JP2674830B2 - Slip detection method and deceleration control method during electric braking in an electric vehicle - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for preventing slips and skids during braking / deceleration in a vehicle, particularly an electric vehicle.

[Prior Art] In an electric vehicle, particularly a battery-powered reach forklift truck, etc., when the brake is applied, the accelerator lever is instantaneously operated from forward to reverse or from reverse to forward from the running state (this is called plugging operation). Then, electric braking is often performed.

[Problems to be Solved by the Invention] However, in a refrigerating or refrigerating warehouse where the road surface has a very low coefficient of friction, the driving wheel gradually decelerates when the above plugging operation is performed, but slips in the reverse rotation. ,
Skid occurs, wear of tires, waste of power consumption,
This is inconvenient because the controllability deteriorates. Further, it has been difficult to enhance deceleration with the conventional deceleration control method.

The present invention detects a slip state electrically during electric braking, and enhances deceleration as much as possible, while suppressing slip occurrence in an electric vehicle. An object is to provide a speed control method.

[Means for Solving the Problems] In order to achieve the above object, the slip detection method at the time of braking of the present invention detects the rotation speed n of the motor that drives the traveling drive wheels of the electric vehicle, and determines the rotation speed n of this rotation speed n. While calculating the deceleration dn / dt, the motor current value i _M of the motor is detected, and the motor generated torque τ _M is calculated from the current value i _M and the motor current-torque characteristic table stored in advance. , The expected deceleration dN / dt of the expected number of revolutions N of the motor is calculated from the sum of the torque τ _M and the required torque τ _R for running, dN / dt = -K (τ _M +
τ _R ) [where K is a constant], and the above dn / dt is dN /
When it is smaller than dt, it is determined that the drive wheels are slipping.

Further, the deceleration control method of the present invention, when it is determined that there is slip by the slip detection method, reduce the motor current, if dn / dt is positive, it is determined that the slip is being corrected, then dn / dt When dt becomes zero, it is judged that the slip correction is completed, and after this judgment, the slip detection is performed while gradually increasing the motor current to the motor current allowable value according to the instruction from the access, and the deceleration is controlled. It was done.

[Operation] According to the above method, the predicted rotation of the motor is calculated from the deceleration of the detected motor rotation speed n, that is, the differential value dn / dt of the rotation speed n and the generated torque obtained in advance from the motor current value i _M at this time. The expected deceleration of the engine speed, that is, the differential value dN / dt of the expected number of revolutions N is obtained, and when the detected deceleration dn / dt is smaller than the expected deceleration dN / dt, it is determined that a slip has occurred. It

At the time of this determination, the motor current is reduced to correct the slip, and then, when the detected deceleration dn / dt becomes zero, it is determined that the slip correction is completed. By repeating this operation, deceleration control is performed.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

First, a reach type forklift truck to which the method of the present invention is applied will be described with reference to FIG. Body 1
Has a drive wheel 2 that also serves as a drive wheel and a steering wheel, and a road wheel 3 that is a driven wheel. The driving force from the traveling motor 4 is transmitted through the speed reducer 5 to the drive wheel 2
Has been transmitted to. The control device 6 receives an instruction from the accelerator lever 7 to move forward or backward, and the accelerator data detecting device 8
And a rotation speed detection signal of the motor 4 is input from the rotation speed detection sensor 9 to perform predetermined traveling control. Although not shown, it has an operating member for controlling the forward / reverse switching device. 10 is steering,
11 is a battery.

Next, a control system mainly including the control device 6 will be described with reference to FIG.

The traveling motor 4 is connected in series with the current detector 11, the forward / reverse switching device 12, and the chopper 13, and is connected between the + terminal (+ B) and the-terminal (GND) of the battery power supply. The control unit 6 is a micro processing unit (MPU) 1
4, the ROM 15, the RAM 16, the A / D converter 18, and the input / output interfaces 19 and 20. Then, the rotation speed detection signal of the motor 4 by the rotation speed detection sensor 9, the output of the A / D converter 18 of the motor current value by the current detector 11, and the output of the accelerator data detection device 8 are sent to the MPU 14 via the input interface 19. Is entered. The MPU 14 outputs a signal for controlling the conduction of the chopper 13 via the output interface 20 based on a predetermined program. To apply the plugging braking, the forward / reverse selector 12 is switched in the opposite direction to that during traveling and the accelerator lever 7 is operated.

As shown in FIGS. 2 and 3, the rotation speed detection sensor 9 includes a light emitting portion 9a, a light receiving portion 9b, and a slit 9c attached to the rotation shaft of the motor 4.

Next, with respect to the slip detection and deceleration control method during electric braking by the control device 6, refer to the flowchart shown in FIG. 4 and the time chart of the rotational speed and torque during deceleration braking shown in FIG. And explain.

First, the motor current i _M is detected by the signal from the current detector 11 (step S1 of the flowchart). On the other hand, the motor current-torque characteristic during plugging braking can be obtained in advance, and this characteristic is described in the ROM 15 as a table. This table and the above detected motor current i _M
The torque generated by the motor τ _M is calculated from (S2). From this value, the expected deceleration (dN / dt) of the expected motor speed N is calculated as dN / dt = K (τ _M + τ _R ), where K is a constant and τ _R is the required running torque. Here, the required travel torque τ _R is the product of the running resistance of the electric vehicle and the radius of the driving wheel tires,
The running resistance is obtained from the wheel rolling resistance, which is obtained by multiplying the frictional resistance between the tire and the road surface by the vehicle weight. This running resistance fluctuates depending on the shape of the tire and the condition of the road surface, but it can be empirically considered that the fluctuation amount is a constant value. Therefore, in the present invention, the required running torque τ _R is fixed depending on the vehicle type. I treat it as a value.

This means that when no slip occurs between the drive wheel and the road surface, the rotation speed n is Here, since GD ² has the relation of the moment of inertia and n ₀ has the relation of the initial value of the rotation speed when t = 0, it is based on that the relation of the formula can be obtained by differentiating both sides of the formula. If there is a slip, the vehicle slips between the drive wheel and the road surface, and the above formula is not satisfied.

Then, the motor rotation speed n is detected by the signal from the rotation speed detection sensor 9 (S4), and the deceleration dn / dt is obtained by differentiating this rotation speed n (S5). Next, it is checked whether or not the slip is determined (S6). If not, whether or not the vehicle is decelerating, that is, the above
Check whether dn / dt is negative (dn / dt <0) (S7),
If it is not negative, deceleration is not in progress, so it is determined that there is no slip (# 9). On the other hand, if negative, deceleration is in progress, so it is checked whether or not the deceleration dn / dt is equal to or higher than the expected deceleration dN / dt (S8), and if so, it is determined that there is no slip (S9).
Then, the motor current i _M (in this case, the reverse drive current) is gradually increased to the motor current allowable value instructed by the accelerator lever 7, the process returns to step S1, and the same operation is repeated.

On the other hand, in step S8, the deceleration dn / dt is the expected deceleration Nd / dt.
If it is smaller, it is determined that there is slip (S11). This state corresponds to the period shown as "slip" in FIG. If it is determined that there is a slip, the motor current set value I _M is reduced to reduce the motor current i _M (current for reverse driving as in the above) (S12). Then, it is checked whether or not the deceleration dn / dt has become positive (dn / dt> 0) (S13), and if it has become positive, it is determined that the slip correction is being performed. This state corresponds to the period displayed as "slip correction" in FIG. After that, deceleration dn / dt
Is determined to be zero (dn / dt = 0) (S14). If the deceleration dn / dt is zero, it is determined that the slip correction has been completed and no slip is determined (S15). This state is the end point of "slip correction" in FIG. After the determination that there is no slip, the process returns to step S1 and the same operation is repeated thereafter.

When it is not determined in step S13 that the slip correction is being performed and when it is not determined in step S14 that the slip correction is completed, the process returns to step S1.

By performing the above operation, as shown in FIG. 5, the motor rotation speed n can be decreased with the passage of time, and at the same time, the generated torque τ _M changes. As can be seen from the figure, the period during which the generated torque τ _M exceeds the level of the limit torque for slipping is the slip period, and the period during which it falls below the same level and decreases is the slip correction period. Thus, slip detection and deceleration control can be performed in small increments and quickly,
Therefore, it is possible to suppress slippage as much as possible according to the friction coefficient μ between the road surface and the driving wheels, and obtain high deceleration performance.

In the above, an example in which the rotation speed n of the motor is detected and the predicted deceleration dN / dt of the predicted rotation speed N is obtained has been shown. However, there is a slip between the rotation speed of the motor and the driving wheels. In a normal electric vehicle that does not, the slip detection and the deceleration control can be similarly performed by using the rotation speed of the drive wheels instead of the rotation speed of the motor.

[Advantages of the Invention] As described above, according to the method of the present invention, the deceleration dn / dt of the rotation speed n during deceleration during electric braking is input with the rotation speed detection value and the motor current detection value of the traveling motor as input. , Slip detection during braking is performed by comparing the deceleration dN / dt of the predicted rotation speed N calculated based on the generated torque obtained from the motor current detection value with the determination of the occurrence of slip. Can be performed quickly and accurately.

Then, when a slip is detected, the braking motor current is reduced, the sign of dn / dt is checked to determine whether or not the slip is being corrected, and the correction is completed.After the correction is completed, the motor current is gradually increased. The deceleration is controlled by repeating the same operation. Therefore, it is possible to reduce the speed in small increments while suppressing the occurrence of slip as much as possible, and it is possible to improve the deceleration performance. In particular, the method of the present invention is extremely useful when used in a reach type forklift truck or the like in which braking is often applied by switching the drive from forward to reverse or from reverse to forward.

[Brief description of the drawings]

FIG. 1 is a block diagram of a control system for carrying out the method of the present invention, FIGS. 2 and 3 are configuration diagrams of a rotation speed detection sensor unit used in the control system, and FIG. 4 is one example of the method of the present invention. FIG. 5 is a flow chart for explaining an embodiment, FIG. 5 is a time chart of rotation speed and torque during deceleration according to the method of the present invention, and FIG. 6 is a reach type forklift truck as an example of an electric vehicle in which the method of the present invention is implemented. It is a side view. 1 ... Car body, 4 ... Running motor, 6 ... Control device, 7
...... Accelerator lever, 9 ...... Rotation speed detection sensor, 11 ......
Current detector, 14 …… MPU.

Claims (2)

(57) [Claims] 1. A rotational speed n of a motor for driving a traveling drive wheel of an electric vehicle is detected, a deceleration dn / dt of the rotational speed n is calculated, and a motor current value i _M of the motor is detected. The motor-generated torque τ _M is obtained from this current value i _M and the table of the motor current-torque characteristics stored in advance, and the predicted motor rotation speed N is calculated from the sum of this torque τ _M and the required travel torque τ _R. expected deceleration dN / dt, dN / dt = -K (τ M + τ R) where K is determined as a constant, that the drive wheels when the dn / dt is smaller than dN / dt is determined to be slipping A characteristic method for detecting slip during electric control in an electric vehicle. 2. When the slip detection method according to claim 1 determines that there is slip, the motor current is reduced,
If dn / dt is positive, it is judged that the slip correction is in progress.If dn / dt becomes 0, it is judged that the slip correction is completed.After this judgment, the motor current is allowed to reach the motor current allowable value according to the instruction from the access. A deceleration control method for an electric vehicle, characterized in that the slip detection is performed while gradually increasing the current.