GB2357199A

GB2357199A - Forklift control apparatus

Info

Publication number: GB2357199A
Application number: GB0027974A
Authority: GB
Inventors: Ikuya Katanaya
Original assignee: Nippon Yusoki Co Ltd
Current assignee: Nippon Yusoki Co Ltd
Priority date: 1999-11-16
Filing date: 2000-11-15
Publication date: 2001-06-13
Anticipated expiration: 2020-11-15
Also published as: FR2801847A1; FR2801847B1; DE10056553A1; GB2357199B; GB0027974D0

Abstract

A control apparatus for an electric vehicle, particularly a forklift truck, limits the speed and acceleration of the vehicle when the accelerator pedal is not depressed. The state of the accelerator 21, and the speed of the vehicle 22 is detected and fed to a CPU 27 to control the output signals 28 to the electric motor drive 13. In one embodiment the speed and acceleration of a vehicle which has been stopped on a slope and not had the parking brake applied is limited to a predetermined level. In a second embodiment the speed of a moving vehicle is detected when the accelerator is released and the speed limited to that detected speed while the accelerator is not depressed. In further embodiments a top speed for the vehicle is calculated from detected values of the amount the accelerator pedal is depressed and the associated speed of the vehicle. The vehicle is then limited to that calculated top speed. The vehicle may be powered by an ac induction motor, fed from batteries via an inverter 13.

Description

2357199 FORKLIFT CONTROL APPERATUS

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a forklift control apparatus which converts the output dc power of a battery carried on board the main body of a forklift to ac power using an inverter, supplies the ac power to an induction motor for power, and drives the induction motor using a drive part to thereby execute the normal power operation or regenerative operation of the forklift.

2. Description of the Related Art

Normally, to run a forklift of a battery operated type, for example, as shown in Fig. 12, power may be supplied to a dc motor 3 for running the forklift using a battery 2 which is carried on board the main body 1 of the f orklif t. In this running operation, by operating a directional lever (or a directional switch) 4 which is capable of switching and setting transmission means (not shown) for transmitting the drive power of the motor 3 to the wheels of the forklift into one of advancing and retreating states or into a neutral state', the transmission means is switched into one of the advancing and retreating states or into the neutral state where the forklift is parked, and the forklift main body 1 is steered by operating a handle 5. By the way, in Fig. 12, reference character 6 designates a mast disposed in the front portion of the forklift main body 1, 7 a lift bracket mounted on the mast 6, 8 a pair of forks respectively mounted on the lift bracket 7, and 9 an accelerator pedal, respectively.

First, there will be described a problem in the case of keeping the forklift in the stop condition on the slope.

In a forklift of the above-mentioned dc motor type, for example, when the forklift stops halfway on a slope, in case where a parking brake is not operated but an operator removes his or her foot from the accelerator pedal, there is raised a problem that the f orklif t main body starts to run by itself, that is, the forklift main body starts to slip down along the slope at its discretion and the slipping-down speed of the forklift main body increases gradually.

On the other hand, recently, there has been proposed a forklift of a type which uses an ac motor as a power source thereof, that is, an induction motor instead of the above-mentioned dc motor 3. In the case of the forklift of this induction motor type, for example, as shown in Fig. 13, by turning on a main switch 11, the output dc power of a battery 2 is smoothed by a smoothing condenser 12 and, at the same time, the power is also converted into an ac power by a three-phase bridge inverter 13 composed of 6 full-bridge connected field-effect transistors Tl - T6; and, the ac power is supplied to a three-phase induction motor 14, thereby being able to make use of the plugging control of the induction motor 14.

Due to the plugging control of the induction motor 14, as described above, when the forklift main body 1 (see Fig.

12) stops halfway on a slope, even in case where the operator removes his or her foot from the accelerator pedal without applying a parking brake, the induction motor 14 is pluggingly braked to thereby prevent the forklift body 1 from slipping down along the slope.

However, in order to be able to apply such plugging braking, it is necessary to continue to apply a given voltage to the induction motor 14, which means that the power of the battery 2isconsumedon. Incase where such condition is left unchanged as it is, the battery 2 is exhausted and thus the plugging braking by the induction motor 14 fails shortly, so that the forklift main body 1 starts to slip down along the slope and the slipping-down speed of the forklift main body 1 increases gradually.

Also, even in case where the operator removes his or her foot from the accelerator pedal without applying a parking brake, due to the plugging braking by the induction motor 14, the forklift main body can be kept stopping halfway on the slope; and, therefore, the operator is unaware that the parking brake has not been applied. This raises a problem that the abovementioned slipping-down of the forklift body 1 after the exhaustion of the battery 2 cannot be prevented.

Second, there will be described a next problem occurring in the case of moving the forklift from a flat road into a slope.

In the forklift using the inductive motor 14 as a power source thereof, in case where the forklift runs from the flat road into the slope, as a method for controlling the speed of the forklift when an operator stops his or her pressing-down action on the accelerator pedal during the running of the forklift just before the forklift runs into the slope to thereby switch the forklift running mode into a so called neutral mode, there is available a method in which a regenerative control is carried out to thereby limit the slope running-down speed of the forklift to a previously determined given speed or lower.

In case where the regenerative control is not executed, the speed of the forklift increases gradually due to the gravity of the forklift as the forklift runs down the slope, with the result that cargoes carried on the forklift can collapse while the forklift goes down the slope and, in braking, there is necessary a more extra braking distance than the operator expects.

When the slope running-down speed of the forklift is limited to a given speed or lower, in spite of the fact that the operator has adjusted the speed of the forklift to a desired speed just before the forklift runs into the slope, in case where the forklift starts to run down the slope once, the forklift runs down the slope at a given speed different from the desired speed, so that the operator is not be able to run the forklift down the slope at the speed that is desired by the operator, which makes the operator feel inconvenient.

Third, there will be described another problem regarding the acelerator pedal opearation in the case of moving the forklift from the flat road to the slope.

As one of methods for controlling the running operation of a forklift, there is known a running control method in which, an accelerator pedal is pressed down to thereby apply acceleration to the forklift. According to this running control method, even in case where the accelerator pedal is continuously pressed down at a given angle, the speed of the f orklif t increases. That is, even in case where the accelerator pedal is continuously pressed down at a certain pressing-down amount, the speed of the forklift is not controlled so as to correspond to the accelerator pedal pressing-down amount, but a difference between the accelerator pedal pressing-down amounts is controlled as a difference between the amounts of acceleration.

Thus, according to the present running control method, it can be apprehensive that the forklift can be accelerated unlimitedly by pressing down the accelerator pedal. However, inthe actual running operation of the forklift, in the forklift, there is produced running resistance including the friction resistance of tires, air resistance and other kinds of resistance; and, the above acceleration can balance with such running resistance, which makes it possible to run the forklift at a constant speed. And, in case where a motor output command value when the accelerator pedal is pressed down to the full is set as a command value to balance with the running resistance at the top speed of the forklift, the top speed of the forklift can be set.

The present control method carries the advantages that the running speed of the forklift can be adjusted according to the pressingdown amount of the accelerator pedal to thereby run the forklift with a driving sense near to one obtained when driving a car and, at the same time, as described above, the top speed of the forklift can be limited. However, according to the present running control method, it is true that to limit the top speed is effective when the forklift runs on a flat road but, when the forklift runs down a slope, the top speed limitation is nullified. That is, when the forklift goes down the slope, the forklift is accelerated little by little regardless of the pressing-down amount of the accelerator pedal and thus the speed of the forklift will exceed the previously set top speed.

Also, the abovementioned running control method is a method in which the pressing-down amount of the accelerator pedal is proportional to the acceleration amount of the f orklif t.

However, there is also known another type of running control method in which the pressing-down amount of the accelerator pedal is proportional to the speed of the forklift. That is, this is a control method in which the forklift can be controlled so as to provide a running speed corresponding to the pressing-down amount of the accelerator pedal; and thus, in case where an operator continues to press down the accelerator pedal at a given angle, the forklift is allowed to run at a speed corresponding to the pressing-down amount of the accelerator pedal.

6 According to the present control method, in case where the running speed of the forklift when the accelerator pedal is pressed down to the full is set as the top speed of the forklift, the forklift can be controlled such that the running speed thereof is limited to the top speed thereof or lower; in particular, not only when the forklift runs on a flat road but also when it goes down a slope, since the top speed of the forklift is determined according to the pressingdown amount of the accelerator pedal, the forklift can be prevented from being accelerated. However, in the present running control method, since the running speed of the forklift corresponds to the pressing-down amount of the accelerator pedal, differently from the driving sense of a car (a sense obtained in driving a car at a low-speed gear), in case where an operator is not accustomed to the present running control method, the operator feels difficult to drive the forklift using the present running control method; and, in case where the operator removes his or her foot from the accelerator pedal, the pressing-down amount of the accelerator pedal becomes zero and thus the running speed of the forklift corresponding to this also becomes zero, with the result that the forklift is caused to stop suddenly (a state in which the motor is suddenly regenerated).

In other words, unless the operator stops pressing down on the accelerator pedal, the running speed of the forklift can be limited to the top speed or lower. However, in the general driving sense of the car, when the forklift running 7 - on a f lat road goes down a slope at the speed as it is, naturally, the forklift is accelerated and, therefore, the operator releases the accelerator pedal, or, in case where the acceleration is large, the operator removes his or her foot from the accelerator pedal. Incase where the operator removes his or her foot from the accelerator pedal according to the above car driving sense, the forklift is suddenly stopped on the slope and the operator is also in danger and, at the same time, since the forklift carries cargoes in the front portionthereof, there is a danger that the cargoes can collapse; and, because the forklift often runs on a narrow passage, there is a possibility that the collapsed cargoes can damage peripheral goods.

As described above, in a normal operation of a forklift, preferably, there may be obtained acceleration corresponding to the pressing-down amount of the accelerator pedal up to the time when the forklift reaches its top speed (that is, from the speed of zero to the top speed); and, in case where the forklift exceeds the top speed, the forklift may be run in such a manner that the running speed of the forklift can be limited to the top speed or lower. In the former example of the above-mentioned conventional forklift control apparatus, the operator is allowed to operate the forklift in such a manner that the operator himself or herself can control the pressing-down amount of the accelerator pedal to thereby obtain acceleration corresponding to the pressing-down amount of the accelerator pedal. However, when the forklift accelerates 8 on a downward slope, the running speed of the f orklif t cannot be limited to the top speed or lower.

On the other hand, in the latter example of the above-mentioned conventional forklift control apparatus, even on the downward slope, the forklift can run in a state where the top speed thereof is limited but, because the running speed of the forklift corresponds to the pressing-down amount of the accelerator pedal, the driving sense obtained up to the time the forklift reaches the top speed (that is, during the time from the speed of zero to the top speed) is different from the car driving sense and, even when the forklift goes down the slope, in case where the operator removes his or her foot from the accelerator pedal, there is a danger that the forklift can stop suddenly.

SUMMARY OF THE INVENTION

In view of the above, it is an object of the invention to provide a forklift control apparatus which, after a forklift stops halfway on a slope, when the pressing-down action of the accelerator pedal by an operator is removed without applying a parking brake, can control the slipp ing-down speed of the main body of the forklift as well as can inform the operator that the parking brake has not been applied.

It is anotherobjectof the invention to provide a forklift control apparatus which allows a forklift to run down a slope at the speed that is desired by an operator.

It is alsoanobjectof the invention to provide a forklift control apparatus which not only allows a forklift to run with acceleration corresponding to the pressingdown amount of an accelerator pedal until the running speed of the f orklif t reaches its top speed but also, when the running speed of the forklift exceeds the top speed, can limit the forklift running speed to the top speed or lower and can exert the control to limit the top speed regardless of the on and off states of the accelerator pedal.

In attaining the above object, according to a first aspect of the invention, there is provided a forklift control apparatus structured such that the output dc power of a battery carried on board the main body of a forklift is converted into ac power by an inverter and is supplied to an induction motor for power, and the induction motor is driven using a drive part of the forklift control apparatus to thereby execute the normal power operation or regenerative operation of the forklift, wherein, after the forklift main body stops, while an accelerator pedal is not pressed down, the output command value of the induction motor using proportional differentiation control is calculated in accordance with the speed and acceleration of the forklift main body when the forklift main body runs by itself in order to be able to maintain the speed of the forklift main body at a given low value or lower.

According to this structure, after the forklift main body stops, the output the output command value of the induction motor is calculated in accordance with the speed and acceleration of the forklift main body when it runs by itself while the accelerator pedal is not pressed down, and the induction motor is controlled in accordance with the thus calculated output command value, thereby being able to maintain the forklift main body speed at a given low value equal to or lower. Thanks to this, when the forklift main body stops halfway on a slope, even in case where the pressing-down action of the accelerator pedal by an operator is removed without applying a parking brake, the forklift main body slips down slowly along the slope at a given low speed or lower.

Therefore, not only the forklift main body slipping-down speed is prevented from increasing as in the conventional forklift control apparatus, but also an operator can observe that the forklift main body slips down slowly, which can make the operator be aware that the operator has forgot to apply the parking brake; that is, the present control apparatus is able to inform the operator of failure to apply the parking brake.

Also, according to a second aspect of the invention, there is provided a forklift control apparatus as set forth in the f irst aspect of the invention, which comprises: a rotation detect part for detecting the number of rotations of the induction motor; a derive part for deriving the speed and acceleration of the forklift main body from a detected value obtained by the rotation detect part; a switching part for switching and setting transmission means for transmitting the drive power of the induction motor to the wheels of the body into one of advancing and retreating states or into a neutral state; an accelerator pedal detect part for detecting whether an accelerator pedal is pressed down or not; and, a control part, on condition that, when stop of the forklift main body is recognized by the rotation detect part, the switching part is set in a neutral state and the off state of the accelerator pedal is detected by the accelerator pedal detect part, for calculating the output command value of the induction motor using proportional differentiation control in accordance with the speed and acceleration of the forklift body when it runs by itself in order to be able to maintain the speed of the forklift main body at a given low value or lower.

According to this structure, under given conditions, the output command value of the induction motor is calculated in accordance with the speed and acceleration of the forklift main body when it runs by itself, and the induction motor is controlled in accordance with the thus calculated output command value, thereby being able to maintain the speed of the forklift main body running by itself at a given low speed value.

Further, according to a third aspect of the invention, in a forklift control apparatus as set forth in the second aspect of the invention, the control part calculates the output command value in an advancing direction and the output command value in an retreating direction respectively according to the directions of the speed derived by the derive part.

According to this structure, depending on whether the forklift main body runs by itself on the slope in the advancing direction or in the retreating direction, there can be calculated the motor output command value with the motor rotation direction taken into account.

According to a f ourth aspect of the invention, there is provided a forklift control apparatus structured such that the output dc power of a battery carried on board the body of a forklift is converted into ac power by an inverter and is supplied to an induction motor for power, and the induction motor is driven using a drive part of the forklift control apparatus to thereby execute the normal power operation or regenerative operation of the forklift body, wherein, when an accelerator pedal is turned off (that is, removed from the pressing-down action by an operator) to thereby change the mode of the forklift over to a neutral mode, the speed of the forklift in transition to the neutral mode is set as atargetspeed, andthespeedof the forklift reaches or exceeds the target speed, the output command value of the induction motor using proportional dif f erentiation control is calculated in accordance with the target speed as well as the speed and acceleration of the forklift in order to be able to maintain the target speed when the speed of the forklift reaches or exceeds the target speed.

According to this structure, in case where the operator removes his or her foot from the accelerator pedal (that is, turns off the accelerator pedal) during the running operation of the forklift to thereby change the forklift over to the neutral mode, the output command value of the induction motor is calculated in accordance with the target speed in transition to the neutral mode as well as the speed and acceleration of the forklift, and the induction motor is controlled in accordance with the calculated output command value, thereby being able to maintain the forklift speed at the target speed or lower.

Therefore, for example, when the forklift is going to run down the slope at the same speed as it advances from a flat road into the slope, in case where the accelerator pedal isturnedoff justbeforethe forklift advances intothe slope, with the then speed set as the target speed, the forklift is allowed to run down the slope while the running speed of the forklift is maintained at the target speed or lower.

That is, in case where the operator adjusts the forklift speed to the operator's desired speed just before the forklift advances into the slope, the forklift is allowed to run down the slope at the then speed as it is.

Also, according to a f if th aspect of the invention, there is provided a forklift control apparatus as set forth in the fourth aspect of the invention, which comprises: a rotation detect part for detecting the number of rotations of the induction motor; a derive part for deriving the speed and acceleration of the forklift from a detected value obtained by the rotation detect part; an accelerator pedal detect part for detecting whether an accelerator pedal is on or off (that is, pressed down or not); and, a control part for changing the forklift over to a neutral mode when the off state (that is, undepressed state) of the accelerator pedal is detected by the accelerator pedal detect part, for setting the speed of the forklift in transition to the neutral mode as a target speed, and for calculating the output command value of the induction motor using a proportional differentiation control in accordance with the target speed as well as the speed and acceleration of the forklift derived by the derive part in order to be able to maintain the target speed when the speed of the forklift reaches or exceeds the target speed.

According to this structure, in case when the off state (undepressed state) of the accelerator pedal is detected by the accelerator pedal detect part and the forklift is thereby changed over to the neutral mode, the output command value of the induction motor is calculated in accordance with the target speed in transition to the neutral mode as well as the speed and acceleration of the forklift obtained by the derive part. Therefore, by controlling the induction motor in accordance with the calculated output command value, the speed of the forklift can be maintained at the target speed in transition to the neutral or lower.

Further, according to a sixth aspect of the invention, in a forklift control apparatus as set forth in the second aspect of the invention, the control part calculates the output command value in an advancing direction and the output command value in an retreating direction respectively according to the directions of the speed derived by the derive part.

According to this structure, the motor output command value with the motor rotation direction taken into account can be calculated depending on whether the forklift body runs by itself d.own the slope in the advancing direction or in the retreating direction.

According to a seventh aspect of the invention, there is provided a forklift control apparatus capable of driving a running motor by power supplied from a battery carried on board a main body of a forklift, the present forklift control apparatus comprising: an accelerator pedal detect part for detecting the pressingdown amount of an accelerator pedal; a forklift speed sensor for detecting a forklift speed detect value corresponding to the running speed of the forklift main body; a forklift speed calculation part for calculating the running speed of the forklift main body from the forklift speed detect value obtained by the forklift speed sensor; a setting part for setting the top speed of the forklift main body; a comparison and calculation part for comparing and calculating the running speed obtained by the forklift speed calculation part and the top speed set by the setting part; and, a control part which, as a result of a 'comparison made in the comparison and calculation part, when the running speed is equal to or lower than the top speed, calculates a motor output command value for providing the forklift main body with acceleration proportional to the accelerator pedal pressing-down amount obtained by the accelerator pedal detect part and, when the running speed exceeds the top speed, calculates a motor output command value for limiting the running speed to the top speed or lower.

According to the above structure, in the running speed of the forklift main body up to the top speed thereof, the forklift is allowed to run with acceleration corresponding to the pressing-down amount of the accelerator pedal and, when the running speed of the forklift exceeds the top speed, the running speed can be limited to the top speed or lower.

Thanks to this, in the normal running operation of the f orklif t, not only the running operation of the forklift can be controlled with such driving sense that can be obtained when driving a car, but also, in the case where the running speed of the forklift becomes higher than the top speed, for example, when the forklift runs down on a slope, the running speed can be limited to the top speed or lower, thereby being able to exert such running control that can keep the saf ety of the forklift.

Also, according to an eighth aspect of the invention, there is provided a forklift control apparatus capable of driving a running motor by power supplied f rom a battery carried on board amainbody of aforklift, the present forklift control apparatus comprising: an accelerator pedal detect part for detecting the on/off states of an accelerator pedal and the pressing-down amount thereof; a forklift speed sensor for detecting a forklift speed detect value corresponding to the running speed of the forklift main body; a forklift speed calculation part for calculating the running speed of the for kliftma in body from the forklift speed detect value obtained by the forklift speed sensor; a setting part for setting the topspeedof theforkliftmainbody; a comparison and calculation part for comparing and calculating the running speed obtained by the forklift speed calculation part and the top speed set by the setting part; and, a control part which, as a result of a comparison made in the comparison and calculation part, when the running speed is equal to or lower than the top speed, calculates a motor output command value for providing the forklift body with acceleration proportional to the accelerator pedal pressing-down amount obtained by the accelerator pedal detect part and, when the running speed exceeds said top speed, calculates a motor output command value for limiting the running speed to the top speed or lower regardless of the on/off states of the accelerator pedal.

According to the above structure, similarly to the structure according to the first aspect of the invention, in the normal running operation of the forklift, not only the running operation of the forklift can be controlled with such driving sense that can be obtained when driving a car, but also, in the case where the running speed of the forklift becomes higher than the top speed, forexample, whentheforklift runs down on a slope, the running speed can be limited to the top speed or lower, thereby being able to exert such running control that can keep the safety of the forklift. In addition to these ef f ects, in the present structure, the running speed of the forklift can be. limited to the top speed or lower regardless of the on and off states of the accelerator pedal.

Due to this, even in case where an operator releases his or her foot from the accelerator pedal while driving the f orklif t on a slope, the running speed of the forklift can be limited to the top speed or lower, which allows the operator to loosen or release his or her f cot hold of the accelerator pedal on the slope similarly when the operator drives a car. Therefore, not only the operator is allowed to drive the forklift with the same driving sense as the operator drives a car, but also the running speed of the forklift can be limited, that is, the safety of the forklift can be enhanced. Further, according to a ninth aspect of the invention, there is provided a

forklift control apparatus capable of driving a running motor by power supplied f rom, a battery carried on board a main body of a f orklif t, the present f orklif t control apparatus comprising: an accelerator pedal detect part for detecting the on/off states of an accelerator pedal and the pressing-down amount thereof; a forklift speed sensor for detecting a forklift speed detect value corresponding to the running speed of the forklift main body; a forklift speed calculation part for calculating the running speed of the forklif tmain body f romthe forklift speed detect value obtained by the forklift speed sensor; a setting part for setting the topspeedof the f orklif tmain body; a comparison and calculation part for comparing and calculating the running speed obtained by the forklift speed calculation part and the top speed set by the setting part; and, a control part which, as a result of a comparison made in the comparison and calculation part, when the running speed exceeds the top speed, calculates a motor output command value for limiting the running speed to the top speed or lower regardless of the on/off states of the accelerator pedal.

According to the above structure, the running speed of the forklift can be limited to the top speed or lower regardless of the on/off states of the accelerator pedal. Thanks to this, even in case where the operator releases his or her foot hold of the accelerator pedal on a slope, the running speed of the forklift can be limited to the top speed or lower.

Therefore, not only the operator is allowed to drive the forklift with the same driving sense as the operator drives a car, that is, the operator is allowed to ease or remove his or her foot hold of the accelerator pedal on the slope, but also the running speed of the forklift can be limited, that is, the safety of the forklift can be enhanced.

Stillfurther, according to a tenth aspect of theinvention, in a forklift control apparatus as set forth in any one of the seventh to ninth aspect of the invention, the present forklift control apparatus further including: a rotation detect part for detecting the number of rotationsof therunning motor; and, a derive part f or deriving the speed and acceleration of the forklift main body from a detect value obtained by the rotation detect part, wherein the control part derives the speed and acceleration of the forklift main body from the number of rotations of the motor obtained by the rotation detect part and, inaccordance with the thus derived speed and acceleration, calculates the output command value.

According to the above structure, since the output command value of the motor is calculated in accordance with the speed and acceleration of the forklift while running, by controlling the motor in accordance with the thus calculated motor output command value, the forklift self running speed can be limited to a set value or less.

Yet further, according to an eleventh aspect of the invention, in a forklift control apparatus as set forth in any one of the seventh to tenth aspects of the invention, the present forklift control apparatus further including:

a switching part for switching and setting transmission means for transmitting the drive power of the running motor to wheels atanyoneof advancing, retreating and neutral states, wherein the control part, in accordance with the switched states of the transmission means by the switching part, calculates the output command value for an advancing direction and the output command value for a retreating direction, respectively.

According to the above structure, depending on whether the forklift runs in an advancing or retreating direction, themotoroutput command value with the motor rotation direction taken into account is calculated; and, the running speed of the forklift can be limited to the top speed or lower set by the setting part in both of the advancing and retreating directions.

Moreover, according to a twelfth aspect of the invention, in a forklift control apparatus as set forth in any one of the seventh to tenth aspects of the invention, the above running motor consists of an induction motor, and the output dc power of the above battery is converted to ac power by an inverter and is then supplied to the present induction motor.

According to the above structure, a control signal from the inverter to the induction motor may be controlled in such a manner that the motor output command value can become the output command value calculated by the control part. Thanks to this, on a flat road, the induction motor can be controlled so as to carry out a normal power operation and, in a slope, the induction motor can be controlled so as to carry out a regenerative operation, which makes it possible to limit the running speed of the forklift to the top speed or lower.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a block diagram of an embodiment of a forklift control apparatus according to the invention.

Fig. 2 is a flow chart to explain the operation of the above embodiment.

Fig. 3 is a flow chart to explain the operation of the above embodiment.

Fig. 4 is a flow chart to explain the operation of the above embodiment.

Fig. 5 is a flow chart to explain the operation of the above embodiment.

Fig. 6 is a flow chart to explain the operation of the above embodiment.

Fig. 7 is a flow chart to explain the operation of the above embodiment.

Fig. 8 is a flow chart to explain the operation of the above embodiment.

Fig. 9 is a flow chart to explain the operation of the above embodiment.

Fig. 10 is a flow chart to explain the operation of the above embodiment.

Fig. 11 is a flow chart to explain the operation of the control apparatus according to the embodiment of the invention.

Fig. 12 is a side view of an ordinary forklift of a dc motor type.

Fig. 13 is a circuit diagram of a control circuit used in an ordinary three-phase induction motor.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

FIRST EMBODIMENT Now, a description will be given below of a f irst embodiment in which the present invention is applied to a forklift of a counter balance type with reference to Figs. 1 to 4. Here, Fig. 1 is a block diagram of a control apparatus according to the embodiment of the invention, and Figs. 2 to 4 are respectively flow charts for explanation of the operation of the forklift control apparatus shown in Fig. 1.

Here, the forklift of a counter balance type is the same in structure as the forklift shown in Fig. 12, except that an induction motor is used instead of the dc motor 3 and, therefore, in the following description, Fig. 12 will also be referred to. Also, in the present embodiment, similarly to the induction motor 14 shown in Fig. 13, there is used a three-phase induction motor and an inverter used to drive the three-phase induction motor is identical in structure with the three-phase bridge inverter 13 shown in Fig. 13; and, theref ore, Fig. 13 will also be ref erred to in the f ollowing description.

As shown in Fig. 1, a detect signal from an accelerator pedal detect part (not shown) proportional to the pressing-down amount of an accelerator pedal 9 is converted into a digital signal by an analog/digital (A/D) conversion part 21, so that a CPU to be discussed later is able to detect the on and off states and preS3ing-down amount of an accelerator pedal based on the pressing-down action of the accelerator pedal 9 by an operator. Also, as shown in Fig. 13, on the rotary shaft of the induction motor 14, there is disposed a rotation detect part 15 which is composed of a rotary encoder; and, output pulses from the rotation detect part 15 are counted by a counter 22 and, from the thus counted value, the number of rotations of the induction motor 14 can be detected by the CPU to be discussed later.

Further, the switched state of a directional lever 4 serving as a switching part which switches and sets the transmission means (not shown) for transmitting the drive power of the induction motor 14 to the wheels of the forklift into one of advancing and retreating states or into a neutral state is input through a parallel input part (P1) 23 into the CPU to be discussed later, and the CPU judges at which one of the advancing,. retreating and neutral states the directional lever 4 is set.

And, not only the data such as the pressing-down amount of the accelerator pedal 9, the number of rotations of the induction motor, and the switched state of the directional lever 4 but also data such as brake on/off data to be detected by a brake detect part (not shown in Fig. 1) and parking brake operation or nonoperation data to be detected by a parking brake detect part are temporarily stored in a RAM 25; and, in accordance with a given control program previously stored in a ROM 26, the CPU 27 outputs PWM control pulses from a pulse width modulation (PWM) pulse output part 28 to the control terminals of the respective transistors Tl - T6 of an inverter 13 to control the output curre nt of the induction motor 14, thereby controlling the normal power operation or regenerative operation of the forklift.

By the way, in the CPU 27, on condition that, when the speed and acceleration of the f orklif t main body 1 are derived from the number of rotations of the motor detected by the rotation detect part 15 and the stop of the forklift main body 1 is recognized from the output of the rotation detect part 15, the directional lever 4 is set at the neutral state and the off states of the accelerator pedal and brake are detected by the accelerator pedal detect part and brake detect part respectively, the output command value of the induction motor 14 using proportional differentiation (PD) control is calculated in accordance with the speed and acceleration of the forklift main body 1 when it runs by itself because the operator forgets to apply the parking brake, that is, when the forklift main body 1 slips down along the slope at its discretion, in order to be able to maintain the speed of the forklift main body 1 at a given low speed (for example, about km/h). Here, it goes without saying that the limit speed using the PD control is not limited to the above-mentioned km/h.

And, the PWM pulse output part 28 is controlled in accordance with the thus calculated output command value to thereby control the number of rotations of the induction motor 14, so that the regenerative operation control of the induction motor 14 can be made.

In this case, depending on the direction of the forklift main body 1, that is, depending on whether the forklift main body 1 runs by itself in the advancing or retreating direction, the CPU 27 derives the positive or negative direction of the speed as well and, in accordance with the derived speed direction, calculates the output command value of the induction motor 14 in the positive rotation direction of the induction motor 14 (for the advancing operation of the forklift main body 1) or in the negative rotation direction of the induction motor 14 (for the retreating operation of the forklift main 26 - body 1). The speed and acceleration deriving processing by the CPU 27 corresponds to a derive part, while the output command value calculation processing of the induction motor 14 corresponds to a control part.

Also, the calculation of the output command value by the CPU 27 can be made according to the two following equations..

that is, Mf = kI x V + U x G (in the case of advancing operation)- (1) Mb = -kl x V - k2 x G (in the case of retreating operation)... (2) where the gains (coef f icients) of a control system are expressed as kI, k2, the output command value of the induction motor 14 in case where the self-running direction of the forklift main body is the advancing direction is expressed as Mf, and the output command value of the induction motor 14 in case where the self-running direction of the forklift main body is the retreating direction is expressed as Mb. Here, the first terms of the right sides of the above equations (1) and (2) respectively express proportion (P) control components in the proportional differentiation (PD) control, whereas the second terms thereof respectively express differentiation (D) control components.

Next, description will be given below of the operation of the above-mentioned forklift control apparatus with reference to the flow charts respectively shown in Figs. 2 to 4.

As shown in Fig. 2, at first, the control apparatus including the RAM 25 is initialized by the CPU 27 (S1), a signal proportional to the pressing-down amount of the accelerator pedal is fetched from the accelerator pedal detect part (S2), the switched state of the directional lever 4 is input through P123 (S3), a count value is fetched from the counter 22 (S4), and the output of the brake detect part is fetched (S5).

And, it is checked whether the accelerator pedal is on (that is, pressed down) or not (S6). If the checking result is found YES, then it is checked whether the switched state of the directional lever 4 is one of the advancing and retreating states, or the neutral state (S7). If the directional lever 4 is found in one of the advancing and retreating states, then a slip-down flag composed of a register incorporated in the CPU 27 is reset (S8), a normal running control processing is carried out (S9), and, after then, the processing goes to a step S16 which will be discussed later.

Here, referring to the normal running control processing in Step 9, this is a processing (S20) which, as shown in Fig.

3, multiplies a given gain (coefficient) by the pressing-down amount of the accelerator pedal 9 to thereby find a motor output command value in a normal running operation.

Next, if the checking result in the above-mentioned step S6 is found NO, then the accelerator pedal is off (that is, not pressed down) and thus it is checked whether the speed of the forklift main body 1 derived from the count value fetched - 28 in Step S3 is zero or not (S10) If this checking result is found YES, that is, if the forklift main body 1 speed is found zero and thus the main body 1 is found stopping, then it is checked from the output of the brake detect part fetched in Step S5 whether the brake is on or not (S11). If this checking result is found YES, then the slip-down flag of the CPU 27 is set (S12) and the output command value of the induction motor 14 is set at zero (S13) and, after then, the processing goes to Step S16 which will be discussed later. By the way, alternatively, the above processing may also be executed in the following manner: that is, while omitting the processings in Steps 5 and 11, it is checked whether the speed of the forklift main body 1 is zero or not and, if this checking result is found YES, then the slip-down flag of the CPU 27 is set (S12).

On the other hand, if the checking result of the above-mentioned step S10 is NO, then it is judged that the forklift main body 1 is running at a certain speed and, in Step S14, it is checked whether the slipdown flag is set or not (S14). If this checking result is NO, then it can be judged that a slip-down control to be discussed later is not necessary and, therefore, together with a case where the checking result of the above-mentioned step S11 is NO, the processing goes to the above-mentioned step S13.

Also, if the checking result in Step S14 is YES, then the processing goes to Step S15 and the slip-down control processing is executed (S15). In the slip-down control processing, as shown in Fig. 4, in accordance with the speed V and acceleration G of the forklift main body 1 derived from the count value of the count value 22 fetched in Step S4, it is checked whether the speed V is positive or negative (S25) and, if the speed V is found positive, then there is calculated the output command value Mf of the induction motor in the above-mentioned equation (1) for the advancing operation (S26); and, if the speed V is found negative, then there is calculated the output command value Mb of the induction motor 15 in the above-mentioned equation (2) for the retreating operation (S27) and, after then, similarly to the above case where the processing of Step S26 is executed, the processing returns to the main routine shown in Fig. 2.

And, as shown in Fig. 2, after the processings in the above-mentioned steps S9, S13 and S15 are executed, the processing goes to the next step S16, in which, in accordance with the output command value of the induction motor 14 calculated in the above-mentioned step S9, the PWM pulse output part 28 is controlled by the CPU 27 and thus the number of rotations of the induction motor 14 is controlled so as to provide a speed corresponding to the pressing-down amount of the accelerator pedal (S16).

On the other hand, in the case of Step S13, the induction motor 14 is controlled. in such a manner that the output of the induction motor 14 provides zero, that is, the induction motor 14 is controlled so as to stop (S16). Also, in the case of Step S15, in accordance with the output command value Mf or Mb calculated in Step S15, the PWM pulse output part 28 is controlled by the CPU 27 and thus the number of rotations of the induction motor 14 is controlled in such a manner that the speed of the forklift main body 1 becomes equal to or less than a preset given low speed, for example, about 5 km/h (S16) and, after then, the processing goes back to the above-mentioned step S2.

Therefore, when the forklift main body 1 stops halfway on the slope, even in case where the operator removes his or her foot from the accelerator pedal without applying the parking brake, by calculating the output command value Mf or Mb of the induction motor 14 in accordance with the speed and acceleration of the forklift main body 1 when it slips down along the slope and then by controlling the induction motor 14 in accordance with the thus calculated output command value, the slip-down speed of the forklift main body 1 can be maintained at a the preset given value, for example, 5 km/h or lower.

Thus, according to the above-mentioned embodiment, because the slip-down speed of the forklift main body 1 does not increase so much as in the conventional forklift control apparatus, there can be reduced a fear that the forklift main body 1 can slip down at a high speed and collide with a wall or an installed thing to thereby break the same.

Also, incase where the operator can find that the forklift main body 1 is slipping down at a slow speed, such slow slip-down of the forklift main body 1 can make the operator be aware that the operator has forgot to apply the parking brake.

That is, according to the present embodiment, there can be obtained a parking brake non-application notice effect.

Further, according to the present embodiment, there can be prevented a possibility that the battery 2 is exhausted up during the braking operation, which occurs in the conventional forklift control apparatus when the forklift main body 1 is made to stop completely by the regenerative braking using the induction motor. That is, it is possible to eliminate the inconveniences caused by the exhaustion of the battery 2.

Bytheway, in the above -mentioned embodiment, description has been given of the case in which the induction motor 14 is composed of a three-phase induction motor. However, of course, the induction motor 14 is not limited to the three-phase induction motor but it may also be composed of a two-phase induction motor or an induction motor having four or more phases.

Also, in the above-mentioned embodiment, description has been given of the case in which the invention is applied to the forklift of a counter balance type. However, the application of the invention is not limited to the forklift of a counter balance type but, of course, the invention can also be applied to other types of forklifts, for example, a forklift of a reach type and a forklift which uses an induction motor of any other type as a power source thereof - In this caseaswell, there can be obtained the effect that is equivalent to the above-mentioned embodiment.

SECOND EMBODIMENT Now, a description will be given below of a second embodiment in which the present invention is applied to a forklift of a counter balance type with reference to Figs.

1, and 5 to 10. Here, Fig. 1 is a block diagram of a control apparatus according to the embodiment of the invention, and Figs. 5 to 10 are respectively flow charts for explanation of the operation of the forklift control apparatus shown in Fig. 1.

As shown in Fig. 1, a detect signal, which is given from an accelerator pedal detect part (notshown) and is proportional to the pressing-down amount of an accelerator pedal 9, is converted into a digital signal by an analog/digital (A/D) conversion part 21, so that the on and off states of the accelerator pedal 9 as well as the pressing-down amount thereof are detected by a CPU to be discussed later. Also, as shown in Fig. 13, on the rotary shaft of the induction motor 14, there is disposed a rotation detect part 15 which is composed of a rotary encoder; and, output pulses from the rotation detect part 15 are counted by a counter 22 and, from the thus counted value, the number of rotations of the induction motor 14 can be detected by the CPU to be discussed later.

Further, the switched state of a directional lever 4 serving as a switching part which switches and sets the transmission means (not shown) for transmitting the drive power of the induction motor 14 to the wheels of the forklift into one of advancing and retreating states or into a neutral state is input through, a parallel input part (P1) 23 into the CPU to be discussed later, and the CPU judges at which one of the advancing, retreating and neutral states the directional lever 4 is set.

And, the data such as the pressing-down amount of the accelerator pedal 9, the number of rotations of the induction motor, and the switched state of the directional lever 4 are temporarily stored in a RAM 25; and, in accordance with a given control program previously stored in a ROM 26, the CPU 27 outputs PWM control pulses from a pulse width modulation (PWM) pulse output part 28 to the control terminals of the respective transistors Tl -T6 of an inverter 13 to control the output current of the induction motor 14, thereby controlling the normal power operation or regenerative operation of the forklift.

By the way, in the CPU 27, the speed and acceleration of the forklift main body 1 are derived from the number of rotations of the motor detected by the rotation detect part 15. Further, in case where, when the off (undepressed) state of the accelerator pedal is detected by the accelerator pedal detect part, the forklift is switched to the neutral mode and the speed of the forklift in transition to the neutral mode is set as a target speed; and, based on the present target speed as well as the speed and acceleration of the forklift that are derived by the CPU 27, the CPU 27 calculates the output command value of the induction motor 14 using proportional differentiation (PD) control in order to be able to maintain the target speed when the forklift speed exceeds the target speed.

In this case, depending on the direction of the forklift main body 1, that is, depending on whether the main body 1 runs by itself in the advancing or retreating direction, the CPU 27 derives the positive or negative direction of the speed as well and, in accordance with the derived speed direction, calculates the output command value of the induction motor 14 in the positive rotation direction of the induction motor - 35 14 (for the advancing operation of the forklift main body 1) or in the negative rotation direction of the induction motor 14 (for the retreating operation of the forklift main body 1). The speed and acceleration deriving processing by the CPU 27 corresponds to a derive part, while the output command value calculation processing of the induction motor 14 corresponds to a control part.

Also, the calculation of the output command value by the CPU 27 can be made according to the two following equations:

that is, Mf = kl x (V - Vt) + k2 x G (in the case of advancing operation) Mb = -kl x (V -Vt) - k2 x G (in the case of retreating operation) where the speed in transition to the neutral mode is expressed is expressed as Vt, the input speed and acceleration derived from the output of the rotation detect part 15 by the CPU 27 are expressed as V and G respectively, the gains (coefficients) of a control system are expressed as kl, k2, the output command value of the induction motor 14 in case where the self-running direction of the body is the advancing direction is expressed as Mf, and the output command value of the induction motor 14 in case where the self-running direction of the body is the retreating direction is expressed as Mb. Here, the first terms of the right sides of the above two equations respectively express proportion (P) control components in the proportional differentiation (PD) control, while the second terms thereof respectively express differentiation (D) control components.

Next, description will be given below of the operation of the above-mentioned forklift control apparatus with reference to the flow charts respectively shown in Figs. 5 to 10.

At f irst, description will be given below of a main routine of the operation of the present forklift control apparatus.

As shown in Fig. 5, at first, the respective devices of the forklift control apparatus including the RAM 25 are initialized by the CPU 27 and a mode f lag composed of registers incorporated in the CPU 27 is set at "neutral" (S101), a signal proportional to the pressing-down amount of the accelerator pedal 9 is fetched from the accelerator pedal detect part (S102), the switched state of the directional lever 4 is input through P123 (S103), a count value is fetched from the counter 22 (S104), and the mode flag is checked as whether it shows "advancing" or not (5105).

If the checking result is found YES (S106), then an advancing control processing to be discussed later is executed (S106); and, if the checking result is found NO, then the mode flag is checked as to whether it shows "retreating" or not (S107). If the checking result is found YES, then a retreating control processing to be discussed later is executed (S108); and, if the checking result is found NO, then the mode flag is checked as whether it shows an "advancing slope running-down controlled speed regeneration" or not (S109) 37 - If the checking result is found YES, then an advancing slope running-down controlled speed regeneration control processing to be discussed later is executed (S110); and, if the checking result is found NO, then the mode flag is checked as whether it shows a "retreating slope running-down controlled speed regeneration" or not (Slll). If the checking result is found YES, then a retreating slope running-down controlled speed regeneration control processing to be discussed later is executed (S112); and, if the checking result is found NO, then the processing goes to a neutral mode processing (S113).

And, after then, the processing goes back to the step S102, similarlyafter the above-mentioned steps S106, S108, S110, and S112 are respectively processed.

Next, description will be given below of the neutral mode processing in Step S113 shown in Fig. 5 with reference to Fig. 6. Here, when the processing is moved to the neutral mode, the speed of the forklift derived from the count value of the counter 22 fetched in Step S104 shown in Fig. 5 is assumed to be a target speed Vt. Firstly, as shown in Fig.

6, the target speed Vt is set as an input speed V (Sl2l) and, basedona signal fromthe accelerator pedal detectpart fetched in Step S103 shown in Fig. 5, it is checked whether the accelerator pedal is on (pressed down) or not (S122).

If this checking result is found YES, then it is checked whether the switched state of the directional lever 4 is "advancing", or "retreating", or "neutral (S123) - If the switched state is found "advancing", then the mode flag is set for "advancing" (S124); if it is found "retreating", then the mode flag is set for "retreating" (S125); and, if it is f ound "neutral ", then the processing goes to Step S12 6 similarly when the checking result in Step S122 is found NO, where it is checked whether the input speed V is positive or negative (S126).

And, if the checking result in the above-mentioned step S106 is found YES, then it can be judged that the forklift was advancing at the time of transition to the neutral mode and, therefore, the mode flag is set for the "advancing slope running-down controlled speed regeneration" (S127). On the other hand, if the checking result is found NO, then it is checked whether the input speed V is positive or negative (S128). If the checking result is found YES, then it can be judged that the forklift was retreating at the time of transition to the neutral mode and, therefore, the mode flag is set for the "retreating slope running-down controlled speed regeneration" (S129).

On the other hand, if the checking result of the above-mentioned step S128 is NO, then, similarly after the above-mentioned steps S124, S125, S127, and S129, the processing goes to Step S130, where the output of the induction motor 14 is controlled so as to be off (S131). After then, the processing goes back to the main routine shown in Fig.

S.

Here, description will be given below of the advancing control processing in Step S106 in Fig. 5 with reference to - 39 Fig. 7. As shown in Fig. 7, the motor output command value in an advancing running operation can be calculated from the product of a given gain (a positive coefficient) and the accelerator pedal pressing-down amount and the output of the induction motor 14 can be controlled in accordance with the thus calculated output command value (S141). And, in accordance with a signal from the accelerator detect part, it is checked whether the accelerator pedal is on or not (S142).

If the checking result is found YES, then it is checked whether the switched state of the directional lever 4 is "advancing", or "retreating", or "neutral" (S143).

And, if the checking result of the above-mentioned step 5142 is found NO, and if the checking result of the above-mentioned step S143 is found "retreating", or "neutral", the processing goes to S1tep S144 and the mode flag is set for "neutral" (S144). Afterthen, similarly when the checking result of Step S143 is found "advancing", the processing goes back to the main routine shown in Fig. 5.

Also, description will be given below of the retreating control processing in Step S108 in Fig. 5 with reference to Fig. 8. As shown in Fig. 8, the motor output command value in a retreating running operation can be calculated from the product of a given gain (a negative coefficient) and the accelerator pedal pressing-down amount and the output of the induction motor 14 is controlled in accordance with the thus calculated output command value (S151). And, in accordance with a signal from the accelerator pedal detect part, it is - 40 checked whether the accelerator is on or not (52) If the checking result is found YES, then it is checked whether the switched state of the directional lever 4 is "advancing", or "retreating", or "neutral" (S153).

And, if the checking result of the above-mentioned step S152 is found NO, and if the checking result of the above-mentioned step S153 is found "retreating", or "neutral", then the processing goes to Step S154 and the mode flag is set for "neutral" (S154). After then, similarly when the checking result of Step S153 is found "retreating", the processing goes back to the main routine shown in Fig. 5.

Further, description will be given below of the advancing slope running-down controlled speed regeneration control processing in step S110 in Fig. 5 with reference to Fig. 9.

As shown in Fig. 9, at first, it is checked whether the target speed Vt is larger than the input speed V or not (S161).

If the checking result is found YES, then the target speed Vt is set as the input speed V (S162) and, after then, similarly when the checking result of Step S161 is f ound NO, the processing goes to Step S163, where the output command value Mf of the induction motor 14 in the case of advancing with respect to the target speed Vt is calculated and, at the same time, the output of the induction motor 14 is controlled in accordance with the thus calculated output command value Mf (S163).

By the way, when the output command value Mf < 0, the output command value Mf is treated as 0.

And, in accordance with a signal from the accelerator 41 - detect part, it is checked whether the accelerator is on or not (S164). If the checking result is found YES, then it is checked whether the switched state of the directional lever 4 is "advancing", or "retreating", or "neutral (S165). If the switched state is found "neutral", then, similarly when the checking result of the above-mentioned step S164 is found NO, the processing goes to Step S166, where it is checked whether the input speed V set in Step S162 is equal to or less than zero or not (S166).

If the checking result is found YES, similarly when the checking result of S165 is found "advancing" or "retreating", the processing goes to Step S167, where the mode flag is set for "neutral" (S167) After then, similarlywhen the checking result of S166 is found NO, the processing goes back to the main routine shown in Fig. 5.

In addition, description will be given below of the retreating slope running-down controlled speed regeneration control processing in Step S112 in Fig. 5 with reference to Fig. 10. In this case, since the speed in an advancing running operation is assumed to be positive, the speed in a retreating running operation is negative.

As shown in Fig. 10, at first, it is checked whether the target speed Vt is smaller than the input speed V or not (Sl'71). If the checking result is found YES, then the target speed Vt is set as the input speed V (S172) and, after then, similarly when the checking result of Step S171 is found NO, the processing goes to Step S173, where the output command 42 - value Mb of the induction motor 14 in the case of a retreating operation with respect to the target speed Vt is calculated and, at the same time, the output of the induction motor 14 is controlled in accordance with the thus calculated output command value Mb (S173). By the way, when the output command value Mb > 0, the output command value Mf is regarded as 0.

And, in accordance with a signal from the accelerator detect part, it is checked whether the accelerator pedal is on or not (S174). If the checking result is found YES, then it is checked whether the switched state of the directional lever 4 is "advancing", or "retreating", or "neutral (5175).

If the switched state is found "neutral", then, similarly when the checking result of the above-mentioned step S171 is found NO, the processing goes to Step S176, where it is checked whether the input speed V set in Step S162 is equal to or more than zero or not (S176).

If the checking result is found YES, similarly when the checking result of S175 is found "advancing" or "retreating", the processing goes to Step S177, where the mode flag is set for"neutral" (S177). Afterthen, similarly when the checking result of S176 is found NO, the processing goes back to the main routine shown in Fig. 5.

As described above, in case where the accelerator is switched off during the normal running operation of the forklift and the forklift is thereby changed over to the neutral mode, the output command value of the induction motor 14 is calculated in accordance with the target speed Vt in transition to the neutral mode as well as the speed V and acceleration G of the forklift, and the induction motor 14 is controlled in accordance with the thus calculated output command value.

For example, when an operator is going to run the forklift at the same speed as the forklift goes from a flat road into a slope, in case where the accelerator pedal is turned off just before the forklift advances into the slope, with the speed in advancing into the slope as a target speed Vt, the forklift is allowed to run down the slope with no acceleration while the speed of the forklift is maintained at the target speed Vt or slower.

Therefore, according to the above-mentioned embodiment, in case where the operator adjusts the pressing amount of the accelerator pedal 9 just before the forklift goes into the slope to thereby adjust the speed of the forklift to a desired speed, the forklift is able to run down the slope at the then speed as it is.

Bytheway, in the above-mentioned embodiment, description has been given of the case in which the induction motor 14 is composed of a three-phase induction motor. However, of course, the induction motor 14 is not limited to the three-phase induction motor but it may also be composed of a two-phase induction motor or an induction motor having four or more phases.

Also, in the above-mentioned embodiment, description has been given of the case in which the invention is applied to the forklift of a counter balance type. However, the application of the invention is not limited to the forklift of a counter balance type but, of course, the invention can also be applied to other types of forklifts, for example, aforkliftof a reach type and a forklift which uses an induction motor of any other type as a power source thereof. In this case as well, there can be obtained the ef fect that is equivalent to the above-mentioned embodiment.

THIRD EMBODIMENT Now, a description will be given below of a third embodiment of a forklift control apparatus according to the invention when the invention is applied to a forklift of a counter balance type with reference to Figs. 1, 3, and 11 to 13. Specifically, Fig. 12 is a schematic view of a forklift to which the present forklift control apparatus according to the invention is applied, Fig. 13 is a circuit diagram of a portion of the present forklift control apparatus, Fig. 1 is a block diagram of the present forklift control apparatus, and Figs. 3 and 11 are respectively flow charts which are used to explain the operation of the present forklift control apparatus.

As shown in Fig. 12, to run a forklift, power may be supplied to a running motor 3 from a battery 2 which is carried on board the main body 1 of the forklift. In this operation, transmission means (not shown), which is used to transmit the drive power of the running motor 3 to wheels, is switched over to one of its operating states, that is, an advancing/retreating state and a neutral state for parking by operating a directional lever (or a directional switch) 4 which is used to switch the transmission means over to one of the advancing/retreating and neutral states, while the forklift is steered using a steering wheel 5. By the way, in Fig. 12, reference character 6 designates a mast disposed in the front portion of the body 1, 7 a lift bracket disposed on the mast 6, 8 a pair of forks disposed on the lift bracket 7, and 9 a accelerator pedal, respectively.

The running motor 3 is composed of, for example, a three-phase induction motor which is an ac motor. That is, as shown in Fig. 13, in case where a main switch 11 is switched on, the output dc power of the battery 2 is smoothed by a smoothing condenser 12 and is also converted into ac power by a three-phase bridge inverter 13, which is composed of 6 field-effect transistors Tl - T6 connected together in a full bridge manner, while the ac power is supplied to a three-phase induction motor 14.

Next, description will be given below of the structure of the present forklift control apparatus. As shown in Fig.

1, a detect signal, which is issued from an accelerator detect part (not shown) and is proportional to the pressing-down amount of the accelerator pedal 9, is converted into a digital signal by an analog/digital (A/D) converter portion 21, while the on/of f states and pressing-down amount of the accelerator pedal 9 can be detected by a CPU which will be discussed later.

Also, as shown in Fig. 13, on the rotary shaft of the induction motor 14, there is disposed a rotation detect part 15 which - 46 is composed of a rotary encoder; an output pulse from the rotation detect portion 15 is counted by a counter 22; and, from the count value of the counter 22, the number of rotations of the induction motor 14 is detected by the CPU (which will be discussed later).

Further, the switched state of the directional lever 4, which serves as a switching part to switch the transmission means (not shown) for transmitting the drive power of the induction motor 14 to the wheels over to one of the advancing /retre at ing and neutral states, is input into the CPU to be discussed later, so that the CPU judges the switched state of the directional lever 4, that is, the CPU checks whether the directional lever 4 is switched and set in the advancing direction, in the retreating direction, or in the neutral state.

Also, there is disposed a setting part 24 which is composed of, for example, a setting switch and is used to set a top speed in three stages, for example, 5 km/h, 10 km/h, and 15 km/h; and, the top speed set by switching the setting part 24 is fetched by the CPU to be discussed later, and the rotation of the induction motor 14 is controlled so that the actual running speed of the forklift can be limited to the top speed or lower set by switching the setting part 24.

And, the data on the pressing-down amount of the accelerator pedal 9, the number of rotations of the motor, the switched state of the directional lever 4, and the top speed set by the setting portion 24 are stored and held in a RAM 25 temporarily. In accordance with a given control program previously stored in a ROM 26, a CPU 27 allows a pulse width modulation (PWM: Pulse Width Modulation) pulse output part 28 to output PWM control pulses to the control terminals of the respective transistors Tl - T6 of the inverter 13, so that the output current of the induction motor 14 is controlled to thereby carry out normal power running operation control or regenerative operation control.

By the way, the CPU 27, during the running operation of the forklift, operates and derives the running speed and acceleration of the body 1 from the motor rotation number (forklift speed detect value) detected by the rotation detect part 15 serving as a forklift speed sensor; and, in accordance with the thus derived running speed and acceleration of the main body 1, the CPU 27 calculates the output command value of the induction motor 14 using the proportional differentiation (PD) in order to be able to limit the running speed to the top speed or lower set by the setting part 24.

In this operation, the running speed and the top speed set by the setting part 24 are compared with each other by the CPU 27. For example, in case where the top speed is set at the speed of 15 km/h, the output command value of the induction motor 14 is calculated in such a manner that the running speed cannot exceed 15 km/h and, in accordance with the thus calculated output command value, the PWM pulse out put portion 28 is controlled to thereby be able to control the number of rotations of the induction motor 14.

In this operation, at the same time, the CPU 27 may derive the positive and negative direction of the running speed according to whether the self-running direction of the main body 1 is in the advancing direction or in the retreating direction and, according to the direction of the running speed, the output command value of the induction motor 14 corresponding to the forward rotation direction (advancing state) of the induction motor 14 or the reversed rotation direction (retreating state) of the induction motor 14 may be calculated.

Also, the output command values by the CPU 27 are respectively calculated by the following equations:

Mf = kl x (V-Vs) + k2 x G (for the advancing state) Mb = -kl x W-Vs) - U x G (for the retreating state) where Vs expresses the top speed set by the setting part 24, V expresses the derived running speed, G expresses the acceleration, kl and U respectively express the gains (coefficients) of the control system, Mf expresses the output command value of the induction motor 14 in case where the running direction is the advancing direction, and Mb expresses the output command value of the induction motor 14 in case where the running direction is the retreating direction.

Here, the first terms of the right sides of the above-mentioned two equations represent proportion (P) control components in the proportional differentiation (PD) control, whereas the second terms of the right sides represent differentiation (D) control components.

Next, description will be given below of the operation

49 - of the present forklift control apparatus with reference to a flow chart shown in Fig. 11.

As shown in Fig. 11, at first, the CPU 27 initializes the whole forklift control apparatus including the RAM 25 (S201), fetches a signal proportional to the pressing-down amount of the accelerator pedal from the accelerator pedal detect part (S202), inputs the switched state of the directional lever 4 through the PI 23 (S203), and fetches the count value obtained by the counter 22 and calculates the then running speed V and acceleration G of the main body 1 from the fetched count value (S204). The calculation of the running speed V by the CPU 27 corresponds to a forklift speed calculation part.

Next, it is checked whether the running speed V calculated in Step S204 is smaller than the top speed Vs or not (S205).

If the checking result is YES, then it can be judged that it is not necessary to put any limit on the running speed V and, therefore, there is executed a normal running control processing (S206). After then, the processing goes to Step S210 which will be discussed later. And, the above-mentioned processing in Step S205 by the CPU 27 corresponds to a comparison and calculation part.

Here, the normal running control processing in Step S206 is a processing (S220) in which, as shown in Fig. 3, a motor output command value in the normal running operation of the forklift is calculated by multiplying a given gain (coefficient) and the pressing-down amount of the accelerator pedal. That is, this is a processing in which the pressing-down amount of the accelerator pedal 9 is detected by the accelerator pedal detect part and the output command value of the induction motor 14 proportional to the pressing-down amount of the accelerator pedal 9 is calculated. And, this processing by CPU 27 corresponds to a control part.

On the other hand, if the checking result in Step S205 is NO, then it can be judged that the then running speed of the forklift is equal to or higher than the top speed and it is necessary to put a limit on the running speed. Accordingly, it is checked whether the switched state of the directional lever 4 is an advancing state or a retreating state (S207).

If the checking result is the advancing state, then there is calculated the output command value Mf of the induction motor 14 according to the above-mentioned equation of the output command value Mf of the induction motor 14 in the case of the motor advancing operation (S208). Or, if the checking result is the retreating state, then there is calculated the output command value Mb of the induction motor 14 according to the above-mentioned equation of the output command value Mb of the induction motor 14 in the case of the motor retreating operation (S209). This calculation processing of the output command values of the induction motor 14 by the CPU 27 in case where the running speed is equal to or higher than the top speed also corresponds to the control part.

And, after execution of the processings of the steps S206, S208, and S209, the processing goes to the next step S210, where the PWM pulse output portion 28 is controlled by the CPU 27 in accordance with the output command value of the induction motor 14 calculated in Step S206, and thus the number of rotations of the induction motor 14 is controlled so that the forklift running speed becomes the speed corresponding to the pressing-down amount of the accelerator pedal (S210).

On the other hand, in the case of Step S208, the PWM pulse output part 28 is controlled by the CPU 27 such that the output of the induction motor 14 becomes Mf and, in the case of Step S209, the PWM pulse output portion 28 is controlled by the CPU 27 such that the output of the induction motor 14 becomes Mb; and, thus the number of rotations of the induction motor 14 is controlled so that the forklift running speed becomes the speed corresponding to the pressing-down amount of the accelerator pedal (S210) and, afterthen, theprocessing returns back to the above-mentioned step S202.

Thanks to the above control procedures, even in case where an operator presses down on the accelerator pedal strongly, the top running speed of the forklift can be limited to the top speed, for example, 15 km/h set by the setting portion 24. In this case, when the pressing-down amount of the accelerator pedal is small and thus the actual running speed does not reach the top speed, the induction motor 14 is held in the normal power operation control state.

Also, even in case where the forklift runs from a flat road into a slope with the accelerator pedal pressed down, the running speed of the forklift when going down the slope can be limited to the top speed, 15 km/h. When the running speed is limited to the top speed or lower in the above manner, the induction motor 14 is held in the regenerative operation control state.

Therefore, according to the above-mentioned embodiment, even in case where the forklift runs from a flat road into a slope with the accelerator pedal pressed down, since the running speed of the f orklif t can be limited to the top speed, there is no possibility that the forklift can accelerate gradually as in the conventional forklift control apparatus, which can eliminate a fear that the cargoes carried on board the forklift can collapse as well as can eliminate the need for setting an extra braking distance when braking the f orklif t.

Thanks to this, the forklift is allowed to run down the slope at the safe speed.

By the way, in the above embodiment, in Step S207 shown in Fig. 11, by checking whether the switched state of the directional lever 4 is the advancing state or retreating state, the motor output command value Mf in the case of the advancing operation and the motor output command value Mb in the case of the retreating operation are calculated. However, alternatively, in Step S204, whether the switched state of the directional lever 4 is the advancing state or retreating state may be judged from the direction of the speed derived from the count value of the counter, and, in accordance with the result of this judgment, the motor output command value Mf in the case of the advancing operation and the motor output command value Mb in the case of the retreating operation may be calculated.

Also, in the above embodiment, the running speed of the forklift is limited to the top speed or lower set by the setting part 24. However, of course, the running speed of the forklift may also be limited to the speed that is slightly larger than the top speed (for example, the top speed + I km/h).

Further, in the above embodiment, description has been given of the case in which the top speed is set in three stages by the setting part 24. However, it goes without saying that the top speed may also be set in two stages or in four or more stages.

Still further, in the above embodiment, description has been given of the case in which the induction motor 14 is used as the power source of the forklift. However, even in the case of a forklift which uses a dc motor as the power source thereof, the present invention can also be applied similarly and also there can be obtained effects equivalent to those in the above embodiment.

Moreover, in the above embodiment, description has been given of the case in which the invention is applied to the forklift of a counter balance type. However, the invention is not limited to the forklift of a counter balance type.

For example, the invention can also be applied to other types of forklifts including a forklift of a reach type and a forklift using other type of induction motor as the power source thereof and, in these cases as well, there can be obtained the equivalent effect to the above embodiment.

Further, the invention is not limited to the above-mentioned embodiment but there are possible various changes and modifications without departing from the scope of the patent claims appended herein.

As has been described heretofore, according to the first aspect of the invention, when the forklift body stops halfway on the slope, even in case where the operator removes his or her foot from the accelerator pedal without applying the parking brake, the forklift main body is made to slip down slowly along the slope at a given low speed or lower, which can prevent the slip-down speed of the forklift main body from increasing gradually, thereby being able to maintain the slip-down speed at a constant level. Also, since the operator can afford to observe that the forklift main body is slipping down slowly, the operator can be aware that he or she has forgot to apply the parking brake; that is, the operator can be informed of the failure to apply the parking brake. This makes it possible to enhance safety in running the forklift.

Also, it is possible to prevent the battery from being exhausted up during the forklift main body slipping-down operation, so that the life of the battery can be extended.

And, according to the second aspect of the invention, since the motor output command value is calculated in accordance with the speed and acceleration of the forklift main body when it runs by itself, by controlling the motor in accordance with the thus calculated output command value, the self -running speed of the forklift main body can be maintained at a given low speed value.

Further, according to the third aspect of the invention, the motor output command value with the motor rotation direction taken into account can be calculated depending on the direction of the forklift main body running by itself on the slope, that is, in either of advancing or retreating direction.

According to the fourth aspect of the invention, in case where the accelerator pedal is turned off, with the then speed as a target speed, the forklift is thereafter allowed to run while the speed of the forklift is being maintained at the target speed or slower. Thanks to this, for example, when advancing into a slope, in case where an operator adjusts the speed of the forklift to a desired speed just before advancing into the slope, the forklift is allowed to run down the slope with the then speed thereof unchanged; that is, in this case, there can be prevented a possibility that the speed of the forklift can accelerate to be faster than the operator expects, so that the forklift is allowed to run down the slope at an optimum speed for the operator. And, according to the fifth aspect of the invention, in case where the

accelerator pedal detect part detects the off state of the accelerator pedal and the forklift operation mode is thereby changed over to the neutral mode, the motor output command value is calculated in accordance with the target speed in transition to the neutral mode as well as the speed and acceleration of the forklift derived by the derive part; and, therefore, by controlling the induction motor in accordance with the thus calculated output command value, the speed of the forklift can be maintained at the target speed in transition to the neutral mode or lower.

Further, according to the sixth aspect of the invention, themotoroutput command value with themotor rotation direction taken into account can be calculated depending on the running direction of the forklift body, that is, whether the forklift main body is going to advance or retreat.

According to the seventh aspect of the invention, in the running speed of the f orklif t up to the top speed thereof, the forklift is allowed to run with acceleration corresponding to the pressing-down amount of the accelerator pedal and, when the running speed of the forklift exceeds the top speed, the running speed can be limited to the top speed or lower.

Thanks tothis, inthenormal running operation of the forklift, not only the running operation of the f orklif t can be controlled with such driving sense that can be obtained when driving a car, but also, in the case where the running speed of the forklift becomes higher than the top speed, for example, when the forklift runs down a slope, the running speed can be limited to the top speed or'lower, thereby being able to exert such running control that can keep the safety of the forklift.

Also, according to the eighth aspect of the invention, in addition to the effects obtained by the above-mentioned 57 - first aspect of the invention, the running speed of the forklift can be limited to the top speed or lower regardless of the on and off states of the accelerator pedal- Due to this, even in case where an operator removes his or her foot from the accelerator pedal on a slope, the running speed of the f orkli f t can be limited to the top speed or lower, which allows the operator to loosen or remove his or her foot hold of the accelerator pedal on the slope similarly when the operator drives a car. Therefore, not only the operator is allowed to drive the forklift with the same driving sense as the operator drives a car, but also the running speed of the forklift can be limited, that is, the safety of the forklift as well as the operator can be enhanced.

Further, according to the ninth aspect of the invention, the running speed of the forklift can be limited to the top speed or lower regardless of the on and off states of the accelerator pedal. Thanks to this, even in case where the operator removes his or her foot hold of the accelerator pedal on a slope, the running speed of the forklift can be limited to the top speed or lower. Therefore, not only the operator is allowed to drive the forklift with the same driving sense as the operator drives a car, that is, the operator is allowed to ease or remove his or her foot hold of the accelerator pedal on the slope, but also the running speed of the forklift can be limited, that is, the safety of the forklift as well as the operator can be enhanced.

Still further, according to the tenth aspect of the invention, since the output command value of the motor is calculated in accordance with the speed and acceleration of the forklift while running, by controlling the motor in accordance with the thus calculated motor output command value, the forklift self-running speed can be limited to a set value or lower.

Yet further, according to the eleventh aspect of the invention, depending on whether the forklift runs in an advancing or retreating direction, the motor output command value with the motor rotation direction taken into account is calculated; and, the running speed of the forklift can be limited to the top speed or lower set by the setting part in both of the advancing and retreating directions.

Moreover, according to the twelfth aspect of the invention, a control signal from the inverter to the induction motor may be controlled in such a manner that the motor output command value can become the output command value calculated by the control part. Thanks to this, on a flat road, the induction motor can be controlled so as to carry out a normal power operationand, onaslope, the induction motor can be controlled so as to carry out a regenerative operation, which makes it possible to limit the running speed of the forklift to the top speed or lower.

59 -

Claims

CLAIMS:

1. A forklift control apparatus, wherein an output DC power of a battery mounted on a f orklif t main body is converted into AC power by an inverter to be supplied to an induction motor; and the induction motor is driven by a drive part of the forklift, to thereby execute a normal power operation or regenerative operation of the forklift main body, characterized in that:

after the forklift main body stops, an output command value of the induction motor using a proportional differentiation control is calculated in accordance with a speed and an acceleration of the forklift main body when the forklift main body runs with an accelerator pedal not Pressed down to maintain the speed at a predetermined value or lower.

2. The forklift control apparatus as set forth in claim 1, comprising:

a rotation detection portion for detecting the number of rotations of the induction motor; a derive portion for deriving the speed and the acceleration of the forklift main body from a detected value obtained by the rotation detect part; a switching portion for switching and setting a transmission for transmitting the drive force of the induction motor to a wheel of the f orklif t main body into one of advancing and retreating states or into a neutral state; an accelerator pedal detection portion for detecting whetehr an accelerator pedal is in the on state or off state; and a control portion, on condition that, when the rotation detect portion detects that the forklift main body stops, the switching portion is set in the neutral state and the of f state of the accelerator pedal is detected by the accelerator pedal detect portion, for calculating the output command value of the induction motor using the proportional differentiation control in accordance with the speed and the acceleration of the forklift main body when the f orklif t body runs in order to maintain the speed at a predetermined low value or lower.

3. A forklift control apparatus as set forth in claim 2, wherein the control part calculates the output command value in the advancing direction and the output command value in the retreating direction respectively according to the directions of the speed derived by the derive portion.

4. A forklift control apparatus, wherein an output Mpowerof a battery mounted on a f orklif t main body is converted into AC power by an inverter to be supplied to an induction motor; and the induction motor is driven by a drive part of the forklift, to thereby execute a normal power operation or regenerative operation of the forklift main body, characterized in that:

when an accelerator pedal is removed f rom a pressing-down action by an operator during the running operation of the forklift and the forklift is thereby changed over to a neutral mode and the speed of the forklift in transition to the neutral mode to be a target speed is -reaches or exceeds the target speed, the output command value of the induction motor using a proportional differentiation control is calculated in accordance with the target speed as well as a speed and an acceleration of the forklift in order to be able to maintain the target speed.

5. The forklift control apparatus as set forth in Claim 4, comprising:

a rotation detection portion for detecting the number of rotations of the induction motor; a derive portion for deriving the speed and acceleration of the forklift from a detect value obtained by the rotation detect portion; an accelerator pedal detection portion for detecting whether the accelerator pedal is pressed down or not; and, a control portion for changing the forklift over to a neutral mode when the undepressed state of the accelerator is detected by the accelerator detect portion, for setting the speed of the forklift in transition to the neutral mode as the target speed, and for calculating the output command value of the induction motor using the proportional differentiation control in accordance with the target speed as well as the speed and acceleration of the forklift derived by the derive portion to maintain the target speed when the speed of the forklift reaches or exceeds the target speed.

6. The forklift control apparatus as set forth in claim 5, wherein the control portion calculates the output command value in an advancing direction and the output command value in an retreating direction respectively according to the directions of the speed derived by the derive portion.

7. A forklift control apparatus capable of driving running motor by power supplied from a battery nounted on forklift main body, the forklift control apparatus comprising:

an accelerator pedal detection portion for detecting the pressing-down amount of an accelerator pedal; a forklift speed sensor for detecting a forklift speed detect value corresponding to the running speed of the forklift main body; a forklift speed calculation portion for calculating the running speed of the forklift main body from the forklift speed detect value obtained by the forklift speed sensor; a setting portion for setting the top speed of theforklift main body; a comparison and calculation portion for comparing and calculating the running speed obtained by the forklift speed calculation portion and the top speed set by the setting portion; and a control portion which, as a result of the comparison made in the comparison and calculation portion, when the running speed is equal to or lower than the top speed, calculates a motor output command value for providing the forklift main body with acceleration proportional to the accelerator pedal pressing-down amount obtained by the accelerator pedal detection portion and, when the running speed exceeds the top speed, calculates a motor output command value for limiting the running speed to the top speed or lower.

8. The forklift control apparatus capable of driving running motor by power supplied from a battery mounted on forklift main body, the forklift control apparatus comprising:

an accelerator pedal detection portion for detecting the on/of f states of an accelerator pedal and the pressing-down amount thereof; a forklift speed sensor for detecting a forklift speed detect value corresponding to a running speed of the forklift main body; a forklift speed calculation portion for calculating the running speed of the forklift main body from the forklift speed detect value obtained by the forklift speed sensor; a setting portion for setting the top speed of theforklift - 64 main body; a comparison and calculation portion for comparing and calculating the running speed obtained by the forklift speed calculation portion and the top speed set by the setting part; and, a control portion which, as a result of a comparison made in the comparison and calculation portion, when the running speed is equal to or lower than the top speed, calculates a motor output command value for providing the forklift main body with acceleration proportional to the accelerator pedal pressing-down amount obtained by the accelerator pedal detect part and, when the running speed exceeds the top speed, calculates amotor output commandvalue for limiting the running speed to the top speed or lower regardless of the on/of f states of the accelerator pedal.

9. A forklift control apparatus capable of driving running motor by power supplied from a battery mounted on main body of a forklift, the forklift control apparatus comprising:

an accelerator pedal detect portion for detecting the on/off states of an accelerator pedal and the pressing-down amount thereof; a forklift speed sensor for detecting a forklift speed detect value corresponding to a running speed of the forklift main body; a forklift speed calculation portion for calculating the running speed of the forklift main body from the forklift speed detect value obtained by the forklift speed sensor; asettingportion for settingthe top speedof the forklift main body; a comparison and calculation part for comparing and calculating the running speed obtained by the forklift speed calculation portion and the top speed set by the setting portion; and, a control portion which, as a result of the comparison made in the comparison and calculation part, when the running speed exceeds the top speed, calculates a motor output command value for limiting the running speed to the top speed or lower regardless of the on/off states of the accelerator pedal.

10. A forklift control apparatus as set forth in any one of Claims 7, 8 and 9, further comprising:

a rotation detection portion for detecting the number of rotations of the running motor; and, a derive portion for deriving the speed and acceleration of the forklift main body from a detect value obtained by the rotation detect portion, wherein the control part derives the speed and acceleration of the forklift main body from the number of rotations of the motor obtained by the rotation detect portion and, in accordance with the speed and acceleration derived, calculates the output command value.

11. A forklift control apparatus as set forth in any one of Claims 7, 8, 9 and 10, er comprising:

a switching portion for switching and setting a transmission for transmitting the drive power of the running motor to a wheel at any one of advancing, retreating and neutral states, wherein the control portion, in accordance with the switched states of the transmission by the switching portion, calculates the output command value for an advancing direction and the output command value for a retreating direction, respectively.

12. The forklift control apparatus as set forth in any one of Claims 7, 8, 9, 10 and 11, wherein the running motor comprises an induction motor, and the output dc power of the battery is converted to ac power by an inverter to be supplied to the induction motor.

13. A forklift control apparatus substantially as hereinbefore described with reference to Figure 1 together with any one or more of Figures 2 to 10 of the accompanying drawings.

14. A forklift control apparatus substantially as hereinbefore described with reference to Figure 11 of the accompanying drawings.