JPH0212141Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a device for controlling the supply flow rate of hydraulic oil in accordance with vehicle speed in power steering for automobiles and the like.

2. Description of the Related Art In order to reduce the burden on a driver when operating a steering wheel, a power steering device is known that sends pressure oil from a pump to a power cylinder when switching the steering wheel to power assist the steering wheel operation.

However, when a vehicle is traveling at high speed, the ground resistance of the wheels decreases, so the steering wheel also becomes lighter.
In order to prevent the steering wheel from wobbling and improve steering stability, it is preferable to reduce or cut power assist.

Therefore, Special Publication No. 54-34211, Special Publication No. 54-4135
A device has been proposed in which the flow rate supplied to the power cylinder is reduced by sensing the vehicle speed.

Now, to explain this with reference to FIG. 1, the body 1 is formed with a pump port 2 through which pressure oil is introduced from a pump (not shown), and a supply port 3 through which pressure oil is sent to a power cylinder (not shown). Ru.

A control valve 5 that constitutes a variable orifice 4 is interposed between the pump port 2 and the supply port 3, and a bypass port that returns a portion of the pressure oil from upstream of the variable orifice 4 to the tank side (not shown). 6 branches. The opening degree of the bypass port 6 is controlled by a flow control valve 7, and the differential pressure across the variable orifice 4 is kept constant, and the pressure is compensated so that the supply flow rate is proportional only to the orifice opening degree.

The flow control valve 7 receives the upstream pressure of the orifice on its front surface 7A and receives the orifice downstream pressure on its rear surface 7B through the passage 8, and is located at a position where the resultant force of these differential pressures and the return spring 9A is balanced. to increase or decrease the bypass flow rate.

Since the pump discharge amount increases in proportion to the engine rotational speed, even if the opening degree of the variable orifice 4 is constant, the differential pressure across the variable orifice 4 increases, and based on this, the flow rate on the supply port 3 side increases. In such a case, the flow control valve 7 increases the opening degree of the bypass port 6 as the differential pressure increases, thereby preventing fluctuations in the supply flow rate by increasing the amount of bypass.

In order to change the opening degree of the variable orifice 4 according to the vehicle speed, the control valve 5 has a metering rod 10 slidably housed in a holder 9 screwed onto the body 1. Armature 12 driven by excitation of solenoid coil 11
is stuck.

The measuring rod 10 has a large-diameter journal portion 14 that slides into guide hole 15 of the holder 9, and is interposed between the end surface of this journal portion 14 and an annular body 17 fitted to the tip of the guide hole 15. Due to the return spring 16, normally the journal part 1
The opposite end surface of the guide hole 15 is urged so as to come into contact with the bottom surface of the guide hole 15 .

In this state, the tip of the measuring rod 10 is connected to the ring body 17.
The opening of the variable orifice 4 is maximized.

On the other hand, when the solenoid coil 11 is energized, the armature 12 is pushed upward against the return spring 16, and the metering rod 10
is inserted into the taper orifice hole 17A.

Corresponding to the amount of protrusion of the metering rod 10, the gap between the taper orifice hole 17A and the metering rod 10, that is, the opening degree of the variable orifice 4 changes.
This increases or decreases the supply flow rate.

Figure 2A shows the relationship between vehicle speed and solenoid drive current; when the vehicle speed exceeds a predetermined low speed value, current is supplied, and then the current value increases in proportion to the vehicle speed to a predetermined high speed value. Thereafter, the solenoid drive current is controlled by a control circuit (not shown) so as to maintain a constant value.

The excitation force of the solenoid coil 11 increases in accordance with the drive current, and the armature 12 is proportionally displaced accordingly.

Therefore, the opening degree of the variable orifice 4 changes depending on the vehicle speed, and as shown in FIG. 2B, as the vehicle speed increases, the flow rate to the supply port 3 decreases.

In this way, a sufficient supply amount to the power cylinder is ensured in the low vehicle speed range, and the supply amount is reduced in the high speed range to improve maneuverability.

However, in this device, if a failure occurs in the electrical system for some reason and the solenoid drive current is cut off (becomes zero), the excitation force of the solenoid coil 11 disappears and the metering rod 10 is pushed back by the return spring 16. , variable orifice 4
opening becomes maximum.

Even if there is no problem while driving at low speeds, if this situation occurs while driving at high speeds, the supply flow will reach its maximum and the high-speed stability of the steering wheel will be lost.
From a so-called fail-safe perspective, this had extremely unfavorable results.

Furthermore, even in normal conditions, the fluid force of the pressure oil flowing from the pump port to the supply port side always acts on the tip of the metering rod 10, and therefore the variable orifice 4 is narrowed by overcoming this fluid force. In order to achieve this, the excitation force of the solenoid must be stable and strong, making it unavoidable to increase the size of the solenoid.Furthermore, if the solenoid becomes unstable at the narrowed position due to variations in the driving force, the orifice opening may become unstable. This had a subtle effect on the flow rate and caused variations in flow rate control accuracy in the high-speed range.

Therefore, the present invention provides an expanded diameter head at the tip of the metering rod that closes the ring body from the upstream side using a return spring when the solenoid excitation current disappears, and a fixed orifice that secures the minimum flow rate when the solenoid is closed. The purpose is to prevent the flow rate supplied to the power cylinder from increasing in the event of a solenoid failure by forming it on the body, etc., and to improve the control accuracy by using a fixed orifice to control the flow rate at high speeds. It is something.

Hereinafter, embodiments of the present invention will be described based on the drawings.

As shown in FIG. 3, an enlarged head 20 is attached to the tip of the measuring rod 10.
is in close contact with the ring body 17 from the upstream side of the tapered orifice hole 17A.

In the close contact surface between the head 20 and the annular body 17, two notches 22 are formed on the upper surface of the annular body 17 in this embodiment as fixed orifices for ensuring a predetermined minimum flow rate.

The metering rod 10 is still driven by a solenoid, but the solenoid coil 11
As shown in FIG. 4A, the excitation current is controlled so that it is large in the low speed range and small in the high speed range.

This means that the opening degree of variable orifice 4 is metering rod 1.
This is because the stroke amount increases as the stroke amount of 0 increases.

Regarding other components, the same parts as in FIG. 1 are given the same reference numerals, and the operation will be explained next.

In a low vehicle speed range, the excitation current to the solenoid coil 11 is large, so that the metering rod 10 makes a full stroke via the armature 12.

In this state, the head 20 is farthest from the ring body 17, the opening degree of the variable orifice 4 is at its maximum value, and a large flow is supplied to the power cylinder, ensuring light steering operation in the low speed range.

As the vehicle speed increases, the excitation current of the solenoid coil 11 decreases, and accordingly, the metering rod 10
The stroke amount of the head 20 decreases, and the head 20 eventually comes into close contact with the ring body 17.

During this time, as shown in FIG. 4B, the supply flow rate decreases as the opening degree of the variable orifice 4 decreases.
After the heads 20 are brought into close contact, pressure oil flows only through the notch 22 and is limited to a minimum flow rate.

This state becomes a kind of fixed orifice, so
The control accuracy of the flow rate is good, and although the variation in the dimensional error of the notch 22 also depends on the processing precision, there is almost no problem, so there is little variation in quality from product to product.

In this manner, the flow rate can be reliably narrowed to a predetermined value in the high speed range, and the high speed stability of steering wheel operation can be improved.

On the other hand, even if a control system failure occurs in this high-speed range and the solenoid drive current becomes zero and the excitation force disappears,
Since the head 20 of the metering rod 10 is held in close contact with the ring body 17 by the biasing force of the return spring 16, the supply flow rate is maintained at the minimum value without increasing, and the maneuverability is not impaired.

In addition, when this failure occurs, the steering wheel becomes heavy at low speeds, but this does not immediately impair steering stability, and in fact, the driver can clearly recognize the failure due to the heavier steering wheel. .

Next, the embodiment shown in FIG.
A is provided on the bottom of the head 20, and the sixth
In the illustrated embodiment, a passage 22B is also provided extending from the head 20 through the metering rod 10, each regulating the minimum flow rate when the head 20 is in close contact with the ring body 17. Note that the fixed orifice can also be formed in the body 9 or the like, bypassing the variable orifice 4.

As described above, according to the present invention, when the solenoid excitation current disappears, the ring body is closed by the expanded diameter head part urged by the return spring, and pressure oil is supplied only from the fixed orifice. The supply flow rate does not increase even if the solenoid malfunctions, and the so-called fail-safe function improves maneuverability.Furthermore, since the flow rate control in the high-speed range is performed using a fixed orifice, the flow rate control accuracy is high. Variations in flow rate for each product can be reduced,
This makes it possible to maintain a constant weight of the steering wheel at high speeds.

[Brief explanation of the drawing]

Figure 1 is a sectional view of a conventional device, Figure 2A is a characteristic diagram showing the relationship between conventional vehicle speed and solenoid drive current,
FIG. 2B is a characteristic diagram showing the relationship between vehicle speed and control flow rate. Figure 3 is a sectional view showing an embodiment of the present invention, Figure 4A is a characteristic diagram showing the relationship between vehicle speed and solenoid drive current of the present invention, and Figure 4B is a characteristic diagram showing the relationship between vehicle speed and control flow rate. It is. FIGS. 5 and 6 are sectional views of main parts of other embodiments. 1...Body, 2...Introduction port, 3...Supply port, 4...Variable orifice, 5...Control valve,
6...Bypass port, 7...Flow control valve, 9...Holder, 10...Measuring rod,
DESCRIPTION OF SYMBOLS 11... Solenoid coil, 12... Armature, 16... Return spring, 17... Annular body, 17A... Taper orifice hole, 20... Expansion head, 22... Notch, 22B... Passage.

Claims (1)

[Scope of utility model registration request] A power steering flow rate control device including a control valve that throttles the flow rate of pressure oil sent from a pump to a power cylinder in accordance with an increase in vehicle speed, wherein the control valve is attached to a rod that slides via a solenoid and to the tip of this rod. An expanded diameter head that approaches and separates from the upstream side of the ring body having an orifice that regulates the maximum flow rate of the pressure oil flow, and when the expanded diameter head is biased by a solenoid return spring and closes the ring body. A power steering flow rate control device comprising: a fixed orifice provided to ensure a minimum flow rate;