The present disclosure relates to power transmission devices. More particularly, a transmission for transferring torque at a variable speed reduction ratio includes a planetary gear drive driven by two sources of power.
Geared transmissions typically function to change the rotational speed of a prime mover output shaft and an input shaft of a desired work output. In a vehicle, the prime mover may include a diesel or gasoline internal combustion engine. It should be noted that there are many more applications than automobiles and trucks. Locomotives are equipped with transmissions between their engines and their wheels. Bicycles and motorcycles also include a transmission. Speed-increasing transmissions allow the large, slow-moving blades of a windmill to generate power much closer to a desired AC frequency. Other industrial applications exist. In each case, the motor and transmission act together to provide power at a desired speed and torque to do useful work. Geared transmissions have also been used in combination with electric motors acting as the prime mover.
Multiple speed transmissions have been coupled to high torque prime movers that typically operate within a narrow speed range, most notably structured as large displacement diesel engines of tractor trailers. Electric motors have a much wider speed range in which they operate effectively. However, the motor operates most efficiently at a single speed. Known multiple speed transmissions attempt to maintain an optimum operating speed and torque of the prime mover output shaft, but only approach this condition due to the discrete gear ratios provided. Accordingly, a need for a simplified variable speed ratio power transmission device exists.
Many existing transmissions incorporate planetary gearsets within the torque path. A traditional planetary gear drive has three major components: a sun gear, an annulus ring gear and a planet carrier. When one of those components is connected to the prime mover, another is used as the output and the third component is not allowed to rotate, the input and output rotate at different speeds, and may also rotate in opposite directions, with the ratio of input to output speeds being a fixed value. If the previously fixed third component is connected to a second input and forced to rotate, the transmission will have a continuously varying speed ratio dependent on the speeds of both the prime mover and this new second input. One example of such a planetary gear drive is made by Toyota. While planetary gearsets have been successfully used in vehicle power transmissions in the past, a need exists for a planetary drive and control system for optimizing the gear drive's efficiency and power density.
This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
A transmission for transferring torque from a prime mover includes a first input shaft adapted to be driven by the prime mover, a second input shaft and an output shaft. A compound planetary gearset includes a sun gear driven by the first input shaft, first pinion gears being driven by the sun gear, a ring gear fixed for rotation with the second input shaft and being meshed with second pinion gears, and a carrier driving the output shaft. A reaction motor drives the second input shaft. A controller controls the reaction motor to vary the speed of the second input shaft and define a gear ratio between the first input shaft and the output shaft based on the second input shaft speed.
A transmission for transferring torque from a prime mover includes a first input shaft adapted to be driven by the prime mover, a second input shaft, an output shaft and an epicyclic gearset. The gearset includes a ring gear being driven by the first input shaft, pinion gears being driven by the ring gear, a sun gear driven by the second input shaft and driving the pinion gears, and a carrier driving the output shaft. A reaction motor drives the second input shaft. A controller controls the reaction motor to vary the speed of the second input shaft and define a gear ratio between the first input shaft and the output shaft based on the second input shaft speed.
A transmission includes a first input shaft adapted to be driven by the prime mover, a second input shaft, an output shaft, and an epicyclic gearset. The gearset includes a sun gear being driven by the first input shaft, pinion gears in meshed engagement with the sun gear, a carrier driven by the second input shaft and rotatably supporting the pinion gears, and a ring gear fixed for rotation with the output shaft. A reaction motor drives the second input shaft. A controller controls the reaction motor to vary the speed of the second input shaft and define a gear ratio between the first input and the output shaft based on the a second input shaft speed.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.
The present disclosure is directed to a transmission that can be adaptively controlled to transfer torque between a first rotary member and a second rotary member. The transmission finds particular application in motor vehicle drivelines such as, for example, a continuously variable torque transfer mechanism. Thus, while the transmission of the present disclosure is hereinafter described in association with particular arrangements for use in specific driveline applications, it will be understood that the arrangements shown and described are merely intended to illustrate embodiments of the present disclosure.
With particular reference to
As shown in
Planetary gearset 40 includes a sun gear 46 fixed for rotation with an output shaft 48 of engine 18. An annulus ring gear 50 is fixed for rotation with an output shaft 52 of reaction motor 42. Planetary gearset 40 also includes a carrier 54 rotatably supporting a plurality of pinion gears 56 that are each in constant meshed engagement with annulus ring gear 50 and sun gear 46. An output shaft 58 is fixed for rotation with carrier 54. The remainder of this disclosure discusses how the sun gear speed ωS to carrier speed ωC ratio is a function of an annulus ring gear speed ωR to sun speed ωS ratio in simple and compound planetary gearsets and how the asymptotic nature of this speed ratio may be exploited to improve the gear drive's efficiency and power density.
If a positive direction of annulus ring rotation is defined to be in the same direction as that of the sun gear and carrier assembly, it can be shown that in the general case, the ratio of sun to carrier speeds is given by:
where ωS, ωC, and ωR are the sun, carrier and annulus ring angular velocities and zR and ZS are the number of teeth in the annulus ring and sun gears, respectively. Note that if ωR=0, equation (1) simplifies to the familiar relationship between sun and carrier speeds for a fixed annulus ring.
We define the ratio of ring speed to sun speed as
Equation (1) may then be rewritten as
It can be noted that there will be a value of ωR/S for which ω/ωC will become asymptotic.
The sensitivity of the speed ratio to its fixed ring ratio is quantified by defining the ratio of the highest to lowest speed ratios as Δ for an arbitrary value of ωR/S selected as +/−10% of the sun's speed, as well as the value of ωR/S for the vertical asymptote. Table 1 presents this data.
Table 1 and
To operate on the same pinion centers, the module, helix angle and number of teeth must satisfy this constraint:
where mR and mS are the normal modules of the ring and sun meshes, respectively. The planet pinions ZPS and ZPR mesh with the sun and annulus, respectively. In addition to the geometry constraint of equation (4), each of the compound planet pinions independent meshes must have the same torque, but because each torque will act at different pitch geometries, the tooth loads may differ significantly and require largely different modules as a result.
If the design of a compound planetary gear set is modified to allow for an annulus gear that may move at a controlled angular speed while still providing the necessary reaction torque for the planet pinions, a similar asymptotic behavior to that seen in
As with equations (1) and (2), equation (5) reduces to the familiar speed relationship for a fixed annulus ring when ωR/S=0. Since a compound planetary gear set is capable for a larger speed ratio ωS/ωC, the benefits of the asymptotic nature of equation (5) can be more fully exploited.
As was done for simple planetary gear drives, tooth combinations shown in Table 2 were selected to attempt to span the practical FRR limits. A FRR less than 5.043 would most likely not justify the additional complexity and expense of a compound planetary over a simple planetary and a FRR larger than 30 may not be practical, as can be seen from
ωS=ωS/R·ωR (6)
The input to output speed ratio u may be expressed as:
At
As was with planetary gearset 40, the power and steady-state torque into the gear drive must balance that exiting the gear drive.
τR+τS=τC (8)
τR·ωR+τS·ωS=τC·ωC (9)
As before, we make the kinematics and steady-state torque substitutions into the power balance equation, and obtain the carrier and sun torques in terms of the ring torque.
As was done in the previous section with planetary gearset 40, we again define the ratio of the reaction power to the input power as K, and write that for the solar arrangement variable speed ratio,
The same relationship for transmission ratio spread as was discussed earlier exists as well. Therefore, for both a planetary and solar epicyclic arrangement, the kinematics exhibits an asymptotic behavior. However, the speeds of the reaction member at which the asymptote is observed will depend on the type of epicyclic arrangement, as well as the fixed reaction member speed ratios. In both cases, the transmission ratio spread required for the application will define the power requirements of the reaction motor/generator.
Another alternate transmission is shown in
ωC=ωC/S·ωS (13)
If we follow the same steps as we did for the planetary and solar epicyclic gear drives, we can rearrange the equation to give us the sun to ring speed ratio.
Note that the negative sign in front of the right hand side means the input and output shafts will rotate in opposite directions when the carrier speed is zero.
τS−τC=−τR (15)
τS·ωS−τC·ωC=τR·ωR (16)
After substitute and rearranging terms of the above equations, the ring and carrier torques may be expressed in terms of the sun torque. The ring and carrier torques must be in a direction opposite to that of the sun. This has been addressed with the negative signs in the equation above.
The ratio of the reactive power to the input power as defined as κ. However, since the carrier and sun torques are in opposite directions, the same will be true of their powers. Therefore, when the carrier and sun speeds are in the same direction κ.<0, and when the carrier and sun are in opposite directions, κ.>0 and we have as was true for the planetary and solar arrangements:
Thus, in all three epicyclic arrangements, when it is desirable to have a greater speed reduction than the fixed reaction-member ratio, the device that powers the input member must also power the reaction device to provide this additional speed reduction ratio. Conversely, if it is desired to have a speed reduction ratio that is less than that of the fixed reaction-member ratio, the reaction device must power the reaction member to achieve this kinematic relationship. The reaction power will exit the gear drive through the output member, adding to the power output of the gear drive.
It should be appreciated that solar gear arrangement 120 and star gear arrangement 150 may be modified to function with compound planet gears as previously described in relation to
The kinematics relationships for the compound solar and star epicyclic arrangements are derived in a manner similar to that previously described.
Regarding
Tables 3, 4 and 5 summarize the speed reduction ratios and planet speeds, torque and power for each epicyclic gear drive considered. Table 6 summarizes the speed reduction ratios using the reactive power quotients for each arrangement and Table 7 summarizes the asymptotic characteristics of where the asymptote occurs and what is the slope as the curve crosses the vertical axis.
It should be appreciated that all speed reduction ratios can be written in the form:
where uF is the fixed reaction member speed ratio specific to the particular epicyclic arrangement and κ is the reactive power quotient. This is true regardless of whether the epicyclic arrangement is planetary, solar, star, simple or compound. The reactive power quotient can be a positive or negative quantity. When κ<0, the speed reduction ratio will be larger than that of a gear drive with a fixed reaction member, and the input drive motor must supply power to both the output and the reaction motor/generator. When κ>0, the speed reduction ratio will be smaller than that of a fixed reaction member gear drive, and the output will be powered by both the input drive motor and the reaction motor/generator.
Furthermore, the ratio spread, or the quotient between the maximum and minimum speed reduction ratios will determine the power requirements of the reaction motor/generator. If the primary drive motor is one with a narrow operating speed range and demands a large spread between the top and bottom speed ratios, the reactive power requirements will be large, possibly several times larger than that of the primary drive motor. If the primary drive motor has a wide operating speed range the reactive power requirements will be small. A ratio spread of 2.0 results in primary and reaction power requirements that are equal. The motor/generator size can be further reduced by mating it with its own fixed reaction member gear drive, using traditional methods to determine its required speed reduction ratio.
The selection of which type of epicyclic arrangement is optimum (i.e., planetary, solar or star) depends on the details and the required speed reduction ratio and ratio spread of the application. The slope of the speed reduction ratio at the ordinate axis of the star arrangement is equal to that of the planetary arrangement and the vertical asymptote of a star arrangement will always occur at a lower reaction member speed to that of a planetary arrangement.
Furthermore, the foregoing discussion discloses and describes merely exemplary embodiments of the present disclosure. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications and variations may be made therein without departing from the spirit and scope of the disclosure as defined in the following claims.
This application is a continuation of U.S. patent application Ser. No. 12/766,954 filed Apr. 26, 2010 which is a continuation-in-part of U.S. patent application Ser. No. 12/617,031 filed on Nov. 12, 2009. The entire disclosure of each of the above applications is incorporated herein by reference.
Number | Date | Country | |
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Parent | 12766954 | Apr 2010 | US |
Child | 13858207 | US |
Number | Date | Country | |
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Parent | 12617031 | Nov 2009 | US |
Child | 12766954 | US |