Abstract: A free wheel hub control system for a free wheel hub mechanism is positioned between a drive shaft and an axle hub supported by a spindle. A flexible printed circuit is disposed between an inner face of the spindle and an outer face of the drive shaft to transmit a control signal to an electric element of the free wheel hub mechanism. A cylindrical collar having contact portions is tightly fitted to the inner face of the spindle to hold the printed circuit in position.

Abstract: A torque distribution deciding control unit and an oil hydraulic clutch having opposite disks are provided. The clutch is disposed in a power transmitting system for four-wheel drive. One of disks is operatively connected to one of side gears of a central differential through a gear train and the other of the disks is operatively connected to the other side gear of the central differential through another gear train, whereby torque is transmitted to front and rear wheels at a distribution ratio. Loads on wheels such as weights on front and rear axles are detected. The control unit operates the clutch so as to distribute the torque at a ratio in accordance with loads on both axles.

Abstract: A control system for a 4WD vehicle includes a drive system for directly transmitting a torque to primary drive wheels such as rear wheels, and transmitting a torque to secondary drive wheels such as front wheels through a torque distributing transfer clutch, a group of sensors for determining a front and rear wheel speed difference, an engine condition such as a throttle opening, and a vehicle speed, and a control unit for controlling the engagement force of the transfer clutch. Normally, the control unit employs a first control mode based on the front and rear wheel speed difference. In rapid acceleration to start the vehicle, the control unit replaces the first mode by a second mode in which the clutch engagement force is increased in accordance with the engine condition such as the throttle opening independent of the wheel speed difference, and thereby prevents undesired spin of the primary drive wheels without delay.

Abstract: A vehicle equipped with four-wheel drive has a transfer case including a center-differential which delivers driving power to both front and rear axle assemblies when needed and is shiftable between a two-wheel and a four-wheel drive mode of operation and between a differential-locked and a differential-unlocked drive mode of operation. A free wheeling drive mechanism with a clutch member is incorporated in an output shaft of an axle differential in association with wheels non-driven in the two-wheel drive mode of operation and is adapted to disconnect when the vehicle is in the two-wheel drive mode of operation. A controller causes a forced drive mode shift of the center-differential from the four-wheel differential-underlined drive mode of operation either to the four-wheel differential-locked or to the two-wheel drive mode of operation when the disconnection of the free-wheeling drive mechanism is detected while the vehicle is in the four-wheel differential-unlocked drive mode of operation.

Abstract: A torque distribution deciding control unit and an oil hydraulic clutch having opposite disks are provided. The clutch is disposed in a power transmitting system for four-wheel drive. One of disks is operatively connected to one of side gears of a central differential through a gear train and the other of the disks is operatively connected to the other side gear of the central differential through another gear train, whereby torque is transmitted to front and rear wheels at a distribution ratio. Loads on wheels such as weights on front and rear axles are detected. The control unit operates the clutch so as to distribute the torque at a ratio in accordance with loads on both axles.

Abstract: In a power transfer mechanism including an input shaft arranged to be applied with drive torque from a prime mover of a motor vehicle, a first output shaft arranged coaxially with the input shaft for drive connection to a first set of drive axles and a second output shaft arranged in parallel with the first output shaft for drive connection to a second set of drive axles, a planetary gearset of the double pinion type is mounted on the first output shaft to transfer the drive torque from the input shaft to the first and second output shafts, the planetary gearset including a ring gear in drive connection to the input shaft, a sun gear in drive connection to the first output shaft and a planet carrier for drive connection to the second output shaft, a limited-slip differential in the form of a viscous fluid coupling is disposed between the ring gear and planet carrier to limit differential action between the first and second output shafts, and a drive train for drive connection between the planet carrier and th

Abstract: A control device of a remote free wheel hub mechanism includes a free wheel hub mechanism, an actuator and a control circuit. The control circuit further includes a two-wheel-drive circuit, a four-wheel-drive circuit, a transfer shift position detecting sensor, and an engine rotation drive detecting sensor. One of the two-wheel-drive circuit and the four-wheel-drive circuit in the transfer shift position detecting sensor moves to a closed condition independently of the shift position when the engine is stopped, and the transfer shift position detecting sensor correspondingly produces a signal of one of the two-wheel-drive and four-wheel-drive conditions, respectively. The engine rotation drive detecting sensor detects a rotational condition of an engine and produces a signal which closes one of the two-wheel-drive and the four-wheel-drive circuits when the engine is stopped.

Abstract: A four-wheel-drive vehicle in which the brakes are individually controlled to prevent locking. According to the invention, during anti-locking brake, the torque transmitted between the front and rear wheels is reduced, either by disconnecting the inter-axle transmission or switching to a loosely coupled viscous coupling.

Abstract: A shift assembly for shifting the gears of a transfer case of a vehicle as between two-wheel drive, four-wheel drive, neutral and four wheel drive range. A mounting plate rigidly mounted to the transfer case has a bottom configuration characterized by two cut out portions separated by a dependent landing portion. The shaft rod and its support housing are pivoted to the plate with a locating pin protruded from the shift rod through the housing and into the configured cut out portions of the mounting plate. The shift rod is biased upwardly relative to the support housing and is retained by the upward biasing into whichever of the cut out portions it is positioned. Repositioning is accomplished by depression of the rod against the upward biasing and pivoting of the rod to position the locating pin to the other cut out portion or on the landing portion separating the cut out portions. A depression in the landing portion identifies the neutral position.

Abstract: A two-axle four-wheel tractor is equipped at its front and rear ends with working implements, individually, which are of the same type, opposite in working direction and shiftable between a working position and a nonworking position. The tractor has a steering system for steering the front and rear four wheels in the same direction through the same angle, a running transmission system for driving only the wheels positioned toward one of the working implements which is lifted to the nonworking position or, in a special case, a system for restraining the wheels positioned rearward with respect to the direction of advance of the tractor in a straight running position without permitting steering.

Abstract: To realize three functions of twin viscous coupling in four-wheel drive, free coupling in two-wheel drive, and further direct (lock) coupling in four-wheel drive, the power transmission apparatus for transmitting power from a propeller shaft (9A) to two right and left rear wheel drive shafts (21A, 23A), comprises first and second hubs (4, 5) coupled to the drive shafts; cylindrical inner and outer casings (3a3b) for forming two working chambers (11, 12) in cooperation with the two hubs; first and second resistance plates (8, 9), and a driven member (17) for selectively engaging the inner casing with the outer casing (TWIN VISCO IN 4WD) and disengaging the inner casing from the outer casing (FREE IN 2WD).

Abstract: A power transfer device of the type which includes a housing, a first shaft rotatably mounted within the housing to transfer drive torque from a power transmission to a set of rear-wheel drive axles, a second shaft rotatably mounted within the housing in parallel with the first shaft for drive connection to a set of front-wheel drive axles, and a pair of clutch sleeves mounted on the first and second shafts and shiftable between respective positions in which they effect drive connection or disconnection between the first and second shafts.

Abstract: The arrangement controls a friction element for limiting a rotational speed compensation between the axles of a two-axle or all-wheel-driven vehicle as a function of the difference of the medium wheel speeds of both axles (longitudinal speed difference). This longitudinal speed difference is compared with two driving-speed-dependent tolerance bands, the first tolerance band being determining for positive and the second tolerance band being determining for negative longitudinal speed differences. If the values of the longitudinal speed differences are above the first or below the second tolerance band, the limiting is increased; if the values are within the tolerance bands, the instantaneous limiting is maintained; and if the values are between the tolerance bands, the limiting is reduced. This arrangement may also be expanded to include an adaptation device of the limit criteria with respect to different tread radii of the wheels and a cornering correction device.

Abstract: To prevent dust or muddy water from entering a hub housing or to prevent a hub clutch from being allowed to be inoperative, a hub clutch for selectively coupling or decoupling a wheel shaft to or from a clutch housing (to which a wheel is fixed), the hub clutch comprises a drive gear fixed to the wheel drive shaft; a slide gear axially slidably coupled to the clutch housing; a diaphragm fixed to the slide gear so as to partition an inner space of the clutch housing into an inner enclosed chamber and an outer enclosed chamber; and a control valve connected to an engine intake manifold vacuum, for selectively applying vacuum into the inner chamber and atmospheric pressure into the outer chamber or vice versa to move the diaphragm. Further, a piston plate and a spring can be used instead of the diaphragm.

Abstract: A clutch control system for the front wheel drive clutch of a four-wheel drive vehicle engages the front wheel drive clutch as a function of three brake-operated switches, a pair of manually-operated "OFF-ON-AUTO" mode switches and a pair of speed responsive switches connected between a battery and the solenoid of a front wheel drive clutch control valve. The system engages the clutch when vehicle speed is above a limit speed and both service brakes are applied even when the mode switches are in their "OFF" position wherein the clutch is normally disengaged.

Abstract: A transfer case for a vehicle having full time four-wheel drive includes an interaxle differential connected to the output of a transmission and driving coaxial driveshafts, each connected to a different axleshaft. One of the driveshafts supports a chain sprocket driveably connected by a chain belt to a driveshaft coaxial with the input shaft and output drive shafts. The differential includes a center driving disc, a housing connected to the input, two friction disc clutches each connected to one of the output driveshafts, driven discs connected to input pressure plates associated with each of the disc clutches, a ball drive assembly for engaging and disengaging the friction disc according to the relative angular position of the pressure plates, and a coiled compression spring urging the clutches to an engaged state.

Abstract: A full time-four-wheel-drive vehicle in which front and rear wheels are always connected to each other through a torque transmission coupling includes an engine; a transmission, a first differential which is driven through the transmission to drive one of a front and a rear wheel systems; a second differential which is drivingly connected to the other of the systems; and a torque transmission coupling which includes an input shaft which is drivingly connected to the transmission and the first differential, an output shaft which is drivingly connected to the second differential, an oil pump which is driven by the relative rotation between the input shaft and the output shaft to generate oil pressure corresponding to the speed of the relative rotation, and a friction clutch mechanism which engages the input shaft and the output shafts with each other by the oil pressure generated by the oil pump.

Abstract: In a power transfer device for four-wheel drive including a differential arranged to split the driving torque from a power transmission into two torque delivery paths, a first output shaft assembly in drive connection to the differential to transfer the split driving torque to front or rear-wheel drive axles and a second output shaft assembly in drive connection to the differential to transfer the split driving torque to rear or front-wheel drive axles, one of the output shaft assemblies being composed of a pair of split shafts, a shift mechanism includes a clutch sleeve slidably mounted on one of the split shafts for rotation therewith and shiftable between a first position where it is engaged with the other split shaft and a second position where it is disengaged from the other split shaft, a manually operated plug member rotatably coupled within a corresponding bore in the peripheral wall of a housing of the transfer device, and a fastening bolt threaded into the peripheral wall of the housing to fasten th

Abstract: A motor vehicle comprises two driven axles, one of which is adapted to be disconnected from the drive member by a disconnecting clutch, which is adapted to be automatically disengaged by clutch control in response to a brake application. In order to decrease the structural expenditure whereas the reliability of the handling of the vehicle is not adversely affected the disconnecting clutch consists of a positive clutch, which when it has been disengaged in response to a brake application is adapted to be automatically re-engaged in response to a release of the brake pedal or an actuation of an accelerator pedal when the engine is running at a speed above a predetermined threshold.

Abstract: A free wheel hub clutch for a drive shaft includes an outer casing, an inner sleeve in the casing for connection to the drive shaft, a slidable clutch in the casing for movement between a lock position wherein the clutch is connected therewith, and a free position wherein the clutch is disconnected from the inner sleeve for free rotation with respect thereto. The slidable clutch selectively and alternatively moves the clutch between the lock position and the free position, either mannually or remotely.

Abstract: A control system for a four-wheel drive vehicle having a continuously variable transmission, and a fluid operated transfer clutch for transmitting the output of the transmission to auxiliary drive wheels is disclosed. A transfer control valve is provided for changing the amount of oil supplied to the transfer clutch to selectively engage the clutch, and a three-way solenoid operated control valve is provided for controlling oil supplied to the transfer control. The solenoid operated control valve has a first port communicated with a pump, a second port communicated with the transfer control valve, a drain port, a valve body selectively closing the first port and the drain port. The solenoid operated control valve is operated by a pulse train. The duty ratio of the pulse train is controlled for rendering amount of drain oil from the drain port minimum at the changing the amount of the oil to the transfer clutch between the engagement and disengagement of the clutch.

Abstract: In a part-time four-wheel drive vehicle equipped with a transfer device adapted to change the operating mode of the vehicle drive system from a two-wheel drive mode to a four-wheel drive mode in response to engagement of a hydraulically operated clutch mechanism provided therein and with a split axle drive mechanism in the form of a differential which includes a clutch mechanism disengageable for disconnecting a pair of side shafts of the differential from a set of non-driven split axle parts when the two-wheel drive mode is selected at the transfer device and engageable for connecting the side shafts to the non-driven split axle parts when the four-wheel drive mode is selected at the transfer device, a control system for the split axle drive mechanism includes a pressure switch arranged to detect a hydraulic pressure applied to the clutch mechanism of the transfer device to be operated when applied with a predetermined hydraulic pressure after engagement of the clutch mechanism of the transfer device and an

Abstract: In order to be able to use a four-wheel drive of a motor vehicle for different vehicle types without significant changes, it is combined into a compact drive unit. For that purpose, a four-wheel-locking mechanism and a free-wheel device with by-pass clutch are arranged adjacent one another and coaxially to one another inside of a housing surrounding the same which is adapted to be flangedly connected to an axle housing of the motor vehicle.

Abstract: The transmission comprises a first differential device which connecs the drive shaft with a front shaft to transmit drive to the front wheels and to a rear shaft to transmit drive to the rear wheels a second differential device which connects the front shaft to the half-shaft of the front wheels and a third differential device which connects the rear shaft to the half-shafts of the rear wheels; the differential devices are of the limited slip type, that is to say in which the drive train which connects the two worm gears of the differential devices includes at least one pair of gear wheels having low transmission efficiency, and preferably the differential devices are of the torsen type.

Abstract: A transfer case for selectively providing four-wheel drive for a motor vehicle comprises a first clutch for shifting the input torque to and between a high speed power path, a low speed power path and a neutral position, as well as a second clutch for selectively engaging first and second output shafts for connection with the low and high speed power paths. Each clutch includes a slidable collar which is aligned with and slidable along the axis of the input shaft of the transfer case. Preferably, a single selector is used to shift the first and second clutch collars to provide the transfer case with four operating modes: a neutral position in which the input shaft is disengaged from the first and second output shafts, a two-wheel drive high speed output, a four-wheel drive high speed output and a four wheel drive low speed output.

Abstract: To incorporate a viscous coupling type power transmission apparatus for a four-wheel driven automotive vehicle with an antiskid braking system, viscous torque transmission from a first rotary transmission shaft (coupled to the front wheel shaft) to a second rotary transmission shaft (coupled to the rear wheel shaft) is intermitted by a clutch mechanism provided for the power transmission apparatus whenever a foot brake is applied. That is, when a foot brake pressure is applied to the brake member of the power transmission apparatus, the clutch mechanism is disengaged via a cam ring to decouple the first rotary transmission shaft from the second rotary transmission shaft.

Abstract: A torque distribution deciding control unit and an oil hydraulic clutch having opposite disks are provided. The clutch is disposed in a power transmitting system for four-wheel drive. One of disks is operatively connected to one of side gears of a central differential through a gear train and the other of the disks is operatively connected to the other side gear of the central differential through another gear train, whereby torque is transmitted to front and rear wheels at a distribution ratio. Loads on wheels such as weights on front and rear axles are detected. The control unit operates the clutch so as to distribute the torque at a ratio in accordance with loads on both axles.

Abstract: An actuator for a four wheel drive transfer mechanism which is laid in a power transmission device and is controlled by an electrical signal sent from a controlling unit comprises a torque generating mechanism which converts electrical energy into a torque, and a torque-thrust conversion mechanism which converts the torque generated by the torque generating mechanism into a thrust force. The thrust force generated from the torque-thrust conversion mechanism is applied to the frictional engaging device to control torque distribution between front and rear vehicle wheels.

Abstract: A drive system for a four-wheel drive motor vehicle, in particular an agricultural tractor, includes a gradually lockable differential for the front wheels, a gradually lockable differential for the rear wheels, and a gradually lockable center differential in the drive to the front and rear differential gears. The degree of locking of the respective differentials is controlled by a control circuit based upon their relative rotational speeds, the steering angle and the temperature in the center differential. In an alternative embodiment, brakes on each wheel and on the shafts connecting the center differential to the front and rear differential are used to supplement or replace the differential locks.

Abstract: A clutch control system for the front wheel drive clutch of a four-wheel drive vehicle engages the front wheel drive clutch when both service brakes are simultaneously released or simultaneously applied, but disengages the clutch when only the left or the right service brake alone is applied. The control system includes three brake-operated switches, a manually-operated switch and a speed responsive switch connected to the solenoid of a front wheel drive clutch control valve.

Abstract: In combination with a power transfer device, a power transmission includes a first shaft rotatably mounted within a housing and having an input end for connection to an output shaft of the transmission and an output end for drive connection to a pair of rear road wheels, a second shaft rotatably mounted within the housing in parallel with the first shaft for drive connection to a pair of rear road wheels, a drive member rotatable on the first shaft, a driven member mounted on the second shaft for rotation therewith and being drivingly connected to the drive member, a limited-clip differential in the form of viscous clutch coupling having an outer casing mounted on the first shaft for rotation therewith and coupled in a liquid-tight manner with an inner sleeve rotatably on the first shaft for defining a viscous fluid chamber and for relative rotation thereto, and a clutch sleeve axially movably mounted on a hub portion of the drive member for rotation therewith and shiftable between a first position where it i

Abstract: A motor vehicle drive system including a transmission having an output gear connected with an idle gear which is provided rotatably on an input member of a front inter-wheel differential gear mechanism which is provided in the front axle assembly. A transfer shaft is provided adjacent to the front axle assembly and has two or more inter-axle differential gear mechanisms which are of different torque split ratios. A selecting mechanism is provided for selectively connecting one of the inter-axle differential gear mechanisms with the idle gear to establish a desired torque split ratio between the front and rear wheels.

Abstract: A viscous coupling is provided in a power transmitting system for transmitting power of an engine to auxiliary driving wheels, and a lock device is provided for locking the viscous coupling so as to directly transmit the power to the auxiliary driving wheels. Driving torque of the engine is detected and compared with a predetermined driving torque and an output signal is produced when the detected driving torque exceeds the predetermined driving torque. An actuator responds to the output signal for operating the lock device to lock the viscous coupling.

Abstract: In combination with a power transmission for an automotive vehicle, a power transfer device includes a transfer casing secured at one side thereof to a casing of the power transmission, a ring gear rotatably mounted within the transfer casing to be applied with driving power from the power transmission through a center differential, and an output shaft assembly mounted within the transfer casing to transmit the driving power from the ring gear to a propeller shaft. The output shaft assembly includes a drive pinion integrally formed with an internally splined hollow shaft portion rotatably mounted within the transfer casing and being in mesh with the ring gear, and an externally splined slide shaft axially slidably coupled within the hollow shaft portion of the drive pinion for rotation therewith and having an output end portion for drive connection to the propeller shaft.

Abstract: A two-wheel and four-wheel drive transfer device includes a reciprocating fork shaft having a shift fork engagable with a sliding dog clutch so as to reciprocate the dog clutch and provide either two-wheel and four-wheel drive operating conditions. A motor is provided so as to rotate a worm gear assembly which is relatively rotatable with an output shaft supported in a casing. This worm gear is connected to and rotates a plate concurrently with rotation of the worm gear. A spring support plate is provided to be secured to the output shaft and two spiral springs, each spring being wound in a different direction and having a different rotating torque, are fixed to the output shaft and have ends brought into contact with the rotating plate and the spring support plate so that the rotating torque of the worm wheel is transmitted to the output shaft through the spiral springs depending on the direction of rotation of the worm gear.

Abstract: A four wheel drive transfer case transmits power from the output of a vehicle transmission to front and rear differential assemblies. The transfer case includes an input shaft coupled to the output shaft of the vehicle transmission, and an interaxle planetary gear differential for dividing power between a rear output shaft connected to the vehicle rear differential and a front output shaft connected to the vehicle front differential. An electromagnetic friction clutch is located in the transfer case and is adapted to selectively lock the planetary gear differential to prevent slip between the front and rear output shafts. An electronic control is operative to selectively engage the electromagnetic clutch to lock the differential for a predetermined time period when a predetermined amount of slip is detected between the front and rear output shafts.

Abstract: A two wheel drive/four wheel drive change over apparatus for four-wheel drive vehicles includes an actuator having a vacuum chamber. A tank storing an engine vacuum through a check valve is integrally formed in the vacuum chamber, whereby the engine vacuum stored in the tank can be used for operating the actuator.

Abstract: A transmission control device according to the present invention comprises a main transmission having a torque converting device provided with a direct clutch for effecting engagement and disengagement of the input member with output member of a torque converting portion; a sub transmission having a speed change mechanism; a drive-mode detecting means for detecting the drive mode of the speed change mechanism of the sub transmission; and a controller for controlling the lock-up characteristics of the direct clutch by means of the output of the drive mode detecting means.

Abstract: An electric control apparatus for a transfer device in a part-time four-wheel drive vehicle is arranged to permit switchover of the transfer device from the two-wheel drive mode to the four-wheel drive mode when a difference in rotational speed between front and rear propeller shafts is smaller than a predetermined value and to prohibit switchover of the transfer device from the two-wheel drive mode to the four-wheel drive mode when the difference in rotational speed between the front and rear propeller shafts is larger than the predetermined value.

Abstract: A transfer case operating apparatus for shifting a part-time four-wheel transfer case of a vehicle having a transfer gear assembly and a center-differential gear assembly, with their associated gear shift devices. The operating apparatus comprises a power drive actuator coupled to one of the shift devices; a mechanical actuator directly coupled to the other; a shift control device operated by a driver in the driver's compartment of the vehicle shift the transfer case between at least two-wheel high-speed drive mode; four-wheel, differential-free drive mode; and four wheel, differential-locked, low-speed drive mode; and a mechanism for, when the shift control device is operated to shift one gear assembly associated to the power drive actuator, disconnecting the mechanical actuator from the shift control device so as not to shift the other gear assembly. The mechanism works with different operating forces for causing the power drive and mechanical actuators.

Abstract: A direct-coupling/differential changeover apparatus is provided with a speed change gear function and includes an input member, two output members, a reaction member, a planetary gear set, and a engage/disengage changeover apparatus for effecting engagement/disengagement between elements of the planetary gear set and the members and between two of the elements of the planetary gear set. The engage/disengage changeover apparatus establishes a direct-coupled power train between all input and output members by engaging any one of the elements of the planetary gear set with the reaction member and by engaging one of the two other elements of the planetary gear set with the input member and the remaining element of the gear set with two output members.

Abstract: In a power transfer device including a housing, an input shaft rotatably mounted within the housing, an output shaft rotatably mounted within the housing and arranged coaxially with the input shaft for relative rotation thereto, a planetary gear unit arranged within the housing and having an input element mounted on the input shaft for rotation therewith and an output element connectable to the output shaft, and a clutch sleeve axially slidably mounted on the output shaft and shiftable between a first position in which it is retained to effect a drive connection between the input and output shafts and a second position in which it is retained to effect a drive connection between the output element of the gear unit and the output shaft, an oil pump assembly is arranged in parallel with the input shaft and mounted on an internal wall of the housing to be driven by the output element of the gear unit to pump up lubricating oil stored within the housing and supply it into an axial bore in the input shaft through

Abstract: A power transmission control system for a four-wheel drive vehicle powered by an engine has a transmission for transmitting the power of the engine to main driving wheels of the four-wheel drive vehicle, and a clutch for transmitting the power to auxiliary driving wheels. A hydraulic circuit for operating the clutch and a solenoid operated valve are provided for operating the clutch.Speed sensors are provided for detecting speeds of the main and auxiliary driving wheels in order to detect the slipping of wheels and vehicle speed.A steering angle is sensed for detecting a large steering angle. An electric circuit is provided to respond to the output of the speed sensors at slipping for engaging the clutch and to respond to large steering angle at low vehicle speed for disengaging the clutch for providing two-wheel driving.

Abstract: A power transmission system for a four-wheel drive vehicle has an automatic transmission for transmitting power of an engine to main driving wheels and a transfer clutch for transmitting the power to auxiliary driving wheels. First and second vehicle speed sensors are provided for sensing vehicle speed dependent on the main driving wheels and the auxiliary driving wheels, respectively. A two-wheel drive switch is provided for producing a two-wheel drive signal. The automatic transmission uses an output signal of the first vehicle speed sensor as data representing driving conditions of the vehicle. In response to the two-wheel drive signal, the transfer clutch is disengaged and an output signal of the second vehicle speed sensor is selected as vehicle speed.

Abstract: A four-wheel-drive vehicle in which the brakes are individually controlled to prevent locking. According to the invention, during anti-locking brake, the torque transmitted between the front and rear wheels is reduced, either by disconnecting the inter-axle transmission or switching to a loosely coupled viscous coupling.

Abstract: A four-wheel drive of a motor vehicle is arranged to effect automatic changes between a two-wheel drive mode and a four-wheel drive mode in dependence on the slip of two wheels (5) which are permanently driven. A frequent change from the four-wheel drive mode to the two-wheel drive mode for a speed comparison is to be avoided in a four-wheel drive which has a relatively simple structure. Two sensors (12) are associated with the two permanently driven wheels (5) and the output signals of said sensors are delivered to a computer (11), which determines for consecutive units of time the occurrences of the speed difference between said two wheels in excess of a predetermined threshold value and generates a distribution curve of said occurrences in consecutive units of time. That distribution curve is compared in the computer with a corresponding stored limiting curve, which is applicable to a minimum coefficient of road friction.

Abstract: A power transmission system suitable for use in a four-wheel drive motorcar. A torque generated from a power source is directly transmitted to a first axle, and it is transmitted to a second axle via a torque transmission device making use of viscosity of fluid. Between the power source and the second axle is provided torque limiter means for limiting a torque transmitted to the second axle to smaller than a preset value. Even if the torque transmission device should take a locked condition, an excessively large torque would not be exerted upon the respective parts in the power transmission system, and hence a torque transmission system can be made light in weight.

Abstract: A hydraulic control system for a four-wheel drive torque transfer mechanism for a vehicle, including an automatic transmission, a transfer mechanism having gear positions of a two-wheel drive direct-coupling mode H.sub.2, a four-wheel drive direct-coupling mode H.sub.4 and a reduced-speed four-wheel drive mode L.sub.4, and a hydraulic control circuit for controlling the transmission and the transfer mechanism. The transfer mechanism includes a reduction gear mechanism, a first output shaft, a second output shaft rotationally connectible to the first output shaft through a link mechanism, a four-wheel drive clutch for releasably coupling the first and second output shafts, a direct-coupling clutch for releasably coupling an input shaft of the reduction gear mechanism with the first output shaft, and a reduction brake for setting the reducing gear mechanism in a gear train of the reduced-speed mode.

Abstract: An improved apparatus for controlling the shift between two and four-wheel drivings comprises sensors for detecting the revolution velocities of a propeller and axle shafts, and a calculation unit for calculating a predetermined time duration during which the difference of the revolution velocities is less than a predetermined value after a shift member of the propeller shaft is shifted. A shift member of the axle shaft is shifted at a time during the predetermined time duration to be calculated by the calculation unit so that the shift is smoothly performed from two to four-wheel drivings without producing any gear sound or noise even in a high speed running.

Abstract: A hydraulic control system for a four-wheel drive torque transfer mechanism for a vehicle, including an automatic transmission, a transfer mechanism having a two-wheel drive direct-coupling gear (H.sub.2), a four-wheel drive direct-coupling gear (H.sub.4) and a reduced-speed four-wheel drive gear (L.sub.4) and a hydraulic control circuit for controlling the transmission and the transfer mechanism. The transfer mechanism includes a reduction gear mechanism, a first output shaft, a second output shaft connected to the first output shaft by means of a linkage, a four-wheel drive clutch for rotatably connecting and disconnecting the first and second output shafts, a direct-coupling clutch for connecting and disconnecting the input shaft of the reduction gear mechanism and the first output shaft and a reduction brake for shifting the reduction gear mechanism into the reduced-speed mode.