Information
-
Patent Grant
-
6830531
-
Patent Number
6,830,531
-
Date Filed
Thursday, July 24, 200321 years ago
-
Date Issued
Tuesday, December 14, 200420 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Bliss McGlynn, P.C.
- Dziegielewski; Greg
-
CPC
-
US Classifications
Field of Search
US
- 475 119
- 475 257
- 475 263
- 475 318
-
International Classifications
-
Abstract
Pursuant to the control strategy of the present invention, torque load may be shared between the low/reverse friction clutch and a one-way clutch to effect low and reverse gear ratios in a transmission. This may be accomplished by engaging the friction clutch during vehicle launch and keeping it engaged until the peak torque has passed. Once the peak torque has been passed, the load capacity of the friction clutch can be reduced to zero. In this operational mode, the one-way clutch is acting to support the remaining drive torque. Thus, with only the one-way clutch carrying a load at the time of the up-shift from first to second gear, a non-synchronous shift can be affected. In this way, the control strategy acts to share the torque load between the low/reverse brake and the low one-way clutch, thereby allowing a reduced capacity, lower spin-loss one-way clutch design.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, generally, to a transmission shifting control strategy and, more specifically, to a control strategy for load sharing between a friction clutch and one-way clutch to effect low and reverse gear ratios in a transmission.
2. Description of the Related Art
Generally speaking, land vehicles require three basic components. These components include a power plant (such as an internal combustion engine), a power train and wheels. The power train's main component is typically referred to as the “transmission.” Engine torque and speed are converted in the transmission in accordance with the tractive-power demand of the vehicle. Transmissions include one or more gear sets which may include an inner gear, intermediate planet or pinion gears which are supported by their carriers, and outer ring gears. Various components of the gear sets are held or powered to change the gear ratios in the transmission. In addition to such planetary gear sets, driveline components may further include multi-disc friction devices that are employed as clutches or brakes. The multi-disc pack clutch is a friction device that is commonly employed as a holding mechanism in a transmission.
The multi-disc pack clutch or brake assembly has a clutch sub-assembly including a set of plates and a set of friction discs that are interleaved between one another. The plates and friction discs are bathed in a continual flow of lubricant and in “open pack” operation normally turn past one another without contact. The clutch or brake assembly also typically includes a piston. When a component of a gear set is to be held, as for example during a particular gear range, a piston is actuated so as to cause the plates and friction discs to come in contact with respect to one another. In certain applications, it is known to employ several multi-disc pack clutch devices in combination to establish different drive connections throughout the transmission to provide various gear ratios in operation, or to brake a component.
When the discs are not engaged, there often remains a differential rotational speed of the drive and driven members which the clutch or brake bridges. Relative rotation between the friction discs and the plates during open-pack mode creates drag. This condition results in parasitic energy losses, reduces the efficiency of the transmission, and ultimately results in lower fuel efficiency.
In addition to multiple friction devices, one-way clutches are frequently employed in transmissions to selectively transmit torque in one rotational direction, but not in the opposite rotational direction. To this end, one-way clutches typically include an inner race, an outer race, and an engagement mechanism disposed therebetween. The engagement mechanism is operable to lock the inner and outer races together thereby transmitting torque in one relative direction. The engagement mechanism is further operable to allow freewheeling rotation between the inner and outer races in the opposite rotational direction. Engagement mechanisms commonly used in one-way clutches of the related art include pawls, sprags, and rollers. A cage, along with biasing members, such as springs, are also sometimes employed to retain the pawls, sprags, or rollers between the inner and outer races as well as to selectively assist in the change of operational modes between torque translation and freewheeling actuation of the clutch, depending on the direction of rotation between the inner and outer races.
As noted above, one-way clutches of this type have been employed in numerous applications in transmission, transfer cases, and differentials. For example, one-way clutches have been employed in conjunction with multiple friction clutches and planetary gear sets to effect low and reverse gear ratios in conventional transmissions. While this arrangement has worked well for its intended purpose, some disadvantages remain. For example, the friction clutch remains a source of significant parasitic losses due to inherent drag between the friction plates when the clutch is operating in “open pack” mode. Still, the clutch is necessary for providing the proper holding torque in low and reverse gears. Accordingly, there remains a need in the art for a shift control strategy that activates the friction clutch to provide the appropriate holding torque for both low and reverse gears in the transmission and yet yields lower manufacturing costs and space requirements than those presently attributable to the one way clutch and multiple plate friction clutch currently used for this purpose. In addition, there is a need in the art for a control strategy that provides for a non-synchronous up-shifting from first to second gear may be effected.
SUMMARY OF THE INVENTION
The disadvantages of the related art are overcome in a transmission shifting control strategy for load sharing between a low friction clutch and a one-way clutch to provide low and reverse gears in a transmission. The control strategy includes a method of controlling an automotive transmission having at least one shaft and at least one gear set operatively coupled to the shaft and adapted to provide low and reverse gear ratios. The gear set includes a sun gear operatively coupled to a source of torque in the transmission assembly, a ring gear mounted for rotation about the sun gear and a plurality of pinion gears supported by a carrier for meshing rotation about the sun gear and between the ring gear and the sun gear. The carrier is operatively coupled to the shaft. In addition, the transmission has a friction clutch assembly including a clutch pack that acts as a holding device and as well as a one way clutch assembly that is interposed between the friction clutch assembly and the gear set. The method includes the steps of selecting a low gear ratio that is provided by the gear set. The friction clutch is actuated to ground the outer race of the one-way clutch assembly and thus the ring gear to the transmission housing. Torque is provided to the sun gear to drive the pinion gears in meshing relationship about the sun gear to transfer torque at a reduced ratio to the carrier and therefore the shaft. Activation of the friction clutch is maintained until the peak torque transmitted through the gear set has been reached. In addition, the method of the present invention includes reducing the load capacity of the friction clutch assembly while the transmission assembly is still in the low gear ratio defined by the gear set and so that the one way clutch assembly acts as the sole holding device on the ring gear of the gear set such that a non-synchronous shift from the low gear to the high gear may be effected.
In this way, the control strategy may be employed to provide load sharing between a friction clutch and a one-way clutch to provide low and reverse gear ratios. The control strategy may result in a reduced capacity one-way clutch that yields lower manufacturing costs and has reduced space requirements when compared to one-way clutches known in the related art. When used in this way, the control strategy results in smooth non-synchronous up-shift from first to second gears.
Other objects, features and advantages of the present invention will be readily appreciated as the same becomes better understood after reading the subsequent description taken in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a schematic diagram depicting a transmission illustrating a low friction clutch and one-way clutch to provide low and reverse gear ratios; and
FIG. 2
is a schematic representation of the friction clutch, one-way clutch and a planetary gear set to provide low and reverse gear ratios in the transmission of FIG.
1
.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
The control strategy of the present invention will be described in connection with a transmission which is schematically illustrated in
FIGS. 1 and 2
. However, those having ordinary skill in the art will appreciate that the control strategy of the present invention may be employed in numerous applications in a transmission.
One representative example of an advantageous use of the control strategy of the present invention is shown in connection with a transmission, schematically illustrated at
50
in FIG.
1
. The transmission
50
has a number of conventional components that are arranged to translate torque between a prime mover, such as an internal combustion engine (not shown) and the output of the transmission at various gear ratios. However, those having ordinary skill in the art will appreciate that the standard components of a transmission may be arranged in numerous ways to provide various gear ratios. Thus, the exact configuration of these components form no part of the present invention and are only discussed to better illustrate the salient features of the control strategy of the present invention.
To this end, the transmission
50
includes a torque converter, generally indicated at
52
, and a plurality of multi-plate friction disc clutches
54
,
56
,
58
,
60
,
62
,
63
or similar mechanisms that serve as holding mechanisms or brakes to translate torque between the primary transmission input shaft
64
and the primary transmission output shaft
66
acting through a plurality of planetary gear sets
68
,
70
, and
72
, as is commonly known in the art. The torque converter
52
includes an impeller assembly
74
operatively connected for rotation with the torque input member
76
from the internal combustion engine. A turbine assembly
78
is fluidly connected in driven relationship with the impeller assembly
74
. The torque connector also includes a stator assembly
80
. These assemblies together form a substantially toroidal flow passage for kinetic fluid in the torque converter
52
. Each assembly includes a plurality of blades or vanes that act to convert mechanical energy into hydrokinetic energy and back to mechanical energy. The stator assembly
80
of a conventional torque converter is locked against rotation in one direction but is free to spin about an axis in the direction of rotation of the impeller assembly
74
and the turbine assembly
78
. A one-way clutch
82
is often employed for this purpose. When the stator assembly
80
is locked against rotation, the torque is multiplied by the torque converter. During torque multiplication, the output torque is greater than the input torque for the torque converter
52
. In addition, conventional torque converters often employ clutches
84
interposed between the torque input member
76
and the turbine assembly
78
which are engaged and “lock up” at higher speed ratios (speed output over speed input). When the clutch
84
is locked up, there is a direct torque translation between the torque input member
76
and the transmission
50
through the turbine assembly
78
.
In the particular transmission
50
illustrated in
FIG. 1
, an underdrive clutch
54
, overdrive clutch
56
, reverse clutch
58
, fourth gear brake
60
, second gear brake
62
and a low/reverse gear brake
63
are employed as holding mechanisms to translate torque from the primary transmission input shaft
64
to various ones of the planetary gear sets
68
,
70
, and
72
, as the case may be. In turn, each of the planetary gear sets include a sun gear operatively coupled to one of the clutches identified above, a ring gear disposed about the respective sun gear, and a plurality of pinion or planetary gears disposed in meshing relationship between the respective sun and ring gears.
In the representative embodiment illustrated herein, a one-way, overrunning clutch assembly
10
is employed in connection with the planetary gear set
72
and the low/reverse gear brake
63
which together provide low and reverse gear ratios. This application is illustrated in FIG.
2
. The one-way clutch may be of any conventional type including an inner race, generally indicated at
12
, and an outer race, generally indicated at
18
, disposed concentrically about the inner race
12
. Engagement members, generally indicated at
24
, are disposed between the inner and outer races. The inner race
12
may include a plurality of torque translating teeth disposed about the circumference of the outer diameter of the inner race. The outer race may include a plurality of cavities or camming surfaces that are formed circumferentially about the inner diameter of the outer race. The engagement members may be supported within the cavities of the outer race and between the inner and outer races
12
,
18
, respectively. The engagement members may include pawls, sprags, or rollers. In addition, the engagement members may include a cage, along with biasing members, such as springs, to retain the pawls, sprags, or rollers between the inner and outer races,
12
,
18
as well as to selectively assist in the change of operational modes between torque translation and freewheeling actuation of the clutch, depending on the direction of rotation between the inner and outer races,
12
,
18
, respectively.
For example, the one-way clutch may be operated to provide torque translation in one direction and may freewheel in the opposite direction. In this case, torque is provided from the underdrive clutch
54
to the sun gear
86
that is splined to the shaft
88
. For a low gear, the outer race
18
is grounded to the transmission case
90
through the low one-way clutch
10
and the low/reverse gear brake
63
. To this end, the low/reverse gear brake
63
includes an annular clutch pack, generally indicated at
98
, which is illustrated in FIG.
2
. The clutch pack
98
is interposed between the outer race
18
and the transmission case
90
through a clutch housing
91
. Thus, the clutch pack
98
operates to connect and disconnect the outer race
18
of the clutch assembly
10
and the transmission case
90
for translating and interrupting torque therebetween. The clutch pack
98
includes a number of annular friction plates
100
splined at
102
to the outer race
18
. A plurality of annular discs
104
are splined at
106
to the friction clutch housing
91
and interleaved between the plates
100
. The plates
100
and friction discs
104
are also axially movable relative to their respective spline, outer race, and clutch housing to come into frictional engagement, thereby reducing or eliminating relative rotation between the plates
100
and discs
104
. A pair of retaining rings are typically mounted to the clutch housing
91
and are disposed on either side of the clutch pack
98
. A backing plate
110
may also be employed to cooperate with the retaining ring to limit axial movement of the plates
100
and friction discs
104
.
Axial movement of the adjacent plates and friction discs is achieved through the actuation of a piston assembly, generally indicated at
112
, which is supported in the clutch housing
91
. The piston assembly
112
and the clutch housing
91
cooperate to define an expandable chamber
114
between the piston assembly
112
and the clutch housing
91
. A source of pressurized fluid is in communication with the expandable chamber
114
via any suitable means. The piston assembly
112
is responsive to the pressure of fluid in the expandable chamber
114
to move between disengaged and engaged positions thereby actuating the clutch pack
98
to connect and disconnect the outer race
18
of the clutch assembly
10
with the transmission case
90
via the clutch housing
91
. The outer race
18
is also operatively connected to the ring gear
96
.
In low gears, the brake
63
is engaged and input torque is thus geared down through the pinion gears
92
supported on the carrier
94
and from the carrier
94
to the transmission output shaft
66
. In this way, a low gear ratio is effected at the output shaft
66
of the transmission
50
. On the other hand, when the brake
63
is released, the clutch
10
is capable of freewheeling in the opposite rotational direction.
When reverse gear is selected, the reverse clutch
58
is engaged and torque is translated to the ring gear
96
of the gear set
72
through the gear sets
68
and
70
. In this operational mode, the clutch
10
carries no torque. The friction brake
63
provides the reaction torque for gear set
72
. In the remaining gears
2
-
4
of the transmission illustrated in
FIG. 1
, the clutch
10
freewheels.
Pursuant to the control strategy of the present invention, in low gear torque load may be shared between the low/reverse friction clutch
63
and the low one-way clutch
10
. This may be accomplished by engaging the friction clutch
63
during vehicle launch and keeping it engaged until the peak torque has passed. Once the peak torque has been passed, the load capacity of the friction clutch
63
can be reduced to zero. More specifically, the piston assembly
112
may be moved to its disengaged position allowing the adjacent plates and friction discs to separate. In this operational mode, the one-way clutch
10
is acting to support the remaining drive torque. Thus, with only the one-way clutch
10
carrying a load at the time of the up-shift from first to second gear, a non-synchronous shift can be effected. In this way, the control strategy may be employed to provide load sharing between a friction clutch and a one-way clutch to provide low and reverse gear ratios. The control strategy may result in a reduced capacity one-way clutch that yields lower manufacturing costs and has reduced space requirements when compared to one-way clutches known in the related art. When used in this way, the control strategy results in smooth non-synchronous up-shift from first to second gears.
The invention has been described in an illustrative manner. It is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the invention may be practiced other than as specifically described.
Claims
- 1. A method of controlling an automotive transmission having at least one shaft, at least one gear set operatively coupled to the shaft and adapted to provide low and reverse gear ratios where the gear set includes a sun gear operatively coupled to a source of torque in the transmission assembly, a ring gear mounted for rotation about the sun gear and a plurality of pinion gears supported by a carrier for meshing rotation about the sun gear and between the ring gear and the sun gear with the carrier operatively coupled to the shaft, a friction clutch assembly having a clutch pack that acts as a holding device and a one way clutch assembly interposed between the friction clutch assembly and the gear set, said method including the steps of:selecting a low gear ratio provided by the gear set; actuating the friction clutch to ground the outer race of the one way clutch assembly and thus the ring gear to the transmission housing; providing torque to the sun gear to drive the pinion gears in meshing relationship about the sun gear to transfer torque at a reduced ratio to the carrier and the shaft; maintaining activation of the friction clutch assembly until the peak torque transmitted through the gear set has been reached; and reducing the load capacity of the friction clutch assembly while the transmission assembly is still in the low gear ratio defined by the gear set and so that the one way clutch assembly acts as the sole holding device on the ring gear of the gear set such that a non-synchronous shift from the low gear to the high gear may be effected.
- 2. The method of controlling an automotive transmission as set forth in claim 1 wherein the friction clutch is actuated to ground the outer race of the one way clutch assembly and thus the ring gear to the transmission housing during vehicle launch.
- 3. The method of controlling an automotive transmission as set forth in claim 1 wherein the step of reducing the load capacity of the friction clutch assembly includes the step of releasing the friction clutch assembly such that the clutch pack is disengaged.
- 4. The method of controlling an automotive transmission as set forth in claim 1 further including the step of shifting the transmission assembly to a higher gear.
- 5. The method of controlling an automotive transmission as set forth in claim 4 wherein the step of shifting the transmission to a higher gear includes shifting the transmission from first gear to second gear.
US Referenced Citations (16)