exceed a target difference. It is generally desirable for the engagement of the first clutch 30 or the second clutch 32 to occur with a relative speed of zero between the engaging components or a relative speed within a relatively small error range. Therefore, a target difference in relative speed between a rotatable portion of the first clutch 30 or the second clutch 32 and a rotational speed of a rotatable output portion of the transmission 24, such as the transmission output 28, may be limited to a target difference.When the transmission 24 is in gear, the transmission input 26 and transmission output 28 speeds differ by an amount that depends on which of the gear ratios 64 and 66 is active to transmit torque. Thus, when the transmission 24 is engaged in the first range, the transmission input speed may be "X%" greater (or less) than the transmission output speed, and when the transmission 24 is engaged in the second range, the transmission input speed may be "Y%" greater (or less) than the transmission output speed. The transmission input speed and the transmission output speed may also be the same in the first or second range, so X% or Y% may equal 0% in some implementations. When the clutch 30 or 32 is to be engaged, the target difference may be X% or Y%, respectively, plus or minus 0.5%, 1%, 2%, or some other tolerance.Analogously, the electronic controller 60 may be understood to adjust a speed of a first clutch engagement portion having a fixed speed relative to the transmission input 26 to a second clutch engagement portion having a fixed speed relative to the transmission output 28. As further explained herein, a target difference in the speeds of the first clutch engagement portion and the second clutch engagement portion within each of the clutches 30 and 32 at clutch engagement portion zero may be plus or minus 0.5%, 1%, 2%, etc. The stated tolerance ranges are merely exemplary and could be narrower or broader in different applications.

[0018] In Fig. 4, the calculations 70 are illustrated, including a calculation of the target input speed 72 and a calculation of the engine control command 80. The calculation 72 may be performed by receiving a logical input of the tracking transmission 74 and a transmission output speed 76 input (a second speed signal, as discussed herein). For example, the logical input of the tracking transmission 74 may include a first input or first input value when the machine 10 is moving at a ground speed suitable for operation in the first range and a second input or second input value when the machine 10 is moving at a ground speed suitable for operation in the second range.In one implementation, machine 10 could be suitable for operation of transmission 24 in the first range at a relatively lower ground speed, indicated by a relatively lower transmission output speed. At a relatively higher ground speed, indicated by a relatively higher transmission output speed, machine 10 could be suitable for operation of transmission 24 in the second range. Additional available gear ratios could be evaluated for suitability in a generally analogous manner.

[0019] Thus, the determined suitability may include a determined suitability of the gear ratio, and the electric drive controller 60 may be configured to determine the suitability of the gear ratio by executing tracking transmission logic that links the availability of the first range or the second range gear ratio to the transmission output speed. It should further be understood that a conclusion about the suitability of the machine 10 for operation of the transmission 24 in the first range could be drawn by determining that the machine 10 is not suitable for operation of the transmission 24 in the second range, and vice versa.Execution of the tracking gear logic could include determining which of the ranges are available, which are unavailable, and other combinations and extensions of these logical functions, including quantitative or qualitative determinations of range availability based on factors external to the machine 10, such as the speed parameters discussed, as well as factors external to the machine 10, such as a ground surface slope or a load weight carried or pushed by the attachment system 18 or pulled by the machine 10.

[0020] Calculation 72 generates (calculates) a target transmission input speed 78, which is fed into calculations 80. Calculations 80 may be performed using a proportional controller, such as a proportional-integral (PI) controller or a proportional-integral-derivative (PID) controller. However, other types of controllers could also be used. In one implementation, electric drive controller 60 is configured to calculate a transmission input speed error and calculate a motor control command 92 to change the speed of electric drive motor 22 based on the transmission input speed error. In a proportional controller implementation, an input for maximum motor speed or upper motor limits 82 and an input for minimum motor speed or lower motor limits 84 may be received to prevent exceeding the limits of electric drive motor 22.Calculations 80 may also be performed based on an active tracking input 86, an integrator reset logic input 88, and a transmission input speed input 90 (a second speed signal as explained herein). The active tracking input 86 may indicate whether tracking transmission logic is enabled. The integrator reset logic input 88 may reset the integrator in a PI or PID controller to avoid excessive overshoot or undershoot when the speed is at or near the speed limits of the electric drive motor 22's capacity.

[0021] Calculations 80 may therefore be understood as calculating a transmission input speed error, such as a numerical input speed error, and calculating a motor control command 92 output to reduce the transmission input speed error and thereby provide a transmission input speed that limits the relative speeds in the first clutch 30 or second clutch 32 upon engagement to zero or a predetermined zero tolerance, as described herein. The motor control command 92 may include a motor torque command or a motor speed command. In the case of a motor torque command, the motor torque command may be output to the inverter 39. Industrial applicability

[0022] With reference to Fig.5, a flowchart 100 is shown illustrating an example methodology and logic flow according to one embodiment. At a block 105, the transmission 24 is neutralized, meaning that the first clutch 30 or the second clutch 32 has been disengaged to neutralize the transmission 24 in the machine 10 operating in a first or second range. When the transmission 24 is neutralized and the machine 10 is moving, it may tend to idle. Depending on ground conditions, such as a slope, the load being transported, pushing or pulling, and whether or not an operator is applying the brakes, the ground speed of the machine 10 may vary after the transmission 24 is neutralized.Thus, while machine 10 may have operated transmission 24 in the second range when transmission 24 is neutralized, machine 10 may be capable of operating transmission 24 in the first range after transmission 24 is neutralized, or vice versa, depending on varying ground speed.

[0023] 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 directly monitoring the transmission output speed as described herein. From block 110, the logic proceeds to block 115 to determine the suitability of the machine 10 for operation of the transmission 24 in the first and / or second ranges. It should be noted that at block 115, the suitability of the machine 10 for operation of the transmission 24 in the first range may be logically analogous to determining the unsuitability of the machine 10 for operation of the transmission 24 in the second range. As also discussed herein, the determined suitability may include a determined gear ratio suitability based on the transmission output speed.

[0024] From block 115, the logic may proceed to a block 120 to calculate the target transmission input speed as described herein, for example, by calculating a target input speed corresponding to a measured transmission output speed, taking into account the determined gear ratio suitability. In other words, in block 120, the electronic controller 60 may be understood to calculate what transmission input speed is appropriate for a current transmission output speed, regardless of whether the first or second range is appropriate.

[0025] From block 120, the logic proceeds to a block 125 to calculate the transmission input speed error, for example, by calculating a difference between the target transmission input speed and a measured transmission input speed. From block 125, the logic may proceed to block 130 to calculate the corresponding engine control command, including an engine torque command or an engine speed command, as discussed herein. From block 130, the logic may proceed to block 135 to command engagement of the first clutch 30 or the second clutch 32 corresponding to the appropriate and available first or second range. Engagement of the corresponding first clutch 30 or second clutch 32 may occur at a time based on the transmission input speed error, for example, at a time when the transmission input speed error is zero or within a predefined tolerance of zero.

[0026] The present description is for illustrative purposes only and should not be construed to limit the scope of the present disclosure in any way. Thus, those skilled in the art will recognize that various changes may be made to the presently disclosed embodiments without departing from the full and fair scope and spirit of the present disclosure. Additional aspects, features, and advantages will become apparent upon examination of the accompanying drawings and claims. As used herein, the items "a" and "an" are intended to include one or more elements and may be used interchangeably with "one or more." When only one item is contemplated, the term "a(1)" or similar language is used. Likewise, the terms "has," "having," "having," or the like, as used herein, are intended to be open-ended terms.Furthermore, the phrase "based on" shall mean "based at least in part on" unless explicitly stated otherwise. The word "or" throughout this document 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, C, or any combination thereof, such as A; B; C; A and B; A and C; B and C; A, B, and C; or multiples of any one item, such as A and A; B, B, and C; A, A, B, C, and C; etc. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 9.855.951

[0004]

Claims

[1] Method for operating an electric drive machine (10), comprising: disengaging a first clutch (30, 32) to neutralize a transmission (24) in the electric drive machine operating in a first range and coupled to an electric drive motor (22); Monitoring an electric drive machine speed parameter indicative of a transmission output speed; Determining the suitability of the electric drive machine to operate 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 a speed of the electric drive motor based on the target transmission input speed; and Engaging a second clutch (30, 32) to operate the transmission in the second range based on the varied speed of the electric drive motor. [2] The method of claim 1, wherein the varied speed of the electric drive motor is such that a difference between a speed of a rotatable portion of the second clutch and a speed of a rotatable output portion (28) of the transmission is limited to a target difference; wherein a traveling speed of the electric drive machine varies after neutralizing the transmission. [3] The method of claim 1, wherein determining suitability of the electric drive machine comprises determining suitability for operation of the transmission in the first range using the first clutch and a first gear ratio between a transmission input (26) and a transmission output (28) or in the second range using the second clutch and a second gear ratio between the transmission input and the transmission output; wherein the transmission includes a finite number of available gear ratios. [4] The method of any one of claims 1 to 3, further comprising calculating a motor control command comprising a motor torque command or a motor speed command, and wherein varying the speed of the electric drive motor comprises varying the speed of the electric drive motor based on the motor control command. [5] The method of claim 4, wherein calculating a motor control command comprises calculating the motor control command via a proportional controller (80); wherein the method further comprises receiving the target transmission input speed and a monitored transmission input speed as inputs to the proportional controller; and wherein the method further comprises calculating a transmission input speed error and calculating the motor control command is based on the transmission input speed error. [6] The method of any one of claims 1 to 5 further comprising supplying electrical energy to the electric drive motor from an electrical energy storage device (34) via an inverter (39), and wherein the motor control command includes a motor torque command output to the inverter. [7] Electric drive system (20) for an electric drive machine (10), comprising: an electric drive motor (22); a transmission (24) having a transmission input (26) coupled to the electric drive motor, a transmission output (28), a first clutch (30) and a second clutch (32) each coupled between the transmission input and the transmission output to operate the transmission in a first and a second range, respectively; a control system (40) including 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 and configured to: to determine the suitability of the electric drive motor to shift the transmission from neutral to a first-range or second-range gear; calculate a target transmission input speed based on the monitored speed parameter and the determined suitability of the electric drive machine to shift the transmission from neutral to a first range or second range gear; to vary a speed of the electric drive motor based on the target transmission input speed; and to command engagement of one of the first or second clutches corresponding to the first or second range based on the varied speed of the electric drive motor. [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 a motor control command for varying the speed of the electric drive motor based on the transmission input speed error. [9] An electric drive system according to claim 7 or 8, wherein the electric drive controller is further configured to calculate the transmission input speed error via a proportional controller configured to receive as inputs a maximum motor speed, a minimum motor speed, and an integrator reset. [10] An electric drive system according to any one of claims 7-9, wherein the determined suitability comprises a determined suitability for a gear ratio based on the transmission output speed; and wherein the transmission comprises a mechanical transmission with a finite number of available gear ratios. [11] Electric drive control system (40), comprising: an electric drive controller (60) constructed to: to receive a first speed signal indicative of a transmission output speed of a transmission (24) in an electric drive machine (10); receive a second speed signal indicative of a transmission input speed of the transmission; to determine the suitability of the electric drive motor for shifting the transmission from neutral to a first or second range of the transmission; outputting a motor control command that varies a speed of an electric drive motor (22) coupled to a transmission input (26) of the transmission; calculate a transmission input speed error based on a difference between the transmission input speed and a target transmission input speed; and issue a clutch engagement command to engage a first clutch (30) or a second clutch (32) corresponding to the first range or the second range, respectively, at a time based on the transmission input speed error. [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 output the clutch engagement command when a magnitude of the transmission input speed error is zero or within a predetermined tolerance of zero. [13] An electric drive system according to 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 via the proportional controller based on the transmission input speed error. [14] An electric drive control system according to any one of claims 11-13, wherein: the determined suitability includes a determined suitability for the gear ratio based on the transmission output speed; and the electric drive controller is further configured to determine the suitability for the gear ratio by executing a 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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