Power plants – System having plural motors or having diverse types of... – Having condition responsive control
Reexamination Certificate
2003-02-28
2004-05-11
Richter, Sheldon J. (Department: 3748)
Power plants
System having plural motors or having diverse types of...
Having condition responsive control
C060S711000, C060S716000, C180S065230, C180S065510, C180S065600, C475S005000, C477S076000, C477S098000
Reexamination Certificate
active
06732526
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a hybrid automatic transmission suitable for a hybrid electric vehicle (HEV) mounting thereon a prime mover such as an internal combustion engine and at least one motor-generator, and specifically to the improvement of a hybrid automatic transmission having a differential device disposed between the prime mover and the motor-generator to steplessly vary a transmission gear ratio.
BACKGROUND ART
In recent years, there have been proposed and developed various hybrid electric vehicles equipped with hybrid automatic transmissions. One such hybrid automatic transmission has been disclosed in Japanese Patent Provisional Publication No. 2000-238555 (hereinafter is referred to as “JP2000-238555”).
FIG. 9
shows a schematic structural drawing of the hybrid automatic transmission as disclosed in JP2000-238555. The hybrid transmission shown in
FIG. 9
uses a simple planetary gearset
31
that is comprised of a sun gear
31
s
, a ring gear
31
r
, and a planet-pinion carrier
31
c
. Input torque from an internal combustion engine is transmitted via a transmission input shaft
32
to carrier
31
c
. On the one hand, a part of the input torque transmitted to carrier
31
c
is transmitted through sun gear
31
s
and a cylindrical hollow shaft (or a sun-gear shaft)
33
to a first motor-generator
34
serving as a generator. On the other hand, the remaining engine torque is transmitted through ring gear
31
r
, a sprocket
35
, a chain belt
36
, and a differential gear
39
to drive wheels
37
,
37
. The ring-gear shaft of ring gear
31
r
is connected to the rotor of a second motor-generator
38
serving as an electric motor.
SUMMARY OF THE INVENTION
Referring now to
FIGS. 10 and 11
, there are shown alignment charts representing the construction of the simple-planetary-gearset equipped hybrid automatic transmission system shown in FIG.
9
. Simple planetary gearset
31
is a differential device having a three-element, two-degree-of-freedom. Thus, second motor-generator
38
(serving as the motor) is connected directly to ring gear
31
r
serving as an output element to which a drive train containing differential gear device
39
is connected. As can be seen from the alignment chart of
FIG. 10
, first motor-generator
34
(serving as the generator) is connected to sun gear
31
s
that is placed in the opposite side of the output element (ring gear
31
r
) with respect to carrier
31
c
serving as an input element to which the engine is connected. The alignment chart of
FIG. 10
is obtained under a specific condition (in a motor propelled vehicle driving mode) where an engine speed Ne is “0”, an engine load torque Te is “0”, and the vehicle is propelled against a wheel load torque T
0
acting on road wheels by driving second motor-generator
38
(serving as the motor operating in the motor propelled vehicle driving mode) to produce a balanced motor-generator torque Tmg
20
at a forward motor-generator rotational speed Nmg
20
. Under the motor propelled vehicle driving mode, first motor-generator
34
(serving as the generator) is driven by a balanced torque Tmg
10
acting in a direction that a reverse motor-generator rotational speed Nmg
10
of first motor-generator
34
drops to “0”, so as to generate electricity. The generated electricity is supplied as a part of electric power used to drive second motor-generator
38
(the motor). The alignment chart of
FIG. 11
shows a transition from the motor propelled vehicle driving mode to an engine start-up mode. The collinear indicated by the broken line in
FIG. 11
corresponds to a lever on the alignment chart of the motor propelled vehicle driving mode shown in FIG.
10
. On the other hand, the collinear indicated by the solid line in
FIG. 11
corresponds to a lever on the alignment chart of the engine start-up mode in which, in order to increase engine speed Ne against the engine load torque Te, the reverse motor-generator rotational speed of first motor-generator
34
is reduced from the speed value Nmg
10
to a speed value Nmg
11
close to “0” by way of a balanced torque Tmg
11
acting on the first motor-generator. At this time, there are the following drawbacks.
Regarding the alignment chart of
FIG. 11
, the input rotation system connected to carrier
31
c
includes the engine whose inertia is great. Likewise, the input rotation system connected to ring gear
31
r
includes the differential gear device and drive wheels and thus the input rotation system has a great inertia. The center-of-gravity G of the lever on the alignment chart indicated by the broken line in
FIG. 11
is positioned between carrier
31
c
(or the engine) having the great inertia and ring gear
31
r
(or the output element) having the great inertia. For the reasons set forth above, when reducing the reverse motor-generator rotational speed of first motor-generator
34
from speed value Nmg
10
to speed value Nmg
11
for an engine start-up from the motor propelled vehicle driving mode, the lever on the alignment chart indicated by the broken line in
FIG. 11
is rotated about the center of gravity G and changed to the lever on the alignment chart indicated by the solid line in FIG.
11
. This means that a reaction force resulting from the great inertia of the input rotation system (the engine) acts to unintentionally reduce the rotational speed of the output rotation system containing the differential gear device and drive wheels, thus resulting in a temporary drop in vehicle speed. At this time, the driver may feel uncomfortable. To avoid this, a balanced motor-generator torque Tmg
21
of second motor-generator
38
has to be controlled or adjusted to a greater value than the balanced motor-generator torque Tmg
20
of the motor propelled vehicle driving mode shown in
FIG. 10
by an incremental torque needed to prevent the undesired vehicle speed drop, when starting up the engine from the motor propelled vehicle driving mode under the same wheel load torque T
0
. In this case, during the motor propelled vehicle driving mode, second motor-generator
38
has to be driven by the remaining electric power obtained by subtracting an electric power corresponding to the previously-noted incremental torque from a possible battery output power to enable engine start-up. The remaining electric power means a reduced vehicle driving performance during the motor propelled vehicle driving mode. To insure the vehicle driving performance greater than a predetermined level, a large capacity of car battery must be used. In addition to the above, owing to the layout of center of gravity G put between carrier
31
c
(or the engine) and ring gear
31
r
(or the output element), there is an increased tendency for engine torque fluctuations, which may occur during the engine start-up period, to be transmitted to the output element, thus resulting in the driver's uncomfortable feeling. To eliminate the driver's uncomfortable feeling, for instance, it is necessary to instantaneously control a generated torque of second motor-generator
38
directly connected to the output element responsively to positive and negative engine torque fluctuations. Actually, it is very difficult to momentarily adjust or control the generated torque of second motor-generator
38
, and therefore it is almost impossible to perfectly eliminate engine torque fluctuations. Such undesired torque fluctuations lead to the problem of deteriorated vehicle's driveability.
Accordingly, it is an object of the invention to provide a hybrid automatic transmission of a hybrid electric vehicle, which avoids the aforementioned disadvantages by improving a position of a center of gravity of a lever on an alignment chart of the hybrid automatic transmission.
In order to accomplish the aforementioned and other objects of the present invention, a hybrid automatic transmission of a hybrid electric vehicle mounting thereon a prime mover, first and second motor-generators and a drive train, and capable of steplessly varying a transmission gear ratio by controlling an o
Minagawa Yuusuke
Oshidari Toshikazu
Foley & Lardner
Nissan Motor Co,. Ltd.
Richter Sheldon J.
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