JPS61291271A - Power steering system - Google Patents

Abstract

PURPOSE:To reduce a pump load by controlling oil pressure which is applied to a reaction chamber of an oil pressure reaction mechanism in a device equiped with both an oil pressure controlling mechanism controlling the feeding and discharging of working oil to a power cylinder and the oil pressure reaction mechanism. CONSTITUTION:A worm shaft 8 is rotatably fitted in a housing 5 which is connected to a power cylinder, and a stubshaft 29 as an input member is connected to the other end of the shaft 8 through a torsion bar 42. And both an oil pressure controlling mechanism 10 which controls the feeding and discharging of working oil to two working chambers 3 and 4 of the power cylinder. And an oil pressure reaction mechanism 20 facing the said mechanism 10 is provided on the other end side of the worm shaft 8. And a bypass hydraulic line 49 is branched from a hydraulic pressure line 47 of a pump P so as to be connected with a hydraulic return line 48. And both a variable throttling mechanism 50, the opening area of which varies depending on a car speed, and a fixed restrictor 51 are connected to the halfway of the said bypass line. And the said bypass line 49 between both of the mechanism 50 and 51 is communicated to reaction chamber 31 and 32 through a hydraulic line 52.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a power steering device.

BACKGROUND ART In general, a hydraulic control mechanism selectively controls the supply and discharge of hydraulic oil to two working chambers in a cylinder separated by a piston to assist the steering operation of a locking member connected to the piston. A power steering system requires sufficient steering assist force when the vehicle is running at low speeds or when the vehicle is turning off. From the standpoint of improving stability, Hado does not require an auxiliary steering force. In other words, it is preferable that the handlebar load is light when the vehicle is running at low speeds or when the vehicle is running at a low speed, and that the handlebar load is heavy when the vehicle is running at high speeds.

Therefore, in order to respond to such requests, the applicant of this case,
For example, it has been proposed in the power steering system ff' described in Japanese Patent Application No. 59-231973. This power steering device includes a bypass path that branches from a supply path 70λ for feeding hydraulic oil discharged from a pump to two working chambers separated by a piston and is connected to a hydraulic oil discharge path. A fixed throttle mechanism that allows a limited flow of hydraulic oil from the supply path toward the bypass path, and a variable throttle that changes the opening area of the bypass path downstream of the fixed throttle mechanism in accordance with vehicle speed. and a hydraulic reaction force mechanism that brakes the movement of the spool valve constituting the hydraulic control mechanism in accordance with the differential pressure between the hydraulic pressure generated in the fixed throttle mechanism and the hydraulic pressure generated in the variable throttle mechanism. This is the configuration provided.

A conventional power steering system having such a configuration has a fixed throttling mechanism installed in the middle of a bypass path that branches from a hydraulic oil supply path, and a spool valve that configures a pressure control mechanism for the bypass path that moves according to vehicle speed. This allows the brakes to be applied gradually, allowing the steering wheel load to be smoothly increased or decreased in accordance with vehicle speed.

Problems to be Solved by the Invention However, in the conventional power steering system, when the vehicle is in a low speed state, the variable throttle mechanism is loosened so that the hydraulic reaction force mechanism does not operate.

Then, the flow rate in the bypass path increases and the flow rate in the supply path decreases. For this reason, the pressure in the working chamber within the cylinder does not rise sufficiently, and the steering assist force cannot be fully exerted.

However, when the variable throttle mechanism is throttled down, the pressure in the hydraulic reaction force mechanism increases, which also hinders steering. On the other hand, when the vehicle is in a high-speed state, it is desirable to have a large steering reaction force from the standpoint of steering stability, so a variable throttle mechanism is used to throttle the vehicle. Since the pressure inside is dropping, the downstream variable throttle restricts it more strongly to increase the pressure introduced into the hydraulic reaction force mechanism. For this reason, the flow i in the bypass path decreases significantly, and the flow rate in the supply path increases accordingly. Along with this, the flow resistance in the hydraulic control mechanism increases, the pressure in the supply path increases, the pump discharge pressure increases, and the pump has to do extra work, causing problems such as energy loss. there were.

Means for Solving Problems In order to solve these conventional problems, the present invention
When a relative rotational displacement occurs between an input member driven by the operating force of the steering wheel, an output member that drives the steering member that applies steering force to the wheels, and these input members and the output member,
The hydraulic control mechanism selectively controls the supply and discharge of hydraulic oil to two working chambers in a cylinder separated by a piston to assist the steering operation of a steering member connected to the piston, and also controls the hydraulic fluid according to the vehicle speed. In a power steering device equipped with a hydraulic reaction force mechanism that provides a reaction force when the hydraulic control mechanism moves, the hydraulic oil discharged from the pump is operated by branching from a supply path for feeding the two working chambers. A bypass path connected to an oil discharge path is provided, two throttle mechanisms are provided in the middle of this bypass path, and at least the throttle mechanism on the upstream side changes the opening area of the bypass path in accordance with the vehicle speed. In addition to the throttle mechanism, an oil path branching from the bypass path between these two throttle mechanisms is provided,
This is configured to communicate with the hydraulic reaction force mechanism.

Operation: The power steering system of the present invention having such a configuration operates the variable throttle mechanism provided on the upstream side of the bypass passage to strengthen the throttle and supply the power to the hydraulic control mechanism when the vehicle is running at low speeds. By increasing the flow rate and increasing the pressure in the working chamber in the cylinder, the auxiliary force is increased, and at the same time, the pressure downstream of this variable throttle mechanism is lowered to reduce the pressure of the hydraulic reaction force mechanism, thereby reducing the reaction force. do. Also, when the vehicle is at high speed, the throttle of the variable throttle mechanism is weakened to increase the bypass flow rate l, thereby reducing the flow t'' in the supply passage, which causes an increase in the supply passage and a decrease in the discharge pressure. This reduces the load on the pump and eliminates energy loss.Also,
As the bypass flow rate increases, higher pressure is introduced into the hydraulic reaction force mechanism by the action of the downstream throttling mechanism, increasing the steering reaction force and stabilizing the steering.

Embodiments of the present invention will be described below based on the drawings.

FIG. 1A is a cross-sectional view showing a first embodiment of the power steering device according to the present invention, and FIG. 2 is a cross-sectional view taken along the line ■--■ in FIG.

As shown in FIG. 1A and FIG. 2, a piston 1 is installed in a cylinder 2 and separated into two working chambers 3.4, and the piston 1 is connected to a sector shaft 40, which is a steering member that drives a steering link. has been done. A housing 5 that opposes one end of the cylinder 2 has a supply hole 6 for supplying and discharging hydraulic oil from the pump P to the two working chambers 3 and 4.
A worm shaft 8 serving as an output member for driving a sector shaft 40 that provides steering force to the wheels is rotatably housed in the housing 5 via a bearing 9. . This worm shaft 8
One end of the piston 1 is screwed into the piston 1 via a ball screw 41. A stub shaft 29, which is an input member connected to a steering wheel 43, is connected to the other end of the worm shaft 8 via a replaceable torsion bar 42. Further, on the other end side of the worm shaft 8, a hydraulic control mechanism 10 is provided which selectively controls the supply and discharge of hydraulic oil to the two working chambers 3 and 4 to assist the steering operation of the sector shaft 40. ing. As shown in FIG. 1A, this hydraulic control mechanism 10c includes a cylindrical valve accommodating portion 11 having a predetermined annular groove on its inner peripheral surface, and a spool slidably inserted into the valve accommodating portion 11. Three valve chambers 13° are formed in the valve-shaped chamber 11 by four land portions formed at predetermined intervals in the axial direction on the outer circumference of the spool valve 12. 14 and 15 are formed. Among these, valve chambers 13.14u located on both sides,
An annular groove 5aζ formed between the housing 5 and the worm shaft 8 communicates with each other via a supply port 16, 17'. Of these, the valve chamber 13c communicates with one working chamber 3 via an oil passage 18, and the valve chamber 14d communicates with the other working chamber 4 via an oil passage 19'. Also,
Among the valve chambers 13, 14 and 15, a valve chamber 15 located in the center communicates with the discharge hole 7 via an oil passage material, and is connected to one stub shaft bin provided on the stub shaft 4. When the spool valve 12 is driven by 30a and slides in the axial direction within the valve-shaped chamber 11, the valve chamber 15
At the same time, the fluid passage area from the valve chambers 13 and 14 to the valve chambers 13 and 14 increases or decreases, and the corresponding fluid passage area from the supply ports 16 and 17 to the valve chambers 13 and 14 decreases or increases. ing.

On the other hand, as shown in FIG. 1A of H1 on the other i side of the worm shaft 8, a hydraulic control mechanism is provided facing the hydraulic control mechanism 10. This hydraulic reaction force mechanism 20 includes a control cylinder 21 fixed to the worm shaft 8, and sealing plates 22, 22 that close the openings at both ends of the cylinder 21.
and 2 slidably inserted into the control cylinder 21.
Two pistons 23, 24,! , reaction force chambers 31 and 32 separated between the pistons 23 and 24 and the sealing plates 22 and 22, and the stub shaft 29.
1:l- A stub shaft pin 30 is implanted and is similarly implanted at a diametrically opposing position of the hydraulic reaction force mechanism 10'& the driving stub shaft pin 30 & facing between the pistons 23 and 24. b, this stub shaft pin 30bl: a set spring 25, 26 that constantly urges the piston 23, 24', and a set spring 25, 26 that is attached to the inner periphery of the cylinder 21 so that the pistons 23, 24 move toward each other. It is composed of a stopper IJ ring γ, 28 that restricts movement.

The reaction force chambers 31, 32fl, the openings 33° of these through holes, and an annular oil passage formed between the worm shaft 8 and the housing 5 communicate with an oil passage 38. In addition,
A stub shaft insertion chamber 45 formed between the pistons 23 and 24 communicates with the hydraulic oil discharge hole 7 via an oil passage 46.

Further, the pump P and the two working chambers 3 and 4 are connected by a supply path 47, and the hydraulic control mechanism 10 is provided in the middle of this supply path 47, and the hydraulic fluid discharged from the pump P is transferred to each working chamber. The feed is switched to 3.4.

A bypass path 49 connected to a hydraulic fluid discharge path branches off from this supply path 47, and in the middle of this bypass path 49, an opening area of the bypass path 49 is set on the upstream side depending on the vehicle speed. A fixed diaphragm mechanism 51 with a constant opening area is provided between the variable diaphragm mechanisms that change the diaphragm mechanism and on the downstream side, respectively. A branch path 52 is provided from the bypass k1849 between the variable throttle mechanism and the fixed throttle device n1, which communicates with the oil passage blade provided in the housing 5. Thus,
Hydraulic pressure is introduced into the reaction force chambers 31 and 32 of the hydraulic reaction force mechanism 20, and the stump shaft bin 30b receives a reaction force in accordance with this oil pressure. The solenoid 5Qa included in the variable throttle mechanism 505 is operated by the control output of an electronic controller 55 that is controlled based on a vehicle speed signal from a vehicle speed sensor and a steering wheel load select switch 54.

Next, the operation of the power steering device according to this embodiment having such a configuration will be explained.

First, a case where the vehicle is running at a low speed will be described.

In this case, the vehicle speed sensor detects the low-speed running state, and the controller 55 uses the vehicle speed signal to control the solenoid 50.
B is activated, and the variable throttle valve 50b constituting the variable throttle mechanism 50 is throttled t'5r: the hydraulic oil flowing through the i-bypass passage 49 to the tank Reduce emissions. 1, the flow loss in the supply path 47 is small and the high pressure is applied to the hydraulic control mechanism 10.
It acts on either the working chamber 3 or 4 in the cylinder 2 through the cylinder 2 to obtain a large steering assisting force. On the other hand, since the hydraulic pressure generated between the variable throttle mechanism and the fixed throttle mechanism 51 is small, from the branch passage 52 to the oil passage side, the annular oil passage n and the through hole 3.
3, 34 to each reaction force chamber 31 in the control cylinder 21.
, 32 becomes smaller, and the steering reaction force becomes smaller. Thus, the steering wheels 43 can be operated with small force at low speeds.

Next, a case where the vehicle transitions from a low-speed running state to a high-speed running state will be described.

In this case, the controller 55 operates the solenoid 50a by detecting that the vehicle speed center t53 has shifted from the low-speed running state to the high-speed running state and uses the corresponding vehicle speed signal to reduce the throttle amount of the variable throttle valve 5Qb. The discharge f of the hydraulic oil passing through the bypass passage 49 and heading toward the tank T is increased, and this flow rate is mainly regulated by the fixed throttle mechanism 51 on the downstream side.

Then, the flow rate in the supply path 47 decreases, the flow resistance in the hydraulic control mechanism 10 becomes small, the pressure in the supply path 47 increases, and the pump discharge pressure does not increase significantly. Defense I
):, kireru. In this way, the pump PH does not do any extra work and there is less energy loss.

On the other hand, since the oil pressure generated upstream of the fixed throttle mechanism 51 is almost close to the oil pressure of the supply path 47, the pressure of the hydraulic fluid introduced from the branch path 52 into each of the reaction force chambers 31 and 32 is relatively high, and the steering The reaction force becomes large. Thus, at high speeds, the operation of the steering wheels 43 becomes moderately heavy, and the steering becomes stable.

FIG. 1B is a sectional view showing a second embodiment of the power steering device according to the present invention.

The embodiment shown in FIG. 1rlB is different from the first embodiment in that the downstream throttle mechanism among the two throttle mechanisms provided in the bypass passage 49 is also a variable throttle mechanism 57.
Similarly to the variable throttle mechanism group on the upstream side, this is controlled by the output of the electronic controller 55 based on the input from the vehicle speed sensor and the steering wheel load selection switch.

In addition, in these embodiments, the case where the present invention is applied to a recirculating type power steering device using eight worm shafts as output members has been described. Used, rack, and.

The present invention may be applied to a pinion type power steering device.

Effects of the Invention As is clear from the above explanation, according to the present invention, a supply path for hydraulic oil from the pump to the working chamber and a discharge path to the tank are provided, and two throttle mechanisms are provided in the middle of this bypass path. At least one of the upstream throttle mechanisms is a variable throttle mechanism that changes the opening area of the bypass passage depending on the vehicle speed, and an oil passage is provided that branches from the bypass passage between these two throttle mechanisms. is communicated with the hydraulic reaction force mechanism, so when the vehicle is at low speed, by greatly restricting the upstream variable restrictor g#, the pressure to the working chamber is increased and the pressure to the reaction force chamber is reduced. When the vehicle is at high speed, the variable throttle mechanism on the upstream side is loosened to increase the flow rate in the bypass passage, and the flow rate in the bypass passage is increased mainly by the downstream throttle mechanism. By restricting the flow rate, a relatively high pressure is introduced into the reaction force chamber to increase the steering reaction force, thereby stabilizing the steering. At the same time, the variable throttle mechanism is loosened to compensate for the increased flow rate in the bypass passage. The flow rate in the supply channel is reduced, which allows the pressure in the supply channel to increase, reducing the load on the pump and eliminating energy loss.

[Brief explanation of drawings]

Figure 1A is a vertical cross-sectional view including a block diagram showing the first embodiment of the power steering device according to the present invention, Figure @IB is a similar vertical cross-sectional view showing the second embodiment, and Figure 2 is a similar vertical cross-sectional view of the second embodiment. FIG. 2 is a cross-sectional view showing the power steering device. 1... Piston, 2... Cylinder, 3, 4... Working chamber, 8... Worm shaft (output member), 1o.
...Hydraulic control mechanism, 12...Spool valve, 2o...
Hydraulic reaction force mechanism, 29... stub shaft (input member)
, 4o... sector shaft (steering member), 43...
Steering wheel, 47... Supply path, Induction... Discharge path, 49...
・Bypass path, criminal... (upstream side) variable throttle mechanism, 5
1... (downstream side) fixed throttle mechanism, 57... (downstream side) variable throttle mechanism, P... pump. 2 people outside

Claims (1)

[Claims] (1) When a relative rotational displacement occurs between an input member driven by the operating force of the steering wheel, an output member that drives the steering member that applies steering force to the wheels, and these input members and the output member, a hydraulic control mechanism that selectively controls the supply and discharge of hydraulic oil to two working chambers in a cylinder separated by a piston to assist the steering operation of a steering member connected to the piston, and a hydraulic control mechanism that assists the steering operation of a steering member connected to the piston; In a power steering device equipped with a hydraulic reaction force mechanism that applies a reaction force when the hydraulic control mechanism moves, the hydraulic oil discharged from the pump is branched from a supply path for supplying the two working chambers. A bypass path connected to the oil discharge path is provided, two throttle mechanisms are provided in the middle of the bypass path, and at least the upstream throttle mechanism is a variable throttle mechanism that changes the opening area of the bypass path in accordance with the vehicle speed. What is claimed is: 1. A power steering device characterized in that an oil passage branching from a bypass passage between these two throttle mechanisms is provided, and the oil passage is communicated with the hydraulic reaction force mechanism.