U.S. patent application number 14/273934 was filed with the patent office on 2015-11-12 for dual ratio constant mesh gearbox.
This patent application is currently assigned to ATIEVA, INC.. The applicant listed for this patent is Atieva, Inc.. Invention is credited to Jean-Philippe Gauthier.
Application Number | 20150323044 14/273934 |
Document ID | / |
Family ID | 53015715 |
Filed Date | 2015-11-12 |
United States Patent
Application |
20150323044 |
Kind Code |
A1 |
Gauthier; Jean-Philippe |
November 12, 2015 |
Dual Ratio Constant Mesh Gearbox
Abstract
A dual ratio constant mesh gearbox is provided that is suitable
for use with an automobile, and particularly well-suited for an
electric vehicle. The gearbox, which may be configured either as a
manual or automatic gearbox, utilizes a planetary gear set and a
pair of clutches to shift between under drive and direct drive
modes.
Inventors: |
Gauthier; Jean-Philippe;
(San Francisco, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Atieva, Inc. |
Redwood City |
CA |
US |
|
|
Assignee: |
ATIEVA, INC.
Redwood City
CA
|
Family ID: |
53015715 |
Appl. No.: |
14/273934 |
Filed: |
May 9, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14273822 |
May 9, 2014 |
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14273934 |
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14273667 |
May 9, 2014 |
9109666 |
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14273822 |
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Current U.S.
Class: |
475/153 ;
475/149 |
Current CPC
Class: |
F16H 2200/0021 20130101;
F16H 2063/3059 20130101; F16H 3/54 20130101; F16H 63/3043 20130101;
F16H 2061/0232 20130101; F16H 2200/2005 20130101; F16H 2200/2035
20130101; F16H 2200/2082 20130101; F16H 2200/0034 20130101; F16H
2057/087 20130101; F16H 61/686 20130101; F16H 61/0213 20130101;
F16H 2200/2066 20130101; F16H 57/10 20130101; F16H 2063/3006
20130101 |
International
Class: |
F16H 3/54 20060101
F16H003/54; F16H 61/686 20060101 F16H061/686; F16H 57/10 20060101
F16H057/10; F16H 61/02 20060101 F16H061/02 |
Claims
1. A dual ratio constant mesh gearbox, comprising: a housing; an
input drive shaft coupled to a vehicle propulsion electric motor; a
sun gear rigidly coupled to said input drive shaft; a ring gear; a
set of planetary gears interposed between said sun gear and said
ring gear, wherein said set of planetary gears are in constant mesh
with said sun gear and said ring gear; a planetary gear carrier
coupled to said set of planetary gears and to an output drive
shaft, wherein said output drive shaft is at least partially
contained within said housing; a sprag clutch assembly contained
within said housing, wherein said sprag clutch assembly permits
rotation of said ring gear in a first direction within said housing
and prevents rotation of said ring gear in a second direction
within said housing; a second clutch assembly separate and
independent of said sprag clutch assembly, wherein engaging said
second clutch assembly locks said ring gear to said sun gear, and
wherein disengaging said second clutch assembly unlocks said ring
gear from said sun gear; and a band brake translatable from at
least a first position to a second position, wherein said band
brake in said first position permits rotation of said ring gear
within said housing, and wherein said band brake in said second
position prevents rotation of said ring gear within said
housing.
2. The dual ratio constant mesh gearbox of claim 1, wherein said
output drive shaft is hollow, wherein said input drive shaft passes
through said output drive shaft, and wherein said input drive shaft
is coaxial with said output drive shaft.
3. The dual ratio constant mesh gearbox of claim 2, said second
clutch assembly comprising a multi-plate clutch assembly.
4. The dual ratio constant mesh gearbox of claim 2, said second
clutch assembly further comprising a pressure plate actuator,
wherein a position corresponding to said pressure plate actuator
determines whether said second clutch assembly is engaged or
disengaged.
5. The dual ratio constant mesh gearbox of claim 4, further
comprising a positioning motor coupled to said pressure plate
actuator, wherein said positioning motor controls said position of
said pressure plate actuator.
6. The dual ratio constant mesh gearbox of claim 2, wherein said
dual ratio constant mesh gearbox operates in a direct drive mode
when said second clutch assembly is engaged and said ring gear is
locked to said sun gear, wherein said sun gear and said set of
planetary gears and said ring gear rotate within said housing as a
single unit when said ring gear is locked to said sun gear, and
wherein said input drive shaft is directly coupled to said output
drive shaft causing said input and output drive shafts to rotate at
the same rate when said ring gear is locked to said sun gear.
7. The dual ratio constant mesh gearbox of claim 2, wherein said
dual ratio constant mesh gearbox operates in an under drive reverse
mode when said second clutch assembly is disengaged and said band
brake is in said second position, wherein reverse input torque
applied by said vehicle propulsion electric motor to said input
drive shaft when said dual ratio constant mesh gearbox is operating
in said under drive reverse mode generates a reaction torque on
said ring gear in said first direction, wherein rotation of said
ring gear in said first direction is permitted by said sprag clutch
and prevented by said band brake in said second position thereby
causing reverse vehicle torque to be applied to at least one
vehicle wheel by said planetary gear carrier and said output drive
shaft.
8. The dual ratio constant mesh gearbox of claim 2, wherein said
dual ratio constant mesh gearbox operates in an under drive mode
when said second clutch assembly is disengaged and said ring gear
is unlocked from said sun gear, wherein forward input torque
applied by said vehicle propulsion electric motor to said input
drive shaft generates a reaction torque on said ring gear in said
second direction, wherein rotation of said ring gear in said second
direction is prevented by said sprag clutch assembly causing
forward vehicle torque to be applied to at least one vehicle wheel
by said planetary gear carrier and said output drive shaft.
9. The dual ratio constant mesh gearbox of claim 2, further
comprising: a controller coupled to said vehicle propulsion
electric motor; a motor speed sensor coupled to said controller;
and an output drive shaft speed sensor coupled to said controller,
wherein upon an initiation of a downshift from a direct drive mode
to an under drive mode said controller is configured to increase a
motor speed corresponding to said vehicle propulsion electric motor
based on a current output drive shaft speed and an under drive gear
ratio.
10. The dual ratio constant mesh gearbox of claim 2, further
comprising: a controller coupled to said vehicle propulsion
electric motor; a motor speed sensor coupled to said controller;
and an output drive shaft speed sensor coupled to said controller,
wherein upon an initiation of an upshift from an under drive mode
to a direct drive mode said controller is configured to decrease a
motor speed corresponding to said vehicle propulsion electric motor
based on a current output drive shaft speed.
11. The dual ratio constant mesh gearbox of claim 2, further
comprising: a pressure plate actuator, wherein a position
corresponding to said pressure plate actuator determines whether
said second clutch assembly is engaged or disengaged; a positioning
motor coupled to said pressure plate actuator, wherein said
positioning motor controls said position of said pressure plate
actuator; a controller coupled to said vehicle propulsion electric
motor and to said positioning motor; and a motor speed sensor
coupled to said controller, wherein said controller is configured
to automatically upshift from an under drive mode to a direct drive
mode and configured to automatically downshift from said direct
drive mode to said under drive mode based on a current motor speed
and a set of preprogrammed shift instructions, wherein said dual
ratio constant mesh gearbox operates in said under drive mode when
said second clutch assembly is disengaged and said ring gear is
unlocked from said sun gear, and wherein said dual ratio constant
mesh gearbox operates in a direct drive mode when said second
clutch assembly is engaged and said ring gear is locked to said sun
gear.
12. The dual ratio constant mesh gearbox of claim 11, further
comprising a drive mode selector switch coupled to said controller,
wherein said drive mode selector switch allows selection between a
plurality of selectable drive modes, wherein corresponding to each
of said plurality of selectable drive modes is one of a plurality
of shift instruction subsets, and wherein said set of preprogrammed
shift instructions is comprised of said plurality of shift
instruction subsets.
13. The dual ratio constant mesh gearbox of claim 11, further
comprising a drive mode over-ride switch coupled to said
controller, wherein activation of said drive mode over-ride switch
alters said set of preprogrammed shift instructions.
14. The dual ratio constant mesh gearbox of claim 13, wherein
activation of said drive mode over-ride switch forces said dual
ratio constant mesh gearbox to remain within said direct drive
mode.
15. The dual ratio constant mesh gearbox of claim 11, further
comprising: a second positioning motor coupled to said band brake
and to said controller, wherein said second positioning motor
controls whether said band brake is in said first position or said
second position; and a reverse mode selector switch, wherein said
reverse mode selector switch is configured to be user selectable,
wherein said controller is configured to shift into a reverse drive
mode when said reverse mode selector switch is selected, wherein
said dual ratio constant mesh gearbox operates in said reverse
drive mode when said second clutch assembly is disengaged and said
band brake is in said second position.
16. The dual ratio constant mesh gearbox of claim 2, further
comprising: a pressure plate actuator, wherein a position
corresponding to said pressure plate actuator determines whether
said second clutch assembly is engaged or disengaged; a positioning
motor coupled to said pressure plate actuator, wherein said
positioning motor controls said position of said pressure plate
actuator; a controller coupled to said vehicle propulsion electric
motor and to said positioning motor; and an output drive shaft
speed sensor coupled to said controller, wherein said controller is
configured to automatically upshift from an under drive mode to a
direct drive mode and configured to automatically downshift from
said direct drive mode to said under drive mode based on a current
output drive shaft speed and a set of preprogrammed shift
instructions, wherein said dual ratio constant mesh gearbox
operates in said under drive mode when said second clutch assembly
is disengaged and said ring gear is unlocked from said sun gear,
and wherein said dual ratio constant mesh gearbox operates in a
direct drive mode when said second clutch assembly is engaged and
said ring gear is locked to said sun gear.
17. The dual ratio constant mesh gearbox of claim 16, further
comprising a drive mode selector switch coupled to said controller,
wherein said drive mode selector switch allows selection between a
plurality of selectable drive modes, wherein corresponding to each
of said plurality of selectable drive modes is one of a plurality
of shift instruction subsets, and wherein said set of preprogrammed
shift instructions is comprised of said plurality of shift
instruction subsets.
18. The dual ratio constant mesh gearbox of claim 16, further
comprising a drive mode over-ride switch coupled to said
controller, wherein activation of said drive mode over-ride switch
alters said set of preprogrammed shift instructions.
19. The dual ratio constant mesh gearbox of claim 18, wherein
activation of said drive mode over-ride switch forces said dual
ratio constant mesh gearbox to remain within said direct drive
mode.
20. The dual ratio constant mesh gearbox of claim 2, further
comprising: a pressure plate actuator, wherein a position
corresponding to said pressure plate actuator determines whether
said second clutch assembly is engaged or disengaged; a positioning
motor coupled to said pressure plate actuator, wherein said
positioning motor controls said position of said pressure plate
actuator; a controller coupled to said vehicle propulsion electric
motor and to said positioning motor; an under drive mode selector
switch, wherein said under drive mode selector switch is configured
to be user selectable; and a direct drive mode selector switch,
wherein said direct drive mode selector switch is configured to be
user selectable, wherein said controller is configured to shift
into an under drive mode when said under drive mode selector switch
is selected, wherein said controller is configured to shift into a
direct drive mode when said direct drive mode selector switch is
selected, wherein said dual ratio constant mesh gearbox operates in
said under drive mode when said second clutch assembly is
disengaged and said ring gear is unlocked from said sun gear, and
wherein said dual ratio constant mesh gearbox operates in a direct
drive mode when said second clutch assembly is engaged and said
ring gear is locked to said sun gear.
21. The dual ratio constant mesh gearbox of claim 20, further
comprising: a second positioning motor coupled to said band brake
and to said controller, wherein said second positioning motor
controls whether said band brake is in said first position or said
second position; and a reverse mode selector switch, wherein said
reverse mode selector switch is configured to be user selectable,
wherein said controller is configured to shift into a reverse drive
mode when said reverse mode selector switch is selected, wherein
said dual ratio constant mesh gearbox operates in said reverse
drive mode when said second clutch assembly is disengaged and said
band brake is in said second position.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 14/273,822, filed 9 May 2014, which is a
continuation-in-part of U.S. patent application Ser. No.
14/273,667, filed 9 May 2014, the disclosures of which are
incorporated herein by reference for any and all purposes.
FIELD OF THE INVENTION
[0002] The present invention relates generally to a vehicle and,
more particularly, to a dual speed gearbox suitable for use with an
electric motor.
BACKGROUND OF THE INVENTION
[0003] In a typical electric vehicle a single speed gearbox is used
between the traction motor and the differential. The ability to use
a single speed gearbox rather than the multi-speed gearbox required
in a conventional vehicle is the result of the wide useful
operating range, both in terms of power and torque, of an electric
motor versus that of an internal combustion engine.
[0004] While a single speed gearbox may be used with an electric
vehicle, its use is not without drawbacks. For example, because of
the maximum speed limit of the motor and the requirement in a high
performance car to reach a certain top speed, the gear ratio is
typically chosen to be longer than what would be optimal to provide
crisp initial acceleration from a standstill. Additionally, due to
torque ripple and vibrations, motor torque may be limited at very
low rotating speeds. As a result, initial acceleration from a
standstill in a typical electric vehicle is typically more sluggish
than what would be expected given the drivetrain's
characteristics.
[0005] Accordingly, what is needed is a dual speed gearbox that may
be optimized for the operating characteristics of an electric
motor, thereby providing the desired level of performance
throughout the vehicle's operating range. The present invention
provides such a dual speed gearbox.
SUMMARY OF THE INVENTION
[0006] The present invention provides a dual ratio constant mesh
gearbox suitable for use with an automobile, and in particular
suited for an electric vehicle. The gearbox is comprised of (i) a
housing, (ii) an input drive shaft coupled to the vehicle's
propulsion electric motor, (iii) an externally toothed sun gear
rigidly coupled to the input drive shaft, (iv) an internally
toothed ring gear, (v) a set of planetary gears interposed between
the sun and ring gears, where the set of planetary gears are in
constant mesh with both the sun and ring gears, (vi) a planetary
gear carrier coupled to the set of planetary gears and to an output
drive shaft, where the output drive shaft is at least partially
contained within the housing, (vii) a sprag clutch assembly
contained within the housing, where the sprag clutch permits
rotation of the ring gear in a first direction while preventing
rotation of the ring gear in a second direction, (viii) a second
clutch assembly separate and independent of the sprag clutch
assembly, where engaging the second clutch assembly locks the ring
gear to the sun gear, and disengaging the second clutch assembly
unlocks the ring gear from the sun gear, and (ix) a band brake
translatable from at least a first position to a second position,
where the band brake in the first position permits rotation of the
ring gear within the housing, and where the band brake in the
second position prevents rotation of the ring gear within the
housing. The gearbox may use a hollow output drive shaft and be
configured to pass the input drive shaft through the hollow output
drive shaft, where the input and output drive shafts are coaxial.
The second clutch assembly is preferably comprised of a multi-plate
clutch assembly. The second clutch assembly may include a pressure
plate actuator where the position of the pressure plate actuator
determines whether the second clutch assembly is engaged or
disengaged; further, a positioning motor may be coupled to the
pressure plate actuator, where the positioning motor controls the
position of the pressure plate actuator.
[0007] In one aspect, the gearbox operates in a direct drive mode
when the second clutch assembly is engaged and the ring gear is
locked to the sun gear, resulting in the sun gear, the ring gear
and the set of planetary gears rotating within the housing as a
single unit and causing the input drive shaft to be directly
coupled to the output drive shaft and for the two drive shafts to
rotate at the same rate.
[0008] In another aspect, the gearbox operates in an under drive
reverse mode when the second clutch assembly is disengaged and the
band brake is in the second position. As a result, when reverse
input torque is applied to the input drive shaft a reaction torque
is generated on the ring gear in the first direction. While
rotation of the ring gear in the first direction is permitted by
the sprag clutch assembly, ring gear rotation is prevented by the
band brake being in the second position, thereby causing reverse
vehicle torque to be applied to the vehicle's wheel(s) when reverse
input torque is applied to the input drive shaft.
[0009] In another aspect, the gearbox operates in an under drive
mode when the second clutch assembly is disengaged and the ring
gear is unlocked from the sun gear. In this mode, forward input
torque applied to the input drive shaft generates a reaction torque
on the ring gear in the second direction, where rotation of the
ring gear in the second direction is prevented by the sprag clutch
assembly. As a result, forward input torque applied to the input
drive shaft causes forward vehicle torque to be applied to the
vehicle's wheel(s) via the planetary gear carrier and the output
drive shaft.
[0010] In another aspect, a controller coupled to the vehicle's
propulsion motor is also coupled to a motor speed sensor and an
output drive shaft speed sensor. When a downshift from the direct
drive mode to the under drive mode is initiated, the controller is
configured to increase the motor's speed based on the current
output drive shaft speed and the under drive gear ratio.
[0011] In another aspect, a controller coupled to the vehicle's
propulsion motor is also coupled to a motor speed sensor and an
output drive shaft speed sensor. When an upshift from the under
drive mode to the direct drive mode is initiated, the controller is
configured to decrease the motor's speed based on the current
output drive shaft speed and the under drive gear ratio.
[0012] In another aspect, the gearbox may further comprise (i) a
pressure plate actuator where the position of the pressure plate
actuator determines whether the second clutch assembly is engaged
or disengaged, (ii) a positioning motor coupled to the pressure
plate actuator that controls the position of the pressure plate
actuator, (iii) a controller coupled to the vehicle's propulsion
motor and to the positioning motor, and (iv) a motor speed sensor
coupled to the controller, where the controller is configured to
automatically upshift from the under drive mode to the direct drive
mode and to automatically downshift from the direct drive mode to
the under drive mode based on current motor speed and a set of
preprogrammed shift instructions, where the gearbox operates in the
under drive mode when the second clutch assembly is disengaged and
the ring gear is unlocked from the sun gear, and where the gearbox
operates in the direct drive mode when the second clutch assembly
is engaged and the ring gear is locked to the sun gear. The gearbox
may include a drive mode selector switch for selecting among a
plurality of selectable drive modes, where each selectable drive
mode corresponds to one of a plurality of shift instruction
subsets, and where the set of preprogrammed shift instructions is
comprised of the plurality of shift instruction subsets. The
gearbox may include a drive mode over-ride switch, where activation
of the drive mode over-ride switch alters the set of preprogrammed
shift instructions, for example forcing the gearbox to remain
within the direct drive mode. The gearbox may further include (i) a
second positioning motor coupled to the band brake and to the
controller, where the second positioning motor controls whether the
band brake is in the first or second position, and (ii) a reverse
mode selector switch configured to be user selectable, where the
controller is configure to shift into a reverse drive mode when the
reverse mode selector switch is selected, and where the gearbox
operates in the reverse drive mode when the second clutch assembly
is disengaged and the band brake is in the second position.
[0013] In another aspect, the gearbox may further comprise (i) a
pressure plate actuator where the position of the pressure plate
actuator determines whether the second clutch assembly is engaged
or disengaged, (ii) a positioning motor coupled to the pressure
plate actuator that controls the position of the pressure plate
actuator, (iii) a controller coupled to the vehicle's propulsion
motor and to the positioning motor, and (iv) an output drive shaft
speed sensor coupled to the controller, where the controller is
configured to automatically upshift from the under drive mode to
the direct drive mode and to automatically downshift from the
direct drive mode to the under drive mode based on current output
drive shaft speed and a set of preprogrammed shift instructions,
where the gearbox operates in the under drive mode when the second
clutch assembly is disengaged and the ring gear is unlocked from
the sun gear, and where the gearbox operates in the direct drive
mode when the second clutch assembly is engaged and the ring gear
is locked to the sun gear. The gearbox may include a drive mode
selector switch for selecting among a plurality of selectable drive
modes, where each selectable drive mode corresponds to one of a
plurality of shift instruction subsets, and where the set of
preprogrammed shift instructions is comprised of the plurality of
shift instruction subsets. The gearbox may include a drive mode
over-ride switch, where activation of the drive mode over-ride
switch alters the set of preprogrammed shift instructions, for
example forcing the gearbox to remain within the direct drive mode.
The gearbox may further include (i) a second positioning motor
coupled to the band brake and to the controller, where the second
positioning motor controls whether the band brake is in the first
or second position, and (ii) a reverse mode selector switch
configured to be user selectable, where the controller is configure
to shift into a reverse drive mode when the reverse mode selector
switch is selected, and where the gearbox operates in the reverse
drive mode when the second clutch assembly is disengaged and the
band brake is in the second position.
[0014] In another aspect, the gearbox may further comprise (i) a
pressure plate actuator where the position of the pressure plate
actuator determines whether the second clutch assembly is engaged
or disengaged, (ii) a positioning motor coupled to the pressure
plate actuator that controls the position of the pressure plate
actuator, (iii) a controller coupled to the vehicle's propulsion
motor and to the positioning motor, (iv) a user selectable under
drive mode selector switch which, when selected, causes the
controller to shift into the under drive mode, and (v) a user
selectable direct drive mode selector switch which, when selected,
causes the controller to shift into the direct drive mode. The
gearbox operates in the under drive mode when the second clutch
assembly is disengaged and the ring gear is unlocked from the sun
gear, and the gearbox operates in the direct drive mode when the
second clutch assembly is engaged and the ring gear is locked to
the sun gear. The gearbox may further include (i) a second
positioning motor coupled to the band brake and to the controller,
where the second positioning motor controls whether the band brake
is in the first or second position, and (ii) a reverse mode
selector switch configured to be user selectable, where the
controller is configure to shift into a reverse drive mode when the
reverse mode selector switch is selected, and where the gearbox
operates in the reverse drive mode when the second clutch assembly
is disengaged and the band brake is in the second position.
[0015] A further understanding of the nature and advantages of the
present invention may be realized by reference to the remaining
portions of the specification and the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] It should be understood that the accompanying figures are
only meant to illustrate, not limit, the scope of the invention and
should not be considered to be to scale. Additionally, the same
reference label on different figures should be understood to refer
to the same component or a component of similar functionality.
[0017] FIG. 1 provides a cross-sectional view of a dual ratio
gearbox in accordance with the invention;
[0018] FIG. 2 provides a cross-sectional view of the gear assembly
taken along plane A-A of FIG. 1;
[0019] FIG. 3 provides a view of the dual ratio gearbox of FIGS. 1
and 2, configured to provide under drive, reverse torque to the
wheels of the vehicle;
[0020] FIG. 4 provides a cross-sectional view of the gear assembly
taken along plane B-B of FIG. 3;
[0021] FIG. 5 provides a view of the dual ratio gearbox of FIGS.
1-4, configured to provide direct drive torque to the wheels of the
vehicle;
[0022] FIG. 6 provides a view of the dual ratio gearbox of FIGS.
1-5, with the inclusion of sensors to monitor input and output
drive shaft speed;
[0023] FIG. 7 provides a view of the dual ratio gearbox of FIG. 6,
with the inclusion of a drive mode over-ride sensor; and
[0024] FIG. 8 provides a view of the dual ratio gearbox of FIG. 6
configured for manual drive selection.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
[0025] As used herein, the singular forms "a", "an" and "the" are
intended to include the plural forms as well, unless the context
clearly indicates otherwise. The terms "comprises", "comprising",
"includes", and/or "including", as used herein, specify the
presence of stated features, process steps, operations, elements,
and/or components, but do not preclude the presence or addition of
one or more other features, process steps, operations, elements,
components, and/or groups thereof. As used herein, the term
"and/or" and the symbol "/" are meant to include any and all
combinations of one or more of the associated listed items.
Additionally, while the terms first, second, etc. may be used
herein to describe various steps, calculations, or components,
these steps, calculations, or components should not be limited by
these terms, rather these terms are only used to distinguish one
step, calculation, or component from another. For example, a first
calculation could be termed a second calculation, and, similarly, a
first step could be termed a second step, and, similarly, a first
component could be termed a second component, without departing
from the scope of this disclosure.
[0026] The gearbox described and illustrated herein is generally
designed for use with devices requiring a two-speed transmission,
and more specifically, for a vehicle using an electric motor, e.g.,
an electric vehicle (EV). As shown in FIG. 1, input drive shaft 101
of gearbox 100 is coupled to the vehicle's electric motor 103 while
output shaft 105 is coupled to one or more wheels of the vehicle.
Although output shaft 105 may be coupled directly to the vehicle's
wheels, preferably it is coupled via a differential, not shown, to
the wheels. In FIG. 1, output shaft 105 is shown coupled to an
output gear 107. Note that output shaft 105 may also be coupled to
an output gear located within gearbox housing 109, for example at a
location 111.
[0027] Input drive shaft 101, which passes into gearbox housing 109
through hollow output shaft 105, is rigidly coupled to a sun gear
111. Although sun gear 111 and input drive shaft 101 may be
fabricated as a single component, i.e., from a single piece of
stock, preferably and as illustrated a spline gear coupling is used
to rigidly couple input drive shaft 101 to sun gear 111. A ring
gear 113 is coupled to a ring gear carrier 115. Preferably ring
gear 113 and ring gear carrier 115 are fabricated as a single
component, i.e., from a single piece of stock. A clutch assembly
comprised of a sprag clutch 117 allows ring gear 113 to only rotate
in a single direction within housing 109. As described in detail
below, sprag clutch assembly 117 allows the forward driving torque
output of gearbox 100 to be adjusted regardless of whether the
gearbox is operating in the indirect or direct drive mode, while
only allowing reverse driving torque output when the gearbox is in
the indirect drive mode.
[0028] Interposed between ring gear 113 and sun gear 111, and in
constant mesh with ring gear 113 and sun gear 111, are planetary
gears 119. A planetary gear carrier 121 is coupled to each of the
planetary gears 119 via bearings 201 and pins 123.
[0029] Gearbox 100 also includes a second clutch assembly, separate
and independent of sprag clutch assembly 117. The clutch assembly,
which is preferably a multi-plate clutch, includes pressure plate
125, discs 127 that are coupled to sun gear 111, plates 129 that
are coupled to ring gear 113 and ring gear carrier 115, and
compression spring 131. A spring mounting plate 130 is coupled to
sun gear 111 using a plurality of bolts 132. Although a variety of
techniques, including a hydraulic control system, may be used to
operate the second clutch assembly, preferably pressure plate
actuator 133 is controlled using an electric positioning motor 135
as shown.
[0030] Gearbox 100 also includes a band brake that is used to
prevent rotation of ring gear 113 in the direction of rotation
allowed by sprag clutch assembly 117. The band brake includes brake
band 137 which surrounds ring gear 113 and its assembly. An
actuator 139, preferably an electric motor, is coupled to brake
band 137 via brake band coupling member 141. Preferably operation
of brake band actuator 139 is controlled by controller 143. In the
preferred embodiment, motor controller 143 is also coupled to, and
controls, vehicle drive motor 103 and clutch controller 135. In
FIG. 1, shaft bearings 145 and 147 are also shown.
[0031] A cross-sectional view of the gear assembly, taken along
plane A-A, is shown in FIG. 2. Note that for clarity the individual
gear teeth of sun gear 111, planetary gears 119 and ring gear 113
are not shown, nor are the splines/grooves used to couple input
drive shaft 101 to sun gear 111. This view of the planetary gear
system also shows brake band 137, along with band brake anchor 203,
actuator 139, and brake band coupling member 141.
[0032] Under Drive Mode--Forward Vehicle Travel
[0033] In order to achieve forward vehicle motion with the gearbox
in under drive, controller 144 uses motor 135 to position actuator
133 and pressure plate 125 such that the clutch assembly is
disengaged as shown in FIG. 1. As a result, sun gear 111 is allowed
to rotate independently of ring gear 113. On forward torque
transmission, the input torque applied by motor 103 to input drive
shaft 101, and thus to sun gear 111, generates a reaction torque on
ring gear 113 in the direction that is locked by sprag clutch
assembly 117. As a result, forward torque is transmitted to the
wheels of the vehicle by planetary gear carrier 121 and output
drive shaft 105.
[0034] Under Drive Mode--Reverse Vehicle Travel
[0035] When the input torque applied by motor 103 to input drive
shaft 101 and sun gear 111 is reversed, sprag clutch assembly 117
no longer locks the ring gear to housing 109. Accordingly in order
to achieve reverse vehicle travel, controller 143 engages band
brake 137 using actuator 139 while keeping the clutch assembly
disengaged using motor 135, actuator 133 and pressure plate 125.
Engaging band brake 143 locks ring gear 133 to housing 109. Then
when reverse torque is applied by drive motor 103 to input drive
shaft 101, ring gear 113 is locked into position relative to
housing 109 and reverse torque is transmitted to the wheels of the
vehicle by planetary gear carrier 121 and output drive shaft 105.
Therefore in reverse, rather than using sprag clutch assembly 117
to lockup ring gear 113, band brake 137 locks the ring gear into
place. As a result of this configuration, both forward and reverse
torque can be applied to the vehicle's wheels when gearbox 100 is
operating in the under drive mode. FIGS. 3 and 4 provide similar
views of gearbox 100 as shown in FIGS. 1 and 2 with band brake 137
engaged.
[0036] Direct Drive Mode--Forward Vehicle Travel
[0037] In order to achieve forward vehicle motion with the gearbox
in direct drive, controller 143 uses motor 135 to position actuator
133 and pressure plate 125 such that the clutch assembly is engaged
as shown in FIG. 5. As a result, ring gear 113 is locked to sun
gear 111 and the entire planetary gear assembly, i.e., gears 111,
113 and 119 will turn as a single unit. As long as ring gear 113 is
rotating in the forward direction, sprag clutch assembly 117
permits motor 103 to apply either forward or reverse torque to
input drive shaft 101.
[0038] During acceleration, shifting from under drive to direct
drive using gearbox 100 is very smooth. As described above, when
the gearbox is in the under drive mode and forward torque is being
applied, sprag clutch assembly 117 prevents ring gear 113 from
rotating. While shifting to direct drive using the multi-plate
clutch assembly (e.g., pressure plate 125, discs 127, plates 129,
compression spring 131, and pressure plate actuator 133), the sprag
clutch 117 continues to insure that the input torque applied by
motor 103 generates forward torque at the wheels. As the clutch
assembly becomes engaged, a friction zone is created that shifts
the gearbox smoothly towards the direct drive mode. The shift to
direct drive is completed once ring gear 113 and sun gear 111 are
synchronized.
[0039] When gearbox 100 downshifts from direct drive to under drive
while the car is accelerating, controller 143 allows the
multi-plate clutch assembly to slip while bringing motor 103 up to
the necessary speed for the under drive gear ratio. Preferably
controller 143 monitors both motor speed using sensor 601 and
output drive shaft speed using sensor 603 (see FIG. 6), thus
allowing controller 143 to quickly and efficiently increase the
speed of motor 103 based on the under drive gear ratio and the
current vehicle speed.
[0040] While coasting, when gearbox 100 shifts from under drive to
direct drive the change in rotational speed of motor 103 may lead
to lurching or shuddering as the multi-plate clutch assembly
becomes engaged, and before the ring gear 113 and sun gear 111 are
synchronized. Drive train shuddering may be aggravated during this
period if motor 103 undershoots the desired motor speed.
Accordingly, in at least one preferred embodiment controller 143
monitors both motor speed and output drive shaft speed using
sensors 601 and 603 as illustrated in FIG. 6. By monitoring both
the motor speed and the output drive shaft speed, when the shift
from under drive to direct drive is initiated, controller 143 is
able to quickly and efficiently lower the speed of motor 103 to
match that of the output drive shaft, thereby minimizing motor
speed mismatch and preventing undershoot. Similarly, downshifting
from direct drive to under drive requires controller 143 to quickly
and efficiently increase the speed of motor 103 in order to
minimize mismatch and the shuddering that can accompany such
mismatch.
[0041] In a typical configuration, shifting between under drive and
direct drive is automatic and performed in accordance with a set of
preprogrammed instructions that are either incorporated into
controller 143 or input into a separate processor that is coupled
to controller 143. Shifting is preferably based on motor speed, as
monitored by sensor 601, although other characteristics such as
vehicle speed may be used to determine when to shift between drive
modes. Additionally in at least one embodiment of an automatic
gearbox, and as illustrated in FIG. 7, the shift points between
under drive and direct drive may be altered based on the input of
switch 701. Switch 701 may monitor accelerator pedal movement, thus
allowing the driver to alter shifting characteristics based on how
rapidly and/or how far the accelerator pedal is depressed.
Alternately, switch 701 may be a drive mode selector that allows
the user to vary the drive mode, and thus the shifting
characteristics, between multiple modes (e.g., sport, normal and
efficiency).
[0042] Many drivers find it difficult to drive over hilly terrain.
Such terrain is especially problematic when coupled with the stop
and go traffic conditions associated with driving in the city.
Under these conditions, accelerating away from a stop when the stop
is on an uphill incline often leads to at least some backwards
vehicle roll, which may make the driver nervous as well as
potentially causing a minor collision if the vehicle rolls
backwards and hits the car behind it. Accordingly, in one
embodiment of the invention switch 701 is associated with a gearbox
over-ride function. When selected, the gearbox remains in direct
drive regardless of motor and/or vehicle speed. Although selecting
this feature reduces acceleration from a dead stop, due to the
locking effect of sprag clutch assembly 117, the car will not roll
backwards when the brake is released, even when stopped on a steep
incline. In an alternate embodiment, switch 701 monitors vehicle
inclination and automatically switches the gearbox, via controller
143, to direct drive when the car is stopped on an uphill incline
greater than a preset angle.
[0043] In an alternate embodiment illustrated in FIG. 8, the dual
ratio gearbox of the invention is configured to be used as a manual
gearbox. In this configuration controller 143 is coupled to a drive
mode selector 801, where the drive mode selector 801 determines
when to shift between under drive and direct drive. Drive mode
selector 801 may be designed to look like a typical gear shift
selector; alternately, drive mode selector 801 may be comprised of
a button, toggle or other switching means mounted on the dash,
central console or steering wheel; alternately, drive mode selector
801 may be comprised of a button or lever mounted to the floor,
thus allowing the driver to shift gears by depressing or otherwise
engaging the floor mounted switch means.
[0044] Systems and methods have been described in general terms as
an aid to understanding details of the invention. In some
instances, well-known structures, materials, and/or operations have
not been specifically shown or described in detail to avoid
obscuring aspects of the invention. In other instances, specific
details have been given in order to provide a thorough
understanding of the invention. One skilled in the relevant art
will recognize that the invention may be embodied in other specific
forms, for example to adapt to a particular system or apparatus or
situation or material or component, without departing from the
spirit or essential characteristics thereof. Therefore the
disclosures and descriptions herein are intended to be
illustrative, but not limiting, of the scope of the invention.
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