JPH0738766B2 - Harvester vehicle speed controller - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a vehicle speed control device for a harvester that increases / decreases a traveling speed in accordance with an increase / decrease in load on a working unit such as a threshing unit and a cutting unit.

[Prior art]

The harvesting machine conveys the grain culms cut by the mowing section to the threshing section, threshes at the threshing section, sorts and picks out the fine grain, and the working sections such as the mowing section and the threshing section. The load increases or decreases depending on the amount of grain culm to be processed in these,
The amount of grain culm to be processed increases or decreases according to the traveling speed of the harvesting machine and the field conditions. Therefore, in the conventional harvester, a vehicle speed control that changes the traveling speed of the harvester according to the increase or decrease of the load in the working unit so that the working unit always performs the respective processing under an appropriate load condition. Some are equipped with devices.

This vehicle speed control device, for example, detects the load of the working part by the number of rotations of the threshing part of the threshing part, and when the detected value exceeds the appropriate range preset near the upper limit of the load in the working part, , Reduce the amount of grain culm to be processed in the working unit,
In order to reduce the load on the working unit, the traveling speed is reduced, and when the detected value falls below the appropriate range and the output of the engine that drives the working unit has a margin, the grain to be processed by the working unit is reduced. The running speed is increased in order to increase the culm volume and the load on the working unit (Japanese Patent Application No. 168707/1985 (Japanese Patent Application Laid-Open No. 62-29909)).

[Problems to be solved by the invention]

In such a conventional vehicle speed control device, the traveling speed is adapted to be changed by a predetermined amount set in advance, and the load on the working unit largely deviates from the appropriate range, and the load is kept within the appropriate range. If it is necessary to drastically change the traveling speed in order to return to the above condition, after changing the traveling speed once, wait until the load on the working unit changes and stabilizes according to the changed speed. , The traveling speed will be changed again according to the detected value of the load after stabilization, and it will take a considerable amount of time to achieve an appropriate traveling speed within which the load of the working unit falls within the proper range. In the meantime, in the working unit, respective processing is performed under an overload or underload condition, and the engine that drives the working unit is forced to operate under an overload condition or the work efficiency decreases. There were difficulties.

In order to eliminate this difficulty, when the amount of change in the traveling speed at one time is large, for example, when the load in the working unit exceeds the proper range and the traveling speed is decelerated, On the contrary, there is a possibility that so-called hunting may occur in which the load falls below the appropriate range, the traveling speed is increased, and the acceleration and deceleration are repeated thereafter.

This also applies to the case where a continuously variable transmission capable of continuously changing the traveling speed is used, and in the conventional vehicle speed control device, the continuously variable transmission is used as if it is a stepped transmission. There was a drawback that it was unavoidable.

The present invention has been made in view of such circumstances, and relates to a vehicle speed control device for a harvester that immediately increases and decreases to an appropriate traveling speed in accordance with an increase or decrease in load on a working unit.

[Means for solving problems]

The vehicle speed control device for a harvester according to the present invention has an engine speed control unit that operates to maintain the engine speed at a set speed regardless of the magnitude of the load, and the traveling unit and the working unit are operated by the engine. The harvester is equipped with a transmission capable of continuously changing its traveling speed, and in order to properly maintain the load on the working unit, the transmission is operated, In a vehicle speed control device for a harvester that controls a traveling speed, a load detection unit that detects a load of the engine related to a load of the working unit, a traveling speed detection unit that detects a traveling speed of the harvester, and the traveling Characteristic storage means for storing the relationship between the speed and the load of the engine in the form of a plurality of load characteristics according to the load state in the working unit, the detection result of the traveling speed detection means, and the load detection Calculating means for selecting one of the plurality of load characteristics from the detection result of the stage, and calculating an upper limit traveling speed corresponding to a preset upper limit value of the load of the engine according to the characteristics; Means for operating the transmission to achieve the calculation result of the means.

[Action]

In the present invention, from the current running speed detected by the running speed detecting means and the current load on the engine,
The load characteristics corresponding to the current load state in the working unit,
It selects from the stored contents of the characteristic storing means, calculates the upper limit traveling speed when the load of the engine reaches the upper limit value according to the characteristic, and changes the traveling speed so as to realize the upper limit traveling speed.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings showing an embodiment thereof. FIG. 1 is a schematic right sectional view of a common harvester equipped with a vehicle speed control device according to the present invention (hereinafter referred to as the present invention device),
The second is a plan view thereof. In the figure, 1 is a machine body mounted on the upper side of the traveling crawler 2, and on the upper left side of the machine body 1 is a threshing section 3 extending over the entire length in the front-rear direction.
The driver's seat DS, the paddy tank T, and the engine 7 are arranged on the right side of the upper part of the vehicle in order from the front, and the cutting unit 4 is mounted on the front side of the machine body 1 so as to be able to move up and down according to the forward / backward movement of the hydraulic cylinder 40. Has been done.

The driving force of the engine 7 is transmitted to the traveling crawler 2 via a main clutch (not shown), a gear meshing type auxiliary transmission device, a main transmission device using a hydrostatic continuously variable transmission device, and a side clutch. And the aircraft 1 is running crawler 2
By the action of, self-propelled on the field. In the operation column 6 provided on the left side of the driver's seat DS, the main transmission lever 60 for changing the gear ratio in the main transmission, and the traveling speed stage of the auxiliary transmission device are "high speed stage" or "low speed stage". A plurality of levers and switches such as an auxiliary shift lever 61 for changing to any of the above and an automatic switch 11 (see FIG. 3) for instructing the apparatus of the present invention to start its operation are provided. The machine body 1 travels at different speeds due to a manual operation of each lever by a worker seated on the floor or a change in the gear ratio of the main transmission device by the operation of the device of the present invention.

In addition, the handling body 31 and the swing sorting device 3 provided inside the threshing unit 3
2 etc. and scraping reel 42, cutting blade 4 equipped on the reaper 4
3, the lateral conveyance auger 44 and the like are also driven by transmitting the driving force of the engine 7.

Thus, a pair of dividers 41, 41 provided on both sides of the front of the mowing section 4
In the meantime, the grain culm introduced with the forward movement of the machine body 1 is pulled backward by the rotation of the scraping reel 42 while the cutting blade 43
By the rotation of the lateral conveying auger 44 provided above the platform 45 in a state of lying on the platform 45 at the rear of the cutting blade 43, and the rear side of the cutting section 4 and the upper front side of the threshing section 3. Is conveyed to the position of the front end opening of the feeder house 5 that communicates with the feeder house 5, is inherited by the chain conveyor 50 provided in the feeder house 5, and is sandwiched between the conveyor 50 and the bottom plate of the feeder house 5. In this state, it is conveyed rearward and upward, and is introduced into the handling chamber 30 of the threshing unit 3 from the rear end opening of the feeder house 5.

The bottom plate of the feeder house 5 is a flat plate inclined with its rear part facing upward, and at a position near the threshing part 3, a grain culm sensor 51 using a piezoelectric conversion element has its pressure receiving surface as the upper surface of the bottom plate. A plurality of them are arranged flush with each other and arranged in parallel in the left-right direction toward the inside of the feeder house 5. The grain culm sensor 51,5
When the grain culm conveyed by the chain conveyor 50 in the feeder house 5 comes into contact with the pressure receiving surface of the feeder house 5, a signal of a level corresponding to the pressure receiving from the grain culm is given to the inside of the feeder house 5. Presence or absence of the grain culm, that is, presence or absence of feeding of the grain culm to the threshing unit 3 is detected.

In the handling chamber 30 of the threshing unit 3, a screw handling body 31 having a double pitch screw and a large number of handling teeth projecting from the peripheral surface thereof.
However, the grain culm is rotatably supported with its axial direction in the front-rear direction, and the grain culm introduced into the handling chamber 30 from the feeder house 5 is accompanied by rotation of the screw handling cylinder 31. While being transferred to the rear by the action, threshing is performed by the action of the handling teeth. Then, the grated product after threshing processing, from the receiving net 33 stretched on the lower side of the handling cylinder 31, falls on the rocking sorting device 32, and the rocking operation of the rocking sorting device 32, 1st thing, such as fine grain, is blasted by the Karato device 34 arranged on the lower front side of the threshing unit 3, and is gravity-sorted with the sorting wind blown in the direction of the white arrow in FIG. 1. Dropped on the first gutter 35 on the upstream side of the sorting wind below the threshing part 3,
Lifting cylinders that have been transported to the right in the 35
35a is conveyed upward and is fed into the paddy tank T, and the second grain such as unhulled grains falls on the second gutter 36 on the downstream side of the sorting wind, and the second gutter It is conveyed in the right direction in the inside of 36, is then conveyed to the upper front in the No. 2 reduction cylinder 36a connected to this, and is again introduced into the handling chamber 30 from the front side and threshing again. Furthermore, other third objects such as straw waste are opened at the rear end of the threshing unit 3 together with the straw discharged from the rear end of the screw handling cylinder 31 without falling from the net 33.
It is discharged from the number 37 on the field.

FIG. 3 is a block diagram showing the configuration of the device of the present invention equipped in the ordinary harvester having the above-described configuration. 10 is a vehicle speed control unit and 20 is an engine speed control unit. The engine rotation speed control unit 20 detects the rotation speed of the engine 7, and moves a fuel rack (hereinafter referred to as a rack) of the fuel injection pump to match the detection result with a set rotation speed, and the engine 7 Is to perform so-called isochronous control for controlling the amount of fuel supplied to the rack. The input side of the rack is mounted coaxially with the rack and detects the position of the rack, for example, by using a differential transformer. The rack position sensor 21 and the engine rotation sensor 22 that is mounted at an appropriate position of the engine 7 and detects the rotation speed of the engine 7 are connected to each other, and an operation command signal is transmitted from the vehicle speed control unit 10 as described later. Has been given.

On the other hand, the output of the engine speed control unit 20 is the input port of the vehicle speed control unit 10 and a rack actuator 23 that drives the rack, for example, a linear actuator using a linear solenoid.
a ₇ are given respectively.

The engine speed control unit 20, the detected rotation speed is a numerical table or an arithmetic expression for obtaining a correction setting rotation speed set to restore the rotation speed to the setting rotation speed when the rotation speed is different from the setting rotation speed due to a change in load, Numeral table or arithmetic expression for obtaining the relationship between the corrected set rotational speed of the engine 7 when there is no load and the position of the rack where it can be obtained, that is, the rack position corresponding to no load, and the rack position corresponding to the no load is detected. A rack position required to obtain the set rotation speed from the rack position, that is, a numerical table or an arithmetic expression for obtaining the target rack position and the maximum allowable position of the rack at each rotation speed are stored.

Then, the engine rotation speed control unit 20 determines that the detected rotation speed input from the engine rotation sensor 22 due to the change in the load is the set rotation speed (the rated rotation speed in this embodiment).
If it is different from the above, the correction setting rotation speed is calculated, and the rack position corresponding to the correction setting rotation speed corresponding to the no-load is read,
From this and the actual rack position input from the rack position sensor 21, a target rack position required to obtain the corrected set rotational speed is calculated, and a signal corresponding to this target rack position is sent to the rack actuator 23. give. In response to this signal, the rack actuator 23 operates to move the rack to the target rack position and adjusts the fuel supply amount to the engine. As described above, the engine speed control unit 20 operates to maintain the engine speed at the rated speed regardless of the load level.
The operation of 20 is performed only when the operation command signal from the vehicle speed control unit 10 is given as described later.

On the other hand, the vehicle speed control unit 10 obtains the current load state of the engine 7 from the target rack position calculated by the engine speed control unit 20, and based on this, the load of the engine 7 does not exceed the preset upper limit value. under the condition that the maximum speed acceptable, i.e. to calculate the upper limit speed, in order to realize the speed, be one that changes the gear ratio in the main transmission, to the input port a ₁ Is
The automatic switch 11 is connected, and when the switch 11 is turned on, the input port a ₁ changes to low level.

A threshing switch 12 that is turned on when the threshing clutch that engages and disengages the power to the threshing unit 3 is engaged in the input ports a ₂ and a ₃ and a mowing clutch that engages and disengages the power to the mowing unit 4. reaper switch 13 which is turned on when the engaged state are respectively connected to the input by turning on the input port a ₂ is also reaper switch 13 by turning on the threshing switch 12 ports a ₃
Each turn to a high level.

Further, the input port a ₄ is connected to the output side of the comparator 51a, and the input port a ₄ turns to high level according to the high level output of the comparator 51a. The + input of the comparator 51a is the grain culm sensor 51, 5 mounted on the bottom plate of the feeder house 5.
It is a signal in which the outputs of 1 ... Are superimposed, and the-input is a predetermined voltage set by the voltage divider 51b. Therefore, in the input port a _{4, when} the grain culm contacts the pressure receiving surface of the grain culm sensor 51, 51, and the + input potential in the comparator 51a becomes higher than the − input potential, that is, the grain culm is sent to the threshing unit 3. High level if paid.

And the vehicle speed control unit 10, when the input port a ₁ is at a low level and the input ports a ₂ , a ₃ , a ₄ are all at a high level, that is, the automatic switch 11, the threshing switch 12 and the reaping switch 13 are All are turned on, and the vehicle speed control is performed only when the grain culm sensor 51 detects the feeding of grain culms.

The input port a ₅ of the vehicle speed control unit 10 is provided at the base end portion of the sub-transmission lever 61, and the sub-transmission switch 14 is turned on when the lever 61 is in the locking position on the "low speed" side. Are connected, and when the switch 14 is turned on, the input port a ₅ changes to low level. As described above, the auxiliary transmission is "low speed".
And has a speed stage of the two types of "high gear", vehicle speed control unit 10, by the input port a ₅ is at low level, that the running speed stage (hereinafter subtransmission stage in the subtransmission device ) Is the "low speed stage", and the input port
husband that it is the same "high-speed stage" by a ₅ is at a high level people recognize.

To the input port a ₆ of the vehicle speed control unit 10, a shift sensor 15 which is mounted on the base end pivotal support portion of the main shift lever 60 and outputs a potential according to the amount of rotation thereof, for example, using a potentiometer, is connected. There is. The main transmission, as described above,
The gear ratio can be changed steplessly, and the vehicle speed control unit 10 recognizes the gear ratio in the main transmission by the level of the signal input to the input port a ₇ .

Further, the signal corresponding to the target rack position which is the output of the engine speed control section 20 is given to the input port a ₇ of the vehicle speed control section 10 as described above.

The signals input to the input ports a ₆ and a ₇ are subjected to predetermined processing by the input interface of the vehicle speed control unit 10, and the vehicle speed control unit outputs digital data according to the level of each signal.
It is designed to be taken in by 10 CPUs 10a.

On the other hand, the output ports b ₁ and b ₂ of the vehicle speed control unit 10 are connected to the shift motor 16 for turning the main shift lever 60 via a drive circuit (not shown), and the output port b ₁ (or b ₂ ) of the output port b ₁ (or b ₂ ). The shift motor 16 rotates normally (or reverses) according to the high level output.
Then, the main shift lever 60 is rotated to the high speed (or low speed) running side.

Output port b ₃ of the vehicle speed control unit 10, the vehicle speed lamp 17 for informing the operator that the vehicle speed control operation is performed,
The output port b _4, the which the rotation operation are respectively connected to the increasing side indicator lamp 18 for indicating to an operator of the speed-increasing side of the auxiliary transmission lever 61, the output port b _3, b ₄ rows Each of the lamps is turned on according to the level output.

The output port b ₅ of the vehicle speed control unit 10 is connected to the input side of the engine speed control unit 20, and the engine speed control unit connected to the output port b ₅ according to the high level output of the output port b _5. When the input ports of 20 become high level, the control unit 20 operates as described above, and causes the engine 7 to rotate at a constant speed at its rated speed regardless of the magnitude of the load applied to it.

The vehicle speed control unit 10 is a CPU 10 that performs input / output instructions and control calculations.
a, a RAM 10b used for control calculation in the CPU 10a, a ROM 10c storing various data and control programs necessary for control calculation, and the like. FIG. 4 is a graph of load characteristics showing the relationship between the vehicle speed of the harvester and the load applied to the engine 7 when the rotation speed of the engine 7 is the rated rotation speed. The axis shows the load factor E with respect to the maximum load of the engine 7, and F ₁ ~
The curve shown as Fn is a load characteristic curve obtained by actually performing harvesting work under various different load conditions in the working units such as the threshing unit 3 and the cutting unit 4.

FIG. 5 is a graph showing the relationship between the gear ratio R in the main transmission and the vehicle speed V of the harvester when the rotation speed of the engine 7 is the rated rotation speed. The "high speed stage" and the broken lines show the above relationships when the auxiliary shift stage is the "low speed stage", respectively.

The respective curves in FIGS. 4 and 5 are stored in the ROM 10c as a mathematical table or an approximate expression approximating these. Further, Ecmax in FIG. 4 is a limit maximum load factor which is an upper limit value of the load for limiting the load applied to the engine 7 during the vehicle speed control to this value or less, and is set to a value of 85 to 90% of the maximum load. This value is also stored in the ROM 10c. In addition to these, the ROM 10c is for calculating an annular load factor E of the engine 7 from the arithmetic expression for obtaining the gear ratio R in the main transmission from the rotational position of the main transmission lever 60 and the rack position of the fuel injection pump. It stores various data such as arithmetic expressions and mathematical expressions.

Now, the operation of the device of the present invention configured as described above will be described with reference to the flowchart showing the control content of the vehicle speed control unit 10 in FIG.

The vehicle speed control unit 10 has a control start condition including that the threshing unit 3 and the reaping unit 4 are operating together, that the grain culm is being fed to the threshing unit 3, and that the automatic switch 11 is turned on. As described above, the vehicle speed control operation is performed only when it is confirmed by the levels of the input ports a _{1 to} a ₄ that all are satisfied.

When the above-mentioned conditions are satisfied, the vehicle speed control unit 10 first sets the output port b ₃ to a low level, lights the vehicle speed lamp 17, and notifies the operator that the vehicle speed control is being performed, and outputs the output. The port b _{5 is set} to a high level, and the engine speed control unit 20 is instructed to start its operation, and the operation of the engine speed control unit 20 causes the engine 7 of the harvester to rotate at a constant speed at the rated speed.

Next, the vehicle speed control unit 10 recognizes whether the sub-gear is “high speed” or “low speed” based on the level of the input port a ₅ , and when it is the low speed, its output port b ₄
To a low level, turn on the speed-up instruction lamp 18,
The operator is urged to rotate the auxiliary shift lever 61 to the high speed side. As shown in FIG. 5, the main transmission is capable of continuously changing the vehicle speed of the harvester from speed 0, and the vehicle speed control operation thereafter is possible regardless of the sub-gear, but the sub-gear If the gear is "high gear", the vehicle speed can be changed in a wider range, and the control range is widened.Therefore, as described above, the speed increase instruction lamp 18 is turned on to instruct the operation of the auxiliary shift lever 61. Therefore, the vehicle speed control unit 10 continues the subsequent operation regardless of whether or not this operation is performed.

Next, the vehicle speed control unit 10 recognizes the rotational position of the main shift lever 60 from the signal input to the input port a ₆ and the rack position from the signal input to the input port a ₇ , respectively, and determines the rotational position. Using the position and the rack position, the current gear ratio R ₁ in the main transmission and the current load factor E ₁ in the engine 7 are calculated according to the respective arithmetic expressions stored in the ROM 10c. The load factor E ₁ calculated in this way may be used as it is for subsequent calculations, but in the isochronous-controlled engine 7, the rack position is frequently changed, so an instantaneous peak of the rack position is generated. In order to prevent unnecessary vehicle speed control operation from being performed depending on the value, it is desirable to use the moving average value of the calculated values of the load factor E ₁ calculated as described above for the past several times in the subsequent calculations.

Then, the vehicle speed control unit 10 obtains the current vehicle speed V ₁ from the gear ratio R ₁ and the previously recognized current sub-gear speed based on the relationship shown in FIG. Load factor E ₁
From the above, on the graph of FIG. 6 stored in the ROM 10c, the state point C ₁ indicating the current load state is specified, and the state point C ₁ is matched from the load characteristic curves F _{1 to} Fn. Select the load characteristic curve F ₁ to be used. Further, when there is nothing to match the state point C ₁ includes two load characteristic curves Fi and Fi ₊₁ close to the state point C ₁ is selected, operation will be described later based on these, and curves Fi Curve It is performed by linear interpolation with Fi ₊₁ .

The load characteristic curve Fi thus selected corresponds to the current load state of the harvester, and changes in the planting density of the grain culms on the field surface or the number of grains attached per grain culm, etc. As a result, unless the load states in the working units such as the threshing unit 3 and the mowing unit 4 change, the load applied to the engine 7 changes along the curve Fi according to the vehicle speed V of the harvester. Therefore, when the load characteristic curve Fi is selected as described above, the vehicle speed control unit 10 next determines the maximum load factor limit on the curve Fi.
Set the vehicle speed corresponding to Ecmax to the target vehicle speed V ₂
The target speed ratio R ₂ in the main transmission is calculated from the calculated value based on the relationship shown in FIG. Then, this is compared with the current gear ratio R _1, and if the absolute value of the difference between the two is less than a positive predetermined value ε that is sufficiently small, it is determined that the current gear ratio R ₁ is an appropriate gear ratio. Then, the current rotational position of the main shift lever 60 is held.

When the absolute value of the difference is larger than the predetermined value ε and R ₂ is larger than R ₁ , the vehicle speed control unit 10 determines that the input port
While calculating the current gear ratio R ₁ from the signal input to a ₆ , the output port b _{1 is set} to a high level, the shift motor 16 is normally rotated, and the absolute value of the difference between R ₂ and R ₁ is Predetermined value ε
Performs speed increasing until less, whereas if R ₂ is smaller than R ₁ may likewise while calculating the speed ratio R ₁ of the current, the output port b ₂ to the high level, the shift motor 16 Reverse rotation is performed and deceleration is performed until the absolute value of the difference between R ₂ and R ₁ becomes the predetermined value ε or less.

After accelerating or decelerating or holding the current gear ratio in this way, the vehicle speed control unit 10 determines whether or not the control start condition is satisfied by the levels of the input ports a _{1 to} a ₄ . examined, which when is satisfied, in order to continue the control operation described above, back to the stage of recognition of the auxiliary gear stage, whereas if the condition is not satisfied, and the output port b ₃ to the high level , The vehicle speed lamp 17 is turned off, the output port b _{5 is set} to the low level, and the engine speed control unit 20
After suspending the operation of, the vehicle speed control unit 10 shifts to a standby mode for waiting until the above condition is satisfied.

In this embodiment, the predetermined value ε is set so that unnecessary acceleration / deceleration is not performed with respect to a minute change in the load of the engine 7, and the target gear ratio R ₂ and the current gear ratio R ₁ are set. When the absolute value of the difference is less than or equal to the predetermined value ε, the rotation position of the main shift lever 60 is not changed, but this is changed after the target speed ratio R ₂ is calculated. It goes without saying that the operation may be performed as it is.

Further, in the present embodiment, the traveling speed is detected by the shift sensor 15 as the rotational position of the main shift lever 60, but the traveling speed is detected by other detecting means such as the rotational speed of the drive shaft of the traveling crawler 2. The speed may be detected.

[Effect] As described in detail above, according to the device of the present invention, the upper limit traveling speed when the load of the engine becomes the upper limit value is calculated from the detection result of the load and the traveling speed in the engine, and the speed is realized. Because the running speed is changed steplessly,
Even when the load deviates significantly above or below the upper limit value, the speed is immediately changed to an appropriate traveling speed, and the engine is forced to operate for a long time under an overloaded or underloaded condition. And an excellent effect such as the highest work efficiency according to the capacity of the engine can be obtained.

[Brief description of drawings]

The drawings show one embodiment of the present invention. FIG. 1 is a schematic right sectional view of an ordinary harvester equipped with the device of the present invention, FIG. 2 is its plan view, and FIG. 3 is the device of the present invention. FIG. 4 is a graph showing the relationship between running speed and engine load, FIG. 5 is a graph showing the relationship between gear ratio and running speed in the main transmission, and FIG. 6 is vehicle speed control. It is a flowchart of. 3 ... Threshing unit, 4 ... Mowing unit, 7 ... Engine, 10 ... Vehicle speed control unit, 14 ... Sub gear shift switch, 15 ... Shift sensor, 16 ... Shift motor, 20 ... Engine speed control unit, 21 ... … Rack position sensor, 60 …… Main shift lever 61 …… Sub shift lever

Claims (1)

[Claims] 1. An engine speed control unit that operates to maintain the engine speed at a set speed regardless of the size of the load, and the running unit and the working unit are driven by the engine. A harvester equipped with a transmission capable of continuously changing its traveling speed and controlling the traveling speed by operating the transmission to properly maintain the load on the working unit. In the vehicle speed control device, load detecting means for detecting the load of the engine related to the load of the working unit, traveling speed detecting means for detecting the traveling speed of the harvester, and the traveling speed and the load of the engine. From the characteristic storage means that stores the relationship of, in the form of a plurality of load characteristics according to the load state in the working unit, the detection result of the traveling speed detection means and the detection result of the load detection means, A calculating unit that selects one of the plurality of load characteristics and calculates an upper limit traveling speed corresponding to a preset upper limit value of the load of the engine according to the characteristic, and realizes a calculation result of the calculating unit. A vehicle speed control device for a harvester, comprising: means for operating the transmission.