A clutch device

Abstract: This clutch or brake device has a first cam mechanism (3,6,4) and a second cam mechanism (3,5,2) disposed on a relatively rotatable a pair of members (8,9). When the first cam mechanism (3,6,4) is pushed by a pushing member (3) to one of the pair of members (8) rotating in a direction, the first cam mechanism (3,6,4) generates a thrust force corresponding to an input torque and thereby the relatively rotating members are engaged. When the second cam mechanism (3,5,2) is activated by one of the pair of members (8) rotating in a reverse direction, the second cam mechanism (3,5,2) generates a thrust force corresponding to the pushing force of the piston, and thereby the relatively rotating members (8,9) are engaged. A return spring (7) giving a biasing force to separate the second cam mechanism (3,5,2) from the one of relatively rotating members (8) is designed not to reduce the thrust force generated by the first cam mechanism (3,6,4) during the action of the first cam mechanism (3,6,4).

Description: The present invention relates to a clutch device according to the preamble of claim 1. Clutch devices are disclosed in Japanese Patent Application Nos. 6-48806 and 6-69632 (corresponding to JP-A-7259885 and JP-A-7279992) filed in the name of the assignee of the present application. The JP-A-7259885 is equivalent to the EP-A-674126 and the JP-A-7279992 is equivalent to the EP-A-676568. From the above-mentioned references clutch devices are known, wherein a cam device is provided between two members rotating relatively to each other so that a force generated due to the relative rotation of the members and acting in the circumferential direction is converted to a thrust acting in the axial direction which is used as a clutch-engagement force. According to the above clutch devices, it is possible to miniaturize the clutch device as a whole by the reduction of the number of clutch disks and by the elimination of a one-way clutch due to the utilization of a booster function and a unidirectional action of the cam mechanism. It was noticed that a self-tightening engagement which increases the engagement force corresponding to increase of rotational torque can be obtained when a cam angle  is chosen to satisfy µ > tan , and a boosting engagement which increases the engagement force corresponding to increase of pushing force which pushes the cam mechanism to one of the relatively rotating members can be obtained when the cam angle  is chosen to satisfy µ < tan , where µ is a friction coefficient between the clutch disk and the cam member. On the basis of the above described observation, two cam mechanisms are installed, one for obtaining the self-tightening engagement and one for obtaining the boosting engagement, i.e. to install a self-tightening cam and a boosting cam in one clutch device, and thereby obtain a self-tightening action when the members relatively rotates in one direction and obtain a boosting action when the members relatively rotates in a direction reverse to the one direction. Hereafter, the relative rotation of the member by which the self-tightening cam generates the thrust force for the self-tightening engagement is called the normal rotation, or rotation in the normal direction. On the other hand, the relative rotation of the member by which the boosting cam generates the thrust force for the boosting engagement is called the reverse rotation, or rotation in the reverse direction. However, the above described clutch device generates unnecessary thrust force which causes a frictional loss when releasing the clutch device rotating in the reverse direction, unless the clutch disk and the cam member are separated from each other in an instant. Therefore, a return spring is attached to give a biasing force for separating the clutch disk and the cam member from each other. Such a clutch device, is known from EP-A-676568, which discloses the preamble to claim 1. However, the biasing force of the return spring decreases the thrust force generated by the self-tightening cam. Accordingly, the clutch device will slip before the direction of the torque is reversed when the torque is relieved from the engaging state at the rotation in the normal direction. The slip of the clutch device causes poor driveability, such as a sudden increase of engine speed, due to a sudden decrease of engine load. Therefore, an object of the present invention is to solve the above drawbacks of the prior art devices and to provide a clutch device with a cam mechanism which can obtain sure self-tightening engagement of the members when the members rotate in one direction and also obtain sure free rotation of the members when the members rotate in a reverse direction. The above-stated object is achieved by means of the combination of the features defined in the independent claim 1. Preferred embodiments of the clutch device according to claim 1 are disclosed in the dependent claims 2 to 6, respectively. According to an embodiment of the invention, the clutch device comprises a pair of members disposed at a distance on a common axis and relatively rotating to each other around the common axis; a cam assembly disposed on the common axis and composed of a first cam mechanism and a second cam mechanism, the first cam mechanism being composed of a pair of cam members and generating an axial thrust force corresponding to rotational torque in order to engage the pair of members after being pushed by a pushing means to one of the pair of members rotating in a direction and thereby causing a frictional engagement of one of the pair of cam members with the one of the pair of members rotating in the direction, and the second cam mechanism being composed of a pair of cam members and generating an axial thrust force corresponding to a pushing force of the pushing means in order to engage the pair of members after being pushed by the pushing means to one the pair of members rotating in a direction reverse to the direction in which the first cam mechanism generates the axial thrust force corresponding to rotational torque and thereby causing a frictional engagement of one of the pair of cam members with the one of the pair of members rotating in the reverse direction; and a biasing means for supplying a biasing force acting on the cam mechanism in a direction contrary to a direction of the pushing force of the pushing means, wherein the axial thrust force generated by the first cam mechanism is kept free from being weakened by the biasing force supplied by the biasing means. The present invention will be described in more detail below with reference to embodiments illustrated in the attached drawings. In the drawings: Fig. 1 is a schematic view illustrating an overall structure of an automatic transmission to which the present invention is applied; Fig. 2 is a table for obtaining various driving speeds; Fig. 3 is a side sectional view of the first embodiment; Fig. 4 is a view for illustrating an overall structure of a cam mechanism of the first embodiment; Fig. 5 to 7 are views for illustrating an operation of the cam mechanism of the first embodiment; Fig. 8 is a view for illustrating a structure of a cam mechanism of the second embodiment; Fig. 9 is a view for illustrating an overall structure of the third embodiment; Fig. 10 is a view for illustrating a structure of a cam mechanism of the third embodiment. Fig. 1 schematically illustrates an overall structure of an automatic transmission for the purpose of explaining where an embodiment of the present invention is used in the automatic transmission. In the figure, AT generally represents an automatic transmission which basically comprises three sets of planetary gear units and plural frictional engagement devices for engaging and disengaging ring gears, sun gears, carriers composing the planetary gear units to and from each other, the details thereof being as follows: X 1 represents an input shaft and connected with an output shaft (not shown) of a torque converter (not shown); PG 1 , PG 2 and PG 3 represent a front planetary gear unit, a rear planetary gear unit and an O/D planetary gear unit, respectively; R 1 , R 2 and R 3 represent a front planetary ring gear, a rear planetary ring gear and an O/D planetary ring gear, respectively; K 1 , K 2 and K 3 represent a front planetary carrier, a rear planetary carrier and an O/D planetary carrier, respectively; S 12 represents a front and rear planetary sun gear common to the front and rear planetary gear units, and S 3 represents an O/D planetary sun gear; C 1 represents a first clutch for engaging and disengaging the input shaft X 1 to and from the front planetary ring gear R 1 ; C 2 represents a second clutch for engaging and disengaging the input shaft X 1 to and from the front and rear planetary sun gear S 12 ; C 3 represents a third clutch for engaging and disengaging the O/D planetary carrier K 3 to and from the O/D planetary sun gear S 3 ; B 1 represents a first brake for selectively locking a clockwise or counterclockwise rotation (seeing from the input shaft X 1 ) of the front and rear planetary sun gear S 12 ; B 2 represents a second brake for locking a counterclockwise rotation of the front and rear planetary sun gear S 12 ; B 3 represents a third brake for locking a clockwise or counterclockwise rotation of the rear planetary carrier K 2 ; B 4 represents a fourth brake for locking a clockwise or counterclockwise rotation of the O/D planetary sun gear S 3 ; F 1 represents a first one-way clutch for locking a counterclockwise rotation of the front and rear planetary sun gear S 12 when the second brake B 2 is operated; and F 2 represents a second one-way clutch for locking a counterclockwise rotation of the rear planetary carrier K 2 . F 3 represents a third one-way clutch for locking a counterclockwise rotation of the O/D planetary carrier K 3 relative to the O/D planetary sun gear S 3 ; CG 1 and CG 2 represent a counter drive gear and a counter driven gear, respectively, which transmit the engine torque to a post-stage mechanism but have no relation to speed changing. The table shown in Fig. 2 shows a combination of the engagement and disengagement of frictional engagement elements to attain desired speeds at each range and gear speed. The embodiments described later are adopted to perform the work of the third brake B 3 and the second one way clutch F 2 . Therefore, by referring to the table shown in Fig. 2, the embodiments are required to perform the following operations; Locking the reverse rotation of the rear planetary carrier K 2 in normal running (vehicle is driven by engine power) with the first speed of D, 2, and L range; Locking the normal rotation of the rear planetary carrier K 2 while coasting (vehicle is driven by inertia force) with the first speed of L range; Locking the normal rotation of the rear planetary carrier K 2 in normal running with the R range; Locking the reverse rotation of the rear planetary carrier K 2 while coasting with the R range; Releasing the locking of the rear planetary carrier K 2 simultaneously with changing the direction of torque of the rear planetary carrier K 2 during up-shift from the first speed to the second speed; and Locking the rear planetary carrier K 2 simultaneously with changing the direction of torque of the rear planetary carrier K 2 while down-shifting from the second speed to the first speed. Fig. 3 illustrates a side sectional view of an automatic transmission to which a first embodiment of the present invention is built in, wherein clutch casing 100 which has an annular recess in which clutch device according to the present invention is disposed is integrally formed with transmission case 200. A second cam member 2, a piston 3 and a first cam member 4 are disposed in the annular recess of the clutch casing 100. A second cam roller 5 is disposed between the second cam member 2 and the piston 3, and the first cam roller 6 is disposed between the first cam member 4 and the piston 3. The piston 3 is always forced to the left in the figure by a return spring 7. The second cam member 2 can be formed integrally with the clutch casing 100 instead of being formed separated from the clutch casing 100 as in this first embodiment. A oil passage 200a for supplying a oil pressure to the piston 3 is formed in the transmission case 200. A clutch disks 8 are axially slidably attached to a connecting member Ka which rotates with the rear planetary carrier K 2 of the rear planetary gear PG 2 , and separator plates 9 are axially slidably attached to the transmission case 200. The clutch disks 8 and the separator plates 9 are engaged to each other when the clutch device 1 is axially elongated and pushed to the right end one of the separator plates 9, thereby the clutch disks 8 are stopped and the rear planetary carrier K 2 is locked. Fig. 4 is a sectional view of the clutch device 1 shown in Fig. 3 from the radial direction. A paired cam surface 2L and 3L are respectively formed on a opposing surface of the second cam member 2 and the piston 3, and a paired cam surface 3R and 4R are respectively formed on a opposing surface of the first cam member 4 and the piston 3. Therefore, the piston 3 has cam surfaces on both axial end surfaces. The cam angle α of the cam surfaces 3R and 4R, and the cam angle β of the cam surfaces 2L and 3L are chosen to satisfy the following equation; tan α < µ and tan β > µ, where µ is a frictional coefficient between the first cam member 4 and the clutch disk 8. Here, if described as "the clutch disk 8" i.e. described in singular form, it means the left end one of the clutch disks 8 in the figure, and if described as "the clutch disks 8" i.e. described in plural form, it means the all set of the clutch disks 8 in the figure. The clutch disks 8 rotate with rear planetary carrier K 2 , when the clutch device 1 does not operate and shown to move right or left in the figure. Here, we prescribe the rotation of clutch disk 8 which is shown to move to the left in relation to the cam members in the figure 4 and like drawn figures as normal rotation because this rotation can cause the self-tightening engagement. On the other hand, the rotation of clutch disk 8 which is shown to move to the right in relation to the cam members in the figure 4 and like drawn figures is prescribed as the reverse rotation because this rotation can cause the boosting engagement. The state shown in Fig. 4 is the state having the shortest axial length of the clutch device 1, wherein the clutch disk 8 and the first cam member 4 are not contacting to each other, and accordingly the clutch disks 8 may not be stopped regardless of the direction of the rotation. When the oil pressure is supplied during the normal rotation, the distance between the second cam member 2 and the piston 3 will increase, so that the piston 3 and the first cam member 4 are pushed to the clutch disk 8 holding the cam roller 5 therebetween. As a result, the first cam member 4 and the clutch disk 8 are frictionally engaged to each other so that the first cam member 4 are dragged by the clutch disk 8 and begins rotation in the normal direction with clutch disk 8. Since cam angle α is chosen to satisfy tan α < µ, the cam surface 4R of the first cam member 4 climbs the cam surface 3R of the piston 3 through the first cam roller 6, and cam thrust force is generated. Thereby, the piston 3 is pushed back downward in the figure, and the once increased distance between the second cam member 2 and the piston 3 is decreased to the minimum, so that the second cam member 2 receives the reaction force of the above generated thrust force. Accordingly, the first cam member 4 and the clutch disk 8 are self-tighteningly engaged. This self-tightening engagement increases a force of engagement relative to a increase of the rotational torque input by the clutch disk 8. Fig. 6 illustrates thus self-tighteningly engaged state. As a result, rear planetary carrier K 2 is locked when the clutch disk 8 is going to rotate normally. On the other hand, when a oil pressure is supplied during the reverse rotation of the clutch disk 8, the first cam member 4 and the clutch disk 8 are frictionally engaged to each other, so that the first cam member 4 starts reverse rotation by being dragged with the clutch disk 8. Accordingly, the piston 3 also starts the reverse rotation through the first cam roller 6, so that the cam surface 3L of the piston 3 climbs the cam surface 2L of the second cam member 2 through the second cam roller 5. Thereby, cam thrust force is generated. As a result, the first cam member 4 and the clutch disk 8 are engaged by the cam thrust force, as shown in Fig. 7. Thus, rear planetary carrier K 2 can be locked when the clutch disk 8 is going to rotate in the reverse direction. The above described engagement is a boosting engagement which boosts the thrust force by oil pressure. The engaging force F of the clutch device 1 of the above described engagement is a sum of the cam thrust force and the force by oil pressure as indicated in the following equation, and changes in relation to the oil pressure. F = a(Fp - Fs) wherein, Fp is the force by oil pressure, Fs is a biasing force of return spring 7, a is a constant decided by the cam angle β which is chosen to satisfy tan β > µ. Therefore, the engagement force F will expire when the force Fp by oil pressure becomes smaller than the biasing force Fs of return spring 7 and the engagement is released. As described above, by the first embodiment the biasing force of the return spring 7 does not act on the first cam member 4, and the self-tightening engagement can be surely obtained when the clutch disks 8 rotates in the normal direction, and free rotation of the clutch disks 8 in the reverse direction can be obtained without generating drag. Thus, the first embodiment can substitute for the work which is performed by the third brake B, and the second one-way clutch F 2 in the prior art. Fig. 8 shows the cam mechanism of the second embodiment, in which the cam surface 2P of the second cam member 2 and the cam surface 3P of the piston 3 are formed without a rounding surface. Other parts are same as those of the first embodiment. By introducing this feature, the second cam roller 5 which is required in the first embodiment is deleted thereby the axial length can be decreased, and a pressure per unit area acting on the cam surface is decreased. The operation of the second embodiment is same as the case of the first embodiment, therefore no detail description is provided. Fig. 9 shows a construction of the third embodiment. As shown in Fig. 9, a cam mechanism for generating engagement force when clutch disk 8 rotates in the normal direction and a cam mechanism for generating engagement force when clutch disk 8 rotates in the reverse direction are separately disposed. Therefore, on a surface of the piston 3a facing to the clutch disk 8 only a surface for frictional engagement is formed, while on a surface facing to the second cam member 2 a cam surface same as 3L in the first embodiment is formed. The clutch disks 8 and the separator plates 9 are disposed between the piston 3a and the first cam member 3b with the third cam member 4a. Cam surfaces similar to 3R and 4R in the first embodiment are formed on the opposing surfaces of the first cam member 3b and the third cam member 4a holding a first cam roller 6 therebetween. When a oil pressure is supplied, the piston 3a moves to the right in the figure and pushes the clutch disks 8. However, no engagement occur until a cam thrust force is generated. Fig. 10 is a sectional view of the third embodiment viewing from the radial direction same as Fig. 4. In Fig. 10, the cam surface 3bR formed on the first cam member 3b and the cam surface 4aR are slanted in the opposite direction to the cam surfaces 3R and 4R which are formed on the piston 3 and the second cam member 4 in the first embodiment, since the clutch disk 8 engages with the back surface of the first cam member 3b. The operation of the third embodiment is fundamentally same as the one of the first embodiment, therefore no detail description is provided. This third embodiment has an advantage that it is adaptable to a case in which the clutch casing 100 and the clutch disks 8 are so closely disposed that cam mechanism can not be located therebetween.

Claims: A clutch device comprising a pair of members (8, 9) disposed at a distance on a common axis and relatively rotating to each other around said common axis, a cam assembly disposed on said common axis and composed of a first cam mechanism (3, 6, 4) and a second cam mechanism (3, 5, 2), said first cam mechanism (3, 6, 4) being composed of a pair of cam members (6, 4) and generating an axial thrust force corresponding to rotational torque in order to engage said pair of members (8, 9) after being pushed by a pushing means (3) to one of said pair of members (8, 9) rotating in a direction and thereby causing a frictional engagement of one of said pair of cam members (6, 4) with said one of said pair of members (8, 9) rotating in said direction, and said second cam mechanism (3, 5, 2) being composed of a pair of cam members (5, 2) and generating an axial thrust force corresponding to a pushing force of said pushing means (3) in order to engage said pair of members (8, 9) after being pushed by said pushing means (3) to one said pair of members (8, 9) rotating in a direction reverse to said direction in which said first cam mechanism (3, 6, 4) generates said axial thrust force corresponding to rotational torque and thereby causing a frictional engagement of one of said pair of cam members (6, 4) with said one of said pair of members (8, 9) rotating in said reverse direction, a biasing means (7) for supplying a biasing force acting on said cam mechanism in a direction contrary to a direction of said pushing force of said pushing means (3), characterized in that said axial thrust force generated by said first cam mechanism (3, 6, 4) is kept free from being weakened by said biasing force supplied by said biasing means (7). A clutch device according to claim 1, wherein said second cam mechanism (3, 5, 2) is separately constructed from said first cam mechanism (3, 6, 4) and said biasing force supplied by said biasing means (7) only acts on said second cam mechanism (3, 5, 2), thereby said axial thrust force generated by said first cam mechanism (3, 6, 4) is kept free from being weakened by said biasing force. A clutch device according to claim 2, wherein said second cam mechanism (3, 5, 2) and said first cam mechanism (3, 6, 4) are both disposed between said pair of members (8, 9). A clutch device according to claim 2, wherein one of said second cam mechanism (3, 5, 2) and said first cam mechanism (3, 6, 4) is disposed between said pair of members (8, 9). A clutch device according to claim 1, wherein at least one of said first cam mechanism (3, 6, 4) and said second cam mechanism (3, 5, 2) has cam surfaces (4R, 3R, 3L, 2L) contacting each other through a cam roller (5, 6). A clutch device according to claim 1, wherein at least one of said first cam mechanism and said second cam mechanism has cam surfaces (2P, 3P) directly contacting each other.

Inventors: MATSUMOTO SHOGO, MURATA KIYOHITO, MATSUMOTO, SHOGO, MURATA, KIYOHITO
Applicants: TOYOTA MOTOR CO LTD, TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1996
Main classification: F16D25
IPC codes: F16D55, F16D65, F16H57, F16D23, F16D25, F16D43