JPS6145583B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a power steering device for a vehicle.

More specifically, the present invention relates to a power steering system that accurately reduces the amount of pressure oil supplied to a power auxiliary part as the vehicle speed increases, maintains steering stability during high-speed running, and that can be mass-produced at low cost. .

In a vehicle's power steering system, the steering power is assisted by hydraulic pressure, and at the same time, in order to improve steering stability during high-speed driving, the discharge flow rate of the hydraulic source pump supplied to the power auxiliary section is adjusted as the speed increases. Attempts have been made to reduce this, and some have already been put into practical use.

However, in these known technologies, the flow rate of pressurized oil is controlled by detecting the rotation speed of a pump driven by the engine, and is not controlled in proportion to the vehicle speed. I had no choice but to accept unnatural changes in the steering sensation each time.

Of course, there is also a conventional vehicle that is equipped with a vehicle speed sensor and controls the flow rate of pressurized oil according to the sensor's signal, conveying an appropriate sense of road resistance to the driver during high-speed driving to obtain driving stability. It is known as No. 51-43529.

In such prior art, a branch path is derived from the oil supply path that communicates the hydraulic oil source and the power cylinder, this branch path is connected to the hydraulic reaction chamber, a control valve is provided in the middle of the branch path, and this control valve is connected to the vehicle speed. The control valve is connected to the discharge path of the discharge pump that operates according to the speed of the vehicle, opens and closes the control valve according to the vehicle speed, and closes the control valve when the vehicle is stopped, thereby stopping the flow of oil to the reaction chamber and reducing the running force. When the vehicle is running, oil flows into the reaction chamber to sense steering torque proportional to road resistance.

However, in the above-mentioned prior example, the oil drain path leading to the discharge pump and the chamber in the control valve are communicated via a communication hole, and this communication hole is opened before the control valve is opened. It has an open structure. In other words, even though the communication hole opens, the control valve itself does not open until the vehicle reaches a certain speed. Therefore, even though the vehicle is ahead at low speed, no hydraulic oil flows into the hydraulic reaction chamber. No flow occurs, and the steering torque is still the same as when stopped, so that a steering torque proportional to road resistance cannot be obtained at low speeds.

The inventors of the present invention have devised the present invention in view of the above-mentioned problems in power steering devices and to effectively solve the problems.

An object of the present invention is to provide a power steering device for a vehicle that can accurately reduce the flow rate of pressure oil supplied to a power auxiliary part as the vehicle speed increases, thereby maintaining steering stability during high-speed running, and also to provide a vehicle speed sensor part. The present invention aims to provide a power steering device in which high pressure does not directly act on the flow rate control portion thereof, which is therefore inexpensive, highly mass-producible, and has a long life.

Furthermore, it is an object of the present invention to utilize the same vehicle speed sensor as the conventional one, by providing a system that can be easily applied to a power steering device having a vehicle speed sensor and a flow rate control section using the vehicle speed sensor as disclosed in Japanese Patent Application Laid-Open No. 51-43529. However, the present invention provides a simple and highly reliable power steering device that allows the driver to sense steering torque proportional to road resistance and steering torque proportional to steering speed as the vehicle speed increases, and further provides a vehicle speed sensor. It is an object of the present invention to provide a power steering device which also has a safety function such that the flow rate of pressure oil to a power auxiliary part is always reduced in the event of a failure of the power auxiliary part.

Next, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. Further objects and advantages of the invention will now become apparent.

FIG. 1 is an explanatory diagram showing a hydraulic circuit of a power steering device according to the present invention, and FIG. 2 is a diagram showing pressure oil flow characteristics of the power steering device according to the present invention.

In FIG. 1, reference numeral 10 denotes a pressure oil source, which includes a pump 11 driven by an engine, pressurizes hydraulic oil from an oil tank 16, and discharges it to the supply path 15. Note that a filter 17 is provided in the tank 16. The pressure oil source 10 is equipped with a flow rate control valve 12 that detects the pressure before and after the metering throttle 13 and short-circuits the discharge side and suction side of the pump 11 in the event of excessive discharge, thereby controlling the rotation speed of the pump 11 and the discharge supply path 15 side. It is configured to force-feed a substantially constant flow rate to the supply path 15 without being affected by pressure fluctuations. A relief valve 14 is also provided to protect the system from excessive pressure build-up.

On the other hand, a pinion shaft 21 rotated by the steering wheel 20
are engaged by teeth 24 and teeth 22 of a rack shaft 23, and both ends of the rack shaft 23 are connected to wheels 25 via tie rods in a well-known manner so as to steer the wheels 25.

A spool-type four-way switching valve 30 is disposed at the end of the pinion shaft 21, and the switching valve 30 uses the thrust force of the teeth 22 to control the spool valve according to the magnitude and direction of the steering torque applied to the pinion shaft 21. 31 slides to switch oil passages, and one chamber of the power cylinder 33 that slidably houses a piston 32 integrated with the rack shaft 23 is used as a pressure oil source, and the other chamber is used as an oil tank 16. They are configured to be selectively connected to each other to obtain desired power assistance. The above configuration is a well-known method for power steering devices.

When no steering torque is applied to the four-way switching valve 30, the four-way switching valve 30 is maintained in the straight-ahead state shown in the figure by plungers 36, 36 which are compressed by a neutral return spring 35 in a hydraulic reaction chamber 34 provided to surround the four-way switching valve 30. In this case, the chambers of the pressure oil source 10, the oil tank 16, and the cylinder 33 are maintained in free communication with each other. The hydraulic reaction chamber 34 is composed of four cylindrical spaces arranged around the four-way switching valve 30, and each of the chambers has a pair of plungers 36, 36 pressed in opposite directions by a spring 35 as described above. It is stored.

The hydraulic reaction chamber 34 has a port 4 of a reaction force limiting valve 40.
Hydraulic pressure from the pressure oil source 10 is introduced through the first branch passage through the throttle 43
The oil passage 54 communicates with a flow rate control section 50 using a vehicle speed sensor.

The reaction force limiting valve 40 is configured to be biased toward the closing side by the pressure in the oil passage 54 downstream of the throttle 43 and biased toward the opening side by the action of the spring 44. Recoil chamber 34
... is configured to press the plungers 36, 36 by the hydraulic pressure and spring 35 introduced therein and resist the sliding movement of the spool valve 31, and has the function of providing an appropriate reaction force to the driver.

A flow control section 50 composed of a vehicle speed sensor is connected to a pipe 5.
A gear is fixed to the tip of an output shaft 51 of the motor 52, and the countershaft of the transmission is mounted on a shaft that rotates at a speed proportional to the vehicle speed. It meshes with the gears. Therefore, even if hydraulic drive torque is applied to the hydraulic motor 52, its rotational speed is limited to a speed proportional to the vehicle speed. The flow rate control unit 50 has a hydraulic motor 52 that operates as a pump when the vehicle backs up.
A relief valve 53 is provided which opens at a relatively low pressure to prevent excessive pressure from building up within 4. Since excessive pressure is prevented from being applied to the hydraulic motor 52 of the relief valve 53, there is also the advantage that there is no need to take the strength of the motor 52 into consideration.

A constriction 19 is provided in the conduit 18 that branches from the conduit 15 to the four-way switching valve 30, and from the downstream of this constriction 19, a port 61 and an oil conduit 62 of a flow rate regulating valve 60 integrally formed on the reaction force limiting valve 40 are provided. through the oil passage 54
This is a second branch that communicates with the A branch pipe line 63 is provided. Like the reaction force limiting valve 40, the flow rate regulating valve 60 is also closed due to the increase in pressure within the oil passage 54, but the timing of its closing is configured to close earlier than the reaction force limiting valve 40.

In the illustrated embodiment, the reaction force limiting valve 40 is also the flow rate regulating valve 6.
0 is also formed on an integrated spool valve, but of course it is also possible to configure it as a separate valve. In this case, the spring that presses the valve toward the opening side is set weakly on the flow rate adjustment valve side.

Next, the operation of the power steering device according to the present invention will be explained.

<When the vehicle is steered while stopped> In this case, the flow rate control unit 50 using the vehicle speed sensor
does not operate, and the oil pressure in the oil passage 54 increases due to its damming effect, causing the flow rate regulating valve 60 and the reaction force limiting valve 4 to increase.
0 is closed. Therefore, the amount of oil leaking through the flow rate control section 50 is kept substantially at zero, and the entire amount of oil pumped from the pressure oil source 10 is effectively consumed as auxiliary power for steering. Further, in this case, since the introduction of hydraulic pressure into the hydraulic reaction chamber 34 is also closed, the hydraulic pressure inside the reaction chamber 34 is suppressed to the minimum, and light and agile steering performance is guaranteed.
In the figure, for example, when the steering wheel 20 is rotated to the right, the thrust force of the pinion gear 22 acts to the right, and the spool valve 31 of the four-way switching valve 30 is activated by the low oil pressure in the reaction chamber 34 and the force of the return spring 35. It slides to the right against the pressure and introduces hydraulic pressure into the right chamber of the power cylinder 33, and the left chamber communicates with the oil tank 16. The wheels 19 are thus steered.

<When the vehicle is steered while running at medium speed> In this case, the oil pressure in the oil passage 54 is controlled by the flow rate control unit 50.
operates and oil is pumped out to the oil tank 16, so it is controlled at a low level, and the flow rate regulating valve 60 and reaction force limiting valve 40
is maintained in the open position. Therefore, a portion of the hydraulic pressure from the pressure oil source 10 is discharged from the flow rate control section 50 and introduced into the hydraulic reaction chambers 34...

Now, when the steering wheel 20 is rotated, the hydraulic reaction chamber 34
A steering torque proportional to the road resistance can be sensed by the hydraulic pressure of
Hydraulic pressure is generated inside, and first, the flow rate adjustment valve 60 attempts to close the port 61. In this way, the port 61 is automatically adjusted to the opening degree necessary to cover the discharge flow rate of the flow rate control section 50. However, at this time, the reaction force limiting valve 4 is still
Since 0 is in the open position, steering torque proportional to road resistance can be sensed. When the steering wheel 20 is further rotated, the oil pressure in the oil passage 54 further increases and the flow rate adjustment valve 6
0 is completely closed, and pressure oil is supplied to the oil passage 54 only through the throttle 43, but then the reaction force limiting valve 40
begins to close, and the steering torque remains constant from then on. As is clear from the above description, the range in which steering torque proportional to road resistance can be sensed increases with vehicle speed.

Furthermore, while the hydraulic power source 10 maintains a substantially constant discharge amount, the flow rate controller 50 discharges a flow rate proportional to the vehicle speed sensor by operating the flow rate adjustment valve 60. 33
The amount of oil sent to the vehicle decreases in proportion to vehicle speed.

In FIG. 2, the thin line represents the flow rate from the pressure oil source 10, and the diagonally shaded portion represents the amount of oil discharged from the flow rate control section 50. Therefore, the flow rate reaching the switching valve 30 decreases with respect to the vehicle speed, as shown by the thick line. The reason why the degree of reduction is moderated at high speeds is due to the influence of conduit resistance. The maximum flow rate for operating the power cylinder 33 is the flow rate shown by the bold line in Figure 2, so when the steering speed is increased, the tracking ability of the auxiliary power section deteriorates as the speed increases, and in extreme cases, the power There may be cases where the required flow rate in the cylinder 33 exceeds the supplied flow rate and auxiliary power cannot be obtained. This operation prevents the steering wheel from turning excessively during high-speed driving, and provides good steering stability.

According to the power steering device according to the present invention as described above, it is possible to obtain steering characteristics that are accurately proportional to the vehicle speed, and furthermore, it is possible to obtain steering characteristics that are related to the steering speed. Also, a vehicle speed sensor section and a flow rate control section 5 based on the vehicle speed sensor section.
Since high pressure does not directly act on the flow rate control valve 60, it is possible to design without much consideration of machining accuracy and strength, which is advantageous in terms of mass production. Furthermore, a reaction force limiting valve 40 and a flow rate regulating valve 60
By placing the and on the integrated spool valve,
High pressure port 6 is not only a space advantage
This brings about advantages such as the leakage loss between 1 and 41 being offset.

It goes without saying that the present invention is not limited to the illustrated embodiment; the neutral return spring of the switching valve may be of a torsion bar type, or the switching valve may be of a rotary type. The technical idea of the present invention can be applied even if
In addition, if a system in which the throttle 19 of the illustrated embodiment is not required is adopted, the branch pipe lines 63 and 62 are not provided, and a port 45 and an oil passage 46 shown by imaginary lines are provided approximately to the left of the illustrated port 40, and the oil The purpose can be achieved by discharging to the flow rate control unit 50 side via the path 46.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, and FIG. 1 is an explanatory diagram showing a hydraulic circuit of a power steering device according to the present invention, and FIG. 2 is an explanatory diagram showing a hydraulic oil flow rate characteristic of a power steering device according to the present invention. FIG. In the drawing, 10 is a pressure oil source, 15 is a supply path, 20 is a steering wheel, 25 is a wheel, 30 is a four-way switching valve, 33
34 is a power cylinder, 34 is a hydraulic reaction chamber, 40 is a reaction force limiting valve, 50 is a flow rate control unit, and 60 is a flow rate adjustment valve.

Claims (1)

[Claims] 1. A pump driven by a prime mover of a vehicle and a pressure oil source 10 having a function of adjusting the discharge flow rate to a substantially constant level, and mechanically controlling wheels 25 by rotation of a steering wheel 20
The power is configured to selectively connect and disconnect the working chamber of the power cylinder 33 that provides auxiliary power and the pressure oil source 10 by a four-way switching valve 30 operated by rotation of the steering wheel 20. In the steering system, a hydraulic reaction chamber 34 that contracts in volume against the switching operation of the four-way switching valve 30 is provided, and a flow rate control section 50 returns an oil amount proportional to the vehicle speed into the oil tank. and oil road 5
4, and from a supply path 15 that communicates the pressure oil source 10 and the four-way switching valve 30, first and second
The first branch passage communicates with the hydraulic reaction chamber 34, the second branch passage communicates with the oil passage 54, and the oil passage 5 is connected in the middle of the first branch passage.
A pressure limiting valve 40 that closes when the pressure in the second branch exceeds a predetermined value is provided, and a flow rate regulating valve 60 that closes before the pressure limiting valve 40 is provided in the middle of the second branch path. A vehicle power steering device characterized by: 2. The power steering system for a vehicle according to claim 1, wherein the pressure limiting valve 40 and the flow rate regulating valve 60 are integrated.