JP2780096B2 - Electric power steering device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus which suppresses power consumption of an electric motor and can be mounted on a heavy-duty vehicle.

(Prior Art) As this kind of apparatus, one described in Japanese Patent Application Laid-Open No. Sho 60-154656 has been conventionally known. FIG. 11 shows a flowchart of the control.

According to this control device, when the ignition switch is turned on, the vehicle speed of the vehicle is input in step 1, and the steering torque is input in step 2.

Then, it is determined in step 3 whether or not the steering torque is larger than a predetermined reference value. If the steering torque is larger than the reference value, the steering direction is determined in step 4.

In step 5, an appropriate value of the output torque T of the electric motor is calculated in step 6 with reference to the output torque management table corresponding to the steering direction, and output to the electric motor in step 7 in accordance with the appropriate value. And in step 8,
It reads the actual output torque T ₁ of the electric motor, determines whether the output torque T ₁ is within a predetermined range in step 9. If the actual output torque is within the predetermined range, the process proceeds to step 10 to determine whether the control has been completed.

Incidentally, when the actual output torque T ₁ is it is out of the predetermined range, to correct the output value in step 12, again reaches step 7.

In this device, a torque constant table and a vehicle speed constant table are provided in the output torque management table in order to control the steering force in response to the vehicle speed. Then, the address of each of these tables is selected, and the torque constant and the vehicle speed constant at that address are derived.

By multiplying the two constants in this way drawer, it was determined motor current I _M for controlling the motor output torque T _M.

(Problems to be Solved by the Present Invention) In the conventional device as described above, the turning resistance is large at the time of low speed or stationary operation (hereinafter, referred to as low speed, etc.), so that the steering is increased accordingly. Requires torque.

On the other hand, since the steering torque is proportional to the current, the current I must be increased in order to obtain a large steering torque. When the current I is increased, power consumption (W) = current (I)
X The voltage (V) also increases.

Therefore, it is necessary to increase the capacity of a battery or an alternator (hereinafter, referred to as a battery or the like). In particular, when this kind of device is to be mounted on a large and heavy vehicle, there is a problem that a large capacity battery or the like is required.

An object of the present invention is to limit the maximum value of a motor voltage depending on a vehicle speed and an engine speed, thereby suppressing an increase in power consumption of a battery or the like at a low speed or the like, and installing the battery in a large and heavy vehicle. An object of the present invention is to provide an electric power steering device that does not cause any inconvenience.

(Means for Solving the Problems) In order to achieve the above object, the present invention relates to a rack having a knuckle arm connected to wheels at both ends,
A motor driving the electric motor includes a torque sensor that detects a steering torque and a vehicle speed sensor that detects a vehicle speed, which are formed by engaging a pinion connected to a steering input shaft and a pinion linked to an electric motor via a speed reducer. An electric power steering device connected to a control device and configured to control the motor control device based on a torque signal transmitted from the torque sensor and a vehicle speed signal transmitted from the vehicle speed sensor is assumed. Things.

While premised on the above device, the motor control device has a microprocessor as a main element, and the microprocessor has stored in advance a maximum duty ratio table for determining a maximum value of the motor voltage, and the vehicle speed sensor Select the address of the maximum duty ratio according to the vehicle speed signal, and maintain the maximum value of the motor voltage while maintaining the maximum duty ratio at high speed, and reduce the maximum duty ratio at low speed to reduce the maximum motor voltage. The value is reduced.

(Operation of the Present Invention) Since the present invention is configured as described above, the duty ratio is reduced and the number of rotations is limited, for example, at a low speed when the electric motor M does not require high rotation.

Since the number of revolutions has been reduced, the desired torque can be output even if the power consumption is constant.

In this case, the number of revolutions N of the electric motor M is low, but at a low speed or the like, a sufficient steering response can be ensured, and there is no problem in driving.

(Effects of the present invention) According to the steering device of the present invention, at low speeds
Even when a large steering torque is required, the power consumption is small, so that it is not necessary to increase the capacity of the battery or the like.

In particular, even when mounted on a large and heavy vehicle, it can be used without increasing the space and weight of a battery and the like.

(Embodiment of the Present Invention) The embodiment of the present invention shown in FIGS.
The pinion 3 is connected to a tip of the steering input shaft 2 connected to the rack 6, and the pinion 3 is engaged with the rack 6. On both sides of the rack 6, via side rods 5,
It is connected to the knuckle arm 4 of the wheel 1.

The electric motor M, which can be rotated forward and reverse, has a speed reducer 7.
Are linked. A pinion 8 is provided on the output shaft side of the speed reducer 7.
And the pinion 8 is engaged with the rack 6.

Further, a torque sensor 9 for detecting a steering torque acting on the input shaft 2 and a vehicle speed sensor for detecting a vehicle speed of the vehicle
10 are provided, but these sensors are connected to the motor control device a.

The torque signal Tin detected by the torque sensor 10 is input to a torque signal processing circuit 11 provided in the motor control device a and a torque sensor abnormality detection circuit 12.

The vehicle speed signal V detected by the vehicle speed sensor 10 is input to a vehicle speed signal processing circuit 13 and a vehicle speed sensor abnormality detection circuit 14. Then, the signal processed by the vehicle speed signal processing circuit 13 is input to the interrupt port INT1 of the microprocessor P and the vehicle speed sensitive circuit 15. The signal input to the interrupt port INT1 is a pulse signal having a different pulse width according to the vehicle speed. An interrupt is generated when the pulse signal rises or falls.

The torque signal processing circuit 11 is connected to a differentiating circuit 16.
By differentiating the output signal V ₁ of the from the signal to increase the responsiveness of
And it outputs a C _{1 1.}

Output signal C _{1 1} from the differentiation circuit 13 is input to the vehicle speed sensitive circuit 15, the signal C to improve the response that depends on the vehicle speed _{1 1 '1 1} next, C outputted from the sensing circuit 15' Are input to the adders 17a and 17b.

The output signal V from the torque signal processing circuit 11
₁ is a forward / reverse direction determination circuit 18 for determining the direction of the torque
And the torque forward / reverse signal T ₀ output from the determination circuit 18 is input to the input port of the microprocessor P.
It is input to the A _1.

Further, the output signal V ₁ from the torque signal processing circuit 11
Is also input to the absolute value circuit 19, where it is converted to an absolute value.
The absolute value | V ₁ |. The absolute value | V ₁ |
Is converted to a digital value. The torque level signal T ₁ which is converted into the digital value is input to the input port A ₂ of the microprocessor P, the torque level signal T ₁ is
For example, in the case of 8 bits, | V ₁ | = 0 is zero, | V ₁ | = max is 255
To respond to.

Each abnormality signal output from each of the abnormality detection circuits 12 and 14 is input to the interrupt port INT2 of the microprocessor P via the OR gate 21.

From the output port C ₁ of the microprocessor P, the forward and reverse signals M ₀ to identify the rotational direction of the electric motor M is, the output level signal M ₁ of the digital value is output from the output port C _2.

These signals M _0, M ₁ is analogized to the output V ₂ becomes the D / A conversion circuit 22, the output V ₂ is input to the adder circuit 17a, and the above-described vehicle speed sensitive response enhancement signal C _{1 1} It is added, the output V _3.

Output V ₃ outputted from the adding circuit 17a is input to the motor drive circuit 23 for controlling the driving of the electric motor M.

Further, from the output port C ₃ of the microprocessor P,
A pulse is output to notify that the program is operating normally.
The signal is input to the OR gate 21 via 24.

The vehicle speed sensing circuit 15 is also connected to an addition circuit 17b separately from the addition circuit 17a.The addition circuit 17b is also connected to the torque signal processing circuit 11, and the output signal V _{1 of the} processing circuit 11 is output. Are input to the adding circuit 17b.

Therefore, from the adder circuit 17b, the signal V ₁ and the differential signal C _{1 1} and the signal V ₄ obtained by adding are output.

The input / output check circuit 27 is connected to the addition circuit 17b. The input / output check circuit 27 is connected to the current sensor 25 via the current signal processing circuit 26. Then, this current sensor 25 detects a current supplied to the electric motor M, a current signal processing circuit 26 outputs a signal V ₅ in accordance with the output signal of the current sensor 25.

The input / output check circuit 27 as described above is
The output signal V ₄ of 17b as an input signal x, the output signal y output signal V ₅ of the current processing circuit 26, an output abnormal range shown in FIG. 10
If any of U _{1 to} U ₄ , output y
Is determined to be an abnormal situation, and the electric motor M is stopped by controlling the motor drive circuit 23 via the OR gate 28.

Further, the OR gate 28 is also connected to the output gate C ₄ of the microprocessor P, via the OR gate 28 the output signal of the microprocessor P, so as to control the motor drive circuit 23.

The maximum duty ratio signal D _max that limits the maximum value of the output voltage output from the output port C ₅ of the microprocessor P is input to the D / A conversion circuit 29.

In this D / A conversion circuit 29, the maximum duty ratio signal D _max
The converted to motor voltage V _D, and outputs to the motor drive circuit 23.

In the motor driving circuit 23, limits the maximum value of the output to the motor based on the motor voltage V _D.

Thus, the microprocessor P operates according to the flowcharts of FIGS.

That is, when the ignition switch for starting the engine is turned on, the program starts in synchronization with the ignition switch.

When the program is started as described above, the output level signal M ₁ = 0 is output from the output port C ₂ in step 1.

Then, by outputting a motor ON signal to operate the motor driving circuit 23 from the output port C ₄ in step 2.

Then, in step 3, the vehicle speed pulse
The count register is set to the maximum value (equivalent to vehicle speed ≒ 0), and the operation preparation is completed.

When the preparation is completed as described above, the process proceeds to steps 4 and 5 in order. Step 4 In is inputted from the input port A ₂ a torque level signal T _1, to input the torque forward and reverse signals T ₀ to the input port A ₁ in step 5.

Next, the process proceeds to step 6. In step 6 and subsequent steps, a calculation for making the output torque and the output voltage sensitive to the vehicle speed is performed.

That is, in step 6, the torque level signal T ₁
Depending on, selects the address of the torque constant table, pulling out the torque constant C _T at that address.

In step 7, the address of the vehicle speed constant table corresponding to the value of the vehicle speed pulse register R is selected, and the vehicle speed constant _CV at that address is derived.

Then, in step 8, the output torque is shifted right by n bits to make the output torque sensitive to the vehicle speed. Thus n
To shift right by bits, (1/2 ⁿ ) × C _V ×
As C _T, obtaining the output level M _1. For example, as shown in FIG. 6, constants are extracted from k vehicle speed constant tables and l torque constant tables, and calculations are performed.

If the bits are not shifted right by n bits as described above, for example, if C _V is 4 bits, _CT is 8 bits, and D / A converter is 8 bits, the result of the multiplication becomes 12 bits. , Exceeding the capability of the D / A converter. Therefore, in this case, n = 4 bits are shifted to the right to make the maximum 8 bits so as not to exceed the capability of the D / A converter.

In step 9, the output forward and reverse signals M _0, the torque forward and reverse signals
Place the same as T ₀ and finish preparing for output.

Next, the process proceeds to step 10 in order to control the maximum output voltage.

In step 10, an address of the maximum duty ratio (voltage) table corresponding to the value of the vehicle speed pulse register R is selected, and the maximum duty ratio γ at that address is derived. Maximum duty ratio γ determines the maximum motor voltage V _D. For example, when γ = 100 (%), V _D = 12 (V)
In the case of γ = 75 (%), V _D = 9 (V). The maximum duty ratio table depends on the vehicle speed v,
For example, as shown in FIG. 7, it may be made to depend on the engine speed n. When the maximum duty ratio γ is limited, the output power can be suppressed. That is, as shown in FIG. 8, when the motor voltage V _M is constant, the electric motor M
The characteristics show that the motor rotation speed N decreases as T _M increases.

For example, if the maximum motor voltage V _M = 12 (V) and the motor output torque T _M = 7.5 (kgf · m), the motor rotation speed N
Is N = 3000 (rpm), but if T _M = 15 (kgf · m), the motor rotation speed N becomes N = 2000 (rpm).

Now, assuming that a torque of 15 (kgf · m) is required at a low speed or the like, the motor current I _M is almost proportional to the motor output torque T _M , so a current of I _M = 50 (A) flows.

The motor voltage V _M the duty ratio _{γ = 100 (%) V M} = 1
2 (V), like point A in the first quadrant in the figure,
The electric motor M that steers the wheels 1 has a motor rotation speed N =
Attempt to rotate at 2000 (rpm).

However, at a low speed or the like, a large torque is required, but it is not necessary to steer the wheels 1 at such a high speed.

Therefore, at a low speed or the like, the duty ratio γ is set to γ = 75.
Down to (%), while limiting the motor voltage V _M to V _M = 9 (V), as point B in the figure, the motor output torque T _M T _M
= 15 (kgf · m), the power consumption W is 9 (V)
× 50 (A) = 450 (W).

In this case, the rotation speed N of the electric motor M is equal to the motor voltage V _M
Is 9 (V), so that N = 1000 (rpm). However, at a low speed or the like, sufficient steering response can be ensured even with N = 1000 (rpm).

In the device of the present invention thus configured, the motor voltage V _M = 12
(V) is the power consumption W, which is 12 (V) × 50
Compared with (A) = 600 (W), the power consumption W can be reduced to about 3/4.

That is, it is possible to secure a sufficient motor output torque and a turning speed according to the traveling conditions while suppressing the power consumption W.

In FIG. 7, the duty ratio γ is 10
Assuming 0 (%), the output motor voltage V _M of the electric motor _M = 12
(V).

This is because it is necessary to steer the wheel 1 quickly at a high speed.

Next, the process proceeds to an output step after step 11. In step 11, is output from the output port C ₁ output forward and reverse signal M _0. In step 12, the output level signal M ₁ is outputted from the output port C _2, in step 13, it is outputted from the output port C ₅ maximum duty ratio signal D _max, with these output forward and reverse signals M _0, the output level the signal M _1, by the maximum duty ratio signal D _max, controls the electric motor M.

Furthermore, in step 14, it is outputted from the output port C ₃ a watchdog pulse, when it discovers abnormal, so that to turn off the electric motor M.

FIG. 4 shows a routine of an interruption process by a vehicle speed pulse.

That is, a pulse signal having a different pulse width is always output from the vehicle speed sensor according to the vehicle speed, and an interrupt is generated when the pulse signal rises or falls.

When a pulse signal is input to the interrupt port INT1 as described above, the value of the pulse counter at that time is set in the register R in step 21, and the pal counter is cleared in step 22 to start counting.

In this way, for example, the time from the rising of the pulse to the next rising is counted. The pulse interval is proportional to the count number, and the vehicle speed v is inversely proportional to the count number.

Therefore, by looking at the value of the register at this time, the vehicle speed v can be grasped.

After completing the abnormal operation, the program returns to the main routine at the time when the interrupt occurred.

FIG. 5 shows a routine of an interrupt process by an abnormal signal. That is, when the abnormality signal is input to the interrupt port INT2, and outputs the motor OFF signal for turning off the electric motor M in step 31 from the output port C _4, to turn off the electric motor M.

Then, in step 32, and outputs an output level signal M ₁ = 0 from the output port C _2, to stop the electric motor M, the state is maintained.

When the electric motor M stops in this way, only the rotational force of the steering input shaft is directly transmitted to the rack 6, and a manual steering state is set.

Further, according to this device, since the vehicle is of the vehicle speed sensitive type, as shown in FIG.
It will change according to the vehicle speed.

[Brief description of the drawings]

1 to 9 show an embodiment of the present invention.
2 is a block diagram of a motor control device, FIG. 3 is a diagram showing an example of a flowchart of a control program, FIGS. 4 and 5 are flowchart diagrams showing an interrupt processing routine, and FIG. diagram showing the operation of the vehicle speed constant table and the torque constant table, FIG. 7 is a graph showing the relationship between the vehicle speed and the motor voltage V _M, FIG. 8 is a characteristic diagram of the electric motor, FIG. 9 is an output level FIG. 10 is a graph showing the relationship with the steering torque, FIG. 10 is a diagram showing a control range based on the input signal x and the output signal y, and FIG. 11 is a flowchart of a control program of the conventional device. 1 ... wheels, 2 ... steering input shaft, 3, 8 ... pinion,
4 ... knuckle arm, 6 ... rack, 9 ... torque sensor, 10 ... vehicle speed sensor, a ... motor control device, P ...
... microprocessor.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B62D 5/04 B62D 6/00

Claims (1)

(57) [Claims] A rack formed by linking a knuckle arm connected to wheels to both ends thereof is engaged with a pinion linked to a steering input shaft and a pinion linked to an electric motor via a speed reducer to reduce steering torque. A torque sensor for detecting and a vehicle speed sensor for detecting vehicle speed are connected to a motor control device for controlling the electric motor, and a torque signal sent from the torque sensor, a vehicle speed signal sent from the vehicle speed sensor, Accordingly, in the electric power steering device configured to control the motor control device, the motor control device has a microprocessor as a main element, and the microprocessor has a maximum value that determines a maximum value of the motor voltage in advance. A duty ratio table is stored, and the maximum duty ratio corresponding to the vehicle speed signal from the vehicle speed sensor is stored. Motor power that maintains the maximum value of the motor voltage by maintaining the maximum duty ratio at high speeds and reduces the maximum value of the motor voltage by reducing the maximum duty ratio at low speeds. Steering device.