CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2019-062604 filed on Mar. 28, 2019, incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The disclosure relates to a steering apparatus.

2. Description of Related Art

There is a so-called steer-by-wire type steering apparatus in which dynamic power transmission between a steering wheel and turning wheels is separated. The steering apparatus includes a reaction motor as a generation source of a steering reaction force that is given to a steering shaft, and a turning motor as a generation source of a turning force by which the turning wheels are turned. At the time of traveling of a vehicle, a control device of the steering apparatus generates the steering reaction force through an electricity supply control of the reaction motor, and turns the turning wheels through an electricity supply control of the turning motor.

The steering apparatus can get, for example, into a situation where it is difficult to turn the turning wheels to a steering increase side, as exemplary by a situation where a turning wheel abuts on a curbstone at the time of stationary steering. At this time, the control device of the steering apparatus attempts to cause the turning angle of the turning wheel to follow up the steering angle of the steering wheel. Therefore, an excessive electric current is supplied to the turning motor, and thereby, the turning motor or a drive circuit for the turning motor may overheats.

Hence, for example, a control device in Japanese Patent Application Publication No. 2006-111099 determines that the turning wheel is in contact with an obstacle, when a prescribed determination condition is satisfied. For example, the determination condition includes a condition that the actual current value supplied to the turning motor is equal to or larger than a current threshold continuously for a predetermined time. When it is determined that the turning wheel is in contact with the obstacle, the control device executes a control prescribed for restraining the overheating of the turning motor.

SUMMARY

Some control devices have not only the function to restrain the overheating of the turning motor due to the contact of the turning wheel with the obstacle, but also, for example, a function to restrain the overheating of the turning motor caused by the temperature of the turning motor. The control device monitors the temperature of the turning motor, and when the temperature is close to a temperature in the overheating state, the control device limits the current amount to be supplied to the turning motor. The situation where the control device limits the current amount to be supplied to the turning motor in this way can be a situation where a power-supply voltage has decreased, or a situation where a pull-in current has increased.

Therefore, for example, when the turning wheel is in contact with the obstacle at the time of the stationary steering for the start of the vehicle, the current amount to be supplied to the turning motor may be limited before the current value of the turning motor reaches the current threshold. In this case, since the current value of the turning motor does not reach the current threshold, there is a concern that the contact of the turning wheel with the obstacle is not properly detected.

The disclosure provides a steering apparatus that can properly detect the contact of the turning wheel with the obstacle.

An aspect of the disclosure is a steering apparatus. The steering apparatus includes a mechanism, a first motor, and a control device. The mechanism is configured to turn a turning wheel of a vehicle. The first motor is configured to generate a driving force that is given to the mechanism. The control device is configured to control the first motor in accordance with a steering state. The control device includes a first computation circuit, a determination circuit, a second computation circuit, a third computation circuit. The first computation circuit is configured to compute a first limiting value to which an electric current to be supplied to the first motor is limited in a particular situation. The determination circuit is configured to determine whether the turning wheel is in touch with an obstacle, based on comparison between the value of the electric current to be supplied to the first motor and a threshold. The second computation circuit is configured to compute a second limiting value to which the electric current to be supplied to the first motor is limited when the determination circuit determines that the turning wheel is in touch with the obstacle. The third computation circuit is configured to compute the threshold to be used by the determination circuit, based on a smaller limiting value of the first limiting value and the second limiting value.

With this configuration, in the case where the turning wheel is in touch with the obstacle, the current amount to be supplied to the motor is limited to the limiting value that is one of the first limiting value and the second limiting value and that has the smaller absolute value. Thereby, the rise in the temperature of the motor is restrained. Further, in the case where the turning wheel is in touch with the obstacle, the threshold to be used by the determination circuit is computed based on the limiting value that is one of the first limiting value and the second limiting value and that has the smaller absolute value. Therefore, even when the current value of the motor is limited, the threshold is restrained from being set to a value larger than the current value of the motor. Accordingly, it is possible to properly determine that the turning wheel is in touch with the obstacle, from the comparison between the current value of the motor and the threshold.

In the above steering apparatus, the third computation circuit may be configured to compute the threshold having a value equal to the smaller limiting value of the first limiting value and the second limiting value.

With this configuration, even when the current value of the motor is limited, the threshold is restrained from being set to a value larger than the current value of the motor. In the above steering apparatus, the second computation circuit may be configured to decrease the second limiting value from a maximal limiting value to a minimal limiting value, when the determination circuit determines that the turning wheel is in touch with the obstacle, the maximal limiting value being set based on a maximal current value that the first motor is able to apply without overheating, the minimal limiting value being set based on a minimal current value that the first motor is able to apply without overheating.

With this configuration, in the case where the turning wheel is in touch with the obstacle, the second limiting value decreases from the maximal limiting value to the minimal limiting value. Therefore, it is possible to limit the electric current of the motor, at least to the minimal limiting value as the second limiting value.

In the above steering apparatus, the second computation circuit may be configured to immediately restore the second limiting value from the minimal limiting value to the maximal limiting value, when the determination circuit cancels the determination that the turning wheel is in touch with the obstacle.

With this configuration, it is possible to reduce a period during which turning performance decreases due to the limitation of the electric current of the motor for protection of the motor from overheating, to a minimal period. The steering apparatus may further includes a second motor. The mechanism may include a steering shaft configured to rotate in conjunction with an operation of a steering wheel and a turning shaft provided such that dynamic power transmission between the steering wheel and the turning shaft is separated. The second motor may be a reaction motor configured to generate a steering reaction force based on a first command value that is computed based on the steering state. The steering reaction force may be a torque that is given to the steering shaft and that is an opposite direction of a steering direction. The first motor may be a turning motor configured to generate a turning force based on a second command value that is computed based on the steering state. The turning force may be a torque that is given to the turning shaft and by which the turning wheel is turned.

In this case, the control device may include a limiting shaft force computation circuit configured to compute a limiting shaft force as a shaft force of the turning shaft, as a control for informing a driver that the turning wheel is in touch with the obstacle, when the determination circuit determines that the turning wheel is in touch with the obstacle, the shaft force of the turning shaft being reflected in the first command value for the reaction motor for virtually limiting the operation of the steering wheel.

With this configuration, in the case where the turning wheel is in touch with the obstacle, the limiting shaft force for virtually limiting the operation of the steering wheel is reflected in the first command value for the reaction motor. Thereby, the driver has a feeling of contact as the steering reaction force. From a sensation in driver's hands through the steering wheel, the driver can recognize the situation where the turning wheel is in touch with the obstacle. In addition, it is possible to virtually limit the operation of the steering wheel by the driver.

In the above steering apparatus, the control device may include: an ideal shaft force computation circuit configured to compute an ideal shaft force, the ideal shaft force being an idealized shaft force of the turning shaft based on a target rotation angle of a rotating body that rotates in conjunction with a turning action of the turning wheel; an estimated shaft force computation circuit configured to compute a shaft force of the turning shaft as an estimated shaft force, based on a current value of the turning motor that reflects a vehicle behavior, a road surface state or the steering state; and a distribution computation circuit configured to compute a mixed shaft force as the shaft force of the turning shaft, by mixing the estimated shaft force and the ideal shaft force based on the vehicle behavior, the road surface state or the steering state, the shaft force of the turning shaft being reflected in the first command value for the reaction motor.

In this case, the distribution computation circuit may be configured to switch the shaft force of the turning shaft from the mixed shaft force to the estimated shaft force, as a control for informing a driver that the turning wheel is in touch with the obstacle, when the determination circuit determines that the turning wheel is in touch with the obstacle, the shaft force of the turning shaft being reflected in the first command value for the reaction motor.

With this configuration, in the case where the turning wheel is not in touch with the obstacle, the mixed shaft force obtained by mixing the ideal shaft force based on the target rotation angle of the rotating body and the estimated shaft force based on the current value of the turning motor depending on the vehicle behavior or the like is reflected in the first command value for the reaction motor. Therefore, the reaction motor generates the driving force corresponding to the mixed shaft force. On the other hand, in the case where the turning wheel is in touch with the obstacle, only the estimated shaft force is reflected in the first command value for the reaction motor. The estimated shaft force reflects the vehicle behavior, the road surface state or the steering state, and therefore the motor generates the driving force corresponding to the shaft force that acts on the turning shaft due to the touch of the turning wheel with the obstacle. Accordingly, the driver has a feeling of contact as the steering reaction force through the steering wheel, and thereby can recognize the situation where the turning wheel is in touch with the obstacle.

With the steering apparatus in the disclosure, it is possible to properly detect the contact of the turning wheel with the obstacle.

