IT201700012623A1 - METHOD AND EQUIPMENT FOR CHECKING THE POSITION CHANGE OF AN ECCENTRIC OF HYDRAULIC VARIABLE DISTRIBUTION HYDRAULIC MOTORS - Google Patents

Description

The present invention relates to a method and an apparatus for controlling the position variation of an eccentric for varying the displacement of hydraulic motors. Radial and / or axial hydraulic motors are known in the art, in which the propulsion members are constituted by telescopic oscillating cylinders which rest on one side on a spherical eccentric of the rotating shaft and on the other side with spherical caps integral with the casing of the motor.

Said motors can be of fixed or variable displacement.

As shown in Figs la, 1b, in variable displacement motors the spherical part 306 of the motor shaft (not shown), in addition to rotating, can also translate with respect to the shaft itself, thus changing its eccentricity and therefore the displacement of engine operation. In this way the value of the displacement can be varied, during the operation of the motor, in order to adapt the latter to the external load conditions, optimizing its performance.

For this purpose, the motor is equipped with sensors which measure the rotation speed of the shaft and the displacement, thus sending respective signals to the control circuits of the eccentric of the machine to which the motor is applied.

Note the position of point E with respect to the center 0 of rotation of the crankshaft, the distance between the two points is known and therefore the operating eccentricity of the same for the instantaneous displacement of the motor, and a control group can intervene to vary the current value of the eccentricity E.

This control of the position variation, with the eccentric locking in the desired position, is however difficult since, to determine the displacement to be imposed on the eccentric, the control circuit must compensate for the forces applied by the thrusters on the eccentric itself. which continuously vary in intensity and direction.

Devices for controlling the position of the eccentric are also known substantially comprising one or the other of mechanical or electronic technologies.

Both technologies act on a proportional control solenoid valve on the basis of a signal supplied by the user; according to the known technique, the proportional valve is operated by opening it a little, for slow displacement changes, or displacement changes for which the set displacement value is close to the current one, and by opening it a lot, for fast displacement changes, or displacement changes for which the set displacement value is far from the current one; opening the valve a little, however, means creating bottlenecks that reduce the pressure at its outlet, up to halving it and also canceling it when the valve is almost closed; in these cases the outlet pressure is no longer sufficient to oppose the forces exerted by the engines and to control the change in displacement which, on the contrary, tends to change out of control.

Both electronic and mechanical technologies also have the limit of having to continually correct the position of the eccentric to adapt not only to the requirements of the specific use, but also to the continuous movements of the eccentric due to the thrust of the propellers themselves.

Although functional, these known devices therefore have drawbacks which limit their effectiveness, both in terms of speed of change of the displacement, and of precision in obtaining the desired displacement value.

In particular, both electronic and mechanical devices are never able to be as fast and precise at the same time as would be required.

For both solutions it is also verified that it is necessary to keep the feedback loop constantly closed and therefore the hydraulic circuits always under pressure, consequently there are continuous leaks of fluid in the rotating seals, which are not watertight and under pressure, they seep oil.

The technical problem therefore arises of providing a method and an apparatus for controlling the position of an eccentric connected to the shaft of a variable displacement hydraulic motor, which solve the problems of the known art, determining in particular variations in eccentricity ( and therefore of displacement) fast and precise, as well as capable of significantly reducing fluid losses.

Within the scope of this problem, it is also required that this apparatus be compact in size, easy and inexpensive to produce and assemble and be easily installed on any motor, even if it is already operating by means of normal standardized connection means.

These results are obtained according to the present invention by an apparatus for controlling the position of an eccentric of the shaft of a variable displacement hydraulic motor according to the characteristics of claim 1

A further object of the invention is a method for controlling the position of an eccentric of the shaft of a variable displacement hydraulic motor according to the characteristics of claim 7

More details can be found from the following description of a non-limiting example of embodiment of the object of the present invention made with reference to the attached drawings, which show:

in figure la, 1b: a schematic section of a variable displacement radial hydraulic motor with eccentric control according to the known technique;

in figure 2: a block diagram of the control feedback loop of the eccentric control valve;

in Figure 3: a diagram of an example of embodiment of a control circuit for the position of the eccentric according to the present invention;

in Figure 4: a diagram illustrating the variation curve of the displacement with respect to time, obtained with the control apparatus according to the invention.

As shown in Figures 1a, 1b, a variable displacement hydraulic motor 300 is made up of a casing 301 in which the thrusters 310 consisting of a cylinder 311 and a piston 312 are housed. More in detail, each of the pistons 312 is placed in communication with a rotating distributor (not shown), housed inside a cover fixed to the casing 301 and able to cyclically place the pistons 312 in supply or exhaust in phase with the rotation of the driving shaft.

In the pistons 312, resting on the caps 302 of the cover, the cylinders 311 are telescopically movable in the radial direction and they rest against the external surface of a spherical body 306, which is eccentrically movable in the radial direction with respect to the axis of the drive shaft upon actuation of relative means 308, said eccentricity variation also causing the engine displacement variation.

According to the conventional technique, the engine is associated with means for detecting the engine displacement comprising, for example, at least one pair of sensors, each of which is arranged on the cap 302 of a respective propeller 310 with a longitudinal axis parallel and offset with respect to the longitudinal axis of the propulsion unit 310 in rest conditions and a data processing unit for detecting and storing the signals emitted by the sensors and carrying out the necessary calculations to also obtain the position of the eccentricity point "E".

The hydraulic motor 300 is subject to an external torque 310a, transmitted through the drive shaft, to a flow rate 310b which flows through the supply and exhaust ports of the motor itself, as well as to a disturbing action, due to the thrust of the thrusters 310 which, by periodically changing intensity and direction during the rotation of the driving shaft, tends to move the eccentric 306 radially, modifying the displacement in a way that is difficult to control.

Fig. 2 also indicates the rotation speed 310c of the crankshaft.

The engine 300 reacts, in general, to variations in torque and flow rate by modifying its operating parameters 320, including the operating pressure 320b of the engine and the rotational speed of the shaft 320c.

In particular, given a displacement value, an increase in the torque 310a leads to an increase in the pressure 320b (and vice versa), while an increase in the flow rate 310b leads to an increase in the speed of the shaft 320c (and vice versa).

Similarly, given a torque 310a and flow rate 310b, an increase in displacement results in a decrease in pressure 320b and speed 320c (and vice versa).

With reference to Fig. 2, the apparatus, according to the invention, for controlling the position of the eccentric 306 of a variable displacement hydraulic motor 300, substantially comprises a control and command unit 200, and an actuation unit 100.

The control and command assembly 200 comprises a feedback loop (hereinafter identified with the same numerical reference 200 as the command assembly) which comprises:

+ a processing unit or controller 260 with microprocessor 262 connected to the drive unit 100 and equipped with a memory unit 261;

+ a measuring system 230 adapted to receive the current values of parameters 320, respectively: 320a, 320b, 320c of the motor 300 and to emit a corresponding signal 230, respectively 230a, 230b, 230c;

+ although all three signals 230a, 230b, 230c may be available, the control 200 preferably processes only one of them according to the initial choice made by the user who can set the operation of the motor on the displacement 320a / 250a; on pressure 320b / 250b; o on speed 320c / 250c;

+ an adder 240 act a

+ receiving in input one of said signals 230a, 230b, 230c corresponding to the respective current value 320a, 320b, 320c and one of the respective and corresponding reference values 250a, 250b, 250c set by the user 250 and stored in the memory unit 261, And

+ to compare the current signal with the respective reference value of the selected signal and to send a relative difference signal 240a, b, c to the processing unit 260;

As illustrated in fig. 3, the actuation assembly 100 in turn comprises a directly operated solenoid valve 110 which provides an inlet 110c for pressurized fluid 500a, and an inlet H 0 for discharged fluid 500b. The solenoid valve 110 is controlled by the control system 200 through two coils IlOe and H Of from which it receives the activation / deactivation signals.

The solenoid valve 110 also has two outlets 110a, 110b whose final terminals are respectively connected to a relative chamber 350a, 350b of a double-acting cylinder 350, which acts, through the piston 308, on the movable eccentric 306, changing its eccentricity and therefore the engine displacement.

The hydraulic circuit comprised between the solenoid valve 110 and the cylinder 350 comprises two branches 120a, 120b each comprising: rotating seals 121a, 121b of the crankshaft, a block valve 122a, 122b piloted inlet by the fluid coming from the corresponding outlet 110a, 110b of the distribution valve 110 and each connected to the opposite branch of the inlet circuit of the other, a throttling element 123a, 123b interposed between the slam-shut valves and the corresponding chamber 350a, 350b of the double-acting cylinder 350 for actuating the eccentric 306 which is thus driven in translation by the loading / unloading feed of the two said chambers 350a, 350b.

The throttling elements 123a, 123b are adapted to determine the rate of variation of eccentricity as will become clearer in the following.

Preferably, the two throttling elements are adjustable to vary their opening / closing.

With this configuration, the operation of the control apparatus of the eccentric 306 for varying the displacement of a variable displacement hydraulic motor is as follows: bearing in mind that the displacement control can take place alternatively at constant pressure, or at constant speed, the system controls continuously the current value of the selected parameter, ie of the displacement 320a; pressure 320b; or of the speed 320c, comparing it with the corresponding desired value 250a; 250b, 250c of the parameter itself, and acts through the drive unit 100 to reach the objective, or the desired value of the selected parameter, by modifying the position of the eccentric cam 306 and hence the displacement through the means 350,308.

In detail:

+ when the engine is switched on, the following are assumed and preferably displayed for the user 250:

the current values of parameter 320 to be controlled: displacement 320a or pressure 320b or speed 320c;

the desired values of the corresponding parameter 250 to be controlled: displacement 250a or pressure 250b or speed 25Oc;

the period of maximum duration of the valve opening pulses is set

+ the processing unit sends said signals 320 in feedback to the adder 240 which compares the signals 320 with the set / memorized reference values 250 and emits and sends a difference signal 240a, b, c to the processor 260;

a) if the two values, current and desired, of the parameter to be controlled coincide and the signal 240a, b, c = 0:

the controller 260 does not intervene on the coils 110e, 110f which remain de-energized, both the outlet connections 110a, 110b of the valve are put in communication with the discharged fluid 500b, so that the block valves 130a, 130b remain closed, sealing the fluid to the interior of the double-acting cylinder 350 in such a way that the eccentric 306 cannot vary its eccentricity;

the engine displacement therefore remains unchanged.

b) if the two values do not coincide and the difference signal 240a, b, c is less than or greater than 0, the controller 260 acts on one or the other of the two coils of the valve 110; in detail:

bl) if 240a, b, c <0: the coil IlOe is energized, and the pressure inlet 500a is connected to the outlet 110b, while the discharge fluid H Od inlet is connected to the output 110a; in this way the pressurized fluid 500a flows towards the chamber 350b of the double-acting cylinder 350, which acts on the eccentric 306 moving it towards a position corresponding to a decrease in the engine displacement; The pressurized fluid 500a, acting along the outlet 110b, also unlocks the valve 122a allowing the fluid to exit from the double-acting cylinder through the chamber 350a;

b2) if 240a, b, c> 0: the coil H Of is energized, and the pressure inlet 500a is connected to the outlet 110a, while the discharge fluid inlet H Od is connected to the output 110b; consequently the pressurized fluid 500a flows towards the chamber 350a of the double-acting cylinder 350, moving it towards a position corresponding to an increase in the engine displacement; the pressurized fluid 500a, acting along the outlet 110a, also unlocks the valve 122b allowing the fluid to exit from the double-acting cylinder through the chamber 350b.

According to a preferred characteristic of the apparatus it is envisaged (fig. 4) that the following control modes of the valve 110 are defined:

++ if the current value of the parameter to be controlled is equal to the desired value of "SET POINT" (240a, b, c = 0), less than an allowable margin of error: the valve 110 is not energized, and the displacement of the motor remains blocked at the current value; the system is located in the field of the so-called "dead band";

++ if the current value of the parameter to be controlled is far from the desired value, the valve 110 is energized with a pulse of high duration, possibly until it is close to the duration of the period, and the displacement of the motor changes at maximum speed to approach the value desired; in this case the system is "out of band";

++ if the current value of the parameter to be controlled is, with respect to the desired value, in an area between the "dead band" and the "out of band" area, by energizing the valve 110 with long pulses, the displacement change it would be too fast and there would be a risk of inaccurate control; in this zone, called "deceleration band", the valve 110 is therefore excited with pulses of variable duration based on the difference calculated between the current value 320a, 320b, 320c and the desired value 250a, 250b, 250c of the parameter to be controlled. The duration of the valve excitation pulse is progressively decreased as the current value approaches the desired value, ie as the parameter to be controlled approaches the "dead band".

It therefore appears that the method and the apparatus according to the invention allow operation of the control with a direct-operated distribution valve 110 always activated at maximum opening, but with a pulse command of variable duration within a predetermined period of maximum duration, thus ensuring that in the thrusters 310, there is always sufficient pressure to control the movements of the eccentric 306 and that the activation of the variable pulse solenoid valve allows the use of pulses of longer duration, when the current value of the parameter to be controlled differs much of the desired value, and pulses of shorter duration, when said value approaches the desired value, while also ensuring the accuracy of displacement variation necessary for the correct operation of the engine.

At the same time, the maximum displacement speed of the eccentric 306 and therefore of the displacement change system can be adjusted through the calibration of the throttling elements 123a, 123b.

In this way, both the required positioning speed and the necessary precision of the eccentricity position are obtained at the same time.

In addition to this, since the hydraulic circuit is under pressure only during the transients of eccentricity variations, high reductions in fluid losses are obtained through the rotating seals of the motor shaft with consequent energy savings.

Although described in the context of some embodiments and some preferred examples of embodiment of the invention, it is intended that the scope of protection of the present patent is determined only by the following claims.

Claims (13)

CLAIMS 1. Apparatus for controlling the position of an eccentric (306) of a shaft of a variable displacement hydraulic motor (300), which comprises: + a control and command group (200), connected in feedback between detection points of one or more current parameters (320a, 320b, 320c) of motor operation (300) and input points of set values (250a, 250b, 250c) for the one or more operating parameters of the motor, and able to control a drive unit (100) of the eccentric (306) connected to the motor shaft (300), the drive unit being inserted in the hydraulic circuit (120) of means (350) for handling the eccentric (306) itself, characterized by the fact that said actuation assembly (100) comprises a direct-acting solenoid valve (110) actuated by pulses of variable duration emitted by the control and command assembly (200) on the basis of a difference between an actual value (320,320b320c) detected and a desired value (250a, 250b, 250c) stored (262) of one of said parameters. 2. Apparatus according to claim 1 characterized in that the control and command unit (200) comprises: + a microprocessor controller (260) (262) connected to the drive unit (100) and a memory unit (261); + a measuring system (230) adapted to receive the current values of the one or more parameters (320a, 320b, 320c) of the motor (300) and to emit corresponding signals (230a, 230b, 230c); + an adder (240) adapted to receive in input said current values (320a, 320b, 320c) and respective reference values (250a, 250b, 250c) set by the user (250) and stored in the memory unit (261), and to emit a difference signal (240a, b, c) of said at least one parameter, to be input to the processing unit (260). 3. Apparatus according to claim 1-2 characterized in that said at least one parameter (320) being controlled is at least one of the displacement (320a), or the pressure (320b) or the speed (320c) variation of the engine eccentricity. 4. Apparatus according to claim 1, 2 or 3 characterized in that said hydraulic circuit comprised between the outlets (110a, 110b) of the solenoid valve (110) and the cylinder (350) for actuating the eccentric (306) comprises two branches ( 120a, 120b) each comprising: rotating seals (121a, 121b) of the crankshaft, a block valve (122a, 122b) piloted inlet by the fluid coming from the corresponding outlet (110a, 110b) of the distribution valve (110) and each connected to the opposite branch of the input circuit of the other. 5. Apparatus according to claim 4 characterized in that each branch of the hydraulic circuit (120) comprises a throttling element (123a, 123b) interposed between the block valves and the corresponding chamber (350a, 350b) of the double cylinder (350) actuation effect and adapted to determine the rate of change of eccentricity of the motor. 6. Apparatus according to claim 5 characterized in that the two throttling elements (123a, 123b) are adjustable to vary their opening / closing. Method for controlling the position of an eccentric (306) of the shaft of a variable displacement hydraulic motor (300) by means of an apparatus according to any claim 1-6, characterized in that it comprises the following steps: + engine ignition e + detection of the present value (320) of at least one parameter (320a, 320b, 320c) of operation thereof; + choice of a period of maximum duration of the valve opening pulses; + choice of one of said operating parameters subject to control; + comparison of the current value (320) of the selected parameter with a corresponding set / stored reference value (250), + emission and sending of a difference signal (240a, b, c) between said values of the selected parameter to the control and command unit (200); + sending by the control and command unit (200) of the difference signal (240a, b, c) to the drive unit (100); + sending to the solenoid valve (110) by the actuation unit (100) of excitation pulses for the opening of the solenoid valve, having a duration determined on the basis of the difference signal (240a, b, c) received; + opening of the solenoid valve (110) for feeding the hydraulic circuit for controlling the translation of the eccentric (306); + said solenoid valve being directly controlled. 8. Method according to claim 7 characterized in that the control pulses of the solenoid valve (110) are of variable duration. 9. Method according to claim 8 characterized in that the control pulses of the solenoid valve (110) have a longer duration if the actual value of the parameter to be controlled differs greatly from the desired value, and a shorter duration if said value approaches the desired value . 10. Method according to claim 7, 8 or 9 characterized in that it comprises a step for adjusting the speed of variation of the motor eccentricity, by means of throttling elements (123a, 123b) arranged on the hydraulic circuit of the actuation unit. 11. Method according to claim 10 characterized in that said throttling elements are adjustable in opening / closing. Method according to any claim 7-11 characterized in that said at least one parameter (320) being controlled is at least one of the displacement (320a), or the pressure (320b) or the speed (320c). 13. Method according to any claim 7-12 characterized in that the command and control unit (200) comprises an adder (240) which receives in input said current values (320a, 320b, 320c) of the at least one parameter and respective values (250a, 250b, 250c) set / stored, and emits a difference signal (240a, b, c) of said at least one selected parameter, which it inputs to a processing unit (260).