FR2537936A1 - ASSISTED STEERING SYSTEM - Google Patents

Abstract

ASSISTED STEERING SYSTEM. THE SYSTEM, TO BE USED ON A VEHICLE, INCLUDES AN ASSISTANCE CYLINDER 3 TO WHICH THE HYDRAULIC FLUID IS DELIVERED FROM A PUMP 1 DRIVEN BY A MOTOR, THE FLUID PASSING THROUGH A SWITCHING VALVE 2. THE SYSTEM INCLUDES A VALVE 11 OF PRESSURE CONTROL MOUNTED ON A BYPASS LINE 8A WHICH EXTENDS BETWEEN HIGH PRESSURE LINE 8, LEADING FROM PUMP 1 TO SWITCH VALVE 2, AND REACTION PISTON 5 OF SWITCH VALVE 2, VALVE 11 OF PRESSURE CONTROL PRESENT A DEGREE OF OPENING WHICH IS CONTROLLED BY A PILOT PRESSURE, AND A PILOT PRESSURE CONTROL VALVE 12 PROVIDED ON A LOW PRESSURE DUCT 8D, ONE END OF WHICH IS CONNECTED BY A PORT 7B TO THE BYPASS DUCT 8A , DOWNSTREAM OF PRESSURE CONTROL VALVE 11, AND WHOSE OTHER END IS CONNECTED TO A FLUID TANK 4.

Description

The invention relates to a steering system

  equipped with a power cylinder, or

  this, to which hydraulic fluid is supplied from a motor driven oil pump, which fluid is supplied through a switching valve. Known power steering systems are unsatisfactory, in many respects they do not allow

  not meet many of the requirements of

  In particular, they do not allow a light action

  when the vehicle is traveling at low speed; they present

  lack of an adequate response and a lack of

  bility in a straight line when the vehicle is traveling at a speed or average / high speed; they do not allow a smooth return

  over the entire speed range; they require a rotation

  steering wheel excessively in case of danger, at high speed; they are an unreliable operation they do not give any security in case of failure of one of their organs; and they consume a lot of energy. The object of the invention is to provide an improved power steering system which avoids the disadvantages of known systems and which, in operation, satisfies the required requirements.

  This goal is achieved by a steering system

  according to the invention which comprises: an input shaft.

  connected to a steering wheel, a torsion bar

  to transmit the rotation of the input shaft to an output shaft; a fluid line change valve arranged to change a fluid passage in response

  at a difference in the angle of rotation between the trees of

  trea and exit; a power cylinder connected to the armature

  exit number; a high pressure fluid line is through which the hydraulic fluid / delivered from an oil pump to the power cylinder through said valve; a first low pressure fluid line through which the hydraulic fluid returns to an oil tank, from the power cylinder, through

  said valve; a reaction piston disposed between the

  input and output bores and arranged to provide a force decreasing the difference in rotation angles between the input and output shafts; a bypass fluid conduit extending from the high fluid line

  pressure to the reaction cylinder; a control valve

  pressure device disposed on the bypass fluid line for controlling the pressure of the hydraulic fluid

  to ensure that it does not exceed a predetermined maximum value

  born; a second low pressure fluid line, one end of which is connected by an orifice to the bypass fluid line downstream of the pressure control valve and the other end of which is connected to the oil tank; a pilot pressure control valve disposed on the second low pressure fluid line for controlling a pilot pressure downstream of the orifice; and 1 $ 5 a pilot fluid pipe transmitting pressure

  pilot to the pressure control valve.

  We will understand the invention when reading the

  description which follows and with reference to the drawings

annexed in which:

  Fig 1 is a hydraulic diagram showing a system

  power steering time according to the invention; Fig 2 is a longitudinal section of a switching valve of the system of Fig 1; Fig 3 is a section along line III-III of Fig 2; Fig 4 is a longitudinal section taken along the line IV-IV of Fig 5 and shows a stop valve; Fig 5 is a longitudinal section along the line VV of Fig 3 and shows the stop valve, a pressure control valve and a pilot pressure control valve Fig 6 is a longitudinal section taken along the line VI-VI of Fig 5 and shows the pressure control valve Fig 7 is a section along line VII-VII of Fig 2; Fig 8 is a graphical representation of the relationship-existing between the vehicle speed and a coefficient; and FIG. 9 is a graphical representation showing the relationship between rotational speed

engine and a coefficient.

  FIG. 1 diagrammatically shows a power steering system according to the invention.

  The system comprises an oil pump 1 arranged to be

  born by a motor (not shown), a rotary valve

  2 fluid line change, a cylinder of

  3, an oil tank 4, a reaction piston 5 provided around the rotary valve 2, a chamber 6 defined

  behind the piston 5, a pipe 8 of high pressure fluid

  extending between the pump 1 and the valve 2, a conduction

  9 of low pressure fluid extending between the rotary valve 2 and the tank 4, a passage hole 7 provided on the pipe 8 of high pressure fluid, a fluid pipe 8a extending between the pipe of fluid 8 at high pressure and the piston chamber 6, a branching fluid line 8b extending between the pipe 8a and the high pressure pipe 8, downstream of the orifice 7a, and a valve of stop 10, normally open, arranged on

bypass line 8 b.

  A valve 11 for controlling the pressure is provided on the pipe Ba. A pipe 8c is connected, via an orifice 7c, to the pipe 8a, downstream of the pressure control valve 11. A pressure control valve 12. pilot for the pressure control valve 11 is provided on the pipe 8c A pipe 8d extends between the pilot pressure control valve 12 and the low pressure pipe 9 The pipe 8d is connected to the pipe 8c upstream of the pilot pressure control valve 12 through an orifice 7d and to the pipe 8a downstream of the

  pressure control valve 11, through an orifice 7b.

  The system also comprises a detector 13 capable of measuring the speed of the vehicle, a detector 14 capable of measuring the speed of the engine, an ignition coil 14a, a distributor 1-4b and a control device 15 A control signal , obtained by calculation, is transmitted to a solenoid 12 c of the pilot pressure control valve 12

  to adjust the degree of opening thereof.

  The rotating valve 2 of driving switching

  fluid is shown by way of example in FIG.

  It comprises an envelope 16 enclosing a support 17 for a rack 18 cooperating with a pinion 19, an entry shaft 2a and a torsion bar 21 connecting the input shaft 2a and the pinion 19 A body of Pump 2b surrounds the input shaft 2a and a valve sleeve 2c surrounds the valve body 2b Hydraulic fluid, coming out of the oil pump 1, passes through the high pressure pipe 8, an annular groove 22a, a passage 23a, a chamber 24, the pipe 9 at low pressure, the tank 4 and returns to the pump 1 If a steering wheel (not shown) is turned to the right to drive the input shaft 2 also to the right, the high pressure line 8 is connected to the passage 23b of the sleeve 2c through a passage in the input shaft 2a, and the hydraulic fluid is delivered from the oil 1, to one of the chambers of the cylinder 3 through the high pressure line 8, the annular groove 22a and the pitch wise 23b to move the piston of the cylinder 3 to the right, while the hydraulic fluid in the other chamber of the cylinder 3 returns to the tank 4 through a passage 23c, the chamber 24 and the low pressure pipe 9 Au contrary, if the steering wheel

  is turned to the left to turn the tree of

  2 also to the left, the high-pressure

  8 is connected to the passage 23c of the sleeve 2c across

  the passage made in the shaft 2a, the fluid being supplied

  neither, from the pump 1, to the other chamber of the cylinder

  3 through the high pressure line 8, the annular groove

  22a and 23c to move the piston of the cylinder.

  lindre 3 to the left, while the fluid in the other chamber of the cylinder 3 returns to the tank 4 through the passage 23 b, the chamber 24 and the conduit to

low pressure 9.

  FIGS. 4 and 5 show, by way of example, the shut-off valve 10. This valve comprises a valve body 1 Oa, a shut-off member 1 Ob attached to the valve casing 16, and a compression spring '10 c disposed between the valve body 1 Oa and the stop element l Oc The spring

  1 oc urges the valve body l Oa to maintain normal

  The valve body 1 Oa can be moved in a direction shown in S. FIGS. 5 and 6 illustrate, by way of example, the control valve 11 of the valve 8. pressure This valve is disposed on the pipe 8a and defines thereon an upstream or inlet side Pl and a downstream or outlet side o Pc, to control the passage section between the sides Pl and Pc The valve 11 comprises a valve body 11a, a

  1 lb. valve sleeve, a shut-off element securing it to the

  a valve spring 16, a compression spring lic disposed between the valve body 1a and the stop element 1a, and a compression spring 1d disposed between the valve body 11a and a valve sleeve 12b of the pilot pressure control valve 12 The valve sleeve 11b

  comprises, on its outer peripheral surface, a step

  wise 24 a connected to the pipe 8 a (Pi), as shown in FIGS. 6 and 7, a passage 24 b (FIGS. 5 and 7) which forms part of a conduit 8 f of the pilot circuit (FIG. 1),

  and a passage 24c (Figs 5 and 7) connected to the passage 8a (Pc).

  The valve body 11a also has on its periphery

  outside, a passage 25 connected to passage 24a and

  a passage 25b connected to the passage 25a through the passage 24c.

  The passage 25b is connected, through the orifice 7c, and the conduit 8f of pilot fluid (or passage 24b) to that of the sides of the valve 1 l in which is located the spring llc, and that of sides of the stop valve 10 in which is disposed a compression spring 1 Od with opposite action, as shown in Figs 1 and 5 The valve body ila still has, on its outer peripheral surface, a passage 26a and a passage axital 26b whose end

  upper is connected to passage 26a and the lower end

  Then, the passage 26a is connected via the orifice 7d to the pipe 8f of pilotetupassage fluid 24b), as shown

  In Figures 1 and 5, passage 25a on the outer periphery

  valve body 11a is connected to passage 26b

through the orifice 7b (FIGS. 1 and 6).

  The pilot pressure control valve 12 is represented by way of example in FIG. 5. This valve comprises a valve body 12a, a valve sleeve 12h and a solenoid 12c for moving the valve body 12 at. An inverted T-shaped passage 27a is formed in the valve body 12a. A passage 28a is provided in the valve sleeve 12b and is connected to the pilot fluid line 8f (or 8c on 1) The passage 27a is connected to the low pressure line 9 (pressure PR of return fluid) through the passages 26b and 26a and a passage 29 (FIG. 6). FIG.

nut 30.

  Referring now to the operation of the power steering system described above, the oil pump 1 driven by the engine has characteristics of

  output that vary according to the speed of rotation of the motor.

  This output has a peak at vehicle start and at low speed, and a sudden decrease at medium speed, while it remains at a constant low level at high speed. The oil pump is described in detail in the model application. Japanese utility

  No. 4939/1982 When the output of oil pump 1 pre-

  a crest, the switching valve 10, mounted on

  the bypass line 8b is in the open position.

  Virtually all the volume of the hydraulic fluid delivered by the pump 1 is supplied to the power cylinder 3 through the rotary valve 2, and virtually no pressure develops in the line 8a As no pressure is delivered to the reaction piston 5 no steering reaction is produced, but a slight steering action is obtained. The control device 15 receives an output signal from the vehicle speed detector part 13 and an output signal from the speed sensor 14. engine This device performs load calculations I in accordance with the following formula taking into account mainly the vehicle speed sensor output signal, but also / the output signal of the engine speed sensor: I (190 (a + (b)) x 0.6 + c in this formula, a and b have a total of not more than 1, a,

  of Oal, is a coefficient whose values are representative of

  FIG. 8 as a function of the vehicle speed in Km / h, these values representing a variation in the current of O

  electric, b / is a c 6 factor whose values are

  shown in FIG. 9 as a function of the speed of rotation of the motor in rpm, these values also representing the variation of an electric current, and c represents a passive current, or an electric current which does not cause any control of the solenoid 12 c Thus, the control device 15 generates a pilot pressure control signal IA and transmits it to the solenoid 12c of the valve 12

  pilot pressure control If there is a

  the amplitude of the output signals of the vehicle speed sensor-13 and the engine speed sensor 14, the device 15 actuates the pilot pressure control valve 12 to close it, and there is an increase in Gradual pilot pressure Pp upstream of the valve 12 The control pressure Pc, downstream of the pressure control valve 11, is delivered to the passage b, and the valve 11 cooperates with the compression spring t Ic to maintain the pressure. control pressure Pc at a level which does not exceed a predetermined maximum value If the pilot pressure Pp is supplied to the compression spring Ilc, the valve Il opens to increase the control pressure PCI which makes it possible to obtain an increase

  gradually in the steering reaction When the vehicle

  at high speed, the pilot pressure Pp increases

  te to close the stop valve 10 so as to increase

  the pressure Pl upstream of the pressure control valve I 1

  As a result, the pressure Pc downstream of the valve 11 increases and acts on the reaction piston 5 to increase the steering reaction, even if the hydraulic fluid

  is delivered to the power cylinder 3 at a practical pressure

  The system described above also has the advantage that the pressure control valve 11 and the valve 12 have the advantage that the steering wheel is kept in the vicinity of its neutral position during the movement of the vehicle at high speed. pilot pressure can be mounted together precisely, as shown in fig 5 This assembly will be

described below.

  (I) The 1 lb valve sleeve of the pressure control valve 11 which contains the valve body 11a is inserted into the valve housing 11 until it comes into operation.

  bearing on a shoulder 31 of the valve casing 16.

  (It) The compression spring 1 ld is placed in the

  sleeve 11b through the opposite end thereof.

  (III) The valve sleeve 12b of the compression valve 12

  pilot pressure gauge is inserted into the valve housing 16 through the opposite end thereof until it

  come into contact with the valve sleeve llb.

  (IV) The solenoid 12c, containing the valve body 12a,

  is inserted until it comes into contact with the man-

chon 12 b.

  The two valves 11 and 12 can thus be precisely inserted by insertion through the opposite ends of the valve housing 16, so that

meet on the shoulder 31.

  Although the invention has been described with reference to a preferred embodiment, it is understood that various alternatives and modifications could be provided without departing from

  framework of the invention as defined in the

  For example, it is possible to modify the control device 15 so that it acts in response to the output of a device capable of detecting the

  angular movement speed of the steering wheel.

Claims (4)

R E V E N D I C A T I 0 N S   1 power steering system characterized in that it comprises: an input shaft connected to a steering wheel   direction, a torsion bar arranged for transmitting   be the rotation of the input shaft to an output shaft; a fluid line change valve arranged to change a fluid passage in response to a rotation angle difference between the input and output shafts a power cylinder connected to the output shaft; a high pressure fluid line through which the fluid   hydraulic system, delivered from an oil pump, to the   power lindre through said valve; a first low pressure fluid line through which the hydraulic fluid returns to an oil tank from the power cylinder through said valve; a reaction piston disposed between the input and output shafts and arranged to provide a force decreasing the difference   angles of rotation between the input and output shafts   tie; a bypass fluid line extending from the high pressure fluid line to the reaction cylinder; a pressure control valve disposed on the bypass fluid line for controlling the pressure of the hydraulic fluid to not exceed a predetermined maximum value; a second low pressure fluid line, one end of which is connected by an orifice to the bypass fluid line downstream of the pressure control valve and the other end of which is connected to the oil tank; a pilot pressure control valve disposed on the second pipe   low-pressure fluid to control pilot pressure   downstream of the orifice; and a pilot fluid line transmitting the pilot pressure to the pressure control valve. 2 Syst'-me according to claim 1, characterized in that it comprises an orifice provided on said high-pressure pipe, and a branch line in parallel on the upstream and downstream portions of said orifice in said high-pressure pipe, and a stop valve disposed in the branch line and adapted to be   actuated by said pilot pressure.   3 System according to one of claims 1 and 2,   characterized in that it comprises means for detecting the instantaneous conditions of the vehicle on which the system is installed, and a control device which   calculates a pilot pressure according to the output of   said means and transmits a pressure control signal   pilot to said pilot pressure control valve.   4 System according to one of claims 1 to 3,   characterized in that it comprises a plurality of detections   to detect the instantaneous conditions of the vehicle simultaneously in a plurality of situations thereof,   and a controller which calculates a pilot pressure   mainly depending on the output of one of said detectors, but also taking into account the output of any other detector, and which transmits a pilot pressure control signal to said control valve pilot pressure.   System according to claim 4, characterized in that said detector detects the speed of movement of the vehicle while the other detector detects the speed   rotation of the engine of said vehicle.   System according to one of claims 4 and 5,   characterized in that the cd = pilot-pilot pressure valve comprises a solenoid which is movable to close said pilot pressure control valve, said   device performing an order according to the formula   of an electric current I which is delivered to the solenoid   lde to control it so as to close the pilot pressure control valve: I = (1 (a + b)) x 0.6 + c,   where a is a coefficient corresponding to the velocity   vehicle and has a value of 0 to   1, b is a coefficient corresponding to the rotational speed   of the vehicle engine, from 0 to 0.6, the sum a + b not exceeding 1, and c represents an inactive current which   does not act on the displacement of the movable organ of the no Ide.