JP2009029424A - Vehicle speed control apparatus of working vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vehicle speed control apparatus of a working vehicle for preventing sudden acceleration when a vehicle speed moves from a state of not reaching to a target speed, due to a heavy load, to a state of releasing the load, and reducing a resultant shock and eliminating uncomfortable operational feeling. <P>SOLUTION: The apparatus comprises an operation variable detecting means for detecting operation variable of accelerator means of the working vehicle, an actual vehicle speed detecting means for detecting an actual vehicle speed of the working vehicle, a measuring means for measuring a load of the working vehicle, and a controller for performing a first control for controlling the vehicle speed so that a difference between the target vehicle speed and the actual vehicle speed of the working vehicle becomes zero according to a load measured by the measuring means after setting the target vehicle speed corresponding to the operation variable detected by the operation variable detecting means, or a second control for controlling the vehicle speed of the working vehicle so that the difference between a corrected target vehicle speed and the actual vehicle speed becomes zero after correcting the target vehicle speed to a low value corresponding to the actual vehicle speed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an apparatus for controlling the vehicle speed of a work vehicle such as a forklift.

  The configuration of the forklift is schematically shown in FIG.

  As shown in FIG. 1, in the forklift 100, the output of the engine 1 is transmitted to the drive wheels 5 through the torque converter 2, the transmission (traveling clutch) 3, the universal joint 21, and the differential gear 4. On the other hand, the output of the engine 1 is transmitted to the work machine 9 via the hydraulic pump 6, the operation valve 7, and the hydraulic cylinder 8. The travel clutch 3 is a hydraulic clutch, and includes a forward clutch 3F and a reverse clutch 3R.

  The accelerator pedal (drive pedal) 10 is operated by an operator, an operation amount (stroke amount) S is detected by a stroke sensor 10 a provided in the accelerator pedal 10, and a signal indicating the operation amount S is input to the controller 30. .

  An actual vehicle speed detection sensor 11 that detects the actual vehicle speed vr of the forklift 100 is provided on the output shaft of the transmission 3. A signal indicating the actual vehicle speed detected by the actual vehicle speed detection sensor 11 is input to the controller 30.

  The work machine operation lever 12 is operated by an operator, the valve position of the operation valve 7 changes according to the operation amount, and the pressure oil at a flow rate corresponding to the operation amount is passed from the hydraulic pump 6 via the operation valve 7. It is supplied to the hydraulic cylinder 8. An operation amount (stroke amount) W is detected by a stroke sensor 12 a provided on the work implement operating lever 12, and a signal indicating the operation amount W of the work implement operating lever 12 is input to the controller 30.

  Further, the drive wheel 5 is provided with a hydraulic brake 13 for braking the drive wheel 5. The hydraulic brake 13 can be manually operated, but is controlled by the controller 30 to adjust the braking force as will be described later.

  As shown in FIG. 2, the controller 30 is set with a target vehicle speed Vp corresponding to the operation amount S output from the stroke sensor 10a of the accelerator pedal 10, and the controller 30 determines the target vehicle speed Vp and the actual vehicle speed. The vehicle speed is controlled so that the deviation from the actual vehicle speed vr detected by the detection sensor 11 becomes zero. Specifically, the vehicle speed is adjusted to the target vehicle speed by controlling the degree of engagement of the traveling clutch 3, the braking force of the hydraulic brake 12, and the rotational speed of the engine 1.

  The forward clutch 3F, the reverse clutch 3R, and the hydraulic brake 13 are respectively provided with control valves 14, 15, and 16. The clutch pressure of the forward clutch 3F changes according to the control electric signal applied to the control valve 14, and the degree of engagement of the forward clutch 3F changes. Similarly, the clutch pressure of the reverse clutch 3R changes according to the control electric signal applied to the control valve 15, and the degree of engagement of the reverse clutch 3R changes. Further, the brake pressure of the hydraulic brake 13 changes according to the control electric signal applied to the control valve 16, and the braking force of the hydraulic brake 13 changes.

  In addition, a target vehicle speed corresponding to the operation amount S of the accelerator pedal 10 is set in the controller 30, and a target rotational speed NEp2 of the engine 1 corresponding to the operation amount W of the work machine operation lever 12 is set. Yes. Note that if the target vehicle speed corresponding to the accelerator pedal operation amount S is not reached only by adjusting the degree of clutch engagement and the hydraulic brake braking force, which will be described later, control for increasing the engine target speed is performed. In order to perform this control, the engine target speed NEp1 is obtained by calculation from the feedback amount. In this case, the larger engine target speed NEp is selected from the two engine target speeds NEp1 and NEp2, and a control signal for setting the engine target speed NEp is output to the throttle actuator 17. The actual engine speed Nr of the engine 1 is detected by the engine speed sensor 20 and input to the controller 30. The controller 30 controls the throttle actuator 17 so that the target rotational speed NEp is obtained using the actual rotational speed Nr of the engine 1 as a feedback amount.

  The controller 30 applies a control signal to the electromagnetic solenoids of the control valves 14, 15, and 16 to control the degree of engagement of the forward clutch 3 </ b> F and the reverse clutch 3 </ b> R and the braking force of the hydraulic brake 13. As described above, the controller 30 controls the rotational speed of the engine 1, the traveling clutch 3, and the hydraulic brake 13 to adjust the vehicle speed to the target vehicle speed.

In the following Patent Document 1, a target vehicle speed corresponding to the operation amount output from the accelerator pedal 10 is set by the controller 30 as described above, and the target vehicle speed and the actual vehicle speed detected by the actual vehicle speed detection sensor 11 are set. Describes a technique for controlling the vehicle speed so that the deviation from the above becomes zero.
Japanese Patent No. 2811523

  However, even if the target vehicle speed Vp is set according to the operation amount S of the accelerator pedal 10 as described above, if the driving torque (running resistance) is large, the actual vehicle speed vr will be the target vehicle speed even if it takes a long time. Vp may not be reached.

  That is, when the vehicle turns while the steering wheel is fully turned, the driving torque (running resistance) increases, and the actual vehicle speed vr may not reach the target vehicle speed Vp even after a long time.

  In addition, as shown in FIG. 1, the forklift 100 uses the output of one engine 1 for both traveling (drive wheels 5) and work (work machine 9). The time until the actual vehicle speed vr reaches the target vehicle speed Vp depends on how much is spent, that is, depending on the size of the work machine load. For this reason, when the work machine load is large, the actual vehicle speed vr may not reach the target vehicle speed Vp even if it takes a long time.

  That is, when the work machine 9 lifts a heavy load, the load applied to the work machine 9 is large and much of the output of the engine 1 is used for work (work machine 9). As a result, the engine output to 5) decreases, and the actual vehicle speed vr may not reach the target vehicle speed Vp even after a long time.

  Hereinafter, a description will be given with reference to FIG.

  FIG. 4 shows the relationship between time t and vehicle speed. In FIG. 2, the thick solid line indicates the target vehicle speed Vp, and the broken line indicates the actual vehicle speed vr.

  If the operation amount S is increased by depressing the accelerator pedal 10 when the load (drive torque, work implement load) is large, the load increases with the target vehicle speed Vp up to a certain actual vehicle speed vr1. For this reason, the vehicle does not increase beyond the constant vehicle speed vr1 even if it elapses for a long time.

  When the load that has been applied from such a state is removed at time t1 (for example, when the vehicle shifts from turning to straight traveling or when the cargo handling operation is completed), the forklift 100 accelerates rapidly toward the target vehicle speed Vp. Resulting in.

  That is, when the load is large, the operator cannot step down the accelerator pedal 10 to the full stroke because the desired vehicle speed cannot be obtained. Therefore, when the load is large, the target vehicle speed increases, and the difference ΔV1 between the large target vehicle speed Vp1 and the actual vehicle speed vr1 increases. Therefore, when the load is removed, the forklift 100 suddenly accelerates toward the target vehicle speed Vp1 in order to fill the large deviation ΔV1. In FIG. 4, 61 indicates a speed change until the actual vehicle speed vr reaches the target vehicle speed Vp <b> 1 after sudden acceleration.

  The operator notices sudden acceleration and reduces the amount of depression of the accelerator pedal 10, but the forklift 100 suddenly accelerates in a short time until the target vehicle speed is reduced, and shocks the vehicle body and the operator itself. . In addition, the car body behaves against the operator's will, giving the operator a sense of discomfort.

  The present invention has been made in view of such a situation, and prevents sudden acceleration that occurs when the vehicle speed shifts from a state in which the vehicle speed does not reach the target vehicle speed to a state in which the load is released due to a large load, and a shock caused thereby. The problem to be solved is to reduce the amount of noise and to eliminate the uncomfortable feeling of operation.

The first invention is
A vehicle speed control device for a work vehicle that transmits engine output to a drive wheel via a travel clutch and transmits engine output to a work machine,
An operation amount detecting means for detecting an operation amount of the accelerator means of the work vehicle;
An actual vehicle speed detecting means for detecting an actual vehicle speed of the work vehicle;
Measuring means for measuring the load of the work vehicle;
The target vehicle speed corresponding to the operation amount detected by the operation amount detection means is set, and the work detected by the target vehicle speed and the actual vehicle speed detection means according to the load measured by the measurement means The first control for controlling the vehicle speed of the work vehicle or the target vehicle speed is corrected to a low value corresponding to the actual vehicle speed so that the deviation from the actual vehicle speed of the vehicle becomes zero, and the corrected corrected target vehicle speed and And a controller for performing second control for controlling the vehicle speed of the work vehicle so that a deviation from the actual vehicle speed becomes zero.

Further, the second invention is the first invention,
The measuring means includes
Drive torque measuring means for measuring drive torque transmitted to the drive wheels of the work vehicle;
The controller is
When the driving torque measured by the driving torque measuring means is lower than a set value, the first control is performed,
The second control is performed when the driving torque is equal to or greater than the set value.

Further, the third invention is the first invention,
The measuring means includes
Further comprising work implement load measuring means for measuring a load applied to the work implement of the work vehicle;
The controller is
When the work implement load measured by the work implement load measuring means is lower than a set value, the first control is performed,
When the work machine load is equal to or greater than the set value, the second control is performed.

  In the first invention, the second invention, and the third invention, for example, the load (drive torque τt) measured by the measurement means (drive torque measurement means) exceeds the drive torque set value line A shown in FIG. If it is, that is, if it enters the region indicated by the oblique line above the drive torque set value line A in FIG. 8, the first control is shifted to the second control.

  For example, when the load (worker load τh) measured by the measuring unit (worker load measuring unit) is large, most of the output (power) of the engine 1 is absorbed by the hydraulic pump 6 and the engine 1 The number of rotations decreases (is difficult to increase). For this reason, the rotational speed of the engine 1 does not reach the target rotational speed NEp.

  Therefore, for example, a predetermined value β is set as a threshold value for determining that the work implement load τh has increased, and the engine speed Nr detected by the engine speed detection sensor 20 is greater than the target speed NEp. If the rotational speed NEp-β is not increased by a predetermined value β, it is determined that the work implement load τh is large. When it is determined that the work machine load τh is large, the process shifts from the first control to the second control.

The fourth invention is the first invention, the second invention, the third invention,
The controller is
When the actual vehicle speed of the work vehicle reaches the corrected target vehicle speed, the second control is terminated, and the work vehicle is made to reach the target vehicle speed at a speed change rate of a certain level or less. It is characterized by controlling the vehicle speed.

  In the fourth invention, similarly to the target speed change rate 71 shown in FIG. 3B, the target speed change rate is limited from the second control end time t15.

  That is, in FIG. 5, when the load is released at time t14, the actual speed vr increases with the speed change indicated by 53 and reaches the target vehicle speed Vp1 (time t15). As a result, the deviation ΔV between the target vehicle speed Vp and the actual vehicle speed vr becomes smaller than the threshold value ΔVth, and thus the second control is terminated. Thereafter, the speed change rate of the actual speed vr is limited to the target speed change rate 52, and the actual vehicle speed vr increases. The actual speed vr increases at a gradual speed change rate that does not exceed the target speed change rate 52, as shown as a speed change 54. Thereafter, the first control is executed as usual.

The fifth invention is the second invention,
The controller is
When the driving torque changes from the set value or more to a state lower than the set value, the second control is terminated and the actual vehicle speed is made to reach the target vehicle speed at a speed change rate of a certain level or less. Further, the vehicle speed of the work vehicle is controlled.

A sixth invention is the third invention,
The controller is
When the work machine load changes from the set value or more to a state lower than the set value, the second control is terminated and the actual vehicle speed is made to reach the target vehicle speed at a speed change rate of a certain level or less. Thus, the vehicle speed of the work vehicle is controlled.

  In the first invention, the second invention, and the third invention, when the load is large, the target speed Vp1 is corrected to a speed (Vp2 = vr1 + α) corresponding to the actual speed vr1, but this processing is not necessarily performed. However, it is only necessary that the increase in the vehicle speed can be moderated when the load is released from the state where the load is increased and the load is reduced.

  The fifth and sixth inventions will be described with reference to FIG.

  In the fifth and sixth inventions, as in the first, second and third inventions described above, the load (drive torque τt or work implement load τh) is measured by each measuring means, and this measurement is performed. Based on the load τt (or τh), it is determined that the load has dropped from the state in which the load has increased and the load has decreased.

  As shown in FIG. 12, based on the measured load τt (or τh), when it is determined at time t18 that the load has been removed from the increased load state and the load has decreased, the same as in FIG. Thus, the actual speed vr is increased by being limited to the target speed change rate 52 having a gentle slope below a certain level.

  According to 1st invention, 2nd invention, and 3rd invention, compared with a prior art, when a big load is applied, the speed change when a load comes off from the state where a vehicle speed does not reach a target vehicle speed is a small thing Therefore, the shock given to the vehicle body and the operator can be reduced, and the uncomfortable feeling of operation can be removed.

  Further, according to the fourth, fifth, and sixth inventions, when a large load is applied, a speed change when the load is released from a state where the vehicle speed does not reach the target vehicle speed can be gradually increased. Therefore, the shock given to the vehicle body and the operator can be reduced, and the uncomfortable feeling of operation can be removed.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a configuration of a forklift 100 according to an embodiment.

  As shown in FIG. 1, in the forklift 100, the output of the engine 1 is transmitted to the drive wheels 5 via the torque converter 2, the transmission (traveling clutch) 3, the universal joint 21, and the differential gear 4. On the other hand, the output of the engine 1 is transmitted to the work machine 9 via the hydraulic pump 6, the operation valve 7, and the hydraulic cylinder 8. The traveling clutch 3 is a hydraulic clutch, and includes a forward clutch 3F and a reverse clutch 3R.

  An accelerator pedal (drive pedal) 10 as an accelerator means is operated by an operator, an operation amount (stroke amount) S is detected by a stroke sensor 10 a provided in the accelerator pedal 10, and a signal indicating the operation amount S is a controller 30. Is input.

  An actual vehicle speed detection sensor 11 that detects the actual vehicle speed vr of the forklift 100 is provided on the output shaft of the transmission 3. A signal indicating the actual vehicle speed detected by the actual vehicle speed detection sensor 11 is input to the controller 30.

  The work machine operation lever 12 is operated by an operator, the valve position of the operation valve 7 changes according to the operation amount, and the pressure oil at a flow rate corresponding to the operation amount is passed from the hydraulic pump 6 via the operation valve 7. It is supplied to the hydraulic cylinder 8. An operation amount (stroke amount) W is detected by a stroke sensor 12 a provided on the work implement operating lever 12, and a signal indicating the operation amount W of the work implement operating lever 12 is input to the controller 30.

  Further, the drive wheel 5 is provided with a hydraulic brake 13 for braking the drive wheel 5. The hydraulic brake 13 can be manually operated, but is controlled by the controller 30 to adjust the braking force as will be described later.

  As shown in FIG. 2, the controller 30 is set with a target vehicle speed Vp corresponding to the operation amount S output from the stroke sensor 10a of the accelerator pedal 10, and the controller 30 determines the target vehicle speed Vp and the actual vehicle speed. The vehicle speed is controlled so that the deviation from the actual vehicle speed vr detected by the detection sensor 11 becomes zero. Specifically, the vehicle speed is adjusted to the target vehicle speed by controlling the degree of engagement of the traveling clutch 3, the braking force of the hydraulic brake 12, and the rotational speed of the engine 1.

  The forward clutch 3F, the reverse clutch 3R, and the hydraulic brake 13 are respectively provided with control valves 14, 15, and 16. The clutch pressure of the forward clutch 3F changes according to the control electric signal applied to the control valve 14, and the degree of engagement of the forward clutch 3F changes. Similarly, the clutch pressure of the reverse clutch 3R changes according to the control electric signal applied to the control valve 15, and the degree of engagement of the reverse clutch 3R changes. Further, the brake pressure of the hydraulic brake 13 changes according to the control electric signal applied to the control valve 16, and the braking force of the hydraulic brake 13 changes.

  In addition, a target vehicle speed corresponding to the operation amount S of the accelerator pedal 10 is set in the controller 30, and a target rotational speed NEp2 of the engine 1 corresponding to the operation amount W of the work machine operation lever 12 is set. Yes. If the target vehicle speed corresponding to the accelerator pedal operation amount S is not reached only by adjusting the clutch engagement degree and the hydraulic brake braking force, control for increasing the engine target rotational speed is performed. In order to perform this control, the engine target speed NEp1 is obtained by calculation from the feedback amount. In this case, the larger engine target speed NEp is selected from the two engine target speeds NEp1 and NEp2, and a control signal for setting the engine target speed NEp is output to the throttle actuator 17. The actual engine speed Nr of the engine 1 is detected by the engine speed sensor 20 and input to the controller 30. The controller 30 controls the throttle actuator 17 so that the target rotational speed NEp is obtained using the actual rotational speed Nr of the engine 1 as a feedback amount.

  The controller 30 applies a control signal to the electromagnetic solenoids of the control valves 14, 15, and 16 to control the degree of engagement of the forward clutch 3 </ b> F and the reverse clutch 3 </ b> R and the braking force of the hydraulic brake 13. As described above, the controller 30 controls the rotational speed of the engine 1, the traveling clutch 3, and the hydraulic brake 13 to adjust the vehicle speed to the target vehicle speed.

  In FIG. 1, the illustration of the traveling direction switching lever for switching the engagement of the forward clutch 3F and the reverse clutch 3R is omitted because it is not related to the present invention.

  FIG. 3A shows a change over time of the operation amount S when the accelerator pedal 10 is depressed from the operation amount zero and reaches the maximum operation amount and then is returned to the operation amount zero. FIG. 3B shows a change over time in the target vehicle speed Vp in correspondence with the accelerator pedal operation amount S shown in FIG.

  As shown in FIG. 3, when the accelerator pedal 10 is depressed from zero, the speed change rate of the actual speed vr is limited to the upper limit value (acceleration upper limit value) 71 of the target speed change rate. The actual speed vr increases at an acceleration that does not exceed the target speed change rate 71. Similarly, when the accelerator pedal 10 is returned to zero, the speed change rate of the actual speed v is limited to the upper limit value (deceleration upper limit value) 72 of the target speed change rate. The actual speed vp decreases with a deceleration that does not exceed the speed change rate 72.

  The target speed change rates 71 and 72 can be set, for example, on the operation panel 22 shown in FIG. 1, and can be adjusted to various sizes as indicated by arrows in FIG.

(First embodiment)
FIG. 5 is a diagram for explaining the control contents of the first embodiment.

  FIG. 5 shows the relationship between the time t and the vehicle speed, as in FIG. 4. The thick solid line shows the target vehicle speed Vp, and the broken line shows the actual vehicle speed vr.

  The controller 30 reads the target vehicle speed Vp corresponding to the operation amount S output from the stroke sensor 10 a from the setting contents of FIG. 2, and calculates the target vehicle speed Vp and the actual vehicle speed vr detected by the actual vehicle speed detection sensor 11. When the actual vehicle speed vr does not reach the target vehicle speed Vp for a predetermined time T1 or longer as a result of the execution of the first control for controlling the vehicle speed and the first control so that the deviation becomes zero, the target vehicle speed Vp is A second control for correcting the vehicle speed so that the deviation between the corrected target vehicle speed vr + α and the actual vehicle speed vr detected by the actual vehicle speed detection sensor 11 becomes zero. And do.

  In FIG. 5, the first control is performed until time t13, and the second control is performed from time t13 to time t15.

  That is, even if the load (drive torque, work implement load) is large, if the accelerator pedal 10 is depressed from the stop state where the vehicle speed is zero to a certain vehicle speed vr1 (time t11), the actual vehicle speed vr will be the target. It rises following the vehicle speed Vp. The speed change 51 of the target speed at this time is limited to the speed change rate 71 described with reference to FIG.

  However, since the load is large, the vehicle does not increase beyond the constant vehicle speed vr1 even after a long time.

  Therefore, the controller 30 determines that the time during which the deviation between the target vehicle speed Vp and the actual vehicle speed vr is equal to or greater than a predetermined level (threshold value) ΔVth is equal to or greater than a predetermined time (threshold value) T1 (predetermined time T1). The first control is terminated and the second control is shifted to the second control.

  In FIG. 5, at the time t13 when the time during which the deviation ΔV1 between the target vehicle speed Vp1 and the actual vehicle speed vr1 is equal to or greater than the threshold value ΔVth reaches the threshold value T1, the first control is terminated and the second control is performed. To migrate.

  In the second control, the target vehicle speed Vp1 is corrected to a low value corresponding to the current actual vehicle speed vr1. Specifically, the vehicle speed vr1 + α, which is a vehicle speed obtained by adding a predetermined increment α to the current actual vehicle speed vr1 and lower than the original target vehicle speed Vp1 at the first control end time t13, is corrected to the corrected target vehicle speed Vp2 (<Vp1 ). Then, the vehicle speed is controlled so that the deviation between the corrected target vehicle speed Vp2 (= vr1 + α <Vp1) and the actual vehicle speed vr becomes zero.

  For this reason, when the load that has been applied until then is removed at time t14 (for example, when the vehicle shifts from turning to straight traveling or when the cargo handling operation ends), the forklift 100 accelerates toward the target vehicle speed Vp2. A speed change until the actual vehicle speed reaches the target vehicle speed Vp1 by acceleration is indicated by 53.

  Here, it compares with FIG. 4 of a prior art.

  In the case of the prior art (FIG. 4), since the target vehicle speed Vp1 itself is large and the load is released in the state where the deviation ΔV1 between the target vehicle speed Vp1 and the actual vehicle speed vr1 is large, acceleration is performed to fill this large deviation ΔV1. The speed change 61 is large.

  On the other hand, in the embodiment of FIG. 5, the corrected target vehicle speed Vp2 is smaller than the original target vehicle speed Vp1, and the load is reduced in a state where the deviation ΔV2 (<ΔV1) between the corrected target vehicle speed Vp2 and the actual vehicle speed vr1 is small. Therefore, the speed change 53 is small when accelerating to fill this small deviation ΔV2.

  When the load is removed as described above, the actual vehicle speed vr reaches the target vehicle speed Vp at time t15, and the deviation ΔV between the target vehicle speed Vp and the actual vehicle speed vr becomes smaller than the threshold value ΔVth. For this reason, 2nd control is complete | finished and it transfers to 1st control after that.

  As described above, according to the present embodiment, the speed change when the load is released is small compared to the conventional technique, so that the shock given to the vehicle body and the operator can be reduced, and the uncomfortable feeling of operation is eliminated. Can do.

(Second embodiment)
When the second control is completed, the target speed change rate is limited to a gradual target speed change rate 52 that is a certain level or less, and the actual speed vr is gradually increased to shift to the first control. Good.

  The second embodiment will be described below with reference to FIG. In the second embodiment, the control content up to time t15 when the second control ends is the same, and therefore the description thereof will be omitted as appropriate.

In the second embodiment, similarly to the target speed change rate 71 shown in FIG. 3B, the target speed change rate is limited from the second control end time t15.

  That is, when the load is removed at time t14, the actual speed vr increases with the speed change indicated by 53 and reaches the target vehicle speed Vp1 (time t15). As a result, the deviation ΔV between the target vehicle speed Vp and the actual vehicle speed vr becomes smaller than the threshold value ΔVth, and thus the second control is terminated. Thereafter, the speed change rate of the actual speed vr is limited to the target speed change rate 52, and the actual vehicle speed vr increases. The actual speed vr increases at a gradual speed change rate that does not exceed the target speed change rate 52, as shown as a speed change 54. Thereafter, the first control is executed as usual.

  As a result, according to the present embodiment, it is possible to further reduce the shock given to the vehicle body and the operator when the load is released, and to further reduce the uncomfortable feeling of operation.

  In this embodiment, after the end of the second control, as shown at 54, the vehicle speed gradually increases over time, so that there is an advantage that there is a margin for returning the accelerator pedal 10 during this time.

(Third embodiment)
In the first and second embodiments described above, at the time t13 when the time when the deviation ΔV1 between the target vehicle speed Vp1 and the actual vehicle speed vr1 is equal to or greater than the threshold value ΔVth reaches the threshold value T1, 1 is terminated and the control is shifted to the second control (FIG. 5). As shown in FIG. 6, the time during which the actual vehicle speed vr does not reach the target speed Vp is simply set to the threshold value T2. When the time is reached, the first control may be terminated and the second control may be started.

  FIG. 6 shows this third embodiment.

  As shown in FIG. 6, when the load (drive torque, work implement load) is large, the actual vehicle speed vr rises slowly, and the inclination of the actual vehicle speed change 55 is gentle relative to the inclination of the target speed change 51. The actual vehicle speed vr does not reach the target vehicle speed Vp even after a predetermined time (threshold) T2 has elapsed.

  Therefore, when the time during which the actual vehicle speed vr does not reach the target vehicle speed Vp is equal to or longer than the predetermined time (threshold value) T2 (when the predetermined time T2 is reached), the controller 30 ends the first control. Then, the process shifts to the second control.

  In the third embodiment of FIG. 6, at the time t16 when the time when the actual vehicle speed vr does not reach the target vehicle speed Vp reaches the threshold value T2, the first control is terminated and the control is shifted to the second control. The subsequent processing is the same as that described in the first embodiment or the second embodiment, and thus description thereof is omitted.

(Fourth embodiment)
In each of the above-described embodiments, when the load is released, the actual vehicle speed reaches the target vehicle speed, and the deviation ΔV between the target vehicle speed Vp and the actual vehicle speed vr becomes smaller than the threshold value ΔVth, the second control is terminated. Even if the load is released, the actual vehicle speed reaches the target vehicle speed, and the deviation ΔV between the target vehicle speed Vp and the actual vehicle speed vr becomes smaller than the threshold value ΔVth, the second control is performed. The control may be continued without ending.

  Hereinafter, the fourth embodiment will be described with reference to FIG. 6 used in the third embodiment.

  In FIG. 6, the load is released and the actual vehicle speed vr reaches the target vehicle speed Vp2 at time t17, and the deviation ΔV between the target vehicle speed Vp and the actual vehicle speed vr becomes smaller than the threshold value ΔVth. At this time, the operator often depresses the accelerator pedal 10 to the full stroke. For this reason, when the load is lost, the actual vehicle speed vp may increase against the operator's intention if the second control is terminated and the control is shifted to the first control.

  Therefore, in the fourth embodiment, as shown in FIG. 6, the actual vehicle speed vr reaches the target vehicle speed Vp2 at time t17, and the deviation ΔV between the target vehicle speed Vp and the actual vehicle speed vr is smaller than the threshold value ΔVth. Even if it becomes, the second control is continued without ending.

  The trigger for shifting from the second control to the first control may be applied when the actual speed does not increase significantly, for example, when the accelerator pedal 10 is returned by a predetermined amount.

  Further, as shown in FIG. 7, the second control is continued from time t17 when the actual vehicle speed vr reaches the target vehicle speed Vp2, and when the predetermined time T3 has passed (time t18), the second control is performed. You may make it complete | finish and make it transfer to 1st control. This is because when the predetermined time T3 elapses, the operator has a margin and the amount of depression of the accelerator pedal 10 can be suppressed.

  As described above, according to the fourth embodiment, since the second control is continuously performed, a margin for returning the accelerator pedal 10 is created, and the actual vehicle speed vr is not greatly increased, thereby further reducing the shock. And the feeling of discomfort in the operation feeling can be further removed.

(Fifth embodiment)
In each embodiment described above, when the actual vehicle speed vr does not reach the target vehicle speed Vp for a predetermined time or more, it is determined that the load (drive torque, work implement load) is large, and the first control to the second control are performed. However, it is also possible to directly measure the load, determine that the load is large from the measured value of the load, and shift from the first control to the second control.

  In the fifth embodiment, the drive torque τt (running resistance) transmitted to the drive wheel 5 is measured by the drive torque measuring means. Specifically, the rotational speed NE of the engine 1 and the rotational speed Ntc of the output shaft of the torque converter 2 are detected (the input / output shaft rotational speed of the torque converter 2 is detected), and the controller 30 detects these rotational speeds NE, Based on Ntc, the slip ratio of the torque converter 2 is obtained, and the drive torque τt is calculated from the slip ratio. Note that the rotational speed of the transmission / reception shaft of the transmission 3 may be detected, the degree of engagement of the speed change clutch 3 may be obtained thereby, and the drive torque τt may be calculated from the degree of engagement.

  On the other hand, as shown in FIG. 8, in the controller 30, a drive torque set value τt0 is set in advance corresponding to the magnitude of the target vehicle speed Vp. This drive torque set value τt0 corresponds to a threshold value for determining that the actual vehicle speed vr in FIGS. 4 and 6 does not reach the target vehicle speed Vp even if the predetermined time T1 (or T2) has elapsed.

  The horizontal axis in FIG. 8 is the target vehicle speed Vp, and the vertical axis is the drive torque τt. A drive torque set value line A is set in which the drive torque set value τt0 increases as the target vehicle speed Vp increases. The drive torque τt calculated as described above exceeds the drive torque set value line A. In this case, that is, when entering the region indicated by the oblique line above the drive torque set value line A in FIG. 8, the first control is shifted to the second control.

  On the contrary, when the calculated drive torque τt is equal to or less than the drive torque set value line A, that is, when the drive torque set value line A in FIG. Control is transferred to the first control.

  When shifting from the second control to the first control, the shifting process described in the second and fourth embodiments may be performed.

  Further, instead of obtaining the driving torque τt by calculation, the driving torque τt may be directly detected by a sensor. Specifically, a torque sensor is provided on the output shaft of the torque converter 2, the output shaft of the transmission 3, etc., and the driving torque τt detected by this torque sensor exceeds the driving torque set value line A. In this case, that is, when entering the region indicated by the oblique line below the drive torque set value line A in FIG. 8, the first control is shifted to the second control. On the contrary, when the drive torque τt detected by the torque sensor is equal to or less than the drive torque set value line A, that is, when the drive torque set value line A in FIG. The second control is shifted to the first control.

(Sixth embodiment)
In the fifth embodiment described above, the drive torque τt is measured, and when the measured drive torque τt is large, the first control is shifted to the second control. The work implement load τh may be measured, and when the measured work implement load τh is large, the first control may be shifted to the second control.

  In the sixth embodiment, the driving torque τt (running resistance) transmitted to the driving wheel 5 is measured by the work implement load measuring means. Specifically, when the rotational speed NE of the engine 1 does not increase to the rotational speed NEp−β that is lower than the target rotational speed NEp by a predetermined value β, it is determined that the work implement load τh is large.

  FIG. 9 is a block diagram for explaining the processing contents for controlling the rotational speed of the engine 1 so that the target rotational speed NEp is obtained.

  As described above, the target vehicle speed corresponding to the operation amount S of the accelerator pedal 10 is set in the controller 30, and the target rotation speed NEp2 of the engine 1 corresponding to the operation amount W of the work machine operation lever 12 is set. Is set.

  If the target vehicle speed corresponding to the accelerator pedal operation amount S is not reached only by adjusting the clutch engagement degree and the hydraulic brake braking force, control for increasing the engine target speed is performed. In order to perform this control, the engine target speed NEp1 is obtained by calculation from the feedback amount.

  In the traveling target rotational speed setting unit 201 in FIG. 9, the feedback amount is obtained when the target vehicle speed corresponding to the accelerator pedal operation amount S is not reached only by adjusting the clutch engagement degree and the hydraulic brake braking force. From the above, the target rotational speed NEp1 of the engine 1 is set.

  On the other hand, in the work machine target rotation speed setting unit 202, the target rotation speed NEp2 of the engine 1 is set corresponding to the operation amount W of the work machine operation lever 12 (the valve opening of the operation valve 7). The work machine target rotational speed setting unit 202 is necessary to obtain a target operating speed corresponding to the operation amount W of the work machine operation lever 12 (the valve opening degree of the operation valve 7) with the hydraulic cylinder 8 (work machine 9). The correct engine speed is set. As the rotational speed of the engine 1 increases, the discharge flow rate of the hydraulic pump 6 increases, the flow rate of the pressure oil supplied to the hydraulic cylinder 8 via the operation valve 7 increases, and the hydraulic cylinder 8 (work machine 9) ) The operating speed increases.

  In the maximum value selection unit 203, the larger one of the target rotational speed NEp1 set by the traveling target rotational speed setting unit 201 and the target rotational speed NEp2 set by the work implement target rotational speed setting unit 202. Select (Maximum).

  The engine speed control unit 204 sets the target rotation speed maximum value selected by the maximum value selection unit 203 as the target rotation speed NEp of the engine 1, and sends a control signal to the throttle actuator 17 for setting the target rotation speed NEp. Output. The throttle actuator 17 operates the throttle of the engine 1 to adjust the rotational speed of the engine 1 to the target rotational speed NEp.

  However, when the work machine load τh is large, most of the output (power) of the engine 1 is absorbed by the hydraulic pump 6 and the rotational speed of the engine 1 is reduced (not easily increased). For this reason, the rotational speed of the engine 1 does not reach the target rotational speed NEp.

  Therefore, a predetermined value β is set as a threshold value for determining that the work implement load τh is increased, and the engine speed Nr detected by the engine speed detection sensor 20 is set to be higher than the target speed NEp. When the rotational speed NEp-β does not increase by the value β, it is determined that the work implement load τh is large. When it is determined that the work machine load τh is large, the process shifts from the first control to the second control.

  On the other hand, when the actual engine speed Nr rises above the speed NEp-β, it is determined that the work implement load τh is small, and the second control is shifted to the first control.

  When shifting from the second control to the first control, the shifting process described in the second and fourth embodiments may be performed.

  Further, as described above, instead of determining the work implement load τh based on the degree of increase in the engine speed, the work implement load τh may be directly detected by a sensor. Specifically, a hydraulic pressure sensor that detects the pump discharge pressure P is provided at the discharge port of the hydraulic pump 6, and when the pump discharge pressure P detected by the hydraulic pressure sensor is equal to or higher than a set value, the work machine load τh Is determined to be large. When the pump discharge pressure P detected by the hydraulic sensor is equal to or higher than the set value, it is determined that the work implement load τh is large, and the first control is shifted to the second control.

  Conversely, when the detected pump discharge pressure P is smaller than the set value, it is determined that the work implement load τh is small, and the second control is shifted to the first control. The set value of the pump discharge pressure P can be set to a value set as a set relief pressure of the relief valve by providing a relief valve at the discharge port of the hydraulic pump 6.

(Seventh embodiment)
In the second embodiment described above, when shifting from the second control to the first control, the actual vehicle speed vr is increased and limited to the target speed change rate 52 having a gentle slope below a certain level. However, the target speed change rate 52 in this case may be a target speed change rate 56 having a constant slope as shown in FIG. 10 (a), and the slope gradually decreases as shown in FIG. 10 (b). The target speed change rate 57 may be used.

  Also, as shown in FIG. 11, during the first control, a target speed change rate (inclination) 51 at the time of acceleration is stored, and the target speed increases and changes at the same speed change rate as the stored inclination 51. As described above, the target speed change rate 52 (inclination) when shifting from the second control to the first control may be set.

(Eighth embodiment)
In each of the embodiments described above, when the load is large, the target speed Vp1 is corrected to a speed (Vp2 = vr1 + α) corresponding to the actual speed vr1, but this process is not necessarily performed and the load is large. It is only necessary that the increase in vehicle speed can be moderated at the time when the load is released and the load is reduced from this state.

  The eighth embodiment will be described with reference to FIG.

  In the eighth embodiment, similarly to the fifth embodiment or the sixth embodiment described above, the drive torque τt or the work implement load τh is measured by the drive torque measurement means or the work implement load measurement means, Based on the measured load τt (or τh), it is determined that the load has dropped from a state where the load has increased and the load has decreased.

  As shown in FIG. 12, based on the measured load τt (or τh), when it is determined at time t18 that the load has been removed from the increased load state and the load has decreased, the same as in FIG. Thus, the actual speed vr is increased by being limited to the target speed change rate 52 having a gentle slope below a certain level.

  Thus, according to the present embodiment, at least the speed change when the load is released can be gently increased, so that the shock given to the vehicle body and the operator can be reduced, and the uncomfortable feeling of operation can be eliminated.

  In the above description, the engine speed is controlled by the throttle actuator 17, but the presence of the throttle actuator 17 is not necessarily required, and the electronic control engine may be used and the throttle actuator 17 may not be present. Good.

  The present invention is not limited to a forklift, and can be applied to any work vehicle equipped with a work machine that has a target vehicle speed set according to the operation amount and performs vehicle speed control. it can.

FIG. 1 is a diagram illustrating a configuration of a forlift according to an embodiment. FIG. 2 is a diagram showing the relationship between the accelerator pedal operation amount and the target vehicle speed. FIG. 3A illustrates the time variation of the operation amount of the accelerator pedal, and FIG. 3B illustrates the time variation of the target vehicle speed corresponding to FIG. 3A. FIG. 4 is a diagram showing the relationship between time and vehicle speed in the prior art. FIG. 5 is a diagram used to explain the first embodiment or the second embodiment, and shows the relationship between time and vehicle speed. FIG. 6 is a diagram used for explaining the third embodiment or the fourth embodiment, and shows the relationship between time and vehicle speed. FIG. 7 is a diagram used to explain the fourth embodiment, and shows the relationship between time and vehicle speed. FIG. 8 is a diagram used for explaining the fifth embodiment, and shows the relationship between the target vehicle speed and the drive torque. FIG. 9 is a diagram used for explaining the sixth embodiment and is a block diagram showing the processing contents for controlling the engine speed. FIGS. 10A and 10B are diagrams used to explain the seventh embodiment, and show the relationship between time and vehicle speed. FIG. 11 is a diagram used to explain the seventh embodiment and shows the relationship between time and vehicle speed. FIG. 12 is a diagram used to explain the eighth embodiment and shows the relationship between time and vehicle speed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 3 Transmission (traveling clutch) 5 Drive wheel 9 Working machine 10 Accelerator pedal (drive pedal) 10a Stroke sensor 11 Actual vehicle speed detection sensor 30 Controller

Claims (6)

A vehicle speed control device for a work vehicle that transmits engine output to a drive wheel via a travel clutch and transmits engine output to a work machine,
An operation amount detecting means for detecting an operation amount of the accelerator means of the work vehicle;
An actual vehicle speed detecting means for detecting an actual vehicle speed of the work vehicle;
Measuring means for measuring the load of the work vehicle;
The target vehicle speed corresponding to the operation amount detected by the operation amount detection means is set, and the work detected by the target vehicle speed and the actual vehicle speed detection means according to the load measured by the measurement means The first control for controlling the vehicle speed of the work vehicle or the target vehicle speed is corrected to a low value corresponding to the actual vehicle speed so that the deviation from the actual vehicle speed of the vehicle becomes zero, and the corrected corrected target vehicle speed and A vehicle speed control device for a work vehicle, comprising: a controller that performs a second control for controlling a vehicle speed of the work vehicle so that a deviation from the actual vehicle speed becomes zero. The measuring means includes
Drive torque measuring means for measuring drive torque transmitted to the drive wheels of the work vehicle;
The controller is
When the driving torque measured by the driving torque measuring means is lower than a set value, the first control is performed,
The vehicle speed control device for a work vehicle according to claim 1, wherein the second control is performed when the driving torque is equal to or greater than the set value. The measuring means includes
It further comprises work implement load measuring means for measuring a load applied to the work implement of the work vehicle, and the controller includes:
When the work implement load measured by the work implement load measuring means is lower than a set value, the first control is performed,
The vehicle speed control device for a work vehicle according to claim 1, wherein the second control is performed when the work implement load is equal to or greater than the set value. The controller is
When the actual vehicle speed of the work vehicle reaches the corrected target vehicle speed, the second control is terminated, and the work vehicle is made to reach the target vehicle speed at a speed change rate of a certain level or less. The vehicle speed control device for a work vehicle according to claim 1, wherein the vehicle speed of the vehicle is controlled. The controller is
When the driving torque changes from the set value or more to a state lower than the set value, the second control is terminated and the actual vehicle speed is made to reach the target vehicle speed at a speed change rate of a certain level or less. The vehicle speed control device for a work vehicle according to claim 2, further comprising: controlling a vehicle speed of the work vehicle. The controller is
When the work machine load changes from the set value or more to a state lower than the set value, the second control is terminated and the actual vehicle speed is made to reach the target vehicle speed at a speed change rate of a certain level or less. The vehicle speed control device for a work vehicle according to claim 3, wherein the vehicle speed of the work vehicle is controlled as described above.

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