Steering system

Patent metadata

Field	Value
Publication number	US-11396325-B2
Application number	US-202016821185-A
Country	US
Kind code	B2
Filing date	Mar 17, 2020
Priority date	Mar 25, 2019
Publication date	Jul 26, 2022
Grant date	Jul 26, 2022

Abstract

Provided is a steering system including a controller that controls an electric motor. The controller has a combined friction torque estimation unit that estimates a combined friction torque combining friction torques occurring in respective transmission devices including a first transmission device. The combined friction torque estimation unit has a slipping speed calculation part that calculates a slipping speed of the first transmission device based on an angular speed of the electric motor, a friction coefficient calculation part that calculates a friction coefficient of the first transmission device based on the slipping speed, a tooth flank normal force calculation part that calculates a normal force acting on a tooth flank of the first transmission device, and a friction torque calculation part that calculates the combined friction torque using the friction coefficient, the tooth flank normal force, and one or more preset correction factors.

First claim

What is claimed is:

1. A steering system comprising:
an electric motor;
a wheel turning shaft that is moved in an axial direction by a torque of the electric motor so as to turn a wheel-to-be-turned;
a plurality of transmission devices;
an angular speed detection unit that detects or estimates an angular speed of the electric motor; and
a controller that controls the electric motor, wherein:
one of the transmission devices is a first transmission device that outputs rotation of the electric motor at a reduced speed;
the controller has a combined friction torque estimation unit that estimates a combined friction torque combining friction torques occurring in the respective transmission devices; and
the combined friction torque estimation unit has a slipping speed calculation part that calculates a slipping speed of the first transmission device based on the angular speed, a friction coefficient calculation part that calculates a friction coefficient of the first transmission device based on the slipping speed, a tooth flank normal force calculation part that calculates a normal force acting on a tooth flank of the first transmission device, and a friction torque calculation part that calculates the combined friction torque using the friction coefficient of the first transmission device, the tooth flank normal force of the first transmission device, and one or more preset correction factors.

2. The steering system according to claim 1 , wherein the friction torque calculation part is configured to calculate the combined friction torque based on a combined friction coefficient and a combined tooth flank normal force, the combined friction coefficient being a value obtained by multiplying the friction coefficient by a predetermined first correction factor of the one or more preset correction factors, the combined tooth flank normal force being a value obtained by multiplying the tooth flank normal force by a predetermined second correction factor of the one or more preset correction factors.

3. The steering system according to claim 1 , wherein the friction torque calculation part is configured to calculate the combined friction torque by calculating a first friction torque occurring in the first transmission device based on the friction coefficient and the tooth flank normal force and then multiplying the obtained first friction torque by a predetermined third correction factor of the one or more preset correction factors.

4. The steering system according to claim 1 , further comprising:
a steering member; and
a steering shaft that rotates integrally with the steering member, wherein:
the first transmission device is a transmission device that outputs the torque of the electric motor to the steering shaft or the wheel turning shaft; and
another of the transmission devices is a second transmission device that converts rotation of the steering shaft into axial motion of the wheel turning shaft.

5. The steering system according to claim 4 , further comprising a torque detection unit that detects a steering torque input from the steering member, wherein the controller has an axial force estimation unit that estimates an axial force acting on the wheel turning shaft based on the steering torque, the torque of the electric motor, the combined friction torque, and an angle of the electric motor.

6. The steering system according to claim 4 , further comprising:
a torque detection unit that detects a steering torque input from the steering member; and
an axial force estimation unit that detects or estimates an axial force acting on the wheel turning shaft, wherein
the tooth flank normal force calculation part sets a first contact force, calculated based on the torque of the electric motor, the steering torque, and the axial force, as the tooth flank normal force when the first contact force is larger than a predetermined value, and sets the predetermined value as the tooth flank normal force when the first contact force is equal to or smaller than the predetermined value.

7. The steering system according to claim 1 , further comprising:
a steering member;
a steering shaft that rotates integrally with the steering member;
a torque detection unit that detects a steering torque input from the steering member; and
an axial force estimation unit that detects or estimates an axial force acting on the wheel turning shaft, wherein:
the first transmission device is a transmission device that outputs a torque of the electric motor to the steering shaft or the wheel turning shaft;
another of the transmission devices is a second transmission device that converts rotation of the steering shaft into axial motion of the wheel turning shaft;
the tooth flank normal force calculation part is configured to calculate a first tooth flank normal force that is the normal force acting on the tooth flank of the first transmission device in a first contact state, based on the torque of the electric motor, the steering torque, and the axial force, and set a second tooth flank normal force that is the normal force acting on the tooth flank of the first transmission device in a second contact state; and
the friction torque calculation part is configured to calculate a combined first tooth flank normal force by multiplying the first tooth flank normal force by a predetermined fourth correction factor of the one or more preset correction factors, calculate a combined second tooth flank normal force by multiplying the second tooth flank normal force by a predetermined fifth correction factor of the one or more preset correction factors, calculate a combined friction coefficient by multiplying the friction coefficient by a predetermined sixth correction factor of the one or more preset correction factors, and calculate the combined friction torque based on one of the combined first tooth flank normal force and the combined second tooth flank normal force, whichever has a larger absolute value, and on the combined friction coefficient.

8. The steering system according to claim 7 , wherein:
the tooth flank normal force calculation part has a first tooth flank normal force correction part that corrects the first tooth flank normal force based on a combined friction torque calculated last time by the friction torque calculation part; and
the friction torque calculation part is configured to calculate the combined first tooth flank normal force by multiplying the corrected first tooth flank normal force by the fourth correction factor, calculate the combined second tooth flank normal force by multiplying the second tooth flank normal force by the fifth correction factor, calculate the combined friction coefficient by multiplying the friction coefficient by the sixth correction factor, and calculate the combined friction torque based on one of the combined first tooth flank normal force and the combined second tooth flank normal force, whichever has a larger absolute value, and on the combined friction coefficient.

Assignees

• Jtekt Corp

Inventors

• Higashi Masayasu
• Miki Daisuke
• Fuchs Robert

Classifications

• B62D5/0409

  Electric motor acting on the steering column · CPC title

• B62D6/006

  using a measured or estimated road friction coefficient · CPC title

• B62D6/008

  Control of feed-back to the steering input member, e.g. simulating road feel in steer-by-wire applications · CPC title

• B62D6/10 Primary

  characterised by means for sensing {or determining} torque · CPC title

• B62D5/046 Primary

  Controlling the motor · CPC title