JPH064418B2 - Power steering device for vehicles used in low temperature environment - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power steering device that uses a DC motor equipped with a permanent magnet as a drive source, and more particularly to protection of the permanent magnet in a low temperature environment. .

2. Description of the Related Art Some vehicle power steering devices use a DC motor (hereinafter, simply referred to as an electric motor) having a permanent magnet as a drive source. This power steering device is configured to detect a steering torque applied to a steering wheel by a steering torque detecting means and supply a current continuously increasing with an increase in the steering torque to an electric motor by an electric motor drive circuit. There are many.

When a vehicle equipped with this type of power steering device is used in a low temperature environment, the permanent magnet may be demagnetized and the electric motor may be damaged. If a current of a certain value or more is supplied to the motor while the temperature of the permanent magnet is below a certain value, the permanent magnet will be demagnetized.As a result, the torque constant will decrease and a large current will flow to the motor. Is supplied to the coil, which may result in burnout of the coil. The magnitude of the current that can be supplied to the electric motor while avoiding the demagnetization of the permanent magnet is suppressed as the temperature of the permanent magnet is lower and the size of the electric motor is smaller.

Therefore, conventionally, for forklifts, automated guided vehicles, and automobiles for extremely cold regions that may be used in refrigerators, use an electric motor of a size that does not cause demagnetization of the permanent magnet even in a low temperature environment. Alternatively, the set value of the excessive current limiting means is lowered to prevent the motor from being damaged in a low temperature environment.

Problems to be Solved by the Invention However, it is wasteful to increase the electric motors of all vehicles, or at least the installation space thereof, in accordance with the vehicles for low-temperature environment, which occupy a relatively small proportion of the total number of vehicles produced. Further, if the set value of the excessive current limiting means is lowered instead of increasing the electric motor, another problem arises in that the maximum follow-up rotation speed of the electric motor decreases and the steering performance of the vehicle deteriorates.

In view of such circumstances, the present invention aims at avoiding demagnetization of a permanent magnet in a low temperature environment without uselessly using a large electric motor and without causing performance deterioration in a normal environment. It was made as.

Means for Solving the Problems In order to solve this problem, the present invention provides a temperature detecting means for detecting temperature in an electric motor in a power steering device including the electric motor, steering torque detecting means and electric motor drive circuit. , The ratio between the temperature detection means and the motor drive circuit when the current supplied from the motor drive circuit to the DC motor at a low temperature equal to or lower than the set temperature is divided by the steering torque detected by the steering torque detection means. The current reducing means is provided so as to make the value smaller when it is lower than that when it is high.

The current reducing means is, for example, in the electric motor drive circuit, proportional to the steering torque detected by the steering torque detecting means,
A current having a magnitude inversely proportional to the difference between the temperature of the electric motor detected by the temperature detecting means and the set temperature may be supplied to the electric motor, and the temperature detected by the temperature detecting means may be the set value. When the temperature is lower than the temperature, the current supplied from the motor drive circuit to the motor is controlled to a value obtained by multiplying the current supplied when the temperature is higher than the set temperature by a predetermined coefficient within a range smaller than 1. be able to.

Actions and effects As described above, when the temperature of the electric motor becomes low, if the current supplied to the electric motor is automatically reduced to a level at which there is no risk of demagnetization of the permanent magnet, Even when used in an environment, there is no risk of damage to the electric motor. Therefore, it is not necessary to install a large-sized electric motor unnecessarily in case of emergency, and the effect of reducing the installation space and cost can be obtained. Also,
It is not necessary to set the set value of the excessive current limiting means to be particularly low, and the performance does not deteriorate under normal environment.

Moreover, the current supplied to the electric motor at a temperature lower than the set temperature is controlled to be smaller when the temperature is low than when the temperature is high, but the current is continuously increased as the steering torque increases. Therefore, the steering wheel does not suddenly become heavy during steering.

For the sole purpose of preventing demagnetization of permanent magnets in a low temperature environment, even when the temperature of the motor is lower than the set temperature, the same value as when the current supplied to the motor is relatively low is the same as when it is higher than the set temperature. When the current reaches a certain value, it may be restricted so that it does not increase any more. However, if this is done, the steering torque increases with the steering. In the process, the assisting torque of the electric motor suddenly changes, and the steering feeling deteriorates. On the other hand, according to the present invention, the permanent magnet can be protected while avoiding the deterioration of feeling.

Embodiment Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment in which the present invention is applied to a power steering device in a reach type forklift, and 10 in the drawing is a steering wheel.
A torque detector 16 is provided between the first shaft 12 and the second shaft 14 fixed to the steering wheel 10. The torque detector 16 includes a first shaft 12 and a second shaft 1.
4, an elastic member capable of being twisted and deformed is arranged, and the relative rotation angle between the first shaft 12 and the second shaft 14 due to the torsion of the elastic member is detected, or the strain gauge is attached to the torsion shaft. It is possible to use a known torque detector, such as one in which the strain of the torsion shaft is detected by sticking with. The second shaft 14 is a gear 1
It is connected to the drive unit casing 22 via a rotation transmission mechanism composed of 8, 20, and the like. The drive unit casing 22 is rotatably supported by a suspension device (not shown) around a vertical axis, and holds the drive / steer wheels 24 rotatably around a horizontal axis at the lower end. The drive and steered wheels 24 are driven by a traveling electric motor 26 via a gear train arranged in the drive unit casing 22 to drive a forklift, and
The direction of the drive unit casing 22 is changed with the rotation of the drive unit casing 22 to perform a steering function.

Another gear 28 is attached to the second shaft 14, and this gear 28 is meshed with a gear 32 fixed to the output shaft of the assisting electric motor 30. A torque calculation circuit 34 is connected to the torque detector 16, and a voltage proportional to the steering torque applied to the steering wheel 10 is supplied to the electric motor drive circuit 36. The electric motor drive circuit 36 supplies a current proportional to the output voltage of the torque calculation circuit 34 to the assisting electric motor 30, and eventually the assisting electric motor 3
0 generates an assisting torque proportional to the steering torque applied to the steering wheel 10, and the gears 32 and 28
It will be added to the second shaft 14 via. The torque detector 16, the torque calculation circuit 34, the electric motor drive circuit 36, etc. constitute the electric motor control device.

The assisting electric motor 30 is a DC electric motor in which the rotor rotates in a stator having a permanent magnet, and a temperature sensor 38 is attached to the stator. It is desirable that the temperature sensor 36 be provided at a position where the temperature of the permanent magnet itself can be detected. However, if the stator housing is made of metal, a large temperature difference does not occur between the stator housing and the permanent magnet, and therefore the stator is not provided. It may be provided in the housing. A temperature calculation circuit 40 is connected to the temperature sensor 38 to detect a detection voltage that changes in proportion to the temperature of the stator.
It is designed to supply two. A relatively low temperature such as 0 ° C. is preset in the current reduction circuit 42, and the current reduction circuit 42 compares the set voltage corresponding to this temperature with the detection voltage from the temperature calculation circuit 40 to detect the temperature. If the voltage is higher, that is, if the temperature of the stator is higher than the set temperature, it will not operate, but if it becomes low, operation will start. That, V = Vs {1-k / (Vt o -Vt)} ··· (1) However, Vs: output voltage Vt _o of torque calculating circuit 34: voltage Vt corresponding to the set temperature: the temperature calculation circuit 40 Detection voltage K: constant is calculated, and the voltage V of the calculation result is output. This voltage V is subtracted from the output voltage Vs of the torque calculating circuit 34, Arawasaru voltage Vu is supplied by: Vu = K · Vs / (Vt o -Vt) ··· (2) The motor drive circuit 36 The Rukoto. That is, the output voltage Vs of the torque calculation circuit 34 has a coefficient K / that decreases as the difference between the set temperature and the stator temperature increases.
(Vt _o -Vt) and than is supplied a voltage of a magnitude multiplied, motor drive circuit 36 which supplies a current proportional to the voltage boosting electric motor 30. In the present embodiment, the temperature sensor 38 and the temperature calculation circuit 40 constitute temperature detecting means, and the current reducing circuit 42 constitutes current reducing means.

When a forklift including the power steering device configured as described above is used in a refrigerator, the ambient temperature is about -20 ° C to -40 ° C. Therefore, if the forklift is left in the refrigerator for a certain period of time, the temperature of the permanent magnet of the assisting motor 30 also becomes -20 ° C to -40 ° C, and when a large current is supplied to the assisting motor 30 in this state, the permanent magnet 30 May cause demagnetization or demagnetization. Demagnetization occurs even when a large current flows for a very short time of about several milliseconds, and when demagnetization occurs, the torque constant decreases and the current increases rapidly, eventually causing the rotor coil to burn out.

However, in the power steering apparatus according to the present embodiment, the current reduction circuit 42 starts to operate when the temperature of the stator falls below the set temperature of 0 ° C., and the electric current is supplied from the electric motor drive circuit 36 to the assisting electric motor 30. The current is kept smaller than before. The current supplied to the assisting electric motor 30 with respect to the steering force applied to the steering wheel 10 is reduced, and the rate of decrease is small when the difference between the stator temperature and the set temperature is small, and is large when the difference is large. Become. As described above, the lower the temperature of the permanent magnet, the smaller the current that causes demagnetization. However, in the present embodiment, the lower the temperature of the permanent magnet corresponds to the constant steering force, and the assisting motor 30 is handled accordingly. Since the supplied current is small, the maximum current that may be supplied to the assisting motor 30 in accordance with the maximum steering torque that is expected to be applied to the steering wheel 10 is not likely to be demagnetized. It can be suppressed to the value. Therefore, it is not necessary to use a large-sized assisting motor 30 unnecessarily, and the motor drive circuit 36
It is not necessary to set the set value of the excessive current limiter in the inside to a particularly small value.

FIG. 2 shows another embodiment of the present invention. In this embodiment, a judgment circuit 44 is connected to the temperature calculation circuit 40, and the judgment circuit 44 compares the detected voltage from the temperature calculation circuit 40 with a preset voltage and detects the detected voltage. A high level signal is supplied to the multiplier 46 while the voltage is higher than the set voltage, and a low level signal is supplied when the voltage is lower than the set voltage. The multiplier 46 supplies a voltage obtained by multiplying the output voltage of the torque calculation circuit 34 by a coefficient 1 to the electric motor drive circuit 36 while the high level signal is supplied from the determination circuit 44, and while the low level signal is supplied. Supplies the voltage obtained by multiplying the output voltage of the torque calculation circuit 34 by a coefficient α smaller than 1 to the electric motor drive circuit 36. The coefficient α depends on the assisting motor 30 even when the predicted maximum steering torque is applied to the steering wheel 10 at the lowest temperature at which the forklift truck may be used.
In order to prevent the demagnetization of the permanent magnet from occurring, the value is set to a value that reduces the voltage supplied to the motor drive circuit 36. That is, in the present embodiment, the determination circuit 44 and the multiplier 46 constitute the current reduction means. Since the parts other than the decision circuit 44 and the multiplier 46 are the same as those in the above-mentioned embodiment, detailed description will be omitted.

In addition, the temperature detection means and the low-temperature current reduction means can be installed in all vehicles of the model that may be used in the refrigerator, but are planned to be used in the refrigerator. It is also possible to provide a special specification only for existing vehicles. In this case as well, the assisting motor 30 itself can be of the same size as the power steering device of a forklift used in a normal environment, so special modifications to the vehicle body, the motor mounting bracket, etc. are required. No need to add, which is convenient.

Further, the present invention can be applied not only to industrial vehicles such as forklifts, but also to electric motors for assisting electric power steering devices for passenger cars and freight vehicles that are used especially in cold regions.

In addition, some electronic components used for temperature detection means and current reduction means do not operate normally at extremely low temperatures. It is also possible to cut off the current supply to the assisting electric motor regardless of the temperature of the assisting electric motor when is below the set value. Further, a temperature sensor and a heating element are provided in these installation spaces, and when the temperature of the installation space falls below a set value, current is automatically supplied to the heating elements and the temperature of the installation space is reduced. It is also possible to prevent the temperature from becoming extremely low.

Further, in the above-described embodiment, the torque calculation circuit 34, the temperature calculation circuit 40, the current reduction circuit 42, the determination circuit 44, the multiplier 46, the gate circuit 48, etc. are constituted by separate electronic circuits. It is also possible to configure all or part of the computer.

Other examples will not be given, but it goes without saying that the present invention can be implemented in various modified and improved modes based on the knowledge of those skilled in the art.

[Brief description of drawings]

FIG. 1 is a system diagram showing a power steering device for a reach type forklift equipped with an electric motor protection device according to an embodiment of the present invention. FIG. 2 is a system diagram showing a part of another embodiment of the present invention. 10: Steering wheel 16: Torque detector 24: Driving and steering wheel 30: Electric motor for assisting

Claims (3)

[Claims] 1. A DC motor having a permanent magnet is used as a drive source, a steering torque applied to a steering wheel is detected by a steering torque detecting means, and a current continuously increasing as the steering torque is increased. In the power steering device for supplying to the DC motor according to the above, the DC motor is provided with temperature detecting means for detecting a temperature,
Between the temperature detection means and the electric motor drive circuit, the ratio when the current supplied from the electric motor drive circuit to the DC motor at a low temperature equal to or lower than a set temperature is divided by the steering torque detected by the steering torque detection means is A power steering device for a vehicle used in a low temperature environment, characterized in that current reducing means is provided to control the temperature to be smaller when the temperature is lower than when the temperature is high. 2. The difference between the temperature of the DC motor detected by the temperature detecting means and the set temperature, which is proportional to the steering torque detected by the steering torque detecting means, in the electric motor drive circuit. The power steering apparatus according to claim 1, wherein a current having a magnitude inversely proportional to is supplied to the DC motor. 3. The current reducing means, when the temperature detected by the temperature detecting means is lower than the set temperature, when the current supplied from the motor drive circuit to the DC motor is higher than the set temperature. The power steering apparatus according to claim 1, wherein the supplied electric current is controlled to a magnitude obtained by multiplying the supplied electric current by a predetermined coefficient in a range smaller than 1.