Drive system control device for working vehicle

In a working vehicle, it is possible to achieve a downsizing of an engine by securing an output torque in a low rotating region of the engine without using any supercharger. In the working vehicle having the engine mounted to a travel machine body, a common rail type fuel injection device which injects fuel to the engine, and a continuously variable transmission which shifts power from the engine, a rotating speed N of the engine is limited to two kinds, N#1 and N#2. Further, a change gear ratio of the continuously variable transmission is changed and regulated in such a manner as not to change a vehicle speed of the travel machine body before and after changing the rotation speed N whichever of the two kinds N#1 and N#2 the rotating speed N of the engine is changed to.

TECHNICAL FIELD

The present invention relates to a drive system (engine and continuously variable transmission) control device for a working vehicle, for example, an agricultural machine and a construction machine.

BACKGROUND OF THE INVENTION

In order to achieve a downsizing of an engine while maintaining a rated output, making a displacement of the engine low and installing a supercharger have been generally carried out (refer, for example, to Patent Document 1). By the downsizing mentioned above, it is possible to make a working vehicle mounting the engine thereon compact and light, and improve a fuel consumption.

CITATION LIST

Patent Literature

Patent Document 1: Japanese Patent Publication of Translated Version No. 2008-514854

SUMMARY OF INVENTION

Technical Problem

However, in the case that the displacement is lowered and the supercharger is utilized for the downsizing, the number of the parts is increased and a cost is increased. Further, there has been a problem that an output torque is smaller in a low rotation region and it is hard to secure the output torque, in comparison with the engine before the displacement is lowered.

Accordingly, a technical object of the present invention is to provide a drive system control device for a working vehicle which dissolves the problem mentioned above.

A drive system control device for a working vehicle according to a first aspect of the present invention is structured such that in the working vehicle provided with an engine which is mounted to a travel machine body, and a common rail type fuel injection device which injects fuel to the engine, a rotating speed of the engine is limited only to two kinds.

The invention of a second aspect is structured such that in the drive system control device for the working vehicle described in the first aspect, a continuously variable transmission shifting power from the engine is provided, and a change gear ratio of the continuously variable transmission is changed and regulated in such a manner as not to change a vehicle speed of the travel machine body before and after changing the rotation speed whichever of the two kinds the rotating speed of the engine is changed to.

The invention of a third aspect is structured such that in the drive system control device for the working vehicle described in the first aspect, the fuel injection device is regulated in such a manner as to reduce a fuel consumption rate in driving the engine by each of the kinds of rotating speed.

A drive system control device for a working vehicle according to a fourth aspect of the present invention is structured such that in the working vehicle provided with an engine which is mounted to a travel machine body, and a common rail type fuel injection device which injects fuel to the engine, a minimum rotating speed of the engine is changeable in a range which is higher than a low idle rotating speed which is unique to the engine.

The invention of a fifth aspect is structured such that in the drive system control device for the working vehicle described in the fourth aspect, a continuously variable transmission shifting power from the engine is provided, and a change gear ratio of the continuously variable transmission is changed and regulated in such a manner as not to change the minimum vehicle speed of the travel machine body from the low idle rotating speed, in the case that the minimum rotating speed is set to a value which is higher than the low idle rotating speed.

The invention of a sixth aspect is structured such that in the drive system control device for the working vehicle described in the fifth aspect, in the case that an engine operating point relating to a rotating speed and a torque of the engine deviates from a previously set optimum fuel consumption line, the engine operating point is changed onto the optimum fuel consumption line, and a change gear ratio of the continuously variable transmission is changed and regulated in such a manner as not to change the vehicle speed of the travel machine body.

According to the inventions of the first to third aspects, in the working vehicle provided with the engine which is mounted to the travel machine body, and the common rail type fuel injection device which injects the fuel to the engine, since the rotating speed of the engine is limited only to two kinds, it is possible to achieve the engine which does not use a low rotation region having a smaller output torque, and to easily secure a higher output horsepower than an output horsepower in an engine having the same displacement of the engine. According to the other side of the coin, it is possible to achieve an engine having a lower displacement than a displacement in an engine having the same output horsepower Therefore, there can be achieved an effect that the downsizing of the engine can be easily realized.

Particularly, in the case of employing the structure in which the continuously variable transmission shifting the power from the engine is provided, and the change gear ratio of the continuously variable transmission is changed and regulated in such a manner as not to change the vehicle speed of the travel machine body before and after changing the rotation speed whichever of the two kinds the rotating speed of the engine is changed to, such as the second aspect, it is possible to maintain the vehicle speed of the travel machine body at the vehicle speed before changing the rotating speed, for example, even if the rotating speed is changed to a low speed side or a high speed side. Therefore, there can be achieved an effect that it is possible to do away with an uncomfortable feeling caused by changing the rotating speed of the engine.

According to the fourth aspect of the present invention, since the drive system control device for the working vehicle is structured such that in the working vehicle provided with the engine which is mounted to the travel machine body, and the common rail type fuel injection device which injects the fuel to the engine, the minimum rotating speed of the engine is changeable in the range which is higher than the low idle rotating speed which is unique to the engine, it is possible to easily secure a higher output horsepower than an output horsepower in an engine having the same displacement. According to the other side of the coin, it is possible to achieve an engine having a lower displacement than a displacement in an engine having the same output horsepower. Therefore, there can be achieved an effect that the downsizing of the engine is easily realized. In addition, since any supercharger is necessary for securing the output horsepower, there can be achieved an effect that a parts cost is suppressed.

According to the invention of the fifth aspect, since the continuously variable transmission shifting the power from the engine is provided, and the change gear ratio of the continuously variable transmission is changed and regulated in such a manner as not to change the minimum vehicle speed of the travel machine body from the low idle rotating speed, in the case that the minimum rotating speed is set to the value which is higher than the low idle rotating speed, the minimum vehicle speed of the travel machine body does not become higher but can be maintained at the low idle rotating speed, even if the minimum rotating speed is made higher than the low idle rotating speed. Therefore, there is achieved an effect that it is possible to obtain a travel performance (a vehicle speed having no uncomfortable feeling) which is not different from a travel performance in the working vehicle mounting the engine having the same displacement of the aforementioned engine, at a time of traveling at a low speed.

According to the invention of the sixth aspect, since in the case that the engine operating point relating to the rotating speed and the torque of the engine deviates from the previously set optimum fuel consumption line, the engine operating point is changed onto the optimum fuel consumption line, and the change gear ratio of the continuously variable transmission is changed and regulated in such a manner as not to change the vehicle speed of the travel machine body, it is possible to securely prevent the vehicle speed fluctuation going with the change of the rotating speed, while executing a low fuel consumption operation. Therefore, there can be achieved an effect that a stable travel performance is obtained.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will be given below of an embodiment which embodies the present invention on the basis of the accompanying drawings.

(1) Outline Structure of Tractor

First of all, a description will be given of an outline structure of a tractor141corresponding to one example of a working vehicle with reference toFIGS. 1 and 2. As shown inFIGS. 1 and 2, a travel machine body142of the tractor141is supported by a pair of right and left front wheels143and a pair of right and left rear wheels144. The tractor141is structured such as to travel forward and backward by driving the rear wheels144and the front wheels143by an engine70which is mounted to a front portion of the travel machine body142. The engine70is covered with a hood146. Further, a cabin147is installed to an upper surface of the travel machine body142. A control seat148and a control steering wheel149moving a steering direction of the front wheels143right and left by a steering operation are installed to an inner portion of the cabin147. A step150which an operator gets on and off is provided in an outer side portion of the cabin147, and a fuel tank151for supplying fuel to the engine70is provided in an inner side of the step150and a lower side than a bottom portion of the cabin147.

As shown inFIGS. 1 and 2, the control steering wheel149within the cabin147is provided on a control column190which is positioned in front of the control seat148. A right side of the control column190is provided with a throttle lever197which sets and keeps a rotating speed of the engine70, and a pair of right and left brake pedals191which operate the travel machine body142so as to brake. In a left side of the control column190, there are arranged a forward and backward movement switching lever198for operating so as to switch a moving direction of the travel machine body142to a forward movement and a backward movement, and a clutch pedal192. A back surface side of the control column190is provided with a parking brake lever200which keeps the brake pedal191at a depressed position.

In a right side of the brake pedal191, there is arranged an accelerator pedal199which increases and decreases a rotating speed in a range from a lower limit rotating speed to a higher speed, the lower limit rotating speed being the rotating speed of the engine70set by the throttle lever197. On a right column of the control seat148, there are arranged a working machine elevating lever193which manually changes and regulates a height position of a rotary tiller164serving as a ground working machine, a PTO shift lever194, and a main shift lever201for a shift operation. A sub shift lever195is arranged on a left column of the control seat148, and a differential lock pedal196is arranged in a front side of the left column.

As shown inFIGS. 1 and 2, the travel machine body142is constructed by an engine frame154having a front bumper152and a front axle case153, and right and left machine body frames156which are detachably fixed to a rear portion of the engine frame154by bolts. A transmission case157for appropriately shifting a drive force of the engine70and transmitting to the rear wheels144and the front wheels143is connected to a rear portion of the machine body frame156. The rear wheel144is attached via a rear axle case158which is installed so as to protrude outward from an outer side surface of the transmission case157. A continuously variable transmission159(refer toFIGS. 3 and 4) shifting the drive force from the engine70is provided within the transmission case157.

A hydraulic type working machine elevating mechanism160moving up and down the rotary tiller164is detachably mounted to an upper surface of a rear portion of the transmission case157. The rotary tiller164is connected to the rear portion of the transmission case157via a three-point link mechanism constituted by a pair of right and left lower links161and a top link162. The rear side surface of the transmission case157is provided with a PTO shaft163for transmitting a PTO drive force to the rotary tiller164so as to protrude rearward.

As shown inFIGS. 1 and 2, a seeding machine170for sowing is attached to the rear portion side of the rotary tiller164so as to be replaceable with a fertilizer distributor (not shown). The seeding machine170is provided with a tank171charging seeds, a feeding portion172feeding the seeds within the tank171at a fixed amount, and an electric motor173driving a feeding roller (not shown) of the feeding portion172. The seeds within the tank171are scattered onto the already tilled ground at the back of the rotary tiller164from the feeding portion172. In the case that the fertilizer distributor is attached to the rotary tiller164, the fertilizer (medical agent) of the fertilizer distributor is scattered onto the already tilled ground at the back of the rotary tiller164.

(2) Hydraulic Circuit Structure of Tractor

Next, a description will be given of a structure of a hydraulic circuit210of the tractor141mainly with reference toFIG. 3. The hydraulic circuit210of the tractor141is provided with a working hydraulic pump204and a traveling hydraulic pump205which are driven by a rotary power of the engine70. The working hydraulic pump204and the traveling hydraulic pump205are provided in a front surface side of a front side wall member222in the transmission case157(refer toFIG. 4). The working hydraulic pump204is connected to a control electromagnetic valve211for supplying a working fluid to an elevation control hydraulic cylinder215of the working machine elevating mechanism160. The control electromagnetic valve211is structured such as to be operable in a switching manner on the basis of an operation of the working machine elevating lever193. When the control electromagnetic valve211is operated so as to be switched by the working machine elevating lever193, the elevation control hydraulic cylinder215is driven so as to expand and contract, and elevates and turns a lift arm169(refer toFIG. 1) connecting the working machine elevating mechanism160and the right and left lower links161. As a result, the rotary tiller164is moved up and down via the lower links161.

The traveling hydraulic pump205is structured such as to supply the working fluid to the continuously variable transmission159of the transmission case157and a hydraulic cylinder203for a power steering. In this case, the transmission case157is also utilized as a working fluid tank, and the working fluid in an inner portion of the transmission case157is supplied to each of the hydraulic pumps204and205. The traveling hydraulic pump205is connected to the hydraulic cylinder203for the power steering via a control valve212for the power steering, and is connected to an automatic brake electromagnetic valve246in relation to a brake cylinder247for a pair of right and left brake actuating mechanisms245.

Further, the traveling hydraulic pump205is connected to a PTO clutch hydraulic electromagnetic valve249actuating a PTO clutch248of a PTO shift mechanism228, a proportional control valve213and a starting electromagnetic valve217in relation to the continuously variable transmission159, a switch valve214actuated by the valves213and217, a high speed clutch electromagnetic valve251actuating a sub shift hydraulic cylinder250of a sub shift mechanism227, a forward moving clutch electromagnetic valve253in relation to a forward moving hydraulic clutch252of a forward and backward movement switching mechanism226, a backward moving clutch electromagnetic valve255in relation to a backward moving hydraulic clutch254, a 4-wheel drive hydraulic electromagnetic valve257in relation to a 4-wheel drive hydraulic clutch256of a 2-wheel drive and 4-wheel drive switching mechanism229, and a double speed hydraulic electromagnetic valve259in relation to a double speed hydraulic clutch258.

The PTO clutch hydraulic electromagnetic valve249, the forward moving clutch electromagnetic valve253, the backward moving clutch electromagnetic valve255, the 4-wheel drive hydraulic electromagnetic valve257, and the double speed hydraulic electromagnetic valve259are structured such as to switch and drive the respective hydraulic clutches248,252,254,256and258by actuating the respective corresponding clutch cylinders on the basis of an appropriate control thereof. In this case, the hydraulic circuit210is provided with a relief valve, a flow rate regulating valve, a check valve, an oil cooler, an oil filter and the like.

(3) Power Transmission System of Tractor

Next, a description will be given of a power transmission system of the tractor141mainly with reference toFIG. 4. A front side wall member222is detachably fixed to a front surface of the transmission case157which is formed as a hollow box shape, and a rear side wall member223is detachably fixed to a rear surface of the transmission case157. An inner portion of the transmission case157is separated into a front chamber224and a rear chamber225by a partition wall221. Although an illustration is omitted, the front chamber224and the rear chamber225are communicated in such a manner that the internal working fluids are movable each other. In the front chamber224side of the transmission case157, there are arranged a forward and backward movement switching mechanism226switching a rotary power from the continuously variable transmission159to a forward turning direction and a reverse turning direction, a mechanical sub shift mechanism227shifting the rotary power via the forward and backward movement switching mechanism226, a PTO shift mechanism228transmitting the rotary power from the engine70to the PTO shaft163while appropriately shifting, and a 2-wheel drive and 4-wheel drive switching mechanism229switching the 2-wheel drive and the 4-wheel drive of the front and rear wheels143and144. Further, the continuously variable transmission159, and a differential gear mechanism230transmitting the rotary power via the sub shift mechanism227to the right and left rear wheels144are arranged in the rear chamber225side of the transmission case157.

A flywheel231is attached in a direct connecting manner to an engine output shaft74protruding rearward from the engine70. The flywheel231and a main driving shaft232extending rearward from the flywheel are connected via a main clutch233for connecting and disconnecting the power. The main driving shaft232and a main shift input shaft234protruding forward from the transmission case157are connected via a power transmission shaft235provided with universal shaft joints in both ends. The rotary power of the engine70is transmitted to the main shift input shaft234from the engine output shaft74via the main driving shaft232and the power transmission shaft235, and is next shifted appropriately by the continuously variable transmission159and the sub shift mechanism227. The shift power is transmitted to the right and left rear wheels144via the differential gear mechanism230. The shift power by the continuously variable transmission159and the sub shift mechanism227is also transmitted to the right and left front wheels153via the 2-wheel drive and 4-wheel drive switching mechanism229and a differential gear mechanism236within the front axle case143.

The continuously variable transmission159in an inner portion of the rear chamber225is of an inline type that a main shift output shaft237is concentrically arranged in the main shift input shaft234, and is provided with a variable displacement type hydraulic pump portion240, and a constant displacement type shifting hydraulic motor portion241actuated by the high-pressure working fluid discharged from the hydraulic pump portion240. The hydraulic pump portion240is provided with a pump swash plate242regulating a working fluid supply amount by variably changing an angle of incline in relation to an axis of the main shift input shaft234. A main shift hydraulic cylinder243changing and regulating the angle of incline of the pump swash plate242in relation to the axis of the main shift input shaft234is associated with the pump swash plate242. An amount of the working fluid supplied to the hydraulic motor portion241from the hydraulic pump portion240is changed and regulated by changing the angle of incline of the pump swash plate242on the basis of a driving motion of the main shift hydraulic cylinder243, and a main shifting motion of the continuously variable transmission159is carried out.

Namely, if the switch valve214is actuated by the working fluid from the proportional control valve213which is actuated in proportion to an amount of operation of the main shift lever201, the main shift hydraulic cylinder190is driven, and the angle of incline of the pump swash plate242in relation to the axis of the main shift input shaft234is changed in conjunction with this. The pump swash plate242of the embodiment can be regulates its angle in a range between one (positive) maximum angle of incline and the other (negative) maximum angle of incline with respect to a neutral angle which is approximately zero in incline (in the vicinity of zero including zero), and is set to an angle inclined to any one (negative and nearly maximum angle of incline in this case) when the vehicle speed of the travel machine body142is the lowest (refer toFIG. 5).

When the angle of incline of the pump swash plate242is approximately zero (neutral angle), the hydraulic motor portion241is not driven by the hydraulic pump portion240, and the main shift output shaft237turns at a rotating speed which is approximately the same as that of the main shift input shaft234. When the pump swash plate242is inclined to one direction (positive angle of incline) in relation to the axis of the main shift input shaft234, the hydraulic pump portion240actuates at increased speed the hydraulic motor portion241, and the main shift output shaft237turns at a rotating speed which is higher than that of the main shift input shaft234. As a result, the rotating speed of the hydraulic motor portion241is added to the rotating speed of the main shift input shaft234, and the added rotating speed is transmitted to the main shift output shaft237. Accordingly, the shift power (vehicle speed) from the main shift output shaft237is changed in proportion to the angle of incline (positive angle of incline) of the pump swash plate242in the range of the rotating speed which is higher than the rotating speed of the main shift input shaft234. When the pump swash plate242is at the positive angle of incline and is in the vicinity of the maximum angle, the travel machine body142comes to the maximum vehicle speed (refer to outline square positions inFIG. 5).

When the pump swash plate242is inclined to the other direction (negative angle of incline) side in relation to the axis of the main shift input shaft234, the hydraulic pump portion240actuates the hydraulic motor portion241so as to decelerate (reversely turn), and the main shift output shaft237turns at a rotating speed which is lower than that of the main shift input shaft234. As a result, the rotating speed of the hydraulic motor portion241is subtracted from the rotating speed of the main shift input shaft234, and the subtracted rotating speed is transmitted to the main shift output shaft237. Accordingly, the shift power from the main shift output shaft237is changed in proportion to the angle of incline (negative angle of incline) of the pump swash plate242in the range of the rotating speed which is lower than the rotating speed of the main shift input shaft234. When the pump swash plate242is at the negative angle of incline and is in the vicinity of the maximum angle, the travel machine body142comes to the minimum vehicle speed (refer to an outline circle position inFIG. 5).

In this case, in the embodiment, if the switch valve214is actuated by the working fluid from the starting electromagnetic valve217which is actuated on the basis of a command of a working machine (shift) controller271mentioned later, the main shift hydraulic cylinder243is driven regardless of an operated position of the main shift lever201, and the angle of incline of the pump swash plate242in relation to the axis of the main shift input shaft234is changed in conjunction with this.

(4) Engine and Peripheral Structure

Next, a description will be given of the engine70and its peripheral structure with reference toFIGS. 6 and 7. As shown inFIG. 6, the engine70is a four-cylinder type diesel engine, and is provided with a cylinder block75to which a cylinder head72is fastened to an upper surface. An intake manifold73is connected to one side surface of the cylinder head72, and an exhaust manifold71is connected to the other side surface. A common rail device117supplying the fuel to each of the cylinders of the engine70is provided below the intake manifold73in a side surface of the cylinder block75. An intake air throttle device81for regulating a pressure of an intake air (an amount of the intake air) of the engine70and an air cleaner (not shown) are connected to an intake pipe76connected to an upstream side of the intake air of the intake manifold73.

As shown inFIG. 7, a fuel tank118is connected to each of injectors115for four cylinders in the engine70via the common rail device117and the fuel supply pump116. Each of the injectors115is provided with a fuel injection valve119of an electromagnetically open and close control type. The common rail device117is provided with a cylindrical common rail120. The fuel tank118is connected to a suction side of the fuel supply pump116via a fuel filter121and a low pressure pipe122. The fuel within the fuel tank118is sucked into the fuel supply pump116via the fuel filter121and the low pressure pipe122. The fuel supply pump116of the embodiment is arranged in the vicinity of the intake manifold73. The common rail120is connected to a discharge side of the fuel supply pump116via a high pressure pipe123. The injectors115for four cylinders are connected to the common rail120via four fuel injection pipes126.

In the structure mentioned above, the fuel in the fuel tank118is pressure fed to the common rail120by the fuel supply pump116, and the fuel having the high pressure is stored in the common rail120. The high-pressure fuel within the common rail120is injected to each of the cylinders of the engine70from each of the injectors115on the basis of an opening and closing control of each of the fuel injection valves119. Namely, an injection pressure, an injection timing, and an injecting period (an injection amount) of the fuel supplied from each of the injectors115are controlled with a high precision by electronically controlling each of the fuel injection valves119. Accordingly, it is possible to reduce a nitrogen oxide (NOx) from the engine70and it is possible to reduce a noise and an oscillation of the engine70.

As shown inFIG. 9, the common rail device117is structured such as to execute a main injection A in the vicinity of a top dead center (TDC). Further, the common rail device117is structured such as to execute a small amount of pilot injection B for the purpose of reducing NOx and the noise at a moment of a crank angle θ1which is about 60 degree before the top dead center, execute a previous injection C for the purpose of reducing the noise at a moment of a crank angle θ2which is just before the top dead center, and execute an after injection D and a post injection E for the purpose of reducing a particulate matter (hereinafter, refer to as PM) and promoting purification of the exhaust gas at a moment of crank angles θ3and θ4which are after the top dead center, in addition to the main injection A.

The pilot injection B is structured such as to promote mixing between the fuel and the air by injecting at a moment which is greatly advanced in relation to the main injection A. The previous injection C is structured such as to shorten a delay of an ignition timing by the main injection A by injecting prior to the main injection A. The after injection D is structured such as to activate a diffusion combustion and afterburn the PM (reduce the PM) by injecting at a moment which is close to the main injection A. The post injection E is structured such as to supply the unburned fuel which does not contribute to an actual combustion process to a DPF50mentioned later, by injecting at a moment which is greatly retarded in relation to the main injection A. The unburned fuel supplied to the DIPF50reacts on a diesel oxidation catalyst53mentioned below, and a temperature of the exhaust gas within the DPF50rises by a reaction heat. A height of peaks of a graph inFIG. 9expresses roughly a difference of the fuel injection amount in each of the injecting stages A to E.

In this case, as shown inFIG. 7, the fuel supply pump116is connected to the fuel tank118via a fuel return pipe129. A common rail return pipe131is connected to an end portion in a longitudinal direction of the cylindrical common rail120via a return pipe connector130restricting a pressure of the fuel within the common rail120. Namely, a surplus fuel of the fuel supply pump116and a surplus fuel of the common rail120are recovered by the fuel tank118via the fuel return pipe129and the common rail return pipe131.

An exhaust gas throttle device82for regulating an exhaust gas pressure of the engine70and the DPF50(diesel particulate filter) corresponding to one example of the exhaust gas purification device are connected to an exhaust pipe77which is connected to a downstream side of the exhaust gas of the exhaust manifold71. The exhaust gas discharged to the exhaust manifold71from each of the cylinders is discharged to an external portion after being applied a purifying process via the exhaust pipe77, the exhaust gas throttle device82, and the DPF50.

As shown inFIG. 6, the DPF50is structured such as to collect the PM in the exhaust gas. The DPF50in the embodiment is structured, for example, such that a diesel oxidation catalyst53such as a platinum and a soot filter54are accommodated in serried in an approximately tubular filter case52within a casing51made of a heat resisting metal material. The diesel oxidation catalyst53is arranged in an upstream side of the exhaust gas of the filter case52, and the soot filter54is arranged in a downstream side of the exhaust gas. The soot filter54is constructed as a honeycomb structure which is divided into a lot of cells by porous partition walls capable of filtering the exhaust gas.

One side portion of the casing51is provided with an exhaust gas introduction port55which is communicated with an exhaust gas downstream side of the exhaust gas throttle device82in the exhaust pipe77. One side portion of the casing51and one side portion of the filter case52are occluded by a first side wall plate56and a second side wall plate57. The other side portion of the casing51is occluded by a first lid plate59and a second lid plate60. A portion between both the lid plates59and60is constructed as an exhaust gas sound damping chamber63which is communicated with the filter case52via a plurality of communication pipes62. Further, an approximately tubular exhaust gas outlet pipe61passes through the second lid plate60. A plurality of communication holes58which are open toward the exhaust gas sound damping chamber63are formed in an outer peripheral surface of the exhaust gas outlet pipe61. A sound absorber64is constructed by the exhaust gas outlet pipe61and the exhaust gas sound damping chamber63.

An exhaust gas introduction pipe is inserted into the exhaust gas introduction port55which is formed in one side portion of the casing51. A leading end of the exhaust gas introduction pipe65cuts across the casing51so as to protrude to a side surface in an opposite side to the exhaust gas introduction port55. A plurality of communication holes66which are open toward the filter case52are formed in an outer peripheral surface of the exhaust gas introduction pipe65. A portion protruding to a side surface in an opposite side to the exhaust gas introduction port55in the exhaust gas introduction pipe65is occluded by a lid67which is detachably attached by screw thereto.

The DPF50is provided with a DIPF differential pressure sensor68detecting a clogged state of the soot filter54, as one example of detecting means. The DPF differential pressure sensor68is structured such as to detect a pressure difference (an exhaust gas differential pressure between an inlet side and an outlet side) of each of the exhaust pressures in the upstream side and the downstream side of the soot filter54within the DPF50. In this case, an upstream side exhaust gas pressure sensor68aconstructing the DPF differential pressure sensor68is installed to the lid body67of the exhaust gas introduction pipe65, and a downstream side exhaust gas pressure sensor68bis installed between the soot filter54and the exhaust gas sound damping chamber63.

In this case, since a specific relevance exists between the pressure difference of the upstream and downstream of the DPF50, and a PM sedimentation amount within the soot filter54(the DPF50) the PM sedimentation amount within the DIPF50can be determined by computation on the basis of the pressure difference which is detected by the DPF differential pressure sensor68. Further, a renewing control of the soot filter54(the DPF50) is executed by actuating and controlling the intake air throttle device81, the exhaust gas throttle device82, or the common rail120on the basis of a computation result of the PM sedimentation amount.

In the structure mentioned above, the exhaust gas from the engine70enters into the exhaust gas introduction pipe65via the exhaust gas introduction port55, jets out into the filter case52from each of the communication holes66formed the exhaust gas introduction pipe65, and passes through the diesel oxidation catalyst53and the soot filter54in this order so as to be purified. The PM in the exhaust gas is collected by the soot filter54(the porous partition wall between the cells). The exhaust gas passing through the diesel oxidation catalyst53and the soot filter54is discharged out to the machine from the exhaust gas outlet pipe61via the sound absorber64.

If the temperature of the exhaust gas is higher than a renewable temperature (for example, about 250 to 300° C.) when the exhaust gas passes through the diesel oxidation catalyst53and the soot filter54, NO (nitrogen monoxide) in the exhaust gas is oxidized into an unstable NO2(nitrogen dioxide) by an action of the diesel oxidation catalyst53. Further, a PM collecting capacity of the soot filter54is recovered by oxidizing and removing the PM deposited in the soot filter54, by oxygen (O) which is discharged when the NO2returns to NO. That is, the soot filter54(DPF50) is regenerated.

(5) Structure Relevant to Control of Engine

Next, a description will be given of a structure which is relevant to a control of the engine70with reference toFIGS. 7 and 8. As shown inFIGS. 7 and 8, the tractor141is provided with an ECU11which actuates the fuel injection valve119of each of the cylinders in the engine70, and a working machine (shift) controller271, as control means. The ECU11has a CPU31which executes various computing processes and controls, a ROM32in which various data is previously stored fixedly, an EEPROM33which stores control programs and various data in a rewritable manner, a RAM34which temporarily stores the control programs and the various data, a timer35for measuring time, and an input and output interface. The working machine controller271also has a CPU281, a ROM282, an EEPROM283, a RAM284, a timer285, and an input and output interface in the same manner as the ECU11.

The ECU11and the working machine controller271corresponding to the control means are combined such that a length of harnesses of the input and output system devices becomes as short as possible so as to control the input and output system devices as a target, and are stored in a controller box (not shown) at respective arranged positions. The ECU11and the working machine controller271are electrically connected to each other via a CAN communication bus272. The ECU11of the embodiment is arranged in the engine70or in the vicinity of the engine70(refer toFIG. 2). The working machine controller271is arranged, for example, below the control seat148within the cabin147(refer toFIG. 2). In this case, the control means may be structured such that three or more means are connected via the communication bus. Each of the input and output system devices mentioned below may be connected to any control means.

To the input side of the ECU11, there are connected at least a rail pressure sensor12detecting the pressure of the fuel within the common rail120, an electromagnetic clutch13turning or stopping the fuel pump116, an engine speed sensor14detecting the rotating speed of the engine70(a cam shaft position of the engine output shaft74) and serving as rotating speed detecting means, an injection setter15detecting and setting a fuel injection frequency (a number of times during one stroke of fuel injection period) of the injector115, an intake air temperature sensor17detecting an intake gas temperature of the intake air system, an exhaust gas temperature sensor18detecting an exhaust gas temperature of the exhaust system, a cooling water temperature sensor19detecting a temperature of a cooling water of the engine70, a fuel temperature sensor20detecting a temperature of the fuel within the common rail120, and the DPF differential pressure sensor68(the upstream side exhaust gas pressure sensor68aand the downstream side exhaust gas pressure sensor68b).

Each of electromagnetic solenoids of respective fuel injection valves119for four cylinders of the engine is connected to an output side of the ECU11. In other words, the high-pressure fuel stored in the common rail120is injected from the fuel injection valves119at a plurality of times in one stroke while controlling the fuel injection pressure, the injection timing, and the injection period, thereby executing a complete combustion in which generation of the nitrogen oxide (NOx) is suppressed and generation of soot and carbon dioxide is reduced, and improving a fuel consumption. Further, to the output side of the ECU11, there are connected the intake air throttle device81for regulating a pressure of intake air (an amount of intake air) of the engine70, the exhaust gas throttle device82for regulating a pressure of exhaust gas of the engine70, an ECU failure lamp22warning and informing a failure of the ECU11, an exhaust gas temperature warning lamp23informing an abnormally high temperature of the exhaust gas within the DPF50, and a renewal lamp24turning on in connection with a renewing motion of the DPF50.

As shown inFIG. 8, various electromagnetic valves which are relevant to the output are connected to the working machine controller271. Namely, there are connected the forward moving clutch electromagnetic valve253in relation to the forward moving hydraulic clutch252, the backward moving clutch electromagnetic valve255in relation to the backward moving hydraulic clutch254, the high speed clutch electromagnetic valve251in relation to the sub shift hydraulic cylinder250, the proportional control valve213actuating the main shift hydraulic cylinder243in proportion to the amount of operation of the main shift lever201, the 4-wheel drive hydraulic electromagnetic valve257in relation to the 4-wheel drive hydraulic clutch256, the double speed hydraulic electromagnetic valve259in relation to the double speed hydraulic clutch258, the right and left automatic brake electromagnetic valves246, the PTO clutch hydraulic electromagnetic valve249in relation to the PTO clutch248, and the control electromagnetic valve211supplying the working fluid to the elevation control hydraulic cylinder215of the working machine elevating mechanism160.

Further, to the working machine controller271, there are electrically connected various sensors and switches which are relevant to an input, that is, a steering potentiometer290detecting an amount of rotating operation (a steering angle) of the steering wheel149, a forward and backward movement potentiometer291which detects an on-off state of the forward moving and backward moving hydraulic clutches252and254on the basis of an operating position of the forward and backward movement switching lever198, a main shift output shaft rotation sensor292which detects an output rotating speed of the main shift output shaft237, a throttle position sensor16which detects an operating position of the throttle lever197, a vehicle speed sensor25detecting a rotating speed (a vehicle speed) of four front and rear wheels143and144, a 4-wheel drive mode switch293which operates so as to switch the 4-wheel drive hydraulic electromagnetic valve257, a double speed mode switch294which operates so as to switch the double speed hydraulic electromagnetic valve259, a brake pedal switch295detecting whether the brake pedal191is depressed, an automatic brake switch296which operates so as to switch the automatic brake electromagnetic valve246, a main shift potentiometer297detecting an operating position of the main shift lever201, a sub shift lever sensor298detecting an operating position of the sub shift lever195, and a minimum rotating speed dial27which sets a minimum rotating speed Na of the engine70.

In this case, the minimum rotating speed dial27is structured such as to change and regulate a position of a knob continuously (in an analog manner) or step by step (in a digital manner) so that the minimum rotating speed dial27can appropriately regulate in a range that the minimum rotating speed Na is higher than a low idle rotating speed Nlow which is unique to the engine70. The rotating speed N in the case that the throttle lever197is operated to the minimum speed side comes to the minimum rotating speed Na which is set by the minimum rotating speed dial27.

As can be known from the description above, in the working vehicle111provided with the engine70which is mounted to the travel machine body142, and the common rail type fuel injection device117which injects the fuel to the engine70, since the minimum rotating speed Na of the engine70can be changed in the range higher than the low idle rotating speed Nlow which is unique to the engine70, it is possible to easily secure a higher output horsepower than a horsepower in the engine having the same displacement of the engine70. According to the other side of the coin, it is possible to achieve the engine having the lower displacement than the displacement in the engine having the same output horsepower of the engine70. Therefore, there can be achieved an effect that the downsizing of the engine70can be easily realized. In addition, since any supercharger is not required for securing the output horsepower, there can be achieved an effect that a parts cost can be suppressed.

An output characteristic map M (refer toFIG. 10) showing a relationship between the rotating speed N and a torque T of the engine70is previously stored in the EEPROM33of the ECU11or the EEPROM283of the working machine controller271. The output characteristic map M is determined by an experiment or the like. In the output characteristic map M shown inFIG. 10, the rotating speed N is set to a horizontal axis, and the torque T is set to a vertical axis. The output characteristic map M is a region surrounded by a solid line Tmx which is drawn convex upward. The solid line Tmx is a maximum torque line which expresses the maximum torque in relation to each of the rotating speeds N.

The ECU11is basically structured such as to determine the torque T of the engine70on the basis of the rotating speed detected by the engine speed sensor14, and an injection pressure and an injection period of each of the injectors115, compute a target fuel injection amount by using the torque T and the output characteristic map M, and execute a fuel injection control for actuating the common rail device117on the basis of the result of computation. In this case, the fuel injection amount of the common rail device117is regulated by regulating a valve opening period of each of the fuel injection valves119and changing an injection period of each of the injectors115.

(6) First Embodiment of Fuel Injection Control

Next, a description will be given of a first embodiment of the fuel injection control by the ECU11with reference toFIGS. 10 and 11. In the first embodiment, the rotating speed N of the engine70is limited only to two kinds including N#1 and N#2, and the ECU11executes a rotating speed limiting control which changes and regulates the change gear ratio of the continuously variable transmission159such that the vehicle speed V of the travel machine body142is not changed before and after changing the rotation speed N, whichever of the above two kinds, N#1 and N#2 the rotating speed N is changed to.

The rotating speed limiting control is executed, for example, as shown by a flow chart inFIG. 11. In other words, the detected value of the engine speed sensor14is read, and it is determined whether or not the rotating speed N at the present moment is in the low speed side N#1 (S201). If the rotating speed N is not in the low speed side N#1 (S201: NO), the fuel injection amount of the common rail device117is regulated in such a manner that the rotating speed N of the engine70becomes in the low speed side N#1 (S202), and thereafter the process returns to the step S201.

If the rotating speed N is in the low speed side N#1 in the step S201(S201: YES), the detected value (the torque Tx at the present moment) of the throttle position sensor16is read, an engine load rate LFx at the present moment is calculated on the basis of the rotating speed N#1, the torque Tx, and the output characteristic map M (S203), and it is determined whether or not the engine load rate LFx at the present moment is higher than a predetermined value X (S204). In this case, the engine load rate means a rate with respect to the maximum torque T (the maximum engine load) at the optional rotating speed N.

If the engine load rate LFx at the present moment is equal to or less than the predetermined value X (S204: NO), the process returns to the step S201. In the case that the engine load rate LFx is higher than the predetermined value X (S204: YES), the fuel injection amount of the common rail device117is regulated in such a manner that the rotating speed N of the engine70becomes in the high speed side N#2 (S205). Next, the detected value Vx (the vehicle speed) of a vehicle speed sensor25is read, and it is determined whether or not the vehicle speed Vx remains in the vehicle speed before changing the rotating speed (S206). If the vehicle speed Vx is changed (S206: NO), the change gear ratio of the continuously variable transmission159in the transmission case157is changed and regulated so as to return the vehicle speed of the travel machine body142to that before changing the rotating speed (S207), and the process returns to the step S206.

If the vehicle speed Vx is maintained at the vehicle speed before changing the rotating speed in the step S206(S206: YES), the detected value of the engine speed sensor14is next read, and it is determined whether or not the rotating speed N at the present moment is in the high speed side N#2 (S208). If the rotating speed is not in the high speed side N#2 (S208: NO), the fuel injection amount of the common rail device117is regulated in such a manner that the rotating speed N of the engine70becomes in the high speed side N#2 (S209), and thereafter the process returns to the step S208.

If the rotating speed is in the high speed side N#2 in the step $208 (S208: YES), a detected value (a torque Ty at the present moment) of the throttle position sensor16is read, an engine load rate LFy at the present moment is calculated on the basis of the rotating speed N#2, the torque Ty, and the output characteristic map M (S210), and it is determined whether or not the engine load rate LFy at the present moment is less than a predetermined value Y (S211). If the engine load rate LFy at the present moment is equal to or more than the predetermined value Y (3211: NO), the process returns to the step S206. In the case that the engine load rate LFy is less than the predetermined value Y (S211: YES), the fuel injection amount of the common rail device117is regulated in such a manner that the rotating speed N of the engine70becomes in the low speed side N#1 (S212), and the process returns to the step S201.

According to the control mentioned above, in the working vehicle141provided with the engine70which is mounted to the travel machine body142, and the common rail type fuel injection device117which injects the fuel to the engine70, since the rotating speed N of the engine70is limited only to two kinds including N#1 and N#2, it is possible to achieve the engine70which does not use the low rotating region having the smaller output torque, and it is possible to easily secure a higher output horsepower than a horsepower in the engine having the same displacement of the engine70. According to the other side of the coin, it is possible to achieve the engine70having the lower displacement than the displacement in the engine having the same output horsepower of the engine70. Therefore, there can be achieved an effect that the downsizing of the engine70can be easily realized.

Particularly, since the change gear ratio of the continuously variable transmission159is changed and regulated in such a manner that the vehicle speed of the travel machine body142is not changed before and after changing the rotation speed N, whichever of the above two kinds, N#1 and N#2 the rotating speed N of the engine70is changed to, the vehicle speed of the travel machine body can be maintained at the vehicle speed before changing the rotating speed, for example, even if the rotating speed N is set to the low speed side N#1 or the high speed side N#2. Therefore, there can be achieved an effect that it is possible to do away with an uncomfortable feeling caused by the change of the rotating speed of the engine70.

(7) Second Embodiment of Fuel Injection Control

Next, a description will be given of a second embodiment of the fuel injection control by the ECU11with reference toFIGS. 12 to 16. In a state in which the travel machine body142is stopped, in principle, the ECU11feedback controls the fuel injection amount of the common rail device117in such a manner that the rotating speed N detected by the engine speed sensor14coincides with the minimum rotating speed Na which is previously set by the minimum rotating speed dial27. Further, in the other states than the stop state, the ECU11feedback controls the fuel injection amount of the common rail device117in such a manner that the rotating speed N of the engine70coincides with the rotating speed which corresponds to the operating position of the throttle lever197.

A series of constant fuel consumption rate curves FL are shown in an output characteristic map M inFIG. 12. The constant fuel consumption rate curve FL is a curve such as a contour, which connects points having an equal fuel consumption rate, and the constant fuel consumption rate curve in an inner peripheral side expresses a small fuel consumption state, that is, a good mileage state. According to the constant fuel consumption rate curve FL in this case, a best mileage area exists in a high speed and high torque side of the engine70. The constant fuel consumption rate curve FL is shown by a broken line in the output characteristic map M inFIG. 12. An optimum fuel consumption line FS connecting the points having the best mileage of the engine70is expressed in the output characteristic map M. It is possible to achieve the low fuel consumption operation of the engine70by changing and regulating the fuel injection amount in such a manner that a engine operating point Q relating to the rotating speed N and the torque T of the engine70is along the optimum fuel consumption line FS. The optimum fuel consumption line FS is shown by a one-dot chain line in the output characteristic map M inFIG. 12.

A series of constant output lines PL is shown in the output characteristic map M. The constant output line PL is a line showing a relationship between the rotating speed N and the torque T in the case that the output horsepower of the engine70is fixed. Since a product of the rotating speed N and the torque T is in a proportionality relation to the output horsepower, the constant output line PL is shown as an inverse proportion curve in the output characteristic map M inFIG. 12. The constant output line PL is shown by a two-dot chain line in the output characteristic map M inFIG. 12.

The ECU11is structured such as to execute a minimum vehicle speed control of changing and regulating the change gear ratio of the continuously variable transmission159in such a manner that a minimum vehicle speed Vlow (a creep speed) of the travel machine body142is not changed from a low idle rotating speed Nlow, in the case of setting a minimum rotating speed Na which is higher than the low idle rotating speed Nlow, as one example of the fuel injection control. Further, the ECU11is structured such as to execute an optimum fuel consumption control of changing and regulating the change gear ratio of the continuously variable transmission159in such a manner that the engine operating point Q is changed onto the optimum fuel consumption line FS and the vehicle speed V of the travel machine body142is not changed, in the case that the engine operating point Q deviates from the previously set optimum fuel consumption line FS. An algorithm shown by flow charts inFIGS. 13 to 16is stored in the EEPROM33. The minimum vehicle speed control and the optimum fuel consumption control are executed by calling the algorithm to the RAM34and processing the algorithm by the CPU31.

The minimum vehicle speed control is executed, for example, as follows (refer toFIG. 13). In this case, a set value of the minimum rotating speed dial27is the minimum rotating speed Na which is higher than the low idle rotating speed Nlow, and the minimum rotating speed of the engine70in the case that the throttle lever197is operated to the minimum speed side is assumed as the set value Na. First of all, it is determined whether or not the brake pedal191is under operation (S01), and the detected value of the engine speed sensor14, and if the brake pedal191is not under operation (S01: NO), the minimum vehicle speed Vlow at the low idle rotating speed Nlow which is previously stored in the ROM32or the EEPROM33is read (S02). Next, if the throttle position sensor16is off (S03: off) and the detected value of the engine speed sensor14comes to the set value Na of the minimum rotating speed dial27(S04: YES), the step next changes and regulates the change gear ratio of the continuously variable transmission159in the transmission case157in such a manner that the minimum vehicle speed of the travel machine body142is not changed from the minimum vehicle speed Vlow at the low idle rotating speed Nlow (S05, change gear ratio control).

The change gear ratio control under minimum vehicle speed control (the change gear ratio control in the step S05) is executed, for example, as shown by a flow chart inFIG. 14. In other words, the detected value V1(the vehicle speed) of the vehicle speed sensor25at the present moment is read (S101), and in the case that the vehicle speed V1at the present moment is higher than the minimum vehicle speed Vlow which is read in the step S02(S102: YES), the change gear ratio of the continuously variable transmission159is reduced (S103), and the process returns to the step S102. In the case that the vehicle speed V1at the present moment is lower than the minimum vehicle speed Vlow (S104: YES), the change gear ratio of the continuously variable transmission159is determined (S105), and the process returns to the step2102. If the minimum vehicle speed Vlow is the same as the vehicle speed V1at the present moment (S104: NO), the process returns while maintaining the state.

As is known from the description above, since the continuously variable transmission159shifting the power from the engine70is provided, and the change gear ratio of the continuously variable transmission159is changed and regulated in such a manner that the minimum vehicle speed of the travel machine body142is not changed from the vehicle speed (Vow) at the low idle rotating speed Nlow, in the case that the minimum rotating speed Na is set to the value higher than the low idle rotating speed Nlow the minimum vehicle speed (the creep speed) of the travel machine body142does not become high but can be maintained at the vehicle speed (Vlow) at the low idle rotating speed Nlow, even if the minimum rotating speed Na is made higher than the low idle rotating speed Nlow. Therefore, there can be achieve an effect that it is possible to obtain a travel performance (a vehicle speed having no uncomfortable feeling) which is not different from a travel performance in the working vehicle141mounting the engine having the same displacement of the engine70, at a time of traveling at the low speed.

An optimum fuel consumption control shown inFIG. 15is executed, for example, as follows. That is, a detected value (a rotating speed N1at the present moment) of the engine speed sensor14, and a detected value (a torque T1at the present moment) of the throttle position sensor16are read (S11), an engine operating point Q1at the present moment by using the output characteristic map M is determined (S12), and it is determined whether or not the engine operating point Q1at the present moment is on the optimum fuel consumption line FS (S13). If the engine operating point Q1at the present moment deviates from the optimum fuel consumption line FS (S13: NO), on the basis of the engine operating point Q1at the present moment, and a relationship between the optimum fuel consumption line FS and the constant output line PL of the output characteristic map M, it is determined whether or not a target engine operating point Q2exists, the target engine operating point Q being identical in the output horsepower to the engine operating point Q1at the present moment and being on the optimum fuel consumption line FS (S14). Since the engine operating point Q1at the present moment and the target engine operating point Q2are the same in the output horsepower, these operating points are positioned on the common constant output line PL.

If the target engine operating point Q2exists (S14: YES), the detected value (the vehicle speed V1) of the vehicle speed sensor25at the present moment and the rotating speed R1of the main shift output shaft237are read (S15), thereafter the fuel injection amount of the common rail device117is regulated, and the engine operating pint is changed from the engine operating point Q1at the present moment to the target engine operating point Q2(S16). Further, an angle of incline of the pump swash plate242in the hydraulic pump portion240is changed and regulated by correcting an applied voltage of the proportional control valve213on the basis of the command from the working machine controller271and actuating the main shift hydraulic cylinder243, and the change gear ratio of the continuously variable transmission159is changed and regulated in such a manner as to maintain the rotating speed R of the main shift output shaft237at the detected value R1in the step S06by controlling a supply amount of the working fluid to the hydraulic motor portion241(a change gear ratio control, S17). In this case, the change gear ratio means a rate (R/N) of the rotating speed1R of the main shift output shaft237with respect to the rotating speed N of the engine70.

The change gear ratio control under the optimum fuel consumption control (the change gear ratio control in the step S17) is basically the same aspect as the change gear ratio control under the minimum vehicle speed control, and is executed, for example, as shown by a flow chart inFIG. 16. In other words, a vehicle speed V2after changing to the engine operating point Q2is read (S111), in the case that the vehicle speed V2after changing is higher than the vehicle speed V1before changing which is read in the step S15(S112: YES), the change gear ratio of the continuously variable transmission159is reduced in such a manner that the rotating speed R of the main shift output shaft237comes to the detected value R1in the step S06(S113), and the process returns to the step S112. In the case that the vehicle speed V2after changing is lower than the vehicle speed V1before changing (S114: YES), the change gear ratio of the continuously variable transmission159is increased in such a manner that the rotating speed R of the main shift output shaft237comes to the detected value R1in the step S15(S115), and the process returns to the step S112. If the vehicle speed. V1before changing is identical to the vehicle speed. V2after changing (S114: NO), the process returns while maintaining the state.

As is known from the description above, since the change gear ratio of the continuously variable transmission159is changed and regulated in such a manner that the engine operating point Q is changed onto the optimum fuel consumption line FS, and the vehicle speed V of the travel machine body142is not changed in the case that the engine operating point Q relating to the rotating speed N and the torque T of the engine70deviates from the previously set optimum fuel consumption line FS, it is possible to securely prevent the fluctuation of the vehicle speed V going with the change of the rotating speed N while executing the low fuel consumption operation. Therefore, there can be achieve an effect that a stable travel performance can be obtained in the working vehicle141.

FIGS. 17 and 18show the other example of the fuel injection control. The other example is structured such as to lower the engine load rate LF so as to efficiently drive the engine70by changing to the target engine operating point Q2′ in the high speed and low torque side having the same output horsepower in the case that the engine70is in an overload state or a close state thereto, thereby accurately dealing with reinforcement of an emission control in the future.

The other example of the fuel injection control is executed, for example, as follows (refer toFIG. 18). In this case, it is assumed that the engine70is carried out an isochronous control for maintaining the rotating speed N constant regardless of a load fluctuation, and the rotating speed N is fixed to a rotating speed N1′ (refer toFIG. 17) by the throttle lever197. In this case, in the isochronous control, if the rotating speed N1′ of the engine70is decided by the throttle lever197, a rotating speed N2′ in the high speed side is automatically set in correspondence thereto.

First of all, the detected value of the engine speed sensor14(the rotating speed N1′ at the present moment) and the detected value of the throttle position sensor16(the torque T1′ at the present moment) are read (S21), an engine load rate LF1′ at the present moment is calculated by using the detected values N1and T1and the output characteristic map M (S22), and it is determined whether or not the engine load rate LF1′ at the present moment is equal to or more than a predetermined value X (S23).

If the engine load rate LF1′ at the present moment is equal to or more than the predetermined value X (S23: YES), a target engine operating point Q2′ in the high speed and low torque side having the same output horsepower as that of the engine operating point Q1′ at the present moment and having the smaller engine load rate LF than the predetermined value X is determined, on the basis of a relationship among the engine operating point Q1′ at the present moment, the constant output line PL of the output characteristic map M, and the rotating speed N2′ in the high speed side (S24). Thereafter, s the detected value (the vehicle speed V1′) of the vehicle speed sensor25at the present moment and the rotating speed R1′ of the main shift output shaft237are read (S25), the fuel injection amount of the common rail device117is regulated, the engine operating point is changed from the engine operating point Q1′ at the present moment to the target engine operating point Q2′, and the rotating speed is risen (N1′→N2′, S26). Further, the main shift hydraulic cylinder243is actuated so as to change and regulate the angle of incline of the pump swash plate242in the hydraulic pump portion240by correcting the applied voltage of the proportional control valve213on the basis of the command from the working machine controller271, the supply amount of the working fluid to the hydraulic motor portion241is controlled, and the change gear ratio of the continuously variable transmission159is changed and regulated in such a manner as to maintain the rotating speed R of the main shift output shaft237at the detected value R1in the step S25(the change gear ratio control, S27).

Next, an engine load rate LF2′ after changing is calculated on the basis of the rotating speed N2′ and the torque T2′ after changing (S28), and thereafter it is determined whether or not the engine load rate LF2′ is equal to or less than a predetermined value Y (S29). If the engine load rate LF2′ after changing is equal to or less than the predetermined value Y (229: YES), the fuel injection amount of the common rail device117is regulated, and the engine operating point is changed from the target engine operating point Q2′ to the original engine operating point Q1′ (S30). Further, by correcting the applied voltage of the proportional control valve213on the basis of the command from the working machine controller271, the main shift hydraulic cylinder243is actuated so as to change and regulate the angle of incline of the pump swash plate242in the hydraulic pump portion240, the supply amount of the working fluid to the hydraulic motor portion241is controlled, and the change gear ratio of the continuously variable transmission159is changed and regulated in such a manner as to maintain the rotating speed R of the main shift output shaft237at the detected value R1in the step S25(S31). In this case, since the change gear ratio control of the steps S27and S31is the same as the case of the flow chart inFIG. 16, a detailed description is omitted.

According to the control mentioned above, the engine70is not continuously driven in the overload state or the close state thereto, and it is possible to efficiently drive the engine70(it is possible to drive the engine70on the safe side). Accordingly, it is possible to appropriately deal with the reinforcement of the emission control in the future, for example, the next EPA regulations.

The present invention is not limited to the embodiments mentioned above, but can be embodied into various aspects. The structure of each of the portions is not limited to the illustrated embodiment, but can be variously modified within a range which does not deviate from the scope of the present invention.

REFERENCE SIGNS LIST