GB2357200A

GB2357200A - Electric vehicle regenerative braking apparatus

Info

Publication number: GB2357200A
Application number: GB0027976A
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: GB0027976D0; GB2357200B; DE10056552A1; FR2801011B1; DE10056552B4; FR2801011A1

Abstract

A control apparatus for an electric vehicle, particularly a forklift truck, whereby the regenerative braking operation of the motor is controlled according to the speed of the vehicle. Above a predetermined threshold speed, V<SB>t</SB>, the regenerative braking force is constant, whereas below the threshold speed the braking force applied is proportional to the speed of the vehicle. The regenerative braking may be applied by a brake pedal, when the accelerator is released, or when the vehicle is put into a neutral mode. A control portion 27 may be provided to detect the rotations of the motor and the respective states of the accelerator and brake pedals and the directional lever. The motor may be an ac induction motor, fed from batteries via an inverter 13.

Description

2357200 FORKLIFT W-AAW A.PPARATUS

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a forklift brake 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 an induction motor is driven by a drive part, thereby braking the forklift using the regenerative braking operation of the induction motor.

2. Description of the Related Art

Normally, to run a forklift to be driven by a battery, for example, as shown in Fig. 6, power is supplied to a dc motor 3 for running by a battery 2 carried on board a body 1 of the forklift. In this running operation, by operating a directional lever (or a directional switch) 4 which is used to switchingly set transmission means (not shown) for transmitting the drive power of the de motor 3 to wheels in one of advancing and retreating states or in a neutral state, the transmission means is switched over to one of advancing and retreating directions or to a neutral state for parking, and the forklift is steered using a steering wheel 5. By the way, in Fig. 6, reference character 6 designates a mast disposed in the front portion of the body 1, 7 a lift bracket mounted on the mast 6, 8 a pair of forks mounted on the lift bracket 7, 9 an accelerator pedal, and 10 a brake pedal, respectively.

Recently, there is proposed a forklift which, as a power source thereof, uses an induction motor consisting of an ac motor instead of the above-mentioned dc motor 3. In the case of this induction motor type forklift, for example, as shown in Fig. 7, by turning on a main switch 11, the output dc power of the battery 2 is smoothed by a smoothing condenser 12 and, at the same time, the battery 2 output dc power is converted into ac power by a three-phase bridge inverter 13 consisting Of six full-bridge connected field effect transistors TI - T6 and is then supplied to a three-phase induction motor 14; that is, by making use of the regenerative braking characteristic of the induction motor 14, the normal power operation control and regenerative operation control of the forklift are carried out.

In the case of the forklift using the induction motor 14 as the power source thereof, in case where an operator press down the brake pedal 10, the on or off (that is, pressed or non-pressed) state of the brake pedal 10 is detected by a brake pedal detect part (not shown) and, in addition to a braking force given by a brake device of a mechanical type or an oil pressure type, there is generated a braking force due to the regenerat.ive braking operation of the induction motor 14 to thereby brake the forklift.

In addition, in the case of the f orklif t using the induction 2 motor 14 as the power source thereof, when, while the forklift is running, the forklift is switched over to a neutral state, that is, when an operator stops pressing down the accelerator pedal 9, or when, while the forklift is running, the operator switches the directional lever 4 over to a neutral state to thereby remove the pressed state of the accelerator pedal 9, the of f (non-pressed) state of the accelerator pedal 9 is detected by an accelerator pedal detect part (not shown), or the switching of the directional lever 4 over to the neutral state is recognized by a control part; and, in response to such detection or recognition, there is generated a braking force due to the regenerative braking operation of the induction motor 14 to thereby be able to brake the forklift in such a manner that corresponds to engine braking used in a car.

However, in the case of the above-mentioned conventional forklift brake apparatus, since the braking force given by the regenerative braking operation of the induction motor 14 is constant independently of the speed of the forklift, even just before the forklift stops after it decelerates to a sufficient degree, the braking force due to the regenerative braking operationof the induction motor 14 remains acting; and, therefore, the braking force is too large as a braking force necessary just before the forklift stops and also the braking force disappear suddenly just after the forklift stops, which makes it impossible for the forklift to stop smoothly and thus there is a fear that 3 cargoes carried on the forklift can collapse.

On the other hand, the conventional forklift also includes a forklift which does not use the above-mentioned braking due to the regenerative braking operation of the induction motor 14. In this structure, in case where the speed of the forklift under loading and unloading is excessively high, an operator must press down the brake pedal 10 frequently for deceleration and thus the operator feels it troublesome to operate the brake pedal 10, which often makes it impossible to concentrate the operator's attention on the loading and unloading operation.

SUMMARY OF THE INVENTION

The present invention has been achieved to eliminate the drawbacks found in the above-mentioned conventional forklift controlapparatus. Accordingly, it is an object of the invention to provide a forklift control apparatus which, as a forklift decelerates, can reduce the braking force due to the regenerative braking operation of an induction motor to thereby be able to stop the forklift smoothly.

It is anohter object of the invention to provide a forklift control apparatus which, when, while the forklift is running, it is switched over to a neutral state, can brake the forklift using a braking force due to the regenerative braking operation of an induction motor, that is, can generate a constant braking force when the speed of the forklift is high and, as the speed 4 of the forklift becomes lower, can generate a braking force proportional to the then forklift speed to thereby be able to stop the forklift smoothly.

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 a body of a forklift is converted into ac power by an inverter and is then supplied to an induction motor for power, and the induction motor is driven by a drive part, thereby braking the forklift by means of the regenerative braking operation of the induction motor, wherein, when a brake pedal is pressed down during the running operation of the forklift, the output voltage of the induction motor is calculated in such a manner that, in case where the then speed of the forklift is found equal to or larger than a predetermined speed, a braking force due to the regenerative braking operation of the induction motor can be made constant independently of the speed of the f orklif t, and, in case where the then speed of the forklift is found smaller than the predetermined speed, a braking force due to the regenerative braking operation of the induction motor can be made proportional to the speed of the forklift.

According to the above structure, when the brake pedal is pressed down during the running operation of the forklift, in case where the then speed of the forklift is found equal to or larger than the predetermined speed, as a braking force due to the regenerative braking operation of the induction motor, there can be applied a constant brakinq force and also, in case where the forklift decelerates and thus the speed of the forklift is found smaller than the predetermined speed, as the braking force due to the regenerative braking operation of the induction motor, there can be applied a braking f orce which is proportional to the speed of the forklift.

Therefore, just before the forklift stops as a result of proper deceleration of the forklift, the braking force due to the regenerative braking operation can be made sufficiently small, which eliminates the inconvenience that, as in,--he conventional forklift control apparatus, the braking force can disappear suddenly just after the forklift stops; and, as a result of this, the forklift can be made to stop smoothly with no sense of incongruity.

Also, according to a second aspect: of the invention, the forklift control apparatus according to the first aspect of the invention 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 body from a detect value obtained by the rotation detect part; a brake pedal detect part for detecting the on or off (pressed or non-pressed) state of a brake pedal; and, a control part which, when the on state of the brake pedal is detected by the brake pedal detect part, checks whether the speed of the forklift derived by the derive 6 part is equal to or larger than a predetermined speed or not and, after such checking, calculates the output voltage of the induction motor in such a manner that, in case where the derived forklift speed is found equal to or larger than the predetermined speed, a braking force due to the regenerative braking operation of the induction motor can be made constant independently of the speed of the forklift and, in case where the derived forklift speed is found smaller than the predetermined speed, the braking force due to the regenerat - ive braking operation of the induction motor can be made proportional to the speed of the forklift.

According to the above structure, the on state of the brake pedal is detected by the brake pedal detect part, whether the forklift speed derived by the derive part is equal to or larger than a predetermined speed or not is checked by the control part and, after such checking, the output voltage of the induction motor is calculated in such a manner that, in case where the derived forklift speed is found equal to or larger than the predetermined speed, the braking force due to the regenerative braking operation of the induction motor can be made constant and, in case where the forklift speed is found smaller than the predetermined speed, the braking f orce due to the regenerative braking operation can be made proportional to the forklift speed.

Thanks to this, by controlling the induction motor in such manner that the calculated output voltage can be obtained, smooth braking characteristic can be realized.

7 Further, according to a third aspect of the invention, in the forklift control apparatus according to the first or second aspect of the invention, the predetermined speed is a speed at which the product of the square of the value of the detected speed of the forklift in the brake pedal pressed state detected time and a previously set coefficient is equal to the product of the value of the detected speed and another previously set coefficient.

According to the above structure, the output voltage of the induction motor can be calculated in such a manner that, in case where the speed of the forklift is found equal to or larger than the predetermined speed, the braking force due to the regenerative braking operation of the induction motor can be made constant and, in case where the forklift speed is found smaller than the predetermined speed, the braking force due to the regenerative braking operation can be made proportional to the forklift speed.

In attaining the above object, according to a fourth aspect of the invention, there is provided a forklift control apparatus structured such that the output dc power of a battery carried on board a body of a forklift is converted into ac power by an inverter and is then supplied to an induction motor for power, and the induction motor is driven by a drive part, thereby braking the forklift by means of the regenerative braking operation of the induction motor, wherein, when, while the forklift is 8 running, an accelerator pedal is switched over to an off state or means for transmitting the drive force of the induction motor to wheels is switched over to a neutral state, the output voltage of the induction motor is calculated in such a manner that, in case where the then speed of the forklift is equal to or larger than a predetermined speed, a braking force due to the regenerative braking operation of the induction motor can be made constant independently of the forklift speed, and, in case where the then speed of the forklift is smaller than the predetermined speed, a braking force due to the regenerative braking operation of the induction motor can be made proportional to the forklift speed.

According to the above structure, in case where, while the forklift is running, the accelerator pedal is switched over to the off (non-pressed) state or the transmitting means is switched over to its neutral position, during the time when the then speed of the forklift is equal to or larger than the predetermined speed, as a braking force due to the regenerative braking operation of the induction motor, there can be applied a constant braking force; and, when the forklift decelerates and the speed of the forklift is thereby smaller than the predetermined speed, as the braking force due to the regenerative braking operation of the induction motor, there can be applied a braking f orce which is proportional to the speed of the f orklif t.

Therefore, while the speed of the forklift is large, there 9 can be applied a relatively large braking force, which c-an eliminate the need that, as in the conventional forklift control apparatus, an operator must operate the brake pedal frequently; and, just before the forklift stops as a result of proper deceleration of the forklift, the braking force due to the regenerative braking operation of the induction motor can be made sufficiently small, which can eliminate the inconvenience that, as in the conventional forklift control apparatus, the braking force can disappear suddenly just after the forklift stops, with the result that the forklift can be made to stop smoothly with no sense of incongruity..

Also, according to a fifth aspect of the invention, the forklift control apparatus according to the first aspect of the invention 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 body from a detect value obtained by the rotation detect part; a switching part for switchingand setting the transmitting means fortransmitting thedriveforceof the induction motor to wheels in one of advancing and retreating states or in a neutral state; an accelerator pedal detect part for detecting the on or off (pressed or non-pressed) state of an accelerator pedal; and, a control part which, when the off state of the accelerator pedal is detected by the accelerator pedal detect part, or when the transmitting means is set in the neutral state, checks whether the speed - 10 of the forklift derived by the derive part is equal to or larger than the predetermined speed or not and, after such checking, calculates the output voltage of the induction motor in such a manner that, in case where the derived forklift speed is found equal to or larger than the predetermined speed, a braking force due to the regenerative braking operation of the induction motor can be made constant independently of the speed of the forklift and, in case where the derived forklift speed is found smaller than the predetermined speed, the braking force due to the regenerative braking operation of the induction motor can be made proportional to the speed of the forklift.

According to the above structure, the off state of the accelerator pedal is detected by the accelerator pedal detect part, it is checked by the control part whether the speed of the forklift derived by the derive part is equal to or larger than the predetermined speed or not, and the output voltage of the induction motor is calculated in such a manner that, in case where the speed of the forklift is found equal to or larger than the predetermined speed, the braking force due to the regenerative braking operation of the induction motor can be made constant and, in case where the derived speed is found smaller than the predetermined speed. the braking force due to the regenerative braking operation can be made proportional to the forklift speed. Thanks to this, by controlling the induction motor so that the calculated output voltage can be obtained, a smooth braking characteristic can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Fig. 2 is an explanatory view of the operation of the present embodiment.

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

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

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

Fig. 6 is a side view of a convenLional forklift of a dc:

motor type.

Fig. 7 is circuit diagram of a control circuit of a conventional three-phase induction motor.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Now, description will be given below of an embodiment of a forklift control apparatus according to the invention which is applied to a forklift of a counterbalance type with reference to Figs. 1 to 5. Specifically, Fig. 1 is a block diagram of a forklift control apparatus according to the present embodiment of the invention, Fig. 2 is an explanatory view of the operation of the present forklift control apparatus, and Figs. 3, 4 and are respectively flow charts to explain the operation of the present forklift control apparatus.

Here, the structure of a forklift of a counter balance type is the same as the structure shown in Fig. 6 except that an induction motor is used instead of the dc motor 3. For this reason, in the following description, Fig. 6 is also referred to. Also, in the present embodiment, in the present embodiment, there is used a three-phase induction motor similar to the induction motor 14 shown in Fig. 7 and an inverter used to drive the induction motor is the same in structure as the three-phase bridge inverter 13 shown in Fig. 7. Therefore, in the following description, Fig. 7 is also referred to.

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 to a digital signal by an analog/digital (A/D) converting part 21; and, the on or off state of the accelerator pedal 9 depending on whether the accelerator pedal 9 is pressed down or not as well as the pressing-down amount of the accelerator pedal 9 can be detected by a CPU which will be discussed later. Also, as shown in Fig.

6, on the rotary shaft of the induction motor 14, there is disposed a rotation detect part 15 which consists of a rotary encoder; and, an output pulse from the rotation detect part 15 is counted by a counter 22 and, in accordance with the count value, the number of rotations of the induction motor 14 can be deteci-ed by the CPU to be discussed later.

Further, the switched state of a directional lever 4 serv_ng as a switching part, which is used to switch and set transmissi-on means (not shown) f or transmitting the drive f orce of the induct J.on motor to wheels at one of advancing and retreating states or at a neutral state, as well as the on or off state of a brake pedal 10 operation, which depends on whether the brake pedal is pressed down or not, to be detected by a brake pedal detect part (not shown) are input through a parallel input part (PI) 23 into the CPU to be discussed later; and, in which one of the advancing, retreating and neutral states the directional lever 4 is switched or set as well as whether the braking pedal is pressed down (on) or not (off) can be checked by the CPU.

And, various data on the pressing-down amount of the accelerator pedal 9, the rotation number of the induction motor 14, the switched state of the directional lever 4, and the on or off state of the brake pedal 10 are stored and held in a RAM 25 temporarily. In accordance with a specified control program which is previously stored in a ROM 26, the CPU 27 allows a pulse width modulation (PWM) pulse output part 28 to output PWM control pulses therefrom to the control terminals of the respective transistors Tl to T6 incorporated in an inverter 13, thereby controlling the output current of the induction motor 14, so that the normal power operation control or regenerative operation control of the induction motor 14 can be carried out.

By the way, the CPU 27 derives the speed and acceleration of the body 1 from the motor rotation number detected by the rotation detect part 15. Further, in case where the on state of the brake pedal 10 is detected by the brake pedal detect part, the CPU 27 judges whether the derived speed of the forklift is equal to or larger than a given value or not. And, after such checking, the CPU 27 calculates the output voltage of the induction motor 14 in the following manner that, in case where the derived value of the speed of the forklift is found equal to or larger than the predetermined value, a braking force given by a regenerative braking operation can be made constant independently of the speed of the forklift; and, in case where the derived value of the speed is found smaller than the predetermined value, the braking force given by the regenerative braking operation can be made proportional to the speed of the forklift. Here, the deriving processing of the speed and acceleration by the CPU 27 corresponds to a derive part, while the calculation processing of the output voltage of the induction motor 14 by the CPU 27 corresponds to a control part.

In addtition, the CPU 27 derives the speed and acceleration of the body 1 from the motor rotation number detected by the rotation detect part 15. Further, if the off state of the accelerator pedal 9 is detected by the accelerator pedal detect part, or when the directional lever A is set in the neutial state, then the CPU 27 checks whether the derived speed of the forklift is equal to or larger than a predetermined value or not. And, after such checking, the CPU 27 calculates the output voltage of the induction motor 14 in the following manner: that is, in case where the derived speed of the forklift is found equal to or larger than the predetermined speed, a braking force given by the regenerative braking operation of the induction motor 14 can be made constant independently of the speed of the forklift; and, if the derived speed is found smaller than the predetermined speed, the braking force given by the regenerative braking operation of the induction motor can be made proportional to the speed of theforklift. Here, thederiving processing of the speed and acceleration by the CPU 27 corresponds to a derive part, while the calculation processing of the output voltage of the induction motor 14 by the CPU 27 corresponds to a control part.

And, based on the thus calculated output voltage value, the PWM pulse output part 28 is controlled and the rotation number of the induction notor 14 is controlled, thereby being able to execute the regenerative operation control of tne induction motor 14.

Also, where the derived speed val:e is expressed as V and the gains (coefficients) of a control system are expressed as - 16 kl, k2, the output voltage Mv of the induction motor 14 can be calculated by the CPU 27 according to one of the following equations (1) and (2) depending on whether the speed value V is equal to or larger, or smaller than a threshold value Vt.

which is a predetermined speed: that is, (1) Mv = kl X V2 (in the case of V >- Vt); and, (2) Mv = kl x V (in the case of V < Vt).

Braking forces, which are obtained when the induction motor 14 is controlled in accordance with the output voltages Mv respectively given by the above equations (1) and (2), are as shown in Fig. 2. Here, the predetermined threshold value Vt, as shown in Fig. 2, corresponds to a speed value obtained when a braking force based on the calculation value according to the equation (1) is equal to a braking force based on the calculation value according to the equation (2).

Next, description will be given 'below of the operation of the present forklift control apparatus with reference to flow charts respectively shown in Figs. 3, 4 and 5.

Fig. 3 shows one operation of the forklift. The CPU 27 firstly initializes the forklift control apparatus including the RAM 25 and other remaining components thereof (S1), a signal proportional to the pressing-down amount of the accelerator pedal 9 is fetched from the accelerator pedal detect part (S2), the switched state of the directional lever 4 is input through the PI 23 (S3), the count value obtained by the counter 22 is fetched (S4), and the output of the brake detect part is fetc,'led (S5).

And, it is checked whether the accelerator pedal 9 is on or not (S6). If the checking result is YES, then it can be judged that the forklift is held in a normal running state.

Therefore, it is checked whether the switched state of t--he directional lever 4 is in the advancing state, or in the retreatj-ng state, or in the neutral state (S7). If the switched state of the directional lever 4 is found in the advancing state or in the retreating state, then a normal running operation control processing is executed (S8) and, after then, the processD.ng goes to Step S15.

Here, the normal running operation control processing in Step S8 is a processing (S20) in which, as shown in Fig. 6, a motor output command value in the normal running operation is calculated by multiplying the predetermined gain (coef f' icier.t) and the pressing-down amount of the accelerator pedal 9.

on the other hand, if the checking result in Step S6 is NO, then the processing goes to Step S9 similarly when the directional lever is found held in the neutral state in Step S7; and, it is checked whether the brake pedal is on or not (S9). If the checking result is YES, then it can be judged that the forklift is held in the braking state and, therefore, - 18 the value V of the forklift speed is derived (S10) And, it is checked whether the value V is equal to or larger than the threshold value Vt or not (S11). If the checking result is YES, then the output voltage Mv of the induction motor 14 according to the above equation (1) is calculated (S12); and, if the checking result is NO, then the output voltage Mv of the induction motor 14 according to the above equation (2) is calculated (S13).

Also, if the checking result in Step S9 is NO, then it can be judged that the forklift is held in the neutral state.

Therefore, after the output voltage Mv of the induction motor 14 is set at zero (S14), the processing goes to Step S15 similarly after the processings in Steps S8, S12 and S13 are executed; and, based on the data calculated in Steps S8, S12 and S13, the rotation number of the induction motor 14 is controlled (S15) and, after then, the processing returns to the above-mentioned step S2.

In this manner, in case where the brake pedal is found on while the forklift is running, during the time when the value V of the f orklif t speed is equal to or larger than the predetermined threshold value Vt, a constant braking force is applied as a braking force given by the regenerative operation braking operation of the induction motor 14; and, when the forklift decelerates and thus the value V of the forklift speed becomes smaller than the predetermined threshold value Vt, a braking force proportional to the value of the forklift speed is applied as a braking force given by the regenerative braking operation of the induction motor 1.

Therefore, according to the above-described embodiment, just before the forklift stops while it is decelerating, the braking force due to the regenerative braking operation of the induction motor becomes sufficiently small. This eliminates a possibility that, as in the conventional forklift control apparatus, the braking force can disappear suddenly just aft the forkliftstops. Thatis, the forklift can be stopped smootnly with no sense of incongruity, so that the cargoes carried on the forklift can be prevented from collapsing.

Next, Fig. 4 shows another operation in the forklift. 'Fhe CPU 27 firstlyinitializes the forklift control apparatus including the RAM 25 and other remaining components thereof (SS1), a signal proportional to the pressing-down amount of the accelerator pedal 9 is fetched from the accelerator pedal detect part (SS2), the switched state of the directional le,7er 4 is input through the PI 23 (SS3), and the count value obtained by the counter 22 is fetched (SS4).

And, it is checked whether the accelerator pedal 9 is on or not (SS5). If the checking result is VES, then the directional lever 4 is checked for the switched state thereof, that -1.s, in which of the advancing, retreating, neutral states the directional lever 4 has been set (SS6) If the switched state of the directional lever 4 is found ir the advancing state or in the retreating state, then a normal running operation control processing is executed (SS7) and, after then, the processing goes to Step SS12.

Here, the normal running operation control processing in Step SS7 is a processing (SS20) in which, as shown in Fig. 5, a motor output command value in the normal running operation is calculated bymultiplying the predetermined gain (coefficient) and the pressing-down amount of the accelerator pedal 9.

On the other hand, if the checking result in Step SS6 is NO, then the processing goes to Step SS8 similarly when the directional lever 4 is found held in the neutral state in Step SS6, the value V of the speed of the forklift is derived (SS8); and, it is checked whether the thus derived value V is equal to or larger than the threshold value Vt or not (SS9). If the checking result is YES, then the output voltage Mv of the induction motor 14 according to the above equation (1) is calculated (SS10); and, on the other hand, if the checking result is NO, then the output voltage Mv of the induction motor 14 according to the above equation (2) is calculated (SS11). After then, the processing goes to Step SS12 similarly when the processings in Steps SS7 and SS10 are executed and, in accordance with the data that have been respectively calculated or obtained in Steps SS7, SS10 and SS11, the rotation number of the induction motor 14 is controlled (SS12). After then, the processing returns to Step S52.

- 21 In this manner, incase where, while the forklift is running, the accelerator pedal 9 is switched over Lo the off (non-pressed) state, or the directional lever 4 is switched over to its neutral state, during the time while the value V of the forklift speed is equal to or larger than the predetermined threshold value Vt, a constant braking force is applied as a braking force given by the regenerative braking operation of the induction motor 14; and, when the forklift decelerates and thus the value V of the forklift speed becomes smaller than the predetermined threshold value Vt, a braking force proportional to the vaLue of the forklift speed is applied as a braking force given by the regenerative braking operation of the induction motor 14.

Therefore, according to the above -described embodiment, while the speed of the forklift is large, there is applied a relatively large braking force, which eliminates the need for an operator to operate the brake pedal 10 so frequently as in theconventional forkliftcontrol apparEtus. On the other hand, just before the forklift stops while it is decelerating, the braking force due to the regenerative braking operation of the induction motor becomes sufficiently small, which elimina-k_es a possibility that, as in the conventional forklift control apparatus, the braking force can disappear suddenly just aft the forklift stops, so that the forklift can be stopped smoothly with no sense of Incongruity, thereby being able to prevent the cargoes carried on the forklift from collapsing.

In the above-described embodiment, description has been given of the embodiment in which the induction motor 14 consists of a three-phase induction motor. However, according to the invention, the inductionmotor 14 is not limited to the three-phase induction motor but, of course, the induction motor 14 may also consist of a two-phase induction motor or an induction motor having four or more phases.

Further, in the above-described embodiment, description has been given of the embodiment in which the invention is applied to the f orklif t of a counterbalance type. However, the invention is not limited to the forklift of a counter balance type but can also be applied to other types of f orklif ts which are capable of using an induction motor as a power source thereof, such as a forklift of a reach type. And, in this case as well, there can be obtained equivalent effects to the above-described embodiment.

Moreover, the invention is not limited to the above-described embodiment, but various changes and modifications are also possible without departing from the scope and spirit of the invention.

As has been described heretofore, according to the first aspect of the invention, since the braking force due to the regenerative braking operation of the induction motor is reduced according as the forklift decelerates, just before the forklift stops through proper deceleration of the forklift, the braking force due to the regenerative braking operation of the induction motor becomes sufficiently small, which can eliminate the possibility that, as in the conventional forklift control apparatus, the braking force can disappear suddenly just after the forklift stops. Therefore, an operator is positively aole to stop the forklift at an operator's expected position, tnat is, the operator is allowed to stop the forklift smoothly with no sense of incongruity, and thus the cargoes carried on -he forklift can be prevented from collapsing, thereby being able to enhance safety in operating the forklift.

Also, according to the second aspect of the inventi,,)n, the pressed state of the brake pedal is detected by the brake pedal detect part, whether the forkl--ft speed to be derived by the derive part is equal to or larger than a predetermined speed or not can be checked by the control part, and the output voltage of the induction motor can be calculated in such a manner that, in case where the derived speed is found equal to or larcler than the predetermined speed, the braking force due to the regenerative braking operation of the induction motor can be made constant and also, in case where the derived speed is found smaller than the predetermined speed, the braking force cue to the regenerative braking operation can be made proportional to the speed of the forklift. Thanks t-o this, by controlling the induction motor in such a manner that the calculated output 2 voltage can be obtained, a smooth braking characteristic can be realized.

Further, according to the third aspect of the invention, the output voltage of the induction motor can be calculated in such a manner that, in case where the speed of the forklift is found equal to or larger than the predetermined speed, the braking force due to the regenerative braking operation of the induction motor can be made constant and, in case where the forklift speed is found smaller than the predetermined speed, the braking force due to the regenerative braking operation can be made proportional to the forklift speed.

As has been described heretofore, according to the fourth aspect of the i-nvention, while the speed of the forklift is large, there is applied a relatively large braking force, which eliminates the need for an operator to operate the brake pedal so frequently as in the conventional forklift control apparatus.

This can set the operator free from the troublesome braking operation, so that the operator is able to concentrate his or her attention on loading and unloading operations.

Also, just before the forklift stops through proper deceleration of the forklift, the braking force due to the regenerative braking operation of the induction motor becomes sufficiently small, which can eliminate the possibility that, as in the conventional forklift control apparatus, the braking force can disappear suddenly just after the forklift stops.

Therefore, the operator is allowed to stop the forklift smootily with no sense of incongruity and thus the cargoes carried on the forklift can be prevented from collapsing, thereby being able to enhance safety in operating the forklift.

Also, according to the fifth aspect of the invention, in case where the off state of the accelerator pedal is detected by the accelerator pedal detect part o.---the switching part is set in its neutral state, the control part checks whether 1-he then speed of the forklift derived by the derive part is equal to or larger than a predetermined speed or not, and the output voltage of the induction motor can be calculated in such a manner that, in case where the derived speed of the forklift is found equal to or larger than the predetermined speed, the brak-,ng force due to the regenerative braking Operation of the induct-' on motor can be made constant and also, in case where the derived speed of the forklift is found smaller than the predetermined speed, the braking force due to the regenerative braking operation can be made proportional to the forklift speed. Thanks to this, by controlling the induction motor in such a manner that the calculated output voltage can be obta-.ned, a smooth braking characteristic can be realized.

Further, according to the sixth as ect of the invention, P the output voltage of the induction motor can be calculated in such a manner that, in case where the speed of the forklift is found equal to or larger than the predetermined speed, the braking force due to the regenerative braking operation of the induction motor can be made constant and, in case where the forklift speed is found smaller than the predetermined speed, the braking force due to the regenerative braking operation can be made proportional to the forklift speed.

27 -

Claims

CLAIMS:

1. A forklift control apparatus, wherein an output Dc power of a battery mounted on a body of a forklift is conver---ed into AC power by an inverter to be supplied to an inducton motor, and the induction motor is driven by a drive part, thereby braking the forklift by means of a regenerative braking operat:-on of the induction motor, characterized in that, when an on-state of a brake pedal is found during the forklift is runnJng, the output voltage of the induction motor is (---alculatedin such a manner that:

a braking force due to the regeneiative braking operatl_on of the induction motor is made consta:,-it independently of 1.he speed of the forklift in case where the speed of the forkl-ft is equal to or larger than a predetermined speed, and, a braking force due to the regenerative braking operation of the induction motor is made proportional to the speed of the forklift in case where the speed of the forklift is smaller than the predetermined speed- 2. The forklift control apparat.-is as set forth in claim 1, the forklift comprising:

a rotation detect portion for d---ecting the number of rotations of the induction motor; a derive portion for deriving the speed and acceleration of the body from a detected value by the rotation detect portion; a brake pedal detect portion for detecting whether or not the brake pedal is in on-state; and, a control portion, when the on-state of the brake pedal is detected by the brake pedal detect portion, for checking whether the speed of the forklift derived by the derive portion is equal to or larger than the predetermined speed or not and, after the checking, the control portion calculating the output voltage of the induction motor in such a manner that:

a braking force due to the regenerative braking operation of the induction motor is made constant independently of the speed of the forklift in case where the derived forklift speed is found equal to or larger than the predetermined speed; and the braking force due to the regenerative braking operation of the induction motor is made proportional to the speed of the forklift in case where the derived forklift speed is found smaller than the predetermined speed.

3. The forklift control apparatus according to claim 1 or 2, wherein the predetermined speed is a speed at which a product obtained by multiplying the square of a value of the speed of the forklift in the brake pedal on-state detected time by a first coefficient predetermined in advance is equal to a value obtained by multiplying a value of the derived speed by a second coefficient predetermined in advance.

- 29 A forklift control apparatus, wherein an output DC power of a battery mounted on a body of a forklift 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, thereby braking the forklift by means of a regenerative braking operati on of the induction motor, characterized in that, when, durine the forklift is running, the off-state of an accelerator pedalis found or a transmission for transmitting the drive force of the induction motor to wheels is switched over to a neutral state, the output voltage of the induction motor is calculated in such a manner that:

a braking force due to the regenerative braking operation of the induction motor is made constant independently of the speed of the forklift in case where the speed of the forklift is equal to or larger than a predetermined speed; and the braking force due to the regenerative braking operation of the induction motor can be made proportional to the speed of the forklift in case where the then speed of the forklift is smaller than the predetermined speed.

5. The forklift control apparatus as set forth in cla.Lm 4, the forklift comprising:

a rotation detect portion for detecting the number of rotations of the induction motor; a derive portion for deriving the speed and acceleration of the body from a detect value obtained by the rotation detect portion; a switching part for switching and setting the transmission for transmitting the drive force of the induction motor to wheels in one of advancing and retreating states or in a neutral state; an accelerator pedal detect portion for detecting the on-state or off-state of the accelerator pedal; and, a control portion, when the off-state of the accelerator pedal is detected by the accelerator pedal detect portion or when the transmission is set in the neutral state, for checking whether the speed of the forklift derived by the derive part is equal to or larger than the predetermined speed or not and, the control portion, after the checking, for calculating the output voltage of the induction motor in such a manner that:

the braking force due to the regenerative braking operation of the induction motor is made constant independently of the speed of the forklift in case where the derived forklift speed is found equal to or larger than the predetermined speed; and the braking force due to the regenerative braking operation of the induction motor is made proportional to the speed of the forklift in case where the derived forklift speed is found smaller than the predetermined speed.

6. A forklift control apparatus according to claim 4 or 5, wherein the predetermined speed is a speed al. which the product obtained by multiplying the square of a value of the speed of the forklift in the brake pedal off-state detected time or in the switching part neutral state set time, by a first coefficient predetermined in advance, is equal to a value obtained by multiplying a value of the derived speed by a second coefficient predetermined in advance.

7. A forklift control apparatus substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings, or with reference to Figures 1 and 2 together with Figures; 3 or 4- of the accompanying drawings.

8. A forklift control apparatus substantially as hereinbefore described with reference to Figures 1, 2, 4 and 5 of the accompanying drawings.