CA2013640C - Electric control apparatus for transfer device in part-time four-wheel drive vehicle - Google Patents

Abstract

In a part-time four-wheel drive vehicle, an electric control apparatus for a transfer device in drive connection to a front or rear differential is arranged to permit selection of the four-wheel drive mode at the transfer device during travel of the vehicle in the two-wheel drive mode only in a condition where travel speed of the vehicle and temperature of lubricating oil in the differential are in a predetermined allowable region. The allowable region is defined to permit engagement of a clutch mechanism in the transfer device during travel of the vehicle in the two-wheel drive mode without causing any heavy load acting thereon.

Description

~ 20 ! 3640 The present invention relates to an electric control apparatus for a transfer device in part-time four-wheel drive vehicles, the transfer device being arranged to be switched over by operation of a manual operation switch to selectively provide a two-wheel drive mode or a four-wheel drive mode of operation for the vehicle.

In Japanese Utility Model Early Publication No.
63-69034, there has been proposed a part-time four-wheel drive system which includes a transfer device drivingly connected to a prime mover of the vehicle to continuously transfer the power from the prime mover to a set of rear road wheels and to selectively transfer the power to a set of front road wheels under control of a clutch lS mechanism provided therein, and a front differential in drive connection to split axle parts of the front road wheels at its output side and being drivingly connected to the transfer device at its input side to selectively transmit the power from the transfer device to the front road wheels under control of a clutch mechanism provided therein. In the part-time four-wheel drive system, each actuator of the clutch mechanisms in the transfer device and differential is activated under control of a manual operation switch. When the operation switch is manipulated by the driver to select a four-wheel drive mode, both the clutch mechani~m~ are engaged by activation of their a~90ciated a~t~ators to transmit the po~?er to the front road wheels through the transfer devic2 and differential. When the ope~ation swi~ch is manipulAted by the driver to ~elect a two-wheel drive mods, both the clutch mechani~ms ~re disengaged by activation of their as~ociated actuators to disconnect the differenti~l from the transfer device and from the split axle parts of the ~ront road wheels. This is 1~ effective to eliminate ~ack drive of the differential and propeller shaft for th~ non-driven front road wheels.

In the tran~fer device, a synchronize~ is assembled with the clutch mechanism to establish synchrcnization between drive and driven members in the transfer device when the clutch mechani~m i~ brought into engagement to select the four-wheel drive mode. The ~amponent parts o~ the synchroni2er are applied with a heavy lo~d from the driven mem~er if the clutch mechanism i-~ engaged in a ~ondition where the vi3cou8 resi~tance o~
20 lubricating oil in the differential i8 inorea~ed due to drop of the ambient t~mperature to cause an increa~e of dra~ resictance of the driven member or in a condition where a difference in rotational ~peed ~etween the drive and driven ~embers i3 large during high speed travel of ~5 the vehicle. This re~ults in defacement of the component par~s of the synchron1zer in a short period of time.

It is, thereore, a primary obiect of the present invention to prcvide an electric control App~ratus for the transfer device in which travel speed of the vehicle and temperature of lubricating oil in the differential are detectel to permit selection of the four-wheel drive mode at the transfer device during travel of the vehicle in the two-wheel drive mode only in a condition where any h~vy load does not act on the clutch mechanism in the transfer device.

Another ob~ect of the present invention is to provide an eiectric cont~ol apparatus for the tran~fer device, havin~ the a~ove-described characteristicR, in which indication means i5 provided to inform the driver of the fact that the selection of ~he four-wheel drive lS mode is prohibited durin~ travel of the vehicle in the two-wheel drive mode.

According to the present invention, there is provided an electric control apparatus for a part-time four-wheel drive vehicle having a transfer device drivingly connected to a prime mover of the vehicle to continuously transfer th~ power from the prime mover to a first set of road wheels, the tran~fer device including a first clutch mechanism arranged to transfer the power to a ~econd set of road wheels when it has been engaged, a differential drivingly connected at its output side to the ~econd set of road ~eels and at its input side to the transfer device, the differential including a second clutch mechanism arranged to transmit the power from the transfer device to the ~cond set of road wheels when it has been engaged, a first actuator assembled with the transfer device to engage the first clutch mec~anism when it has been operated in one direction and to disengage the first clutch mechanism when it has ~een operated in the opposite direction, and a second sctuator asqembled w$th the differential to engage the second clutch mechanism when it has been operated in one direction and to disengage the second ~lutch mechanism when it has been operated in the opposite direction.

The electric control apparatus comprises a manual operation switch ~or selecting a two-wheel drive mode or a four-wheel drive mode at the transfer device, a ~peed sensor for detecti~g t~avel ~peed of the vehicle to produce a speed signal i~dicative the travel speed of the veh~cle, a temperature 8ensor for detecting temperature of lubricating oil in the dif~erential to prod~ce a temperature signal indic~tive of the oil temperature, and control means in the forn of a microcomputer responsive to the spe~d and temperature signals for operating the first and second actuatols respectively in the one ~ 2013640 direction when the manu~ operation switch has been manip~lated to select t~e four-wheel drive mode at the transfer device only in a condition where the travel speed and oil temperature are in a predeter~ined allowable region during travel of the vehicle in the two-wheel drive mode and for rendering the f irct and ~econd actuators inoperative when the manual operation 5Wi tch has been manipul~ted to select the four-wheel drive mode in a condition where the ~ravel speed and oil temperature are out of the predetermined allowable region .

In a practical embodiment of the present invention, the predeternined allowable region is defined to permit engagement of the first clutch mechanism during 1; travel of the vehicle in the two-wheel drive mode without causing any heavy load ~cting thereon. It is preferable that the electric contr~l apparatus further comprises indicat$on means for visually informing the driver o~ the fact that the first and second actuators have been rendered inoperative under control of the control means.
In the case that the tr~snfer device includes a change-speed mechani~m, for instance in the form of a planetary gear unit, arranged to selectively provide low and high speed power tr~ins for transfer of the power to the first and second sets of road wheels and a detection switch associated with the change-speed mechanism to produce a low speed sig~al therefrom when the change-speed mechanism ~s conditioned to provide the low ~peed power train and to produce a high ~peed signal S therefrom when the chan~e-speed mechanis~ i~ conditioned to provide the high speed power train, the control means of the electric control apparatus is further responsive to the high speed signaL f rom the detection switch to operate the first and s~cond actuators respectively in th~ one direction when the manual operation switch has been manipulated to se~ct the four-wheel drive mode at the tran~fer device in a condition where the travel ~peed and oil temperature are in the predetermined allowable region during travel of the vehicle in the high speed two-wheel drive mode.

For a better ~nderst;~nding of the present invention, and to show how the same may be carried into effect, ~eference will now be made, by way of example, to the accompanying drawi~gs, in which:
Fig. l is a schematic illustration of a part-time four-wheel drive vehicle equipped with a tran~fer device to be controlled by an electric control apparatu~ in accordan~ with the pre~ent invention;
~ig. 2 is a ~hematic illustration of component ~5 parts of the transfer device and a front differential drivingly connected thereto;

Fig. 3 is a block diagram of the eLectric control apparatu~;
Figs. 4~A) and 4(8) illustrate a flow chart of a program for a microcomp~ter in the electric control apparaut~
Fig. 5 is a g~ph showing a relationship between temperature of lubricating oil in the ~ront differentlal and travel speed of the vehlcle;
Fig. 6 i~ a b~ock diagram of a modification of the electric control apparatus shown in Fig. 3;
Flg. 7 is a flow chart illustratlng a program for a microcomputer in the electric control circuit shown in Fig. 6;
~ ig. 8 is a f~ll sectional view of a practical embodiment of the transfer device schematically shown in Fig. 2;
Fig. 9 is an ~nlarged elevation of n electric motor and a fork shaft shown in Fig. 8: .~
Fig. 10 is a cross-sectional view taken along line x-X in Fig. 9;
Fig. 11 is a cross-sectional view taken along line XI-XI in Fig. 10~
Fig. 12 is a cross-~ectional view taken along line XII-XII in Fig. 95 Fig. 13 is a full ~ectional view of a practical embodiment of the frort differential schematically shown in Fig. 2:

Fig. 14 is a blo~ diagram of an electric control apparatus modified for the tran~fer device and front differential shown in Figs. 8 and 13; and Fig. 15(A) and 15ls) illustarate a flow chart representing a program executed by the microcomputer shown in Fig~ 14.

Referring now to the drawing~, in particular to ~ig. 1, there is illustrated a part-time four-wheel drive vehicle which comprises an internal co~bustion engine 11 1~ mounted on the front portion of a vehicle body structure, a power transmission 1~ attached to the rear end of engine 11 through a conventional clutch mechanism, and a transfer device 20 uni~ed with the power transmi~sion 12.
The transfer device 20 is arranged to continuously transfer the power from transmission 12 to a set of rear road wheels and to se~c~ively transfer the power to a set of front road wheel~ under control of a clutch mechanism 20a shown in Fig. 2.

AQ shown in Pigs. 1 and 2. the transfer dQvice ~0 includes an input ~haft 21 drivingly connected to an outpu~ shaft of trans~ission 12, a first output shaft 22 coaxially connected tc the input shaft 21 for drive connection to a rear propeller shaft 13, and a second output shaft 23 arranqed in parallel with the first _q output shaft 22 for drive connection to a front propeller shaft 14. The first o~tput shaft 22 i8 provided thereon with a d{ive sprocket ~4 which is integrally provided wi~h an externally ~plined clutch h~ 28 and is arranged for relative rotation to the input shaft 22. An externally splined clutch hub 27 is mounted on the firat output shaft 22 for rotation therewith, and an internally spltned clutch sleeve 32 is axially slidably mounted on the clutch hub 27. The clutch sleeve 32 i~ shiftable between a first position where it is disengaged from the clutch h~b 28 and a second position where it is engaged with the clutch hub 28 The clutch ~leeve 32 i~ ~rranged to be shifted by a vac~um actuator 34 of the diaphragm type through a fork shaft 33a and a ~hift fork 3~b. A
driven sprocke~ 25 is ~ounted on the second outp~t shaft 23 for rotation therewlth and is driving~y connected to the drive sprocket 24 by means of a drive chain 26.

The clutch mechanism 20a of transfer device 20 includes a ~ynchronize~ ring 31 rotatably coupled with a conical portion of clutch hub 28 to establish synchronization be~ween the clutch hubs 27, 28 in shifting operation of ~he clutch sleeve 32 toward the second po~ition. The ~acuum actuator 34 i8 assembled with the transfer device 20 in an appropriate manner, ~5 which includes a diaphragm piston 34a assembled within 20~3~
.

an actuator housing to subdivide the interior of the housing into f irst and second pneumatic chamber~ 34b and 34c. The fork shaft 33a is connected at its outer end to the diaphragm piston 34a, and the pneumatic chambers 34b, 34c are connected to a vacuum tank 15 respectively through electrically operated switchove~ valves 35, 36.
As shown in ~ig. 3, t~ switchover valve 35 is provided with a solenoid 35a, while the switchover valve 36 is provided with a solenoid 36a. During deenergization of the solenoids 35a, 36a, the switchover valve~ 35, 36 each are maintained in a first position to communicate the pneumatic chambers 34b, 34c with the atmospheric air.
When the solenoid 35a or 36a i9 3electively energized, the switchover valve 35 or 36 is switched over from the first position to a second position to communicate the pneumatic chamber 34b or 34c to the vacuum tank 15. ~he vacuum ~ank is connec~d to an intak manifold of engine ~1 .

The front propeller shaft 14 is drivingly connscted at it~ front end to a front differential 40 and at its rear end to the second output shaft 23 of tran~fer device 20. The front differential 40 i8 arranged to selectively transmit the power from propeller shaft 14 to split axle shafts 17a, 17b of the front road wheels under control of a clutch mechanism 40a. ~he front 20~ 3B40 differential 40 include~ a differential case 42 rotatably mounted within a differenti~l carrier 41. The differential case 42 is provided therein with a pair of pinion ge~rs 43a, 43b and a pair cf side gears 44a, 44b in mesh with pinion gears 43a, 43b. The differential case 42 is provided t~ereon with a ring gear 45 in mesh with a drlve pinion 46 connected to the front prope~ler shaft 14 for rotation therewith. Disposed between the split axle shafts 17a, 17b are tubular drive shafts 47, 48 which are divided into inner shafts 47a, 48a and outer shafts 47b, 48b, respectively. The inner shafts 47a, 48a are drivingly connected at their inner ends to the side gears 44a, 44b, while the outer shafts 47b, 48b are drivingly connected at their outer ends to the split axle shafts 17a, 17b, respectively.

The clutch m~hanism 40a of front differential ~0 includes an intern~lly ~plined cLutch s~eeve 51 axially slidably mounted on the inner shaft 47a and an operation rod ~2 conne~ting the clutch ~leeve 51 to the inner shaft 48a. Wher shifted from a first position to a second position, the clutch sleeve 51 is en~aged with the outer shaft 47b to e3tabli~h drive connection between the inner and outer shaft~ 47a, 47b. Simultaneously, the operation rod 52 is ~hifted to establish drive connection between the inner and outer shafts 48a, 48b. The clutch 2 ~

sleeve 51 is arra~ged to be shifted by a vacuum actuator 54 of ~he diaphragm type through a fork ~haft 53a and a YALft fork 53b.

The vacuum a~uator 54 is a~sembled with the front differential 40 in an apprapriate manner, which includes a diaphragm piston 54a assembled within an actuator housing to subdivide the interior of the hou~ing into first and second pneumatic chambers 54~ and 54c.
The fork shaft 53a is connected at its outer end to the 1~ diaphragm piston 54a, and the pneumatic chambers 54b, 54c are connected to the ~cuum tan~ 15 respective~y through electrically operated switchover valves 55, 56. A8 shown Ln Fig. 3, the ~witchover valve 55 i8 provided with a solenoid 55a, while t~ switchover valve 56 i~ provided with a solenoid 56a. During deenergization of the solenoids 55a, 56a, t~ switchover valves 55, S~ each are maintained in a first position to communicate the pneumatic chambers 54~, 54c with the atmospheric air.
When the solenoid 55a or 56a is selectively energized, the switchover valve 55 or 56 i8 switched over from the first po8ition to a second po~ition to communicate the pneumatic chamber 54b or 54c to the vacuum tank 15.

A~ shown in Figs. 1 and 3, an electric control apparatu8 60 for the transfer device ~ and front 2~1 3640 dlffe~ential 40 inclu~s a manual operation switch 61, a detection switch 62, a speed sensor 63 and a thermo-sen~or 64. The manual operation ~witch 61 i~ in the form of a normally open switch of the momentary contact type which is provided on an instrument panel (not qhown) of the vehicle to be closed by manipulation of the driver. The detection switch 62 i in the form of a normally open switch mounted on the housing of transfer device 2~ and arranged to face the clutch sleeve 20a as shown in Fig. 2. Thus, the dete~tion ~witch 62 is maintained in its open po~ition when the clutch sleeve 32 i~ in the ~irst position and is clo~ed by engagement with a projection of clutch sleeve 32 when it is shifted to and maintained in the second position as shown by imaginary lines in Fig. 2. The ~peed ~ensor 63 is mounted on the housin~ of transfer device 20 to detect the rotational speed o first output shaft 22 thereby to produce an electric s~ed signal V indicative of travel ~peed of the vehicle. The thermo-~ensor 64 is mounted on the housing of front differential 40 to detect a temperature of lubricating oil in the differential carrier 41 thereby to produce an electric oil temperature signal T indicative of the temperature of lubricating oil.

- ~4 -~ 20 7 3~

The electric control apparatu~ 60 includes a microcomputer 65 which is connected to the switches 61, 62 and sen~ors 63, 64. The computer 65 comprises a rear-only memory or RO~ 65~, a central proces~ing unLt or CPU 65c, a random acc~g~ memory or RAM 65d and an input-output device or I/O 65e which are connected to one another by means of a common bus line 65a. The ROM 65b is arranged to memorize a program represented by a flow chart shown in Fig. 4 ~nd to memorize control data in the form of a table defini~g allowab~e and prohitive regions A and B based on a relationship between travel speed of the vehicle and temperature of the lubricating oil ~hown in Fig. 5. In the allowable region A, the clutch mechanism 20a can ~e e~gaged witho~t causing any heavy li load acting on the synchronizer 31. In the prohibitive region B, the synchronizer 31 is applied with a heavy load in engagement of the clwtch mechanism 20a. The CPU
65c is arranged to ini~ate execution of the program when an ignition switch ( not shown ) is closed and to repeat 2C execution of the program. The RAM 65d i~ arranged to temporarily memorize necessary data for execution of the program. The I/O 65e is connected to the switches 61, 62 and ~en~orq 63, 64 and connected to re~ay control circuits 66, 67, a lamp control circuit 68 and a buzzer control circuit 71.

The relay control circuits 66, 67 are connected to relay circuits 7~, 73 to selectively energize relay coils 72a and 73a under control of the computer 65. The relay circuit 72 includes a relay switch 72b the movable contact of which is maintained in engagement with a fixed contact Cl during dee~rgization of the relay coil 72a to be engaged with a fixed contact C2 in response to ene~gization of the r~ay coil 72a. Similary, the relay circuit 73 includes a relay switch 73b ~he movable contact of which is maintained in engagement with a fixed contact Cl during dee~rgization of the relay coil 73a to be engaged with a fixed contact C2 in response to energization of the relay coil 73a. With such arrangements, the solenoids 35a, 36a of switchover valves 35, 36 are selectively energized under control of the relay 3witch 72~, whi~ the solenoids 55a, 56a of switchover valves 55, 56 are selectively energized under control of the relay ~tch 73b. The lamp control circuit 68 is arranged to light an indication lamp 74 on the in~rument panel under control of the computer 65.
The buzzer control ci~uit 71 is arranged to energize a buzzer in the vehicle compartment under control of the computer 6~. -2Ql~
.

Hereinafter, the operation of the co~puter 65 will be described in ~tail with reference to the flow chart shown in Figs. 4~A) and 4~B). Ascuming that the ignition switch is ma~tained in its open position, the S switchover ~alves 35, 36 and 55, 56 are maintained in their first positions to communicate the pneumatic cham~ers 34b, 34c and 54b, 54c of vacuum actuators 34 and 54 with the atmospheric air. Accordingly, the clutch mechanisms 20a and 40a in the transfer device 20 and front differential 40 are each maintained in a position defined by the prior mDde of operation. When the ignition switch is cl~ed to start the engine 11, the electric control apparatus ~0 is actLvated by supply of the electric power from an electric power source (not qhown) in the form of a vehicle battery, and in turn, the CPU 65c of computer 65 starts to execute the program at step lOQ in the flow ~art of Fig. ~. When the pro~ram proceeds to step 101, the CPU 65c determ1nes as to whether the detection switch 62 is turned on or not.

If the four-~eel drive mode is previously selected at the transfer device 20, the detection switch 62 is turned on. Thus, the CPU 65c determines a "Yes~
answer at step lOl and cause~ the program to proceed to step 102. At step 102, the CPU 65c produces control 2~3 ~4Q
.

signa~s for energization of the relay coils 72a, 73a and causes the program to proceed to step 103 where the CPU
~5c produces control ~ignals for energization of the indication lamp 74 and for maintaining the buzzer 75 in its deenergized condition. As a result, the relay control circuits 66 a~ 67 act to energize the relay coils 72a, 73a in res~nse to the control signals from the CPU 65c so that the movable contacts of relay switches 72~, 73b are connected to the fixed contacts C2 to energize the solencids 35a, ~5a of switchover valves 35, 5~. On the other hand, the solenoids 36a, 56a of switchover valves 36, 56 are maintained in their deenergized condition. In such a condition, the ~witchover valves 35 and 55 are switched over from their lS first positions to their second positions to communicate the pneumatic chamberE 34b, 54b of actuators 34, 54 with the vacuum tank 15, while the switchover valves 36, 56 are maintained in the~ first positions to communicate the pneumatic chamber~ 34c, 54c with the ~tmospheric air.
Thus, the diaphragm piston 34a of actuator 34 is moved by the difference in pressure between the pneumatic chambers 34b and 3~c to shift the clutch sleeve 32 from the fir~t position to the second position thereby to establish drive connection between the fir~t and second output shafts 22 and ~3. Sinultaneously, the diaphragm piston 54a of actuator S4 is moved by the difference in pressure 2 ~
.

between the pneumatic cham~ers 54b and 54c to shift the clutch sleeve 51 from the first position to the second position thereby to establish drive connection between the inner shafts 47a, 48a and the outer shafts 47b, 48b.
Under such control a~ described above, the transfer device 20 is maintained in the four-wheel ~rive mode, the indication lamp 74 is lighted to inform the driver of the four-wheel drive mode, and the buzzer 75 is maintained in its deenergized condition.

If the two-w~el drive mode i~ previously selected at the transfer device 20, the de~ection switch 5~ is turned off. Th~, the CPU 65c determines a "NoH
answer at 5tep 101 and causes the program to proceed to step 104. At ~tep 104, the CPU 65c produces control 1; signals for maintaini~ the relay coils 72a, 73a in their deenergized conditions and cauqes the program to proceed to step 105 where the CPU 65c produces control ~ignal~
for maintaining the i~ication lamp 74 and buzzer 75 in their deenergized con~tions. As a result, the relay control circuits 66 and 67 act to maintain the relay coils 72a, 73a in their deenergized conditions in response to the control signals from the CPU 65c so that the movable contacts ~ relay switches 72b, 73b are maintained in connection to the ~ixed contacts Cl to energize the solenoids 36a, 56a of switchover valves 36, ~0 ~ 3~
56. On the other hand, the ~olenoids 35~, 55a of switchover valves 35, 55 ~re maintained in their deenergized condition~. In such a condition, the switchover valves 36, S6 are switched over from their first positions to their second positions to communicate the pneumatic chamber 34c, 54c of actu~tors 34 r 54 with the vacu~m tank 15, while the switchover valves 35, 55 are maintained in the$r first positions to communicate the pneumatic chamber~ 34b, 54b with the atmospheric air.
Thus, the diaphragm piston 34a of actuator 34 is moved by the difference in pretsure between the pneumatic chambers 34b and 34c to shift the clutch sleeve 32 from the second position to the first position thereby to disconnect the second output shaft 23 from the fir~t output sh~ft 22.
Simultaneously, the diaphragm piston 54a of actuator 54 i~ moved by the difference in pressure between the pneumatic chambers 54~, 54c to shift the clutch sleeve 51 f rom the second position to the first po~ition thereby to disconnect the outer shafts 47b, 48b from the inner shafts 47a, 48a. Under such control as described above, the transfer device 20 is maintained in the two-wheel drive mode, the indic~tion l~mp 74 is put out, and the buzzer 75 is maintained in its deenergized condition.

After execution of the initial set~ing routine at steps 101-iO5, the program proceeds to step 106 where - 2~ -the CPU 65c determines ~8 to whether the manual operatLon switch 61 has been oper~ted or not. If the answer is "No" at ~tep 106, the ~P 65c will repeat the execution at step 106. When the manual operation ~witch 61 is operated, the CPU 65c determines a ~Yes" answer at step 106 and causes the progcam to proceed to step 107 where the CPU 65c determines as to whether the detection ~witch 62 is turned on or not. When the four-wheel drive mode is previously selected at the transfer device 20, the CPU
65c determines a "Yes" answer at step 107 and causes the program to proceed to ~tep 108. At step 108, the CPU 65c produces control signals for maintaining the relay coils 12a, 73a in their deenergized conditions. At the following step lOg, the CPU 65c produces control signals for maintaining the indication lamp 74 in Lt~ deenergized condition. As a result, the relay coils 72a, 73a are maintained in their deenergized conditions under control o~ the relay controi circuits 66, 67 to energize the solenoids 36a, 56a of switchover valves 36, 56. Thus, the vacuum actuators 3~, 35 are operated to disengage the clutch ~echanisms 2Qa ~nd 40a thereby to esta~lish the two-wheel drive mode. In such a condition, the indication lamp 74 is put out under control of the lamp control circuit 68-` ~ 2~13640 Assuming that the two-wheel drive mode is previously selected at the transfer device when the operation switch 61 has been operated, the CPU 65c determines a "No" answer at step 107 and causes the program to proceed to step 110 where the CPU 65c reads out a speed signal V from sensor 63. At the following step 111, the CPU 65c reads out an oil temperature signal T from sensor 64 and causes the program to proceed to step 112 where the CP~ 65c reads out the control data defined by the graph of Fig. 5 from the ROM 65b. When the program proceeds to step 113, the CPU 65c determines as to whether or not travel speed of the vehicle and temperature of the lubricating oil are in the allowable region A shown in Fig. 5. If the answer is "Yes" at step 113, the CPU 65c produces the control signals for energization of the relay coils 72a, 73a at step 114 and produces the control signal for energization of the indication lamp 74. As a result, the relay coils 72a, 73a are energized under control of the relay control circuits 66, 67 to energize the solenoids 35a, 55a of switchover valves 35, 55. Thus, the vacuum actuators 34, 35 are operated to engage the clutch mechanisms 2Oa and 40a thereby to establish the four-wheel drive mode. In such a condition, the indication lamp 74 is lighted under control of the lamp control circuit 68.

X ~ 22 -201 364~

If the answer ~s "No" at step 113, the program proceeds to step 1}6 where the CPU 65c produces a control signal for intermittently ener~izing the indication lamp 74 and causes the progr~m tO proceed to step 117 where the ~PU 65c produces a control ~ignal for energization of the buzzer 75 and return~ the program to step 1~6 for repetltive execution at steps 106 - 113. In such a condition, the indication lamp 74 is intermittently lighted under control o~ the lamp control circuit 68, and the buzzer 75 issues a~rm sounds for a predetermined period of time under co~trol of the buzzer control circuit 71. Even if in suc~ a condition the operation switch 61 is operated, the four-wheel drive mode will not be selected at the tra~er device 20.

lS Fr~m the above description, it will be unders~oo~ that the mode of operation of the transfer devlce 20 can be switc~d ove- from the two-wheel drive mode to the four-wheel drive mode only in a condition where travel speed of the vehLcle and temperature of the lubricating oil are in the allowable region A shown in ~ig. ~. This is effec~ive to eliminate a heavy load acting on the syr.chronizer ~1 in engagement of the clutch mech~ni~m ~Oa.

20 1 ~6~0 In ~g. 6, there i~ illustrated a modification o~ the electric control apparatus shown in Fig. 3, wherein the manual oper~tion switch 61 is in the form of a self-hold type switc~ which ic adapted to select the S two-whee3~ drive mode in its open position and to select the four-wheel drive mode Ln its closed po~ition, and wherein the detection s~itch 62 is connected at its one end to the electric power source through the relay coiL
73a and grounded at its other end, the relay coil 73a being connected in par~lel with a resistor rl. In this modification, the ROM ~b of computer 65 is arranged to mem~rize a program represented by a flow chart shown in Fig., and to memorize the control data of Fig. 5. The indication lamp 74 and buzzer 75 are connected in lS parallel to one anothe~ through a diode Dl and connected at their one ends to t~ electric power ~ource. The indication lamp 74 is connected at its other end t~ a connection polnt between the detection switch 62 and re~ay co~l 73a through a diode D2 and an additional detection switch 76. As shown in Fig~ 2, ~he additional detection switch 76 is mounted on the front differential 40 to detect the position of the clutch mechanism 40a and is arranged to be opened when the clutch ~leeve 51 is retained in the first position and to be closed when the clutch sleeve 51 is shLfted to the second position to engage the clutch mechanism 40a. The buzzer 75 is connected at its other end to the I/O 65e of computer 65 in such a manner that the I/O 65e maintains a connection point between the buzzer 75 and diode Dl in a open condition. Only when the indication lamp 74 and buzzer 75 are controlled, the voltage at the connection point between buzzer 75 and diode Dl is alternately switched over between the source voltage +V and ground voltage.
The relay 72a is connected in parallel with a resistor r2. The other arrangements are substantially the same as those of the electric control apparatus shown in Fig. 3.

Hereinafter, the operation of the modified electric control appatatus will be described in detail with reference to Fig. 7. When the ignition switch is maintained in its open position, the transfer device 20 and front differential 40 are each maintained in a condition defined by the prior mode of operation. When the ignition switch is closed to start the engine ll, the electric control apparatus is activated by supply of the electric power, and in turn, the CPU 65c of computer 65 starts to execute the program at step 200 in the flow chart of Fig. 7. When the program proceeds to step 201, the CPU 65c determines as to whether or not the operation switch 61 is maintained in the closed position.

20 1 364~

If the four-wheel drive mode is previously selected at the transfer device 20, the oper2tion switch 61 i~ maintained in its closed position. Thus, the CPU
65c determines a "Yes" answer at step 201 and cause~ the program ~o proceed to ~tep 202 where the CUP 65c produces a control signal for energization of the relay coil 72a.
As a result, the relay control circuit 66 acts to energize the rel~y coil 72a in response to the control signal ,rom the CPU 65c so that the movable contact of relay switch 72b i~ connected to the fixed contact C2 to energize the sole~oid 35a of switchover valve 35 and to deenergize the solenoid 36a of switchover valve 36. In such a condition, the ~witchover valve 35 is switched over from the first po~ition to the second position to communicate the pne~matic chamber 34b of actuator 34 with the vacul~ tank lS, while the switchover valve 36 is maintalned in the fir~ position to communicate the pneumatic chamber 34c ~ith the atmospheric air. Thus, the diaphragm piston 34a of actuator 34 is moved by the difference in pressure between pneumatic cham~ers 34b and 34c to shi~t the clut~ sleeve 32 from the first position io the second position thereby to establish drive connection between the first ~nd second output 3hafts 22 and 23 in the transfer device 20. As the detection 2~ switch 62 is turned or by movement of the clutch sleeve - 2~ -20136a~
.

32 to the ~econd position, the relay coil 73a is energized to connect rhe movable contact of relay switch 73b to the fixed contac~ C2. Thus, the solenoid S5a of switchover valve 55 is energized, while the ~olenoid 55a 5 of switchover valve 56 is deenergized. In turn, the switchover valve 55 is switched over from the first position to the second position to communicate the pneumatic chamber 54b ~ th the vacuum tank 51, while ~he ~wit~hover valve 56 is maintained in the first position iO to communicate the pneumatic chamber 54c with the atmo~pheric air~ Thus, the diaphargm piston 54a of actuator 54 is moved by the difference in pres3ure betwee~ pneumatic chambers 54b and 54c to -~hift the clutch 51eeve 51 to th~ ~econd position from the first i5 position ~hereby to establish drive connection between the inner sha~ts 47a, ~8~ and the o~ter ~hafts 47b, 4~b.
Under such ~ontrol as described above, the mode of operation of the vehi~le is maintained in t~.e four-wheel drive mode. As the detection switch 76 is turned on by ~0 movement cf the clutch sleeve 51 tQ the second position, the indication lamp 74 is gr~unded through the diode D2 and switches 76, 62. ~s a result, the indication lamp 74 is lighted to inform ~e driver of the four-wheel drive mode.

20~3~40 If the two-w~el drive mode is previously selected at the tr~nsfer device 20, the operation swltch 61 is ~aint~ined in i~ open position. Thus, the CPU 65c determines a "No" ans~er at step 2~1 and causes the progra~ to proceed to step 203 where the CUP 65c produces a control signal for ~aintalning the relay coil 72a in its deenerglzed condition. A~ a result, ~he ~ovable contact of relay swit~ 72b is maintained in connection with the fixed contact C~ under the relay control circuit ~6 to energize the solencid 36a of switchover valve 36 ~nd tc de~nergize tne solenoid 35a of switchover valve 35. In 3uch a condition, the switchover valve 36 i~
awitched over f rcm the first position to the second position to communicate the pneumatic chamber 34c of actuator 34 with the ~acuum tank 15, while the switchover valve 35 is maintained in the first position to communieate the pneum~ic chamber 34b w~th the atmospheric air. Thu~, the diaphr~gm piston 34a of actuator 34 is moved by the difference in pressure between pneumatic chambers 34b and 34c to shift the clutch sleeve 32 from the second position to the first po3ition th~reby to disconnect the first output shaft 22 from the second output shaft 23 ~n the transfer device ~0. As the detection switch 62 is turned off by movement of the cLutch sleeve 32 to the first position, the relay ~ 2013~L0 coil 73a is deenergi~ei to connect the movable contact of relay switch 73b to the flxed contact C1. Thus, the solenoid 56a of switchover va~ve 56 is energized, while the solenoid 55a of switchover valve 55 is deenergized.
In turn, ~he switchover valve 56 is switched over.from the $irs~ position to the second position to communicate tne pneumatic chamber 54c with the vacuum tank 51, while the swLtchover valve ~5 is maintained in the first pOgltiOn tO communicate the pneumatic chamber 54b with the atmospheric air. Thus, the diaphargm piston 54a of actuAtor ~4 is moved ~ the difference in pressure between pneumatic cha~bers 54b and 54c to shift the cl~-~tch sleeve 51 to the first position from the second po~ition thereby to disconnect the inner shafts 47a, 48a 1~ from tne outer shafts 47b, 48b. Under such control as descri~ed above~ the mode of operation of the vehicle is mainta'ned.in the two-wheel drive mode. As the detection switches 62 an~ 76 are turned off by movement of the clut~h ~leeves 32 and 51 to their first positions, the indication lamp 7~ is put out to inform the driver of the two-wheel drive ~ode.

After execution of the initial setting routine at steps 201-~03, the program proceeds to step 204 where the CPU 6;c determine as to whether the operation switch ~3~
.

61 has been operated or not. If the answer ls "Yes" at step 204, the CPU 650 causes the program to proceed to 3tep 2Q5 where the CPU 65c determines as to whether or not the operation swi~h 61 i~ maintained ln its closed c po~ition. When the o~ration switch 61 i~ switched over from it~ closed position to its open position for selecting the two-wheel drive mode, the CPU 65c de~ermines a "No'l ans~r at step 2~5 and causes the program to proceed to step 206 where the CPU 65c produces a co~.trol signal ~or ~enegizing the relay coil 72a. As a result, the mode of operation of the vehicle is ~wi~ched over from the four-wheel drive mode to the two-wheel drive mode in such a manner as described above.
When the operation switch 61 is sw~tched over from its open posi~ion to its closed position for selectlng the four-wheel dri~e mode, the CPU 65c determines a "Yes"
answer at step 20~ and cause~ the program to proceed to ~tep ~07 where the CPU 65c reads out an electric speed signal V ~rom sensor 63. At the following step 208, the ~ CPU 65c reads out an electric oil temperature signal ~
from ~ensor Ç4 and causes the program to proceed to ~tep 2Q9 where the CPU ~Sc reads out the control data from the ROM 65b. When the prcgram proceed~ to step 210, the CPU
65c determines as to whether or not travel speed of the vehicle and temperature o~ the lubricating oil are in the - 3~ -~ 2~13~

allowa~le region A shovn in Fig. 5. If the answer is "Yes" at qtep 210, the CPU 65c produces a control signal for energization of the relay coil 72a. As a result, the mode of operation of the vehicle is 3witched over from the two-wheel dri~e mode t~ the four-wheel drive mode.

~ the answer is ~No~ ~t step 21~, the program proceeds to step 212 ~here the CPU 65c acts to produce a con~rol signal for intermittently energizing the indica~ion lamp 74 and to produce a command signsl for energizing the buzzer 15 and apply it to the I/O 65e.
When applied with the command signal, the I~O 65e act~ to alternately switch over the voltage app~ied to ~he buzzer 75 and indication lamp 74 between the source voltage +V
and ground voltage. Thus, the indication lamp 74 is i5 intermitten~ly lighted and the bu7zer 75 issues alarm sounas there~rom to in~orm the driver of the fact that the Lour-wheei drive mode may not be selected ~t the tr~nsfer device ~0. A~ter execution at step 212, the program proceeds to st~p 213 where the CPU 65c determines as to whether the oper~tion switch 61 has been returned to its open positLon or not. When the operation switch 61 is returned to its open position, the CPU 65c determine~ a ~Yes" ansu~r at step 213 and causes the program to prcceed to Step 214 where the CPU 65c produces 20~364~

A command s~gnal for d~nergizing the indication lamp 74 and bu~zer 75 and applies lt to the I/O 65e. When applie-~ with the co~ma~ signal, the I/O 65e acts to make the connection point between buzzer 75 and diode Dl in a open condition. In turn, ~he indication lamp 74 and buzzer 75 are deenerg~ed, and the program return~ to step 204~

In Fig. 8 there is illustrated a practical em~odiment of the transfer device 20~ wherein the same component pa~ts and portions as those shown in Fig. 2 are indLcated by the same reference numerals. In ~his embodi~ent, the transfer device 20 comprises a planetary gear unit 80 for selectively providing low and high speed power tralns between the input and output shafts 21 and i5 22 in accordance with operation of a manual lever 81.
The pianetary gear unit 80 includes a sun gear 82 mounted ~n the input shaft 21 for rotation therewith, a ring gear 83 flxedly mounted within the housing of transfer device ~0 in surrounding rel~tionship with the sun gear 82, a carrier 84 rotataly ~unted on a left-hand side wall of the transfer hous~ng, and a plurality of planetary gears 85 rotatably supporte~ by the carrier 84 and in mesh with the sun and ring gears 82 and 83. An internally splined clutch cleeve 88 i~ a~ially slidably mounted on ~ 2~640 an externally cplined hub member 86 which is fixed to the cutput shaft 22. The clutch sleeve 88 is arranged to be shifted by the manual lever 81 through a fork shaft ~7a and a shift fork 87b. When shifted leftward by operation of tne manual lever 81, the clutch sleeve 88 is connected to an externally spli~d inner end of input shaft 21 to transmlt the power from input shaft 21 to the output shaft 2~ at a high sp~d. When shifted righward by operation of the manual lever 81, the clutch sleeve 88 i9 engaged at it~ left e~ with an annu~ar spline piece 89 fix~d to the carrier ~4 to transmit the power from input shaft 21 to the output shaft 22 throu~h the sun and planetary gears 82 an~ 85 at a low speed.

In ~he practlcal embodimen~ of ~ransfer device 20, a palr of axially spaced ~ynchr~nizers are mounted on the output shaft 22 to effect synchroniz~tion in shifting operation of the clut~h sleeve ~8, and the clutch mechanism 20a includes synchronizer rings 31a, 31b and 31c which are mounted on the output shaft 22 to e~ect 20 ~ynchrcnization in shifting operation of the clutch sleeve 32. The clutch sleeve 32 is arranged to be shifted by an electric motor 91 through the fork shaft 33a and shift fork 33~. In this embodiment, the electric motor 91 is substituted for the vacuum actuator 34 Qhown 2~ in Fig. 2.

2013~
.

As shown in Fig. 11, the electric motor 91 is mounted to the transfee housin~ and has an output shaft ~la integrally formed ~ith a worm 91a which i~ in mesh with a wheel 92 of ins~lation material shown in Fig. 10.
A~ shown in Fig. 1~, ~e wheel 92 is mounted on a hollow rotary ~haft 92a for ~tation therewith. The rotary shaft 92a ls coaxially arranged to a rotary ~haft 94a through first and sec~d spiral springs 93a and 93b. The rotary shafts 9~a and 94a are rotatably mounted within the tran~fer housing, and the rotary shaft 92a i~
rotatably coupled over the rotary -~haft 94a for relative rotation. Th~ spiral springs 93a and 93b are wound around the rotary shaft $4a relatively in opposite directions and fixed at their inner ends to the rotary ~haft 94a. The spiral ~prings 93a, 93b are preloaded relatively in opposite directions by engagement with an arm 94~ fixed to the rotary shaft 94a a~ their outer end~. The outer ends of spiral spring~ 93a, 93b are fl1rther engaged with an arm 92c fixed to the hub member 92b of wheel 92 to be moved by rotation of the wheel 92 relatively in opposite directions. A first gear 94 is mounted on the outer end of rotary shaft 94a for rotation therewith and meshed ~ith a second gear 9S which is rotatably mounted on the transfer housing. The ~econd gear 95 & inte~rally formed with a pinion 95a which is meshed with a rack portion 33al of fork shaft 33a.

20 1 36¢0 As shown in Figs. 10 and 11, the wheel 92 is covered with a circular insulation plate 96 attached thereto. The circular insulation plate 96 is formed at its inner periphery with a semi-circular recess 96a and at its outer periphery with a semi-circular recess 96b.
A detection switch assembly 97 is mounted within the transfer housing in such a manner as to face the circular insulation plate 96. The detection switch assembly 97 includes three contacts 97a, 97b, 97c which are slidably in contact with the circular insulation plate 96 to detect rotation of the wheel 92. When engaged with the recess 96a of insulation plate 96, the contact 97c becomes conductive and the other contacts 97a, 97b become non-conductive. When engaged with the recess 96b of insulation plate 96, the contact 97a becomes conductive and the other contacts 97b, 97c become non-conductive.
As shown in Figs. 9 and 12, a detection switch 62a is mounted on the transfer housing to detect movement of the fork shaft 33a thereby to detect the mode of operation of the transfer device 20.

In Fig. 13 there is illustrated a practical embodiment of the front differential 40 shown in Fig. 2, wherein the same component parts and portions as those shown in Fig. 2 are indicated by the same reference ~20~'~64~

numerals. In this em~diment, the right-hand drive shaft 48 i~ connected at its inner end to the right-hand side gear 44b for rotation therewith. In a condition where the clutch sleeve 51 is retained in the first position to disconnect the outer chaft 47b from the inner shaft 47a, the ri~ht-hand side g~r 44b is rotated ~y he torque applied thereto from the right-hand road wheel through the drive ~haft 48. ~is causes the pinions ~3a, 43b, side gear 44a and inner shaft 47a to rotAte with the side ~ear 44. In this instance, the differential case 42 and drlve pinion shaft 46 are maintained still.

In Fig. 14 t~re i~ illustrated an electric contro} apparatus for the transfer device 20 and ~ront differential 40 described above, wherein the same components as those s~own in ~ig. 6 are indicated by the same reference nume~a~s and characters. ln this electric contr~l apparatus, the ROM ~5b is arranged to memori~e a program represented by a flow chart shown ir. Figs. 15(A) and 15~B) ~ ~nd the I/O ~5e is ~onnect~d to a detection swi~ch 77 which is as~ciated with the planetary gear unit 80 as shown in Fig. 8 to dete~t movement of the fork shaft 87a. The detection switch 77 is arranged to be turned on when the fork shaft 87a is retained in a fir~t position to establish a high ~peed power train at - 3~ -Q-.

the planetary gear unit 80 a~d to be turned of f when the fork shaft 87a has bee~ shifted rightward to ~ ~econd position from the f irst position to e3tablish a low 3peed power ~rain at the pl~etary gear unit 80.

The ~/O 6 ~e ~ computer 6 5 i s connected to a motor control circuit which i~ substituted for the relay control circuit 66 and relay circuit 72 shown in Fig. 6.
The ~,otor co~trol circuit incl~des a pair of relay . circuits 78 and 79. ~e relay circuit 78 includes a relay coil 78a connected in parallel with a resistor r3 and connected at its one end to the I/O 65e. Similarly, the relay circ~it 79 includes a relay coil 79a connected in parallel with ~ resistor r4 and connected at it~ one end to the I/O 65e. T~ {elay coils 78a, 79a are connected at their ot~er ends to the contacts 97a, 97c of detectiGn switch assenbly 97 shown in Figs. 10 and ll.
The co~tact g7b is in the form of a movable contact grounded at its one e~d. ~he relay circl~it 78 i~ provided with a relay switch 78b the movable contact of which is 2~ connected to an input terminal of electric motor 91 shown in Fig. 8, while the ~elay circuit 7~ i3 provided with a relay ~witch 79b the novable contact of which is connected to another input terminal of electric motor 91.
The movable contacts of relay switches 78b, 79b are ~13~4~

arranged to be engaged with fixed contacts Cl during deener~lzation of the relay coil~ 78a, 79a and to be engaged with fixed co~acts C2 during ener~ization of the rel~y coils 78a, 79a. The fixed contacts Cl are grounde~
at their one ends, whL~e the fixed contacts C2 are connected to the electric power source. In the a~ove arrangement, the electric motor 91 i8 in ~he form of a reversible ~.C. motor.

~ereina~ter, the operation of the electric control apparatus sho~n in Fig. 14 will be deqcribed in detail with reference to the flow chart of Figs. 15(A~
and 15~B). When the ignition swltch is ma~ntained in its open positioQ, the transfer device 20 and front differential 40 are e~ch maintained in a condition d~fined by the prior ~ode of operation. In such a condition, a speed reduction mechanism composed of the worm 91a and wheel g2 acts to reta~n the transfer device 20 in the prior m~de ~ operation, and the detection switcA ~2a is also retained in a po~ition defined by the prior mode of op~rati~n. ~hen che ignition switch is closed to start the ergine 11, the electric control apparatus is activated by supply of the electric power, and ln turn, the CPU ~c of computer 65 starts to execute the program at step 3~0 in the flow chart of Fig. 15.

~ 38 -20 i 36~0 When the program proceed3 to step 30L, the CPU 65c determines as ~o whether the operation switch 61 has been operated or not. If the answer is "No" at step 301, the CPU 65c causes the prog~m to proceed to step 317 for 5 execution at the following steps 318-3~2.

If the answer is "Yest' at step 3~1, the program proceeds to step 3Q2 where the CPU 65c determines as to whether or not the oper~tion switch 61 has heen switched over from its open position ~for selection of the two-wheel drive mode) to its closed position ~for selection of the four-w~el dri~e mode~. If the answer is IINo'i at step 302, the program proceeds to step 303 where the CPU 65c deter~nes as to whether the detection switch 77 is turned off or not. When the planetary gear unit 80 i3 conditior.ed to prov$de the low ~peed power train, ~he CPU 65c dete~mines a "No" an~wer at step 303 and causes the program to return to ~tep 301. When the planetary gear unit 80 i8 conditioned to provide the high ~peed power train, the CPu 65c determines a "Yes" an~wer 2~ at step 3C3 and causes ~he program to proceed to step 304 where the CPU ~5c produces a command signal ~or energizing the relay coil 79a and returns the program to step 3Ql. When applied with the co~ ~d ~ignal from the CPU 65c, the I/O 65e a~s to apply the ~ource voltage to ~ 20~ 36~

thP rel~y c~il 79a for a predetermined period Or time (~or in~-ance, 5 seconds~. In this in-~tance, the contact ~7b of detection switch 97 LS previously maintained Ln engagement with the contact 97c through the recess 96b of plate g6 to energize the relay coil 79a. Thus, the mova~le contact of relay switch 79~ is engaged with the f ix~d contact C2 to pernNt an electric current flowing theretnrough to the electrio ~otor 91 a~ shown by a broken arrow in the figure. This causes the electric motor 91 to rotate in a reverse direction. In turn, the wheel 9~ i8 driven by the electric motor 91 through worm 91a to rotate the pLate g6 in a direction shown by a broken arrow in Fig. 11, When the reces~ 96a of plate 96 is positioned to face the detection switch 97, the contact g7b is dis~rgaged ~rcm the contact 97c to deenergize the relay coil 79a, and in turn, t~e movable contact of relay swi.ch 79b is engaged with the fixed con~-act C~ to deactivate the electric motor 91. In such a condition, the contact 97b of detection switch 97 is brought into engagement with the contact 97a. On the other hand, rotation of the wheel 9; is tran-Rmitted to the pinion 95a through the spiral spri~g g3a ~or g3b) and gears 94, 95 t~ d1splace the f3rk sh~t 33a in a direction shown by ~ 2013640 a broken arrow ln Figs. 9 and 12. In turn, the clutch ~leeve 32 is di~placed rightward in Fig. 8 to release drive connsctlon between the output shafts 22 and 23, and the detertion ~witch 62a is turned off by rightward displacement of the for~ shaft 33~. Simultaneou~ly, the clutch sleeve 51 in frort differenti~l 40 is moved from the seco~d posltion to the first position to disc~nnect the oi~ter shaft 47~ fron the inner shaft 47a in the same manner as desc~ibed abo~. As a re~ult, the mode of operation of the vehicle i5 ~witched over from the high speed four-wheel drive mode to the high speed two-wheel drive mode, and the ind~ation lamp 74 is put out.

When the operation switch 6~ has been switched over from it3 open posi~ion for selection of the two-wheel drlve mode to its clo~ed position for selection o~ the fol~r-wheel drive mode during execution of the program ar step 3C2, th~ CPU 65c determines a l'Yes"
hnswer at step 302 and causes the program to proceed to step 3~5 where the CPU 65c determines d9 to whether the detection switch 77 is ~rned off or not. When the planetary gear unit 80 is conditioned to provide the low speed power train, the detection switch 77 is turned on.
In such a condition, th~ CPU 65c determine~ a "No" answer at step 305 and returns the program to step 301. As 20 1 3~40 a result, the mode of operation of the vehicle is maintained in the low speed four-wheel drive mode L4.

When the planetary gear unit 80 is conditioned to provide the high speed power train during execution of the program at step 305, the detection switch 77 is turned off. In such a condition, the CPU 65c determines a "Yes" answer at step 305 and causes the program to proceed to step 306 for execution of the program at steps 306-309 in the same manner as described above. If travel speed of the vehicle and temperature of the lubricating oil in front differential 40 are in the allowable region A during execution of the program at step 309, the CPU
65c determines a "Yes" answer and causes the program to proceed to step 310 where the CPU 65c produces a command signal for energizing the relay coil 78a and returns the program to step 301. When applied with the command signal, the I/O 65e acts to energize the relay coil 78a for the predetermined period of time. In this instance, the the contact 97b of detection switch 97 is previously maintained in engagement with the contact 97a through the recess 96a of plate 96 to energize the relay 78a, and in turn, the movable contact of relay switch 78b is engaged with the fixed contact C2 to permit the electric current flowing therethrough to the electric motor 91 in X' 2 ~
.

a direction shown by a s~lid arro~ in Fig. 14. Thus, the electric motor ~1 is activated to rotate in a forward direction, and in turn, the wheel g2 is driven by the electric motor 91 throu~ worm 91a to rotate the plate 96 in a direction shown by ~ solid arrow n Fig. 11.

When the recess 96b of plate 96 is positioned to face the dete~tion swit~ g7, the contact 97b i5 disenga~ed from the con~ct g7a to de2nergi2e the relay coil 78a, and in turn, ~e movable contact of relay ~witch 78b iq engaged w~th the fixed contact Cl to deactivate the electric motor 91. In such a condition, the contact 97b of dete~ion switch 97 is brought into engaqement with the con~ct 97c. On the other hand, rotation of the wheel 92 i~ transmitted to the pinion 95a iS thrG~sh the spiral spri~ 93b (or 93a) and gears 94, 95 to dlsplace the fork shaft 33a in a direction shown ~y a ~olid arrow in Figs. 9 and 12. In turn~ the clutch ~leeve 32 is displaced leftward in Fig. 8 to establish drive connection betwee~ the output shafts 22 and 23, and the detection switch 62a is turned on by leftward displacement of the fork shaft 33a. Simultaneously, the clutch sleeve 51 in front differential 40 is moved from the first position to t~ second position to establish drive connection be~ween the inner and outer ~hafts 47a ~ 2013640 and 47b in the same ~an~r as described above. As a result~ the mode of operation of the vehicle is switched over from the high 9peed ~wo-wheel drive mode H2 to the high speed four-wheel drive mode ~4, and the indication 5 lamp 74 is lighted.

If the CPU 65c determines a "No" answer during execution of the program at step 309, the program prcceeds to step 311 where the CPU 65c produce~ a command sigr.al for intermittently energizing the indication lamp lCl 74 and for ~nergizing the buzzer 75. When applied with the command singal, the I/O 65e acts to alternately ~witch ovPr the voltage applied to the indication lamp 74 and buzzer 75 between t~e source voltage +V and ground voltag~. Thus, the indication lamp 74 is inter~ittently Lighted, and the buzzer 75 issues alarm sounds therefrom to inform ~he drive of the fact that the four-wheel drive mode may not be selected a~ the transfer device 20.
Aftcr execution at step 311, the program proceeds to step 312 where the CPU 65c d~termines as to whether the opera~ion switch 61 has been returned to its open position or not. When the oper~tion ~witch 61 is returned tO its open poSition for selection of the two-wheel drive mode, t~e CPU 65c determines a "Yes'l answer at step 312 and causes the program to proceed to s~ep ~14 where the CPU 65c produces a command signal for deenergizing the indLcation lamp 74 and buzzer 75 and applies it to the I/O 65e. When applied with the command signal, ~he I/O ~5e acts to make the connection point between buzzer and diode Dl in a open condition. In turn, ,he indication lamp 74 and buzzer are deenergized, an~ the program return~ to ~tep 301.

When the planetary gear unit 80 is switched over ~y operation of the manlal lever 81 to provide the low 1~ ~peed power train during execution of the program at ~tep 312, the detection switch 77 i5 turned on. In this instance~ the CPU ~5c d~termines a ~Yes" answer at step 313 and causes the program to proceed to step 315 where the CP~ 55c produces a ~ommand signal for deenergizing the ,ndicatior. lamp 74 ~nd buzzer 75 and applies it to the I/O 65e. As a result, the indication lamp 74 and buzzer 75 are deenergized under con~rol of the I/O 65e in the Qam~ manner as desc~ibed above, and the program proceed-~ to step 316. ~t step 316, the CPU 65c produces a control signal for energizing the relay ccil 78a for the predetermined period of time and returns the program tO ~tep 301. The execution at step 316 i9 the same as tnat at step 310. Thu~ the mode of operation of the vehicle i~ switched over from the high ~peed two-wheel drive mode H2 to the lcw speed four-wheel drive mode L4.

In the part-time four-wheel drive system of the vehicle, the manual lever 81 is adapted to 3electively provide the high speed two-wheel drive mode ~2, the high speed four-whael drive ~ode H4 and the low speed four-wheel drive mode ~. Assuming that the detection switch 77 i8 maintained in a position defined by the prior mode of operation the CPU 65c determines a ~No~
an~wer at step~ 301 and 317 to repeat the execution at ~teps 301 and 317. Whe~ the planetary gear unit 80 is switched over by operation of the manual lever 8l to provide the low speed Pswer train in a ~ondition where the operation switch 61 is maintained in its open position to select the two-wheel drive mode at the transfe~ device 20, the detection switch 77 lS turned on.
In thi4 instance, the CPU ÇSc determines a "Yes" answer respectively At steps 317, 318 and 319 and causes the program to proceed to s~p 320 where th~ CPU 65c produces 2~ a command sign31 fcr en~gizing the relay coil 78a. In turn, the relay coil 78a is energized under control of the I/O 65e tO cause ri~tward movement of the fork ~haft 33a in the same manner as that at step 31~. As a re~ult, the mode of operation of the vehicle is switched over ~ ~6 -~ 3 6 ~ 0 ~rom the high ~peed two-wheel drive moae H2 to the low speed four-whe~l drive node.

When the planetary gear ~nit 80 is switched over by operat~on of the man~al lever 81 to provide the low speed power train in a ~ndition where the operation switch ~1 is maintained in its closed position to select the four-wheel drive mode at the transfer device 20, the detection .qwitch 77 is turned on. In this instance, the .CPU 65c deter~ines a "Y~" answer respectively at steps 317 and 318 and determi~s a "No" answer at step 319 to return the program to 9~p 301. Thus, the mode of operation of the vehicle is switched over from the high speed four-wheel drive n~de ~4 to the low speed four-wneel drive mode L4. When the planetary gear unit 80 i~ swi~ched over ~y o~eratlon of the manual lever 81 to pro~ide the high speed power train in a condition wh~re the operation switch 61 is maintained in its closed positlon to ~elect the four-wheel drive mode at the transfer devlce 20, the detection switch 77 i~ turned 20 off. In this in~tance, ~he CPU 65c determines a "Yes"
answer at step 317 and determines a ~No' answer at step 318. Thus, the program proceeds to step 321 where the CPU 65c ~etermines as to whether cr ~ot the operation ~witch 61 ~s maintained in its open po~ition for 2013 ~

selection of the two-wheel drive mode. I~ the answer i8 "Ye~n at step 321, the program proceeds to step 3~2 where the CPU produces a comn~nd signal for energizing the relay coil 79a, and in turn, the relay coil 79a i8 ene~gized under control of the I/O 65e to cause leftward movement of the fork shaft 33a in the same manner as that at step 304. As a result, the mode of operation of the vehicle is switched over from the low speed four-wheel drlve mode L4 to the high speed two-wheel drive mode H2.
lQ If the answer is "No" at step 321, the program returns to step 301. In this inst~nce, the mod~ of operation of the vehi~le is switched over from the low speed four-wheel drive mode L4 to the high speed four-wheel drive mode H4.

A1though the above embodiments have been adapted i5 to a part-time four-wheel drive vehicle the rear road wheels of which are continuously driven, it is apparent that the pre~ent invention can be adapted to a part-time four-wheel drive vehicle the front road wheels of which are continuou~1y driven.

Having now fully set forth certain preferred embodiments of the concept underlying the present invention, various other applications and embodiments as well as certain modifications of the embodiments herein .

shown and de~cribed will obviously occur to those skilled in the art upon becomi~ familiar with said underlying concept. It is to be understood, therefore, that within the ~cope of the appended claims, the invention may be practiced otherwi5e tham as specif ically 8et forth here i n.

Claims (6)

1. An electric control apparatus for a part-time four-wheel drive vehicle having a transfer device (20) drivingly connected to a prime mover of the vehicle to continuously transfer the power from said prime mover to a first set of road wheels, said transfer device including a first clutch mechanism (20a) arranged to transfer the power to a second set of road wheels when it has been engaged, a differential (40) drivingly connected at its output side to said second set of road wheels and at its input side to said transfer device (20), said differential (40) including a second clutch mechanism (40a) arranged to transmit the power from said transfer device to said second set of road wheels when it has been engaged, a first actuator (34) assembled with said transfer device to engage said first clutch mechanism when it has been operated in one direction and to disengage said first clutch mechanism when it has been operated in the opposite direction, and a second actuator (54) assembled with said differential to engage said second clutch mechanism when it has been operated in one direction and to disengage said second clutch mechanism when it has been operated in the opposite direction, the electric control apparatus comprising:
a manual operation switch for selecting a two-wheel drive mode or a four-wheel drive mode at said transfer device;
a speed sensor for detecting travel speed of the vehicle to produce a speed signal indicative of the travel speed of the vehicle;
a temperature sensor for detecting temperature of lubricating oil in said differential to produce a temperature signal indicative of the oil temperature; and control means responsive to said speed and temperature signals for operating said first and second actuators respectively in the one direction when said manual operation switch has been operated to select the four-wheel drive mode at said transfer device in a condition where the travel speed and oil temperature are in a predetermined allowable region during travel of the vehicle in the two-wheel drive mode and for rendering said first and second actuators inoperative when said manual operation switch has been operated to select the four-wheel drive mode in a condition where the travel speed and oil temperature are out of the predetermined allowable region.

2. An electric control apparatus for a part-time four-wheel drive vehicle having a transfer device drivingly connected to a prime mover of the vehicle to continuously transfer the power from said prime mover to a first set of road wheels, said transfer device including a first clutch mechanism arranged to transfer the power to a second set of road wheels when it has been engaged, a differential drivingly connected at its output side to said second set of road wheels and at its input side to said transfer device, said differential including a second clutch mechanism arranged to transmit the power from said transfer device to said second set of road wheels when it has been engaged, a first actuator assembled with said transfer device to engage said first clutch mechanism when it has been operated in one direction and to disengage said first clutch mechanism when it has been operated in the opposite direction, and a second actuator assembled with said differential to engage said second clutch mechanism when it has been operated in one direction and to disengage said second clutch mechanism when it has been operated in the opposite direction, the electric control apparatus comprising:
a manual operation switch for selecting a two-wheel drive mode or a four-wheel drive mode at said transfer device;

a detection means provided on said transfer device to be operated when the four-wheel drive mode has been selected at said transfer device;
a speed sensor for detecting travel speed of the vehicle to produce a speed signal indicative of the travel speed of the vehicle;
a temperature sensor for detecting temperature of lubricating oil in said differential to produce a temperature signal indicative of the oil temperature;
control means of responsive to said speed and temperature signals for operating said first actuator in the one direction when said manual operation switch has been manipulated to select the four-wheel drive mode at said transfer device in a condition where the travel speed and oil temperature are in a predetermined allowable region during travel of the vehicle in the two-wheel drive mode and for rendering said first actuator inoperative when said manual operation switch has been manipulated to select the four-wheel drive mode in a condition where the travel speed and oil temperature are out of the predetermined allowable region; and means for operating said second actuator in the one direction in response to operation of said detection means.

3. An electric control apparatus as claimed in Claim 1 or 2, wherein the predetermined allowable region is defined to permit engagement of said first clutch mechanism during travel of the vehicle in the two-wheel drive mode without causing any heavy load acting thereon.

4. An electric control apparatus as claimed in Claim 1, further comprising indication means for visually informing the driver of the fact that said first and second actuators have been rendered inoperative under control of said control means.

5. An electric control apparatus as claimed in Claim 4, wherein said indication means includes an indication lamp mounted on an instrument panel of the vehicle and means for continuously energizing said lamp when the four-wheel drive mode has been selected at said transfer device by operation of said first actuator and for intermittently energizing said lamp when said first and second actuators have been rendered inoperative.

6. An electric control apparatus as claimed in Claim 1, wherein said transfer device includes a change-speed mechanism arranged to selectively provide low and high speed power trains for transfer of the power to said first and second sets of road wheels and means associated with said change-speed mechanism to produce a low speed signal therefrom when said change-speed mechanism is conditioned to provide the low speed power train and to produce a high speed signal therefrom when said change-speed mechanism is conditioned to provide the high speed power train, and wherein said control means is further responsive to said high speed signal for operating said first and second actuators respectively in the one direction when said manual operation switch has been manipulated to select the four-wheel drive mode in a condition where said change-speed mechanism is conditioned to provide the high speed power train and where the travel speed and oil temperature are in the predetermined allowable region during travel of the vehicle in the two-wheel drive mode.