DE3406228C2 - - Google Patents

Description

The invention relates to a hydraulic system for farmers Community tractor according to the preamble of the patent saying 1.

Such a hydraulic system is in the main circuit and divided into the secondary circle, the latter to the Versor development of vehicle technology significant for the tractor Units such as power steering, one Servo brake or the like. The main circle supplies the by means of a lifting cylinder actuated for a Attachments to the tractor, such as a plow, and the Zu, which can be optionally activated via the directional valves set devices such. B. hydraulic motors, cylinders etc. The power lift is controlled by the control device a power lift control unit and a setpoint device for  this includes, controlled, the setpoint generator in multiple work areas is adjustable.

The main circle, like the secondary circle, is made up of one its own hydraulic pump, which is supplied by the Hydrau Likpumpen supplied pressure fluid flow from the pump rotation number depends, which in turn is a function of engine speed of the tractor.

In order for the power steering in all driving conditions, i.e. H. in the Idling as well as at the highest engine speed, a ge suitable pressurized fluid supply or oil supply must, the pressure fluid led into the secondary circuit current be approximately constant. This is done by a Current divider reached by the hydraulic pump of the Secondary circuit is unnecessary depending on the driving condition branches off conveyed residual fluid stream which, as is known, advantageous for supplying the main circuit with can be pulled. However, since the corresponding to the respective desired operating states of the power lift and Additional equipment in the main circuit required pressure fluid flow is different in operating conditions with low pressure fluid requirement, such as in Continuous operation, due to the constant connection of the rest fluid streams an excessive amount of pressurized fluid at Be drive pressure provided that is unused in one Storage container must be returned. A conventional Lich hydraulic system is therefore with considerable ver pleasure benefits burdened that a large warming of the Require pressure fluids, so that this cooling devices are indispensable.

From DE-OS 28 37 605 is already a hydraulic system with the features of the preamble of claim 1 known, also a main circle and a sub-circle  is provided. These circles are basically permanent connected with each other, but by means of a complex valve arrangement in cooperation with one Check valve can be ensured that in one certain operating status, namely with short-term actuation Pre-control belonging to the valve arrangement slide and subsequent pressure increase in separate Line sections of the residual fluid flow from a branch tion in its entirety via the main control spool for Return is directed. Only with a longer acting This separation of impulses on the pilot spool canceled in both circles.

Apart from the fact that the circuitry complexity in known case is relatively large, require the individual Valves of the valve arrangement for timely coupling and Decoupling the hydraulic circuits on a relatively agile coordination with each other, which makes the connection of the residual fluid flow to the main circuit with variable load reacted differently quickly. The well-known hydraulics system is therefore flexible in terms of Limited consideration of various parameters.

The invention is therefore based on the object Hydraulic system according to the preamble of the claim 1 to create that with reduced circuitry in is able to further reduce power losses, by switching the connection on and off between residual fluid flow and main circuit of a variety of operating parameters in a targeted and timely manner.

This task is carried out in the characterizing part of the Features specified claim 1 solved.

According to the invention, a simple solenoid valve is used  Control of the residual fluid flow used, the Parallel connection of switching elements in the electrical Circuit opens up the possibility of control of the residual fluid flow several operating parameters simultaneously to consider. That depends on the operation Parameter controlled valve leads the residual fluid flow Main circle only if this due to certain Actuations or operating states of the units in the main circle is required. This is the case, for example Case when the additional devices are switched on or if the lifting cylinder has a great way to excavate an implement of the agricultural tractor should proceed. In continuous operation with essentially unch changed operating states, the valve blocks the feed to the main circuit and the residual fluid flow goes directly to Reservoir returned. Controlling this rest Fluid flow takes place according to the invention in a timely manner the respective requirement behavior of different Gensets in the control circuit, being based on the switching character teristics of the valve can be influenced. The control of the residual fluid flow can in particular under Simplification of the circuit and thus much more flexible take place, so that for example work areas of Power lift can be considered.

Advantageous developments of the invention are the subject of subclaims.

According to claim 3, the rest is switched on fluid flows to the main circuit already when individual Operating parameters that determine the requirement behavior for Characterize the pressure fluid of an aggregate in the main circuit, Accept values that indicate an increased pressure fluid requirement demonstrate.  

With the developments according to claim 4 and 5 he follows a sensible adjustment of the hydraulic system to the different different modes of operation Power lift, advantageously by the inventor In accordance with the series connection of the timing relay with the two th switching element is used to the device keep the technical effort as low as possible.

From DE-PS 71 230 is the use of magnet valves in a two-circuit hydraulic system known. in the Contrary to the subject of the invention, however, is that of Auxiliary pump powered hydraulic circuit only effective as a control circuit to the directional control valves of the main control circle. In detail there is no solenoid valve shown that depending on different operating states of the hydraulic system a residual amount of fluid in the Main circuit feeds.

Below is a schematic drawing Embodiment of the invention explained in more detail. It shows:

Figure 1 is a block diagram of the hydraulic system with built-in solenoid valve.

Figure 2 is an electrical circuit for driving the solenoid valve. and

Fig. 3 is a signal timing diagram for a branch of the circuit of FIG. 2.

1, a hydraulic system for an agricultural tractor is divided into a main circuit and a secondary circuit, which are supplied with pressurized fluid separately from a first hydraulic pump 1 and a second hydraulic pump 2 . In the main circuit, a power lift control device 3 is arranged, which is struck by a setpoint generator 4 provided in a control circuit and regulates the pressure fluid flow for a lifting cylinder, which is integrated in a power lift (not shown) for an attachment, such as a plow, on a tractor . On the setpoint generator, three working areas for the power lift or the attachment can be set: in a first work area A , the lifting cylinder of the power lift is completely lowered and the attachment is in a so-called floating position in which the power lift does not exert any force on it. In a work area B , the attachment is brought into a working position in which a position control or traction control is carried out by means of the control circuit and an optional stepless setpoint specification by the setpoint generator. When setting a work area C there is a quick excavation of the attachment, in which this is moved upwards by the power lift.

Furthermore, in the main circuit, manually operable directional control valves 5 (represented by a block) are arranged via which any additional devices such as hydraulic motors or cylinders can be connected, which can be connected to the main circuit via quick couplings.

The auxiliary circuit is used to supply vehicle-technically important units such as a servo steering, a servo brake or the like. Since the size of the hydraulic fluid flows delivered by the hydraulic pumps depends on the engine speed of the tractor, the power steering, however, requires an essentially constant mass flow over the entire speed range, i.e. from idling to the maximum engine speed, the secondary circuit is preceded by a flow divider 6 , which is one of the hydraulic pump branches off excess fluid flow. This residual fluid flow is fed to a valve 10 which , in the exemplary embodiment, is designed as a magnet-operated 3/2-way valve. When the solenoid coil is not energized, the solenoid valve assumes a position I due to a spring load, in which the residual fluid flow is directed to the suction side of the hydraulic pumps or into a storage container 7 , while when the solenoid coil is excited, it assumes a position II in which the residual fluid flow is fed to the main circuit becomes. However, this supply should only take place if the main circuit actually requires the amount of pressure fluid actually offered.

This is achieved in that the solenoid valve 10 is controlled by an electrical circuit (Fig. 2). This circuit comprises a parallel circuit consisting of two branches, the magnet coil being excited as soon as one branch is switched through, ie the current flow is not interrupted. Thus, a first branch is switched through as soon as a first group of operating parameters meets certain values, and a second branch carries current if this applies to a second group of operating parameters. It is obvious that in the case of a larger number of units in the main circuit, the respective course of the operating state of which should result in a connection of the residual fluid flow, that is to say an excitation of the solenoid coil, the number of branches of the parallel connection is expanded accordingly, with further branches in addition to switching elements in each branch suitable control elements can be provided.

As mentioned, the connection of the residual fluid flow to the main circuit should only take place if it requires a larger amount of pressurized fluid. In the exemplary embodiment, this is the case on the one hand if one or more additional devices are switched on, ie the directional valves 5 are partially or completely actuated. This connection should only take place if such changes in the operating state of the additional devices are made, for example the extension of a cylinder which requires a larger flow of pressurized fluid. This is achieved by a switching element S 1 arranged in the first branch of the parallel connection, which is sufficient for one certain extent exceeding the actuation of a hand lever of the respective Wegeven valve is closed; the solenoid valve goes into position II. In the case of fine control or continuous operation of the additional device, the solenoid valve should be in position I. The hydraulic motors used in agriculture require only relatively low pressurized fluid flows in continuous operation, which can easily be covered by the hydraulic pump 1 . The respective directional control valve is only actuated to a small extent and does not cause the switching element S 1 to close.

On the other hand, a connection of the residual fluid flow to the main circuit should take place when the power lift requires a larger amount of pressure fluid; with continuous use of the power lift in operating area B , z. B. during plowing work with traction control, the main circuit is constantly pressurized according to the Regelim pulse, but the amount of pressure fluid required to carry out these controls is relatively small and can be supplied by the hydraulic pump 1 . For this reason, activation is only required when changing the work areas from A to B or from B to C and should then only be maintained for a short time until the new operating state is reached. This is achieved by connecting a switching element S 2 in series with a timing relay 11 in the second branch of the parallel connection; the switching element and the timing relay interact according to the signal timing diagram shown in FIG. 3, as will be explained below.

The time t is plotted on the abscissa of the diagram. The position 0 or I on the ordinate means that the switching element or the timing relay are open or the solenoid valve occupies position I, while in the position 1 or II the switching element or timing relay are closed or the solenoid valve Occupies position II. If the setpoint generator is set in working range A , the switching element S 2 is in position 0 (open), while it is in setting 1 in working areas B and C in position 1 (closed), with a transition from Work area B to work area C there is a brief, pulse-like opening of the switching element. The timing relay is determined so that it also closes when the switching element closes, ie when the switching element closes; after the lapse of a time period T , which corresponds to the time constant of the time relay, it opens again, regardless of whether the switching element S 2 is closed or not. Since the solenoid of the solenoid valve is only energized when the switch and the timing relay are closed at the same time, the solenoid valve is, as FIG. 3 also shows, each time the work areas change from A to B and from B to C in the Position II and switches the residual fluid flow to the main circuit during the suitably dimensioned time constant T , so that the lifting cylinder can be moved to the new requested position with the entire available pressure fluid flow of the hydraulic system at the maximum possible speed.

As can be seen from the above, the hydraulic pump for the main circuit can be optimally designed for those pressure fluid flows which are required in continuous operation in operating area B , since the residual fluid flow is switched on for the peak loads when switching to other operating areas, so that the ratio is moderate low hydraulic heat loss is developed. In addition, a considerable amount of energy is saved in the operation of the hydraulic system described above. In many cases, even a cooler for the pressure fluid can be saved or at least reduced due to the greatly reduced loss line, which results in heating of the pressure fluid.

Claims (5)

1.Hydraulic system for agricultural tractors with at least two hydraulic pumps for the separate supply of a main circuit for a power lift or the like controlled by a control device and for auxiliary devices which can be actuated by directional control valves on the one hand and a secondary circuit for a power steering or the like on the other hand, which is independent of the performance of its hydraulic pump a certain pressure fluid requirement, said a via schüssig conveyed residual fluid flow to the main circuit supplied and the supply of the rest of the fluid flow is controlled to the main circuit by a valve arrangement, the feeding either allows or interrupts, characterized in that for controlling the residual fluid flow to the main circuit in response to Various operating parameters, the valve arrangement is formed by a solenoid valve ( 10 ) which is controlled by an electrical circuit which comprises a parallel connection, in a first branch the parallel connection, a first switching element ( S 1 ) controlled by an actuation extent of the directional control valves ( 5 ) and, in a second branch, a second switching element ( S 2 ) controlled in series by working areas ( A, B, C ) of a setpoint generator ( 4 ) of the control device a timing relay ( 11 ) is arranged. 2. Hydraulic system according to claim 1, characterized in that the valve ( 10 ) is a 3/2-way valve and with an interrupted supply leads the residual fluid flow to a pre-storage container ( 7 ). 3. Hydraulic system according to claim 1 or 2, characterized in that the valve ( 10 ) allows the supply when one or more groups of operating parameters assume corresponding values. 4. Hydraulic system according to one of claims 1 to 3, characterized in that the first switching element ( S 1 ) closes when the actuation of the directional control valves ( 5 ) causes an operating state change of the additional devices, in which they have an increased pressure fluid requirement. 5. Hydraulic system according to one of claims 1 to 4, wherein the setpoint generator in a first working area causes a complete lowering of the power lift, in a second working area a traction or position control of the power lift and in a third working area a quick stroke of the power lift that the second switching element ( S 2 ) is open in the first working area ( A ) and closed in the second ( B ) and third working area ( C ), that it is opened briefly during the transition from the second to the third working area and that the time relay ( 11 ) also closes after a closing of the second switching element for a certain period of time ( C ) and then opens again.