Display control system for a working vehicle

A display control system for a working vehicle comprising a plurality of sensors arranged on a vehicle body, a display for displaying messages relating to various information, and a display controller operable in response to information from the sensors for selecting information to be displayed on the display. The display controller has an ordinary display mode for displaying, on the display during an operation, information necessary to the operation, an adjusting mode for displaying, on the display during a non-operating time, information for correcting signals from the sensors, and a diagnostic mode for displaying, on the display during a non-operating time, information for checking the signals from the sensors. The system includes a display mode selecting device for selecting one of the three display modes according to a state of the working vehicle.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 This invention relates to a display control system for a working vehicle
 having a plurality of sensors arranged on a vehicle body, a display for
 displaying messages on various information, and a display control device
 for selecting information to be displayed on the display based on
 information from the sensors.
 2. Description of the Related Art
 Techniques relating to a working vehicle having a display as noted above
 are disclosed in Japanese Patent Laying-Open Publications S58-26652 and
 S62-39716, for example. In these publications, plural types of information
 are displayed on one display. In the former publication, vehicle running
 information and alarm items are switchable for display. In the latter
 publication, an inspection image is displayed before an engine start, and
 vehicle running information after the engine start.
 Taking an agricultural tractor for an example of working vehicles, one
 developed in recent years performs not only a lift control and rolling
 control of a plow, but various other controls such as a change speed
 control of front wheels based on a steering wheel operation and a braking
 control of rear wheels based on a steering wheel operation. The sensors
 required for the lift control of the plow, for example, may include a
 setter for setting a target height of the plow relative to the tractor
 body, a sensor for measuring a pivoting angle of a rear cover, and a
 sensor for measuring a height of the plow relative to the tractor body. To
 perform these lift controls smoothly, a conventional tractor further
 includes an engine speed sensor to correct the controls based on an engine
 speed. It is important for the display to keep displaying information on a
 quantity of fuel needed in time of an operation, and on a temperature of
 engine cooling water. In addition, the technique as disclosed in the
 former of the above prior art publications is useful, when a normal
 operation cannot be performed, to utilize the display for allowing the
 operator to promptly recognize the situation. The technique as disclosed
 in the latter prior art publication is also useful to utilize the display
 in inspecting and adjusting the sensors arranged on the tractor body.
 The prior art noted above facilitates maintenance and inspection of the
 numerous sensors arranged on the tractor body, in that whether the sensors
 are normal or abnormal may be determined on the display screen based on
 the signals from the sensors. However, the display cannot be used to the
 extent of correcting values of the signals from the sensors. In this
 sense, there is room for improvement. Particularly, it is unsatisfactory
 that an inspection image (safety monitor screen) is always displayed
 immediately before an engine start, and that too many pieces of
 information displayed are difficult to discern.
 SUMMARY OF THE INVENTION
 An object of this invention is to provide a display control system for
 making effective use of a display disposed on a vehicle body to display
 various information necessary to operations, and for allowing the
 operator, by using this display, to grasp and check, without difficulty,
 conditions of numerous sensors arranged on the vehicle body.
 The above object is fulfilled, according to this invention, by a display
 control system for a working vehicle comprising a plurality of sensors
 arranged on a vehicle body; a display for displaying messages relating to
 various information; a display controller operable in response to
 information from the sensors for selecting information to be displayed on
 the display, wherein the display controller has an ordinary display mode
 for displaying, on the display during an operation, information necessary
 to the operation, an adjusting mode for displaying, on the display during
 a non-operating time, information for correcting signals from the sensors,
 and a diagnostic mode for displaying, on the display during a
 non-operating time, information for checking the signals from the sensors;
 and a display mode selecting device for selecting one of the three display
 modes according to a state of the working vehicle.
 With this construction, during an operation, displays are made in the
 ordinary display mode for the operator to obtain information necessary to
 the operation from the display. When correcting signals from the sensors
 in a non-operation time, necessary information may be obtained from the
 display in the adjusting mode. When checking the signals from the sensors
 in a non-operation time, necessary information may be obtained from the
 display in the diagnostic mode.
 In one preferred embodiment of this invention, in the ordinary display
 mode, at least one of remaining fuel information and engine cooling water
 temperature information is displayed as a standard display on the display;
 and when the sensors detect an abnormality in time of the standard
 display, the standard display is overridden by messages corresponding to
 the abnormality to be displayed as an alarm display on the display. With
 this construction, when an operation is carried out with displays made in
 the ordinary display mode, the operator may obtain from the display at
 least one of the remaining fuel information and engine cooling water
 temperature information displayed as a standard display. When the sensors
 detect an abnormality, the standard display is overridden by the alarm
 display to be shown on the display. Based on the alarm display, the
 operator may take appropriate action to deal with the abnormally.
 In another preferred embodiment, in the adjusting mode, messages for
 operations to be carried out by an operator are displayed on the display,
 and in the diagnostic mode, information on the sensors diagnosed is
 displayed on the display. Thus, in the adjusting mode, the operator may
 carried out a proper operation based on the messages appearing on the
 display. In the diagnosis mode, states of the sensors may be determined
 reliably from the information on the sensors shown on the display.
 In a further preferred embodiment, in the adjusting mode, messages for
 plural types of operations to be carried out by the operator are displayed
 in a predetermined order on the display, the messages being excluded after
 the operations are determined to have been carried out properly, based on
 signals from the sensors, and the messages being displayed again when the
 operations are determined not to have been carried out properly, based on
 signals from the sensors. Thus, in the adjusting mode, the operator may
 carried out an operation based on the messages appearing on the display,
 and the same messages are not displayed after a proper operation are
 carried out. When an operation cannot be carried out as indicated by the
 messages or an improper operation is carried out, the same messages are
 displayed again for the operator to carry out an operation according to
 the display. A necessary operation may be carried out properly since the
 messages are displayed until this is done.
 In a further preferred embodiment, in the diagnostic mode, when a signal
 from one of the sensors diagnosed shows an abnormal value, a message
 indicating the one of the sensors diagnosed to be abnormal or a signal
 value from the one of the sensors is displayed on the display. Thus, in
 the diagnosis mode, when one of the sensors diagnosed shows an abnormal
 value, the state of the sensor may be determined with ease.
 In a further preferred embodiment, one of the adjusting mode and the
 diagnostic mode is selectable by operating an engine starting switch to a
 power supply position with a plurality of working switches turned on. With
 this construction, to set the display to the adjusting mode or diagnosis
 mode, the engine starting switch must first be operated to the power
 supply position in a way not performed in time of usual engine starting.
 The display controls in the adjust mode or diagnostic mode never take
 place in time of an ordinary operation. One of the adjusting mode and
 diagnosis mode may be selected only when the operator intends to do so.
 As described above, the display control system according to this invention
 utilizes the display disposed on the vehicle body to show various
 information necessary to an operation. In addition, the operator may grasp
 and check the states of the numerous sensors disposed on the vehicle body.
 Further, the operator may confirm what is shown on the display during an
 operation. When an abnormality occurs, the operator may immediately take
 steps to eliminate the abnormality based on the information shown on the
 display. The operator may adjust the sensors properly, based on
 information shown on the display, without referring to manuals. When
 checking the sensors, the operator may readily grasp correct information
 shown on the display 35, to make adjustment or determine whether certain
 sensors need to be changed. Although the engine starting switch is used to
 start the adjusting mode and diagnostic mode, the displays in the adjust
 mode or diagnostic mode never take place when the engine is started for an
 actual operation. Thus, the operator is free from troublesomeness
 concerning the display.
 Other features and advantages of this invention will be apparent from the
 following description of the embodiments to be taken with reference to the
 drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Embodiments of this invention will be described hereinafter with reference
 to the drawings.
 As shown in FIGS. 1 and 2, an agricultural tractor, which is one example of
 working vehicles, has dirigible front drive wheels 1 and rear drive wheels
 2 for supporting a tractor body. An engine E is mounted on a front portion
 of the tractor body. Power of engine E is transmitted through a main
 clutch 3 to a transmission case 4 disposed to extend from a middle portion
 to a rear portion of the tractor body. A driver's seat 5 and a steering
 wheel 6 are arranged centrally of the tractor body. The transmission case
 4 supports, in rear end positions thereof, a pair of right and left
 hydraulic lift cylinders 7 extending vertically for raising and lowering a
 pair of right and left lift arms 8. Through a three point link mechanism L
 vertically movable by these lift arms 8, a rotary plow A is coupled to the
 rear end of the tractor body.
 The three point link mechanism L includes a top link 9 disposed in an upper
 rear end position of the tractor body, and a pair of right and left lower
 links 10 arranged at opposite rear sides of the tractor body. The right
 and left lower links 10 and right and left lift arms 8 are supported in
 suspension through lift rods 11. The rotary plow A is vertically movable
 with pivotal movement of lift arms 8. A lift arm sensor 8S of the
 potentiometer type is provided for measuring an amount of pivotal movement
 of lift arms 8. One of the lift rods 11 has a hydraulic, double-acting,
 rolling cylinder 12 extendible and contractable for allowing a free
 rolling motion of rotary plow A. A rolling sensor RS of the potentiometer
 type is mounted in a rearward position of the tractor body for measuring a
 rolling of the tractor body. To measure an amount of operation of rolling
 cylinder 12, a sensor wire 14 supporting an inner wire 14A and an outer
 wire 14B is connected to an extension and contraction portion of rolling
 cylinder 12, and a rotatable stroke sensor SS of the potentiometer type is
 connected to the other end of sensor wire 14 to be operable by the sensor
 wire 14.
 As shown in FIGS. 1, 2 and 6, the rotary plow A includes numerous tines 16
 rotatable about a drive shaft extending transversely of the plow, and a
 rear cover 18 attached to a rear position of a main plow body 17 to be
 pivotable about a transverse axis. Rods 19 pivotally connected to the rear
 cover 18 extend to outer positions of a frame 17F of main plow body 17,
 with compression springs applying a downward biasing force to the rear
 cover 18. Support positions between the rods 19 and rear cover 18 may be
 varied to fix the rear cover 18 to a raised state. A cover sensor 18S is
 mounted on an upper surface of the main plow body for measuring an amount
 of pivotal movement of the cover 18.
 Referring to FIGS. 3 and 10, the driver's seat 5 has connectable and
 disconnectable, right and left seat belt straps 20. At the right side of
 driver's seat 5 are a control panel CP, and a position lever 21 for
 adjusting a pivoting angle of lift arms 8 to control raising and lowering
 of rotary plow A. At the left side of driver's seat 5 are a main shift
 lever 22 and a creep shift lever 23 for setting running speeds. A backward
 and forward drive change lever 24 is disposed at the left side of steering
 wheel 6 to be pivotable longitudinally of the tractor body. An accelerator
 lever 25 and a forcible lift lever 26 are arranged at the right side of
 the steering wheel. A main clutch pedal 27 is disposed at the left side on
 a floor to be depressible to disengage the main clutch 3. Side brake
 pedals 28 are disposed at the right side on the floor to be depressible to
 brake the right and left rear wheels 2 independently of each other. A
 panel disposed forwardly of steering wheel 6 includes a meter section M, a
 display select switch 29, a running mode select switch 30 and a key switch
 31. The select switch may be pressed to select one of four modes which are
 "2WD", "4WD", "double-speed" and "AD double-speed".
 Controls in the four modes of "2WD", "4WD", "double-speed" and "AD
 double-speed" will be described later. In the "2WD" mode, drive
 transmission to the front wheels 1 is disconnected to cause the tractor to
 run only by the drive of rear wheels 2. In the "4WD" mode, the tractor is
 driven by both front and rear wheels, with drive transmitted to the front
 wheels 1 to rotate at the same peripheral speed as the rear wheels 2 (i.e.
 standard drive state). In the "double-speed" mode, a switch is made from
 the standard "4WD" mode to a drive mode for increasing the driving speed
 of front wheels 1, when the front wheels 1 are steered by a larger angle
 than a predetermined steering angle, to cause the tractor to make a turn
 by a small radius. In the "AD double-speed" mode, a switch is made from
 the standard "4WD" mode to a drive mode for increasing the driving speed
 of front wheels 1 and at the same time braking an inward one of the rear
 wheels 2, when the front wheels 1 are steered by a larger angle than a
 predetermined steering angle, to cause the tractor to make a turn by a
 still smaller radius.
 As shown in FIG. 10, the meter section M includes a pointer type, engine
 speed meter 34 disposed centrally thereof, a liquid crystal display 35
 disposed above, a status area 36 with a plurality of indicator lamps to
 the left, and a display area 37 to the right having display lamps for
 indicating operating modes.
 Specifically, the status area 36 includes a lamp marked with a sign
 indicating an alarm state, a lamp with characters "brakes uncoupled"
 indicating that couplings (not shown) for interconnecting the side brake
 pedals 28 are released. a lamp with letter "P" indicating that a parking
 brake is on, a lamp with characters "AD double-speed" indicating that the
 "AD double-speed" has been selected, a lamp with characters "double-speed"
 indicating that the "double-speed" has been selected, and a lamp with
 characters "4WD" indicating that the tractor is in the four-wheel drive
 mode. The display area 37 includes a lamp with characters "monro"
 indicating that the rotary plow A is under rolling control, a lamp with
 characters "auto" indicating an operative state of a lift control relative
 to the ground using the cover sensor 18S, a lamp with characters "E auto"
 indicating that a vertical position of rotary plow A is controlled based
 on variations in the speed of engine E, a lamp with characters "pompa"
 indicating a lift control based on operation of the forcible lift lever
 26, a lamp with characters "back up" indicating that a control is effected
 to raise the rotary plow A to a predetermined height automatically when
 the tractor is driven backward, and a lamp with characters "auto up"
 indicating that a control is effected to raise the rotary plow A to a
 predetermined height when the front wheels 1 are steered more than a
 predetermined angle.
 The transmission case 4 houses a transmission system as shown in FIG. 5.
 Specifically, the transmission system includes a first change speed
 mechanism T1 having a four sets of gears and two sets of shifters 41 and
 42 of the synchromesh type for changing the power transmitted from engine
 E through main clutch 3 into four speeds, a hydraulic clutch C disposed
 downstream of the first change speed mechanism T1, a second change speed
 mechanism T2 disposed downstream of the hydraulic clutch C and having two
 sets of gears and a shifter 43 of the synchromesh type for changing the
 power into two speeds, a backward and forward drive switching mechanism
 Tfr having a reversing gear line and one shifter 44 of the synchromesh
 type for transmitting the power from the second change speed mechanism T2
 in forward rotation or backward rotation, a third change speed mechanism
 T3 disposed downstream of the backward and forward drive switching
 mechanism Tfr and having two sets of gears and one shifter 45 of the
 synchromesh type for changing the power into two speeds, and a creep
 change speed mechanism Tcr disposed downstream of the third change speed
 mechanism T3 and having one set of gears and a shifter 47 of the constant
 mesh type for transmitting the power received from the third change speed
 mechanism T3 as it is or in a substantially decelerated state.
 A propelling transmission system is constructed to transmit the power from
 this transmission system to the rear wheels 2 through a rear differential
 48, and to the front wheels 1 through a front wheel change speed device TF
 and a front wheel drive shaft 50. The front wheel change speed device is
 operable by a shifter 49 to selectively provide the standard drive state
 for driving the front wheels 1 at the same peripheral speed as the rear
 wheels 2, an accelerating state for driving the front wheels 1 at a higher
 peripheral speed than the rear wheels 2, and a state for disconnecting the
 power transmission to the front wheels 1. The front wheel accelerating
 device TF has functions to transmit accelerated drive to the front wheels
 1 when, in the "double-speed" mode and "AD double-speed" mode, the front
 wheels 1 are steered by a larger angle than a predetermined steering
 angle.
 The first change speed mechanism T1 and second change speed mechanism T2
 constitute a main change speed device TM for providing eight forward
 traveling speeds. The main change speed device TM has a first hydraulic
 cylinder P1, a second hydraulic cylinder P2 and a third hydraulic cylinder
 P3 for operating the three shifters 41, 42 and 43, respectively. The
 shifter 44 of the backward and forward drive switching mechanism Tfr
 mechanically interlocked to the backward and forward drive change lever
 24. The third change speed mechanism T3 has a fourth hydraulic cylinder P4
 for operating the shifter 45. The shifter 47 of the creep change speed
 mechanism Tcr is interlocked to the creep shift lever 23.
 As shown in FIG. 7, a hydraulic system is constructed for controlling the
 respective hydraulic cylinders P1-P4 and hydraulic clutch C. The first,
 second and fourth hydraulic cylinders P1, P2 and P4 are double-acting
 cylinders for setting the shifters 41, 42 and 45 to control positions at
 opposite ends and to a neutral position. The third hydraulic cylinder P3
 is a double-acting cylinder for setting the shifter 43 to control
 positions at opposite ends. These hydraulic cylinders P1, P2, P3 and P4
 are controllable by seven electromagnetic cylinder control valves V1, V2,
 V3 and V4 which receive hydraulic oil from a hydraulic pump 51 driven by
 the engine E. An oil line is formed for supplying hydraulic oil from the
 hydraulic pump 51 to the hydraulic clutch C through a pilot operated
 switch valve Vc. An oil line is also formed to adjusts pressure with an
 electromagnetic proportional pressure control valve Vp when the hydraulic
 clutch C is engaged. Further, hydraulic oil is supplied through an orifice
 52 to a pilot oil line 53. In addition, an oil line is provided to operate
 the switch valve Vc with a pressure in the pilot oil line 53. Oil lines
 are also provided to reduce the pressure to the pilot oil line 53 through
 five check valves 54. Four of the five check valves 54 are mechanically
 operable when operating the hydraulic cylinders P1, P2, P3 and P4. The
 remaining one check valve 54 is interlocked to be operable when the
 backward and forward drive change lever 24 is operated. The pilot oil line
 53 has a pressure sensor 55.
 When each of the first, second and fourth double-acting hydraulic cylinders
 P1, P2 and P4 receives hydraulic oil simultaneously from the two control
 valves, the piston in the cylinder is placed in a neutral position. When
 hydraulic oil is supplied from one control valve, the piston is moved to
 one end. When hydraulic oil is supplied from the other control valve, the
 piston is moved to the other end.
 Upon start of an operation of each hydraulic cylinder P1, P2, P3 or P4, the
 corresponding check valve 54 is opened to reduce the pressure in the pilot
 oil line 53, whereby the switch valve Vc is operated to a drain position
 to disengage the hydraulic clutch C. In this way, the hydraulic cylinder
 is operable to effect a shifting operation in a timed relationship with
 disengagement of the hydraulic clutch C. Subsequently, upon completion of
 the operation of the hydraulic cylinder, the check valve 54 is closed
 again to operate the switch valve Vc to an oil supplying position. As a
 result, hydraulic oil is supplied to the hydraulic clutch C with the
 pressure adjusted by the control valve Vp to engage the hydraulic clutch
 C. Thus, a shifting operation is carried out without requiring the main
 clutch 3 to be manually disengaged.
 Similarly, when the backward and forward drive change lever 24 is operated,
 the corresponding check valve 54 is opened to reduce the pressure in the
 pilot oil line 53, whereby the switch valve Vc is operated to the drain
 position to disengage the hydraulic clutch C to allow a drive switching.
 Subsequently, upon completion of the operation of the backward and forward
 drive change lever 24, the check valve 54 is closed again to operate the
 switch valve Vc to the oil supplying position. As a result, hydraulic oil
 is supplied to the hydraulic clutch C with the pressure adjusted by the
 control valve Vp to engage the hydraulic clutch C. When the above change
 operation is carried out, the pressure in the pilot oil line 53 increases
 again after being reduced. When such pressure variations are detected by
 the pressure sensor 55 of the electric switch type, a controller
 (described later) adjusts a current applied to an electromagnetic solenoid
 of the control valve Vp. In this way, the pressure to the hydraulic clutch
 C is increased while adjusting the pressure of hydraulic oil supplied to
 the hydraulic clutch C according to predetermined characteristics, to
 engage the clutch smoothly without generating a shock.
 A shift cylinder PF is provided for operating the shifter 49 of front wheel
 change speed device TF. This shift cylinder PF is a double acting
 cylinder, as is the first hydraulic cylinder P1, for setting the shifter
 49 to control positions at opposite ends and to a neutral position. An oil
 line is provided to supply hydraulic oil from the hydraulic pump 51 to
 electromagnetic shift control valves VF for controlling the shift cylinder
 PF.
 As shown in FIG. 8, a hydraulic system is constructed for enabling the lift
 control and rolling control of rotary plow A. Specifically, a flow
 priority valve 57 is mounted on an oil line for receiving hydraulic oil
 from the hydraulic pump 51. An electromagnetic rolling valve 58 is mounted
 on an oil line for transmitting control oil from the flow priority valve
 57 to control the hydraulic oil to the rolling cylinder 12. An
 electromagnetic proportional control valve V is mounted on an oil line for
 transmitting surplus oil from the flow priority valve 57 to control the
 hydraulic oil to the lift cylinders 7. The electromagnetic proportional
 control valve V includes a raising valve 59 disposed in a position for
 supplying hydraulic oil to the lift cylinders 7, a pilot pressure
 controlling, raising pilot valve 60 for operating the raising valve 59, a
 lowering valve 61 disposed in a position for draining hydraulic oil from
 the lift cylinders 7, a pilot pressure controlling, lowering pilot valve
 62 for operating the lowering valve 61, and a relief valve 63. The raising
 pilot valve 60 and lowering pilot valve 62 are constructed for adjusting
 opening degrees of the raising valve 59 and lowering valve 61 by varying
 pilot pressure through adjustment of the current value of control electric
 power applied to electromagnetic solenoids. By adjusting the opening
 degrees, a raising speed and lowering speed of the rotary plow A may be
 set as desired.
 As shown in FIG. 4, side brakes 66 are disposed on transmission shaft lines
 for transmitting power from the transmission case 4 to the right and left
 rear wheels 2. These right and left side brakes 66 are operable by arms
 66A interlocked to the side brake pedals 28 through linkages 67 such as
 control rods and control wires to be operable independently of each other
 by depression of the pedals. Further, hydraulic brake cylinders 68 are
 provided to control the right and left side brake 66 independently of each
 other.
 As shown in the same figure, a steering control system includes a
 hydraulically operable power steering unit 69 for receiving an operating
 force of the steering wheel 6. Tie rods 71 are provided between a pitman
 arm 69A of power steering unit 69 and knuckle arms 70 of right and left
 front wheels 1. A steering angle sensor AS of the potentiometer type is
 provided for measuring a steering angle of the front wheels 1 from an
 amount of pivotal movement of a knuckle arm 71.
 As shown in FIG. 9, oil lines are provided for supplying hydraulic oil from
 the hydraulic pump 51 to the power steering unit 69, and to
 electromagnetic brake valves VB for controlling the right and left brake
 cylinders 68.
 As shown in FIG. 11, the control panel CP has an open/close lid 75 disposed
 on an intermediate portion thereof. A plowing depth setting dial 76 is
 disposed in a position exposed forwardly of the lid 75 when the lid 75 is
 closed. In a position exposed rearwardly of the lid 75 are a set of a
 switch 77 and a lamp 77L for auto up ON/OFF, a set of a switch 78 and a
 lamp 78L for backup control ON/OFF, a set of a switch 79 and a lamp 79L
 for ON/OFF en bloc of an automatic plowing depth control of standard
 sensitivity and a standard rolling control, and a manual rolling switch
 80.
 The portion covered by the lid 75 includes a set of a link specification
 select switch 81 and two lamps 81L for correcting a control reference
 value according to the specifications of the three point link mechanism L;
 a set of a plowing depth control mode select switch 82 and three lamps 82L
 for selecting one of a standard automatic plowing depth control which sets
 sensitivity to a standard, a sensitive automatic plowing depth control
 which sets sensitivity to high, and an engine load plowing depth control
 based on an engine load; a set of a rolling control mode switch 83 and two
 lamps 83L for selecting a standard rolling control or a rolling control
 for a sloping ground; a set of a rotary specification select switch 84 and
 three lamps 84L for correcting a control reference value according to the
 specifications of the rotary plow A; a rolling angle setting dial 85; and
 an upper limit setting dial 86. The lamps forming the sets with the above
 switches are lit when the switch are turned on or to indicate modes
 selected by the switches.
 FIG. 12 shows a control system including the controller 90 which has a
 microprocessor. A display controller is included in this controller 90.
 The display controller includes a display mode selecting device for
 selecting a display mode, built therein in the form of hardware and
 software.
 The key switch 31 has power lines for driving a glow plug 91 and a cell
 motor 92. A line is provided to input a signal to controller 90 from the
 line through which the key switch 31 drives the glow plug. The controller
 90 has an input interface for receiving signals from the display select
 switch 29, running mode select switch 30, a main shift sensor 22S of the
 potentiometer type for detecting a control position of the main shift
 lever 22, sensors for lifting, sensors for rolling, steering angle sensor
 AS and measuring sensors; and an output interface for transmitting control
 signals to the display 35, status area 36, display area 37, cylinder
 control valves V1, V2, V3 and V4, raising and lowering pilot valves 60 and
 61, rolling valve 58, shift control valves VF and brake valves VB.
 The sensors for lifting include a lever sensor 21S for detecting a control
 position of the position lever 21, lift arm sensor 8S, a plowing depth
 setter 76S operable by the plowing depth setting dial 76, cover sensor
 18S, and a speed sensor ES for measuring a speed of engine E. The sensors
 for rolling includes the rolling sensor RS, stroke sensor SS, a rolling
 angle setter 85S operable by the rolling angle setting dial 85, and manual
 rolling switch 80.
 The measuring sensors include a fuel sensor for measuring the quantity of
 fuel remaining in a fuel tank, a voltage sensor for measuring battery
 voltage, a cooling water temperature sensor for measuring the temperature
 of cooling water of engine E, an oil pressure sensor (not shown) for
 measuring the pressure of engine oil.
 The main shift lever 22 is operable to a parking position, a neutral
 position, 12 forward speed positions and 8 backward speed positions. When
 the main shift lever 22 is operated, the controller 90 detects a speed
 stage based on the signal from main shift sensor 22S, and provide a change
 speed state corresponding to this speed stage by selecting which of the
 hydraulic cylinders P1-P4 should be driven, and selecting and energizing
 the cylinder control valve or valves corresponding to the hydraulic
 cylinder or cylinders selected. Regarding the main change speed mechanism
 TM, the first change speed mechanism T1 can provide four speeds, while the
 second change speed mechanism T2 can provide two speeds. In addition, the
 third change speed mechanism T3 can provide two speeds. Thus, 16 speeds
 are available for forward running. However, a setting is made by software
 to provide only 12 speeds, with no shifting operation taking place in a
 range of small gear ratios.
 The running mode select switch 30 may be pressed repeatedly to select
 successively the "2WD" mode, "4WD" mode, "double-speed" mode and "AD
 double-speed" mode. When each mode is selected, the controller 90 turns on
 the corresponding lamp for "4WD", "doublespeed" or "AD double-speed" in
 the status area 36. When the "2WD" mode is selected, the controller 90
 controls the shift control valves VF to place the front wheel change speed
 device TF in neutral for breaking power transmission to the front wheels
 1. When the "4WD" mode is selected, the shift control valves VF are
 controlled to set the front wheel change speed device TF to the state for
 transmitting power to the front wheels 1 at a drive speed to cause the
 front wheels to rotate at the same peripheral speed as the rear wheels 2.
 When the "double-speed" mode is selected, and provided that the signal
 from the steering angle sensor AS indicates the steering angle of front
 wheels 1 being less than the predetermined angle, the shift control valves
 VF are controlled to set the front wheel change speed device TF to the
 state for transmitting power to the front wheels 1 at the drive speed to
 cause the front wheels to rotate at the same peripheral speed as the rear
 wheels 2. On the other hand, if the signal from the steering angle sensor
 AS indicates that the steering angle of front wheels 1 exceeds the
 predetermined angle, the shift control valves VF are controlled to set the
 front wheel change speed device TF to the state for transmitting power to
 the front wheels 1 at a drive speed to cause the front wheels to rotate at
 a higher peripheral speed than the rear wheels 2. Further, when the "AD
 double-speed" mode is selected, and provided that the signal from the
 steering angle sensor AS indicates the steering angle of front wheels 1
 being less than the predetermined angle, as when the "double-speed" mode
 is selected, the shift control valves VF are controlled to set the front
 wheel change speed device TF to the state for transmitting power to the
 front wheels 1 at the drive speed to cause the front wheels to rotate at
 the same peripheral speed as the rear wheels 2. On the other hand, if the
 signal from the steering angle sensor AS indicates that the steering angle
 of front wheels 1 exceeds the predetermined angle, the shift control
 valves VF are controlled to set the front wheel change speed device TF to
 the state for transmitting power to the front wheels 1 at the drive speed
 to cause the front wheels to rotate at a higher peripheral speed than the
 rear wheels 2, and at the same time the brake valve VB corresponding to
 the rear wheel 2 inwardly of the turn is controlled to operate the side
 brake 66 of the inward rear wheel 2.
 Control modes for raising and lowering the rotary plow A will be described
 next.
 [Position Control]
 The position control is a control for setting and maintaining the rotary
 plow A at a target height relative to the tractor body. To effect this
 control, the operator sets the position lever 21 to a selected position,
 whereby the signal value from the lever sensor 21S indicates a control
 target. A signal is outputted to the electromagnetic proportional control
 valve V for operating the lift cylinders 7 to raise or lower the rotary
 plow A, so that the lift arm sensor 8S measure a signal corresponding to
 this target height. When the rotary plow A reaches the target height, the
 raising or lowering operation is stopped.
 [Auto Plowing Depth Control]
 The auto plowing depth control is a raising and lowering control for
 maintaining the rotary plow A at a target plowing depth with reference to
 the ground. To effect this control, the plowing depth mode select switch
 82 is operated to select the standard or sensitive auto plowing depth
 control mode. The rear cover 18 is placed in a freely pivotable state as
 shown in FIG. 6A. The plowing depth setting dial 76 is set to a target
 plowing depth. Then, the position lever 21 is set to a position for
 maximum depth to set the signal value from the plowing depth setter 76S to
 a control target. A signal is outputted to the electromagnetic
 proportional control valve V to raise or lower the rotary plow A, so that
 the signal from the cover sensor 18S be maintained at the control target.
 This control automatically raises or lowers the rotary plow A to maintain
 the rotary plow A at a target height relative to the ground even when the
 wheels sink into the ground or when the tractor body pitches.
 [Engine Load Control] (E Auto)
 The engine load control is a control for maintaining the rotary plow A at a
 target plowing depth with reference to the ground, and raising and
 lowering the rotary plow A to maintain the rotational frequency of engine
 E occurring at this target height. To effect this control, the plowing
 depth mode select switch 82 is operated to select the engine load plowing
 depth control mode. The rods 19 are manipulated to set the rear cover 18
 to the raised state shown in FIG. 6B. With the plowing depth setter 76S
 set to a target plowing depth, the position lever 21 is set to the
 position for maximum depth. As a result, a pivoting angle of lift arms 8
 corresponding to the signal value from the plowing depth setter 76S is
 derived. This pivoting angle is set as a control target. A signal is
 outputted to the electromagnetic proportional control valve V to raise or
 lower the rotary plow A, so that the signal value from the plowing depth
 setter 76S be maintained at the control target. The engine speed sensor ES
 measures the rotational frequency of engine E occurring at the time the
 rotary plow A is maintained at the level corresponding to the control
 target. This measurement is stored in memory. In this way, a control is
 carried out for automatically raising or lowering the rotary plow A in a
 direction to maintain the engine speed against variations in the load
 acting on the engine E which may occur when the wheels sink into the
 ground or when the tractor body pitches.
 [Forcible Lift Control]
 The forcible lift control includes a control for raising the rotary plow A
 to the upper limit, overriding the controls for raising and lowering the
 rotary plow A, and a control for lowering the rotary plow A back to a
 height selected or existing before this raising control. For raising the
 rotary plow A, the forcible lift lever 26 is operated upward, whereby a
 signal is outputted to the electromagnetic proportional control valve V to
 raise the rotary plow A until the lift arm sensor 8S measures a value of
 control target set by the upper limit setting dial 86. After this raising
 operation, the forcible lift lever 26 is operated downward to return to a
 preceding control mode, whereby the lowering control is performed to
 reinstate the former level.
 [Backup Control]
 The backup control is a control for raising the rotary plow A to the upper
 limit when, with the rotary plow A lying in a level other than the upper
 limit, the backward and forward drive change lever 24 is set to a backward
 position. This control is effected only if the backup switch 78 is kept
 ON. When the control is performed, a signal is outputted to the
 electromagnetic proportional control valve V to raise the rotary plow A
 until the lift arm sensor 8S measures the value of control target set by
 the upper limit setting dial 86. After this raising operation, the
 forcible lift lever 26 is operated downward to return to a preceding
 control mode, whereby the lowering control is performed to reinstate the
 former level.
 [Auto Up Control]
 The auto up control is a control for raising the rotary plow A to the upper
 limit when, with the rotary plow A undergoing the auto plowing depth
 control or engine load control, the front wheels 1 are steered in excess
 of the predetermined angle. This control is effected only if the auto up
 switch 77 is kept ON. When the control is performed, a signal is outputted
 to the electromagnetic proportional control valve V to raise the rotary
 plow A until the lift arm sensor 8S measures the value of control target
 set by the upper limit setting dial 86. After this raising operation, the
 forcible lift lever 26 is operated downward to return to a preceding
 control mode, whereby the lowering control is performed to reinstate the
 former level.
 This tractor is capable of a rolling control for maintaining rotary plow A
 in a selected rolling posture when the tractor body rolls. This rolling
 control is effecting by keeping ON the switch 79 for ON/OFF en bloc of the
 automatic plowing depth control of standard sensitivity and a standard
 rolling control. When the tractor body tilts sideways, a target amount of
 operation of the rolling cylinder 12 is computed from a signal from the
 rolling sensor RS and a signal value set by the rolling angle setter 85S.
 A signal is outputted to the electromagnetic proportional control valve V
 to extend or contract the rolling cylinder 12 until the stroke sensor 22
 measures this target value. With the rolling angle setter 85S set to a
 horizontal position, a control is performed to maintain the rotary plow A
 in horizontal posture even when the tractor body rolls. When the manual
 rolling switch 80 is pressed, this rolling control is overridden by a
 control to roll the rotary plow A in a selected direction, and upon
 release of this switch, the original rolling control is reinstated.
 The rolling control mode switch 83 is used for causing the tractor to run
 along a contour line on a sloping ground, and is basically similar to the
 standard rolling control. However, a target inclination angle is
 automatically corrected to anticipate sinking of the wheels on the
 downhill side of a sloping ground.
 Next, details of information shown on the display will be described.
 The display 35 is used to present messages in the form of characters and
 graphics. In time of a normal operation, as shown in FIG. 13, the display
 35 shows, in a right-hand region thereof, a remaining quantity of fuel and
 temperature of cooling water in bar graphs extending parallel and one
 above the other. In a leftward end region of the display, a speed stage
 provided by the propelling transmission system is shown in numerals or
 letters. The middle region between these two regions shows an integrated
 value of operating time, a value indicating a trip value of travel
 distance, or a value indicating a running speed. What should be displayed
 in the middle region may be selected by turning on the select switch 30.
 (These displays are called the standard displays.) FIG. 13 shows three
 display types. The upper display type shows that the main shift lever 22
 is set to a parking position to render parking brakes operative. The
 middle display type shows the main shift lever 22 being in neutral
 position. The lower display type shows that the main shift lever 22 is set
 to the third speed stage.
 When the key switch 31 is operated to electrify the glow plug 91 in order
 to start the engine E, the upper display type is employed from among the
 three display types shown in FIG. 14. A symbol of glow plug 91 appears in
 the left end region of display 35 for showing speeds. The right-hand
 region of display 35 shows the remaining quantity of fuel and temperature
 of cooling water as noted above. The middle region shows a selected
 numerical value.
 Next, immediately after start of engine E, a message "Fasten seat belt"
 appears over the entire surface of display 35 for about three seconds, as
 shown in the display type in the middle of FIG. 14, unless the seat belt
 straps 20 are connected. When, upon start of engine E, the signal from the
 cover sensor 18S indicates that the rear cover 18 is raised, a message
 "E-auto and auto OFF" is given as shown in the lower display type in FIG.
 14. This message is shown to notify the operator that the automatic
 plowing depth control mode is impossible while the rear cover 18 is in the
 raised state.
 When abnormal situations occur while in the standard display mode noted
 above during an operation, the display 35 shows the following alarms over
 the entire surface thereof.
 As an alarm display, when the fuel sensor detects the remaining quantity of
 fuel being less than a predetermined quantity, a message "Replenish fuel"
 and a symbol of refilling are displayed as shown in the upper display type
 in FIG. 15. When the voltage sensor measures the voltage of a battery (not
 shown) to be low, a message "Charging abnormal" and a battery symbol are
 displayed as shown in the middle display type in FIG. 15. When the oil
 pressure sensor detects a low engine oil pressure, a message "Engine oil
 pressure abnormal" is displayed as shown in the lower display type in FIG.
 15.
 When the cooling water temperature sensor measures the temperature of
 cooling water to be above a predetermined temperature, a message
 "Overheat" and a message "Idle engine" are alternately displayed as shown
 in FIG. 16. When the temperature of cooling water lowers to the
 predetermined temperature, the above messages are replaced by a message
 "Check after cooling".
 When, in the standard display mode, a signal from a sensor shows an
 abnormal value, or when a short circuit or disconnection of the
 electromagnetic solenoid of the electromagnetic valve is detected, alarms
 are given on the entire surface of display 35 as described hereinafter. It
 is to be noted that the following devices are used for detecting a short
 circuit or disconnection of the electromagnetic solenoid. Where a current
 value applied to the electromagnetic solenoid is fed back for controlling
 the current, a short-circuit or disconnection is detected based on a
 signal from the feedback line. Where no feedback is employed, an
 additional sensor is used and a short-circuit or disconnection is detected
 based on a signal from this sensor.
 Some examples of these displays will be cited hereunder. When an
 abnormality occurs with the stroke sensor SS, as shown in FIG. 17, a
 message "Stroke sensor abnormal" and a message "Use manual switch" appear
 alternately at intervals of 1.5 seconds. These displays notify the
 operator that an abnormality has occurred with the stroke sensor, and at
 the same time that an adjustment of the roll posture of rotary plow A may,
 if necessary, be carried out by operating the manual rolling switch. When
 an abnormality occurs with the cover sensor 18S, as shown in FIG. 18, a
 message "Cover sensor abnormal" and a message "E auto available" appear
 alternately at intervals of 1.5 seconds. These displays notify the
 operator that an abnormality has occurred with the cover sensor 18S, and
 at the same time that a lift control may be carried out by E auto.
 When an abnormality occurs with the main shift sensor 22S, as shown in FIG.
 19, a message "Main shift sensor abnormal" and a message "Change not
 acceptable +On hold" appear alternately at intervals of 1.5 seconds. These
 displays notify the operator that an abnormality has occurred with the
 main shift sensor 22S, and at the same time that a shifting operation is
 impossible and the current speed is maintained. When an abnormality occurs
 with the solenoid of cylinder control valve V1, as shown in FIG. 20 a
 message "Shift solenoid 1 abnormal" and a message "1st, 2nd & 9th speeds
 unavailable" appear alternately at intervals of 1.5 seconds. These
 displays notify the operator that an abnormality has occurred with the
 cylinder control valve V1, and at the same time that some of the speeds
 cannot be provided. When an abnormality occurs with the steering angle
 sensor AS, as shown in FIG. 21, a message "Steering angle sensor abnormal"
 and a message "Double-speed & auto up not acceptable" appear alternately
 at intervals of 1.5 seconds. These displays notify the operator that an
 abnormality has occurred with the steering angle sensor AS, and at the
 same time that the control in the double-speed mode and the auto up
 control are impossible.
 During a usual operation, as described above, the display 35 is maintained
 in the standard display mode for continuously displaying information
 necessary to the operation. Based on this displayed information, the
 operation may be carried out with ease. In time of abnormality, the
 standard display mode is overridden by specific messages of abnormality
 shown on the entire surface of display 35 for causing the operator to
 recognize the abnormality. Where a message is given to indicate how to
 deal with the abnormally, the operator can take a proper step promptly. It
 is to be noted that the above standard displays and alarm displays
 constitute the contents of display made in an ordinary display mode.
 In addition, this tractor is capable of displaying on the entire surface of
 display 35, information in an adjusting mode for making fine adjustment of
 the sensors, and information in a diagnostic mode for checking conditions
 of the sensors and the solenoids of the electromagnetic valves. For
 performing controls in the adjusting mode or diagnostic mode, for example,
 it is necessary to set the key switch to a power supply position, with the
 display select switch 29 and running mode select switch 30 turned on at
 the same time. When this operation is carried out, as shown at #a in FIG.
 22, the display 35 shows three messages "fine adjust", "diagnosis" and
 "select model", and a selected one of the messages in inverse and blinks.
 This display may be switched successively by turning on the display select
 switch 29. A selection may be finalized by keeping the display select
 switch 29 on for two seconds or more. The "select model" is used in making
 settings corresponding to types of vehicles and working implements
 attached thereto, and will not be described herein.
 When "fine adjust" (adjusting mode for fine-adjusting the sensors) is
 selected, as shown at #b in FIG. 22, the display 35 shows three messages
 "double speed", "MA" and "shift", and a selected one of the messages in
 inverse and blinks. This display may be switched successively by turning
 on the display select switch 29. A selection may be finalized by keeping
 the display select switch 29 on for two seconds or more.
 When "MA" is selected, as shown at #c in FIG. 22, a message "MA fine adjust
 mode" is displayed first, and then, as shown at #d in FIG. 22, a message
 "tractor to horizontal" is displayed to prompt the operator to make the
 rolling posture of the tractor body horizontal. Next, a message "lift arms
 to upper limit" is displayed, as shown at #e in FIG. 22, to prompt the
 operator to raise the lift arms 8 to the upper limit. Next, a message
 "rotary to horizontal" is displayed, as shown at #f in FIG. 22, to prompt
 the operator to make the rolling posture of rotary plow A horizontal.
 Next, a message "lever to upper end" is displayed, as shown at #g in FIG.
 22, to prompt the operator to operate the position lever 21 to a upper
 limit position. Next, a message "set angle to horizontal" is displayed, as
 shown at #h in FIG. 22, to prompt the operator to operate the rolling
 angle setting dial 85 to a "horizontal" position. Next, a message "upper
 limit to high" is displayed, as shown at #i in FIG. 22, to prompt the
 operator to operate the the upper limit setting dial 86 to a "high"
 position. The displays at #d to #i in FIG. 22 are repeated in the state
 order at intervals of 1.5 seconds. Where the settings prompted by these
 messages are or have already been made, the corresponding displays are not
 displayed again. Only messages for outstanding steps are repeatedly
 displayed.
 When all these steps have been taken, a message "condition settings OK"
 indicating that all the settings are completed, and a message "press
 display select for 3 sec. or more" prompting the operator to press the
 display select switch 29, as shown at #j and #k in FIG. 23, are repeatedly
 displayed at intervals of 1.5 seconds. When the display select switch 29
 has been pressed for three seconds or more as prompted by the display,
 signals are inputted from the rolling sensor RS, lift arm sensor 8S, cover
 sensor 18S, stroke sensor SS, lever sensor 21S, rolling angle setter 85S
 and upper limit setter 86S. Differences between the signal values and
 ideal values are stored as correction values in a nonvolatile memory such
 as an EEPROM. Subsequent controls may be corrected based on these
 correction values. When the above operation has been completed, a message
 "fine adjustment completed" indicating completion of fine adjustment, and
 a message "key switch off" prompting the operator to turn off the switch
 31, are displayed as shown at #1 and #m in FIG. 23. The controls are
 completed by turning off the key switch 31 as prompted.
 Further, for performing a diagnosis of the sensors and the like also, it is
 necessary to set the key switch to the power supply position with the two
 switches turned on at the same time. When this operation is carried out,
 as shown at #a in FIG. 24, the display 35 shows the three messages "fine
 adjust", "diagnosis" and "select model". The "diagnosis" is selected, and
 then "double speed" is selected from among the three messages "double
 speed", "MA" and "shift" as shown at #b in FIG. 24.
 When "double speed" is selected, as shown at #c in FIG. 24, a message
 "double speed self-diagnostic mode" is displayed first, and then, as shown
 at #d in FIG. 24, a message "front wheels to straight" is displayed to
 prompt the operator to turn the front wheels straight. At the same time, a
 diagnosis is performed to check the sensors and solenoids of
 electromagnetic valves used in the "double speed" and "AD double speed".
 When they are found normal, a message "normal" is displayed as shown at #e
 in FIG. 24.
 When the self-diagnosis finds the steering sensor AS abnormal, a message
 "steering sensor abnormal" is displayed as shown at #f in FIG. 24. When,
 among the shift control valves, the one for providing 4WD is found
 abnormal, a message "4WD SOL abnormal" is displayed as shown at #g in FIG.
 24. When, among the shift control valves, the one for providing double
 speed is found abnormal, a message "double speed SOL abnormal" is
 displayed as shown at #h in FIG. 24. When the left brake valve is found
 abnormal, a message "AD SOL (left) abnormal" is displayed as shown at #i
 in FIG. 24. When the right brake valve is found abnormal, a message "AD
 SOL (right) abnormal" is displayed as shown at #j in FIG. 24.
 As described above, this invention utilizes the display 35 disposed on the
 tractor body to show information necessary to an operation, including a
 remaining quantity of fuel, a temperature of cooling water, speeds and so
 on. Immediately after a start of engine E, the operator is prompted to
 fasten the seat belt 20 and confirm the plowing depth control mode. In
 addition, when any of the numerous sensors and solenoids of the
 electromagnetic valves breaks down during an operation, the display 35 is
 used to show immediately the occurrence of abnormality and abnormal
 component on the entire surface thereof. Necessary steps and alternative
 control modes are displayed to enable the operator to take proper action
 with ease.
 Further, when setting values for correcting the sensors, messages prompting
 to take necessary steps are shown on the display 35 simply by selecting an
 object or objects to be fine-adjusted after selecting the fine adjust
 mode. A proper operation may be carried out only by following the
 information displayed. When checking for faults of the sensors, messages
 prompting to take necessary steps are shown on the display 35 simply by
 selecting an object or objects for self-diagnosis after selecting the
 self-diagnostic mode. Results of the self-diagnosis are displayed
 subsequently. When an abnormality is found, the abnormal component is
 indicated. That is, necessary information may be confirmed on the display
 35 during an operation, and an abnormality, if any, may be shown on the
 display 35 to immediately notify the operator of the situation and enable
 the operator to take appropriate action. The operator may adjust the
 sensors properly, based on information shown on the display 35, without
 referring to manuals. Thus, when checking the sensors, the operator may
 readily grasp correct information shown on the display 35, to make
 adjustment or determine whether certain sensors need to be changed.
 Although the key switch 31 for starting the engine is used to start the
 adjust mode and diagnostic mode, the controls in the adjust mode or
 diagnostic mode never take place when the engine E is started for an
 actual operation. Thus, the operator is free from troublesomeness
 concerning the display.
 This invention is not limited to the embodiment described hereinbefore.
 Controls in the self-diagnostic mode, for example, may be set such that
 potentiometer type sensors are selected and an actual voltage value of
 each sensor is shown on the display.