Apparatus and method for limiting vehicle speed of a working vehicle

• US 6,052,644 A
• Filed: 06/26/1997
• Issued: 04/18/2000
• Est. Priority Date: 12/27/1994
• Status: Expired due to Term

• Current Assignee: Komatsu Ltd.
• Original Assignee: Komatsu Ltd.
• Inventors: Sato, Susumu, Murakami, Takanobu, Hasegawa, Nobuki
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): PIPALA, EDWARD J
• Application Number:
  US08/860,258
• Time in Patent Office: 1,027 Days
• Field of Search: 701/1, 701/29, 701/36, 701/70, 701/93, 701/94, 701/97, 701/99, 180/170, 180/171, 180/178, 180/179, 123/319, 123/342, 123/349, 123/350, 123/351, 123/352, 123/361
• US Class Current: 701/93
• CPC Class Codes: B60K 2031/0091 Speed limiters or speed cutters
• CPC Class Codes: B60K 31/0058 responsive to externally generated signalling
• CPC Class Codes: B60K 31/047 the memory being digital
• CPC Class Codes: B60K 31/18 including a device to audibly, visibly, or otherwise signal the existence of unusual or unintended speed to the driver of the vehicle devices primarily intended for indicating speed to other traffic B60Q1/54
• CPC Class Codes: B60W 10/06 including control of combustion engines
• CPC Class Codes: B60W 10/11 Stepped gearings
• CPC Class Codes: B60W 10/18 including control of braking systems
• CPC Class Codes: B60W 2050/0022 Gains, weighting coefficients or weighting functions
• CPC Class Codes: B60W 2050/0057 Frequency analysis, spectral techniques or transforms
• CPC Class Codes: B60W 2520/105 Longitudinal acceleration
• CPC Class Codes: B60W 2540/10 Accelerator pedal position
• CPC Class Codes: B60W 2540/12 Brake pedal position
• CPC Class Codes: B60W 30/146 Speed limiting
• CPC Class Codes: B60Y 2200/41 Construction vehicles, e.g. graders, excavators
• CPC Class Codes: F16H 61/0213 characterised by the method for generating shift signals

Abstract

The present invention relates to an apparatus and a method for limiting the vehicle speed of a working vehicle which can provide a smooth traveling condition during vehicle speed limit, and which can set a vehicle speed limit suited to environmental conditions. To this end, a vehicle speed control device (10) judges a vehicle speed limit traveling period when a vehicle speed signal is equal to or greater than a vehicle speed limit value, to calculate a corrected depressing stroke signal by a control gain based on a deviation value between the vehicle speed signal and the vehicle speed limit value so that the deviation value becomes smaller to output to an engine control device (40), and judges an accelerated traveling period, when the vehicle speed signal is smaller than the vehicle speed limit value and the corrected depressing stroke signal is larger than a depressing stroke signal, to output the depressing stroke signal to the engine control device (40).

Claims

1. An apparatus suitable for limiting a vehicle speed of a working vehicle, wherein the working vehicle includes:

an accelerator pedal;

a depressing stroke detector, for detecting a depressing stroke amount of said accelerator pedal;

an engine control device, for outputting an accelerating signal based on a magnitude of a depressing stroke signal inputted from said depressing stroke detector; and

an engine, a speed of which is controlled by said accelerating signal;

said apparatus comprising;

a vehicle speed detector, for detecting a vehicle speed of the working vehicle to output a vehicle speed signal; and

a vehicle speed control device, connectable to said depressing stroke detector, said vehicle speed detector, and said engine control device, and having;

a vehicle speed limit control means,

an acceleration-deceleration/constant speed judging means, and

a control gain changing means;

wherein said vehicle speed limit control means;

inputs said vehicle speed signal and said depressing stroke signal to compare said vehicle speed signal with a predetermined vehicle speed limit value,

judges a vehicle speed limit traveling period, when said vehicle speed signal is equal to or greater than said predetermined vehicle speed limit value, to calculate a corrected depressing stroke signal by a control gain which obtains a correction amount of said depressing stroke signal, based on a deviation value between said vehicle speed signal and said predetermined vehicle speed limit value so that said deviation value becomes smaller, to output said corrected depressing stroke signal to said engine control device; and

wherein said acceleration-deceleration/constant speed judging means;

judges a stable vehicle speed period, when said deviation value in said vehicle speed limit traveling period is less than or equal to a predetermined value over a predetermined period of time, and

judges an acceleration-deceleration period, in a case other than said stable vehicle speed period, to output to said control gain changing means a result of a judgment by said acceleration-deceleration/constant speed judging means; and

wherein said control gain changing means outputs, to said vehicle speed limit control means, a control gain in said stable vehicle speed period or a control gain in said acceleration-deceleration period, based on the results of the judgment by said acceleration-deceleration/constant speed judging means.

2. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 1, further comprising:

a warning device for inputting a warning signal from said vehicle speed control device to give a warning to a driver,

wherein said vehicle speed control device outputs an accelerating stop signal such that said corrected depressing stroke signal is zero, and outputs said warning signal when said deviation value is not within a predetermined range of values even if said accelerating stop signal is continuously outputted for a predetermined period of time.

3. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 1 further comprising:

a control constant setting means having one of;

(a) a set value input means for setting in advance said vehicle speed limit value and said control gain as set values, and

(b) said set value input means and a set value display means for displaying said set values; and

wherein said control constant setting means and said vehicle speed control device mutually input and output set value information including said set values.

4. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 3, further comprising:

an environmental condition detecting means, for detecting a traveling situation of the working vehicle and an external environmental situation, to output a detected situation signal to said vehicle speed control device; and

wherein said vehicle speed control device inputs said predetermined vehicle speed limit value and said control gain, corresponding to said situation signal, from said control constant setting means, to calculate said corrected depressing stroke signal based on the inputted predetermined vehicle speed limit value and the inputted control gain.

5. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 1, further comprising:

a transmission having a plurality of speed stages;

a speed change control device, for inputting, in advance, downshift judging vehicle speed value data and upshift judging vehicle speed value data, for comparing the judging vehicle speed value data with current vehicle speed data to judge a possibility of a speed change of said speed stages, and for outputting a shifting signal to a corresponding speed stage to control said transmission when a speed change is possible; and

a brake control device, for outputting a brake control signal based on a braking signal to control a brake;

wherein said vehicle speed control device outputs an accelerating stop signal such that said corrected depressing stroke signal is zero, and outputs one of;

said downshift judging vehicle speed value data,

said upshift judging vehicle speed value data, or

said braking signal

when said deviation value is not within a predetermined range of values even if said accelerating stop signal is continuously outputted for a predetermined period of time.

6. An apparatus suitable for limiting a vehicle speed of a working vehicle, wherein the working vehicle includes:

an accelerator pedal;

a depressing stroke detector, for detecting a depressing stroke amount of said accelerator pedal;

an engine control device, for outputting an accelerating signal based on the magnitude of a depressing stroke signal inputted from said depressing stroke detector; and

an engine, a speed of which is controlled by said accelerating signal;

said apparatus comprising;

a vehicle speed detector, for detecting the vehicle speed of said working vehicle to output a vehicle speed signal; and

a vehicle speed control device, connected to said depressing stroke detector, said vehicle speed detector, and said engine control device;

wherein said vehicle speed control device;

inputs said vehicle speed signal and said depressing stroke signal to compare a predetermined vehicle speed threshold value, which is smaller than a vehicle speed limit value, with said vehicle speed signal,

judges a vehicle speed limit traveling period, when said vehicle speed signal is equal to or greater than said predetermined vehicle speed threshold value, to calculate a corrected depressing stroke signal, by a control gain which obtains a correction amount of said depressing stroke signal based on acceleration calculated from said vehicle speed signal and a deviation value between said vehicle speed signal and said predetermined vehicle speed limit value so that said deviation value becomes smaller, and to output said corrected depressing stroke signal to said engine control device, and

judges an accelerated traveling period, when said vehicle speed signal is smaller than said predetermined vehicle speed threshold value, to output said depressing stroke signal to said engine control device.

7. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 6, wherein said vehicle speed control device comprises:

an acceleration-deceleration/constant speed judging means, for;

judging a stable vehicle speed period, when said deviation value in said vehicle speed limit traveling period is less than or equal to a predetermined value over a predetermined period of time, and

judging an acceleration-deceleration period, in a case other than said stable vehicle speed period, to output a result of a judgment by said acceleration-deceleration/constant speed judging means;

a control gain changing means, for outputting said control gain in response to a result of the judgment by said acceleration-deceleration/constant speed judging means; and

a vehicle speed limit control means, for judging one of said vehicle speed limit traveling period and said accelerated traveling period to output to said engine control device one of said calculated corrected depressing stroke signal and said depressing stroke signal, in response to the thus judged one of said vehicle speed limit traveling period and said accelerated traveling period.

8. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 6, further comprising a warning device, for inputting a warning signal from said vehicle speed control device, to give a warning to a driver,

wherein said vehicle speed control device outputs an accelerating stop signal such that said corrected depressing stroke signal is zero, and outputs said warning signal when said deviation value is not within a predetermined range of values even if said accelerating stop signal is continuously outputted for a predetermined period of time.

9. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 6, further comprising:

a control constant setting means, having one of;

(a) a set value input means for setting, in advance, said predetermined vehicle speed limit value and said control gain as set values, and

(b) said set value input means and a set value display means for displaying said set values; and

wherein said control constant setting means and said vehicle speed control device mutually input and output set value information including said set values.

10. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 9, further comprising:

an environmental condition detecting means, for detecting a traveling situation of the working vehicle and an external environmental situation, to output a detected situation signal to said vehicle speed control device; and

wherein said vehicle speed control device inputs from said control constant setting means said vehicle speed limit value and said control gain corresponding to said detected situation signal, to calculate said corrected depressing stroke signal based on the inputted predetermined vehicle speed limit value and the inputted control gain.

11. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 6, further comprising:

a transmission having a plurality of speed stages;

a speed change control device, for inputting downshift judging vehicle speed value data and upshift judging vehicle speed value data in advance, for comparing the downshift judging vehicle speed data and the upshift judging vehicle speed data with the present vehicle speed data to judge a possibility of a speed change of said speed stages, and for outputting a shifting signal to a corresponding speed stage to control said transmission when a speed change is possible; and

a brake control device, for outputting a brake control signal based on a braking signal to control a brake;

wherein said vehicle speed control device outputs an accelerating stop signal such that said corrected depressing stroke signal is zero, and outputs one of;

said downshift judging vehicle speed value data,

said upshift judging vehicle speed value data, and

said braking signal

when said deviation value is not within a predetermined range of values even if said accelerating stop signal is continuously outputted for a predetermined period of time.

12. An apparatus suitable for limiting a vehicle speed of a working vehicle, wherein the working vehicle includes:

an accelerator pedal;

an accelerator lever, operated based on a depressing stroke amount of said accelerator pedal; and

an engine, a speed of which is controlled by said accelerator lever through a mechanical governor device;

said apparatus comprising;

a vehicle speed detector, for detecting a vehicle speed of the working vehicle;

a vehicle speed control device, for inputting a vehicle speed signal from said vehicle speed detector, and having;

a vehicle speed limit control means,

an acceleration-deceleration/constant speed judging means, and

a control gain changing means;

a driving device, for inputting a command signal from said vehicle speed control device; and

an actuator, driven by said driving device and correcting said depressing stroke amount to control said accelerator lever;

wherein said vehicle speed limit control means;

judges a vehicle speed limit traveling period, when said vehicle speed signal is equal to or greater than a predetermined vehicle speed limit value, to output to said driving device a command signal calculated by a control gain, based on a deviation value between said vehicle speed signal and said vehicle speed limit value or based on acceleration calculated by said vehicle speed signal and said deviation value, such that said deviation value becomes smaller, and

judges an accelerated traveling period, when said vehicle speed signal is smaller than said predetermined vehicle speed limit value and the calculated command signal is smaller than a predetermined initial value, to output a command of said predetermined initial value to said driving device;

wherein said acceleration-deceleration/constant speed judging means;

judges a stable vehicle speed period, when said deviation value in said vehicle speed limit traveling period is less than or equal to a predetermined value over a predetermined period of time, and

judges an acceleration-deceleration period, in a case other than said stable vehicle speed period, to output to said control gain changing means a result of a judgment by said acceleration-deceleration/constant speed judging means, and

wherein said control gain changing means outputs to said vehicle speed limit control means, a control gain in said stable vehicle speed period or a control gain in said acceleration-deceleration period, in response to a result of a judgment by said acceleration-deceleration/constant speed judging means.

13. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 12, further comprising:

a depressing stroke detector, for detecting said depressing stroke amount; and

an accelerator lever operating position detector, for detecting an operating position of said accelerator lever;

wherein said vehicle speed control device inputs said depressing stroke amount and said operating position, converts said operating position into the depressing stroke amount based on a mechanical location, and compares a converted depressing stroke amount with the inputted depressing stroke amount to conduct a fault diagnosis.

14. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 12, further comprising a depressing stroke detector, for detecting said depressing stroke amount;

wherein said vehicle speed control device calculates a correction of a position command signal for said actuator based on said control gain in response to said depressing stroke amount to output a corrected position command signal.

15. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 14, further comprising:

a warning device, for inputting a warning signal from said vehicle speed control device, to give a warning to a driver;

wherein said vehicle speed control device outputs said warning signal when said accelerator lever is placed in a total close position by said corrected position command signal and when said deviation value is not within a predetermined range of values even if the state of said total close position is continued for a predetermined period of time.

16. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 12, further comprising:

a control constant setting means, having one of;

(a) a set value input means, for setting in advance said predetermined vehicle speed limit value and said control gain as set values, and

(b) said set value input means and a set value display means for displaying said set values;

wherein said control constant setting means and said vehicle speed control device mutually input and output set value information including said set values.

17. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 16, further comprising one of:

(a) a radio receiver, and

(b) said radio receiver and a radio transmitter, attached to said control constant setting means;

wherein said set value information, which is received by radio from an outside station, is outputted to said vehicle speed control device; and

wherein said set value information and a situation signal, inputted from said vehicle speed control device, are transmitted by radio to said outside station.

18. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 12, further comprising:

an environmental condition detecting means, for detecting a traveling situation of the working vehicle and an external environmental situation, to output a detected situation signal to said vehicle speed control device; and

wherein said vehicle speed control device selects said predetermined vehicle speed limit value and said control gain corresponding to said situation signal to calculate a correction value of a position command signal for said actuator.

19. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 18, further comprising one of:

(a) a radio receiver, and

(b) said radio receiver and a radio transmitter, attached to said control constant setting means;

wherein said set value information, which is received by radio from an outside station, is outputted to said vehicle speed control device; and

wherein said set value information and said situation signal, inputted from said vehicle speed control device, are transmitted by radio to said outside station.

20. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 12, further comprising:

a transmission having a plurality of speed stages;

a speed change control device, for inputting, in advance, downshift judging vehicle speed value data and upshift judging vehicle speed value data, for comparing said downshift judging vehicle speed value data and said upshift judging vehicle speed value data with present vehicle speed data to judge a possibility of a speed change of said speed stages, and for outputting a shifting signal to a corresponding speed stage to control said transmission when a speed change is possible; and

a brake control device, for outputting a brake control signal based on a braking signal to control a brake;

wherein said vehicle speed control device calculates a corrected position command signal for said actuator based on said control gain, and outputs one of;

said downshift judging vehicle speed value data,

upshift judging vehicle speed value data, and

said braking signal

when said accelerator lever is placed in a total close position by said corrected position command signal and said deviation value is not within a predetermined range of values even if a state of said total close position is continued for a predetermined period of time.

21. An apparatus suitable for limiting a vehicle speed of a working vehicle, wherein the working vehicle includes:

an accelerator pedal;

an accelerator lever, operated based on a depressing stroke amount of said accelerator pedal; and

an engine, a speed of which is controlled by said accelerator lever through a mechanical governor device;

said apparatus comprising;

a vehicle speed detector, for detecting a vehicle speed of the working vehicle;

a vehicle speed control device, in which a vehicle speed limit value and a predetermined vehicle speed threshold value, which is smaller than said vehicle speed limit value, are set in advance, to which a vehicle speed signal is inputted from said vehicle speed detector, and which has;

a vehicle speed limit control means,

an acceleration-deceleration/constant speed judging means, and

a control gain changing means;

a driving device, for inputting a command from said vehicle speed control device; and

an actuator, driven by said driving device, for correcting said depressing stroke amount to control said accelerator lever;

wherein said vehicle speed limit control means;

judges a vehicle speed limit traveling period, when said vehicle speed signal is equal to or greater than said predetermined vehicle speed threshold value, to output to said driving device a command calculated by a control gain, based on a deviation value between said vehicle speed signal and said predetermined vehicle speed limit value or based on acceleration calculated from said vehicle speed signal and said deviation value such that said deviation value becomes smaller, and

judges an accelerated traveling period, when said vehicle speed signal is smaller than said vehicle speed threshold value, to output a command of a predetermined initial value to said driving device;

wherein said acceleration-deceleration/constant speed judging means;

judges a stable vehicle speed period, when said deviation value in said vehicle speed limit traveling period is less than or equal to a predetermined value over a predetermined period of time, and

judges an acceleration-deceleration period, in a case other than said stable vehicle speed period, to output to said control gain changing means a results of a judgment by said acceleration-deceleration/constant speed judging means; and

wherein said control gain changing means outputs to said vehicle speed limit control means a control gain in said stable vehicle speed period or a control gain in said acceleration-deceleration period in response to a result of a judgment by said acceleration-deceleration/constant speed judging means.

22. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 21, further comprising:

a depressing stroke detector, for detecting said depressing stroke amount; and

an accelerator lever operating position detector, for detecting an operating position of said accelerator lever;

wherein said vehicle speed control device inputs said depressing stroke amount and said operating position, converts said operating position into the depressing stroke amount based on a mechanical location, and compares a converted depressing stroke amount with an inputted depressing stroke amount to conduct a fault diagnosis.

23. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 21, further comprising a depressing stroke detector for detecting said depressing stroke amount;

wherein said vehicle speed control device calculates a corrected position command signal based on said control gain in response to said depressing stroke amount to output said corrected position command signal.

24. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 23, further comprising a warning device for inputting a warning signal from said vehicle speed control device to give a warning to a driver;

wherein said vehicle speed control device outputs said warning signal when said accelerator lever is placed in a total close position by said corrected position command signal and when said deviation value is not within a predetermined range of values even if the state of said total close position is continued for a predetermined period of time.

25. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 21, further comprising a control constant setting means having one of:

(a) a set value input means for setting, in advance, said predetermined vehicle speed limit value and said control gain as set values, and

(b) said set value input means and a set value display means for displaying said set values;

wherein said control constant setting means and said vehicle speed control device mutually input and output set value information including said set values.

26. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 25, further comprising one of:

(a) a radio receiver, and

(b) said radio receiver and a radio transmitter, attached to said control constant setting means; and

wherein set value information received by radio from an outside station is outputted to said vehicle speed control device and said set value information and said situation signal inputted from said vehicle speed control device are transmitted by radio to said outside station.

27. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 21, further comprising:

an environmental condition detecting means, for detecting a traveling situation of the working vehicle and an external environmental situation to output a detected situation signal to said vehicle speed control device; and

wherein said vehicle speed control device selects said predetermined vehicle speed limit value and said control gain corresponding to said detected situation signal to calculate a corrected position command signal for said actuator.

28. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 27, further comprising one of:

(a) a radio receiver, and

(b) said radio receiver and a radio transmitter, attached to said control constant setting means; and

wherein set value information received by radio from an outside station is outputted to said vehicle speed control device and said set value information and said situation signal inputted from said vehicle speed control device are transmitted by radio to said outside station.

29. An apparatus suitable for limiting a vehicle speed of a working vehicle in accordance with claim 21, further comprising:

a transmission having a plurality of speed stages;

a speed change control device, for inputting, in advance, downshift judging vehicle speed value data and upshift judging vehicle speed value data, for comparing said downshift judging vehicle speed value data and said upshift judging vehicle speed value data with present vehicle speed data to judge a possibility of a speed change of said speed stages, and for outputting a shifting signal to a corresponding speed stage to control said transmission when a speed change is possible; and

a brake control device, for outputting a brake control signal based on a braking signal to control a brake;

wherein said vehicle speed control device calculates a corrected position command signal based on said control gain, and outputs one of;

said downshift judging vehicle speed value data,

said upshift judging vehicle speed value data, and

said braking signal

when said accelerator lever is placed in a total close position by said corrected position command signal and said deviation value is not within a predetermined range of values even if a state of said total close position is continued for a predetermined period of time.

30. An apparatus suitable for limiting a vehicle speed of a working vehicle, wherein the working vehicle includes:

an accelerator pedal;

an accelerator lever, operated based on a depressing stroke amount of said accelerator pedal; and

an engine, a speed of which is controlled by said accelerator lever through a mechanical governor device;

said apparatus comprising;

a vehicle speed detector, for detecting a vehicle speed of the working vehicle;

a vehicle speed control device, for;

inputting a vehicle speed signal from said vehicle speed detector, and

judging a vehicle speed limit traveling period, when said vehicle speed signal is equal to or greater than a predetermined vehicle speed limit value, to output to said driving device a command calculated such that a deviation between said vehicle speed signal and said predetermined vehicle speed limit value becomes smaller;

a driving device, for inputting a command from said vehicle speed control device;

an actuator, driven by said driving device, for correcting said depressing stroke amount to control said accelerator lever;

a first shaft, having said accelerator pedal adhered to an outer periphery thereof;

a first member, of which a first end is adhered to said first shaft, and which rotates about a first central axis of said first shaft in proportion to said depressing stroke amount; and

a second shaft, through which a second end of said first member is passed in a direction of a second central axis, which is parallel to said first central axis, and which freely rotates about said second central axis while being supported by said first member;

wherein said actuator rotates said second shaft about said second central axis; and

wherein said second shaft is rotated by at least one of said actuator and said accelerator pedal to actuate said accelerator lever.

31. A method of limiting a vehicle speed of a working vehicle to be equal to or lower than a vehicle speed limit value, based on a depressing stroke amount of an accelerator pedal and the vehicle speed, said method comprising:

judging a vehicle speed limit traveling period, when said vehicle speed is equal to or greater than said vehicle speed limit value, to calculate a corrected depressing stroke amount based on a deviation value between said vehicle speed and said vehicle speed limit value so that said deviation value becomes smaller, to control said vehicle speed by said corrected depressing stroke amount;

judging an accelerated traveling period, when said vehicle speed is lower than said vehicle speed limit value and said corrected depressing stroke amount is larger than said depressing stroke amount, to control said vehicle speed by said depressing stroke amount;

judging a stable vehicle speed period, when said deviation value in said vehicle speed limit traveling period is less than or equal to a predetermined value over a predetermined period of time; and

judging an acceleration-deceleration period, in a case other than said stable vehicle speed period, to control said vehicle speed by a corrected depressing stroke amount calculated, based on different control gains in said stable vehicle speed period or in said acceleration-deceleration period, and said deviation value so that said deviation value becomes smaller.

32. A method of limiting a vehicle speed of a working vehicle to be less than or equal to a vehicle speed limit value, based on a depressing stroke amount of an accelerator pedal and the vehicle speed, said method comprising:

setting in advance a predetermined vehicle speed threshold value, which is smaller than said vehicle speed limit value;

judging a vehicle speed limit traveling period, when said vehicle speed is equal to or greater than said vehicle speed threshold value, to calculate a corrected depressing stroke amount based on acceleration calculated from said vehicle speed and a deviation value between said vehicle speed and said vehicle speed limit value so that said deviation becomes smaller, and to control said vehicle speed by said corrected depressing stroke amount; and

judging an accelerated traveling period, when said vehicle speed is lower than said vehicle speed threshold value, to control said vehicle speed by said depressing stroke amount.