JPS6221658B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a servo valve suitable for a power steering device.

An object of the present invention is to obtain an optimal steering feeling by improving the valve shape to change the pressure characteristic to a so-called two-step characteristic in which part of the pressure characteristic changes linearly. .

Another object of the present invention is to simplify the shape of the orifice component by combining two types of orifices, thereby facilitating the manufacture of the valve member.

Still another object of the present invention is to perform efficient valve control to reduce power loss in the power cylinder.

By making the pressure characteristics of a part of the steering range of the power steering system closer to linear, and by reducing the pressure in the neutral range to further reduce the ratio of the output of the power system to the steering force, the steering wheel can be improved. It is known that the steering feel is extremely good.

In order to obtain such pressure characteristics, for example,
As described in Publication No. 4807, there is a spool valve member in which a recess with a special curve is formed in the land portion, but this conventional servo valve has the required pressure characteristics even with a single recess. Therefore, it was necessary to perform special processing on the land portion of the spool valve member.

Therefore, in the present invention, two types of pressure control orifices are formed between the spool valve member and the sleeve valve member, and by combining these two types of orifices, necessary pressure characteristics are obtained and compared to conventional servo valves. The shape of the side end of each land is simplified, making it easier to manufacture the valve member, and the direction control orifice communicating with the pressure fluid supply port is installed before the pressure control orifice communicating with the discharge port is closed. This is characterized in that the orifice is closed to prevent the supply fluid from colliding with the discharge fluid discharged from the power cylinder, thereby efficiently controlling the pressure loss.

Embodiments of the present invention will be described below based on the drawings. FIG. 1 shows an example in which the servo valve of the present invention is applied to a rack and pinion type power steering device. In the figure, 10 indicates a housing body forming the main body of the power steering device, and this housing body 10 includes a pinion shaft. 11 is rotatably supported at both ends by bearings 12 and 13, respectively, and meshes with rack teeth 15 of a rack shaft 14 that is slidable in a direction intersecting the bearings. Both ends of the rack shaft 14 are connected to steering wheels via a required steering linkage, and a piston 17 (see FIG. 2) of a power cylinder 16 is operatively connected to the rack shaft 14.

The housing body 10 includes a valve housing 18.
is fixed, and the servo valve 20 of the present invention is accommodated in the valve hole 19 of this valve housing 18. This servo valve 20 includes a sleeve valve member 21 that is relatively rotatable about the axis of the pinion shaft 11.
and a spool valve member 22, this sleeve valve member 21 is connected to the pinion shaft 11 by a connecting pin 23, and a steering shaft 24 connected to a steering handle is integrally connected to the spool valve member 22. The steering shaft 24 is flexibly connected to the pinion shaft 11 via a torsion bar 25.

As shown in FIG. 2, first grooves 31 are formed on the inner peripheral surface of the sleeve valve member 21 at symmetrical positions vertically and horizontally with respect to its axis of rotation. Supply ports 33 to which pressure fluid is supplied from the pump are open. Furthermore, second and third grooves 38 and 7 are provided on the inner circumferential surface of the sleeve valve member 21 between the first groove 31.
8 are formed, and these second and third grooves 38, 78
The left and right chambers 16 of the power cylinder 16 are located on both sides of the power cylinder 16.
Land portions 34 and 35 are formed by opening distribution ports 36 and 37 that communicate with a and 16b.

On the other hand, the outer periphery of the spool valve member 22 has a first groove 31 of the sleeve valve member 21 in the neutral state.
The first land portion 39 corresponding to the second land portion 41 and the third groove 78 corresponding to the second groove 38
A third land portion 71 corresponding to the grooves 42 and 43 is formed to sandwich the grooves 42 and 43. A first orifice 50 for direction control is formed between the first land 39 and the lands 34 and 35, and between the second land 41 and the lands 34 and 35 and between the third land 71 and the land. Between the parts 34 and 35 are second and third orifices 60 and 70 for pressure control.
is formed. Note that the second and third orifices 60 and 70 are different from the case of the second land portion 41 and the case of the third orifice.
In the case of the land portion 71, the left and right sides are reversely arranged. The second land portion 41 and the third land portion 7
A discharge port 44 is formed in the center of 1, and this discharge port 44 includes a passage 45 formed between the spool valve member 22 and the torsion bar 25, a through hole 46,
A chamber 47 leads to the reservoir. (1st
(See figure) In the servo valve having the above configuration, when a steering torque is applied to the steering shaft 24 in the counterclockwise direction as shown in FIG. do. As a result, the first land portion 39
one side end portion overlaps the land portion 34, and the second land portion 41 and the third land portion 71 rotate to a position approaching the land portion 35. Thereby, the supply port 33 connected to the pump communicates with the left chamber 16b of the power cylinder 16 via the first groove 31 and the distribution port 37, and the other distribution port 36
is connected via grooves 42 and 38 to an outlet 44 which is connected to a reservoir. By forming this passage, the left chamber 16b of the cylinder 16
Pressure fluid flows into the piston 17 to move it to the right,
It is designed to assist the manual operation force.

In the servo valve 20 having such a configuration, the present invention performs direction control using the first orifice 50 communicating with the supply port 33, and pressure control using the second and third orifices 60, 70 communicating with the discharge port 44. It is characterized by the fact that it is designed to be carried out.

That is, FIGS. 3 and 4 show the relationship between the first land portion 39 of the spool valve member 22 and the lands 34 and 35 of the sleeve valve member 21 in the neutral state, and FIGS. 5 and 6 show the relationship in the neutral state. The second land portion 41 of the spool valve member 22 in the state
and the land portions 34, 35 of the sleeve valve member 21, and FIGS. 7 and 8 show the relationship between the third land portion 71 of the spool valve member 22 and the land portions 34, 35 of the sleeve valve member 21 in the neutral state. 3
As is clear from this figure, the clearance L1 of the first orifice 50 is set smaller than the respective clearances L2 and L3 of the second orifice 60 and the third orifice 70, For example, when the spool valve member 22 is rotated counterclockwise in FIG. pressure control. Therefore, the second
Alternatively, when the third orifices 60 and 70 are gradually narrowed and pressure fluid begins to be supplied from the supply port 33 to the left chamber 16b of the power cylinder 16 through the concave groove 31, the first orifice 50 is already completely closed. Right chamber 16a of power cylinder 16
The discharged fluid discharged from the outlet through the distribution port 36 and the concave groove 42 is smoothly discharged to the discharge port 44 without colliding with the supply fluid, and as a result, there is no pressure loss due to an increase in exhaust pressure, and the power of the power cylinder 16 is increased. can be used effectively.

Furthermore, the servo valve 20 of the present invention is characterized by the second and third orifices 60, 70.
The purpose is to vary the degree of change in opening area and the final closing angle to obtain the required pressure characteristics.

That is, as is clear from FIGS. 5 to 8, the right end of the second land portion 41 and the left end of the third land portion 71 have an arc shape in the longitudinal direction of each land portion 41, 71, and An operating surface 53 inclined at an angle α1 and an operating surface 54 inclined at an angle α2 are continuously formed, and as the spool valve member 22 rotates, the opening area A1 of the third orifice 70 is initially gradually reduced. Then, at the end, it suddenly becomes smaller. On the other hand, the left end portion of the second land portion 40 and the right end portion of the third land portion 71 are only gently bent in the longitudinal direction of each land portion 41, 71, and no working surface is formed. The degree of decrease in the opening area A2 of the second orifice 60 as the spool valve member 22 rotates is greater than that of the third orifice 70. Moreover, this second land portion 41 is the land portion 34.
The distance until the third land portion 71 overlaps with the land portion 34, that is, the gap L3 of the third orifice 70 is set to be larger than the distance that the third land portion 71 overlaps with the land portion 34, that is, the gap L2 of the second orifice 60, The final closing angles of the second and third orifices 60 and 70 are different.

FIG. 9 shows such second and third orifices 60,
70, the steering angle θ of the spool valve member 22 is plotted on the horizontal axis, and the opening area of the orifices 60, 70 is plotted on the vertical axis. A change in the opening area A1 of the third orifice 70 is shown, and (b) shows a change in the opening area A2 of the second orifice 60. As is clear from this figure, the opening area A1 of the third orifice 70 changes more slowly than the opening area A2 of the second orifice 60, and after the second orifice 60 is closed, the opening area A1 of the third orifice 70 changes more slowly than the opening area A2 of the second orifice 60. This shows that the orifice 70 is closed. Since this embodiment has two sets of orifices 60 and 70 as described above, the total opening area is twice the sum of the opening areas A1 and A2 of these two sets of orifices 60 and 70, that is, 2 (A1 + A2). A
becomes. Therefore, this total opening area A changes as shown in FIG. 9C.

Figure 10 shows the change ratio of opening area (Ao/A) ²
The horizontal axis represents the steering angle θ of the spool valve member 22, and the vertical axis represents the ratio of change in opening area (Ao/A) ² . Note that since the output pressure of the servo valve 20 changes at approximately the same rate as this opening area change ratio (Ao/A) ² , this diagram can be considered to be the pressure characteristic of the servo valve 20. Further, Ao represents the total opening area of the second and third orifices 60 and 70 in the neutral state. As is clear from this figure, the pressure changes within a range close to the neutral state is extremely small, and there is also a part in the middle where the pressure changes almost linearly depending on the steering angle, and after this linear part the pressure suddenly changes. Since it has a so-called two-stage bending characteristic that increases, it has pressure characteristics that are extremely suitable for use as a servo valve in a power steering device, and excellent steering feeling can be obtained.

Note that in the above embodiment, the working surfaces 53 and 54 are formed on the second and third land portions 41 and 71 on the spool valve member 22 side.
The present invention is not limited to this embodiment, and for example, as shown in FIG. The degree of change as well as the final closing angle may be different.

FIG. 12 shows a servo valve in which the sleeve valve member 21 and the spool valve member 22 are formed with concave grooves and land portions in a relationship opposite to that of the above embodiment. 2nd and 3rd orifice 50, 6
By setting the clearance of 0.70 to satisfy the relationship L1<L2<L3 and forming the working surface on the land portion constituting the third orifice 70, the same effect as in the previous embodiment can be achieved.

As described above, in the servo valve of the present invention, two types of orifices for pressure control are formed between the spool valve member and the sleeve valve member, and as the spool valve member rotates relative to each other, the two types of orifices are Since they are made to act simultaneously, it is possible to obtain excellent pressure characteristics as a servo valve of a power steering device having a so-called two-stage bending characteristic having a linear portion.

In addition, since the present invention obtains the necessary pressure characteristics by combining two types of orifices, there is no need to process the side end of each land into a complicated shape as in conventional devices, and it is not necessary to process the side end of each land into a complicated shape, but instead with a simple straight line. Alternatively, it can be configured by a combination of circular arcs, which has the advantage that the valve member can be easily and precisely machined.

Furthermore, since the present invention performs direction control using an orifice communicating with the supply port, and pressure control using an orifice communicating with the discharge port, collision between the supply fluid and the discharge fluid from the power cylinder may occur. This has the advantage that it can be prevented and the power of the power cylinder can be effectively exerted.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention, and FIG. 1 is a cross-sectional view of a main part of a power steering device incorporating the servo valve of the present invention, and FIG. 1, FIGS. 3 and 4 are main part sectional views and plan views showing the relationship between the first land portion and the first groove, and FIGS. 5 and 6 are views of the second groove. A main part sectional view and a plan view showing the relationship between the land part and the second groove, FIGS. 7 and 8 are a main part sectional view and a plan view showing the relationship between the third land part and the third groove, FIG. 9 is a diagram showing changes in the opening area of the orifice to obtain optimal pressure characteristics, and FIG. 10 is a diagram showing optimal pressure characteristics.
12 is a partial cross-sectional view of the servo valve showing another embodiment of the present invention shown in FIGS. 11 and 12. FIG. 21... Sleeve valve member, 22... Spool valve member, 16... Power cylinder, 33... Supply port, 36, 37... Distribution port, 44... Discharge port, 5
0...first orifice, 60...second orifice, 70...third orifice.

Claims (1)

[Claims] 1 Consists of a sleeve valve member and a spool valve member that are rotatable relative to each other, and between the sleeve valve member and the spool valve member, communication between a pressure fluid supply port and a pair of distribution ports communicating with the left and right chambers of the power cylinder is controlled. a first orifice for directional control, and second and third orifices for pressure control that control communication between the pair of distribution ports and the discharge port; The degree of change in opening area due to relative rotation of the spool valve member with respect to the member is greater than that of the third orifice;
A servo valve characterized in that, after the second orifice with a large degree of change in opening area closes, the third orifice with a small degree of change in opening area closes.