Power steering device

Details Power steering device Power steering device

1997-10-20

2001-05-22

Boehler, Anne Marie (Department: 3618)

Motor vehicles

Steering gear

With fluid power assist

C091S37500R

Reexamination Certificate

active

06234271

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power steering device utilizing a torsion bar.
2. Description of the Prior Art
When a power steering device utilizing a torsion bar is used, one factor that is felt as a response by the driver at the steering wheel is the torsional resistance of the torsion bar. However, when the steering is in a neutral position, there is almost no torsional resistance of the torsion bar, which results in weaker rigidity of neutrality and hence reduces the stability of the vehicle during a straight travel.
Under such circumstances, various devices have been proposed to provide a preset force to achieve rigidity of neutrality. By way of example, one of such devices will be described below.
FIGS. 9 through 12
show such a power steering device.
In this device, a power cylinder
1
incorporates a piston (not shown) through which an output shaft
2
is penetrated. The piston and the output shaft
2
are linked through a ball nut which is not shown.
Further, a sector gear which is not shown is engaged with the piston to be rotated as the piston moves. The rotation of the sector gear causes a steering wheel linked therewith to turn. This is a so-called integral type power steering device.
A valve case
3
is secured to the power cylinder
1
. The base end of the output shaft
2
is rotatably supported by the valve case
3
.
The output shaft
2
is hollow, and an end of an input shaft
4
is rotatably inserted therein in a position toward the base end thereof.
The input shaft
4
and output shaft
2
are linked through a torsion bar
5
. Specifically, one end of the torsion bar
5
is inserted in the input shaft
4
and secured thereto by a pin
6
that is pierced through the portion where it is inserted. The other end of the torsion bar
5
is secured to the output shaft
2
by a pin which is not shown.
The input shaft
4
and output shaft
2
rotate relative to each other while twisting the torsion bar
5
.
A rotary spool
7
is formed to be integral with an outer circumferential surface of the input shaft
4
inserted in the output shaft
2
. An inner circumferential surface of the output shaft
2
that faces the rotary spool
7
serves as a rotary sleeve
8
. The rotary spool
7
and rotary sleeve
8
are fitted to each other such that they can rotate relative to each other to form a steering valve v.
When the input shaft
4
and output shaft
2
rotate relative to each other, the steering valve v is switched in accordance with the rotating direction to supply operating fluid into one of pressure chambers defined in the power cylinder
1
and to discharge operating fluid in the other pressure chamber to a tank. As a result, the piston moves to rotate the sector gear, thereby applying an assistant force to the wheels linked thereto.
In a power steering device having such a configuration, a spring containing chamber
9
is formed on one end of the output shaft
2
and is blocked from the steering valve v by a seal member
10
.
As shown in
FIG. 10
, the spring containing chamber
9
is substantially in the form of a square surrounded by walls
12
,
12
and walls
19
,
19
formed by boring the end of the output shaft
2
.
The input shaft
4
is inserted in the spring containing chamber
9
in which a pair of spring members
13
are disposed such that they sandwich the input shaft
4
, and balls or rollers
21
are interposed between the spring members
13
and the input shaft
4
.
A pair of first support grooves
17
are formed in opposite positions on the outer circumferential surface of the input shaft
4
. The first support grooves
17
are arranged such that they face the walls
12
of the spring containing chamber
9
to maintain the state shown in
FIG. 10
in the neutral state wherein the input shaft
4
and output shaft
2
are not in relative rotation.
As shown in
FIG. 12
, the spring member
13
is constituted by a flat spring having a flat portion
14
, convex portions
15
formed on both sides of the flat portion
14
and slopes
16
continuous with the convex portions
15
.
A second support groove
20
which is a V- or U-shaped groove is formed in the middle of the flat portion
14
. Further, the ends of both of the slopes
16
are bent to form anchoring portions
18
.
The convex portions
15
serve as stoppers to prevent the ball or roller
21
from dropping from the gap between the spring member
13
and input shaft
4
when it comes out the first and second support grooves
17
and
20
.
When the spring member
13
is in a free state, the distance between the anchoring portions
18
,
18
on both sides thereof is longer than the distance between the walls
19
,
19
of the spring containing chamber
9
.
Thus, as shown in
FIG. 9
, when the spring members
13
are placed in the spring containing chamber
9
, it is anchored thereto by the anchoring portions
18
being urged into contact with the walls
12
and the walls
19
which are normal to the walls
12
at the corners of the spring containing chamber
9
.
The first support grooves
17
are put in a face-to-face relationship with the second support grooves
20
on the spring members
13
in the neutral state wherein the input shaft
4
and output shaft
2
are not in relative rotation. When the spring members
13
are anchored as described above, the distance between the first support grooves
17
and the second support grooves
20
is smaller than that in the state wherein the balls or rollers
21
are interposed therebetween.
When the balls or rollers
21
are interposed between the first and second support grooves
17
and
20
, a spring force acts in the direction toward the center of the input shaft
4
to appear as an initial load. The first and second support grooves
17
and
20
are both formed to a small depth that only supports the balls or rollers
21
therein rather than holding them securely.
The operation of this power steering device will now be described.
When the steering wheel is kept in the neutral position, the input shaft
4
and output shaft
2
are in the neutral position shown in FIG.
10
. The initial load from the spring members
13
is exerted to the input shaft
4
in the direction of sandwiching the input shaft
4
to act as a preset force through the balls or rollers
21
.
Thus, rigidity of the neutral position can be improved to provide stability during a straight travel.
Let us assume that the steering wheel is turned in this state to rotate the input shaft
4
in the direction indicated by the arrow k relative to the output shaft
2
.
Then, as shown in
FIG. 11
, the balls or rollers
21
move over the edges of the supporting grooves
17
and
20
while deflecting the spring members
13
to ride on circumferential portions of the input shaft
4
.
Further relative rotation of the input shaft
4
and output shaft
2
causes the balls or rollers
21
to move between the flat portions
14
of the spring members
13
and the circumferential portions of the input shaft
4
in the direction indicated by m in a rolling motion with the spring members
13
kept deflected.
Thus, the steering reaction force generated at this time is a combination of the torsional resistance of the torsion bar
5
and the spring force of the spring members
13
.
When the input shaft
4
and output shaft
2
have rotated relative to each other by predetermined amounts, the balls or rollers
21
contact the convex portions
15
of the spring members
13
. Therefore, the balls or rollers
21
will not come out from the gap between the flat portions
14
of the spring members
13
and the input shaft
4
.
As described above, the relative rotation of the input shaft
4
and output shaft
2
switches the steering valve v to control the operating fluid in to the power cylinder
1
, thereby providing an assistant force. When the wheels is steered to a target value as a result of the application of the assistant force, the input shaft
4
and output shaft
2
return the neutral position. At this time, the balls or rollers
21
also roll to ret

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