Motor vehicles – Power – Electric
Reexamination Certificate
2000-10-06
2003-12-02
Johnson, Brian L. (Department: 3618)
Motor vehicles
Power
Electric
Reexamination Certificate
active
06655485
ABSTRACT:
This application is based on Japanese Patent Application No. 11-288034 filed October 8, the contents of which are incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a hybrid-vehicle drive system, particularly to a hybrid-vehicle drive system having an engine and an electric motor which are mechanically connected to each other by a planetary gear device, and more particularly to a control when the vehicle drive mode is switched from a motor-drive mode to an engine-drive mode.
2. Discussion of Related Art
There is known a drive system for a hybrid automotive vehicle, which includes (a) an engine operated by combustion of a fuel to produce a drive force, (b) an electric motor, (c) an output member operatively connected to drive wheels, (d) a planetary gear device associated with the engine, electric motor and output member, for synthesizing and distributing a drive force or forces, and (e) a plurality of frictional coupling devices such as clutches and brakes for selectively connecting and disconnecting rotary elements of the planetary gear device to and from each other or a stationary member. An example of such a hybrid vehicle drive system is disclosed in JP-A-9-37411, wherein various vehicle drive modes are selectively established for driving the vehicle, by controlling the operating states of the clutches and brakes. For instance, the drive modes include a motor-drive mode in which the vehicle is driven by the electric motor as a drive power source, and an engine-drive mode in which the vehicle is driven by the engine as the vehicle drive source.
A hybrid-vehicle drive system as described above is not necessarily satisfactory in the manner of control in which the vehicle-drive is switched from the motor-drive mode to the engine-drive mode, when the clutch is engaged while the operating speed of the engine is relatively low. Namely, the known hybrid-vehicle drive system suffers from a reduced vehicle drive force when the clutch is engaged at a relatively low speed of the engine, for switching the vehicle drive mode from the motor-drive mode to the engine-drive mode.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a hybrid-vehicle drive system which is improved in the manner of control in which the vehicle drive mode is switched from the motor-drive mode to the engine-drive mode.
The above object may be achieved according to a first aspect of the present invention, which provides a hybrid-vehicle drive system, A hybrid drive system for an automotive vehicle, comprising: (a) an engine operable by combustion of a fuel to generate a drive force; (b) an electric motor; (c) an output member operatively connected to a drive wheel of the vehicle for driving the vehicle; (d) a planetary gear device having a first rotary element connected to the engine, a second rotary element connected to the electric motor, and a third rotary element; (e) a first clutch through which the second rotary member is connected to the output member; (f) a second clutch through which the third rotary member is connected to the output member; (g) forward-motor-drive control means for engaging the first clutch and releasing the second clutch to thereby establish a forward motor drive mode in which the automotive vehicle is driven in a forward direction by operation of the electric motor while the engine is at rest: (h) forward-engine-drive control means for engaging at least the second clutch to establish an engine-drive mode in which the automotive vehicle is driven in the forward direction by operation of the engine; and (i) second-clutch control means operable upon switching of a vehicle drive mode from the forward motor drive mode to the forward engine drive mode, for engaging the second clutch only after an operating speed of the engine has exceeded an operating speed of the electric motor.
In the hybrid drive system constructed according to the first aspect of this invention described above, the second-clutch control means is operated upon switching of the vehicle drive mode from the forward motor drive mode (established by the forward-motor-drive control means) to the engine drive mode (established by the forward-engine-drive control means). The second-clutch control means is arranged to engage the second clutch only after the operating speed of the engine has exceeded that of the electric motor. This arrangement permits a smooth transition of the vehicle drive mode to the engine drive mode, for thereby rapidly increasing the vehicle drive force, without a reduction of the vehicle drive force during the transition, where the transition to the engine drive mode is required due to an increase in the operating amount of the accelerator pedal, for example. That is, if the second clutch were engaged while the engine speed is lower than the motor speed, the vehicle drive force would be partly consumed by an increase of the engine speed to the motor speed.
In one preferred form of the hybrid drive system according to the first aspect of the invention described above, the second clutch is a hydraulically operated frictional coupling device capable of effecting a slipping engagement, and the second-clutch control means is adapted to initiate a gradual increase of a hydraulic pressure to be applied to the second clutch for engaging the second clutch, when the operating speed of the engine has exceeded the operating speed of the electric motor.
In another preferred form of the hybrid drive system described above, the electric motor consists of a motor/generator, and the planetary gear device is a double-pinion type planetary gear device having a sun gear as the first rotary element, a carrier as the second rotary element, and a ring gear as the third rotary element. In this instance, the sun gear is connected to the engine, while the carrier is connected to the motor/generator, and is further connected through the first clutch to the output member. Further, the ring gear is connected through the second clutch to the output member. For example, the output member may be an input shaft of an automatic transmission, which is preferably a continuously variable transmission of belt-and-pulley type. The planetary gear device may be of a single-pinion type, and the transmission may be a continuously variable transmission of other types such as toroidal type.
The motor/generator indicated above selectively functions as an electric generator as well as an electric motor. Preferably, the motor/generator is operated as the electric motor serving as a vehicle drive power source, and as the electric generator for applying a regenerative brake to the vehicle and generating an electric energy for charging an electric energy storing device, for instance. The motor/generator may be used as an electric motor only. The hybrid drive system may use both an electric motor and an electric generator as two separate units, or two separate motor/generators.
Each of the first and second clutches indicated above may be a hydraulically operated friction clutch of a single-disc type or multiple-disc type, which is frictionally engaged by a suitable hydraulic actuator such as a hydraulic cylinder. Alternatively, the first and second clutches may be electromagnetic clutches. At least one additional clutch and/or brake may be used in addition to the first and second clutches, as needed.
In the hybrid drive system wherein the second clutch is engaged only after the engine speed has exceeded the motor speed, the determination as to whether the engine speed has exceeded the motor speed may be effected by directly comparing these two speeds, or by comparing the operating speeds of selected two rotary elements of the planetary gear device. For instance, the planetary gear device having a first, a second and a third rotary element may be arranged such that when the speed of the first rotary element becomes higher than that of the second rotary element, the speed of the third rotary element becomes higher than that of the secondary ro
Endo Hiroatsu
Hoshiya Kazumi
Ito Masatoshi
Oba Hidehiro
Bottorff Christopher
Johnson Brian L.
Kenyon & Kenyon
Toyota Jidosha & Kabushiki Kaisha
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