Power transmission system for a two-wheel and four-wheel drive vehicle

Abstract: In a transmission system for a two or four-wheel drive motor vehicle a multiple disc wet clutch (7) is arranged to couple and uncouple a rear axle differential (8). The wet clutch (7) is hydraulically actuated by a piston (7f). To avoid problems of control caused by centrifugal forces the piston (7f) a bearing (27) is interposed between the piston (7f) and a drum (7a) of the clutch (7) to absorb rotary notion of the drum.

Description: The present invention relates to a power transmission system for a two-wheel and four-wheel drive motor vehicle, and more particularly to a system having a fluid-operated multiple-disk friction clutch for distributing the power of an engine to front and rear-wheels. Japanese Patent Publication 61-28531 discloses a system in which a fluid-operated multiple-disk friction clutch is provided as a transfer device for distributing the power of the engine to the front-wheels and rear-wheels. The clutch is disposed in an extension case of an automatic transmission. The clutch comprises a clutch drum and a clutch hub, each having a plurality of disks, and a piston oil chamber formed between the clutch drum and a piston. The piston is slidably mounted on the hub with splines for pushing the disks of the clutch drum to the disks of the hub. When the clutch hub rotates, the piston rotates together with the hub. When the clutch rotates at a high speed, the centrifugal force of oil in the piston oil chamber is applied to the piston. When the clutch is being disengaged the pressure of oil is reduced. However, the centrifugal force acts to push the piston towards the disks of the clutch drum, so that the clutch cannot be completely disengaged. Further, the centrifugal force causes various disadvantages in accurate control of the pressure of oil. In order to provide a sufficient transmitting torque for the clutch, the diameter of the piston must be increased. However, since the piston is mounted on the clutch drum, an increase of the diameter of the piston entails an increase of the diameter of the clutch drum. If the clutch drum becomes large, the resistance of the lubricating oil in the clutch during operation becomes large, which causes reduction of power transmission efficiency. Japanese Patent Application Laid-Open 61-155027 discloses a system in which a pair of transfer clutches for front-wheels and for rear-wheels are provided in a transfer device provided for distributing the torque to the front-wheels and the rear-wheels. Claim 1 is characterised by reference to Japanese Patent Application Laid-Open 61-155027. Japanese Patent Application Laid-Open 61-146637 also discloses a system in which a transfer clutch is provided between a final reduction gear of a differential and a transfer device. A piston of the transfer clutch is mounted in the final reduction gear. Accordingly, in such systems, the centrifugal force is similarly exerted on the piston when the power transmission system rotates. GB 21 89 861 discloses an arrangement in which a transfer clutch incorporates a rotating mechanical oil pump in which the oil pressure depends only on the speed of rotation and is thus not independently controllable. DE 37 20 168 discloses a system in which oil pressure is provided separately to one side of a clutch actuating piston. The present invention seeks to provide a power transmission system in which no centrifugal force is produced in a transfer clutch. According to the present invention, there is provided a power transmission system according to claim 1. Embodiments of transmission systems for four-wheel drive vehicles will now be described, by way of example only, with reference to the accompanying drawings, in which:- Fig. 1 is a schematic diagram showing a first embodiment, Fig. 2 is a sectional view of transfer clutches of the first embodiment, Fig. 3 is a hydraulic control circuit of the first embodiment, Fig. 4 and 5 show modifications of the first embodiment, respectively, Fig. 6 is a schematic diagram showing of a second embodiment, Fig 6A is a sectional view through a second transfer clutch and rear differential of the second embodiment, Fig 6B shows a sectional view of a pump in the second embodiment, Fig. 7 shows a hydraulic control circuit of the second embodiment, Fig. 8 is a schematic diagram showing a third embodiment, Fig. 9 is a sectional view partly showing the system of the third embodiment, Fig. 10 is a schematic diagram showing a fourth embodiment of the present invention, Fig. 11 is a sectional view showing a main part of the system of the fourth embodiment. Fig. 1 shows a power transmission system of a four-wheel drive motor vehicle having a trans-axle power transmission system to which the present invention is applied. In a front portion of the motor vehicle, an engine 1 a clutch 2 and manual transmission 3 are laterally mounted. The power transmission system has a front power train and a rear power train. The front power train has a front differential 4. The rear power train comprises a transfer device 5, a propeller shaft6, and a rear differential 8. The power of the engine 1 is transmitted to the transmission 3 through the clutch 2. The output torque of the transmission is transmitted to front wheels F through an output gear 9, a final reduction gear 10, the front differential 4, and axles 4a. The final reduction gear 10 engages with an input gear 11 of the transfer device 5, which is securely mounted on a transfer shaft 5a. The transfer shaft 5a is operatively connected to the propeller shaft 6 through a pair of bevel gears 12, thereby transmitting the power. The power is transmitted to rear wheels R through a final reduction gear 13, the rear differential 8 and axles 8a. Referring to Figs. 1 and 2, in the first embodiment, a transfer clutch 32 is provided as a first transfer clutch and another transfer clutch 38 in the form of a multiple-disk friction clutch is provided on the transfer shaft 5a of the transfer device 5 as a second transfer clutch. The transfer clutch 32 is the same as the transfer clutch in the second embodiment. The second transfer clutch 38 comprises a drive drum 38a secured to a flange 11a of an input gear 11b and a driven drum 38b splined to the transfer shaft 5a. A plurality of disks 38c are splined on the drum 38a together with a pair of retainers 38d provided adjacent both end disks 38c and a plurality of disks 38e are splined on the drum 38b, disposed alternately with the disks 38c. A ring piston 38f is slidably engaged with an inner periphery of an annular casing 35a secured to the casing 35. The ring piston 38f is engaged with a knock pin 36a mounted in the annular casing 35a so as to prevent the piston from rotating. A piston chamber 38g is formed between the piston 38f and the casing 35a. A bearing 39 is disposed between the piston 38f and the retainer 38d. The bearing 39 has an inner race 39a engaged with piston 38f, an outer race 39b splined on the drive drum 38a and engaged with the retainer 38d. Fig. 3 shows a hydraulic system of the first embodiment comprising the valve unit 25 and a control unit 19. The valve unit 25 has a pressure regulator valve 15a, a transfer control valve 16a, a solenoid operated valve 17a and a pilot valve 18a. Oil from an oil pump 14' is supplied to the pressure regulating valve 15a by which the pressure of oil is regulated to a predetermined value. The oil is fed to a piston chamber 32g of the transfer clutch 32 through the transfer control valve 16a. The pilot valve 18a operates to provide a constant pilot pressure. The solenoid operated control valve 17a is operated by pulses from the control unit 19 at a duty ratio dependent on the driving conditions of the vehicle so that the drain of oil from the control valve 17a provides a control pressure. The control pressure is applied to an end of the control valve 16a to control the oil supplied to the clutch 32 so as to control the clutch pressure. In order to control the second transfer clutch 38, a second solenoid operated control valve 17b applied with a signal from the control unit 19 and a second transfer control valve 16b communicated with the piston chamber 38g are connected to the hydraulic circuit for the first transfer clutch 32. The second valves 16b and 17b are communicated with an oil pump 14', a pressure regulator valve 15a, and a pilot valve 18a. Fig. 4 shows a modification of the first embodiment. In place of the second transfer clutch 38, another second transfer clutch 41 having the same structures as the transfer clutch 38 is provided on an end portion of the transfer shaft 5a. The transmitting power from the final reduction gear 10 is transmitted to the transfer device 5 through the input gear 11, a drive drum 41a secured to a flange 11c of the input gear 11, and a driven drum 41b splined on the transfer shaft 5a. Fig. 5 shows a further modification. A second transfer clutch 42 is provided between rear drive shafts 6a and 6b connected to the propeller shaft. The construction of the transfer clutch 42 is substantially the same as the clutch 41. Figures 6 and 6A show a second embodiment in which the transfer clutch 32 is provided as a first transfer clutch in the following manner. A transfer clutch 32 in the form of a multiple-disk friction clutch is disposed between the final reduction gear 10 and the front differential 4 of the power transmission system. The transfer clutch 32 is mounted on an inside wall of a differential case 33 of the front differential 4. The differential case 3 is used as a driven drum 32b of the clutch 32. A drive drum 32a is secured to a hub of the gear 10 at an end thereof. Secured to the other end of the drive drum 32a is a supporting plate 34 which is rotatably mounted on a hub of the differential case 33 and rotatably supported in a casing 35 through a bearing 35a. The casing 35 is secured to a case of the transmission 3. The supporting plate 34 has four windows 34a and secured to the drive drum 32a at a part of the outer periphery thereof. A plurality of disks 32c are splined on an inner periphery of the drive drum 32a together with a pair of retainers 32d provided adjacent both end disks 32c and a plurality of disks 32e are splined on an outer periphery of the driven drum 32b, disposed alternately with the disks 32c. A ring piston 32f is slidably engaged with an inner periphery of the casing 35. The ring piston 32f is slidably engaged with a knock pin 36 mounted in the casing 35 so as to prevent the piston from rotating. A piston chamber 32g is formed between the piston 32f and the casing 35. A bearing 37 is disposed between the piston 32f and the retainer 32d. The bearing 37 has an outer race 37a engaged with a boss 32h of the piston 32f and an inner race 37b. The inner race 37b has four projections 37c each of which passes through the window 34a of the supporting plate 34 and is splined with the drive drum 32a and engaged with the retainer 32d. In the second embodiment as shown in figures 6 and 6A A transfer clutch 7A is provided as follows. The transfer clutch 7A, a carrier 20 of the rear differential 8 which is suspended from a body of the vehicle has a cylindrical portion 24 as a casing for the clutch 7A. The cylindrical portion 24 is integrally formed with the carrier 20 to form an oil chamber 24d therein. An extension case 23 is secured to a front end of the cylindrical portion 24. An input shaft 22 is rotatably mounted in the extension case 23 and connected to the propeller shaft 6. A drive pinion shaft 21a having a drive pinion is rotatably mounted in the carrier 20 of the rear differential 8. An end of the drive pinion shaft 21a is rotatably mounted in a hollow end 22c of the input shaft 22. The drive pinion 21 engages with the final reduction gear 13. The transfer clutch 7A is mounted on the drive pinion shaft 21a in the cylindrical portion 24 and an oil pump 14 is secured to a side of the cylindrical portion 24 for supplying oil to the transfer clutch 7A. The transfer clutch 7A comprises a drive drum 7A secured to a flange 22a of the input shaft 22 and a driven drum 7b splined on the drive pinion shaft 21a. A front end of the driven drum 7b engages with a thrust washer 26 which abuts on the end of the input shaft 22. A plurality of drive disks 7c are splined on the drum 7a together with a pair of retainers 7d provided adjacent both end disks 7c, and a plurality of driven disks 7e are splined on the drum 7b, disposed alternately with the disks 7c. A piston 7f is slidably mounted on an inner wall of the cylindrical portion 24 and on a guide cylinder 24c thereof with splined. The piston 7f engages with the outermost retainer 7d through an angular contact bearing 27. A piston chamber 7g is defined by the piston 7f, a partition 24b and the guide cylinder 24c of the cylindrical portion 24. The bearing 27 has an outer race 27a engaged with an operating end of the piston 7f, and splined with the guide cylinder 24c at a projecting end 27b, and an inner race 27c engaged with the retainer 7d and splined on the drum 7a at the outer periphery thereof. Thus, the outer race 27a is engaged with the guide cylinder 24c for preventing the rotation of outer race 27a and the inner race 27c is engaged with the drum 7a rotating in the same direction. Oil seals 28 and 29 are provided in inner peripheries of the partition 24b and the extension case 23, respectively. Since characteristics of the oil for the transfer clutch 7A and for hypoid gears of the differential 8 are different from each other, the oil seal 28 is provided for preventing both the oils from mixing. Oil passages 22b and 21b are formed in the hollow end 22c of the input shaft 22 and in the drive pinion shaft 21a, respectively, so as to communicate an outer space of the drive drum 7a with an inner space of the drive drum 7b. When the clutch drum 7a rotates, the oil in the oil chamber 24d in the cylindrical portion 24 is drawn up by the outer wall of the drive drum 7a, and supplied to the opening of oil passage 22b through an oil guide (not shown). The oil passes through the passages 22b and 21b and enters the chamber in the driven drum 7b. Further, the oil is supplied to disks 7c and 7e through passages (not shown) radially formed in the spline portion of the driven drum 7b. The oil pump 14' is secured to a housing portion 24a formed on the side of the cylindrical portion 24. As shown in Fig. 3, has an oil reservoir 14g is provided on the underside of the cylindrical portion 24. A valve unit 25, which will be described hereinafter, is provided in the reservoir 14g. The oil pump 14 has an electric motor 14a, an inner rotor 14b mounted on an output shaft of the motor 14a and an outer rotor 14c engaged with the inner rotor 14b. These rotors are mounted in the housing portion 24a and covered by a cover 14d which is secured to the housing portion 24a by bolts together with the motor 14a. An inlet port 14'e is communicated with an oil strainer of the oil reservoir 14'g and a discharge port 14f is communicated with the valve united 25. With reference to Fig. 7a the hydraulic control system comprises the valve unit 25 and the control unit 19 as described with reference to figure 3. However to control the second transfer clutch 7A an independent hydraulic circuit is provided. The independent hydraulic circuit has an oil pump 14A, a regulator valve 15b, and a pilot valve 18b in addition to the valves of the circuit shown in Fig. 3. Referring to figure 7b, the system is provided with an FF switch 40a for establishing a front-wheel drive system, an FR switch 40b for establishing a rear-wheel drive system, and a four-wheel control switch 40c. When a signal from the FF switch 40a is applied to the control unit 19, the control unit 19 produces a duty ratio signal of 0% which is applied to the solenoid operate valve 17a of the first transfer clutch 32. The first transfer clutch 32 is entirely engaged and the second transfer clutch 7A is disengaged so that the engine torque is transmitted only to the front wheels F to provide the front-wheel drive system. When a signal from the FR switch 40b is applied to the control unit 19, the duty ration signal of 0% is applied to the solenoid operated valve 17b of the second transfer clutch 7A. Thus, the first transfer clutch 32 is disengaged and the second transfer clutch 7A is engaged to transmit the torque only to the rear wheels R to provide a rear-wheel drive system. When a signal from the 4WD control switch 40c is applied to the control unit 19, the CPU 150 calculates the duty ratios for the solenoid operated control valves 17a and 17b between 0% and 100% in accordance with a map stored in the memory 151. The solenoid operated valves 17a and 17b actuate to control the oil for the transfer control valves 16a and 16b so that the respective clutch pressures supplied to the transfer clutches 32 and 7A varies in accordance with the driving conditions of the motor vehicle. Thus, a four-wheel drive mode is provided for distributing the torque to the front wheels F and the rear wheels R. When the vehicle turns a corner at a small radius during four-wheel driving, an inside circulating torque produces in the power transmitting system because of the difference between cornering radii of the front wheels and the rear wheels, which causes tight corner braking effect on the vehicle. In the system of Figs. 6 and 7, the difference between front-wheel speed and rear-wheel speed is detected by the sensors 159 and 160. In accordance with the speed difference, the clutch pressure applied to one of the first and the second transfer clutches is reduced to produce slip in the corresponding clutch, thereby preventing the tight corner braking effect. In accordance with the second embodiment, since one of the transfer clutches is disposed in the front differential and the other clutch is disposed in the rear differential which is independently provided, the transfer device is compact in structure. Further, the appropriate driving mode of the vehicle is selected in accordance with the driving conditions for ensuring stability, steerability and starting characteristics of the vehicle. Figs. 8 and 9 show a power transmission system of a third embodiment of the present invention. The transmission system has an engine 51 longitudinally mounted on a front portion of the vehicle, a clutch 52, a synchromesh manual transmission 53 and a transfer device 54, which are disposed in the longitudinal direction of the vehicle. A front differential 57 and a rear differential 58 are connected to the transfer device 54 by way of propeller shafts 55 and 56. Referring to Fig. 9, the transfer device 54 comprises a transfer drive sprocket 61 splined to an output shaft 59 of the transmission 53, a transfer driven sprocket 62 splined to a front drive shaft 60, and a drive belt 63 made of a chain provided between sprockets 61 and 62. The output shaft 59 is connected to the propeller shaft 56 through a companion flange 64 and the front drive shaft 60 is connected to the propeller shaft 55 through a companion flange 65. A first transfer clutch 66 is provided in the front differential 57 and a second transfer clutch 67 is provided in the rear differential 58. Each of the clutches 66 and 67 has the same structure as the clutch 7A of Fig. 2 and the oil supply system is the same as the system of Fig. 7. Figs. 10 and 11 show a fourth embodiment of the present invention. The motor vehicle has an engine 71 at a front portion thereof, a clutch 72, a manual transmission 74, a transfer device 75 having a first transfer clutch 87, and a front differential 73. A rear differential 78 having a second transfer clutch 88 is connected to the transfer device 75 through a propeller shaft 76 and a rear drive shaft 79. Referring to Fig. 11, the transmission 74 has an input shaft 80 operatively connected to a crank shaft 71a of the engine 71 and a hollow output shaft 81 disposed in parallel with the input shaft. A front drive shaft 82 is disposed in the output shaft 81. A drive pinion 82a of the front drive shaft 82 engages with a final reduction gear 73a (Fig. 10) of the front differential 73. The power of the engine is transmitted to the output shaft 81 through the input shaft 80 of the transmission and to the front wheels F through the first transfer clutch 87, the front drive shaft 82, the drive pinion 82a, the final reduction gear 73a and the front differential 73. The output shaft 81 is operatively connected to the rear drive shaft 79 through the transfer drive gears 83a and a driven gear 79a to transmit the power of the engine to the rear wheels R through the propeller shaft 76, the second transfer clutch 88, a final reduction gear 78a of the rear differential 78. The transfer device 75 comprises the transfer driven gear 79a integrated with the rear drive shaft 79, a gear sleeve 83 mounted on the output shaft 81, the transfer drive gear 83a integrated with the sleeve 83 and engaged with the driven gear 79a, an intermediate shaft 84 secured to a rear portion of the front drive shaft 82, a cylindrical supporting member 85 splined to the intermediate shaft 84, and the first transfer clutch 87 disposed between the supporting member 85 and the gear sleeve 83. The transfer clutch 87 comprises a drive drum 87a secured to a boss of the drive gear 83a, a driven drum 87b splined on a flange of the supporting member 85, a plurality of disks 87c splined on the drum 87a together with retainers 87d, and a plurality of disks 87e splined on the drum 87b, alternately arranged. A ring piston 87f is slidably mounted on the gear sleeve 83 through a seal ring 86a. The piston 87f is slidably engaged with an inner periphery of the drum 87a at an outer flange having an oil seal 86b. A piston chamber 87g is formed between the piston 87f and the drum 87a. A return coil spring 88 is provided between the piston 87f and a retainer 89 secured to the sleeve 83. When the oil in the oil chamber 87g is drained, the piston 87f is pushed by the spring 88 to disengage the clutch. An oil pump 94 for the first transfer clutch 87 is housed in a pump housing 97 disposed in a rear portion of the transmission 74. The pump 94 is operated by the engine through the crank shaft 71a and a pump drive shaft 94a. An inlet of the oil pump 94 is communicated with an oil reservoir 90 attached to the underside of the transfer device 75 through a suction passage 92 and a discharge passage 93 formed in a partition 95. A valve unit 25a is provided in the reservoir 90. Oil seals 96 and 98 are provided in the partition 95 and the pump housing 97, respectively. The second transfer clutch 88 has the same structure as the clutch 7A of the second embodiment.

Claims: A power transmission system in a two and four wheel drive vehicle having: a transmission (3,74,75) coupled to an engine (1, 71), a front wheel differential (4,57,73) arranged to distribute torque from the transmission between the front wheels (F), a rear wheel differential (8,58,78) arranged to distribute torque from the transmission between the rear wheels (R), an output (9) from the transmission to connect the transmission with at least one of the differentials (4,57,75,8,58,78), a first fluid operable transfer clutch (32,66,87) provided to control the connection between the output member (9) and the front wheel differential (4,57,73) and disposed in one of the front differential (4,57) or the transmission (3,74,75), and a second fluid operable transfer clutch (38,7A,67,88) operable to control the connection between the output member (9) and the rear wheel differential (8,58,78), characterised in that said second fluid operable transfer clutch (38,7A,67,88) is disposed in one of: the transmission (3) or the rear wheel differential (8) when the first transfer clutch (32,66,86) is disposed in the front wheel differential (4), or in the rear wheel differential (78) when the first transfer clutch (87) is disposed in the transmission (74,75). A system according to claim 1 wherein the transmission includes a gear box (3), the front wheel differential (4) is disposed in a front wheel differential casing (35) ,said front wheel differential (4) distributing torque from the gear box (3) between the front wheels (F), and said front wheel differential casing (35) being mounted on a casing of the gear box (3), said rear wheel differential (8) mounted in a carrier casing (20, 24) and coupled to the output member (9), said first transfer clutch (32) being mounted in the front wheel differential casing (35) and having, a drive drum (32a) coupled to the output (9) and a driven drum (32b) coupled to the differential (32) by mounting the driven drum (32b) on a cage (33) of the differential (4), a piston (32f) mounted in a piston chamber (32g) and operable to couple and de-couple the drive and driven drums (32a, 32b), said piston bearing against said driven drum (32b) via an intermediate rotary bearing (37a) which absorbs the relative rotary motions of the piston (32f) and the driven drum (32b) so the piston chamber (32g) can be stationary and hence not subject to centrifugal forces, an hydraulic circuit (25) having; an oil pump (14') provided to supply oil to said piston (32f) via control valves in order to actuate the clutch (32) in accordance with driving conditions of the vehicle. A system according to claim 2, wherein the bearing (37a) is an angular contact bearing. A system according to claim 2, or claim 3 wherein the second transfer clutch (38, 41) is co-axially mounted on a transfer shaft (5a) of a transfer device (5) in the front differential casing (35) whereby torque is transmitted from the output member (3) to the rear differential (8) via a prop-shaft (6), said transfer shaft (5a) being mounted parallel with the axis of the front differential (4). A system according to claim 2 wherein the gear box (3) is coupled to the rear differential (8) via a transfer device (5) and a prop-shaft (6), said transfer device (5) including a transfer shaft (5a) lying parallel to the axis of the front differential (4) and a spur gear (12) coupling the transfer shaft (5a) to the prop-shaft (6) said prop-shaft (6) being formed of two co-axial parts (6a, 6b) arranged to be coupled via the second transfer clutch (41, 42). A system according to claim 5 wherein the second transfer clutch (7A) is mounted on the rear differential (8) to couple a prop-shaft (6) to the rear differential (8). A system according to claim 5 wherein the gear box (53) is coupled to either one or both of the front or rear differentials (57, 58) via a front prop-shaft (55) and a rear prop-shaft (56), said prop-shafts being coupled to the gear box via a transfer device (54), said transfer device (54) having companion flange (64) coupling the gear box output shaft (59) with the rear prop-shaft (56), a transfer drive sprocket (61) splined on the gear box output shaft (59) and coupled to a transfer driven sprocket (62) via a drive belt (63) said driven sprocket (62) being coupled to the front prop-shaft (55). A system according to claim 2 wherein the first transfer clutch (32, 41, 42) and the second transfer clutch (8) are located in the front differential casing (35) and an oil pump (14') is provided to supply oil to both the first transfer clutch (32, 41, 42) and the second transfer clutch (8). A system according to claim 2 wherein the rear transfer clutch (7A) is located in the carrier casing (20, 22) together with an oil pump (14A). A system according to any one of claims 2 to 9 wherein each transfer clutch (32, 66, 87, 38, 7A, 67, 88) is controlled via the control unit (19) and the hydraulic circuit (25). A system according to claim 10 wherein the control unit (19) is provided with sensors responsive to; throttle position, battery voltage, rear-wheel speed, front-wheel speed, shift range and idle state.

Inventors: KOBAYASHI TOSHIO, MARUYAMA KEIICHI, OHNUKI YUKIO, KOBAYASHI, TOSHIO, MARUYAMA, KEIICHI, OHNUKI, YUKIO, KOBAYASHI, TOSHIO, C/O FUJI JUKOGYO K.K., Maruyama, Keiichi, c/o Fuji Jukogyo K.K., Ohnuki, Yukio, c/o Fuji Jukogyo K.K.
Applicants: FUJI HEAVY IND LTD, FUJI JUKOGYO KABUSHIKI KAISHA
Application year: 1989
Main classification: B60K23
IPC codes: B60K23, B60K17