EP2199622A2 - Hydraulic system - Google Patents

Abstract

The hydraulic system (10) has a drive motor (25), a hydraulic adjusting pump (18) driven by the drive motor, a hydraulic load (12) driven by the adjusting pump, and an electronic control unit (32). A feed flow controller (20) is provided, which comprises an adjusting unit (38) controlled by a control unit. The controlled pressure difference value is changed in the feed flow controller by the electronic control unit. The electronic control unit detects an input speed dependent signal.

Description

The invention relates to a hydraulic system with a drive motor, a driven by the drive motor hydraulic variable displacement pump driven by the variable displacement hydraulic consumer and an electronic control unit, wherein the variable displacement pump is equipped with a flow regulator, with which adjusting between consumer and variable pressure difference on a preset control pressure difference value is adjustable.

Agricultural machines are known, for example tractors, or other types of working machines, such as construction machines or telescopic loaders, which have a hydraulic system with which one or more hydraulic consumers are operated, eg hydraulic cylinders, hydraulic motors or other hydraulically operated components. Such hydraulic systems include hydraulic pumps which translate directly or via a rigid transmission gear into fast or slow, with the drive shaft, a drive motor are connected. The maximum deliverable volume flow of the hydraulic pump thus changes with the speed of the drive motor. The faster the drive motor turns, the larger the volume flow that can be delivered by the hydraulic pump. In adjustable load-sense controlled hydraulic pumps, so-called hydraulic variable displacement pumps, as they are used today as state of the art, the subsidized maximum delivery volume can be adapted to the demand required by the hydraulic consumer. This is usually done via a so-called flow regulator, which is a preset control pressure difference between the pressure at the output of the variable and the consumer reported Load sense signal (called LS signal below) regulates or maintains. The delivery flow regulator of an LS-controlled variable displacement pump now works in such a way that it adjusts the delivery volume flow of the variable displacement pump so that the preset control pressure difference, which can be set permanently on the delivery flow regulator via an adjusting spring, is always kept constant. The exact mode of action of such a (pressure) flow regulator, can be read in the relevant literature and is as such prior art.

The delivery volume flow which can be delivered from a hydraulic valve to a consumer, for example a hydraulic cylinder or a hydraulic motor, is directly dependent on this preset control pressure difference. About the adjusting spring and a control piston of the flow control a certain pressure to be regulated is set, which forces the variable to maintain a set pressure corresponding control pressure difference between the output of the variable and consumer (LS signal) upright. In order to achieve this control pressure difference, the adjustable in accordance with an adjusting piston or adjustable Fördervolumenverstelleinheit the variable and starts to promote a corresponding flow rate. The adjusting piston is hydraulically connected to the flow controller and changes its position in dependence on the control pressure difference present or set on the flow regulator. The Fördervolumenverstelleinheit may for example comprise a swash plate which is connected to control or reciprocating piston, wherein the rotary motion is converted into a longitudinal movement of the reciprocating piston by rotating the swash plate becomes. The volume flow conveyed by the variable flow pump flows through the lines and valves of the hydraulic system and generates certain pressure losses in the lines and at the respective valves to the consumers. The pressure, which then sets behind the valves or at the consumer, is reported as load pressure (LS signal) back to the variable displacement pump (via a load pressure line (LS line), which is connected to the flow regulator) and causes the variable displacement pump to do so To promote such a volume flow that the pressure at the output of the variable by the control pressure differential value is higher than the load signal supplied by the LS signal at the consumer.

The further now a valve is removed from the variable displacement pump, the larger the pressure loss due to the longer flow path, which leads to the effect that valves which are farther away from the variable displacement pump than other valves will allow less volumetric flow to reach a consumer, although there are valves of the same type. To compensate for this effect, it is known to use valves that report an increased load signal to the pump, such as in the EP 176 0 325 A2 is disclosed.

Simplified applies accordingly, that one needs a certain pressure to push a certain volume flow through a pipe and / or a valve. Since the pressure losses increase as it flows through the volume flow, so it would be advantageous to constructively keep the cross sections and guides of the lines and holes as large as possible and the losses through the valves as small as possible, if a certain amount of hydraulic oil for a Wants to harness consumers. If the losses are too big now and take From the volumetric flow, this can be compensated by increasing the cross section of the valve openings, ie volume changes can be changed, ie raised or lowered, by changes in the cross section of the valve openings.

Other ways to change the volume flow aim to change an acting on the flow control of the variable displacement force. So will in the EP 0 439 621 B1 discloses that for fine operation of the hydraulic system by manually triggering a force on the flow controller, the control pressure difference of the variable displacement can be reduced, resulting in a lower maximum flow in the hydraulic system and the valves result.

Now there is the problem that it may be advantageous for environmental and economic aspects to operate a hydraulic system of a working machine in the lower engine speed range. This has the consequence that in today's variable displacement pump sizes then too little flow for the applications is available, resulting in the use of larger variable displacement, so that at low engine speeds large volume flows can be promoted. This in turn means that at high engine speeds much larger (not exhaustible) volume flows are promoted, which lead to very large power losses in the overall power balance. One could overcome these problems, at least in part, by increasing the control pressure difference of the pump, which would eventually lead to a higher fuel consumption of the machine, since you need a certain power, or a certain flow rate required to the To achieve control pressure difference. It is also possible to design all lines and valves to the maximum pump capacity, which in turn would lead to very high costs of the individual components and space problems on the machine. EP 349 092 B1 discloses another way to allow high volume flows at low engine speeds, but to limit the flow rate at high engine speeds. In this case, the maximum delivery volume delivered by the variable displacement pump is limited, the delivery rate of the variable displacement pump being measured (eg by measuring the position of the delivery volume adjustment mechanisms, eg the adjustment angle of an adjusting disc or swashplate) and monitored. However, these variable displacement pumps and the corresponding control electronics are complex and expensive.

The object underlying the invention is seen to provide a hydraulic system of the type mentioned, by which the aforementioned problems are overcome. In particular, a hydraulic system is to be created with simple, safe and cost-effective means, which provides a large delivery volume at low input speeds, but limits this at higher input speeds to a certain maximum value.

The object is achieved by the teaching of claim 1. Further advantageous embodiments and modifications of the invention will become apparent from the dependent claims.

According to the invention, a hydraulic system of the type mentioned above is formed such that the flow regulator by the control unit comprises controllable actuating means, through which the control pressure differential value on the delivery flow controller via the electronic control unit is variable, wherein the electronic control unit detects a drive speed-dependent signal, as a function of which a control signal for the controllable actuating means can be generated by the control unit, which change the control pressure difference value on the flow controller. By detecting the drive speed and generating a corresponding control signal for the remotely controlled by the control unit actuating means on the flow controller, a preset control pressure difference on the flow controller in response to the drive speed can be selectively changed.

This means that at a low drive speed, the control pressure difference, for example, P = P1 bar. This setting is suitable for example to promote a volume flow through the valves up to a size of V1 l / min. However, due to its maximum delivery volume, the variable displacement pump has the option of delivering delivery volumetric flows of Vmax l / min at a maximum input speed, which would lead to high losses in the lines and valves. At idling speed, this pump now conveys eg a maximum volumetric flow rate of Vleer l / min (Vleer <V1 <Vmax) and with increasing input speed (U +) the volumetric flow rate (V) increases. Now it is conceivable that on reaching the V1 l / min limit, the control pressure difference P bar is further reduced (P = P1-P (U), where P (U) is to be understood as a function of the drive speed and increases with increasing drive speed ) and thus reduces the delivery volume of the variable, so that at maximum drive speed of eg Umax rpm still only V (1) l / min are funded by the variable displacement. Is that sinking? Drive speed again, one raises the control pressure difference and thus the volume again slowly (P = P1 - P (U), where P (U) decreases with decreasing input speed) until the original value (P = P1) has been reached again. The corresponding functions and calculation algorithms are preferably stored in the electronic control unit. A corresponding control signal is generated by the control unit and directed to the actuating means on the flow regulator for controlling the same. By controlling the actuating means of the control pressure differential value is changed on the flow controller.

When a presettable input speed value is exceeded, the control pressure difference value of the variable displacement pump can be reduced. Depending on the application, the presettable input rotational speed value, which triggers the adjustment of the control pressure differential value, can preferably be predetermined via an input module on a driver's display of a working device or via another suitable input interface of the control unit. However, according to the capacity of the variable displacement pump, a fixed drive speed value may already be predetermined and stored in the control unit.

When a presettable input speed value is exceeded, the control pressure difference value can be changed in proportion to the input speed, wherein the control unit reduces the control pressure difference value with increasing input speed and increases with decreasing input speed. In this regard, the control signal generated by the control unit is preferably continuously adapted to a drive speed change, so that an operator of the Systems does not notice the change in the volume of delivery directly.

For special applications, it is envisaged to exploit the maximum possible delivery volume of the variable. For this adjustment means are provided, in dependence of which the control signal is modifiable, and the control pressure difference value via the adjusting means is variable, such that the control pressure difference value can be reduced or increased independently of the drive speed. Thus, an operator can quasi "override" the control of the control means taken control of the flow control valve and disable by appropriate inputs to the setting means, for example on an input module or on an input button with thumbwheel or a potentiometer the drive speed-dependent control function of the control unit and by directly specifying a via the setting means predeterminable input signal modify the control signal, so that despite the original drive speed-dependent generation of a control signal, the signal input by the setting means is prioritized. This makes it possible to bypass a drive-speed-dependent control and operate, for example, even at high input speeds, the hydraulic system with a high control pressure differential value or set any control pressure difference value at any drive speed. There are special applications where the operator desires to take advantage of the maximum displacement of the variable displacement pump, regardless of the power losses. Such an application would be, for example, the operation of a front loader in which the operator would like to achieve the shortest possible cycle times and thus more handling capacity. In such a case would a variable displacement pump does not help much, if not all lines and valves would also be enlarged. Here, it may then be useful to increase the control pressure difference targeted to ensure that at higher input speeds, the variable can fully swing up to promote more flow.

The hydraulic system may further include a temperature sensor that detects the temperature in the hydraulic system and provides a corresponding signal to the control unit. In particular, the viscosity of a hydraulic fluid depends on the temperature, so that it may be advantageous, at low temperatures, or at a high viscosity of the hydraulic fluid to adjust the control pressure difference value on the flow regulator further depending on the viscosity or temperature, for example, to increase , Furthermore, it may be advantageous to counteract viscosity-related cavitation problems at extremely low temperatures so that the control pressure differential value is limited or reduced at the delivery flow regulator and an increase takes place only at a certain temperature, regardless of or dependent on the drive speed. Likewise, it may be advisable to adapt the control pressure difference value on the delivery flow regulator to the lower flow losses at higher temperatures, that is to say to reduce it, for example. Thus, both depending on the input speed alone, as well as in combination depending on the temperature in the hydraulic system can enter state conditions for which an adjustment of the control pressure differential value at the flow controller is advantageous. Corresponding control functions or control algorithms can be implemented in the electronic control and stored as corresponding state diagrams be. Based on these control functions or control algorithms corresponding control signals, both in dependence on the drive speed, as well as in dependence on the temperature, for driving the actuating means or for adjusting the control pressure difference value can be generated at the flow controller.

The adjusting means on the delivery flow regulator preferably comprise an electric motor, which can be controlled by the control unit and can adjust the adjusting spring in the delivery flow regulator. Furthermore, it is also conceivable to use an electromagnet which adjusts the adjusting spring in the flow regulator. Preferably, the adjustment of the flow control valve or the adjusting spring should be made directly to the bias of the adjusting spring of the flow control valve. This adjustment can be effected electrically or electromagnetically as mentioned above, but also hydraulically, pneumatically or purely mechanically, with an electrical or electromagnetic adjustment being preferred, since this adjustment is easier to handle than other types of adjustment. This adjustment can now increase or decrease the spring preload, whereby the control pressure difference is automatically adjusted. The adjustment can take place, for example, via a proportional magnet which is effective in both directions. Of course, it is also conceivable to allow an adjustment in one direction only. Since it can always happen that the electronics on the work vehicle fails, it makes sense to provide measures that prevent failure of the electronics that it comes to a failure of the entire hydraulic system. For this reason, the use of a stepper motor for the adjustment of the control pressure difference is particularly suitable. The stepper motor has the advantage that it has a certain self-locking and can be moved very precisely in a certain position (angle of rotation), which he does not leave, unless he gets a new control signal or a very strong force pulls at him.
Such a stepper motor can be easily connected to the adjusting screw for adjusting the control pressure difference of the flow control valve and can then very accurately and very quickly turn this adjusting screw depending on the control signal, so that the control pressure difference can be adjusted very sensitively. Should a failure of the electronics occur, the stepper motor would simply remain in its last position, thus ensuring that at least a certain minimum operation of the hydraulic system remains ensured.

An inventive hydraulic system is used in work vehicles used in agriculture, ie in agricultural vehicles, such as tractors with or without front loader and telescopic loaders. Furthermore, such a hydraulic system is also suitable for use in construction machines, for example in excavators or wheel loaders.

The hydraulic system according to the invention enables optimum operation of a hydraulic system in all drive-dependent operating states of the vehicle and serves, in particular, to reduce power losses and to provide large volume flows at low drive speeds. Furthermore, existing smaller line cross-sections and valves can be used in spite of a variable displacement pump. If required, very large flow rates are possible despite small pipe cross-sections and valves. A retention of existing valves and lines, regardless of the use of a larger variable displacement pump, this is possible. Furthermore, it can be ensured in spite of electronic control of the flow control valve in case of failure of the electrical system that the existing hydraulic system is still available.

Reference to the drawing, which shows an embodiment of the invention, the invention and further advantages and advantageous developments and refinements of the invention are described and explained in more detail below.

Fig. 1

einen schematischen hydraulischen Schaltplan eines erfindungsgemäßen Hydrauliksystems mit einem Elektromotor als Stellmittel,

Fig. 2

einen schematischen hydraulischen Schaltplan eines alternativen erfindungsgemäßen Hydrauliksystems mit einem Proportionalventil als Stellmittel und

Fig. 3

ein Arbeitsfahrzeug mit einem Hydrauliksystem gemäß Figur 1 oder 2.

It shows:

Fig. 1

a schematic hydraulic circuit diagram of a hydraulic system according to the invention with an electric motor as adjusting means,

Fig. 2

a schematic hydraulic circuit diagram of an alternative hydraulic system according to the invention with a proportional valve as the actuating means and

Fig. 3

a work vehicle with a hydraulic system according to FIG. 1 or 2 ,

FIG. 1 shows a hydraulic system 10 for operating a hydraulic consumer 12, for example a hydraulic cylinder for raising and lowering a front loader 14.

The hydraulic system 10 comprises a hydraulic tank 16, a hydraulic variable displacement pump 18 with a delivery flow regulator 20 for setting a control pressure difference value between the variable displacement pump 18 and the consumer 12, a pressure limiter 22 for limiting the operating pressure for the variable displacement pump 18, and an adjusting piston 23 for adjusting and limiting the delivery volume of the variable displacement pump 18 which can be adjusted by means of a delivery volume adjusting unit 18. Further, a stop 23 designed as an adjusting spindle is provided provided for the adjusting piston 23 which is engageable with the adjusting piston 23 into engagement and with which a maximum delivery volume of the variable displacement pump 18 is adjustable. The variable displacement pump 18 is driven by a drive motor 25. Between the consumer 12 and variable displacement pump 18, a hydraulic control valve 26 is connected, via which the hydraulic consumer 12 is controlled. Between load 12 and control valve 26, a load pressure line 28 is connected, which is connected to the flow regulator 20, wherein the load pressure line 28 has a connected to the tank 16 pressure relief diaphragm 29 and a closing in the direction of the consumer 12 check valve 30, wherein the check valve 30 between the Pressure relief diaphragm 29 and the consumer 12 is arranged. Furthermore, the hydraulic system 10 has an electronic control unit 32 which is connected to a speed sensor 34 and an adjusting device 36. The delivery flow regulator 20 has adjusting means 38, which are designed as electric motors, preferably as stepping motors, and can be controlled by the electronic control unit 32.

The drive motor 25 is connected directly to the variable displacement pump 18, which is shown here only by way of example. Of course, here also sub or transmission gear can be interposed. The drive shaft of the motor 25, preferably as an internal combustion engine is formed, but may for example be designed as an electric motor is provided directly with the speed sensor 34, which passes a speed signal to the electronic control unit 32. Furthermore, the electronic control unit 32 may receive input signals from the adjustment device 36, which then takes into account in the generation of a control signal for the actuating means 38. In the generation of a control signal, only a speed signal supplied by the rotational speed sensor 34 is considered in the first place, as a function of which the electronic control unit 32 generates the control signal for the actuating means 38. However, if an additional input via the adjustment 36, so the first based on the speed signal control signal is modified accordingly. This has the background that can be signaled by the adjustment means 36 by an operator that no speed-dependent control of the actuating means 38 is to take place on the flow controller 20, but rather by the operator prescribable control variables for controlling the actuating means 38 are to be used. For example, the operator can specify the maximum delivery volume value or another adjustable delivery volume value for the variable displacement pump 18 via the setting means 38, which is to be set by the electronic control unit 32 independently of the rotational speed of the drive motor 25.

The delivery flow regulator 20, which is preset with a fixed control pressure difference value via a biasing spring 40, can now be adjusted by adjusting the bias of the biasing spring 40 via the adjusting means 38, so that the control pressure differential value can be both raised and lowered. Depending on the prevailing pressure ratio of the between Control valve 26 and consumer 12 present system pressure and the present at the variable pump output system pressure results in a pressure difference, which is the flow controller 20 via the load-sensing pressure line 28 and a connected to the output of the variable displacement pump 18 control pressure line 42. According to the preset control pressure difference value, the adjusting piston 23 connected to the delivery flow regulator 20 via the pressure limiter 22 is brought into a corresponding control position. In accordance with the control position of the adjusting piston 23, in turn the delivery volume adjusting unit 24 of the variable displacement pump 18 is adjusted. Thus, the delivery volume of the variable displacement pump 18 is controlled or regulated via the regulating pressure differential value set on the delivery flow regulator 20. The regulating pressure difference value on the delivery flow regulator 20 can be adjusted by way of the biasing spring 40, so that the regulating pressure difference value can be adjusted via the adjusting means 38 connected to the pretensioning spring 40 and can thus be controlled or adjusted or regulated via the electronic control unit. Thus, in dependence on the signal supplied by the rotational speed sensor 34, a control of the actuating means 38 on the delivery flow regulator 20 and thus of the delivery volume of the variable displacement pump 18 can be made.

For this purpose, stored or stored threshold values are preferably implemented in the electronic control unit 32, by means of which a corresponding control program can be started so that, for example, after reaching a predefinable speed value on the drive motor 25, the control pressure differential value is reduced further as a function of the further increasing speed To reduce delivery volume accordingly and to limit the flow rate.

Via the adjusting means 36, an operator can now "lever out" or "override" the preset threshold values, so that independently of the rotational speed, a control of the actuating means 38 which can be predetermined via the adjusting means 36 can take place. For example, the control pressure difference value can be set to a constant value via the setting means 36, wherein the control unit 32 then controls the setting means 38 independently of the rotational speed of the drive motor 25. The adjusting means 36 may comprise a plurality of occupied switches or an input display or an adjustable potentiometer, etc., with which corresponding setting variables can be specified. Furthermore, activation or deactivation of the speed-dependent control of the delivery flow regulator 20 can also take place via the adjustment means 36.

The temperature sensor 37 detects, as already mentioned, the temperature of the hydraulic fluid and supplies a corresponding temperature signal to the control unit 32. The control unit 32, both in dependence on the drive speed alone and in combination depending on the temperature, the control pressure difference value on the flow controller by adjusting the Adjusting means 38 change or control or regulate. Thus, the control pressure difference value on the delivery flow regulator can additionally be reduced or increased as a function of the temperature of a hydraulic fluid of the hydraulic system 10. Corresponding control signals are generated by control functions or control algorithms implemented in the control unit 32 as a function of the drive speed and / or of the temperature.

In an alternative embodiment of the invention, instead of in FIG. 1 an electric proportional solenoid 38 'is used as shown in FIG FIG. 2 is shown. The proportional magnet 38 'is preferably also effective in both directions, wherein generally an adjustment of the flow controller 20 in only one direction is quite conceivable, so that, for example, only a reduction of the control pressure difference value is made possible.

FIG. 3 shows an agricultural vehicle 44 in the form of a tractor, which is equipped with a front loader 14, which by a in FIG. 1 or 2 described hydraulic system is operated. In this case, other applications for the hydraulic system according to the invention are conceivable, for example for use in construction machines or telescopic loaders. The hydraulic system according to the invention can also be used to supply other hydraulic consumers not explicitly listed here, for example for supplying three-point hitch devices to agricultural tractors.

Although the invention has been described by way of example only, in light of the foregoing description and the drawings, those skilled in the art will recognize many different alternatives, modifications and variations which are within the scope of the present invention.

Claims (8)

Hydraulic system (10) with a drive motor (25), a hydraulic variable displacement pump (18) which can be driven by the drive motor (25), a hydraulic consumer (12) which can be driven by the variable displacement pump (18) and an electronic control unit (32), wherein the variable displacement pump ( 18) is equipped with a flow control device (20), with which a between the consumer (12) and variable (18) adjusting pressure difference can be regulated to a preset control pressure differential value, characterized in that the flow controller (20) by the control unit (32) controllable Adjusting means (38, 38 ') by which the control pressure differential value on the flow controller (20) via the electronic control unit (32) is variable, wherein the electronic control unit (32) detects a drive speed-dependent signal, in dependence on the control unit (32) Control signal for the controllable actuating means (38, 38 ') can be generated, which is the rule change the pressure difference value on the flow regulator (20). Hydraulic system (10) according to claim 1, characterized in that the control signal when exceeding a presettable input speed value reduces the control pressure difference value. Hydraulic system (10) according to claim 1 or 2, characterized in that the control signal when exceeded a presettable input speed value changes the control pressure difference value in proportion to the input speed, wherein the control unit (32) reduces the control pressure difference value with increasing input speed and increases with decreasing input speed. Hydraulic system (10) according to one of claims 1 to 3, characterized in that adjusting means (36) are provided in response to which the control signal is modifiable, and the control pressure difference value via the adjusting means (36) is variable, such that the control pressure difference value independent of the drive speed can be reduced or increased. Hydraulic system (10) according to one of claims 1 to 4, characterized in that a temperature sensor (37) is provided and in response to a temperature signal from the temperature sensor (37) supplied the control signal is modifiable, such that the maximum delivery volume in addition to Temperature of a hydraulic fluid of the hydraulic system can be reduced or increased. Hydraulic system (10) according to one of claims 1 to 5, characterized in that the adjusting means (38) comprise an electric motor. Hydraulic system (10) according to one of claims 1 to 5, characterized in that the adjusting means (38 ') comprise an electromagnet, preferably a proportional magnet. Work vehicle (44), in particular agricultural vehicle or construction machine, with a hydraulic system (10) according to one of claims 1 to 7.

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