Patent Application
20080200298
This application claims the benefit of Japanese Patent Application No. 2007-035374 which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a forward and rearward motion switching mechanism of an automatic transmission for a vehicle.
2. Related Background Art
An automatic transmission of a vehicle is equipped, between an input shaft connected to a torque converter and an output shaft, with a forward and rearward motion switching device and an automatic transmission device. The forward and rearward motion switching device and the automatic transmission device are constituted by a plurality of braking mechanisms, a plurality of clutch mechanisms and a plurality of planetary gear mechanisms together in combination. In the planetary gear mechanism, a sun gear having a small diameter and external teeth and a ring gear having a large diameter and internal teeth are provided coaxially and a pinion gear supported by a planetary carrier is disposed between the sun gear and the ring gear.
The automatic transmission device is arranged such that each of the sun gear, the ring gear and the planetary carrier of the planetary gear mechanism corresponds to either of an input element, an element to be fixed and an output element, and a ratio of speed of the output element with respect to the input element is changed, depending on which member is corresponding to which element. Then, selection of each of the members as the input element, the element to be fixed or the output element is performed by fastening or releasing a braking mechanism and a clutch mechanism connected to the respective elements.
Also in the forward and rearward motion switching device, each of the sun gear, the ring gear and the planetary carrier of the planetary gear mechanism is made correspond to either of an input element, an element to be fixed and an output element by fastening or releasing the braking mechanism and the clutch mechanism, so that the direction of rotation of the output element with respect to the input element is switched to the same as the direction of rotation of the input element or to the direction reverse thereto.
Automatic transmission systems for a vehicle are classified into those of a step variable transmission scheme utilizing a planetary gear mechanism as described above and those of a stepless or continuously variable transmission scheme which has higher fuel efficiency and has a belt and a pulley with no speed change shock, compared with those of the step variable transmission scheme (see Japanese Patent Application Laid-Open Nos. 2002-89687 and 2004-144139). There is also disclosed those with the above schemes combined together (see Japanese Patent Application Laid-Open No. 2002-98171). However, even in a vehicle employing a continuously variable transmission (hereinafter called a “CVT”), a planetary gear mechanism is used as a device for switching forward and rearward motions. In the above patent publications, a driving force inputted from an engine through a torque converter is used to switch forward and rearward motions by using a forward and rearward motion switching device (3) shown in FIG. 1 of Japanese Patent Application Laid-Open No. 2002-89687, or a forward and rearward motion switching device 60 shown in FIG. 1 of Japanese Patent Application Laid-Open No. 2004-144139, or a forward and rearward motion switching device 41 shown in FIG. 1 of Japanese Patent Application Laid-Open No. 2002-98171.
As the forward and rearward motion switching device employed in these CVTs, a single pinion type planetary gear mechanism or a double pinion type planetary gear mechanism is used. Generally, when the double pinion type planetary gear mechanism is used, the device makes a sun gear as an input element, a ring gear as an element to be fixed and a planetary carrier as an output element in rearward motion and outputs a rotation in the reverse direction to the rotation of the input element. When the single pinion type planetary gear mechanism is used, the device makes the sun gear as the input element, the planetary carrier as the element to be fixed and the ring gear as the output element, or the ring gear as the input element, the planetary carrier as the element to be fixed and the sun gear as the output element, in rearward motion and outputs a rotation in the reverse direction to the rotation of the input element. In these planetary gear mechanisms of the forward and rearward motion switching device, a wet type multiple disc brake is employed as a brake to be used as an element for fixing the ring gear or the planetary carrier in rearward motion.
However, in the forward and rearward motion switching device, the element to be fixed of the planetary gear mechanism is always rotating even when the engine is in rotation and the brake is not applied.
For this reason, when a wet type multiple disc brake is used in the planetary gear mechanism of the forward and rearward motion switching device, a drag torque between a friction disc and a separator disc of the wet type multiple disc brake gives adverse influence on the efficiency of the CVT. Since the fuel efficiency is highly demanded recently and improvement in efficiency of the CVT is strongly required, such reduction of the drag torque is highly demanded.
The present invention has been contrived in view of these problems, and an object of the invention is to provide a forward and rearward motion switching device in which a drag torque can be reduced, compared with a wet type multiple disc brake having the equivalent capacity, thereby reducing a power loss and improving the fuel efficiency.
In order to solve the above problems, according to the present invention, there is provided a forward and rearward motion switching device to be used in an automatic transmission system for a vehicle, comprising: a planetary mechanism provided with an input element, an element to be fixed and an output element which are disposed coaxially and are rotatable relative to each other, the planetary mechanism outputting a rotational driving force of an internal combustion engine transmitted to the input element as a rotational driving force in the same direction as or reverse direction to the rotation of the input element from the output element through the input element, the element to be fixed and the output element; and a brake means capable of fixing the element to be fixed of the planetary mechanism, wherein the brake means comprises a rotational drum which is integrally formed with the element to be fixed and has an outer peripheral surface, and a brake band that surrounds the outer peripheral surface of the rotational drum to fix the same.
According to the present invention, the planetary mechanism is preferably a planetary gear mechanism comprising:
Preferably, the forward and rearward motion switching device of the present invention is used in an automatic transmission system employing a continuously variable transmission.
In the forward and rearward motion switching device of the present invention, it is preferable that, in the planetary gear mechanism, the sun gear constitutes the input element, the ring gear constitutes the element to be fixed and the planetary carrier constitutes the output element, and when the ring gear is fixed by the brake band a rotational driving force of the internal combustion engine transmitted to the sun gear is outputted as a rotational driving force in the reverse direction to the rotation of the sun gear from the planetary carrier through the pinion gear.
Also, in the forward and rearward motion switching device of the present invention, it is preferable that, in the planetary gear mechanism, the sun gear constitutes the input element, the planetary carrier constitutes the element to be fixed and the ring gear constitutes the output element, and when the planetary carrier is fixed by the brake band a rotational driving force of the internal combustion engine transmitted to the sun gear is outputted as a rotational driving force in the reverse direction to the rotation of the sun gear from the ring gear through the pinion gear.
In the forward and rearward motion switching device of the present invention, it is preferable that, in the planetary gear mechanism, the ring gear constitutes the input element, the planetary carrier constitutes the element to be fixed and the sun gear constitutes the output element, and when the planetary carrier is fixed by the brake band a rotational driving force of the internal combustion engine transmitted to the ring gear is outputted as a rotational driving force in the reverse direction to the rotation of the ring gear from the sun gear through the pinion gear.
In the forward and rearward motion switching device of the present invention, preferably the output element is coupled to an input shaft of the automatic transmission system employing the continuously variable transmission.
With a forward and rearward motion switching device according to the present invention, it is possible to reduce a drag torque approximately by half, compared with a wet type multiple disc brake having the same capacity. Since capable of thus reducing a power loss, if used as a brake of a forward and rearward motion switching device of an automatic transmission, this arrangement can contribute to reduce fuel expenses. Particularly when this device is used in a vehicle employing a continuously variable transmission, higher efficiency of the continuously variable transmission can be achieved, to thereby greatly contribute fuel efficiency.
A forward and rearward motion switching device according to the present invention will be described below with reference to drawings.
The continuously variable transmission 25 is provided with the primary shaft 30, a primary pulley 32 supported by the primary shaft 30, a secondary shaft 34 serving as an output shaft of the continuously variable transmission 25, a secondary pulley 36 supported by the secondary shaft 34, and a metal belt 38 spanning the primary pulley 32 and the secondary pulley 36 for coupling these two pulleys 32 and 36. The primary pulley 32 is provided with a fixed half pulley 32a which is integrally rotated with the primary shaft 30 and a movable half pulley 32b. The movable half pulley 32b is movably disposed to approach to or separated from the fixed half pulley 32a in the axial direction. A V-shaped groove is formed between the fixed half pulley 32a and the movable half pulley 32b. The secondary pulley 36 is provided with a fixed half pulley 36a which is integrally rotated with the secondary shaft 34 and a movable half pulley 36b. The movable half pulley 36b is movably disposed to approach to or separated from the fixed half pulley 36a in the axial direction. A V-shaped groove is formed between the fixed half pulley 36a and the movable half pulley 36b.
The movable half pulley 32b of the primary pulley 32 and the movable half pulley 36b of the secondary pulley 36 are respectively movable in the axial direction by using oil pressure. The width of the V-shaped grooves of the primary pulley 32 and the secondary pulley 36 can be changed upon movement of these movable half pulleys 32b and 36b. The structure is arranged such that the diameter of an arc formed by the metal belt 38 spanning the pulleys 32 and 36 is varied by changing the width of the V-shaped grooves of these pulleys 32 and 36.
The secondary shaft 34 is connected to an unillustrated differential gear device, and the differential gear device is connected to an unillustrated driving wheel.
In forward running of the vehicle, the clutch 3 is engaged through the control device 20, and a rotational driving force of the engine which is transmitted to the input shaft 2 through an unillustrated torque converter is transmitted to the sun gear S and the ring gear R, whereby the sun gear S and the ring gear R are integrally rotated in the same direction as the rotation of the input shaft 2. Upon the integral rotation of the sun gear S and the ring gear R, the planetary carrier CR is integrally rotated in the same direction through the pinion gears P1 and P2. That is, the sun gear S, the planetary gear CR and the ring gear R are integrally rotated in the same direction as the rotation of the input shaft 2, so that the rotation of the input shaft 2 is transmitted as it is to the primary shaft 30 of the continuously variable transmission 25 which is integrally coupled to the planetary carrier CR.
The primary pulley 32 which is integrally rotated with the primary shaft 30 is also rotated in the same direction, and the rotation of the primary pulley 32 is transmitted to the secondary pulley 36 through the metal belt 38. Here, when the movable half pulley 32b of the primary pulley 32 and the movable pulley 36b of the secondary pulley 36 are respectively moved in the axial direction by oil pressure, the width of the V-shaped grooves 32 and 36 of the two pulleys 32 and 36 is changed, and the diameter of the arc of the metal belt 38 spanning the two pulleys 32 and 36 is changed. With this, the rotation of the primary pulley 32 is continuously varied and is transmitted to the secondary pulley 36.
Thus, the rotational driving force in the same direction as the rotation of the input shaft 2 transmitted to the secondary shaft 34 is transmitted to the unillustrated driving wheels through the unillustrated differential gear device, whereby the vehicle is enabled to run forward.
On the other hand, in rearward running of the vehicle, the clutch 3 is released or disengaged through the control device 20, and the brake 4 which will be described later with reference to
In the forward and rearward motion switching device 1 of the present embodiment, the brake band 10 is used as a braking means for fixing the ring gear R which serves as the element to be fixed of the planetary gear mechanism 5 in the rearward running of the vehicle.
When a force is applied by the apply pin (not shown)onto the apply bracket 13, the apply bracket 13 is displaced to come close to the anchor bracket 12, whereby the inner diameter of the brake band 10 is reduced and the inner peripheral surface of the brake band 10 is brought into pressure contact with the outer peripheral surface of the rotational drum D which is integrally formed on the outer periphery of the unillustrated ring gear R. With this arrangement, the outer peripheral surface of the rotational drum D is wound and fixed by the brake band 10, and the ring gear R is fixed in a stationary state.
In
In the present embodiment, in a forward running of the vehicle, the clutch 3 is engaged through the control device 20, and a rotational driving force of the engine which is transmitted to the input shaft 2 through an unillustrated torque converter is transmitted to the sun gear S and the planetary carrier CR, whereby the sun gear S and the planetary carrier CR are integrally rotated in the same direction as the rotation of the input shaft 2. Upon the integral rotation of the sun gear S and the planetary carrier CR, the ring gear R is also integrally rotated in the same direction through the pinion gear P. That is, the sun gear S, the planetary gear CR and the ring gear R are integrally rotated in the same direction as the rotation of the input shaft 2, so that a rotation of the input shaft 2 is transmitted as it is to the primary shaft 30 of the continuously variable transmission 25 which is integrally coupled to the ring gear R. The rotational driving force in the same direction as the rotation of the input shaft 2 transmitted to the primary shaft 30 is transmitted to the driving wheels through the similar rotation transmission path to that in the forward running of the first embodiment, whereby the vehicle is enabled to run forward.
On the other hand, in rearward running of the vehicle, the clutch 3 is released or disengaged through the control device 20, and the brake 4 which will be described later with reference to
Also in the forward and rearward motion switching device 1 of the present embodiment, the brake band 10 shown in
In the present variation, in forward running of the vehicle, the clutch 3 is engaged through the control device 20, and a rotation of the engine which is transmitted to the input shaft 2 through the torque converter is transmitted to the ring gear R and the planetary carrier CR, whereby the ring gear R and the planetary carrier CR are integrally rotated in the same direction as the rotation of the input shaft 2. Upon the integral rotation of the ring gear R and the planetary carrier CR, the sun gear S is also integrally rotated in the same direction as the rotation of the input shaft 2 through the pinion gear P. That is, the sun gear S, the planetary gear CR and the ring gear R are integrally rotated in the same direction as the rotation of the input shaft 2, so that the rotation of the input shaft 2 is transmitted as it is to the primary shaft 30 of the continuously variable transmission 25 which is integrally coupled to the sun gear S. The rotational driving force in the same direction as the rotation of the input shaft 2 transmitted to the primary shaft 30 is transmitted to the driving wheel through the similar rotation transmission route to that in the forward running of the second embodiment, whereby the vehicle is enabled to run forward.
On the other hand, in rearward running of the vehicle, the clutch 3 is released or disengaged through the control device 20, and the brake 4 which will be described later with reference to
In the forward and rearward motion switching device 1 of the present variation, the brake band 10 shown in
In the present variation, in forward running of the vehicle, the clutch 3 is engaged through the control device 20, and the rotation of the engine which is transmitted to the input shaft 2 through the torque converter is transmitted to the ring gear R and the sun gear S, whereby the ring gear R and the sun gear S are integrally rotated in the same direction as the rotation of the input shaft 2. Upon the integral rotation of the ring gear R and the sun gear S, the planetary carrier CR is also integrally rotated in the same direction as the rotation of the input shaft 2 through the pinion gear P. That is, the sun gear S, the planetary gear CR and the ring gear R are integrally rotated in the same direction as the rotation of the input shaft 2, so that the rotation of the input shaft 2 is transmitted as it is to the primary shaft 30 of the continuously variable transmission 25 which is integrally coupled to the sun gear S. The rotational driving force in the same direction as the rotation of the input shaft 2 transmitted to the primary shaft 30 is transmitted to the driving wheels through the similar rotation transmission route to that in the forward running of the second embodiment, whereby the vehicle is enabled to run forward.
On the other hand, in rearward running of the vehicle, the clutch 3 is released or disengaged through the control device 20, and the brake 4 which will be described later with reference to
In the forward and rearward motion switching device 1 of the present variation, the brake band 10 shown in
Also in the forward and rearward motion switching device 1 according to the second embodiment and the first and second variations of the second embodiment, the drag torque between the brake band 10 and the element to be fixed of the planetary gear mechanism 5 is, as seen from
As described above, when the forward and rearward motion switching device according to the present invention is used, even in a state that the engine is in rotation and the brake of the forward and rearward motion switching device is not applied, the drag torque between the brake and the fixed element of the planetary gear mechanism is largely reduced so that the power loss is also reduced. As a result, it is possible to improve the efficiency of the automatic transmission and reduce of the fuel expenses. Particularly, when the forward and rearward motion switching device is used in CVT which is strongly required to have higher efficiency, a great effect can be obtained.
Note that, the forward and rearward motion switching device according to the present invention is not limited to the foregoing embodiments and variations, but can be modified in various manners.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-035374 | Feb 2007 | JP | national |
