Motor vehicles – Steering gear – With fluid power assist
Reexamination Certificate
1998-11-24
2001-01-09
Hurley, Kevin (Department: 3611)
Motor vehicles
Steering gear
With fluid power assist
Reexamination Certificate
active
06170599
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. HEI 9-323040 filed on Nov. 25, 1997 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power steering apparatus and, more particularly, relates to a power steering apparatus suited to generate a steering assisting force in a vehicle.
2. Description of Related Art
An apparatus generating a steering assisting force in a vehicle is disclosed, for instance, in Japanese Patent Application Laid-Open No. HEI 2-34473 (which is based on U.S. Pat. No. 4,819,545). This apparatus includes a valve shaft and a valve body. The valve shaft is concentric with the valve body and the former can rotate relative to the latter. The valve shaft and the valve body form a relative rotational angle, which will hereinafter be referred to as an operational angle.
A steering wheel is coupled to the valve shaft, while wheels to be steered are connected with the valve body via a pinion gear. The valve body and the valve shaft are coupled to each other via a torsion bar and a mechanical type reaction force mechanism. The mechanical type reaction force mechanism is composed of {circle around (1)} a first V-groove ring that has a first V-shaped groove and is attached to the valve shaft, {circle around (2)} a second V-groove ring that has a second V-shaped groove and is attached to the valve body, {circle around (3)} a steel ball sandwiched between the V-shaped groove in the first V-groove ring and the V-shaped groove in the second V-groove ring and {circle around (4)} a spring member urging the first V-groove ring toward the second V-groove ring.
The mechanical type reaction force mechanism thus constructed prevents the valve shaft and the valve body from forming an operational angle unless a torque effective therebetween exceeds a predetermined value. If an operational angle is formed between the valve shaft and the valve body, the torsion bar generates an angle of torsion equal to the operational angle.
If the torsion bar generates an angle of torsion, a steering reaction force corresponding to the angle of torsion is transmitted to the steering wheel. The aforementioned apparatus based on the related art is constructed such that a steering assisting force corresponding to an operational angle formed between the valve shaft and the valve body is transmitted to the valve body. Thus, the aforementioned conventional apparatus can {circle around (1)} prevent generation of a steering assisting force unless the steering torque inputted to the steering wheel exceeds a predetermined value and {circle around (2)} generate a steering assisting force corresponding to the steering torque if the steering torque exceeds the predetermined value.
Since no steering assisting force is generated until the steering torque exceeds a predetermined value, the conventional apparatus achieves a high rigidity feel in the neutral position of the steering wheel as well as enhanced steering stability. In addition, since a steering assisting force corresponding to the steering torque is generated when the steering torque exceeds the predetermined value, nimbleness during the steering operation can be achieved. Thus, the aforementioned apparatus based on the related art can provide stability and nimbleness during the steering operation.
In the aforementioned apparatus, the steel ball of the mechanical type reaction force mechanism is inhibited from being displaced solely by the first V-shaped groove in the first V-groove ring and the second V-shaped groove in the second V-groove ring. In other words, the apparatus is not equipped with any member for restricting displacement of the steel ball except for the first V-groove ring and the second V-groove ring. Thus, the apparatus may allow the steel ball to pass across the V-shaped groove in the first V-groove ring or the V-shaped groove in the second V-groove ring and slip out of its predetermined location. In this respect, the mechanical type reaction force mechanism does not provide the apparatus with the optimal structure for ensuring improved durability as well as high reliability.
SUMMARY OF THE INVENTION
The present invention is directed towards solving the aforementioned inconvenience. It is an object of the present invention to provide a power steering apparatus capable of achieving rigidity in a neutral position of a steering wheel and ensuring enhanced durability as well as high reliability without adversely affecting stability or nimbleness during the steering operation.
With a view to achieving the aforementioned object, a first aspect of the present invention provides a power steering apparatus including an input shaft, an output shaft, a groove member, a reaction force member, an elastic member and means for generating a steering assisting force corresponding to an operational angle formed between the input shaft and the output shaft. The input shaft is adapted to be coupled to a steering wheel, while the output shaft is adapted to be connected to the wheels to be steered. The groove member has a groove and rotates together with either the input shaft or the output shaft. The reaction force generating member is supported by the other of the input shaft and the output shaft and is unmovable in a radial direction with respect to one of the input shaft and the output shaft and movable in an axial direction of the input shaft and the output shaft by a distance smaller than a predetermined value. The elastic member urges one of the groove member and the reaction force generating member toward the other of the groove member and the reaction force generating member.
In the first aspect of the present invention, the elastic member urges the reaction force generating member to engage the groove in the groove member. The reaction force generating member and the groove in the groove member prevent the input shaft and the output shaft from forming an operational angle therebetween unless the steering torque inputted to the input shaft exceeds a predetermined value. The reaction force generating member and the groove allow the input shaft and the output shaft to form an operational angle therebetween if the steering torque inputted to the input shaft exceeds the predetermined value. If an operational angle is formed between the input shaft and the output shaft, a steering assisting force corresponding to the operational angle is generated. Hence, the driver of a vehicle incorporating the present invention will experience from the steering wheel a feeling of high rigidity if the steering torque is below a predetermined value and a feeling of nimbleness during the steering operation if the steering torque exceeds the predetermined value.
Further, since the reaction force generating member is unmovable in the radial direction in the present invention, the reaction force generating member is not disengaged from the groove in the groove member, and thus prevents the reaction force generating member from slipping out of a predetermined location. The present invention ensures high durability as well as high reliability by providing that the reaction force generating member is movable in the axial direction by a distance not exceeding a predetermined value.
The first aspect of the present invention may be modified such that the operational angle formed between the input shaft and the output shaft is limited to a value not exceeding a predetermined maximum operational angle. A maximum relative displacement amount in the axial direction is generated between the groove member and the reaction force generating member in correction with the maximum operational angle, and the groove has a depth larger than the maximum relative displacement amount. Hence, the reaction force generating member does not pass across the groove while the power steering apparatus is in operation. Since the reaction force generating member is always engaged with the groove, it is possible to effectively prevent th
Kameda Yoshikazu
Kikuti Mitugu
Hurley Kevin
Pillsbury Madison & Sutro LLP
Toyota Jidosha & Kabushiki Kaisha
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