Control system of self propelled industrial machine

1. A self propelled industrial machine comprising:

a self propelled vehicle body;

a transmission installed in said self propelled vehicle body;

an operator presence detection switch provided to generate an operator presence or absence signal relating to an operator on a seat arranged on said self propelled vehicle body;

a velocity sensor provided to detect a velocity of said self propelled vehicle body; and

a control unit provided to compare the detected velocity and a first predetermined velocity, provided to set a transmission lock state in response to said operator absence signal when the detected velocity is smaller than said first predetermined velocity, and provided to set said transmission to a neutral state when said transmission lock state is set.

2. The self propelled industrial machine according to claim 1 , wherein said operator presence signal is active during a period while the operator is on said seat and a predetermined period after the operator leaves said seat, and said operator absence signal is active when said operator presence signal is inactive.

3. The self propelled industrial machine according to claim 1 , wherein said control unit comprises:

an engine signal generator provided to generate an engine signal when an engine is started or an acceleration pedal is not pressed, and

wherein said control unit sets said transmission to said neutral state in response to said engine signal when the detected velocity is smaller than a second predetermined velocity, wherein said first predetermined velocity is smaller than said second predetermined velocity.

4. The self propelled industrial machine according to claim 1 , further comprising:

a first switch provided to instruct a forward direction movement;

a second switch provided to instruct said neutral state; and

a third switch provided to instruct a rear direction movement,

wherein said control unit releases said transmission lock state when said second switch is turned on, in a state that said first and third switches are all turned off, and said first and third switches are turned on with said second switch being turned off.

5. The self propelled industrial machine according to claim 4 , wherein said control unit controls said transmission to said neutral state when said second switch is turned on, said first and third switches are turned off, and controls said transmission such that the forward or rear direction movement is carried out when said first switch or said third switch is turned on, respectively, and said second switch is turned off.

6. A control method in a self propelled industrial machine with a self propelled vehicle body and a transmission, comprising:

generating an operator presence or absence signal relating to an operator on a seat arranged on the self propelled vehicle body;

detecting a velocity of said self propelled vehicle body;

comparing the detected velocity and a first predetermined velocity;

setting a transmission lock state in response to said operator absence signal when the detected velocity is smaller than said first predetermined velocity; and

controlling said transmission to a neutral state when said transmission lock state is set.

7. The control method according to claim 6 , wherein said operator presence signal is active during a period while the operator is on said seat and a predetermined period after the operator leaves said seat, and said operator absence signal is active when said operator presence signal is inactive.

8. The control method according to claim 6 , further comprising:

generating an engine signal when an engine is started or an acceleration pedal is not pressed, and

wherein said controlling comprises:

controlling said transmission to said neutral state in response to said engine signal when the detected velocity is smaller than a second predetermined velocity, and said first predetermined velocity is smaller than said second predetermined velocity.

9. The control method according to claim 6 , further comprising:

generating a forward direction movement instruction;

generating a neutral state instruction;

generating a rear direction movement instruction; and

releasing said transmission lock state when (a) said neutral state instruction is generated, (b) said forward and rear direction movement instructions are not generated, or (c) said forward and rear direction movement instructions are generated and said neutral state instruction is not generated.

10. The control method according to claim 9 , further comprising:

controlling said transmission to said neutral state in response said generating of a neutral state instruction, when said forward and rear direction movement instructions are not generated; and

controlling said transmission in response to said forward or rear direction movement instruction such that the forward or rear direction movement is carried out.