JP2528724B2 - Power steering system - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power steering system used in an automobile, and more particularly to a hydraulic reaction force type power steering system having steering response characteristics and vehicle speed response characteristics.

BACKGROUND ART Normally, in a hydraulic reaction force type power steering having a so-called steering response characteristic capable of correcting a steering delay, a correction pressure oil is injected into a reaction force chamber during steering, but a booster is a control valve. Since the oil passage is longer than that of, and the inertia of the link system is large, even if the control valve is operated, the operation of the booster lags behind the control valve, and as a result, the Only the control valve will operate, and the steering force has changed.

OBJECTS AND PROBLEMS OF THE INVENTION An object and object of the present invention is to provide a hydraulic reaction force type power steering system having steering response characteristics in which a change in steering force is suppressed when a steering delay is corrected.

SUMMARY OF THE INVENTION FOR OBJECTS AND PROBLEMS Content of Claimed Invention In relation to the above objects and problems, a power steering system of the present invention is a main booster for steering front wheels,
A control unit that has a pair of reaction chambers and that is arranged in a main hydraulic passage that connects the main booster to an oil pump and an oil reservoir and that controls the direction of pressure oil supplied to and discharged from the main booster. A sub booster is provided with a valve and a reaction force adjusting valve arranged in a hydraulic reaction force communication passage that connects the pair of reaction force chambers to each other.
A steering linkage for the front wheels enables steering correction of the front wheels, and a pair of electromagnetic pilot steering correction valves connect the oil pump and oil reservoir to the correction hydraulic passage and its sub-booster. It is placed in a hydraulic reaction force communication path that connects a pair of reaction force chambers to each other, and the pump port and reaction force port are always closed, and the tank port is passed through the cylinder port to the pump port.
The underlap width of the land for the port is made wider than that of the land for the reaction force port, and the cylinder port is configured to open before the reaction force port. It is being supplied to its sub-booster before it is injected into the reaction chamber of the control valve.

Description of Specific Examples Specific specific examples of the power steering system of the present invention will be described below with reference to the drawings.

The figure shows a tenth embodiment of the power steering system of the present invention applied to a truck (not shown).

The power steering system 10 has a main booster 11 for steering the front wheels 135, 136, a pair of reaction force chambers 49, 50, and an oil pump 14 and an oil reservoir.
Main hydraulic passage 23,2 connecting its main booster 11 to 15
The control valve 13 is arranged in 4 to control the direction of the pressure oil supplied to and discharged from the main booster 11 and the hydraulic reaction force communication passage 16 for communicating the pair of reaction force chambers 49 and 50 with each other. The reaction force adjusting valve 17 and a sub booster 12 connected to the steering link mechanism 129 of the front wheels 135, 136 of the front wheels 135, 136 for steering correction, and the oil pump 14 and the oil reservoir 15 of the sub booster 12 The auxiliary hydraulic passages 25, 26, 27, 28, 29, 30 and the pair of reaction force chambers 49, 50 connected to each other are arranged in a hydraulic reaction force communication passage 16 that communicates with each other, and the pump port 96 and Force port 99,1
Close 00 and pass the cylinder port 98 through the tank port 97 and the underlap width (a) of the land 105 for its pump port 96 to that of the land 106 (b) for its reaction force port 99,100. And the cylinder port 98 is widened to open the cylinder port 98 before the reaction force ports 99 and 100, and the reaction force is adjusted in response to signals from the pair of electromagnetic pilot steering correction valves 18 and 19 and the vehicle speed sensor 21 and the steering sensor 22. A control unit 20 for controlling the current flowing through the valve 17 and the electromagnetic pilot steering correction valves 18, 19, a steering wheel 118, a steering shaft 119, and a worm
Shaft 120, worm nut 121, and sector gear
124, sector shaft 125, and Pitman arm 12
6 including a drag link 127 and a knuckle arm 128, when steering, first, pressure oil is supplied to the sub booster 12 according to the steering direction, and then, for a predetermined time. After that, the steering delay is corrected by being injected into the corresponding reaction force chambers 49, 50 of the control valve 13.
It was manufactured so that the change in steering force at that time was suppressed.

The main booster 11 is manufactured as an integral type with the control valve 13 assembled, and knuckle-king pins are provided at both ends of a front axle 130 arranged in front of a chassis frame (not shown) of the truck. One of the front wheel shafts 131, 132 rotatably supported by rotatably supported front wheels 135, 136 via 133, 134, and the pitman
Arm 126, drag link 127, and knuckle
They are connected via an arm 128. Of course, its front axle 1
31,132 are connected to each other by a tie rod 137 and a pair of tie rod arms 138,139.

The main booster 11 has a cylinder bore 32 inside.
Cylinder body 31 having a pair of oil ports 36 and 37 opened at predetermined positions in the cylinder bore 32, and the control valve 13 and the cylinder body 31. Is reciprocally slidably fitted within 32 and its oil ports 36, 37
Was assembled from a rack piston 33 forming a pair of cylinder chambers 34, 35 connected to each other in the cylinder bore 32.

In addition, the main booster 11 assembled in that way is, in terms of hydraulic circuit, its oil ports 36, 37.
Is one of the main hydraulic passages 23, 24, and the supply-side main hydraulic pipe 23 connected to the oil pump 14,
The other side of the main hydraulic passages 23, 24, and the return side main hydraulic pipe 24 connected to the oil reservoir 15 is switch-connected by the control valve 13, and in terms of the link mechanism, The sector gear 124 meshes with the rack of its rack piston 33, and
The worm shaft 120 is the rack piston 33
Are fitted to each other through the recirculating ball, and the force acting on the rack piston 33 and its movement are applied to the front wheel 136 of the sector gear 124,
Transmission via sector shaft 125, pitman arm 126, drag link 127 and knuckle arm 128, and its tie rod arm 138, tie
It transmits to the front wheel 136 via the rod 137 and the tie rod arm 139, and enables the front wheels 135 and 136 to be manually steered and power steered.

The sub-booster 12 uses a single-sided rod-type double-acting hydraulic cylinder and is connected to the other 132 of the front wheel shafts 131 and 132 via a knuckle arm 129.

The sub-booster 12 has a cylinder body 38 having a cylinder bore 39 formed therein, and a pair of oil ports 44 and 45 opened at predetermined positions in the cylinder bore 39, and a cylinder body 38 thereof. Reciprocally slidably fitted in cylinder bore 39 and its oil port 4
A piston 40 having a pair of cylinder chambers 42, 43 connected corresponding to 4, 45 formed in the cylinder bore 39, and one end fixed to the piston 40, and the cylinder
The rod cover of the body 38 was assembled with a piston rod 41 whose other end can be inserted and removed.

Also, its sub-booster assembled in that way
In terms of hydraulic circuit, 12 is a supply / discharge common auxiliary hydraulic pipe 29,30 whose oil ports 44,45 are its auxiliary hydraulic passages 29,30.
Auxiliary hydraulic pipe 29,30
Is switched and connected to the supply side auxiliary hydraulic pipes 25, 26 and the return side auxiliary hydraulic pipes 27, 28 that are the auxiliary hydraulic passages 25, 26, 27, 28 by the electromagnetic pilot steering correction valves 18, 19. Of course, the supply side auxiliary hydraulic pipes 25 and 26 are branched from the supply side main hydraulic pipe 23, while the return side auxiliary hydraulic pipe 2 is provided.
7 and 28 are branched from the return main hydraulic line 24.

The sub-booster 12 thus assembled and hydraulically connected has a link mechanism in which the head cover of the cylinder body 38 is rotatably connected to the front of the chassis frame. And the other end of the piston rod 41 is attached to the knuckle arm 129.
Rotatably coupled to the piston 40 and its movement to its front wheel 136 via its knuckle arm 129, and its tie rod arm 139, tie rod. 137 and the tie rod arm 138 to transmit to its front wheel 135 and its front wheel 13
Allows correction of steering delay of 5,136.

The control valve 13 was assembled to the cylinder body 31 of the main booster 11 and manufactured into a hydraulic reaction type spool valve which is operated by the steering wheel 118 for valve switching.

This control valve 13 has a valve bore inside.
Valve body 46 forming 47 and its valve bore 47
Is reciprocally slidable in the valve bore and
Spool 4 forming a pair of reaction chambers 49, 50 at both ends of 47
8 and a pair of centering springs 51, 52 arranged in the reaction chambers 49, 50 and pushing the spool 48, and the spool 48 responds to the rotation of the steering wheel 118. Its valve bore 4
The pressure oil discharged from the oil pump 14 that is slid into the inside 7 is directionally controlled and supplied to the main booster 11, and at the same time, the pressure oil worked by the main booster 11 is directionally controlled. Return the pressure oil to the oil reservoir 15.

The valve body 46 is assembled to the cylinder body 31 of the main booster 11 and, at a predetermined position, the pump body opened to the valve bore 47.
Ports 53 and 54, tank port 55, and cylinder
Equipped with ports 56,57 and also its pump ports 53,54
Is connected to the oil pump 14 side.

Its pump ports 53, 54 and tank port 5
The ring groove 59, 60, 61 has an opening formed on the inner peripheral surface of the valve bore 47.

Also, the cylinder ports 56, 57 are
Opened in the inner surface of its valve bore 47 between 9-60 and 59-61, and the oil boost of its main booster 11
Connected to ports 36 and 37.

Further, a check valve 62 was arranged at the connection port 58. Of course, the check valve 62 is arranged in the valve chamber 63, and the valve 65 for opening and closing the valve seat 64 of the valve chamber 63 and the valve seat 64 for the valve seat 64.
It was assembled with the valve spring 66 that presses 65.

The valve body 46 also includes a pair of reaction ports 67,68 located on the end faces of the reaction chambers 49,50 and open into the valve bore 47.

The spool 48 has bores 69, 70 opened at both end faces to increase the volume of its reaction force chambers 49, 50, and at the same time, one end side of its centering springs 51, 52 is fitted to serve as a spring guide. The bores 69 and 70 are functioning.

Further, the spool 48 has a center land 71 and end lands 72, 73 formed on both sides of the center land 71 at predetermined intervals in the axial direction on the outer peripheral surface. Of course, the center land 71 and end land
72,73 as its spool 48 slides back and forth within its valve bore 47, its pump ports 53,54 to its cylinder ports 56,57, simultaneously to its tank
Switch and connect port 55 to its cylinder ports 56,57.

In addition, the spool 48 has its root screwed in and its tip through its cylinder port 57 to its oil port.
The spool slide pin 74 extended to 37 is implanted. Of course, the spool slide pin is a worm that is fitted to the worm shaft 120.
The ball 75 is fitted into the socket 123 formed at the tip of the spool slide arm 122 of the nut 121 to be coupled, and the spool 48 is attached to the steering wheel 118.
Are reciprocally slid into the valve bore 47.

Also, so that its cylinder ports 56,57
This control valve 13 attached to its main booster 11 by contacting its oil ports 36,37
Further, in terms of hydraulic circuit, the connection port 58 is the supply side main hydraulic pipe 23 to the discharge port of the oil pump 14, and the tank port 55 is the return side main hydraulic pipe 24 to the oil. Each connected to a reservoir 15, and
Its spool 48, which is slid into its valve bore 47 in response to rotation of its steering wheel 118.
Thus, the pressure oil discharged from the oil pump 14 is supplied to the main booster 11, and at the same time, the pressure oil worked in the main booster 11 is returned to the oil reservoir 15.

The oil pump 14 is driven by a diesel engine (not shown) mounted on the truck, enables supply of pressure oil to the control valve 13 by the supply-side main hydraulic pipe 23, and also supplies the control oil. Side main hydraulic piping 23, supply side auxiliary hydraulic piping 25, 26, and supply / discharge common auxiliary hydraulic piping 2
At 9,30 it is possible to supply pressure oil to its sub-booster 12, and in particular this oil pump 14 has its oil reservoir
The oil in 15 is sucked in and pressurized, and the discharge amount of the pressure oil which is almost proportional to the rotation speed of the diesel engine is obtained. Of course, the oil pump 14 is manufactured in the same structure as the oil pump used for the existing power steering, and therefore the description of the structure will be omitted.

The hydraulic reaction force communication passage 16 is connected to the control valve.
Thirteen pairs of reaction force chambers 49 and 50 are connected to each other. That is, the hydraulic reaction force communication passage 16 has one end in the reaction force port 67 opened in the one reaction force chamber 49 and the other end in the reaction force port 68 opened in the other reaction force chamber 50. By connecting them, the reaction force chambers 49 and 50 are connected to each other.

A hydraulic pipe having a predetermined inner diameter and length was used for the hydraulic reaction force communication passage 16, but the hydraulic reaction force communication passage 16 does not use such a hydraulic pipe, and the valve body 46 Alternatively, holes may be formed in the cylinder body 31 of the main booster 11.

The reaction force adjusting valve 17 has a valve bore 77 formed therein, and a valve body 76 having a pair of ports 81 and 82 opened in the valve bore 77, and an internal port 83.
And a rotary valve 78 slidably rotatably fitted in the valve bore 77, and the rotary valve 78
It is assembled from a stepping motor 79 that directly connects the motor shaft 80 to the valve 78 and slidably rotates the rotary valve 78 in the valve bore 77. Its port on passage 16
81, 82 are connected and arranged in the hydraulic reaction force communication passage 16,
Then, in the electric circuit, the stepping motor 79 is electrically connected to the output side of the control unit 20.

In this reaction force regulating valve 17 made in such a rotary type and arranged in the hydraulic reaction force communication passage 16, the rotary valve 78 is slid into the valve bore 77 by the stepping motor 79. In response to the dynamic rotation, the flow rate of the pressure oil flowing between the ports 81 and 82 is adjusted, and as a result, the pressure in the reaction force chambers 49 and 50 of the control valve 13, the so-called hydraulic reaction force, is adjusted. Is adjusted.

Further, the reaction force adjusting valve 17 is described as a rotary type, but the form is arbitrary as long as it regulates the flow rate of the pressure oil flowing between the ports 81 and 82, and for example, a spool type is used. It may be configured.

The pair of electromagnetic pilot steering correction valves 18, 19 are assembled from pilot steering correction valves 84, 85 and electromagnetic valves 86, 87, respectively. Of course, the steering correction valves 84, 85 are pilot switching valves, and The solenoid valves 86 and 87 are pilot valves.

Then, the pair of electromagnetic pilot steering correction valves 18, 19
Then, the pilot steering correction valves 84, 85 connect the supply-side auxiliary hydraulic pipes 25, 26 to the supply / discharge common auxiliary hydraulic pipes 29, 30.
In addition, the supply / discharge common auxiliary hydraulic pipes 29, 30 are switched and connected to the return side auxiliary hydraulic pipes 27, 28, and the supply side auxiliary hydraulic pipes 25, 26 are connected to the hydraulic reaction force communication passage 16 Supply side auxiliary hydraulic piping 25,2
6, return side auxiliary hydraulic piping 27, 28, supply and discharge common auxiliary hydraulic piping 2
9, 30 and the hydraulic reaction force communication passage 16, and the solenoid valves 86, 87 connect the pilot hydraulic chamber 93 of the pilot steering correction valve 84, 85 to the return side auxiliary hydraulic pipes 27, 28. Pilot pipes 88, 89 are installed.

The pilot steering correction valves 84 and 85 are spring-offset spool valves.The valve body 90 has a valve bore 91 formed therein, and the valve bore 91 is reciprocally slidably disposed to the valve body 90. A pilot hydraulic chamber 93 is provided at one end of the bore 91, and a back pressure chamber is provided at the other end of the valve bore 91.
The spool 92 and the valve spring 95, which are respectively arranged in the pilot hydraulic chamber 93 and always apply a force offset to the back pressure chamber 94 side, to the spool 92.

The valve body 90 comprises, in position, a pump port 96, a tank port 97, a cylinder port 98, and a pair of reaction force ports 99,100 opened into its valve bore 91, and The pump port 96 has its supply-side auxiliary hydraulic pipes 25 and 26, its tank port 97 has its return-side auxiliary hydraulic pipes 27 and 28, and its cylinder port 98 has its supply / discharge common auxiliary. Hydraulic piping 29,3
0, and the hydraulic reaction force communication passage 16 is connected to the reaction force ports 99 and 100, respectively.

The pump port 96 is located at the axial center of the valve bore 91, the tank port 97 is located at the back pressure chamber 94 side of the valve bore 91, and the cylinder port 98 is located at the pump port. Between 96 and its tank port 97,
And the reaction force port 99,100 is the valve bore 91.
Located on the pilot hydraulic chamber 93 side of each of them and opened to the valve bore 91,
96, tank port 97, and reaction force ports 99,100
The opening on the inner peripheral surface of the valve bore 91 is formed into the ring groove 10
They are formed at 1, 102 and 103, respectively.

Further, the valve body 90 has a pilot port 104 located in the pilot hydraulic chamber 93 and opened to the valve bore 91. Of course, the pilot pipes 88 and 89 are connected to the pilot port 104, and the pilot hydraulic pressure is transmitted from the pilot hydraulic chamber 93 to the oil reservoir 15 in accordance with the operation of the solenoid valves 86 and 87. It is made to escape via the pipes 88 and 89 and the return side auxiliary hydraulic pipes 27 and 28.

The spool 92 has a center land 105 corresponding to the pump port 96 and a center land 105 corresponding to the tank port 97 and reaction force ports 99, 100.
End lands axially spaced on both sides of the
106 and 107 are formed on the outer peripheral surface. Of course, the center land 105 and the end lands 106 and 107 always close the pump port 96 and the reaction force ports 99 and 100 to the cylinder port 98 through the tank port 97,
When the spool 92 slides into the valve bore 91, it closes the tank port 97 and closes the pump port.
96 and reaction ports 99,100 open and their pump ports
96 connects to its cylinder port 98 and reaction ports 99,100.

In particular, in this spool 92, its center land 105 for its pump port 96 and its reaction port 99,
Its end land 106 for 100 has its center land 105 underlap width (a) wider than its end land 106 underlap width (b) and its pump port 96 It is dimensioned to open before the reaction ports 99,100. Of course, the under lap widths (a) and (b) of the center land 105 and the end land 106 are the same as those of the power steering system 10.
When steering, the pressure oil is supplied to the sub booster according to the steering direction.
12 and then after a predetermined time delay to inject it into the corresponding reaction force chambers 49 and 50 of the control valve 13 to correct the steering delay while suppressing the change in steering force, Dimensioned.

Further, one end of the spool 92 is opened to the outer peripheral surface between the center land 105 and the end land 106, and the other end is opened to the end surface on the back pressure chamber 94 side. Oil hole 108 and its pilot hydraulic chamber 93
And a bore 109 opened at the end face on the side, and the volume of the pilot hydraulic chamber 93 is increased in the bore 109, and at the same time, one end side of the valve spring 95 is fitted to function as a spring guide. ing.

Furthermore, this spool 92 is
It has a throttle 110 which connects 93 to its pump port 96. Of course, the throttle 110 is formed on the spool 92 by having one end opened at one end of the oil hole 108 and the other end opened at the bore 109.

The solenoid valves 86,87, so-called solenoid pilot valves 86,87,
A valve body 112 having a valve bore 112 formed therein and having inlet and outlet ports 115, 116 opened in the valve bore 112, and reciprocally slidably fitted into the valve bore 112, And its exit port
Assembled on the valve body 111, the poppet 113 that opens and closes the 116, the valve spring 114 that is placed in the valve bore 112 and that always gives the poppet 113 a force that is offset in the direction of closing the outlet port 116. The poppet 113 against the valve spring 114
Is assembled with a solenoid coil 117 that slides the valve into the valve bore 112, and in the hydraulic circuit, the pilot piping 88, 89 has its inlet and outlet ports 11
5,116 were connected and placed in the pilot pipes 88,89 and, in the electrical circuit, the solenoid coil 117 was electrically connected to the output of the control unit 20.

The control unit 20 has the vehicle speed sensor 21
And the input side is electrically connected to the steering sensor 22, and output to the stepping motor 79 of the reaction force adjusting valve 17 and the solenoid coil 117 of the solenoid valve 86, 87 of the electromagnetic pilot steering correction valve 18, 19 The side is electrically connected, and in response to signals from the vehicle speed sensor 21 and the steering sensor 22,
Its stepper motor 79 and solenoid coil
The current flowing through the valve 117 is controlled to rotate the rotary valve 78 into the valve bore 77 of the valve body 76 to change the passage cross-sectional area of the reaction force adjusting valve 17, while the poppet 113 is moved to the valve. -Sliding inside the valve bore 112 of the body 111 against the valve spring 114 to open and close the outlet port 116 thereof, mainly for input and output circuits, memory circuits, arithmetic circuits, control circuits, and , A power supply circuit, and the power supply circuit shares the battery 140 of the truck.

The vehicle speed sensor 21 detects the traveling speed of the truck, is arranged on the output shaft of a transmission (not shown) mounted on the truck, and is electrically connected to the input circuit of the control unit 20. It was

The steering sensor 22 corresponds to the steering wheel 11
A rotation sensor for detecting the rotation speed, the rotation direction, and the rotation angle of the steering shaft 119.
The steering shaft 11 in place.
It was placed around 9 and was electrically connected to the input circuit of its control unit 20.

Next, the operation of the power steering system 10 described above will be described with reference to the traveling state of the truck.

When the diesel engine is driven and the truck is running straight, the oil pump 14 is driven by the diesel engine, so that pressure oil is discharged from the oil pump 14 and the connection port The check valve 62 of 58 is pushed open and sent to the pump ports 53, 54 of its control valve 13.

Then, the pressure oil sent to the pump ports 53, 54 has its spool 48 in the neutral position shown in FIG.
Returned to its oil reservoir 15 from port 55.

At the same time, the control unit 20 receives a signal from the vehicle speed sensor 21, controls the current flowing through the stepping motor 79 of the reaction force adjusting valve 17, and controls the reaction force chamber 49 of the control valve 13. Change the hydraulic pressure in 50,
The steering force of the steering wheel 118, that is,
It is prepared to obtain a hydraulic reaction force suitable for the traveling speed, and the control unit 20 is equipped with the vehicle speed sensor.
21 and the steering sensor 22 to input signals to selectively control the current flowing through the solenoid coils 117 of the solenoid valves 86 and 87 of the solenoid pilot steering correction valves 18 and 19 to make the solenoid valves 86 and 87 compatible. It is ready to be switched to.

In such a situation, the steering wheel of the truck must move in order to move from straight running to left turning.
When 118 is rotated to the left, there is play between its steering shaft 119, worm shaft 120, worm nut 121 with spool slide arm, and spool slide pin 74, so that spool Its control unit prior to the 48 being kinematically moved by its steering wheel 118.
The rotation sensor 22 senses the rotation of the steering shaft 119 and is electrically converted by the steering sensor 22.

In the control unit 20, the steering sensor
The electric signal is input from 22 and is calculated, and the current flowing through the electromagnetic valve 86 of the electromagnetic pilot steering correction valve 18 is determined.

Then, the determined current is
Solenoid coil of its solenoid valve 86 by unit 20
As it flows to 117, its solenoidal coil 117 is energized, which in turn causes its poppet 113 to slide into its valve bore 112 against its valve spring 114, opening its outlet port 116.

That way, when its exit port 116 is opened,
In the pilot steering correction valve 84, the oil pressure in the pilot hydraulic chamber 93 is released to the oil reservoir 15 via the pilot pipe 89, the return side auxiliary hydraulic pipe 27, and the return side main hydraulic pipe 24. The hydraulic pressure in the back pressure chamber 94, the so-called back pressure, causes the spool 92 to slide into the valve bore 91 against the valve spring 95, first opening the pump port 96. The cylinder port 98 is contacted and at the same time the tank port 97 is closed and shut off from the cylinder port 98.

As the pump port 96 is connected to the cylinder port 98, the pressure oil discharged from the oil pump 14 is supplied to the supply-side main hydraulic pipe 23, the supply-side auxiliary hydraulic pipe 25, and It is supplied to the cylinder chamber 42 of the sub-booster 12 through the supply / discharge common hydraulic pipe 27.

Then, in the sub-booster 12, the piston 40 is slid into the cylinder bore 39 by the pressure oil, and the piston rod 41 is pushed out of the cylinder body 38 by the rod cover. Be done.

In that way, its knuckle arm 129 is swung by its sub-booster 12, as its piston rod 41 is pushed out of its cylinder body 38.
Then, the front wheels 136 start steering to the left.

In that way, when the front wheels 136 start turning to the left,
Its tie rod 137 and tie rod arm 138,1
The front wheel 135 also starts turning to the left via 39, and the steering delay is corrected.

And its front wheels 135,13 by its sub booster 12
The steering of 6 is transmitted to the rack piston 33 of the main booster 11 via the drag link 127, the pitman arm 126, and the sector gear 124.

Then, in the pilot steering correction valve 84, the time corresponding to the difference between the under lap width (a) of the center land 105 and the under lap width (b) of the end land 106 is delayed, and the anti-rotation time is delayed. The power ports 99,100 are opened and contacted to their pump ports 96.

As such, its pump port 96 is its reaction force port.
When contacted to 99, 100, the pressure oil discharged from the oil pump 14 passes through the supply-side main hydraulic pipe 23, the supply-side auxiliary hydraulic pipe 25, and the hydraulic reaction force communication passage 16 to the control valve 13 of the control valve 13. It is injected into the reaction chamber 49.

In the control valve 13 infused with the pressure oil, the spool 48 is slid into the valve bore 47, the pump port 54 is opened and communicated with the cylinder port 57, and at the same time, the The tank port 55 is opened and communicated with its cylinder port 56, and its pump port 53 is closed.

The pump port 54 is connected to the cylinder port 57 so that the pressure oil discharged from the oil pump 14 flows through the supply side main hydraulic line 23 and vice versa at its connection port 58. The stop valve 62 is pushed open to flow to its pump port 54, and then supplied to the cylinder chamber 43 of the main booster 11 via its cylinder port 57 and oil port 37.

In the main booster 11, when the rack piston 33 is slid into the cylinder bore 32 by the pressure oil and the steering delay is corrected by the sub booster 12, the rack booster 33 is operated by the sub booster 12. The change in steering force
It was suppressed by the pressure oil injected into the reaction force chamber 49 of the control valve 13 after a predetermined time delay with respect to the sub booster 12.

When the truck is traveling to the right, the power steering system 10 operates in reverse to the above-mentioned operation.

Next, the reaction force adjustment performed in the power steering system 10 during steering by the power steering system 10 will be described.

First, when the truck is traveling at a low speed, the control unit 20 inputs a signal from the vehicle speed sensor 21, calculates based on the input signal, and controls the stepping motor 79 of the reaction force adjusting valve 17 to perform the calculation. Since the current flowing is determined and the current flowing through the stepping motor 79 is controlled, in the reaction force adjusting valve 17, the rotary valve 78 is slidably moved into the valve bore 77 by the stepping motor 79. Is rotated. However, in this case, the rotary valve 78 is operated by the stepping motor 79 so that the relative displacement between the ports 81, 82 of the valve body 76 and the internal port 83 of the rotary valve 78 is small. It is slidably rotated in the bore 77, and the passage sectional area of the reaction force adjusting valve 17 is wide.

In such a state, its steering wheel 118
When it is rotated, in its control valve 13, its spool 48 becomes its steering shaft 11
9, a worm shaft 120, a worm nut 121 with a spool slide arm, and a spool slide pin 74, which is slid into its valve bore 47 by its steering wheel 118 and its spool 48.
The pressure oil flows through the hydraulic reaction force communication passage 16 and is moved between the reaction force chambers 49 and 50.

However, since the passage cross-sectional area of the reaction force adjusting valve 17 is narrowed down, the pressure drop by the reaction force adjusting valve 17 becomes small, and the pressure difference between the reaction force chambers 49, 50 becomes small. The pressure oil flowing between the reaction force chambers 49 and 50 does not give a large resistance to the movement of the spool 48, in other words, steering during low speed traveling is performed with a small operating force. Of course, when the truck is stationary, the internal speed of the internal port 83 is 8 because the running speed is zero.
Its rotary valve 78 in its stepper motor 79 in a position substantially aligned with 1,82.
Since it is slidably rotated inside 77, the pressure difference between the reaction force chambers 49 and 50 is extremely small, and as a result, the stationary bearing is
It is performed with extremely small operating force.

Also, when the truck is traveling at high speed, the control unit 20 inputs a signal from the vehicle speed sensor, calculates based on the input signal, and then calculates the reaction force adjusting valve.
Since the current flowing to the stepping motor 79 of 17 is determined and the current flowing to the stepping motor 79 is controlled,
In the reaction force adjusting valve 17, the rotary valve 78
Is slidably rotated by its stepper motor 79 into its valve bore 77. However, in this case, the rotary valve 78 is operated by the stepping motor 79 so that the relative displacement between the ports 81, 82 of the valve body 76 and the internal port 83 of the rotary valve 78 is large. It is slidably rotated in the bore 77, and the passage cross-sectional area of the reaction force adjusting valve 17 is adapted to the vehicle speed in this case and narrowed.

In such a state, the steering wheel 118
When the control valve 13 is rotated, its spool 48 becomes its steering wheel 11
Corresponding to the rotation of 8 is slid into the valve bore 47,
Along with the movement of the spool 48, the pressure oil flows through the hydraulic reaction force communication passage 16 and is moved between the reaction force chambers 49 and 50.

However, since the reaction force adjusting valve 17 has a large passage cross-sectional area, the pressure drop due to the reaction force adjusting valve 17 becomes large, and the pressure difference between the reaction force chambers 49, 50 becomes large. The pressure oil flowing between the reaction force chambers 49 and 50 becomes a great resistance against the movement of the spool 48.

In this way, a relatively large operating force was required for steering during high-speed traveling, and steering stability was ensured.

Convenience and Benefits of the Invention As will be understood from the above, the power steering system of the present invention has a main booster for steering the front wheels, a pair of reaction force chambers, and an oil pump and an oil reservoir. A control valve that is arranged in the main hydraulic passage that connects the main booster and controls the direction of the pressure oil that is supplied to and discharged from the main booster, and a hydraulic reaction force communication passage that connects the pair of reaction force chambers to each other. A sub-booster is connected to the steering link mechanism of the front wheel to enable steering correction of the front wheel, and a pair of electromagnetic pilot steering correction valves are provided for the oil pump. And an auxiliary hydraulic passage that connects the sub booster to the oil reservoir and a hydraulic reaction passage that connects the pair of reaction chambers to each other. Always close the pump port and the reaction port and let the pump port
Since the underlap width of the land for the port is made wider than that of the land for the reaction force port and the cylinder port is opened before the reaction force port, In the steering system, the pressure oil flowing between the reaction force chambers via the hydraulic reaction force communication passage is throttled and adjusted by the reaction force adjustment valve according to the vehicle speed, speed sensitive characteristics are obtained, and steering stability is secured, Further, before the steering of the front wheels is performed by the main booster, the steering delay is corrected by the sub booster to which the pressure oil is supplied, and at that time, with respect to the sub booster. The pressure oil injected into the reaction force chamber of the control valve corresponding to the sub booster after a predetermined time delay suppresses the change in the steering force by the sub booster, thus The steering delay can be corrected while suppressing the change in the steering force, that is, the steering response characteristic is improved, and further, such steering response characteristic has a speed sensitive characteristic. It can be easily applied to the car and becomes very useful and practical for automobiles.

Relationship between the Invention and Specific Examples As described above, from the specific examples of the present invention described with reference to the drawings, various design modifications can be made to those having ordinary knowledge in the technical field to which the present invention belongs. And changes are easily made, and moreover, the content of the present invention is essential for the establishment of an invention that accomplishes the subject of the invention, and is derived from the technical essence of the invention, which is the nature of the invention. And then it is easily replaced by an objectively recognized embodiment.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a specific example of the power steering system of the present invention applied to a truck, and FIG. 2 is a schematic diagram of a pilot steering correction valve used in the power steering system shown in FIG. It is an expanded sectional view. 11 ... Main booster, 12 ... Sub booster, 13 ... Control valve, 16 ... Hydraulic reaction force communication passage, 17 ... Reaction force adjusting valve, 18,19 ... Electromagnetic pilot steering compensation valve, 31 ... Cylinder body, 33 … Rack piston, 38… Cylinder body, 40… Piston, 41… Piston rod, 46… Valve body, 48… Spool, 49,50… Reaction chamber, 51,52… Centering spring, 84,85 … Pilot steering correction valve, 86,87… solenoid valve.

Claims (1)

(57) [Claims] 1. A main booster for steering a front wheel, a pair of reaction chambers, and a main booster arranged in a main hydraulic passage connecting the main booster to an oil pump and an oil reservoir. A control valve for controlling the direction of pressure oil supplied to and discharged from the engine, and a reaction force adjusting valve arranged in a hydraulic reaction force communication passage for communicating the pair of reaction force chambers with each other, the sub-booster comprising: A pair of electromagnetic pilot steering compensation valves are coupled to the front wheel steering linkage to enable steering compensation of the front wheels, and a pair of electromagnetic pilot steering compensation valves connecting the sub-booster to the oil pump and oil reservoir and its auxiliary hydraulic passage. It is placed in a hydraulic reaction force communication passage that connects a pair of reaction force chambers to each other, and the pump port and reaction force port are always closed to close the cylinder port. Through the tank port, the underlap width of the land for the pump port is made wider than that of the land for the reaction port, and the cylinder port is opened before the reaction port. A characteristic power steering system.