Motor vehicles – Steering gear – With fluid power assist
Reexamination Certificate
2000-07-05
2002-02-26
Boehler, Anne Marie (Department: 3618)
Motor vehicles
Steering gear
With fluid power assist
C137S625230
Reexamination Certificate
active
06349788
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power steering apparatus which includes a control valve for controlling the change-over of a working fluid passage with respect to a power cylinder.
2. Description of the Related Art
Conventionally, an engine speed sensitive type control valve
1
as shown in
FIG. 10
, or a vehicle speed sensitive type control valve
6
as shown in
FIG. 11
have been used as a control valve of a power steering apparatus.
In the control valve
1
shown in
FIG. 10
, a rotary pool
1
B is fitted into a sleeve
1
A, and the rotary spool
1
B and sleeve
1
A are coaxially arranged so as to be relatively displaceable in accordance with a steering torque. The sleeve
1
A is formed with a port group (four sets in FIG.
10
). One set of the port group is composed of three ports, that is, a supply port
2
connected to a pump side supply passage, and a first port
3
A and a second port
3
B which are arranged on both sides of the supply port
2
and are connected individually to a first chamber and a second chamber of a power cylinder. The supply port
2
and first and second ports
3
A and
3
B are arranged around the central axis so as to be symmetrical with respect to the axial point. Moreover, the rotary spool
1
B is formed with a plurality of return ports
4
(four in
FIG. 10
) which communicate with a tank side return passage and are arranged around the central axis so as to be symmetrical with respect to the axial point. The control valve
1
includes longitudinal grooves
5
A to
5
D. Longitudinal grooves
5
A and
5
B are formed at an inner surface of the sleeve
1
A and at a position including the first port
3
A and the second port
3
B. A longitudinal groove
5
C is formed at an outer surface of the rotary spool
1
B and at a position relative to the supply port
2
of the sleeve
1
A, and a longitudinal groove
5
D is formed at the outer surface of the rotary spool
1
B and at a position including the return port
4
. These adjacent ports (supply port
2
, first port
3
A, second port
3
B, return port
4
) are capable of mutually communicated via these longitudinal grooves
5
A to
5
D.
In the control valve
1
shown in
FIG. 10
, in the case of neutral steering, a working fluid supplied to the supply port
2
flows from the longitudinal groove
5
C to the return port
4
via the longitudinal grooves
5
A,
5
B and
5
D. In the case of steering wheel turn, the working fluid supplied to the supply port
2
flows from the longitudinal groove SC to the first port
3
A (or the second port
3
B) via the longitudinal groove
5
A (or
5
B) which is correlated with a steering wheel turn direction, and then, is supplied to the first chamber (or the second chamber) of the power cylinder so as to assist a steering force. At that time, a high pressure is applied to a portion of the longitudinal groove
5
A (or
5
B) of the sleeve
1
A.
In the control valve
6
shown in
FIG. 11
, the sleeve
1
A is formed with a second supply port
7
connected to a pump side supply passage, in addition to the construction of the control valve
1
shown in FIG.
10
. The control valve
6
includes the following longitudinal grooves
8
A and
8
B. longitudinal grooves
8
A and
8
B are formed at an inner surface of the sleeve
1
A and arranged on the both sides of the second supply port
7
, and a longitudinal groove
9
is formed at an outer surface of the rotary spool
1
B and at a position relative to the second supply port
7
of the sleeve
1
A. The adjacent second supply port
7
and return port
4
of the rotary spool
1
B are capable of mutually communicated via these longitudinal grooves
9
,
8
A,
8
B and
5
D.
In the control valve
6
shown in
FIG. 11
, a working fluid force fed by a pump is supplied to only supply port
2
during low vehicle speed, and is supplied to both supply port
2
and second supply port
7
during high vehicle speed. The assist force is greater during low vehicle speed, and is reduced during high vehicle speed.
The aforesaid prior art has the following problems.
{circle around (1)} In the control valve
1
shown in
FIG. 10
, the sleeve
1
A is formed with the longitudinal grooves
5
A and
5
B at its inner surface. Longitudinal grooves
5
A and
5
B are arranged in parallel with each other in a longitudinally wide range of the sleeve
1
A with the same length. This makes rigidity of the sleeve
1
A low (see FIG.
10
B). In the sleeve
1
A, an oil pressure applied to any longitudinal groves
5
A and
5
B becomes uniform in the case of neutral steering. The oil pressure elevates to a high pressure state in the case of a low vehicle speed. As a result, in the sleeve
1
A, there is generated a diamond-shaped distortion such that a certain portion of these longitudinal grooves
5
A and
5
B are outwardly bulged (see FIG.
10
C).
{circle around (2)} In the control valve
1
shown in
FIG. 11
, the sleeve
1
A is formed with the longitudinal grooves
5
A and
5
B at its inner surface, and further, includes the longitudinal grooves
8
A and
8
B. These longitudinal grooves
5
A and
5
B and
8
A and
8
B are arranged in parallel with each other in a longitudinally wide range of the sleeve
1
A with the same length. This makes rigidity of the sleeve
1
A low (see FIG.
11
B). In the sleeve
1
A, a working fluid is supplied to only supply port
2
in the case of a low vehicle speed, and is not supplied to the second supply port
7
. For this reason, pressure distribution acting to a circumferential direction of the sleeve
1
A becomes unbalanced and distortion is generated in the sleeve
1
A (see FIG.
11
C).
{circle around (3)} In the prior art, the aforesaid distortion of the sleeve
1
A stated in the above items {circle around (1)} and {circle around (2)} gives an influence to a relative rotation (ie., valve characteristic) of the sleeve
1
A and the rotary spool
1
B. In order to avoid the aforesaid influence, the clearance formed between the sleeve
1
A and the rotary spool
1
B is made large. However, this is a factor which increases oil leakage and lowers pump efficiency.
SUMMARY OF THE INVENTION
It is, therefore, an object of the preset invention to improve rigidity of a sleeve constituting a control valve, and to minimize a clearance formed between the sleeve and a rotary spool so as to reduce oil leakage while preferably securing operation of the sleeve and the rotary spool, and thus, to improve the valve characteristic.
According to the present invention, there is disposed a power steering apparatus including
a control valve for controlling a change-over of a pump side supply passage and a tank side return passage with respect to a first chamber and a second chamber of a power cylinder of a steering arrangement,
The control valve comprises a sleeve and a rotary spool fitted into the sleeve.
The sleeve and the rotary spool are coaxially arranged so as to be relatively displaceable in accordance with a steering torque.
The sleeve has a supply port connected to the pump side supply passage, and first and second ports which are connected individually to the first and second ambers of the power cylinder and are arranged around a central axis so as to be symmetrical with respect to an axial point.
The rotary spool has a return port which is connected to the tank side return passage and is arranged around a central axis so as to be symmetrical with respect to an axial point.
Upon assembling the sleeve and the rotary spool, each longitudinal groove extending in a valve axial direction is formed at an inner surface of the sleeve so that adjacent ports of the sleeve and the rotary spool communicate with each other. Each upper end of the adjacent longitudinal grooves is arranged in a stagger layout.
Furthermore, according to the present invention, there is disclosed a power steering apparatus including
a control valve for controlling a change-over of a pump side supply passage and a tank side return passage with respect to a first chamber and a second chamber of a power cylinder of a steering arra
Serizawa Akihiko
Wang Chaojiu
Boehler Anne Marie
Orum & Roth
Showa Corporation
Winner Tony
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