Machine element or mechanism – Gearing – Interchangeably locked
Reexamination Certificate
2002-09-30
2004-01-27
Wright, Dirk (Department: 3681)
Machine element or mechanism
Gearing
Interchangeably locked
Reexamination Certificate
active
06681650
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a driving state switching unit with a synchro-mechanism that employs the synchro-mechanism to perform switching of a driving state.
BACKGROUND ART
In part-time four-wheel-drive vehicles capable of switching of a two-wheel-drive state (2WD) and a four-wheel-drive state (4WD), in the case where 2WD is selected, a transfer is constructed such that the transmission of power to either wheel side (generally front wheels) of the front and rear wheel sides is disconnected and that only the other wheel side (generally rear wheels) is driven. At this time, on the front wheel side where the transmission of power is disconnected, power loss will become greater in the case where all parts in the front driving system (e.g., a front propeller shaft, a front differential gear, a front axle shaft, etc.) rotate, as compared with the case where only tires and wheels are rotating.
Hence, free wheel mechanisms have hitherto been employed which are constructed so as to reduce power loss during 2WD and enhance fuel consumption, by releasing the connection between the front wheels and the front axle shaft, or by disconnecting the front axle front, during 2WD.
Also, in part-time four-wheel driving vehicles, in which a center differential unit with a limited slip differential mechanism is equipped in a transfer, driving performance as a four-wheel-drive (4WD) car, as well as conventional direct 4WD which is obtained by locking the center differential unit, is assured by setting the center differential unit free so that tight corner breaking is suppressed.
As described above, in the case of the four-wheel-drive vehicle, equipped with the free wheel mechanism, and capable of selecting center diff-4WD, there is a need to lock the free wheel mechanism being set free during 2WD, in switching the transfer from 2WD to center diff-4WD.
In the case where switching to center diff-4WD in the transfer is completed prior to locking of the free wheel mechanism, however, if a starting operation is performed before the free wheel mechanism is locked, the center differential unit will go to a idling state without transmitting engine power to the front wheels. As a result, the durability of the limited slip differential mechanism will be deteriorated and also a vehicle's driving stability will be lost.
Also, in the case where the free wheel mechanism has not been locked, there is a possibility that synchronization of the front driving system (driving system on a non-driving wheel side) will collapse in the course of a switch from 2WD to center diff-4WD. If switching is performed with the synchronization of the front driving system being in a collapsed state, there is a possibility that at the clutch parts of the synchro-mechanism, gear grind will take place and overloading be given.
Because of this, when switching the transfer from 2WD to center diff-4WD, the free wheel mechanism needs to be locked first, and switching to center diff-4WD needs to be then completed. For instance, in the technique disclosed in Japanese Patent No. 2572064, a direct 4WD state is first gone through when the transfer is switched from 2WD to center diff-4WD. And when this direct 4WD state is detected by a switch, the free wheel mechanism is locked. In this manner the above-mentioned problem is solved.
If a dedicated switch for detecting a direct 4WD state is provided as in the above-mentioned technique, however, costs will increase by that amount. In addition, if the direct 4WD state is gone through in switching the transfer from 2WD to center diff-4WD, driving performance, which would be obtained during 2WD or center diff-4WD, cannot be obtained during the direct 4WD state, and consequently, drivers will feel a sense of incompatibility.
Therefore, it is preferable that switching be performed directly from 2WD to center diff-4WD without going through the direct 4WD state. However, it becomes important to accurately judge the synchronous state of the synchro-mechanism of the transfer in order to prevent the drawbacks due to the aforementioned synchronization collapse on the non-driving wheel side. It is also important to suppress an increase in the cost by utilizing the existing equipment without providing dedicated switches, etc.
Furthermore, the importance of the judgement of the synchronization of the synchro-mechanism is not limited to the above-mentioned switching of a driving state in the transfer, but is generally common to units that employ a synchro-mechanism to perform switching of a driving state by the connection of gears. For example, the judgement of the synchronization of the synchro-mechanism becomes important even in automatic clutch systems.
The automatic clutch system abolishes a clutch pedal and automates shift switching, by adding actuators (a clutch actuator and a shift actuator) and sensors to a normal manual transmission. In this automatic clutch system, engaging and disengaging of a clutch are performed by a clutch actuator instead of driver's clutch-pedal manipulation. If the engaging timing of the clutch is much earlier than the synchronization of the synchro-mechanism of a transmission, however, there is a possibility that gear grind or overloading will occur. Conversely, if the engaging timing is much later, the time to change the vehicle speed will become longer and therefore the driver will feel a sense of incompatibility.
Because of this, in the conventional automatic clutch system there is a need to provide a stroke sensor (or a switch) for shift position detection in order to confirm the completion of the shift switching made by the shift actuator. However, if a dedicated switch for detecting shift position is provided in this manner, however, costs will increase by that amount.
As described above, in transfers, automatic clutch systems, etc., which employ a synchro-mechanism to perform switching of a driving state by the connection of gears, an accurate judgement of the synchronous state of the synchro-mechanism has been demanded in order to prevent gear grind or delay of switching due to a difference between the switch timing, and the synchronous timing of the synchro-mechanism, and also the realization of synchronization judging means, making use of the existing equipment, which will not incur an increased cost due to equipment such as dedicated sensors, switches, etc., has been desired.
The present invention has been made in view of such problems, and it is the object of the present invention to provide a driving state switching unit with a synchro-mechanism, capable of an accurate judgement of the synchronous state of the synchro-mechanism without providing dedicated sensors, switches, etc.
DISCLOSURE OF THE INVENTION
To achieve the above-mentioned object, the driving state switching unit with a synchro-mechanism of the present invention comprises a first gear and a second gear coaxially disposed; a gear connecting member axially movable so that the first gear and the second gear can be connected; and a synchro-mechanism interposed between the first gear and the second gear. By moving the gear connecting member by an electric actuator, the first gear and the second gear are connected through the gear connecting member, while they are being synchronized by the synchro-mechanism. When this occurs, control means controls a supply current to the electric actuator, and judgement means judges synchronization of the synchro-mechanism, based on a change in the supply current value to the electric actuator.
With this, the judgement of the synchronization of the synchro-mechanism becomes possible without providing dedicated sensors, switches, etc., and by performing the judgement on the basis of a change in the supply current value, an accurate judgement, corresponding even to an individual difference in the sliding resistance between members and a change in running conditions, becomes possible.
Preferably, the judgement means compares the aforementioned supply current value with an average supply current value for a predetermined time, and when a differenc
Ikushima Yoshihiro
Niwa Takahisa
Sawase Kaoru
Yoshida Shigeyuki
Yoshioka Tadashi
Mitsubishi Jidosha Kogyo Kabushiki Kaisha
Wright Dirk
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