Planetary gear transmission systems or components – Steering by driving – With infinitely variable drive
Reexamination Certificate
2001-07-25
2003-09-09
Bonck, Rodney H. (Department: 3681)
Planetary gear transmission systems or components
Steering by driving
With infinitely variable drive
C475S027000, C475S073000, C475S074000, C475S080000, C475S218000, C475S329000
Reexamination Certificate
active
06616559
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a continuously variable transmission having a hydraulic continuously variable transmission (hereinafter referred to as an “HST”). Especially, it relates to a hydraulic and mechanical composite transmission (hereinafter referred to as an “HMT”) as a combination of an HST and a mechanical speed change mechanism having a differential part as a planetary gearing, wherein the mechanical speed change mechanism is constructed such that the output rotation of the HST and the rotation of its input part receiving engine power are transmitted into the differential part, and then, the differential rotation of the differential part is transmitted to a speed change output shaft part thereof. Further especially, it relates to that have the mechanical speed change mechanism provided with setting means which can electrically set a rotational speed ratio of the speed change output shaft part to the speed change input shaft part. This ratio is referred to as a speed ratio.
BACKGROUND ART
Conventionally, there is a well-known HMT as a combination of an HST and a mechanical speed change mechanism, wherein the mechanical speed change mechanism is constructed such that the rotational force of an input part thereof for receiving engine power (a speed change input part) and the output rotational force of the HST are transmitted to a differential part thereof having a group of planetary gears and the differential rotation of the group of planetary gears in the differential part is transmitted to a speed change output part thereof.
In the conventional HMT, the input part of the differential part for receiving engine power is constructed separately from a pump shaft of the HST. Referring to the above art, an input shaft for the whole HMT serves as a rotational axis of the differential part. However, power from the differential part is transmitted to a pump shaft of the HST through a gear train, thereby detracting efficiency of transmission. Furthermore, the pump part of the HST cannot be disposed coaxially to the differential part, thereby inhibiting minimization of the HMT. Furthermore, as well-known from U.S. Pat. No. 4,259,881, the differential part is radially expanded because it includes a ring gear having an inner peripheral gear, thereby also inhibiting minimization of the HMT.
In the conventional HMT, as well-known, power can be selectively transmitted to the output part thereof from either a motor shaft of the HST (hereinafter, such a transmission mode is referred to as an “HST mode”) or the differential part (hereinafter, such a transmission mode is referred to as an “HMT mode”). For transmission of engine power to the output part with the least loss, it is desirable that a gear is interposed between the input part and the output part in the HMT so as to transmit power without the HST and the differential part. In other words, the power transmission with such a gear train may be selected during a high-speed traveling or so on. However, such a gear train is not provided in the conventional HMTs. Of course, there is no control system for selecting the transmission with such a gear train.
As for control of the HMT, an electromagnetic clutch is conventionally used for changing a transmission mode between the HST mode and the HMT mode. A certain speed ratio is set for determining the timing of this mode change. However, in the conventional clutch during its disengagement, only one clutch side is rotated while the other is stationary. Thus, when the clutch is engaged, the stationary clutch side resists against the rotating clutch side, thereby not only changing the rotating speed suddenly but also stressing the abutting surfaces of the clutch greatly. Therefore, the conventional clutch is made of strong material such as sintered metal, which is expensive and enlarged so as to inhibit its minimization.
As for the change of transmission mode, if a lag in completing the operation of the electromagnetic clutch, that is caused by transmitting an electric output signal to the electromagnetic clutch and a time of actual operation of the electromagnetic clutch, is not considered, speed is suddenly changed because of a difference of output/input speed ratio between pre-operation and post-operation of the clutch. The above-mentioned conventional art does not consider adjustment of the output/input speed ratio, or the timing, for changing the transmission mode.
If a brake is provided on the output part, the braked output part resists against the transmission system from the differential part or the motor shaft of the HST, thereby damaging a clutch between the output part and the transmission system. The above-mentioned conventional art does not consider a relationship between the brake and the clutch.
The adjustment of the output/input speed ratio of the HMT depends upon the adjustment of the amount of oil discharged from the HST. In a composition of two variable displacement hydraulic units shown in U.S. Pat. No. 5,421,790, the actuations of both the hydraulic units are sequential. For example, when one hydraulic unit discharges, the other hydraulic unit is in neutral, i.e., the functions of both the hydraulic units as a hydraulic pump and a hydraulic motor are exchanged with each other in respective ranges of speed ratio. However, if speed ratio setting means is to be greatly shifted so as to greatly change the speed ratio, it takes a long time to change the speed reduction under such hydraulic control so that a vehicle is uncomfortably accelerated or decelerated. If both the hydraulic units were adjusted in their discharge simultaneously, a target speed ratio could be attained soon. However, if the speed ratio is varied across a point for changing the transmission mode, the clutch is greatly stressed under the situation where both the hydraulic units are actuated.
If load is applied, the output part is decelerated by the load so that the actual speed ratio becomes different from the set speed ratio. In this case, usually, an engine rotation is adjusted by a governor. The conventional HMT does not consider the speed ratio to be adjusted for amendment of output rotation. If the speed ratio is to be adjusted, a relation of actuation between both the hydraulic units constituting the HST must be considered. Furthermore, if the actual speed ratio is changed according to such variance of load while a speed ratio is set in the vicinity of the change point of transmission mode, the transmission mode is frequently alternated, thereby damaging the clutch and making the travel of a vehicle unstable.
Regarding a continuously variable transmission including an HST (whether it may be an HMT or constituted only by an HST), in the case where the speed ratio is controlled electrically, e.g., correspondingly to a voltage issued from a position sensor which detects a position of a lever for setting a speed ratio, it is assumed that the variance ratio of the speed ratio is constant in its whole range to be set. On this assumption, if the variance ratio is set in correspondence to a low speed range, the lever must be shifted to a considerably large degree for establishing a high speed. If the variance ratio is set in correspondence to a high speed range, the speed ratio is greatly varied in a low speed range while the lever is shifted to a small degree so that the low speed travel of a vehicle during a work or so on becomes unstable.
Furthermore, conventionally, such an electric speed ratio control system does not have control means for adjusting acceleration and deceleration in corresponding to the speed of shifting.
Conventionally, for setting the speed ratio to zero, the discharge of the variable displacement hydraulic unit of the HST is set to zero. However, hydraulic control for establishing a neutral condition is difficult. Even if oil extremely slightly escapes, a motor shaft is, so far from certainly stationary, moved. Especially, such a problem arises when a vehicle is stopped on a slope. For solving this problem, for example, biasing means for neutral returning is provid
Hitachi Junichi
Hori Yasuhiko
Kubota Yukio
Sakamoto Kunihiko
Bonck Rodney H.
Ho Ha
Sterne Kessler Goldstein & Fox P.L.L.C.
Yanmar Co. Ltd.
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