Engine control device for tractor

In structure of an engine control device for a tractor, when a standard engine performance curve is selected by a mode selection device, and a PTO drive device, which drives an implement attached to a tractor, is turned on, switching to the engine speed maintenance control mode is performed. Further, when a fuel efficient engine performance curve is selected by the mode selection device, and the PTO drive device, which drives the implement, is turned on, switching to the engine speed change control mode is performed. The problem that an engine stall tends to occur when control for maintaining the engine speed is performed while the fuel efficient engine performance curve with lower consumption rate than normal consumption rate is selected can be solved.

FIELD

The present invention relates to an engine control device for a tractor, which operates such that, in the tractor, the output of the engine is controlled in a fuel efficient engine performance curve for reduced fuel consumption and in a standard engine performance curve for normal fuel consumption.

BACKGROUND

A work vehicle such as a construction machine is designed to run or work in an energy-saving output mode in which the fuel consumption rate is lower than a normal fuel consumption rate.

For example, Patent Literature 1 discloses an engine control method for a construction machine, in which fuel consumption is improved by switching engine control to a fuel efficient mode specification, that is, an energy-saving output mode, by a mode selection device.

CITATION LIST

Patent Literature

SUMMARY

Technical Problem

Where an energy-saving output mode in which the fuel consumption rate is lower than a normal fuel consumption rate is selected, since the energy-saving output mode is lower than a standard output mode in terms of maximum permissible load, the possibility of reaching the maximum permissible load is high. Therefore, when control for maintaining the engine speed is performed, the engine may stall immediately when reaching the maximum permissible load in the energy-saving output mode.

Solution to Problem

To achieve the object by solving the foregoing problem, the invention described in claim1provides an engine control device for a tractor. The tractor comprises: a mode selection device (134) configured to switch between a standard engine performance curve (N) to obtain predetermined output and a fuel efficient engine performance curve (S) to reduce fuel consumption than that in the standard engine performance curve (N); and an engine speed maintenance control mode (B) in which when load is applied, an engine speed is maintained at a preset speed, and an engine speed change control mode (A) in which when load is applied, the engine speed is controlled to decrease, and the engine control device is configured to control the tractor such that switching to the engine speed maintenance control mode (B) is performed when the standard engine performance curve (N) is selected by the mode selection device (134), and a PTO drive device (151), which drives an implement attached to the tractor, is turned on, and the engine control device is configured to control the tractor such that switching to the engine speed change control mode (A) is performed when the fuel efficient engine performance curve (S) is selected by the mode selection device (134), and the PTO drive device (151), which drives the implement, is turned on.

In the engine control device for the tractor, when work is undertaken while the standard engine performance curve (N) is selected by the mode selection device (134), and the PTO drive device (151) is turned on, the engine speed control is performed in the engine speed maintenance control mode (B) automatically. When a determination is made that there is a margin in the engine load, the fuel efficient engine performance curve (S) is selected by the mode selection device (134). In response to this selection, automatic switching to the engine speed change control mode (A) is performed.

In the engine control device for the tractor, when work is undertaken while the fuel efficient engine performance curve (S) is selected by the mode selection device (134), and the PTO drive device (151) is turned on, the engine speed control is performed in the engine speed change control mode (A) automatically. When a determination is made that there is no margin in the engine load, the standard engine performance curve (N) is selected by the mode selection device (134). In response to this selection, automatic switching to the engine speed maintenance control mode (B) is performed.

In the invention described in claim2, the tractor further comprises: an engine speed storage device (152) configured to store the engine speed; and an engine speed reproduction device (153) configured to reproduce the engine speed stored in the engine speed storage device (152), and the engine control device is configured to control the tractor such that switching to the engine speed change control mode (A) is performed when the fuel efficient engine performance curve (S) is selected by the mode selection device (134), and the engine speed reproduction device (153) is turned on.

In the engine control device for the tractor, the engine speed storage device (152) stores the engine speed. The engine speed reproduction device (153) reproduces the engine speed stored in the engine speed storage device (152). When cultivation work, traction work, or the like, is undertaken, the engine speed stored in the engine speed reproduction device (153) is reproduced as mentioned above. By reproducing the stored engine speed and selecting the fuel efficient engine performance curve (S) by the mode selection device (134), automatic switching to the engine speed change control mode (A) is performed.

In the invention described in claim3, the tractor further comprises a manual switch (150), and the engine control device is configured to control the tractor such that switching to the engine speed maintenance control mode (B) always is performed when the manual switch (150) is turned on.

In the engine control device for the tractor, when the manual switch (150) is turned on, switching to the engine speed maintenance control mode (B) always is performed.

Advantageous Effects of Invention

According to the invention described in claim1, automatic switching to the engine speed change control mode (A) is performed when the fuel efficient engine performance curve (S) is selected by the mode selection device (134) and the PTO drive device (151) for driving an implement is turned on. This yields the effects described below.

That is, since the maximum permissible load for the fuel efficient engine performance curve (S) is lower than that for the standard engine performance curve (N), a possibility of reaching the maximum permissible load is high. Therefore, this may lead to the problem that where work is undertaken in the engine speed maintenance control mode (B) with the fuel efficient engine performance curve (S) selected, the engine may immediately stall when reaching the maximum permissible load.

However, when the work is undertaken using the fuel efficient engine performance curve (S) in the engine speed change control mode (A), the engine speed decreases in proportion to the strength of the load, thereby preventing the problem that the engine speed immediately leads to stalling or the engine's having to be restarted. Additionally, according to the load, the engine speed decreases, making it easier for an operator to notice the load state.

In addition, automatic switching to the engine speed maintenance control mode (B) is performed when the standard engine performance curve (N) is selected by the mode selection device (134) and the PTO drive device (151) for driving the implement is turned on. Accordingly, since work can be undertaken at a constant speed until the maximum permissible engine load is reached, engine capacity can be utilized to the maximum and work efficiency thus improved.

According to the invention described in claim2, when the engine speed reproduction device (153) is turned on, work is basically undertaken. Accordingly, switching to the engine speed change control mode (A) is performed when the fuel efficient engine performance curve (S) is selected by the mode selection device (134) and the engine speed reproduction device (153) is turned on. Therefore, the invention described in claim2has effects similar to those in claim1.

That is, since the maximum permissible load for the fuel efficient engine performance curve (S) is lower than that for the standard engine performance curve (N), a possibility of reaching the maximum permissible load is high. Therefore, this may lead to the problem that where work is undertaken in the engine speed maintenance control mode (B) with the fuel efficient engine performance curve (S) selected, the engine may immediately stall when the curve (S) reaches the maximum permissible load.

However, by undertaking work using the fuel efficient engine performance curve (S) in the engine speed change control mode (A), the engine speed decreases in proportion to the strength of the load, thereby preventing the problem that the engine speed immediately leads to stalling or the engine's having to be restarted. Additionally, in proportion to the strength of the load the engine speed decreases, making it easier for an operator to notice the load state.

According to the invention described in claim3, when the manual switch (150) is turned on, switching to the engine speed maintenance control mode (B) is always performed, thus enabling more efficient work and running.

DESCRIPTION OF EMBODIMENTS

The invention will be described in detail below with reference to the drawings. It should be understood that the present invention is not limited to the embodiments below. It should also be understood that the compositional elements in the embodiments below include ones that could easily be anticipated by those skilled in the art and ones that are substantially identical to the compositional elements, that is, ones that fall in the range of so-called equivalents. Additionally, the compositional elements in the embodiments below may be combined as required.

FIG. 1is a diagram of the entire configuration of a fuel injection system of pressure accumulator type. A fuel injection system of pressure accumulator type is used in, for example, a multi-cylinder diesel engine but may be one used in a gasoline engine. The fuel injection system of pressure accumulator type includes, for example: a common rail1that accumulates the pressure of fuel to injection pressure by which the fuel is appropriately controlled; a rail pressure sensor2attached to this common rail1; a high-pressure fuel pump4that pressurizes fuel forced to flow from a fuel tank3, and feeds the fuel to the common rail1under pressure; high-pressure injectors6by which the high-pressure fuel accumulated in the common rail1is injected into a cylinder5of an engine E; a control device (an engine ECU12) that controls operations, such as the control of the high-pressure fuel pump4, high-pressure injectors6, and so on.

As described above, the common rail1is used to adjust fuel to be injected into each cylinder5of the engine E, to pressure required for output demanded. Fuel in the fuel tank3is sucked into the high-pressure fuel pump4, driven by the engine E, through an intake passage via a fuel filter7. The high-pressure fuel obtained through pressurization by the high-pressure fuel pump4is guided to the common rail1through a discharge passage8and stored in this rail1.

High-pressure fuel in the common rail1is supplied to the high-pressure injectors6for the cylinders through corresponding high-pressure fuel supply passages9. Based on a command from the engine control device (ECU)12, the high-pressure injectors6are actuated. Consequently, the high-pressure fuel is injected and supplied to the chamber of each cylinder5of the engine E. A surplus of fuel (i.e., return fuel) in each high-pressure injector6is guided to a common return passage10athrough a corresponding return passage10, and is returned to the fuel tank3through this return passage10a.

The high-pressure fuel pump4is provided with a pressure control valve11in order to control fuel pressure in the common rail1(common-rail pressure). In response to a signal from the engine ECU12, this pressure control valve11adjusts the flow area of the passage10athrough which a surplus of fuel is returned to the fuel tank3from the high-pressure fuel pump4. Thereby, the amount of fuel supplied to the common rail1is adjusted and the common-rail pressure can be controlled.

Specifically, a target common-rail pressure is set according to conditions for operating the engine E, and the common-rail pressure detected by the rail pressure sensor2is feed-back controlled via the pressure control valve11so that this common-rail pressure equals a target common-rail pressure.

The engine ECU12of a diesel engine E with a common rail1in agricultural machines such as a tractor has three types of control mode, which are engine speed change control mode A (droop control mode A), engine speed maintenance control mode B (isochronous control mode B, and heavy load C, all relating to engine speed and output torque, as shown inFIG. 2.

The engine speed change control mode A is configured such that the output changes in response to a change in the engine speed. Basically, the mode A is used when a vehicle is traveling. In order to prevent sudden engine stall, this mode is used even during work. For example, during the vehicle is traveling, when the vehicle is decelerated or stopped by braking, the engine speed decreases with the increase in running load. This mode enables the vehicle to decelerate or stop safely. In addition, when a workload is applied during the vehicle works, the engine speed is caused to decrease according to the load.

The engine speed maintenance control mode B is a control for maintaining the engine speed constant even when a load increases. Basically, this mode is used during work. For example, according to this mode, where a tractor cultivating is subject to resistance applied to one of its cultivating blades due to soil hardness, or where a combine harvesting is subject to load increase, the engine speed can be maintained.

The heavy load mode C is a control in which a heavy load control for increasing the output by increasing the engine speed when it becomes near the load limit is added to the control for maintaining the engine speed constant regardless of load change as in the engine speed maintenance control mode B. In particular, this mode is used where work is undertaken near the load limit. For example, where a tractor cultivating encounters hard arable soil, the engine performance may increase beyond the normal limit. Even in such a case, this mode enhances the work efficiency without interrupting the work.

FIG. 3Ais a diagram illustrating the relation between the engine speed and the output, and indicating the output characteristics of the engine E. Each of a fuel efficient engine performance curve S and a standard engine performance curve N indicates the relation between the engine speed (rpm) and output (kW).

The fuel efficient engine performance curve S indicates a control in which the amount of fuel supplied is decreased compared to the rate of fuel consumption indicated by the standard engine performance curve N. Accordingly, in the overall rotation area, the output indicated by the fuel efficient engine performance curve S is about 10% lower than that indicated by the standard engine performance curve N.

FIG. 3Bis a diagram illustrating the relation between the engine speed and the torque, which indicates the output characteristics of the engine E. Symbol ST indicates the relation between the engine speed (rpm) and the torque (N•m) in the fuel efficient engine performance curve S, and symbol NT indicates the relation between the engine speed (rpm) and the torque (N•m) in the standard engine performance curve N.

Use of the engine E by switching between the fuel efficient engine performance curve S and the standard output curve N, is set by operating a mode selection device (hereafter referred to as an engine power selection switch)134.FIGS. 6 and 9show the engine power selection switch.

When the tractor drives, automatic switching to the engine speed change control mode A is performed. Then, by selecting the standard engine performance curve N by the engine power selection switch134and also turning on a PTO drive device (hereafter referred to as a PTO drive switch)151for driving any implement attached to the tractor, automatic switching to the engine speed maintenance control mode B is performed. In the PTO drive device, the operation of a lever or the like may be detected by using, for example, a switch.

By selecting the fuel efficient output curve S by the engine power selection switch134and also turning on the PTO drive switch151for driving the implement, automatic switching to the engine speed change control mode A is performed.

During work while the PTO drive switch151is turned on and the standard engine performance curve N is selected by the engine power selection switch134, the engine speed is automatically controlled in the engine speed maintenance control mode B. If a determination is made that there is a margin in the engine load, the fuel efficient engine performance curve S is selected by the mode selection device134. As a result of this selection, automatic switching to the engine speed change control mode A is performed.

During work while the PTO drive switch151is turned on and the fuel efficient engine performance curve S is selected by the engine power selection switch134, the engine speed is automatically controlled in the engine speed change control mode A. If a determination is made that there is no margin in the engine load, the standard engine performance curve N is selected by the engine power selection switch134. As a result of this selection, automatic switching to the engine speed maintenance control mode B is performed.

Since the maximum permissible load of the fuel efficient engine performance curve S is lower than that of the standard engine performance curve N, the output curve S has a higher possibility of reaching the maximum permissible load than the output curve N. Therefore, where the fuel efficient engine performance curve S, for example, is selected, trouble may occur in that when it reaches the maximum permissible load during work in the engine speed maintaining mode B, the engine may immediately stall.

To avoid this, work is carried out on the fuel efficient engine performance curve S and in the engine speed change control mode A. Consequently the engine speed decreases according to the load, thus enabling avoidance of the engine speed's possibly leading to immediate stalling or any necessity to restart the engine. Additionally, the engine speed decreases according to the load, thus making it easier for an operator to notice a status of the load.

When the standard engine performance curve N is selected by the engine power selection switch134and also the PTO drive switch151for driving the implement is turned on, automatic switching to the engine speed maintenance control mode B is performed. This makes it possible for the tractor to work with a constant engine speed up to the maximum permissible load of the engine itself. Engine capacity can be utilized to the maximum, hence improving work efficiency.

When the PTO drive switch151is turned on, a PTO clutch sol (solenoid)54b, shown inFIG. 6and described below, is supplied with power and a PTO clutch54a, shown inFIG. 5, is turned on.

As shown inFIG. 6, the engine control device includes: an engine speed storage device (hereafter referred to as engine speed storage switch)152, which stores a specific engine speed; and an engine speed reproduction device (hereafter referred to as an engine speed reproduction switch)153, which reproduces the stored specific engine speed. This engine speed reproduction switch153enables automatic setting of the specific engine speed. Accordingly, any need to operate an acceleration lever, etc., is eliminated and operability is improved.

When the fuel efficient engine performance curve S is selected by the engine power selection switch134and also the engine speed reproduction switch153is turned on, automatic switching to the engine speed change control mode A is performed.

Using the engine speed storage switch152, an operator stores a desired specific engine speed into a running-control device120. Then, the stored engine speed is reproduced by operating the engine speed reproduction switch153. When work is undertaken, the stored specific engine speed is reproduced with the engine speed reproduction switch153in such a manner. When the stored engine speed is reproduced and the fuel efficient engine performance curve S is selected by the engine power selection switch134, automatic switching to the engine speed change control mode A is performed.

As described above, by reproducing the stored engine speed and selecting the fuel efficient engine performance curve S by the engine power selection switch134while working, automatic switching to the engine speed change control mode A is performed. Accordingly, the engine speed decreases according to the load, thus enabling avoidance of the engine speed's possibly leading to immediate stalling and the engine's having to be restarted. The engine speed decreases according to the load, thus making it easier for an operator to notice a status of the load.

In another configuration, the load rate of a PTO output shaft54c(FIG. 5) driving the implement is detected, and where the vehicle is working or driving with about 70% or less of the highest output of the standard engine performance curve N for a fixed length of time, automatic switching to the fuel efficient engine performance curve S is performed. This enables efficient, fuel efficient work and running. The load rate of the PTO output shaft54cis calculated from the current engine speed with respect to a predetermined engine speed.

Conversely where the vehicle is working or driving with about 70% or more of the highest output of the fuel efficient engine performance curve S for a fixed length of time, automatic switching to the standard engine performance curve N is performed. Thus, by utilizing the engine's own capacity, the vehicle can work and drive.

Where a range shift lever (not shown) is shifted to an on-street driving position (a position indicating a high speed driving at a high speed change position) or the vehicle is driving with the standard engine performance curve N for a fixed length of time (about 10 min), automatic switching to the fuel efficient engine performance curve S may be performed.

With regard to the engine speed change control mode A, the engine speed maintenance control mode B, and the heavy load mode C, automatic switching to the engine speed maintenance control mode B may be performed in response to, for example, a speed change operation with the range shiftlever of an agricultural vehicle (e.g., a tractor, a combine harvester, or a seedling transplanter) or in response to an on-off switching operation of a task clutch (i.e., a PTO clutch for rotary cultivator drive or the like in a tractor, or the drive clutch of a reaping part or threshing part in a combine harvester). Incidentally, there is a case where, even when the PTO clutch is turned off in the tractor, a lift arm connecting an implement may be raised and lowered while the lifting arm is located lower than its uppermost position. In such a case, since plowing or plow-soiling is being performed, the engine speed maintenance control mode B or heavy load mode C is used automatically.

Manual switching among the engine speed change control mode A, engine speed maintenance control mode B, and heavy load mode C may be performed by operating an engine speed control mode switch148(FIG. 6). In the case of a manual operation, selection is determined by an operator.

Shifting a sub-speed change shift lever to an on-street driving position causes automatic switching to the engine speed change control mode A. However, a load is small in case of on-street driving. Therefore, automatic switching to the fuel efficient engine performance curve S may be performed. In this case, when the sub-speed change shift lever is operated to a position other than the on-street driving position, a return to the standard engine performance curve N is performed if this standard engine performance curve N has been selected in advance. Thus, the efficient driving is possible.

When the engine power selection switch134is turned on, the engine speed change control mode A may always be used. Also, when the engine power selection switch134is turned off and the transmission is automatically performed by an operation of an accelerator pedal, the engine speed change control mode A may be used.

When the engine power selection switch134and a manual switch150(FIG. 6) are turned off and, furthermore, the PTO clutch is turned on, the engine speed maintenance control mode B may be used automatically. Instead of the condition that this PTO clutch is turned on, the condition that an implement is in a lowered position or that the engine speed reproduction switch153is turned on may be used. When the PTO clutch is turned off, the implement is raised, or the engine speed reproduction switch153is turned off, automatic switching to the engine speed change control mode A may be performed.

When the manual switch150is turned on, the engine speed maintenance control mode B is always used. This enables efficient work and driving.

FIG. 4illustrates a tractor15as one example of a work vehicle in which the present invention is applied.

The tractor15has an engine E in the hood of the forward region of a vehicle body. The rotating power of the engine E is transmitted to a speed change device in a transmission case16, and rotating power decelerated by the speed change device is transmitted to front wheels17and rear wheels18. An operator's seat22on the vehicle body is enclosed in a cabin19. A steering wheel20extends upward from a dashboard13provided with an instrument panel117, which is located in front of the operator's seat in the cabin19. Disposed around the steering wheel20is a lever for forward/backward movement, a parking brake lever, a PTO selector lever, etc. This engine E is a diesel engine of common rail type, mentioned above.

An implement such as a rotary cultivator is attached by providing a hitch21and three-point linkage (not shown) between the left and right rear wheels18and18.

FIG. 7is an enlarged view of an instrument panel117.FIG. 8is an enlarged view of a liquid crystal data display part14in the instrument panel117and illustrates a display example.FIG. 9is an enlarged perspective view of the vicinity of the right side of the steering wheel20extending upward from the dashboard13.

An engine tachometer24is disposed in the center of the instrument panel117in front of the steering wheel20, the liquid crystal data display part14is disposed on the right side of the tachometer24, and an energy-saving monitor lamp23is disposed on the left side of the tachometer24.

The data display part14includes a gear speed display14afor displaying current gear speed, a fuel consumption rate display14b, and so on. The fuel consumption rate display14bchanges with a driving speed display14cafter fixed periods of time. The fuel consumption rate is the proportion of the amount of fuel actually injected to achieve maximum output in relation to the engine speed at the time. The data display part14displays a fuel gauge14dand an engine cooling water temperature gauge14eas well.

The energy-saving monitor lamp23lights up when the fuel efficient engine performance curve S has been selected by the engine power selection switch134. It lights up in green.

As shown inFIG. 9, the engine power selection switch134is provided on the right side of the steering wheel20and on the dashboard13. By depressing this engine power selection switch134, the engine is controlled with the fuel efficient engine performance curve S.

FIG. 5is a diagram of a speed change mechanism for the speed change device in the transmission case16. A configuration for transmission of power from the engine E to the front wheels17and rear wheels18will now be described.

To an input shaft25directly connected to the output shaft of the engine E, a first gear26is fixed and a forward/backward movement switching clutch27is fastened.

One of the gears of the forward/backward movement switching clutch27, namely a second gear28, engages with a third gear30, which is fixed to a first speed change shaft29, thereby causing deceleration. The other one of the gears of the forward/backward movement switching clutch27, namely a fourth gear31, engages via a counter gear32with a fifth gear33, which is fixed to the first speed change shaft29, thereby transmitting power while rotating in the reverse direction. Specifically, when the forward/backward movement switching clutch27is coupled to the second gear28, the rotation of the input shaft25is transmitted to the first speed change shaft29such that the shaft29rotates in the reverse direction. When the clutch27is coupled to the fourth gear31, the rotation of the input shaft25is transmitted to the first speed change shaft29such that the shaft29rotates in the normal direction. The neutral state in which the clutch27is separated from both the second and fourth gears28and31is the main clutch off-state in which power is not transmitted. By controlling a hydraulic valve, this main clutch off-state can be held. That is, the forward/backward movement switching clutch27, activated when automatic control is exerted, when the forward/-reverse lever is operated, or when the clutch pedal is operated, functions as the main clutch.

To the first speed change shaft29downstream of the forward/backward movement switching clutch27in the transmission, a first speed change clutch34for switching to first speed/third speed and a second speed change clutch35for switching to a second speed/fourth speed are attached.

The first clutch gear36and a second clutch gear37of the first speed change clutch34for switching to first speed/third speed engage with a third clutch gear39and a fourth clutch gear40, respectively, which are fixed to a second counter shaft38. The rotation of the first speed change shaft29is transmitted to the second counter shaft38by switching to the first or third speed.

A fifth clutch gear41and a sixth clutch gear42of the second transmission clutch35for switching to a second speed/fourth speed engage with a seventh clutch gear43and an eighth clutch gear44, respectively, which are fixed to the second counter shaft38. The rotation of the first speed change shaft29is transmitted to the second counter shaft38by switching to the second or fourth speed.

Downstream of the second counter shaft38in the transmission is a third counter shaft45connected by a coupling46such that power is transmitted directly. A small gear47and a large gear48are fixed to this third counter shaft45. The small gear47and large gear48engage with a large clutch gear51and small clutch gear52of a high/low speed switching clutch50, which is attached to a second speed change shaft49, thereby transmitting rotation of the third counter shaft45to the second speed change shaft49at high or low speed.

A sixth gear53is fixed to the downstream end of the second speed change shaft49in the transmission. This sixth gear53engages with a large gear56of a large-and-small gear section55, which is rotatably supported on a third drive shaft54, thereby transmitting power while decelerating.

A small gear57of the large-and-small gear section55engages with a seventh gear60of two sub-speed change clutches59, which are pivotally supported on a bevel gear shaft58, thereby transmitting power while decelerating. Additionally, an eighth gear61provided integrally with the seventh gear60engages with a second large gear63, which is fixed to a fifth counter shaft62, thereby transmitting power while decelerating.

To the fifth counter shaft62, a second small gear64is also attached. This second small gear64engages with a third large gear65on the bevel gear shaft58, thereby transmitting power while decelerating. Accordingly, while decelerating, rotation of the second speed change shaft49is transmitted from the sixth gear53, through the large gear56, the small gear57, the seventh gear60, the eighth gear61, the second large gear63, and the second small gear64, to the third large gear65.

A first shifter66and a second shifter67of the two corresponding sub-speed change clutches59operated by a sub-speed change shift lever engage with the bevel gear shaft58so as to able to slide in the axial direction of the shaft58. When the first shifter66is slid to and engaged with the seventh gear60, rotation of the seventh gear60is transmitted to the bevel gear shaft58. When the second shifter67is slid to and engaged with the eighth gear61, rotation of the eighth gear61is transmitted to the bevel gear shaft58, and is gradually decelerated. Consequently, the bevel gear shaft58is rotated at low speed.

The rotation of the bevel gear shaft58is transmitted to a differential gear70through a first bevel gear68and a second bevel gear69, and is transmitted from the differential gear70to the rear wheels18through a vehicle shaft71and a planetary gear72.

The foregoing may be summarized as follows: rotation of the input shaft25is first switched to normal rotation or reverse rotation by the forward/backward movement switching clutch27; normal or reverse rotation is changed in speed to four levels, i.e., from first to fourth speeds, by the first transmission clutch34for switching to first speed/third speed and by the second transmission clutch35for switching to second speed/fourth speed; the resultant rotation is changed in speed to two levels, i.e., low and high speeds, by the high/low speed switching clutch50, and is further changed in speed to three levels, i.e., high, medium, and low speeds, by the two sub-speed change clutches59; and rotation of the input shaft25, thus changed in speed, is transmitted to the bevel gear shaft58. That is, rotation of the input shaft25is changed in speed to 24 levels (4×2×3) and transmitted to the vehicle shaft71.

Driving force is transmitted to the front wheels17in the manner described below. A ninth gear74is fixed to the bevel gear shaft58, which ninth gear74is engaged with a relay gear75, and the relay gear75is engaged with a tenth gear77, which is fixed to a third drive shaft76, thereby driving this third drive shaft76. Using a second coupling78, the third drive shaft76is connected to a speed change shaft80to which a front-wheel acceleration clutch79is attached. An eleventh gear81and twelfth gear82of the front-wheel acceleration clutch79are engaged with a thirteenth gear84and a fourteenth gear85, respectively, which are fixed to a seventh counter shaft83, thereby switching to front-wheel acceleration from regular front-wheel drive. Incidentally, by shifting the front-wheel acceleration clutch79to neutral, drive of the front wheels17is discontinued and only the rear wheels are driven.

Using a third coupling86, the seventh counter shaft83is connected to a front-wheel drive shaft87. Further, using a fourth coupling88, a extension shaft89, and a fifth coupling90, the front-wheel drive shaft87is connected to a front-wheel drive bevel shaft91.

Power from the front-wheel drive bevel shaft91drives the front wheels17by its being transmitted through a first front bevel gear92, a second front bevel gear93, a front differential gear94, a front differential gear95, a third front bevel gear96, a fourth front bevel gear97, a vertical shaft98, a fifth front bevel gear99, a sixth front bevel gear100, and a planetary gear101in that order.

A PTO output shaft54cis connected to the downstream side of the third drive shaft54in the transmission. The PTO output shaft54cis driven through a PTO speed change device54d, a PTO counter shaft54e, and this third drive shaft54.

Next, control flow is explained with reference to a control block diagram inFIG. 6.

First, the engine ECU (engine control device)12receives the following input: exhaust temperature from an engine exhaust temperature sensor106, engine speed from an engine revolution sensor107, engine lubricating oil pressure from an engine oil pressure sensor108, cooling water temperature from an engine water temperature sensor109, and pressure of common rail1from a rail pressure sensor2. A drive signal is output to the high-pressure fuel pump4, and a fuel supply adjustment control signal is output to the high-pressure injector6.

Next, an implement raising/lowering control device110receives the following inputs: an operation signal from a position control sensor111provided for an implement raising/lowering lever, an ascent/descent signal from a lifting arm sensor112, raised-position restriction signal from a raised-position restriction dial113, and a lowering-speed set signal from a lowering-speed adjustment dial114. An implement raising/lowering signal is output to main raising and lowering solenoids115and116, respectively, thereby activating an implement raising/lowering cylinder.

Control signals are exchanged (CAN1and CAN2communications) among the engine ECU12, the implement raising/lowering control device110, and the driving-control device120described below, thereby displaying on an instrument panel117whether the engine E uses the normal engine performance curve N or fuel efficient engine performance curve S, the raised/lowered state of the implement, driving speed of the driving device, and so on, also displaying on an operation panel118the current positions of each lever and pedal, and so on.

The driving-control device120receives the inputs of clutch turn-on signals from first, second, third, and fourth speed change clutch pressure sensors121,122,123, and124, that is, the gear speeds of a multi-gear speed change device. Specifically, signals from the first speed change clutch34for switching to first speed/third speed and from the second speed change clutch35for switching to second speed/fourth speed. The driving-control device120also receives input from the transmission position of a sub-clutch from a Hi (High speed) clutch pressure sensor125and a Lo (Low speed) clutch pressure sensor126. That is, it receives a signal from the high/low speed switching clutch50.

The driving-control device120receives inputs regarding forward/neutral/backward movement of the main clutch from a forward-movement clutch pressure sensor127and a backward-movement clutch pressure sensor128. That is, it receives a signal from the forward/backward movement switching clutch27. The running-control device120also receives inputs regarding transmission operation positional signals from a forward/-reverse lever operated-position sensor129, which detects the position of a forward/reverse-lever used to move the tractor forward/backward, and from a sub-speed change shift lever operated-position sensor130, which detects the operated position of a sub-transmission lever.

The driving-control device120receives the following inputs: driving speed from a vehicle speed sensor131, mission oil temperature from a mission oil temperature sensor132, a clutch pedal depression signal from a clutch pedal-depression sensor133, a selection signal for the standard engine performance curve N or fuel efficient engine performance curve S from the engine power selection switch134, and an engine control mode switching signal from the engine speed control mode switch148. The device120also receives an on/off signal from the manual switch150.

Furthermore, the driving control device120receives the following inputs: a signal from an acceleration speed change setting switch144, which carries out automatic transmission for the vehicle when driving (on a street) with the foot throttle pedal depressed, an operation signal from a main speed change acceleration/deceleration operating switch145, which carries out acceleration or deceleration in manual speed change, an acceleration operation signal from an acceleration sensor146, which detects the position of an hand throttle lever, and an acceleration adjustment signal from an acceleration fine adjustment lever sensor147, which finely adjusts acceleration.

With regard to output from the driving control device120, a switching signal from a forward/backward movement switching clutch is output to a forward/backward movement switch sol (solenoid)135; a relief pressure adjustment signal for oil pressure, which drives the forward/backward switching sol (solenoid), is output to a linear pressure-rise sol (solenoid)136, thereby reducing clutch connection shock; and an on/off signal is output to a clutch sol (solenoid)137.

Additionally, a first or second speed input signal is output to a transmission1-3switching sol (solenoid)138of a hydraulic cylinder, which drives the first transmission clutch34for switching to first or third speed, and a relief pressure adjustment signal for oil pressure, which drives the first transmission clutch34for switching to first or third speed, is output to the transmission1-3pressure-rise sol (solenoid)139, thereby reducing clutch connection shock. A second or fourth speed input signal is output to a transmission2-4switching sol (solenoid)140of a hydraulic cylinder, which drives the second speed change clutch35for switching to second or fourth speed, and a relief pressure adjustment signal for oil pressure, which drives the second speed change clutch35for switching to second or fourth speed, is output to the transmission2-4pressure-rise sol (solenoid)141, thereby reducing clutch connection shock. A high-speed clutch on-signal and a low-speed clutch on-signal are respectively output to a Hi (High speed) clutch switching sol (solenoid)142and a Lo (Low speed) clutch switching sol (solenoid)143, which activate a hydraulic cylinder for driving a high/low speed switching clutch50.

REFERENCE SIGNS LIST

A ENGINE SPEED CHANGE CONTROL MODEB ENGINE SPEED MAINTENANCE CONTROL MODEE ENGINEN NORMAL ENGINE PERFORMANCE CURVES FUEL EFFICIENT ENGINE PERFORMANCE CURVE134MODE SELECTION DEVICE (ENGINE POWER SELECTION SWITCH)150MANUAL SWITCH151PTO DRIVE DEVICE (PTO DRIVE SWITCH)152ENGINE SPEED STORAGE DEVICE (ENGINE SPEED STORAGE SWITCH)153ENGINE SPEED REPRODUCTION DEVICE (ENGINE SPEED REPRODUCTION SWITCH)