AU760385B2

AU760385B2 - Driving control apparatus for electric industrial vehicle

Info

Publication number: AU760385B2
Application number: AU54294/01A
Authority: AU
Inventors: Kazuo Ishikawa
Original assignee: Toyoda Jidoshokki Seisakusho KK; Toyoda Automatic Loom Works Ltd
Current assignee: Toyota Industries Corp
Priority date: 2000-07-10
Filing date: 2001-07-10
Publication date: 2003-05-15
Anticipated expiration: 2021-07-10
Also published as: AU5429401A; DE10133228A1

Description

TITLE OF THE INVENTION Driving Control Apparatus for Electric Industrial Vehicle BACKGROUND OF THE INVENTION The present invention relates to a driving control apparatus for an electric industrial vehicle such as a reach type forklift.

A typical reach type forklift has a pair of reach legs, which extend forward. A pair of front wheels, which are coasting wheels, are supported by the reach legs, respectively. A rear wheel and a caster are located at the rear bottom portion of the vehicle body. The rear wheel functions as a driving wheel and a steered wheel and the caster functions as a coasting wheel. A mast assembly is located between the reach legs. The mast assembly includes a fork, which is lifted and lowered. The mast assembly is moved 20 forward and rearward along the reach legs.

o0 o oeoo The load acting on the rear wheel, which functions as a driving wheel, varies in accordance with the position of the mast assembly and the weight of a load carried by the fork.

When the mast assembly is located at the most front position and the weight of a load on the fork is the maximum acceptable value, the load acting on the driving wheel is minimized. In this state, if the forklift is started on a wet concrete floor or on the floor in a freezer, the driving wheel will skid.

This not only prevents the vehicle from being quickly accelerated but also causes the rear of the vehicle to sway to left and right. Also, skidding prematurely wears the driving wheel.

To prevent the driving wheel to skid, Japanese Unexamined Patent Publications No. 2-299402, No. 3-27701 and No. 11- 178120 each disclose an apparatus that lowers the torque of a motor. Specifically, each apparatus lowers the torque of a motor that drives a driving wheel when the driving wheel skids.

In the apparatuses of the publications No. 2-299402 and No. 3-27701, whether a driving wheel is skidding is detected based on the speed of a motor and a current supplied to the motor. In the apparatus of the publication No. 11-178120, whether a driving wheel is skidding is detected based on the rotation speed and the acceleration of the driving wheel.

2 *o o 2 The above publications do not disclose any method for controlling the motor torque. Typically, a motor is feedback controlled such that the motor torque is reduced by a degree that corresponds to the degree of skidding. To control the motor torque for reliably preventing a driving wheel from skidding, several factors such as the range of the load acting on the driving wheel, the friction of the driving wheel and the characteristics of the motor need be considered. However, these factors vary in each vehicle. Thus, the control procedure need be adjusted to correspond to each vehicle and the adjustment of the procedure is complicated.

S

SUMMARY OF THE INVENTION Accordingly, it is an objective of the present invention 30 to provide a driving control apparatus for an electric industrial vehicle that reliably prevents a wheel from skidding with a simple structure.

To achieve the foregoing and other objectives and in -2accordance with the purpose of the present invention, a driving control apparatus for an electric industrial vehicle having a driving wheel that is driven by a motor is provided.

The apparatus includes an operation member, which is operated for adjusting the torque of the motor, skid detection means for detecting a skid value, which represents the degree of skidding of the driving wheel, and means for controlling the motor. The motor controlling means computes a target torque of the motor according to the operation amount of the operation member and controls the motor such that the motor generates the target torque. When the absolute value of the skid value exceeds a predetermined skid determination value, the motor controlling means reduces the target torque at a predetermined rate to execute a skid prevention procedure.

Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

.BRIEF DESCRIPTION OF THE DRAWINGS The invention, together with objects and advantages thereof, may best be understood by reference to the following 25 description of the presently preferred embodiments together with the accompanying drawings in which: S.o.

Fig. 1 is a block diagram illustrating a reach type forklift according to a first embodiment of the present 30 invention; Fig. 2 is a side view of the forklift shown in Fig. 1; Fig. 3 is a top plan view of the forklift shown in Fig.

1; Fig. 4 is a graph showing a map M1 for computing a target 3 torque of a motor; Fig. 5 is graph showing the relationship between a skid value 8VD and the friction coefficient between a rear wheel and a road surface during a powering mode; Fig. 6 is a graph showing the relationship between a determination value Va and a vehicle speed; Figs. 7(a) to 7(c) are graphs showing the changes of a front wheel moving speed VF, a rear wheel moving speed VD and the skid value AVD when the forklift is started on a wet road surface; Fig. 8(a) to 8(c) are graphs showing the changes of the front wheel moving speed VF, the rear wheel moving speed VD and the skid value AVD when an acceleration lever is manipulated for direction switching under the same condition as in Figs. 7(a) to 7(c); Fig. 9 is a flowchart of a routine for determining whether to permit a skid prevention procedure according to a second embodiment of the present invention; 20 Fig. 10 is a diagram showing the relationship between the value of an acceleration flag FA in relation with the go acceleration or the deceleration of the forklift Fig. 11 is a flowchart showing a routine for setting the acceleration flag FA; 25 Fig. 12 is a graph showing the changes of the front wheel moving speed VF, the rear wheel moving speed VD, a vehicle acceleration AC and the skid value AVD when the forklift is running on a dry road surface; Fig. 13 is a graph showing brake pressure data M2 for 30 determining an auxiliary brake pressure PK according to a fourth embodiment; Fig. 14 is a flowchart showing a brake control procedure executed during the regenerative mode; Fig. 15 is a flowchart showing a brake control procedure 4 executed during the regenerative mode according to a fifth embodiment; and Fig. 16 is a flowchart showing a driving control routine according to a sixth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will now be described with reference to Figs. 1 to As shown in Figs. 2 and 3, an industrial vehicle, which is a reach type forklift 10 in this embodiment, includes a vehicle body 14 and left and right reach legs 15, which extend forward. Coasting wheels, which are left and right front wheels 11L and 11R, are supported by the reach legs 15, respectively. A rear wheel 12 and a caster 13 are located at the rear of the vehicle body 14. The rear wheel 12 is driven and steered.

Each of the front wheels 11L and 11R has a brake 16.

Each brake 16 is, for example, hydraulic friction drum brake.

20 A mast assembly 17 is located between the reach legs 15. The ooo mast assembly 17 is moved along the reach leg 15. A reach cylinder 171 is located at the lower portion of the vehicle body 14 to move the mast assembly 17. The mast assembly 17 includes a fork 17a. The fork 17a is lifted and lowered by a 25 lift cylinder (not shown). The fork 17a is also tilted :*together with the mast assembly 17 by the lift cylinder.

The body 14 has a cab 20, in which an operator stands.

The cab 20 is located in the rear right section of the body 14. The caster 13 is located below the cab 20. An instrument panel 21 is located in the front of the cab 20. An operation member, which is an acceleration lever 23 in this embodiment, a lift lever 24, a reach lever 25 and a tilt lever 26 are located on the instrument panel 21. A box 14a is located to the left of the cab 20. A steering wheel 22 is located on the box 14a. The steering wheel 22 is manipulated to steer the rear wheel 12.

A drive unit 18 is located in the box 14a. The drive unit 18 includes a driving motor 19, which is, for example, an alternating current induction motor. The rear wheel 12 is supported by the drive unit 18 and driven by the driving motor 19. The drive unit 18 and the caster 13 are supported by the body through a suspension mechanism (not shown). The suspension mechanism prevents the load acting on the rear wheel 12 from being greatly changed by a displacement of the center of gravity of the forklift A brake pedal 100 is located on the floor of the cab The brake pedal 100 is depressed when braking the rear wheel 12. Although not shown in the drawings, the brake pedal 100 is connected to a rear brake through a linkage. When the brake pedal 100 is not depressed, the rear brake brakes the 20 rear wheel 12. When the brake pedal 100 is depressed, the go rear brake releases the rear wheel 12.

The circuit construction for controlling the driving motor 19 and the brake 16 will now be described. As shown in 25 Fig. 1, a loading motor 31 actuates an oil pump 32 to send oil from an oil tank 30 to a brake control valve unit 33 and oil control valve 34. The oil control valve 34 controls the supply of oil to the lift cylinder, the reach cylinder 171 and the tilt cylinder. The oil control valve 34 controls the supply of oil to the cylinders in accordance with manipulation of the levers 23, 24 and The brake control valve unit 33 includes an electromagnetic valve 33b and an accumulator 33a. Oil sent -6from the oil pump 32 is first stored in the accumulator 33a.

The electromagnetic valve 33b is actuated based on commands from the controller 44. The controller 44 controls the electromagnetic valve 33b to adjust the pressure of oil that is supplied to the brakes 16 from the accumulator 33a. Each brake 16 brakes the corresponding front wheel 11L, 11R by a force that corresponds to the pressure of the supplied oil.

The controller 44 includes, for example, a microcomputer that has a CPU and a memory and controls all the operations of the forklift 10. The controller 44 also includes an inverter circuit. An acceleration lever sensor 40 is located below the instrument panel 21. The acceleration lever sensor 40 detects the manipulation amount ACC of the acceleration lever 23, or the position of the acceleration lever 23, and sends a signal that corresponds to the detected manipulation amount ACC to the controller 44. The controller 44 supplies a current that corresponds to the lever manipulation amount ACC to the driving motor 19.

o r The acceleration lever 23 also functions as a directional lever to change the moving direction of the vehicle. That is, the acceleration lever 23 is normally at a neutral position.

The lever 23 is moved forward, or to a forward position, when 25 moving the forklift 10 forward and is moved rearward, or to a reverse position, when moving the forklift 10 backward. When the acceleration lever 23 is at the neutral position, the acceleration lever sensor 40 defies the lever manipulation amount ACC as zero. The lever manipulation amount ACC 30 represents the amount of forward or rearward movement of the acceleration lever 23 from the neutral position.

A forward movement detection switch 401 and a rearward movement detection switch 402 are off when the acceleration 7 lever 23 is at the neutral position. When the acceleration lever 23 is moved to the forward position from the neutral position, the forward movement detection switch 401 is turned on and sends a forward movement signal SF to the controller 44. When the acceleration lever 23 is moved to the reverse position from the neutral position, the rearward movement detection switch 402 is turned on and sends a forward movement signal SR to the controller 44. Based on signals from the detection switches 401, 402, the controller 44 judges the rotation direction of the driving motor 19, which has been commanded by the acceleration lever 23. In other words, the controller 44 determines the moving direction of the forklift that is commanded by the acceleration lever 23. The determined direction does not necessarily represent the actual direction in which the forklift 10 moves.

A pair of rear wheel speed sensors 41a, 41b face a gear that is fixed to the output shaft of the driving motor 19.

Each wheel speed sensor 41a, 41b detects the teeth of the gear 20 and outputs pulse signals, which corresponds to the rotation .o speed NM of the driving motor 19, to the controller 44. Based on the received pulse signals, the controller 44 computes the rotation speed NM of the driving motor 19 and the speed ND of the rear wheel 12, which will be discussed below.

The rear wheel speed sensors 41a, 41b are spaced apart by a predetermined angular interval such that the phases of the signals from the rear wheel sensors 41a and 41b are offset by ninety degrees. Based on the phase difference between pulse signals from the sensors 41a, 41b, the controller 44 detects the current rotation direction of the driving motor 19, or the current moving direction of the forklift A wheel angle sensor 42 is located in the vicinity of the -8drive unit 18. The wheel angle sensor 42 detects the angle 6 of the rear wheels 12 and sends a signal that represents the detected wheel angle 8 to the controller 44.

A pressure switch 43 is located in the brake control valve unit 33. When the oil pressure in the accumulator 33a falls below a predetermined value, the pressure switch 43 sends a signal to the controller 44. When receiving a signal from the pressure switch 43, the controller 44 actuates the loading motor 31 to increase the oil pressure in the accumulator 33a.

A pair of front wheel speed sensors 45L, 45R are located on the reach legs 15 to correspond to the front wheels 11L, 11R, respectively. The left front wheel speed sensor sends a pulse signal the frequency of which corresponds to the rotation speed NLF of the left front wheel 11L to the controller 44. The right front wheel speed sensor 45R sends a pulse signal the frequency of which corresponds to the 20 rotation speed NRF of the right front wheel 11R to the controller 44.

S

S e The controller 44 controls the rotating direction, the driving torque and the braking torque of the driving motor 19 25 based on the a lever manipulation amount ACC, the rear wheel speed ND, the motor speed NM, the wheel angle 8 and the front wheel rotation speeds NLF, NRF. The driving torque refers to V a torque generated by the driving torque 19 to move the forklift 10. The braking torque refers to a torque generated 30 by the driving motor 19 to brake the forklift 555555 In this embodiment, the driving motor 19 generates a braking torque due to regenerative braking during direction switching. Direction switching refers to switching of the -9acceleration lever 23 from the forward position to the reverse position or from the reverse position to the forward position while the forklift 10 is running for switching the moving direction of the vehicle. Direction switching permits the forklift 10 to start moving in a direction that is opposite to the current moving direction after temporarily stopping. From when the acceleration lever 23 is manipulated for direction switching to when the forklift 10 stops, in other words, when the actual moving direction of the forklift 10 is different from the direction indicated by the acceleration lever 23, the moving motor 19 generates braking torque to brake the rear wheel 12.

When the acceleration lever 23 is moved to the forward position or the reverse position from the neutral position, the corresponding one of the switch 401, 402 outputs a signal (the forward moving signal SF or the rearward moving signal SR). When the acceleration lever 23 is manipulated for direction switching, the moving direction signal sent to the controller 44 is changed from the forward moving signal SF to the rearward moving signal SR or from the rearward moving signal SR to the forward moving direction SF. Based on the forward moving signal SF or the rearward moving signal SR, the controller 44 detects the moving direction of the forklift 25 that is indicated by the acceleration lever 23, which does not necessarily match the actual moving direction.

The controller 44 computes the rotation speed NM of the driving motor 19 based on pulse signals from the rear wheel speed sensors 41a, 41b and detects the rotation direction of the driving motor 19, or the current moving direction of the forklift 10. Then, the controller 44 computes a target value of torque that need be generated by the driving motor based on the motor speed NM, the lever manipulation amount ACC by 10 referring to a map M1, which is shown in Fig. 4.

The map M1 of Fig. 4 is previously stored in a memory of the controller 44. The map M1 defines the values of the target torque in relation with the motor speed NM and the lever manipulation amount ACC. If the current moving direction of the forklift 10 is the same as the moving direction indicated by the acceleration lever 23, the controller 44 defines the motor speed NM as a positive value and refers to the map M1 to control the driving motor 19 in a powering mode. In this case, the computed target torque is a target value of the driving torque for moving the forklift in a direction indicated by the acceleration lever 23. Also, if the acceleration lever 23 is at the forward position or the reverse position when the forklift 10 is not moving, the controller 44 defines the motor rotation speed NM as a positive value and refers to the map M1 to control the driving motor 19 in the powering mode.

20 When the current moving direction of the forklift 10 is different from the moving direction indicated by the acceleration lever 23, the controller defines the motor speed r NM as a negative value and refers to the map M1 to control the driving motor 19 in a regenerative mode (braking mode). In this case, the computed target torque is a target value of the braking torque for braking the forklift 10. During direction switching, the driving motor 19 is controlled in the regenerative mode so that the motor 19 generates braking torque.

S When the lever manipulation amount ACC is decreased during the powering mode, the value of the computed target driving torque may be negative. In such a case, the target driving torque substantially represents the target braking 11 torque and the driving motor 19 generates braking torque.

Thus, the powering mode in this specification may include the state of the regenerative mode, in which the driving motor 19 generates braking torque.

The controller 44 gradually increases or decreases the torque of the driving motor 19 so that the torque of the motor 19 reaches the computed target value. The torque is not suddenly changed and shock is therefore not generated.

As described above, when the current moving direction of the forklift 10 is the same as the moving direction indicated by the acceleration lever 23, the driving motor 19 is controlled to generated a driving torque that corresponds to the motor speed NM and the lever manipulation amount ACC. As a result, the forklift 10 moves in a direction that is indicated by the acceleration lever 23. When the current moving direction of the forklift 10 is opposite to the direction indicated by the acceleration lever 23, that is, 20 when the acceleration lever 23 is manipulated for direction switching, the driving motor 19 is controlled to generate braking torque that corresponds to the motor speed NM and the lever manipulation amount ACC. As a result, the rear wheel 12 is braked and the forklift 10 is decelerated.

When the forklift 10 is accelerating or decelerating, the controller 44 judges whether the rear wheel 12, which is the driving wheel, is skidding relative to the road surface. If the rear wheel 12 is skidding, the controller 44 adjusts the torque of the driving motor 19 to stop skidding of the rear wheel 12.

A skid prevention procedure will now be described. The controller 44 computes the moving speed of the rear wheel 12 12 13 in relation with the road surface based on the rear wheel speed ND and the diameter of the rear wheel 12. The rear wheel moving speed VD represents the vehicle speed at the rear wheel 12. Since the rear wheel moving speed VD is computed based on the rear wheel speed ND, the computed rear wheel speed VD is different from the actual moving speed of the rear wheel 12 when the rear wheel 12 is skidding relative to the road surface.

The controller 44 computes the moving speed VLF of the left front wheel 11L relative to the road surface based on the left front wheel rotation speed NLF and the diameter of the left front wheel 11L. The controller 44 also computes the moving speed VRF of the right front wheel 11R relative to the road surface based on the right front wheel rotation speed NRF and the diameter of the right front wheel 11R. The controller 44 detects which one of the front wheels 11L, 11R is located radially outside during a turn based on the wheel angle 2 of the rear wheel 12. Then, the controller 44 selects the moving speed of the radially outer front wheel as the front wheel moving speed VF. When the wheel angle 2 is zero, that is, when the forklift 10 is moving in a straight line, the moving speed of one of the front wheels 11L, 11R is S 25 selected as the front wheel moving speed VF.

Then, the controller 44 computes a moving speed VDP of the rear wheel 12 by multiplying the front wheel moving speed VF by a conversion factor, which will be discussed below. To distinguish the moving speed VDP from the rear wheel moving speed VD, which is computed based on the rear wheel speed ND, the moving speed VDP will hereinafter be referred to as a converted moving speed VDP or an estimated moving speed VDP. The converted moving speed VDP corresponds to the vehicle speed at the rear S.i wheel 12, which is estimated based on the \\melb_files\homeS\Leanne\Keep\54294-01.doc 12/02/03 speed of one of the front wheels 11L, 11R.

The conversion factor is either a factor KL, which is used when the forklift 10 is turning left, or a factor KR, which is used when the forklift 10 is turning right. The conversion factors KL, KR are computed according to the following equations.

KL LW (LW'cose (LT LD)sine) KR LW (LW-cose (LT LD)sine) In the equations, LW represents the wheelbase, LT is the half of the tread between the front wheels IlL and 11R, and LD represents the lateral displacement of the rear wheel 12 relative to the center between the front wheels 11L and 11R.

As described above, different conversion factors are used when the forklift 10 is turning left and when the forklift 10 is turning right. This is because the rear wheel 12, which is the steered wheel, is laterally displaced from the center between the front wheels 11L, 11R (see Fig. When the 20 wheel angle 8 is zero, that is, when the forklift 10 is moving in a straight line, the conversion factors KL and KR are both one. Therefore, when the wheel angle 8 is zero, either one of the conversion factors KL, KR is used.

25 The converted moving speed VDP is computed based on the e eooo rotation speed NLF, NRF of the front wheels 11L, 11R. The front wheels IlL, 11R coast along the movement of the forklift 10 while contacting the road surface. Therefore, unlike the *rear wheel 12, which is the driving wheel, the front wheels 11L, 11R do not skid on the road surface when the forklift a is accelerating of decelerating. Thus, the converted moving

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speed VDP substantially represents the accurate moving speed of the rear wheel 12.

14 Then, the controller 44 computes a skid value AVD of the rear wheel 12 based on the rear wheel moving speed VD and the converted moving speed VDP according to the following equation.

AVD VD VDP As in the equation, the skid value nVD represents the difference between the rear wheel moving speed VD and the converted moving speed VDP. If the rear wheel 12 skids during the powering mode, or during acceleration, the skid value AVD is positive. When the rear wheel 12 skids during the regenerative mode, or during deceleration, the skid value AVD is negative. When the absolute value of the skid value AVD exceeds a determination value Va, the controller 44 judges that the rear wheel 12 skids on the road surface.

When judging that the rear wheel 12 is skidding, the controller 44 limits the torque of the driving motor 19 to stop skidding. Specifically, the controller 44 reduces the 20 normal target torque, which is computed based on the map M1 of Fig. i, by, for example, 10% and sets the resultant as a target torque of the driving motor 19. As a result, the driving torque of the driving motor 19 is limited during the ;powering mode, which stops skidding of the rear wheel 12 due 25 to acceleration. During the regenerative mode, the braking torque of the driving motor 19 is limited, which stops skidding of the rear wheel 12 due to deceleration.

*When the absolute value of the skid value AVD exceeds the 30 determination value Va during the regenerative mode, the controller 44 controls the valve unit 33 to actuate the brakes 16 as necessary. As a result, the reduction of the braking torque due to limiting of the driving torque of the motor 19 is compensated for.

15 Fig. 5 is a graph that shows the relationship between the skid value AVD and the friction coefficient of the rear wheel 12 and the road surface. The friction coefficient is maximum when the skid value AVD is 0.1 m/s. As the skid value AVD increases from zero to 0.1 m/s, the friction coefficient increases relatively abruptly. As the skid value AVD increases from 0.1 m/s to 0.3 m/s, the friction coefficient decreases relatively abruptly. As the skid value AVD increases from 0.3 m/s, the friction coefficient gradually decreases.

In an industrial vehicle that has a relatively slow maximum speed such as the reach type forklift 10, the relationship between the skid value AVD and the friction coefficient is substantially constant regardless of the vehicle speed. The determination value Va is set to correspond to a range of the skid value AVD where the friction coefficient is relatively great, or in a shaded area of Fig.

Preferably, the determination value Va is changed in '°accordance with the running state of the forklift 10. For i example, if a relatively driving torque need be generated by the driving motor 19 as when starting the forklift 10, the determination value Va is set relatively small compared to other cases. In an example shown in the graph of Fig. 6, the .determination value Va is set to 0.1 m/s in a low vehicle speed range that includes acceleration for starting the 30 forklift 10. In other vehicle speed ranges, the determination gooes ovalue Va is set to 0.2 m/s. The vehicle speed is represented, for example, by the converted moving speed VDP. The determination value Va when the forklift 10 is accelerating may be different from when the forklift 10 is decelerating.

16 /7 Figs. 7(a) to 7(c) are graphs showing the front wheel moving speed VF, the rear wheel moving speed VD and skid value MVD when the forklift 10 is started on a wet road surface.

The forklift 10 is moving forward and the wheel angle 8 is zero. The mast assembly 17 is at the most forward position and the weight of load on the fork 17a is the maximum acceptable value. The determination value Va is set to 0.1 m/s from time zero, at which the forklift 10 is started, until 5.5 second has elapsed. Thereafter, the determination value Va is set to 0.2 m/s.

When the absolute value of the skid value AVD exceeds the determination value Va, the target driving target torque of the driving motor 19 is reduced by 10% from the normal value, which is computed according to the map M1 of Fig. 4. During the skid prevention control procedure in the powering mode, the skid value AVD fluctuates about 0.2 m/s in a range of 0.1 to 0.2 m/s. The rear wheel moving speed VD, which is shown in 20 Fig. increases together with the front wheel moving 0000 speed VF, which is shown in Fig. while fluctuating in a 0° o •range of 0.1 to 0.2 m/s. Thus, the forklift 10 is started on 0 a wet road and the load acting on the rear wheel 12 is *09% minimum, the rear wheel 12 is prevented from skidding and the forklift 10 is reliably started.

0 *000 •oo, The determination value Va is set to 0.1 m/s from when the forklift 10 is started to when 5.5 seconds has elapsed.

*#see In other words, compared to other speed ranges, the 30 determination value Va is relatively small in a low speed se 0ogo range such as immediately after the forklift 10 is started.

fee*.: Therefore, when the forklift 10 is started, the driving force of the rear wheel 12 is reliably transmitted to the road surface and the forklift 10 is smoothly accelerated.

17 When the skid prevention control procedure is executed, the rate at which the normal target torque is decreased is determined such that the absolute value of the skid value AVD falls below the determination value Va at least four times a second. Therefore, during the skid prevention procedure, the cycle of changes of the forklift acceleration is four times a second or more. As the rate at which the normal target torque is decreased is small, the cycle of changes of the acceleration is shortened, which improves the ride quality.

On the other hand, to obtain the maximum driving force while preventing the rear wheel 12 from skidding, the rate at which the normal target torque is decreased is preferably great.

Thus, in this embodiment, the rate at which the normal target torque is decreased is set to 10%, which guarantees a maximum driving force without disturbing the operator.

Figs. 8(a) to 8(c) show changes of the front wheel moving speed VF, the rear wheel moving speed VD and the skid value S 20 AVD when the acceleration lever 23 is manipulated for 0006 0000 direction switching under the same conditions as the case of ee Figs. 7(a) to In the case of Figs. 8(a) to the determination value Va is always 0.2 m/s. After the S: acceleration lever 23 is manipulated for direction switching, 25 the regenerative mode is performed for six seconds, and OSOOSS ee e0 thereafter, the powering mode is performed.

0060 When the absolute value of the skid value AVD exceeds the determination value Va, the target driving torque of the 30 driving motor 19 is reduced by 10% from the normal target @000 value, which is computed according to the map M1 of Fig. 4.

During the skid prevention control procedure in the regenerative mode, the skid value MVD fluctuates about -0.2 m/s at a range of 0.1 to 0.2 m/s. The rear wheel moving speed 18 VD, which is shown in Fig. decreases together with the front wheel moving speed VF, which is shown in Fig. 8(a), while fluctuating in a range of 0.1 to 0.2 m/s. Thus, when the forklift 10 is running on a wet road surface and the load acting on the rear wheel 12 is minimum, the rear wheel 12 is prevented from skidding and the forklift 10 is reliably decelerated.

During the skid prevention control in the regenerative mode, the normal target torque is decreased by Therefore, the braking force can be maximized without disturbing the operator.

As described above, when the absolute value of the skid value AVD exceeds the determination value Va, the target torque of the driving motor 19 is reduced by a predetermined rate from the normal target value so that the rear wheel 12 stops skidding. Thus, the rear wheel 12, which is the driving wheel, is reliably prevented from skidding by a simple 20 structure.

o The skid value AVD represents the difference between the rear wheel moving speed VD and the converted moving speed VDP.

Thus, even if the vehicle speed changes, the skid value AVD 25 has substantially the same relationship with the friction coefficient between the rear wheel 12 and the road surface.

Therefore, the skid prevention procedure is reliably executed based on the skid value AVD regardless of the vehicle speed.

*99.

30 The determination value Va is set to correspond to a range of the skid value AVD in which the friction coefficient is relatively great (in the shaded area of the graph of Fig.

When the skid prevention procedure is performed, the skid value MVD fluctuates about the determination value Va (see 19 g 0 Figs. 7(c) and Thus, during the skid prevention procedure, the friction coefficient between the rear wheel 12 and the road surface is maintained at a relatively great value, and the rear wheel 12 has a sufficient grip.

During the skid prevention procedure, the rate at the normal target torque is decreased is not limited to 10%, but may be varied in ranges 10% to 20%, 5% to 30% or 0% to Also, during the skid prevention procedure, the number of times when the skid value AVD falls below the determination value Va in one second may be changed.

A second embodiment according to the present invention will now be described with reference to Figs. 1 to 8(c).

Mainly, the differences from the first embodiment will be discussed below. In the second embodiment, the skid prevention procedure based on the skid value AVD and the determination value Va is permitted only when the running condition of the forklift 10 satisfies a predetermined permission condition. When the running state of the forklift does not satisfy the permission condition, the skid prevention procedure is not performed even if the absolute value of the skid value AVD exceeds the determination value 25 oooo o°°eo Va.

Fig. 9 shows a flow chart for determining whether to permit the skid prevention procedure. The controller 44 performs the routine of Fig. 9 at predetermined intervals.

At step Sl, the controller 44 judges whether a permission flag FX is one. The permission flag FX indicates whether to permit the skid prevention procedure. The value one of the permission flag FX indicates that the skid prevention 20 procedure is permitted, and the value zero indicates that the skid prevention procedure is prohibited. When the permission flag FX is zero, the controller 44 proceeds to step S2.

At step S2, the controller 44 judges whether the absolute value of the skid value AVD is greater than a predetermined permission determination value Vb. The permission determination value Vb is greater than the skid determination value Va, which is used for judging whether the rear wheel 12 is skidding. The permission determination value Vb is determined in consideration of the skid value AVD when the rear wheel 12 cannot maintain a great grip to a road surface on which the rear wheel 12 is unlikely to skid, for example, a road surface of a relatively great friction coefficient such as a dry road surface. In this embodiment, the permission determination value Vb is set to 0.5 m/s.

If the absolute value of the skid value AVD is greater than the permission determination value Vb at step S2, the oooo S 20 controller 44 proceeds to step S3 to permit the skid prevention procedure. At step S3, the controller 44 sets the permission flag FX to one and temporarily suspends the current routine. If the absolute value of the skid value AVD is equal to or less than the permission determination value Vb, the 25 controller 44 maintains the permission flag FX to zero and temporarily suspends the current routine.

If the permission flag FX is one at step Sl, the controller 44 proceeds to step S4. At step S4, the controller 30 44 judges whether the vehicle speed V is less than a predetermined a stop determination value Vc. The stop determination value Vc represents an extremely slow value of the vehicle speed V at which the forklift 10 is substantially stopped and is set to Ikm/h. The vehicle speed V, for 21 example, represents the average of the converted moving speed VDP or the average of the front wheel moving speeds VLF, VRF in the embodiment of Figs. 1 to 8(c).

If the vehicle speed V is less than the stop determination value Vc at step S4, the controller 44 proceeds to step S5 to prohibit the skid prevention procedure. At step the controller 44 sets the permission flag FX to zero and temporarily suspends the current routine. If the vehicle speed V is equal to or greater than the stop determination value Vc, the controller 44 maintains the flag FX to one and temporarily suspends the current routine.

As described above, when the forklift 10 is accelerating or decelerating, the permission flag FX is maintained at zero until the absolute value of the skid value AVD once exceeds the permission determination value Vb. While the permission flag FX is zero, the skid prevention procedure is not performed even if the absolute value of the skid value LVD 20 exceeds the skid determination value Va.

g For example, when the forklift 10 is moving on a road i.:"a surface on which the rear wheel 12 is not likely to skid, for example, on a dry road surface, or when the load acting on the rear wheel 12 is relatively great, the absolute value of the skid value AVD may be between the skid determination value Va o and the permission determination value Vb. In such a case, the rear wheel 12 is judged to be maintaining a relatively great grip with the road surface and the permission flag FX is 30 set to zero so that the skid prevention procedure is not performed. In other words, when the grip of the rear wheel 12 with the road surface is judged to be great, the skid prevention control is not performed even if the absolute value of the skid value AVD exceeds the skid determination value Va.

22 When the absolute value of the skid value AVD exceeds the permission determination value Vb, the permission flag FX is maintained at one until the vehicle speed V falls below the stop determination value Vc. While the permission flag FX is maintained at one, the skid prevention procedure is performed based on the comparison between the skid value AVD and the skid determination value Va.

When the forklift 10 is running on a ground on which the forklift 10 is likely to skid, for example, on a wet road surface, or when the load acting on the rear wheel 12 is relatively small, the absolute value of the skid value AVD may exceeds both of the skid determination value Va and the permission determination value Vb. In such case, the rear wheel 12 is judged to be unable to maintain a great grip with the road surface and the permission flag FX is set to one so that the skid prevention procedure is permitted. In other :i words, when the rear wheel 12 is judged to be unable to 20 maintaining a great grip with the road surface, the skid prevention procedure is permitted.

As described above, the skid prevention procedure is prohibited when the forklift 10 is unlikely to skid.

25 Therefore, the skid prevention procedure is not performed too frequently. As a result, the forklift 10 is reliably 5Soo accelerated and decelerated while preventing the rear wheel 12 from skidding.

30 When the absolute value of the skid value AVD exceeds the permission determination value Vb, the skid prevention procedure is permitted. Thereafter, when the vehicle speed V falls below the stop determination value Vc, the skid prevention procedure is prohibited. Whether the skid 23 prevention procedure is permitted is properly judged simply by comparing the skid value AVD and the vehicle speed V with the corresponding determination values.

A third embodiment of the present invention will now be described with reference to Figs. 10 to 12. Mainly, the differences from the second embodiment of Fig. 9 will be discussed below. In addition to the procedure of the second embodiment of Fig. 9, a determination value for judging whether the rear wheel 12 is skidding is changed in accordance with acceleration or deceleration of the forklift Specifically, when acceleration or deceleration is small, a relatively small first skid determination value Val is used.

When acceleration or deceleration is great, a relatively great second skid determination value Va2 is used. For example, the first skid determination value Val is set to 0.2 m/s, and the second skid determination value Va2 is set to 0.3 m/s.

If the forklift 10 can be accelerated or decelerated at a 20 relatively high rate, the forklift 10 is in a state where the S"rear wheel 12 is not likely to skid. Therefore, when o acceleration or deceleration is great, the second skid determination value Va2 is used to prevent the skid prevention procedure from being excessively performed.

.s The controller 44 computes the vehicle acceleration AC based on the change of the vehicle speed V during a predetermined period AT. The vehicle acceleration AC has a positive value when the forklift 10 is accelerating and has a 30 negative value when the forklift 10 is decelerating. The controller compares the absolute value of the vehicle acceleration AC with a predetermined acceleration determination value to judges whether the forklift 10 is in a great acceleration state or in a great deceleration state.

24 When judging that the forklift 10 is in the great acceleration state or in the great deceleration state, the controller 44 sets the acceleration flag FA to one. Otherwise, the controller 44 sets the acceleration FA to zero. The value zero of the acceleration flag FA indicates that the forklift is in a small acceleration state or a small deceleration state.

Fig. 11 is a flowchart showing a routine of setting the acceleration flag FA. The controller 44 repeatedly executes the routine of Fig. 11 at the period AT.

At step SlI, the controller 44 judges whether the permission flag FX is one. The permission flag FX is the same as that in the second embodiment and is used for judging whether the skid prevention control is permitted. If the permission flag FX is not one but zero, the controller 44 judges the that the skid prevention procedure is prohibited and temporarily suspends the current routine.

a 3 If the permission flag FX is one at step SII, the controller 44 judges that the skid prevention procedure is permitted and proceeds to step S12. At step S12, the controller 44 judges whether the acceleration flag FA is zero.

If the acceleration flag FA is zero, the controller 44 proceeds to step S13. At step S13, the controller 44 judges whether the absolute value of the vehicle acceleration AC is greater than a predetermined first acceleration determination value AC1.

If the absolute value of the vehicle acceleration AC is greater than the first acceleration determination value AC1, the controller 44 judges that the forklift 10 has been changed from the small acceleration state to the great acceleration 25 state or from the small deceleration state to the great deceleration state. Thereafter, the controller 44 proceeds to step S15. At step S15, the controller 44 sets the acceleration flag FA to one and temporarily suspends the current routine. If the absolute value of the vehicle acceleration AC is less than the first acceleration determination value ACl at step S13, the controller 44 judges that the forklift 10 is maintained in the small acceleration state or in the small deceleration state, while maintaining the value zero of the acceleration flag FA. Thereafter, the controller 44 temporarily suspends the current routine.

If the acceleration flag FA is one at step S12, the controller 44 proceeds to step S14. At step S14, the controller 44 judge whether the absolute value of the vehicle acceleration AC is less than a predetermined second acceleration determination value AC2. The second acceleration determination value AC2 is less than the first acceleration determination value AC1.

When the absolute value of the vehicle acceleration AC is less than the second acceleration determination value AC2, the controller 44 judges that the forklift 10 has been changed from the great acceleration state to the small acceleration state or from the great deceleration state to the small deceleration state and proceeds to step S16. At step S16, the controller 44 sets the acceleration flag FA to zero and, thereafter, suspends the current routine. If the absolute value of the vehicle acceleration AC is greater than the second acceleration determination value AC2, the controller 44 judges that the forklift 10 is maintained in the great acceleration state or in the great deceleration state. In this case, the controller 44 maintains the value one of the acceleration flag FA and suspends the current routine.

26 As described above, when the current acceleration flag FA is zero, the absolute value of the vehicle acceleration AC is compared with the first acceleration determination value AC1.

When the current acceleration flag FA is one, the absolute value of the vehicle acceleration AC is compared with the second acceleration determination value AC2, which is less than the first acceleration determination value AC1. These comparisons are performed for compensating for hysteresis errors of the vehicle acceleration AC. In this embodiment, the first acceleration determination value AC1 is set to m/s 2 and the second acceleration determination value is set to 0.2 m/s 2 When accelerating, the forklift 10 is changed from the small acceleration state to the great acceleration state at m/s 2 and is changed from the great acceleration state to the small acceleration state at 0.2 m/s 2 When decelerating, the forklift 10 is changed from the small deceleration state to the great deceleration state at -1.0 m/s 2 and is changed from the great deceleration state to the small deceleration state at -0.2 m/s 2 When the permission flag FX is one, the controller 44 determines the skid determination value, which is used in the skid prevention control, in accordance with the acceleration flag FA. That is, if the acceleration flag FA is zero, the controller 44 performs the skid prevention procedure based on the comparison between the skid value AVD and the first skid determination value Val. When the acceleration flag FA is one, the controller 44 executes the skid prevention procedure based on the comparison between the skid value AVD and the second skid determination value Va2.

27 Fig. 12 is a graph showing the front wheel speed VF, the rear wheel speed VD, the vehicle acceleration AC and the skid value AVD when the forklift 10 is running on a dry road surface. The wheel angle 8 is zero. The mast assembly 17 is at the most rearward position. The load weight on the fork 17a is zero. The running state of the forklift 10 is the most unlikely to cause the forklift 10 to skid.

In the graph of Fig. 12, the acceleration lever 23 is manipulated for directing switching between time T 2 and T 3 Thus, the forklift 10, which is in acceleration state, is changed to deceleration state by the direction switching and is then stopped. Thereafter, the forklift is started in the opposite direction.

The vertical axis of the graph of Fig. 12 represents the speed or acceleration. For convenience of description, the determination values, Val, Va2, ACi and Vb have negative values when the vehicle acceleration AC and the skid value AVD have negative values.

o o 20

'S

S.

S S

S

The period between time T 1 and T 2 is a period for accelerating the forklift 10 before the direction switching is performed. The period between time T 5 and T 6 is a period for accelerating the forklift 10 in the reverse direction. During these periods T 1

-T

2

T

5

-T

6 the forklift 10 is judged to be in the great acceleration state, and the acceleration flag FA is set to one. The period between time T 3 and T 4 is a period for deceleration of direction switching. During the period T 3

-T

4 30 the forklift 10 is judged to be in the great deceleration state, and the acceleration flag FA is set to one.

Accordingly, during the period T 1

-T

2 during the period T 3

-T

4 and during the period T 5

-T

6 the second skid determination value Va2 is used as the skid determination value that is used 28 in the skid prevention procedure. Specifically, the skid determination value is set to 0.3 m/s. In periods other than the ones listed above, the first skid determination value Val, which is 0.2 m/s, is used as the skid determination value.

When the forklift 10 is accelerating prior to direction switching, the skid value AVD does not exceed the permission determination value Vb. Thus, the skid prevention procedure is not executed. When the forklift 10 is stopped and started during direction switching, the skid value AVD temporarily exceeds the permission determination value Vb approximately at time T 4 and when falls below the second skid determination value Va2. At time T 5 which is immediately after time T 4 the second skid determination value Va2 is selected. Thus, the skid prevention procedure is not executed.

Suppose that the skid prevention procedure based on the permission determination value Vb is not prohibited during deceleration in direction switching. In this case, the skid o 20 prevention procedure is executed immediately before time T 3 based on the comparison between the skid value AVD and the first skid determination value Val. At time T 3 the second skid determination value Va2 is used. Since the skid value AVD does not the second skid determination value Va2, the skid .25 prevention procedure is not executed.

Suppose that the skid prevention procedure is prohibited eoo•, based on the permission determination value Vb while the forklift 10 is decelerating during direction switching. In 30 this case, the skid value AVD does not exceed the permission determination value Vb as shown by broken line D in Fig. 12.

Therefore, the skid prevention procedure is not executed despite that the skid value AVD exceeds the first skid determination value Va immediately before time T 3 The skid 29 value AVD exceeds the second skid determination value Va2 after time T 3 However, since the skid value AVD does not exceed the permission determination value Vb, the skid prevention procedure is not executed.

As described above, the second skid determination value Va2, which is relatively great, is used when acceleration or deceleration of the forklift 10 is relatively great. If the forklift 10 can be accelerated or decelerated at a relatively great rate, the running state is unlikely to cause the forklift 10 to skid. Therefore, using the second skid determination value Va2 when the acceleration or the deceleration is great prevents the skid prevention procedure from excessively executed. Accordingly, the forklift 10 is reliably accelerated or decelerated.

The embodiments of Figs. 9 to 12 may be modified as follows.

*fl.

20

C..

C5

C

2 Instead of changing the skid determination value in accordance with the acceleration or the deceleration of the forklift 10, the skid prevention procedure may be prohibited regardless of the skid value AVD when the forklift 10 is in the great acceleration state or in the great deceleration state. In other words, the skid prevention procedure may be permitted only when the forklift 10 is judged to be in the small acceleration state or in the small deceleration state.

This simplifies the procedure.

Instead of prohibiting the skid prevention procedure based on the permission determination value Vb, only the skid determination value may be changed in accordance with the acceleration or the deceleration of the forklift 10. That is, the procedure of the embodiment shown in Fig. 9 may be 30 C C

CC..

omitted, and the only procedures of the embodiment shown in Figs. 10 to 12 may be executed. In this case, step Sll of the routine of Fig. 11 is omitted.

In the embodiment of Figs. 10 to 12, the second skid determination value Va2 may be changed in accordance with the running state of the forklift 10. For example, when the mast assembly 17 is at the most forward position, the second skid determination value Va2 when the load on the fork 17a is zero may be different from when the load is not zero. This enables a fine control to be performed.

Instead of using the two acceleration determination value ACl, AC2 for determining the acceleration state of the forklift 10, a single acceleration determination value may be used.

The skid determination value or the acceleration determination value may be different when the forklift 10 is o 20 accelerating from when the forklift 10 is decelerating.

The vehicle acceleration AC may be detected by an additional acceleration sensor.

A fourth embodiment of the present invention will now be described with reference to Figs. 13 and 14. Mainly, the differences from the first embodiment of Figs. 1 to 8(c) will be discussed below. The embodiment of Figs. 13 to 15 relates to braking procedure for the front wheels 11L, 11R, which is 30 executed with the skid prevention procedure of the regenerative mode. That is, as in the first embodiment of Figs. 1 to when the braking torque of the driving motor 19 is limited tor preventing the rear wheel 12 from skidding during the regenerative mode, the brakes 16 are activated as 31 necessary for braking the front wheels 11L, 11R in this embodiment. As a result, the reduction of the braking force due to limiting of the braking torque of the driving motor 19 is compensated for. This embodiment relates to details of such braking control procedure.

When the skid prevention procedure is performed during the regenerative mode, the deceleration of the forklift 10 is determined by the braking force applied to the driving wheel 12 from the driving motor 19 (main braking force) and the braking force applied to the front wheels 11L, 11R from the brakes 16 (auxiliary braking force). The auxiliary braking force is determined by the pressure of oil supplied from the brake control valve unit 33 to the brakes 16, or the auxiliary braking pressure. The controller 44 adjusts the auxiliary braking force according to a brake pressure data M2 shown in Fig. 13 such that the deceleration of the forklift 10 remains in a proper range. The braking pressure data M2 shown in Fig.

13 is previously stored in the memory of the controller 44.

*9*e The brake pressure data M2 is used for determining the auxiliary brake pressure PK, which correlates with the auxiliary braking force. The brake pressure data M2 sets four stages of the auxiliary brake pressure PK, that is, first to

S

25 fourth braking pressure P0 to P3. The third brake pressure P2 is a reference value P. The first brake pressure PO is zero.

The third brake pressure P1 is thirty percent less than the reference value, or 0.7P. The fourth brake pressure P3 is thirty percent more than the reference value P, or 1.3P.

The controller 44 selects one of the first to fourth brake pressures P0 to P3 based on the vehicle deceleration by referring to the brake pressure data M2. The selected brake pressure is set as the auxiliary pressure PK. The 32 vehicle deceleration 1 is computed based on the change of the vehicle speed V in a predetermined period. The vehicle speed V is represented, for example, by the average of the front wheel moving speeds VLF, VRR, which is discussed in the first embodiment of figs. 1 to 8(c).

As shown in the brake pressure data M2 in Fig. 13, the first brake pressure P0 corresponds to a range of the vehicle deceleration 1 that is equal to or greater than 15. The second brake pressure P1 corresponds to a range of the vehicle deceleration 1 between 13 and 16. The third brake pressure P2 corresponds to a range of the vehicle deceleration 1 between 1I and 14. The fourth brake pressure P3 corresponds to a range of the vehicle deceleration 1 that is equal to or less than 12. The values of the vehicle deceleration 1i to 16 satisfy the inequality 0 1I 12 13 14 15 16. The first to fourth brake pressure PO to P3 and the vehicle deceleration 1 satisfy the following equations.

PO: 1 0 20 P1: 13 1 16 P2: 1i 1 3 4 rr P3: 1 12 During the skid prevention procedure, the controller 44 e. 25 starts actuating the brakes 16 at the third brake pressure P2, which has the reference value P. If the vehicle deceleration Sis in a range that corresponds to the current auxiliary pressure PK, the controller 44 judges that the current auxiliary brake pressure PK is proper and maintains the 30 current auxiliary brake pressure PK. If the vehicle C C deceleration 1 is out of the range that corresponds to the current auxiliary brake pressure PK, the controller 44 judges that the current auxiliary brake pressure PK is inappropriate and changes the auxiliary brake pressure PK such that the 33 auxiliary brake pressure PK corresponds to the vehicle deceleration 3. That is, as shown in Fig. 13, when the vehicle deceleration f exceeds the upper value of the range that corresponds to the current auxiliary brake pressure PK, the auxiliary brake pressure PK is lowered by one step. When the vehicle deceleration f falls below the lowest value of the range that corresponds to the current auxiliary brake pressure PK, the auxiliary brake pressure PK is increased by one step.

Each of the ranges of the vehicle deceleration 3 that correspond to the first to fourth brake pressures PO to P3, respectively, overlaps the ranges of the vehicle deceleration f that correspond to the adjacent brake pressure ranges. This is for compensating for the hysteresis errors of the vehicle deceleration 3.

Fig. 14 is a flowchart showing a braking control routine that is executed during the regenerative mode. The routine of Fig. 14 is initiated when the regenerative mode is started and 20 repeated at predetermined intervals during the regenerative mode. The regenerative mode is started, for example, by *to manipulating the acceleration lever 23 for direction .00.

switching.

40009: 25 At step S21, the controller 44 judges whether the current routine is initiated for the first time after the regenerative mode had been started. If the current routine is the first routine, the controller 44 proceeds to step S22. If the current routine is second or later execution, the controller 30 44 proceeds to step S24.

At step S22, the controller 44 judges whether the vehicle speed V is equal to or greater than a predetermined low speed determination value Vd. If the vehicle speed V is less than 34 the low speed determination value Vd, the controller 44 judges that the forklift 10 is in a low speed range and terminates the current routine. In this case, the controller 44 will not execute this routine until the regenerative mode is finished.

If the vehicle speed V is equal to or greater than the low speed determination value Vd, the controller 44 judges that the forklift 10 is not in the low speed range and proceeds to step S23.

At step S24, the controller 44 judges whether the brakes 16 are operating. If the brakes 16 are not operating the controller 44 proceeds to step S23. If the brakes 16 are operating the controller 44 proceeds to step At step S23, the controller 44 judges whether the absolute value of the skid value AVD is greater than the determination value Va. When the absolute value of the skid value AVD is equal to or less than the determination value Va, :..the controller 44 judges that the rear wheel 12 is not @00p 20 skidding and temporarily suspends the current routine. When the absolute value of the skid value AVD is greater than the determination value Va, the controller 44 judges that the rear

S"S

wheel 12 is skidding and proceeds to step S25. When the rear wheel 12 is judged to be skidding, the braking torque of the 25 driving motor 19 in the manner of the first embodiment of Figs. 1 to 8(c) to stop the skidding.

At step S25, the controller 44 judges whether a .predetermined standby period t has elapsed since the brakes 16 30 were activated. The standby period t corresponds to time from when the brakes 16 are activated to when the vehicle deceleration 0 is stable. The standby period t is for example, one hundred to three hundred milliseconds. If the standby period t has not elapsed, the controller 44 proceeds 35 to step S31 and actuates the brakes 16 with the current auxiliary brake pressure PK. That is, the controller 44 supplies a current that corresponds to the auxiliary brake pressure PK to the electromagnetic valve 33b of the brake control valve unit 33.

When the rear wheel 12 is judged to be skidding, the auxiliary brake pressure PK is first set to the third brake pressure P2, which is the reference value P (see Fig. 13) Therefore, when the rear wheel 12 is judged to be skidding at step S23, the brakes 16 are activated at the third brake pressure P2 at step S31.

If the standby period t has elapsed at step S25, the controller 44 proceeds to step S26 and computes the vehicle deceleration 3. At step S27, the controller 44 judges whether the auxiliary brake pressure PK is proper for the vehicle deceleration 3 by referring to the brake pressure data M2 of Fig. 13. That is, the controller 44 judges the vehicle 0@Oe deceleration f is in a range that corresponds the current auxiliary brake pressure PK.

OSOO

0 If the vehicle deceleration 3 is in a range that corresponds to the current auxiliary brake pressure PK, the 25 controller 44 judges that the current auxiliary brake pressure PK is proper and proceeds to step S31. At step S31, the controller 44 activates the brakes 16 at the current auxiliary esee

O

SoSO brake pressure PK. That is, the current auxiliary brake "Se"pressure PK is maintained.

5.55 If the vehicle deceleration 1 is out of the range of the current auxiliary brake pressure PK, the controller 44 judges that the current auxiliary brake pressure PK is not proper and proceeds to step S28. At step S28, the controller 44 judges 36 whether the vehicle deceleration 3 is greater than the upper value of the range that corresponds the current auxiliary brake pressure PK.

If the outcome of step S28 is positive, the controller 44 proceeds to step S29 and lowers the auxiliary brake pressure PK by one step. However, if the current auxiliary brake pressure PK is the first brake pressure P0, or the lowest value, the auxiliary brake pressure PK is maintained at the first brake pressure PO.

If the outcome of step S28 is negative, that is, if the vehicle deceleration P falls below the lowest value of the range that corresponds to the current auxiliary brake pressure PK, the controller 44 proceeds to step S30. At step S30, the controller 44 increases the auxiliary brake pressure PK by one step. However, if the current auxiliary brake pressure PK is the fourth brake pressure P3, or the highest value, the auxiliary brake pressure PK is maintained at the fourth brake 20 pressure P3.

oooe After proceeding to step S31 either from step S29 or from e eo o.step 330, the controller 44 activates the brakes 16 by the new auxiliary brake pressure PK. That is, the brakes 16 perform 25 braking by the auxiliary brake pressure PK, which has been *shifted by one step.

At step S32, the controller 44 judges whether the driving motor 19 is maintained at the regenerative mode. For example, if the acceleration lever 23 is manipulated in a direction that matches the current moving direction of the forklift during deceleration in direction switching, the regenerative mode is judged to be suspended. Also, if the acceleration lever 23 is switched to the neutral position during 37 deceleration of direction switching, the regenerative mode is judged to be suspended.

If the regenerative mode is suspended, the controller 44 proceeds to step S34 and controls the brake control valve unit 33 such that the brakes 16 stop braking. Thereafter, the controller 44 terminates the routine. If the regenerative mode is judged to be maintained, the controller 44 proceeds to step S33.

At step S33, the controller 44 judges whether the vehicle speed V is equal to or less than the stop determination value Vc. The step determination value Vc is a value of a low vehicle speed at which the forklift 10 is assumed to be still as discussed at step S4 of the flowchart shown in Fig. 9. The stop determination value Vc is, for example, 1 km/h. If the vehicle speed V is greater than the stop determination value Vc, the controller 44 temporarily suspends the current routine and then starts repeating this routine.

25 If the vehicle speed Vc is equal to or less than the stop determination speed Vc, the controller 44 proceeds to step S34. At step S34, the controller 44 controls the brake control valve unit 33 such that the brakes 16 stop braking and terminates the current routine. Therefore, immediately before the forklift 10 is stopped, braking of the front wheels 11L, 11R by the brakes 16 is released. This prevents braking the forklift 10 from generating shock due to braking transmitted to the vehicle body.

As described above, if the rear wheel 12 skids during deceleration in the regenerative mode, the brakes 16 are activated at the third brake pressure P2, which brake the front wheels 11L, 11R by a force that corresponds to the third 38 brake P2. Braking with the third brake pressure P2 is continued for the standby period t. After the standby period t, that is, after the vehicle deceleration 1 is stable, steps S26 to S31 are repeated so that the auxiliary brake pressure PK is adjusted to the value that corresponds to the vehicle deceleration 1. If the vehicle deceleration 1 increases, the auxiliary brake pressure PK is lowered, accordingly, to decrease the braking force. If the vehicle deceleration P is decreased, the auxiliary brake pressure PK is increased to increase the braking force. In this manner, the braking force is adjusted in accordance with the vehicle deceleration 1, and the vehicle deceleration 1 is maintained in a predetermined proper range.

As shown at step S24, the skid determination of step S23 is not executed while the brakes 16 are operating for the following reason. That is, skidding of the rear wheel 12 indicates that the braking distance of the forklift 10 is relatively long. Thus, after the rear wheel 12 is judged to 20 be skidding at step S23, the braking distance is minimized by continuously activating the brakes 16 without executing the o .skidding determination.

o o.

Since the brakes 16 are hydraulically operated, 25 electricity need be supplied only to the electromagnetic 0valves 33b to actuate the brakes 16. Since the forklift 10 is driven by electricity of the battery, power consumption is .preferably minimized. This embodiment, in which the front wheels 11L, 11R are braked by the hydraulic brakes 16, is S 30 therefore preferable for reducing power consumption.

.oo.

The brake pressure data M2, which is previously stored in the memory of the controller 44, referred to which permits the auxiliary brake pressure PK to be readily and reliably 39 controlled in accordance with the vehicle deceleration The auxiliary brake pressure PK is selected among several steps. Therefore, compared to a case where the auxiliary brake pressure PK is continually changed, the control of the present embodiment is simple.

The auxiliary brake pressure PK is changed in accordance with a single parameter, which is the vehicle deceleration 3.

Therefore, the control is simple.

When the standby period t has elapsed after the brakes 16 are activated at the reference brake pressure P2, the auxiliary brake pressure PK is controlled in accordance with the stable vehicle deceleration f. That is, the auxiliary brake pressure PK is prevented from having an inappropriate value due to unstable values of the vehicle deceleration immediately after the brakes 16 are activated.

20 If the vehicle speed V is less than the low speed determination value Vd immediately after the regenerative mode is started, that is, if the braking distance is expected to be short without braking the front wheels 11L, 11R, the brakes 16 are not activated. This prevents the brakes 16 from 25 unnecessarily activated and saves the battery.

A fifth embodiment of the present invention will now be described with reference to Fig. 15. The fifth embodiment is a modification of the embodiment of Figs. 13 and 14. As shown in Fig. 15, steps S26 to S30 of Fig. 14 are omitted, and only steps S21 to S24, S31 to S34 are executed. That is, at step S31, braking is performed by a predetermined single auxiliary brake pressure PK. The auxiliary brake pressure PK is not changed according to the vehicle deceleration 3.

40 The embodiments of Figs. 13 to 15 may be modified as follows.

When the acceleration lever 23 is moved to the neutral position while the forklift 10 is running, the skid prevention procedure and the brake control procedure may be executed.

That is, at step S32 shown in Fig. 14 or Fig. 15, whether the acceleration lever 23 is moved to the neutral position need not be considered for judging whether the braking need be stopped.

The auxiliary brake pressure PK may be computed in accordance with the difference between the vehicle deceleration 3 and a predetermined target value. In this case, the load weight on the fork 17a may be detected and the target value may be set in accordance with the load weight.

20 "o 25 2 The condition for starting the skid prevention procedure may be different from the condition for starting the braking control procedure. For example, the skid determination value, which is the reference value for staring the braking control procedure, may be smaller than the skid determination value Va, which is the reference value for starting the skid prevention procedure.

The braking force of the brakes 16 may be adjusted by a method other than changing of the auxiliary brake pressure PK.

For example, activation and deactivation of the brakes 16 may be repeated at short intervals, and the ratio of activation in each cycle may be changed to control the braking force.

The second embodiment of Fig. 9 may be combined with the embodiments of Figs. 13 to 15. That is, when the skid 41 prevention procedure is prohibited based on the permission determination value Vb, the braking control procedure of Figs.

13 to 15 may be prohibited.

The embodiment of Figs. 10 to 12 may be combined with the embodiments of Figs. 13 to 15. That is, in the embodiments of Figs. 13 to 15, the skid determination value may be changed in accordance with the acceleration or the deceleration of the forklift A fourth embodiment of the present invention will now be described with reference to Fig. 16. Mainly, the differences from the first embodiment of Figs. 1 to and from the fifth embodiment of Fig. 15 will be discussed below. Like the first embodiment of Figs. 1 to the skid prevention procedure for the rear wheel 12 and the brake control procedure for the front wheels 11L, 11R are executed when skidding of the rear wheel 12 is detected during the regenerative mode. Further, in the embodiment of Figs. 16(a) 20 to 16(c), the brake control procedure for the front wheels oo 11L, 11R is executed when skidding of the rear wheel 12 cannot be detected during the regenerative mode due to, for example, a malfunction.

25 As discussed in the first embodiment of Figs. 1 to the skid value AVD, which is used for judging whether the rear wheel 12 is skidding, is represented by the difference between the rear wheel moving speed VD and the converted moving speed oooe o ~VDP. The converted moving speed VDP is computed based on the front wheel rotation speeds NLF, NRF, which are detected by the front wheel speed sensors 45L, 45R. Therefore, if at least one of the front wheel speed sensors 45L and malfunctions, the skid value AVD cannot be obtained, and whether the rear wheel 12 is skidding cannot be detected.

42 Fig. 16 shows a running control routine of the forklift The routine of Figs. 16(a) to 16(c) is executed at predetermined intervals while the forklift 10 is moving.

At step S41, the controller 44 judges whether the front wheel speed sensors 45L, 45R are both normal. That is, the controller 44 judges whether it is receiving pulse signals that represents the front wheel rotation speeds NLF, NRF from the front wheel speed sensors 45L, 45R, respectively. If the outcome is positive, that is, if the front wheel speed sensors 45R are normal, the controller 44 proceeds to step S42.

Steps S42 to S50 relate to the target motor torque setting procedure and the skid prevention procedure, which are discussed in the first embodiment of Figs. 1 to 8(c).

Therefore, see the corresponding descriptions in the first embodiment of Figs. 1 to 8(c) as necessary.

20 2 oo2 o o At step S42, the controller 44 computes the front wheel moving speed VF based on the front wheel rotation speeds NLF, NRF. The front wheel speed VF represents the moving speed of one of the front wheels 1LL, 11R, which is located radially outside during a turn.

At step S43, the controller 44 computes the rear wheel speed ND based on the motor speed NM, which is detected by the rear wheel speed sensors 41a, 41b. The controller 44 also computes the rear wheel moving speed VD based on the rear wheel speed ND. At step S44, the controller 44 computes a converted moving speed VDP based on the front wheel moving speed VF. At step S45, the controller 44 computes the skid value AVD by subtracting the converted moving speed VDP from the rear wheel moving speed VD.

43 At step S46, the controller 44 computes a target torque of the driving motor 19 based on the motor speed NM and the lever manipulation amount ACC by referring to the map Ml, which is shown in Fig. 4. When the driving motor 19 is being controlled in the powering mode, the target driving torque is computed. When the driving motor 19 is being controlled in the regenerative mode, the target braking torque is computed.

At step S47, the controller 44 judges whether the absolute value of the skid value AVD exceeds the determination value Va. If the absolute value of the skid value AVD is equal to or less than the determination value, the controller 44 judges that the rear wheel 12 is not skidding and proceeds to step S48. At step S48, the controller 44 controls the driving motor 19 according to the normal target torque, which was computed at step S46.

20 r o.

a o ooo 25 If the absolute value of the skid value AVD exceeds the determination value Va, the controller 44 judges that the rear wheel 12 is skidding and proceeds to step S49. At step S49, the controller 44 reduces the normal target torque, which was computed at step S46, by a predetermined rate and sets the resultant as a new target torque for preventing skidding.

Thereafter, the controller 44 proceeds to step S50. At step the controller 44 controls the driving motor 19 according to the reduced target torque.

r cr At step S51, which is subsequent to step S48, the controller 44 stops the brakes 16 and temporarily suspends the current routine. That is, if the rear wheel 12 is not judged to be skidding, the front wheels 11L, 11R are not braked.

At step S52, which is subsequent to step S50, the 44 controller 44 judges whether the vehicle speed V is equal to or less than the predetermined stop determination value Vc.

The vehicle speed V is represented by, for example, the average of the front wheel moving speeds VLF, VRF. As discussed at step S33 of the flowchart shown in Fig. 14, the stop determination value Vc is a value of the vehicle speed V at which the forklift 10 is substantially stopped. If the vehicle speed V is equal to or less than the stop determination value Vc, the controller 44 executes step S51 and temporarily suspends the current routine.

If the vehicle speed V is greater than the stop determination value Vc, the controller 44 proceeds to step S53 and judges whether the driving motor 19 is being controlled at the regenerative mode. That is, the controller 44 judges whether the current moving direction of the forklift 10 is opposite to the direction indicated by the acceleration lever 23.

20 If the driving motor 19 is not being operated at the Sregenerative mode, that is, if the driving motor 19 is being operated at the powering mode, the controller 44 proceeds to step S51 and temporarily suspends the current routine. If the driving motor 19 is being operated at the regenerative mode, 25 the controller 44 proceeds to step S54. At step S54, the controller 44 activates the brakes 16 and temporarily suspends the current routine. That is, if the rear wheel 12 is judged to be skidding during the regenerative mode, the skid prevention procedure for the rear wheel 12 and the brake 30 control procedure for the front wheels 11L, 11R are executed.

If the outcome of step S41 is negative, that is, if at least one of the front wheel speed sensors 45F, malfunctions, the controller 44 proceeds to step S55. At step 45 as at step S46, the controller 44 computes the target torque of the driving motor 19 based on the motor speed NM and the lever manipulation amount ACC by referring to the map M1 shown in Fig. 4. At step S56, the controller 44 controls the driving motor 19 according to the normal target torque, which was computed at step After step S56, the controller 44 proceeds to step S53.

As described above, the controller 44 judges whether the driving motor 19 is being operated at the regenerative mode at step S53. If the driving motor 19 is being operated at the regenerative mode, the controller 44 proceeds to step S54 and activates the brakes 16.

20 25 *oo, r I r 25 ooo o As described above, when at least one of the front wheel speed sensors 45L, 45R is judged to be malfunctioning, that is, when skidding of the rear wheel 12 cannot be detected, the skid prevention procedure is not executed and the driving motor 19 is controlled according to the normal target torque.

If the driving motor 19 is being controlled at the regenerative mode, the front wheels 11L, 11R are braked by the brakes 16. That is, if skidding of the rear wheel 12 cannot be detected in the regenerative mode, the front wheels 11L, 11R are braked regardless whether the rear wheel 12 is skidding.

r The driving motor 19, which is an alternating current induction motor, is operated by adjusting the magnitude and the frequency of three-phase alternating current supplied to the driving motor 19 according to signals from the rear wheel speed sensors 41a, 41b. Thus, the driving motor 19 can be controlled even if the front wheel speed sensors 45L, malfunction. However, if the rear wheel speed sensors 41A, 41b malfunction, the driving motor 19 cannot be controlled.

46 *7 As described above, when skidding of the rear wheel 12 cannot be detected during the regenerative mode, the front wheels 11L, 11R are braked regardless of whether the rear wheel 12 is skidding. Therefore, if the front wheel speed sensors 45L, 45R malfunction or when lines of the sensors are broken, the front wheels 11L, 11R are braked to minimize the braking distance of the forklift When only one of the front wheel speed sensors 45L, malfunctions, the skid value AVD may be computed based on the front wheel speed detected by the normal one of the sensors 45R, and the skid prevention procedure may be executed by using the computed skid value AVD.

Not only when the front wheel speed sensors 45L, malfunction, but also when the skid value AVD cannot be computed due to malfunction of the rear wheel sensors 41a, 41b, the front wheels 11L, 11R may be braked. In this case, the driving motor 19 may be replaced by a direct-current S-motor, which can be controlled even if the rear wheel speed S"sensors 41a, 41b malfunction.

r A brake pedal 100 (see Fig. 3) may be located on the 25 floor of the cab 20, and when the brake pedal 100 is depressed for braking the rear wheel 12, skidding of the rear wheel 12 may be detected. If the rear wheel 12 is judged to be skidding, the front wheels 11L, 11R are braked by the brakes 16. When skidding of the rear wheel 12 cannot be detected, 30 the braking control procedure of the front wheels 11L, 11R by Zthe brakes 16 may be executed.

The braking of the front wheels 11L, 11R may be executed according to any one of the methods described in the 47 embodiments of Figs. 13 to The embodiments of Figs. 1 to 16 may be modified as follows.

In the illustrated embodiment, the skid value AVD represents the difference between the moving speed VD and the converted moving speed VDP. However, the skid value AVD may represent skid ratio. In this case, the skid value AVD is computed based on the following equations. The upper equation is used during the powering mode, or when the forklift 10 is accelerating. The lower equation is used during the regenerative mode, or when the forklift 10 is decelerating.

The determination value Va is set to correspond to the skid ratio.

AVD (VD VDP) VD AVD (VDP VD) VDP 20 When the absolute value of the speed of the rear wheel 12 or the absolute value of the moving speed of the rear wheel 12 exceeds a predetermined determination value, the rear wheel 12 oomay be judged to be skidding.

"25 The regenerative mode may be started by manipulating an operating member other than the acceleration lever 23. For example, a pedal may be used.

In the illustrated embodiments, the rear wheel 12 is 30 electrically braked during the regenerative mode. However, r the rear wheel 12 may be electrically braked by plugging.

That is, any type of braking method may be applied as long as the motor 19 is electrically controlled to generate braking torque.

48 The driving motor 19 need not be an alternating-current motor-but may be a direct-current motor.

The brakes 16 need not be hydraulic drum brakes, but may be hydraulic disk brakes. Also, the brakes 16 need not be hydraulically controlled but may be driven by electrical actuators.

The front wheels 11L, 11R need not be fully coasting wheels. For example, when the rear wheel 12 skids, the front wheels 11L, 1LR may be driven or braked by motors as necessary.

The present invention may be applied to industrial vehicles other than the reach type forklift 10. The present invention may be applied to an industrial vehicle in which the front wheels are driving wheels and the rear wheels are coasting wheels.

Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.

~For the purposes of this specification it will be clearly understood that the word "comprising" means "including but not limited to", and that the word "comprises" has a corresponding meaning.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

Claims

1. A driving control apparatus for an electric industrial vehicle having a coasting wheel and a driving wheel that is driven by a motor, the apparatus including: an operation member, which is manipulated by an operator; skid detection means for detecting a skid value, which represents the degree of skidding of the driving wheel; and means for controlling the motor, wherein the motor controlling means computes a target torque of the motor according to the manipulation amount of the operation member and controls the motor such that the motor generates the target torque, wherein the apparatus is characterized in that: the skid detection means computes the moving speed of the driving wheel relative to the road surface based on the rotation speed of the driving wheel, and computes the moving speed of the coasting wheel relative to the road surface based on the rotation speed of the coasting wheel, and wherein the skid detection means computes the skid value based on the driving wheel moving speed and the coasting wheel moving speed, and when the absolute value of the skid value exceeds o a predetermined skid determination value, the motor controlling means reduces the target torque at a *go*predetermined rate to execute a skid prevention procedure.

2. The apparatus according to claim 1, characterized in that the motor controlling means operates the motor in a powering mode or in a braking mode in response to a manipulation of the operation member, wherein, when the motor is operated in the powering mode, the motor controlling means controls the motor to generate driving torque to apply driving force to the driving wheel, and wherein, when the motor is operated in the braking mode, the motor controlling means controls the motor to generate braking torque to apply braking force to the driving \\melbfiles\home$\Leanne\Keep\5429 4 -01.doc 12/02/03 51 wheel.

3. The apparatus according to claims 1 or 2, characterized in that the skid determination value is set to correspond to a range of the skid value in which the friction between the driving wheel and the road surface is relatively great.

4. The apparatus according to any one of claims 1 to 3, characterized in that the motor controlling means sets the skid determination value smaller when the vehicle speed is slow than when the vehicle speed is great. The apparatus according to any one of claims 1 to 4, characterized in that the motor controlling means sets the rate at which the target torque is decreased such that the absolute value of the skid value fluctuates about the skid determination value four or more times in one second.

6. The apparatus according to any one of claims 1 to wherein the skid detection means estimates the moving speed of the driving wheel relative to the road surface based on the coasting wheel moving speed and sets the estimated moving speed as a converted moving speed, and oooo wherein the skid detection means computes a value that is correlated with the difference between the driving wheel moving speed and the converted moving speed and sets the *..*computed value as the skid value.

7. The apparatus according to any one of claims 1 to 6, characterized by permission means that permits the motor controlling means to execute the skid prevention procedure only when the running condition of the vehicle satisfies a predetermined permission condition. The apparatus according to claim 7, characterized in that the permission means permits the motor controlling *e *means to execute the skid prevention procedure only in a period from when the absolute value of the skid value \\melb~file\home$\Leanne\Keep\54294-O1.doc 12/02/03 52 exceeds a predetermined permission determination value, which is greater than the skid value, to when the vehicle speed decreases to a stop determination value, which is close to zero.

9. The apparatus according to claim 7, characterized in that, when the absolute value of the vehicle acceleration exceeds a predetermined acceleration determination value, the permission means prohibits the motor controlling means from executing the skid prevention procedure. The apparatus according to any one of claims 1 to 8, characterized in that the motor controlling means changes the skid determination value in accordance with the absolute value of the vehicle acceleration.

11. The apparatus according to claim 10, characterized in that the motor controlling means sets the skid determination value greater when the absolute value of the vehicle acceleration is great than when the absolute value of the vehicle acceleration is small.

12. The apparatus according to claim 2, characterized by: a brake for braking the coasting wheel; and eeeo 25 brake controlling means, wherein, when the skid prevention procedure is executed in the braking mode, the brake controlling means actuates the brake.

13. The apparatus according to any one of claims 1 to 11, wherein the vehicle includes an additional wheel, the apparatus being characterized by: a brake for braking the additional wheel; and ~brake controlling means, wherein, when the skid prevention procedure is executed due to braking of the driving wheel, the brake controlling means actuates the "0 rake.

14. The apparatus according to claim 13, characterized in that the brake is a friction brake. \\melbfiles\homeS\Leanne\Keep\54294-l.doc 12/02/03 53 The apparatus according to claims 13 or 14, characterized in that the brake controlling means changes the braking force applied to the additional wheel by the brake according to the vehicle deceleration.

16. The apparatus according to claim 15, characterized in that the brake controlling means increases the braking force of the brake as the vehicle deceleration decreases.

17. The apparatus according to claims 15 or 16, characterized in that the brake controlling means discretely changes the braking force of the brake.

18. The apparatus according to claim 17, characterized in that the brake controlling means assigns each of several steps of the braking force to a predetermined range of the vehicle deceleration, and wherein the brake controlling means adjusts the braking force of the brake such that the vehicle deceleration is within a range that corresponds to the braking force.

19. The apparatus according to any one of claims 15 to 18, characterized in that, regardless of changes of the S 25 vehicle deceleration, the brake controlling means g maintains the braking force of the brake at a predetermined reference value from when the brake is actuated to when a predetermined period has elapsed.

20. The apparatus according to any one of claims 13 to 19, characterized in that, if the vehicle speed when braking of the driving wheel is started is less than a predetermined low speed determination value, the brake controlling means prohibits the brake from being actuated. o.

21. The apparatus according to any one of claims 13 to 20, characterized in that, after the brake is once actuated, the brake controlling means continues actuating the brake until the vehicle speed decreases to a \\melb_files\home$\Leanne\Keep\54294-Ol.doc 12/02/03 54 predetermined stop determination value, which is close to zero.

22. The apparatus according to claim 12, characterized in that, if the braking mode is executed when the skid detection means cannot detect the skid value, the brake controlling means actuates the brake.

23. The apparatus according to claim 22, characterized in that the skid detection means includes a first sensor for detecting the rotation speed of the driving wheel and a second sensor for detecting the rotation speed of the coasting wheel.

24. The apparatus according to any one of claims 13 to 21, characterized in that, if the driving wheel is braked when the skid detection means cannot detect the skid value, the brake controlling means actuates the brake.

25. A driving control apparatus, substantially as hereinbefore described with reference to the accompanying drawings. Dated this 12th day of February 2003 25 KABUSHIKI KAISHA TOYODA JIDOSHOKKI SEISAKUSHO By their Patent Attorneys GRIFFITH HACK Fellows Institute of Patent and Trade Mark Attorneys of Australia 9 9• 9*9 o 09** 9* .09.99 9 \\melb_files\home$\Leanne\Keep\54294-01.doc 12/02/03