Patent Description:
The open center electro-hydraulic control valves are widely used in the field of operating machines and in particular in the field of agricultural and work vehicles for the control of the related hydraulic components such as arms and buckets.

Such valves are controlled by means of a current signal generated in proportion to the angular position of a control lever arranged, for example, in the vehicle cabin.

As a consequence of the current signal applied to the electro-hydraulic valve, a relative movable spool moves inside the valve, partitioning a first flow of hydraulic oil addressed to a hydraulic actuator and a second flow of hydraulic oil addressed to the hydraulic oil recovery tank T; in particular, when the spool is at a first end position of the relative displacement, the first flow is zero and the second flow is maximum, while when the spool is in a second end position opposite to the first one, the first flow is maximum and the second flow is zero.

A pump, generally with a fixed displacement, takes the hydraulic oil from the hydraulic tank T and pumps it into the hydraulic circuit that feeds the electro-hydraulic control valve.

<FIG> and <FIG> show respectively an electro-hydraulic diagram and a block diagram of the known controls implementing electro-hydraulic open center control valves.

A problem with open-center control valves OCV is that the partitioning of the flows depends not only on the position of the spool, but also on the load applied to the hydraulic actuator.

This means that in relation to this load, the operator must start to operate the control lever of the hydraulic organ really slowly as long as the partitioning of the first and second flows is such that to balance the load. This means that there is no fixed relationship between the position of the organ control lever and the beginning of the movement of the organ itself.

It is clear that the load applied to the organ affects the relative hydraulic actuator, therefore it is equivalent referring to the load applied to the organ or its hydraulic actuator. It is also evident that the position of the actuator control lever affects the position of the movable spool, but this is not sufficient to ensure that the actuator and thus the relative member begins to move when the lever reaches a predetermined position. On the contrary, this means that the operator must gradually act on the control lever, until the organ begins to move, and then he can further adjust the progression of its movement.

In the first phase of "offset search", the operator must act gradually, as sudden actions could induce, once the position of the spool balances the load applied to the organ is exceeded, sudden, uncontrolled and potentially dangerous movements of the operated organ.

A known solution is to replace the open center control valve with a closed center electrohydraulic valve. An other example is shown in patent application <CIT> that describe a control device to regulate the signal pressure as a function of the input and a speed of the engine to control the flow control valve. Further examples are disclosed in patent <CIT> about a Calibration system and method for work machines using electro hydraulic controls, or patent <CIT> about a method for controlling a work machine, or patent <CIT> related to a valve calibration routin. Closed center valves are much more complex and expensive.

If not specifically excluded in the detailed description below, what is described in this chapter is to be considered as an integral part of the detailed description.

The purpose of the present invention is to present in independent claim <NUM> a control system and in independent claim <NUM> a control method for control of an open center electro-hydraulic control valve, which overcomes the problems of the known art.

In other words, the main object of the present invention is to cause an open center valve to behave like a closed center valve.

The basic idea of the present invention is to implement a feedback control that identifies the offset of the control signal corresponding to the offset of the spool position, such as to balance the load, by means of the implementation of an associated position sensor to the hydraulic actuator.

Obviously, the weight of the load varies from time to time and therefore the offset of the spool control signal must also vary accordingly.

In other words, the idea is to manipulate the signal generated by the control lever of the organ so that in a predetermined angular position of the control lever of the organ controlled by the lever begins to move regardless of the load applied to it.

Advantageously, a "drowback" in the open center valves is compensated through the control of the same, so that in practical terms, the operator control the hydraulic parts of an operating machine as in case the control valves of the relative actuators were of the closed type.

To avoid uncontrolled movements following the implementation of the present invention, a so-called dead band is provided, adjacent to the release position of the control lever of the controlled organ, in which the signal generated by the same lever is null or considered null, so that only when the dead band is exceeded, the calculation of the offset signal value to be applied to the signal generated by the control lever is triggered.

Since the amount of the load can vary even suddenly, for example because it is released, then the offset signal is reset when the lever is released or in any case when it enters the dead band.

Further objects and advantages of the present invention will become clear from the following detailed description of an example of its embodiment (and its variants) and from the attached drawings given purely by way of non-limiting explanation, in which:.

The blocks shown in hatched are optional.

It should also be noted that the terms "first", "second", "third", "upper", "lower" and the like can be used here to distinguish various elements. These terms do not imply a spatial, sequential or hierarchical order for the modified elements unless specifically indicated or inferred from the text.

The elements and features illustrated in the various preferred embodiments, including the drawings, can be combined with each other without however departing from the scope of this application as described below.

With reference to <FIG> and <FIG>, a position sensor SS is associated with the hydraulic actuator ACT controlled by the open center control valve OCV and when from a release condition the control lever J reaches the limit of the dead band DB, then it is increased control signal OCV of the control valve until actuator ACT movement is detected by the sensor SS. Then, the signal value is stored and added stably to the signal generated by the control lever.

Therefore, the control method of the open center electro-hydraulic control valve OCV for operating a hydraulic actuator ACT of an organ A, B of a work or agricultural vehicle VHE, powered by a pump P, in which a control signal of the control valve is generated in proportion to a position of a control lever J, the method, with reference to <FIG>, comprises.

With reference to <FIG>, the second step is a closed loop control in which the feedback variable consists of the movement start of the hydraulic actuator. In fact, all the signals converge in the processing unit CPU which receives the signal generated by the control lever J at its input and generates an increase in the valve control signal based on the position signal received from the position sensor SS.

The AMP block representing a signal amplifier is voluntarily represented as external to the CPU block to make the invention easier to understand, but it must be clear that the entire method object of the present invention can be entirely implemented in the processing unit CPU.

<FIG> shows a comparison of the control signal generated by the block AMP in two different conditions, i.e. when the organ, for example the arm of a loader, is lifted without load (left in <FIG>) or if it is lifted with load (on the right in <FIG>).

When the load is not applied, the behavior of the control is completely identical to what occurs according to the known art.

Conversely, in the case of applied load, the intensity of the command signal is manipulated by adding the Offset value calculated in step <NUM>, while the remaining portion LS of the curve is connected, for example linearly, from the Offset value in DB up to the maximum value of the control signal in AM, which represents the position of maximum inclination of the control lever J.

It is worth highlighting that if the original curve, i.e. without load, is not linear, for example hyperbolic or parabolic, the same behavior can be maintained after the application of the Offset, taking into account that the maximum value of the signal applied to the valve must remain unchanged to avoid damaging the valve.

In other words, the overall control signal of the control valve is the sum of a first contribution given by the offset (positive), calculated in DB, and a second LS contribution proportional to the current position of the control lever.

Preferably, each time the lever returns to the release position or in the dead band, a fourth step (Step <NUM>) is performed to cancel the previously stored control signal value (Offset) to start over from the first step, i.e. from the beginning of this method.

It is worth noting that the processing unit is extremely fast by performing a significant number of calculation cycles in the time unit, therefore, the offset calculation is almost instantaneous. However, the increase in the command signal value up to the detection of the actuator displacement can be linear or follow different laws to make this identification of the Offset even faster.

For example some laws can be exponential or parabolic.

According to a preferred variant of the invention, it is also taken into account that the flow of hydraulic liquid entering the open center electro-hydraulic control valve OCV can vary.

With high flow rates of hydraulic liquid, small displacements of the movable spool can induce large actuator movement, therefore it is advisable that the law of increasing the command signal carried out during the second step for searching the Offset value is inversely proportional to the hydraulic liquid flow generated by the hydraulic fluid source.

Generally, the hydraulic source is a pump driven by the prime mover, which typically is an internal combustion engine, therefore, the law of increasing the drive signal of the movable spool in step <NUM> can have a progression inversely proportional to the flow generated by the hydraulic source or equivalently to the speed of rotation of the prime mover which drives the hydraulic pump which feeds the control valve OCV.

The present invention can be advantageously realized by means of a computer program which comprises coding means adapted to cause a control system as claimed in claim <NUM> and described before to carry out all steps of the claimed control method Therefore it is intended that the scope of protection extends to said computer program and further to computer readable means comprising a recorded computer program, said computer program comprising program coding means adapted to cause a control system as claimed in claim <NUM> and described to perform all steps of the claimed control method.

Implementation variants of the described non-limiting example are possible, without however departing from the scope of protection of the present invention as defined by the appended claims, including all the equivalent embodiments for a person skilled in the art, within the scope of the present invention as defined by the appended claims.

Claim 1:
Control system of an electro-hydraulic open center control valve (OCV) for operating a hydraulic actuator (ACT) of an organ (A, B) of a work or agricultural vehicle, powered by a pump (P), the control system comprising
- a control lever (J) of the organ configured to generate a first signal proportional to a position of the control lever,
- processing means (CPU, AMP) configured to generate a control signal (LS) of the control valve, proportionally to said first signal,
- wherein the processing means (CPU, AMP) are configured to detect the overcoming of a predetermined position (DB) of the control lever (J) of the organ and consequently to increase the control signal and then to set a positive offset to the control signal (LS), as long as the position of the control lever (J) of the organ exceeds said predetermined position (DB),
characterized in that, the control system comprises
detection means (SS) configured to detect a movement of said hydraulic actuator as a result of the application of said control signal,
wherein the processing means are operatively connected with said detection means
and configured to measure a control signal value (Offset) at a starting of a movement of said hydraulic actuator and then to set the positive offset approximately equal to said control signal value (Offset).