FR2734778A1 - HYDRAULIC SERVO CONTROL, ESPECIALLY HYDRAULIC SERVODIRECTION FOR MOTOR VEHICLES - Google Patents

Abstract

A hydraulic servo-control, in particular a servo-steering, comprises a manual control element such as a steering wheel, a controlled device such as the steered wheels of a vehicle, a hydraulic servomotor and a hydraulic pump controlled according to the manual force applied. and detected by a sensor. A dynamometric sensor (19) is placed in the transmission (4, 5) between the servomotor (6) and the controlled device, and the flow rate of hydraulic fluid to the servomotor (6) is controlled so that an actual value force, determined by this sensor (19), corresponds to a setpoint dependent on the manual force, which is detected by another dynamometric sensor (18) on the steering shaft (2). Applicable in particular to the steering of motor vehicles.

Description

The invention relates to a hydraulic servocontrol

  particularly a hydraulic power steering system for motor vehicles, comprising a control element

  manual, for example a steering wheel, a

  tif controlled, forcibly coupled to this element, for example

  the steering wheels of a vehicle, a hydraulic servomotor

  hydraulics connected to the device controlled for its

  and a hydraulic pump that can be connected to

  to the servomotor and which can be ordered

  function of the applied manual effort, palpable on the

  manual control and can be determined by means of a sensor, or a manually applied torque.

  Such assisted steering for vehicles beyond

  tomobiles is the subject of document DE 34 35 544 A1. This-

  it describes a rack-and-pinion steering assisted hy-

  hydraulically, in which the rack is connected for driving to a double-acting cylinder (cylinder) acting as a servomotor and whose two sides are

  connected to a gear pump with a direction of discharge

  versible and whose flow can be controlled. This pump

  is ordered, as to the meaning of refoulement and its

  bit, depending on the signal of a sensor placed on the

  the steering wheel between the steering wheel and the sprocket of

  rack-and-pinion sensor, which reacts to the torque transmitted between the steering wheel and the pinion and / or to the movement

of rotation transmitted.

  DE-OS 29 15 890 discloses a steering system, provided for motor vehicles, in which a steering wheel can be rotated against a

  resistance. The flow of a pump and a control valve

  the pressure side of the pump, are

  according to the resistance encountered and the direction of rotation of the flywheel, the valve being able to connect each time one side of a double acting cylinder acting as a servomotor to the discharge side of the aforementioned pump, and the other side of this cylinder has a hydraulic tank with virtually no pressure. In a centered position of the control valve, the discharge side of the pump

  is connected directly to the reservoir, while the cy-

  lindre is hydraulically blocked. Apart from this position, the cylinder operates the steering wheels of the vehicle in a manner similar to the steering movement of the steering wheel. Moreover, current motor vehicles commonly use hydraulic servo drives in which a slide valve is changed position according to the palpable actuation force on the steering wheel, the distributor having two circuits

  throttling on the discharge side of a heat pump

  hydraulics to a tank virtually without pressure. Cha-

  one of these choke circuits has an inlet choke and an outlet choke between which

  find a breakpoint for a motor coupling me-

  to either side of a hydraulic servomotor

  It can be driven in two directions. When the distributor spool is moved in one direction, the inlet choke of a throttling circuit is

  gradually open and the output choke

  given is progressively closed at the same time, while the chokes of the other choke circuit are

  each set in the opposite direction. In this way, a difference

  The finely adjustable pressure differential can be generated in either direction between the motor couplings in order to produce an assist force by the servomotor.

  adjustable accordingly, in one or the other direction.

  Power steering mentioned last

  are certainly remarkable for their good behavior

  mande. However, the construction expenditure is compared

  high, especially when a retroactive control is provided, whereby the manual effort is controlled in a similar way to the force of assistance

produced by the servomotor.

  The power steering mentioned at the beginning, are remarkable by a comparatively low expense for construction. On the other hand, they do not allow

  not a really sensible command.

  The object of the invention is to create a servo

  particularly economical control and which can be

sensibly.

  According to the invention, this result is achieved.

  sultat, with a servocontrol of the type indicated at the beginning, in that a load cell is arranged in the drive connection between the servomotor, and the

  controlled device and the inflow of hy-

  the actuator can be controlled in such a way that a real value of force determined by the sensor

  load cell, corresponds to a de-

  pendent of the manual effort applied.

  The invention is based on the general concept

  prefixing, depending on the manual effort

  plicated and palpable on the control element

  a set value for the force supplied by

  the servomotor and to regulate this servomotor by the com-

  of the flow rate of the hydraulic fluid according to

  the result of the comparison between the value of

setpoint and the actual value.

  Such regulation is achievable at a relatively small expense. The proposed solution

  guarantees at the same time that the manual effort changes

  analogous to the assistance force, with the possibility of prefixing, in principle, all

  desired between the manual effort and the assistance force.

  Other features and advantages of the

  will become clearer from the description

  which will follow of a particular embodiment

  advantageous, but in no way limiting, as well as

annexed, in which:

  - Figure 1 shows the principle of servodi-

  rection according to the invention for self-driving vehicles.

  mobile, in its neutral position; - Figure 2 is a similar representation when turning the direction in one direction; and FIG. 3 represents a diagram showing possible functional relationships between

  the manual effort and the assistance force.

  The direction of the example shown is a rack-and-pinion direction. The steering movement of a steering wheel 1 is transmitted by a steering shaft 2 to a pinion 3 which meshes with a rack 4. This is coupled by force, by coupling rods 5, to the steering wheels - not shown - the vehicle in sight

their robbery.

  A toothless part of the rack

  also kills the piston rod of a cylinder of

  double-acting rection 6 including working chambers 7

  and 8, located on either side of the piston 10, are

  linked to one another through a distributor 9 four-way and three positions when the distributor occupies the neutral position shown in Figure 1, of

  so that the piston 10 of the cylinder 6 and consequently also

  the rack 4, then remain passively mobile.

  In the two other positions of the distributor 9, one or the other of the working chambers 7 and 8 is connected to the

  the discharge side P of a pump 12 driven by an electric motor

  11, while the other chamber is connected to the suction side S of the pump 12 or to a hydraulic tank

13 close to the pump 12.

  The distributor 9 is centered or recalled to the neutral position shown in Figure 1 by springs

  14 and can be brought selectively by electromagnets

  15 and 16 at one or the other activation position

  and be maintained there as long as the electromagnet 15 or 16 co-

  ordered at this activation position remains excited.

  To control the electromagnets 15 and 16, we have

  provided an electronic control device 17 which

  also commands the power of the electric motor 11 and

as a result the flow rate of the pump 12.

  On the side of its input, the control device 17 is connected to a first load cell 18 whose signals reproduce the torque transmitted between the flywheel 1 and the pinion 3. For this purpose, it is possible, for example, to carry out the steering shaft 2 in two

  interconnected parts through a

  piezoelectric device capable of generating electrical voltage

  corresponding to the transmitted torque and which is

  sent as an input signal to the control unit 17.

  The input of the control unit is connected

  in addition to a load cell 19 which can also

  essentially consist of a pedestrian element

  zoélectrique. In this way, the control apparatus 17

  "knows" the steering or transient steering forces

  put between the rack 4 or the steering cylinder

  6 and the steering wheels of the vehicle.

  It is preferable that dynamometers

  19 are coordinated with the two coupling rods

5.

  The operation of the system shown is as follows. When the steering wheel 1 is maneuvered, the dynamometric sensor 18 generates a signal reproducing the effort

  applied manual and which differs according to the meaning of rota-

  steering wheel. In response to this signal, the apparatus of

  electronic control 17 excites one or the other of

  15 and 16, so that the distributor 9 is moved from the neutral position shown in FIG. 1 to an activation position, for example to that visible on FIG.

figure 2.

  The electric motor 11 is at the same time switched on or brought to an increased power, so that

  the pump 12 delivers hydraulic fluid accordingly.

  With this fluid, the steering cylinder 6 generates an assistance force which supports the braking movement.

steering wheel 1.

  The actual value of this assistance force is detected by means of the dynamometer sensor (s) 19 and the control device 17 then adjusts the electric motor 11 so that a prefixed relation is established between the manual force detected by the sensor. 18

  and the assist force detected by the sensor 19.

  As shown in Figure 3, it is pos-

  for example, to ensure that this relationship

  corresponds to curve K1, according to which a

  M relatively low, applied to the steering wheel, already generates a large force of assistance F in one or the other direction. If necessary, the control device 17 can take into account additional parameters, such as

  example of the positions of a switch that can be ac-

  at will, or the speed of the vehicle, and

  consequently, the functional relation between the manually applied torque M and the assistance force F. for example so that this relation corresponds to the

  K2 curve. In this case, an assistance force F

  high level is obtained only during the application

  a larger manual torque M.

  The relations defined by the curve K1 are advantageous when the vehicle is traveling very slowly, for example to park. The K2 curve relationships are suitable for a higher running speed, it being understood that the control behavior of the controller 17 is generally changed continuously to

  as speed increases. Curves K1 and K2 are

  simply produce the relations at constant speeds, the speed being very low for the first

  and higher for the second curve.

  The regulation of the assistance force F by

  the control apparatus 17 is effected by means of a

  think comparatively weak since it only requires commutations of the distributor 9 and a command

  the power of the electric motor 11.

  Dynamometer sensors 18 and 19 can

also be simple type.

  Overall, therefore, with a low construction cost, a servo control with

  a retroactive effect that can be prefixed.

  In contrast to the representation according to FIG. 1, the distributor 9 may also be constituted by a proportional action distributor, as indicated

symbolically Figure 2.

  The distributor 9 can, moreover, be

  also pneumatically.

Claims (4)

  1. Hydraulic servocontrol, in particular hydraulic power steering for motor vehicles, comprising a manual control element, for example a steering wheel, a controlled device, coupled   force to this element, for example the wheels   of a vehicle, a hydraulic servomotor connected to the device controlled for its drive and a hydraulic pump that can be connected to the servomotor and can be controlled according to the effort   applied manual, palpable on the control element ma-   which can be determined by means of a sensor,   or depending on a manually applied torque,   characterized in that a load cell (19) is dis-   placed in the drive link (4, 5) between the   (6) and the controlled device, and the flow rate of   riveted hydraulic fluid to the servomotor (6) can be   controlled in such a way that a real value of force,   the torque sensor (19) corresponds to   a set value depending on the manual effort plicated.   2. Power steering system according to claim 1,   characterized in that a control valve (distributor 9) is interposed between the pump (12) and the servomotor (6), which can be driven in two directions, which valve,   in a neutral position, connects both sides of the servo   motor (6) between them and / or a tank (13), thus leaving the servomotor (6) passively movable, and that in two actuating positions of the valve (9), one side of the servomotor (6) is connected to the discharge side of the pump (12) and the other side of the booster (6) is connected at the same time to the suction side of the pump (12) or the tank (13). 3. Servo control according to claim 2, characterized in that the valve (9) is held elastically (14) in its neutral position or requested elastically towards this position.   4. Servo control according to one of claims 2 and 3, characterized in that the valve (9) is made   in the form of a proportional action valve.