KR0175160B1 - Speed-controlling apparatus for reaping machine - Google Patents

Abstract

A vehicle speed control device for a mowing machine, wherein the vehicle speed control device includes a change amount calculating means (102) for calculating an engine speed change amount by subtracting the engine speed before? T seconds from the current engine speed detected by the speed detection means (102). And deviation calculating means 103 for calculating a deviation obtained by subtracting a preset rotational speed of the engine from the current engine speed detected by the rotational speed detection means and the transmission device 9 to decelerate the vehicle speed of the work machine. And a vehicle speed reduction control means 10 for instructing a deceleration amount. The control means instructs the speed reduction device when the change amount is a negative value even if the deviation is either positive or negative, and the deceleration control means. Is a negative value, and the larger the absolute value is, the larger the deceleration amount is set.

Description

Vehicle speed control device for mowing machines

1 is an overall side view of the combine.

2 is a control diagram.

3A is a diagram showing a discussion preliminary harvesting state as a preparation step for carrying out a harvesting operation;

3B is a view showing a path of paddy harvesting work.

4A is a time series diagram showing a relationship between an engine speed and a working state.

4B is a time series diagram showing the relationship between the engine speed and the working state.

5 is a membership function for deviations.

6 is a membership function for the amount of change.

7 is a membership function for the deceleration amount.

8 is a control rule for fuzzy reasoning.

9 is a flow chart for deceleration control.

* Explanation of symbols for main parts of the drawings

9: Transmission 14: Actuator

100: vehicle speed control means 101: deceleration control means

102: change amount calculation means 103: deviation calculation means

S0: working state detecting means S1: rotating speed detecting means

Technical Field of the Invention

The present invention relates to a vehicle speed control apparatus for a mowing machine having a transmission for shifting the transmission for driving, a rotation speed detecting means for detecting engine speed, and a working state detecting means for detecting whether a mowing operation state is present. .

[Prior art]

In a general rice field, as shown in FIG. 3A, as shown in FIG. 3A, a mowing operation is performed in advance in both ends of the longitudinal direction of all the answers, and the space to which the mowing machine turns is turned at both side ends (upper and lower ends A and A in the drawing). It is known to install at ').

In addition, the mowing machine finishes the mowing operation (corresponding to route 1a in FIG. 3b) in the upper left side, for example, as shown in FIG. 3b, and then mowing in the lower right side of the next right stage (path 2a in FIG. 3b). Gas movement (corresponding to paths 1b, 1c, and 1d in FIG. 3b) is performed to perform the corresponding operation. When the mowing operation of the portion of the path 2a is finished, the mowing operation of the path 3a is performed after moving to the left direction (corresponding to the paths 2b, 2c, 2d) in the drawing of the base. The method of repeating the following steps and performing the mowing operation of the whole answer is known. In the movement of the mowing machine, first, the path 1b corresponding to the right 90 degree turning of the body immediately after the mowing ends of the left end, the path 1c corresponding to the straight portion after the 90 degree turning, and the right 90 after finishing the straight. Also, the path 1d corresponding to the turning is included. In a normal mowing operation, the work machine receives the greatest resistance in this right turn portion. In other words, the engine speed is expected to decrease the most during this turning. As described above, the variation in the engine speed of the work machine in the mowing operation is shown in FIGS. 4A and 4B in the ordinary rice field. As is apparent from these drawings, it is expected that in normal mowing operations, the engine speed decreases at the time of 90 degree turning of the gas, and the engine speed during movement of the gas corresponding to the path of 1c in FIG. 3b is expected to be the highest. . However, the surface resistance may sometimes be unpredictable depending on the situation of the discussed road surface, and therefore, the advantages are well understood by those skilled in the art.

As described above, in the vehicle speed control apparatus of the harvesting machine, conventionally, on the basis of the detection information of the rotational speed detecting means after detecting that the working state detecting means has changed from the harvesting working state to the non-picking working state. The engine speed is lower than the preset value (usually, it was set lower than the engine speed at the time of mowing), and at the same time, the engine speed does not tend to increase, that is, the load is not being reduced. Is detected, the actuator may be configured to decelerate the actuator at a deceleration amount proportional to the deviation between the current engine speed and the set speed, that is, the amount of fall from the set value of the engine speed. In this way, when the work machine is configured and the mowing operation at the work stroke (corresponding to route 1a in FIG. 3b) is finished and the vehicle is turned to the next work stroke (corresponding to route 2a), turning (third 3b) Accompanied with the route 1b and the route 1d in FIG. 1, the driving load increases and the engine is stopped.

[Problems that the invention tries to solve]

However, in the above conventional configuration, since it is detected that the current engine speed is lower than the set speed, deceleration control is executed, which has the following disadvantages.

That is, even when the engine speed when the mowing operation is completed is higher than the set speed, for example, even when the engine speed suddenly decreases in conjunction with the turning operation of the gas, the engine speed is set. Deceleration control is not executed until the speed decreases. Therefore, a time delay occurs between the time when the running load increases and when the deceleration of the running speed starts, and the deceleration operation is not performed even though the running load is large therebetween.

As a result, the deceleration operation of the gas running speed is delayed with respect to the actual increase in the running load, so that the amount of the engine speed drop due to the increase of the load may increase more than necessary. There have been disadvantages such as an increase in discomfort to the operator due to a sudden deceleration or a possibility of stopping the engine when the running load is large.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and an object thereof is to provide a vehicle speed control apparatus for a mowing machine, which makes it possible to reduce the traveling speed at an appropriate timing and at an appropriate deceleration amount in correspondence with the traveling load situation of the traveling body. It is at that point.

[Means for solving the problem]

According to the characteristic structure of Claim 1, the change amount which calculated | required the value before the unit time from the present value of the engine speed detected by the rotation speed detection means by the change amount calculation means is calculated | required. Then, a deviation obtained by subtracting the preset rotational speed set by the deviation calculation means from the engine rotational speed detected by the rotational speed detection means is obtained.

Then, after detecting that the work state detecting means has changed from the harvesting work state to the non-picking work state, the deceleration control means is based on the change amount obtained by the change amount calculating means and the deviation obtained by the deviation calculating means. Even if the deviation is positive or negative, the engine speed change amount is a negative value when the engine speed change amount is a negative value, and in the overload state, the larger the absolute value of the engine speed change amount and the larger the absolute value of the deviation value increases the deceleration amount. It is set larger.

That is, when setting the deceleration amount that the vehicle speed reduction control means should instruct the speed change apparatus, not only the absolute value of the engine speed change amount but also the absolute value of the deviation is a condition of the deceleration amount setting.

Therefore, when the amount of change in which the value before the unit time is subtracted from the present value of the engine speed is large, that is, when the amount of fall per unit time of the engine speed is large, the engine rotates by a sudden running load even if the deviation is any value. As the number is decreasing, it is an overload condition. In this state, the larger the absolute value of the change amount, that is, the sharper the decrease in the engine speed due to the running load, the larger the deviation, the larger the fall amount of the engine speed, It is set to large.

As a result, irrespective of whether or not the engine speed is lower than the set speed as in the conventional example, in an overload state with a large change amount of minus, the deceleration amount is set larger as the change amount is larger, and the running speed is decelerated by the deceleration amount. Therefore, the deceleration is performed in a state where the response delay is small with respect to the increase in the running load. Moreover, since the larger the deviation is, the larger the deceleration amount is set, the deceleration is always performed at an appropriate deceleration amount with respect to the magnitude of the running load.

According to another feature configuration of the present invention, the deceleration control means is configured to set the deceleration amount larger as the engine speed is lower, provided that the change amount is a negative value and the value is constant. Therefore, the change amount is a negative value, and in the case of a constant value, as the engine speed is lower, it is determined that the engine load of the mowing machine is greater, and the deceleration of the running speed of the work machine is efficiently performed.

According to another feature of the present invention, the deceleration control means is configured to set the deceleration amount when the engine speed is lower than a predetermined value even if the change amount is a positive value, that is, even when the engine speed is in the increasing direction. . With such a configuration, even if the engine speed is in the increasing direction, the running speed of the gas is decelerated when the engine speed of the harvesting machine is lower than a predetermined value, that is, when the engine load of the harvesting machine is still quite large. Therefore, the engine load of the traveling gas can be reduced more quickly, and smoother mowing operation and gas running are possible.

According to another feature configuration of the invention, the deceleration control means is configured to store in advance the deceleration amount fuzzy inferred by using the change amount and the deviation in the deceleration control means, and obtain a deceleration amount based on the stored value. It is. Such a configuration makes it easier to set a more appropriate value without considering the dispersion due to individual differences compared to the configuration of setting the measured values based on the experimental results in response to various driving conditions as map data.

According to another feature configuration of the present invention, the transmission is configured such that the deviation between the engine speed detected by the rotation detection means and a predetermined target rotation speed is reduced while the working state detection means detects a mowing operation state. A vehicle speed control means for operating the sphere on the speed increasing side or the deceleration side is provided so that the deceleration control means is configured to make the set speed as the set speed higher than the target speed.

During mowing, the engine speed is controlled to be maintained at the target speed. That is, the vehicle speed is controlled so that the engine load which adds the work load accompanying the mowing operation and the running load is maintained at an appropriate value. After the change from the harvesting operation state to the non-picking operation state, the rotation speed higher by the set amount than the target rotational speed is set as the set frequency, and the deceleration control is executed based on the set rotation speed.

That is, immediately after the non-working state, the load accompanying the mowing operation is eliminated, and the engine load is reduced so much that the set rotational speed as a reference for determining the load state of the engine is equivalent to the load accompanying the mowing operation. By setting the rotational speed as high as possible, it becomes possible to more accurately determine the load state of the engine in turning driving during non-working.

Embodiment of the Invention

[Mowing machine]

Hereinafter, the combine as a mowing machine which concerns on this invention is demonstrated.

As shown in FIG. 1, the combine is equipped with the threshing apparatus 2 in the vehicle body V provided with a pair of left and right crawler traveling apparatuses 1, and the boarding control part ( 4) is provided, and the pre-treatment processing part 3 is provided in the horizontally front side of the boarding control part 4 freely in a drive-up. The harvesting pretreatment unit 3 is a posture changing device (5) for causing rice straw on the rice paddy field, towing (6) for cutting under the stump of the raised rice straw stem, and changing the posture to the posture collapsed side Each of the conveying apparatuses 7 conveyed toward the threshing feed chain 8 of the vehicle body back side is provided.

Then, under the stump of the crest which is conveyed to the place at the transport start end side of the conveying apparatus 7, a stub sensor S0 which is turned on and operated is provided. More specifically, accompanying the start of the mowing operation, the crest of the stump cut under the stub with the towing 6 contacts the sensor S0 under the stub so that the sensor S0 under the stub is turned ON and at the same time, the mowing operation Accompanying this end, the crest stem supply is stopped and the sensor S0 under the stub is turned off. In other words, the stub sensor S0 corresponds to the work state detecting means for detecting whether the combine is in the mowing state.

As shown in FIG. 2, the power of the engine E is not necessarily limited to the hydraulic continuously variable transmission 9 (hydraulic continuously variable transmission through the belt transmission mechanism. For example, the belt continuously variable transmission may be sufficient. ), And the output after the shift is transmitted to the right and left crawler traveling apparatuses 1 and 1 via the traveling mission 10. On the other hand, the power transmission system is configured such that the power of the engine E is freely intermittently transmitted to the threshing apparatus 2 through the threshing clutch 11.

[Vehicle Speed Control Device]

Next, the configuration of the vehicle speed shift operation will be described based on FIG.

An electric motor 14 as an actuator for shifting the transmission 9 is linked to the linkage mechanism 12 between the manual shift lever 13 and the transmission 9 via a frictional transmission 15. have.

That is, the shift operation by the manual overrides the shift operation by the electric motor 14, so that the shift operation can be performed by both the manual shift lever 13 and the electric motor 14.

Further, the engine E is provided with an improved water sensor S1 as a rotation speed detection means for detecting the rotation speed RPM, and the traveling vehicle speed of the work machine is based on the rotation speed of the electric shaft in the middle of the traveling motorometer. The vehicle speed sensor S2 for detecting is provided.

Next, the combine control configuration will be described. As shown in FIG. 2, a control device 16 for use with a microcomputer is provided, and the control device 16 is provided from the stub sensor S0, the rotation speed sensor S1, and the vehicle speed sensor S2. At the same time as the signal is input, the drive signal to the electric motor 14 is output from the control device 16.

The control device 16 is provided with a vehicle speed control means 100.

The vehicle speed control means 100 detects the engine speed detected by the rotation speed sensor S1 and the first preset rotation while the sensor S0 under the stub detects a mowing state (ON state). The electric motor 14 is operated on the speed increasing side or the deceleration side so that the deviation from the number (or cutting speed) is reduced. The control means 16 is a deceleration control for decelerating and starting the electric motor 14 by detecting that the sensor S0 under the stub is changed from a cutting operation state (ON state) to a non-cutting operation state (OFF state). Means 101, change amount calculating means 102 for obtaining a change amount obtained by subtracting a value before a unit time? T from a current value of the engine speed detected by the rotation speed sensor S1, and the rotation speed sensor Each of the deviation calculation means 103 which calculates the deviation which subtracted the reference rotation speed as a 2nd preset rotation speed (or traveling rotation speed) preset from the engine speed detected by S1 is obtained.

In addition, the deceleration control means 101 sets the second rotational speed (driving speed) higher than the first predetermined rotational speed (logging speed) by a set amount corresponding to the rotational speed drop amount accompanying the mowing operation. It is configured to set as.

Here, the second set rotation speed is the engine rotation speed when the work machine is traveling inside the rice field in the state where the mowing operation is not performed, which is set arbitrarily.

In addition, a 1st set rotation speed is an engine speed predicted at the time of a normal mowing operation.

Therefore, the difference between the first set rotational speed and the second set rotational speed corresponds to the engine speed reduction amount caused by the ordinary mowing operation. These relationships are made clear by the following equation.

Load during mowing operation = Gas running load + Mowing load

1st set rotation speed = engine speed in normal mowing operation

2nd set rotation speed = engine speed at the time of driving of a working machine

= 1st set speed + engine speed decrease by mowing load

No-load speed = 2nd set speed + engine speed reduction amount by running load of mowing machine

Deviation = Current Engine Speed-Second Set Speed

[Relationship between Engine Speed and Work Process (Figure 4a)]

In FIG. 4A, typical examples of the engine speed in the mowing operation described in FIG. 3B and the movement paths (paths 1a, 1b, 1c, 1d, 2a, ..., respectively) of the working gas are shown.

In other words, in the path 1a of the ordinary mowing operation, the vehicle speed control means 100 described later operates so that the engine speed approximates the target rotation speed (or the first predetermined rotation speed).

Immediately after the mowing operation of the path 1a is finished, a 90 degree turn corresponding to the path 1b is executed. At this time, even if the harvesting operation is finished, the working machine has the highest resistance against the road surface as discussed with the timer of the working machine, so that the engine load increases. As a result, the engine speed is expected to decrease most in the path 1b corresponding to a 90-degree turn. After the 90-degree turn is completed, since the road is driven on the field surface of the straight portion corresponding to the path 1c, the load of the work machine decreases, and the engine speed is the highest in this state. In this way, after the work machine completes the movement along the path 1c, the work machine advances along the path 1d of the 90 degree turning before the transfer to the next harvesting path 2a. When the working gas turns along this path 1d, the engine load is subjected to the same engine load as the turning path 1b, so that the engine speed decreases to the same level as the path 1b. After the movement of the path 1d is finished, the work machine executes a mowing operation along the path 2a. As shown in FIG. 3B, the cycles of the paths 1a-1d are executed, and the same cycles are repeated in the following manners, such as the paths 2a-2d and, moreover, the paths 3a-3d. Will be executed in turn.

The state of the fluctuation of the engine speed corresponding to these paths 2a-2d and 3a-3d is substantially the same as the engine speed fluctuation corresponding to the path 1a-1d shown in FIG. 4A.

The vehicle speed control means 100 reads the engine speed in the no-load state before the mowing operation, and rotates as low as the fall amount corresponding to the load accompanying the normal operation (that is, the driving load and the mowing operation load) from the no-load rotational speed. Is set as the first set rotation speed.

In the mowing operation, the electric motor 14 is operated on the increasing or decelerating side so that the difference between the engine speed detected by the rotation speed sensor S1 and the first set rotation speed (cutting speed) is reduced. The vehicle speed is controlled so that the load of (E) is always in an appropriate state.

Then, the deceleration control means 101, even if the deviation is any value based on the change amount obtained by the change amount calculating means 102 and the deviation calculated by the deviation calculating means 103, the change amount When the value is negative, it is an overload state and is configured to set the deceleration amount larger as the absolute value of the change amount is larger.

Further, the deceleration control means 101 is configured such that the value (deviation) obtained by subtracting the current engine speed from the second set speed (rotation speed when driving) is negative, and the larger the absolute value is, the larger the deceleration amount is set. It is.

In setting the deceleration amount as described above, the deceleration control means 101 stores in advance the deceleration amount fuzzy inferred using the deviation and the change amount and obtains the deceleration amount based on the stored information. It is.

[Setting Deceleration Amount by Fuzzy Inference]

That is, the deceleration amount is calculated by fuzzy inference based on the membership function shown in FIGS. 5 to 7 and the control rules shown in FIG.

FIG. 5 shows the member ratio function of the deviation, FIG. 6 shows the member ratio function of the change amount, and FIG. 7 shows the membership function of the deceleration amount used as the weight coefficient when calculating the deceleration amount. The control rule describes the deviation and change amount as two fuzzy variables in the first half and the deceleration amount as the second half. The suitability of the deviation and change amount in the control rule is the value of the smaller one of the goodness of fit of the respective member number ratio functions (FIGS. 5 and 6). In addition, the deceleration amount is obtained from the membership function (Fig. 7) based on the goodness of fit thus obtained.

Further, as is apparent from FIGS. 5 to 8, even if the deviation is in either positive or negative range, when the amount of change is negative, it is an overload state, and the larger the absolute value and the larger the absolute value of the deviation, the deceleration amount It is set to be large. The smaller the deviation is, the more negative the change is and the greater the absolute value becomes. In the case where the deviation is small, even if the deviation is negative, the absolute value is large and the deceleration amount is set as the overload condition.

Further, when the value of the change amount corresponds to PB as shown in FIG. 8, the deviation is negative and the absolute value is a large value NB, the shift amount is set in NS despite the positive value. This phenomenon corresponds to the point Pa of FIG. 4A, that is, the point of time when the mowing operation is about 90 degrees after the completion of one step. That is, it corresponds to a transition period in which the gas slowly progresses over the highest engine load. In this state, since the load of the gas decelerates every unit time (Δt sec), the engine speed is increased but the engine speed is still very low compared to the set speed, so the deceleration amount of the deceleration control means 101 is reduced. Is a small value, but is configured to be set.

By setting in this way, even if the mowing operation is completed by one end and the aircraft is turned 90 degrees, the running speed of the working gas is decelerated for a while when the engine speed is low.

In addition, in this embodiment, the deviation is small and the change amount is negative and the absolute value is small (corresponding to NS in FIG. 8). Or 0 (corresponds to ZE in FIG. 8). Further, when the absolute value is larger (corresponding to PB in FIG. 8) and the absolute value is large, the deceleration amount is set to 0 (state indicated by ZE in FIG. 8), that is, the deceleration operation is not performed.

[Flowchart of Deceleration Control Operation]

Next, the deceleration control operation by the deceleration control means 101 will be described based on the control flowchart shown in FIG. Further, this control is executed repeatedly every set unit time [Delta] t seconds (for example, several msec to several tens msec).

First, if it is detected that the sensor S0 under the stub is switched from the ON state to the OFF state, and it is detected that the change from the mowing operation state to the non-cutting operation state is equivalent to the target rotational speed (the first set rotation speed or the cutting rotation speed). ) Is set as the reference rotational speed (corresponding to the second preset rotational speed or the traveling rotational speed) by a set amount corresponding to the rotational speed drop accompanying the mowing operation (stems 1 and 2).

Then, the engine rotation speed read in the previous time from the engine speed read this time by reading the detected value (engine rotation speed) of the rotation speed sensor S1 and the detected value (current vehicle speed) of the vehicle speed sensor S2 (step 3). Is subtracted to calculate the change amount of the engine speed (step 4).

Further, as described above, the deviation is calculated by subtracting the preset reference speed from the engine speed read this time (step 5).

As described above, the deceleration amount is calculated based on the control information stored in advance based on the fuzzy inference (step 6), and the electric motor 14 is decelerated to decelerate the vehicle speed by the deceleration amount obtained from the current vehicle speed. (Step 7).

In this way, with respect to the increase in the running load caused by turning driving, the deceleration operation can be performed by an appropriate deceleration amount corresponding to the load situation in the state where the time delay is small as much as possible, and the vehicle speed is higher than necessary due to the response delay. This deceleration can avoid disadvantages such as discomfort to the operator or deterioration in work efficiency.

[Individual Embodiment]

(1) In the above embodiment, the deceleration control means is configured to make the overload state when the change amount becomes negative as the deviation becomes smaller as the deviation becomes smaller, and decelerates when the deviation is small and at the same time the absolute value of the change amount is small. It is indicated that the amount is set to zero, that is, the deceleration operation is not executed. However, in place of such a configuration, even if the deviation is small and at the same time the absolute value of the change amount is small, the deceleration operation may be performed with a small deceleration amount.

(2) Substituting the deceleration amount into fuzzy inference based on the deviation and the change amount, for example, and calculating the appropriate deceleration amount based on the experimental result as a parameter between the deviation and the change amount. May be configured as a map data.

(3) The second set rotation speed (running rotation speed) as the second set rotation speed (driving rotation speed) is replaced with a configuration in which the rotation speed as high as a set amount is used for the first set rotation speed (return rotation speed) used in the vehicle speed control means. It is good also as a structure which uses 1 set rotation speed as a 2nd set rotation speed (driving speed) as it is. With this configuration, it is not necessary to set the reference speed every time the state changes from the harvesting work state to the non-picking work state, so that the deceleration control can be performed quickly.

Further, as shown in Fig. 4B, no-load rotation speed may be used as the second set rotation speed. In this case, since the deviation of the engine speed becomes a negative value at all points in the gas non-cutting working state (corresponding to paths 1b-1d), the larger the absolute value of the deviation, the lower the engine speed.

(4) As the working state detecting means, a limit switch may be used to detect that the pre-treatment processing unit has risen by a set amount or more in place of the stubble sensor S0.

In other words, when the turning operation is completed after the mowing operation in the working stroke is completed, it may be made to detect that the cutting state is brought into the non-cutting operation state based on this raising operation from raising the pre-harvesting processing section to the maximum position.

(5) As the transmission, a variety of transmissions, such as a belt continuously variable transmission or a frictionless continuously variable transmission, can be used in place of the hydraulic continuously variable transmission.

(6) As the actuator, another actuator such as a hydraulic cylinder may be used in place of the electric motor.

(7) Although the above has been described using a combine as an example of a mowing machine, the present invention can also be applied to vehicle speed control of a mother machine as a power receiving machine. Moreover, it is possible to apply this vehicle speed control to the agricultural work machine as a whole in the field installed in the middle of the slope of the mountain, not only in the work of the faucet on the plain.

(8) This engine is a type in which the rotation speed decreases when a load is applied.

In addition, although the code | symbol is recorded in the term of a claim for easy contrast with drawing, this invention is not limited to the structure of an accompanying drawing by the said writing.

Claims (9)

Rotation speed detection means (S1) for detecting the rotation speed of the engine; Vehicle speed detecting means (S2) for detecting a traveling speed of the body; Working state detecting means (S0) for detecting whether the gas is in a mowing operation state; A transmission 9 for gas traveling; And a vehicle speed control device for a mowing machine including shift mechanisms 13 and 14 for shifting the speed shift device 9, wherein the current speed of the engine is detected by the speed detection means S1. Change amount calculating means (102) for calculating an engine speed change amount by subtracting the engine speed before? T seconds from the number; Deviation calculation means (103) for calculating a deviation obtained by subtracting a preset rotational speed of the engine from the current engine speed detected by the rotational speed detection means (S1); And a vehicle speed reduction control means (101) for instructing the speed reduction device (9) to decelerate the vehicle speed of the harvesting machine, wherein the work state detecting means (S0) is set from the mowing state. After detecting the change to the mowing state, the deceleration control means 101 determines that the absolute value of the engine speed change amount is larger when the engine speed change amount is a negative value even if the deviation is either positive or negative. And the larger the absolute value of the deviation, the larger the deceleration amount is set. The vehicle speed control apparatus according to claim 1, wherein the set rotation speed is set to the rotation speed at no load of the engine. 2. The vehicle speed control apparatus according to claim 1, wherein the deceleration control means (101) sets the deceleration amount larger as the engine speed is lower when the rotation speed change amount is constant at minus. 3. The vehicle speed control apparatus according to claim 2, wherein the deceleration control means (101) sets the deceleration amount when the engine speed is lower than the lower limit speed which can be set even though the rotation speed change amount is positive. The vehicle speed control apparatus according to claim 2, wherein the deceleration control means (101) sets the deceleration amount to zero when the rotational speed change amount is positive. 2. The vehicle speed control apparatus according to claim 1, wherein the set rotation speed is set to an average engine rotation speed during mowing operation of the work machine detected by the rotation speed detection means. 2. The deceleration control means (101) according to claim 1, wherein the deceleration control means (101) is configured to store in advance the deceleration amount, which is fuzzy inferred using the change amount and the deviation, in the deceleration control means, and obtain a deceleration amount based on the stored value. Vehicle speed control device characterized in that. 2. The engine speed detected by the rotation speed detecting means S1 and the preset cutting speed, while the cutting operation state detecting means S0 detects the cutting operation state. A vehicle speed control means 100 for operating the transmission mechanisms 14 and 15 on the speed increasing side or the deceleration side is provided so that the difference is small, and the deceleration control means 101 has a set speed higher than the rotation speed of the mowing operation. And the vehicle speed control apparatus so as to be the set rotation speed. The vehicle speed control apparatus according to claim 8, wherein the set amount is substantially equal to an engine speed lowered by a mowing operation of the mowing machine.