In recent years the automobile has been sophisticated, which entails incremental use of a variety of rotary torque sensors or rotary angle sensors for sensing rotary torque or a rotary angle of a steering shaft in order to control a power steering device or a braking device.
One of the foregoing conventional rotary angle and rotary torque sensing devices is described hereinafter with reference to FIG. 5 which is a sectional view of this conventional device.
In FIG. 5, conventional device 20 is formed of the following structural elements: first rotator 1, holder 2, magnet 3, second rotator 4, first ferromagnetic body 5, second ferromagnetic body 6, spacer 7, printed circuit board 8, magnetic sensing element 9, controller 11, coupler 12, third rotator 13, first sensor 14, second sensor 15, magnets 16A, 17A, and magnetic sensing elements 16B, 17B.
First rotator 1 is shaped like a cylinder and rotates together with the steering shaft. Holder 2 is shaped like a cylinder. Magnet 3 is shaped like a cylinder where multiple N-poles and S-poles are alternately and adjoiningly arrayed. Magnet 3 adheres to a lower section of an outer wall of holder 2, which adheres to an upper section of an inner wall of first rotator 1.
Second rotator 4 shapes like a cylinder. First and second ferromagnetic bodies 5 and 6 are shaped like a ring respectively, and spacer 7 is also shaped like a ring. Second rotator 4 is placed below first rotator 1. First ferromagnetic body 5 is placed above second ferromagnetic body 6, and these two ferromagnetic bodies adhere to an upper section of second rotator 4 such that they confront an outer wall of magnet 3 with a given space therebetween via spacer 7.
Printed circuit board 8 has multiple wiring patterns (not shown) on both the faces, and placed beside, substantially in parallel with, first rotator 1 and second rotator 4. Magnetic sensing element 9 includes a Hall element and is disposed between first ferromagnetic body 5 and second ferromagnetic body 6 on a face confronting magnet 3.
Rotary torque sensing section 10 is formed of first and second ferromagnetic bodies 5 and 6, magnet 3 confronting ferromagnetic bodies 5 and 6, and magnetic sensing element 9. Controller 11, which includes electronic components such as a microprocessor, is formed on printed circuit board 8. Controller 11 is coupled to magnetic sensing element 9.
Between first rotator 1 and second rotator 4, coupler 12 is provided such that an upper section of coupler 12 adheres to rotator 1 and a lower section thereof adheres to rotator 4. Coupler 12, e.g. torsion bar, is made of steel and shaped like a pole.
Third rotator 13 includes a spur gear at its underside. First and second sensors 14, 15 include spur gears on their outer walls. Third rotator 13 is rigidly mounted to a lower end of second rotator 4, and first sensor 14 mates with spur gear of third rotator 13 and second sensor 15 mates with spur gear of first sensor 14.
Magnets 16A and 17A are mounted at the center of first sensor 14 and at the center of second sensor 15 respectively by insert-molding. Printed circuit board 8 is placed beside and generally in parallel with those magnets 16A and 17A. Printed circuit board 8 includes magnetic sensing elements 16B and 17B such as AMR (anisotropic magnetic resistance) at places confronting magnets 16A and 17A respectively.
Magnet 16A and magnetic sensing element 16B form rotary angle sensor 16, and magnet 17A and magnetic sensing element 17B form rotary angle sensor 17. Magnetic sensing elements 16B and 17B are connected to controller 11. Rotary angle and rotary torque sensing device 20 is thus formed.
Sensing device 20 discussed above has first rotator 1 coupled to the steering shaft and is mounted below the steering wheel of the automobile. Controller 11 is coupled to an electronic circuit of the automobile via connectors and lead-wires (not shown).
With the foregoing structure, turning of the steering wheel entails rotation of first rotator 1, and also entails rotation of second rotator 4 which is connected to first rotator via coupler 12. Therefore, third rotator 13 adhering to the lower end of second rotator 4 rotates. This mechanism allows first sensor 14 mated with third rotator 13 and second sensor 15 mated with first sensor 14 to rotate together with third rotator 13.
The rotation of first and second sensors 14 and 15 entails the rotation of magnets 16A and 17A, which are mounted at the centers of sensors 14 and 15 respectively. Since magnetisms emitted from magnets 16A and 17A vary due to the rotation, magnetic sensing elements 16B and 17B sense the varying magnetisms, and then a rotary angle sensing signal is supplied to controller 11, where the rotary angle sensing signal repeats fluctuations and draws like a sine-wave, cosine-wave or saw-tooth wave.
Controller 11 carries out a given calculation based on the rotary angle sensing signal, supplied from rotary angle sensors 16 and 17, as well as the number of teeth of respective gears. Controller 11 thus senses the rotary angle of third rotator 13, i.e. the rotary angle of the steering shaft, and the result is supplied to the electronic circuit of the automobile.
The rotations of the steering shaft and first rotator 1 entail coupler 12 to twist, and then second rotator 4 starts rotating slightly behind first rotator 1. For instance, smaller rotary torque is required for turning the steering wheel when the automobile is driven, so that the delay of second rotator 4 relative to first rotator 1 is small. To the contrary, greater rotary torque is needed when the automobile is halted, so that second rotator 4 starts rotating with a greater delay relative to first rotator 1.
The rotations of first and second rotators 1 and 4 entail magnet 3 adhering to those rotators to rotate, and also prompt first and second ferromagnetic bodies 5 and 6 to start rotating after slight delays from magnet 3. Magnetic sensing element 9 senses variation in the magnetism of magnet 3, formed of multiple N-poles and S-poles placed alternately and adjoiningly to each other, via first and second ferromagnetic bodies 5 and 6, and supplies the sensed variation in the magnetism to controller 11.
At this time, magnetic sensing element 9 senses weak magnetism when second rotator 4, to which first and second ferromagnetic bodies 5 and 6 adhere, starts rotating after a small delay from first rotator 1, whereas sensing element 9 senses strong magnetism when second rotator 4 starts rotating after a great delay from first rotator 1.
Based on magnitude of the magnetism sensed via ferromagnetic bodies 5 and 6 by sensing element 9, controller 11 calculates the rotary torque of first rotator 1, i.e. the rotary torque of the steering shaft. The calculated rotary torque is supplied to the electronic circuit of the automobile. Using this calculated rotary torque and other data, the electronic circuit controls the power steering device, the braking device, and other devices of the automobile, where the other data includes the rotary angle of the rotary shaft discussed previously and supplied from controller 11, and various other data supplied from other sensors including a velocity sensor mounted somewhere in the automobile.
As discussed above, in response to the rotary angle or the rotary torque supplied from controller 11, conventional rotary angle and rotary torque sensing device 20 controls not only the effectiveness of the braking device in accordance with an angle of the steering wheel turned by a driver but also the operating force for turning the steering wheel.
Patent Literature of Unexamined Japanese Patent Application Publication No. 2008-82826 is known to the public as one of related art to the present invention.
Conventional sensing device 20 discussed previously includes magnet 3, first and second ferromagnetic bodies 5 and 6, which work for sensing the rotary torque, and those elements are covered with first rotator 1 and second rotator 2. However, when foreign matters such as iron powders attach to those structural elements 3, 5, or 6, magnetic sensing element 9 senses an error in the magnetism emitted from magnet 3 via first and second ferromagnetic bodies 5 and 6. As a result, sensing device 20 fails to sense accurate rotary torque.