WO1997004253A1

WO1997004253A1 - Safety circuit

Info

Publication number: WO1997004253A1
Application number: PCT/EP1996/001908
Authority: WO
Inventors: Winfried RÜB
Original assignee: Mannesmann Rexroth Gmbh
Priority date: 1995-07-21
Filing date: 1996-05-07
Publication date: 1997-02-06
Also published as: DE19526754A1

Abstract

The description relates to a safety circuit for the alternating running of consumers, e.g. gear components of a power shift gear, and a proportional valve for such a safety circuit, in which the proportional valve can preferably be electrically adjusted. The proportional valve has a switch output to which one of the consumers is connected, while a proportional output of the proportional valve is taken to another consumer. It is possible by the corresponding control of the proportional magnet to switch over gently from one consumer to another without the need for a hydraulic device to modulate the switching process.

Description

description

Safety circuit

The invention relates to a safety circuit and a suitable proportional valve for alternating

Control of n consumers according to the generic term of

Claim 1 or the preamble of claim 9.

Such safety circuits are frequently used to prevent errors in the electrical, hydraulic or mechanical control of transmission elements of a hydraulic system, the safety circuit being intended to ensure that the individual control elements or consumers of the hydraulic system are only controlled alternately.

In power shift transmissions, for example, actuating elements such as synchronous clutches, friction load clutches and friction load brakes are actuated hydraulically. The shift logic for the individual gears and the shift sequence sequences are subject to predetermined schemes, the stipulations of which must be adhered to. If several control elements that cannot be combined are switched on at the same time, the gear unit may become blocked and destroyed. In addition, an unstable operating state can be achieved in that the unforeseen activation of consumers poses a considerable risk to the operator. Such powershift transmissions are used, for example, in heavy agricultural vehicles.

With machine tools, handling machines, such as assembly robots, etc., certain work Sequence preprogrammed, with individual control elements being controlled according to the program sequence. Precautions must also be taken in the case of such devices in order to prevent the individual actuating elements from being activated at the same time and thus to prevent damage to the device and endanger third parties.

A number of designs are known to solve the aforementioned problems.

For example, powershift transmissions with two starting clutches are used in agricultural utility vehicles. To ensure that both starting clutches cannot be activated at the same time, they are metered via a mechanical valve and selected by an electrical switching valve. If the control slide is stuck in the event of a defect in the electric switching valve, the starting clutch cannot be changed, and the transmission can only be operated with the gear that is specified by the blocked switching valve. On the other hand, however, no operating state can occur due to the interposition of the electrical switching valve, in which both starting clutches are activated at the same time.

In order to achieve a smooth transition between the individual shift stages of a powershift transmission, the hydraulic systems of the powershift transmissions are often designed with complex hydraulic modulation circuits, hydraulic elements being provided which on the one hand are the shifting process and on the other hand the modulation when changing are assigned between the switching stages.

Such a circuit is shown in sections in FIG. 1. Accordingly, the illustrated power shift Transmission two transmission areas 2, 4, with a high / low changeover taking place via the transmission area 2, for example to choose between a high-speed driving area and a low-speed driving area of an agricultural utility vehicle. The transmission area 4 is only shown in sections in FIG. 1 and contains a multiplicity of transmission elements 6, 8, 10 etc. connected in series, which can be switched on and off alternately.

The known safety circuit is intended to ensure that not more of the gear elements 6, 8, 10 etc. of the gear range 4 or the gear elements 12, 14 of the gear range 2 are switched on at the same time.

The transmission elements (clutches, brakes, etc.) are supplied with hydraulic fluid via a pump 16 and a pump line 17, from which branch lines are led to the individual transmission areas 2, 4.

Since these are practically identical in terms of the modulation circuit and the switching device, only the switching elements of the transmission area 2 are to be explained here. However, a detailed description is omitted here, since it is of subordinate importance for the understanding of the present invention.

The control of the gear elements 12, 14 takes place via two switching valves 18, 20 connected in series, each of which is pre-controlled via a switching valve 22 or 24. The changeover valve 20 assigned to the gear element 14 is fed via the changeover valve 18, which is assigned to the gear element 12 of the gear range 2. That is, the transmission element 14 is only supplied with hydraulic fluid from the pump 16, if the switching valve 18 remains in its starting position shown and the switching valve 20 is moved from its shown starting position into its second switching position by corresponding actuation of the switching valve 24, so that the hydraulic fluid via the pump line 17, the switching valve 18, the Changeover valve 20 is guided to the gear element 14. In the event that the switching valve 22 is brought from its starting position into its second switching position, the switching valve 18 also switches over, so that the transmission element 12 is supplied with hydraulic fluid via the pump line 17. At the same time, the gear element 14 is connected to the tank T, regardless of the position of the changeover valve 20, so that a simultaneous engagement of the gear elements 12 and 14 is prevented.

The switching valves 22 and 24 are actuated electromagnetically and connected to a central control (not shown), via which the individual gear elements are selected.

In the known exemplary embodiment, a solution with a pilot control of the changeover valves 18, 20 via the switching valves 22 and 24 is selected, since large gears generally require considerable amounts of oil, so that a piloted solution is easier to handle in a smaller installation space.

In order to prevent sudden loads in the hydraulic system from occurring during the switching processes, ie when changing the gear elements, the changeover / switching valves 18 to 24 are preceded by a modulation unit 26, which in turn consists of two valve arrangements (not described in more detail here) consists. - o-

As is apparent from FIG. 1, a modulation unit 26 is assigned to each transmission area 2, 4, while a combination of changeover valve and switching valve is assigned to each transmission element 6 to 10 etc. The circuitry outlay for such powershift transmissions is very large, since the modulation units 26 are very complicated and a combination of a changeover valve and a shift valve must be assigned to each transmission element.

In contrast, the object of the invention is to create a safety circuit and a proportional valve for such a safety circuit, with which a reliable alternating control of at least two consumers is made possible with minimal circuit complexity.

With regard to the safety circuit, this object is achieved by the features of patent claim 1 and, with regard to the proportional valve, by the features of patent claim 9.

The measure of assigning a (proportional) valve with a switching valve function to the (n-1) consumers, so that the proportional valve is practically designed with a proportional output and a switching output, allows one of the consumers - for example a transmission area - to use the Switching output can be supplied with hydraulic fluid. With appropriate control of the proportional valve, the switching output is shut off, while the hydraulic output or the other consumers of the hydraulic system or the valve arrangements assigned to them can be supplied with hydraulic fluid by gradually opening the proportional output. This means that the proportional valve both the modulation of the switching process and the optional control of the Consumer can take over, so that the complex valve arrangement according to FIG. 1 of the safety circuit can be replaced by a comparatively simple valve arrangement.

By using the proportional valve according to the invention, the circuitry complexity of the safety circuit can be reduced considerably since the function of several valves of known safety circuits is combined in a single valve. In the event that the entire safety circuit is combined to form a total valve, its installation space can thus be reduced to a minimum, since the individual elements are only relatively compact units.

The complexity of the circuitry can be further reduced if the proportional valve is actuated electromagnetically via one or more proportional magnets, so that the switching position of the control slide and the adjustment range of the proportional valve can be traversed one after the other by appropriately controlling the proportional magnet via a central control unit.

The operational reliability of the circuit can be further increased by the control slide of the proportional valve according to the invention being biased into its switching position by means of a valve spring, so that a defined switching position is specified, for example, when the proportional magnet is defective.

A further increase in operational safety consists in designing the proportional valve as a pressure reducing valve (DRE) by tapping a control pressure at the switching connection and acting on the control slide against the proportional solenoid. The transition from the switching range of the proportional valve to the proportional range can be optimized by designing the proportional valve with a positive overlap, so that in the transition range between the switching range and the proportional range, both the switching connection and the proportional connection with reference to one Pressure connection of the proportional valve are shut off.

The circuitry complexity can be further reduced if, in the case of a circuit with n consumers, the last consumer in the series is assigned a pressure reducing valve instead of the above-described proportional valve according to the invention, to the output of which the nth consumer is connected. Since the nth consumer is the last link in the chain, the associated valve does not need a switching output.

This means that only two basic valve types (1st proportional valve according to the invention, 2nd pressure reducing valve) are used in the safety circuit according to the invention for controlling n consumers, so that the modular system can be easily adapted to different requirements .

Because of the two simple basic valve types, the circuit diagram of the overall valve is considerably simplified, so that a simple channel construction of the complete control valve housing is also possible.

The activation of the consumers can be further optimized by electromagnetically actuating both the proportional valve according to the invention and the pressure reducing valve assigned to the nth consumer, and both valve arrangements have a common control unit is assigned. The modulation can be set very easily by the central control unit and can also be adapted to different operating states. The development effort for the actual hydraulic system is comparatively low, since the modulation is shifted exclusively to the electrical components.

Proportional valves are particularly well suited for the safety circuit according to the invention, in which the proportional function is only taken up after the control slide has been brought from its switching position into the middle position.

Further advantageous developments are the subject of the other subclaims.

A preferred exemplary embodiment of the invention is explained below on the basis of schematic exemplary embodiments.

Show it:

1 shows a section of a circuit diagram of a known safety circuit;

2 shows a circuit symbol of a proportional valve according to the invention;

3 shows a characteristic curve of the proportional valve from FIGS. 2 and

4 shows a safety circuit with the proportional valve from FIG. 2.

2 shows the circuit symbol of a proportional valve 30 according to the invention. Accordingly, this is designed as a 4-way valve and has a pressure connection P, a tank connection T, a first connection A and a second connection B. As will be explained further below, the proportional valve according to the invention is a combined switching / proportional valve, the first connection A being referred to below as the proportional connection A, and the second connection B being referred to as the switching connection B, since the control of the proportional connection A by means of the proportional function and the control of the switching connection B by means of the switching function of the proportional valve 30.

Several exemplary embodiments of such a proportional valve are shown in the applicant's patent application P 44 20 164.8. In order to avoid unnecessary repetitions, reference is made to the disclosure of this application with regard to the specific structure, which is to be included in the disclosure of the present application.

A slide valve 32 of the proportional valve 30 is actuated via a proportional magnet 34, with DC solenoids generally being used in which a force or a path is generated as an output variable in proportion to the electrical current as an input variable.

A valve spring 36 is provided on the end face of the control slide 32 remote from the proportional magnet 34, via which the control slide 32 is biased into its initial position (c) shown in FIG. 2.

The pressure in the area of the proportional connection A is led via a control pressure line 38 to the end of the control slide 32 which is acted upon by the valve spring 36, so that the proportional valve 30 acts practically as a pressure relief valve with reference to the pressure in the proportional connection A.

In its basic position shown in FIG. 2, the tank connection T with the valve slide 32 Proportional connection A and the pressure connection P are connected to the switching connection B. Accordingly, the hydraulic fluid in the switching position (c) of the proportional valve 30 is guided to the consumer connected to the switching connection B, while the consumer connected to the proportional connection A is connected to the tank.

With increasing current at the proportional magnet 34, the control slide 32 is switched to its central position (b), in which the pressure connection P is closed and the proportional connection A and the switching connection B are connected to the tank connection T. This means that hydraulic fluid cannot be supplied to the consumption connected to the proportional connection A or to the switching connection B, but that the hydraulic fluid in the supply line to the consumers is expanded into the tank.

With further excitation of the proportional magnet 34, the control slide 32 reaches the proportional range, so that any intermediate position between the central position (b) and the end position (a) on the left in FIG. 2 can be set, and thus the connection from the pressure ¬ circuit P to the proportional connection A is opened as a function of the current at the proportional magnet 34, while the connection of the control connection B to the tank T is maintained.

Accordingly, with increasing current at the proportional agent 34, the pressure in the area of the proportional output A will continuously increase to a predetermined value.

By correspondingly controlling the proportional magnet 34, a predetermined pressure at the proportional connection A can thus be set. The pressure at the switching connection B in the switching position (c) corresponds approximately to that Pressure at the pressure port P or is somewhat lower due to the throttling effect in the valve.

As already mentioned, the pressure at the proportional connection A is led via the control pressure line 38 to the spring side of the control slide 32, so that the corresponding control pressure acts against the proportional magnet 34. When a predetermined limit pressure in the proportional connection A is exceeded, the force exerted by the control pressure and the valve spring 36 outweighs the force exerted by the proportional magnet 34, so that the control slide 32 moves out of its proportional position (between the end position (a) and the middle position (b ») is moved back to its initial position (c), so that the proportional connection A is again connected to the tank T and the pressure at the proportional connection A is reduced. In this way, the fluid pressure at the proportional connection A can be limited to a maximum value, so that the Proportional valve 30 acts as a pressure relief valve for the pressure in the proportional connection A.

In the exemplary embodiment described, the valve spring 36 is in principle only intended to move the valve spool back into its basic position (c) shown in the event of a power failure, etc. The actual adjusting movement of the control slide 32 is essentially influenced by the force of the proportional magnet 34 and the control pressure in the control pressure line 38.

It is therefore a combined switching / proportional valve, the positions (a) and (b) the setting range of the proportional part of the valve arrangement and the switching positions (c) and the middle position (b) the switching positions of the switching part of the valve show arrangement. Since both functions by a common control slide 32 in a common compact If the valve housing is perceived, the space for a safety circuit according to the invention can be reduced to a minimum.

3 shows a characteristic curve of the proportional valve 30 according to the invention, the pressure curve at the proportional connection A and at the switching connection B being shown as a function of the current intensity I at the proportional solenoid 34.

As already mentioned above, the control slide 32 is initially biased into its initial position (c) due to the pretension via the valve spring 36, so that the pressure at the proportional connection A is zero, while the pressure at the switching connection B is approximately the same or slightly less than is the pressure at the pressure port P. With increasing current, the proportional valve 30 initially remains in its switching position (c), so that the pressure conditions remain unchanged, i.e. the pressure PB is present at the switching connection B, while the pressure at the proportional connection A is zero.

After exceeding a predetermined threshold current, the proportional valve - or more precisely, its control slide - is moved into the central position (b), in which both the proportional connection A and the switching connection B are connected to the tank connection T, so that the pressure P _j ^ remains unchanged while the pressure Pg drops to zero.

The control slide 32 has now reached that area in which the proportional opening A of the proportional connection A takes place. As already mentioned at the beginning, the proportional range is only reached after a current ΔX, so that it is ensured that the pressure at the proportional connection A only then increases can, if the pressure at the switching port B has dropped to zero. That is, the design of the proportional valve 30 according to the invention corresponds approximately to that of a valve arrangement with a positive overlap, with all working connections of the valve being closed during the "switching process".

After passing through the current ΔX, the pressure P at the proportional connection A increases approximately proportionally to the current I, so that any pressure between zero and approximately the inlet pressure can be set.

It is clear from FIG. 3 that by modulating the proportional magnet 34 accordingly, the modulation of the pressure P / ^ can be adjusted in any way.

4 shows an exemplary embodiment of a safety circuit, part of a circuit diagram of a hydraulic tractor transmission being shown. This hydraulic powershift transmission in turn has two transmission ranges 40, 42, a high-low shift taking place via the transmission range 40, while four forward gears and one reverse gear are shifted in the transmission range 42. The transmission areas 40, 42 are supplied with hydraulic fluid via a pressure line 44 and a pump 46, branch lines 47, 48 branching off from the pressure line 44, which, for example, lead to a torque converter 49 or to a clutch 50. A pressure limiting valve 52 is assigned to the torque converter 47 and an electromagnetically actuated pressure reducing valve 54 is assigned to the clutch 50. As a result, the torque converter 49 is only activated when a limit pressure at the pressure relief valve 52 is exceeded, while the pressure at the clutch 50 is reduced by the pressure ornamental valve 54 is limited to a presettable maximum value.

The transmission areas 40, 42 are practically connected in parallel to the clutch 50, the pressure line 44 leading to the pressure connection P of a first proportional valve 56 according to the invention.

The tank connection T is connected to a tank via a connecting line, while the proportional connection A is connected to the transmission element for the large transmission ratio (HIGH) and the switching connection B is connected to a transmission line with the low transmission ratio (LOW). An electrically operated first pressure reducing valve DRE 60 is connected between the gear element LOW and the switching connection B, so that the pressure at the gear element LOW is limited to a maximum value. The DRE 60 is controlled by a proportional magnet, a connection to the tank being opened when a predetermined maximum pressure at the transmission element LOW is exceeded.

As can be seen from the above explanations, the transmission element HIGH is thus connected to the tank in the basic position shown, while the transmission element LOW can be connected to the pump 46 with appropriate control via the first DRE 60 and the first proportional valve 56 and the pressure lines 44 so as to supply the transmission element LOW with hydraulic fluid.

When the first proportional valve 56 is switched to its central position, both working ports A and B are first connected to the tank, while the pressure port P is shut off. When the proportional solenoid is subjected to a further current, the control slide of the first proportional valve 56 is portional range shifted so that the proportional connection A is slowly opened in order to supply the transmission element HIGH with hydraulic fluid and a smooth switchover from LOW to HIGH is ensured.

In the same way, of course, the switch back from HIGH to LOW can be modulated by correspondingly controlling the proportional magnet, so that sudden switching operations are excluded.

While only two transmission elements (HIGH, LOW) are to be actuated in the transmission area 40, a total of five transmission elements (first, reverse, second, fourth, third) are to be actuated in the transmission area 42, but the structure of the circuit is basically that of the transmission area 40 corresponds to.

As can be seen from FIG. 4, each of the transmission elements first (first gear), reverse (reverse gear), second (second gear) and fourth (fourth gear) is assigned a proportional valve according to the invention, so that the safety circuit also has a second one has a third, a fourth and a fifth proportional valve 62, 64, 66, 68.

The proportional valves 62 to 68 are connected in series, the switching output B of the upstream proportional valve being connected to the pressure port P of the adjacent downstream proportional valve. The tank connection T is connected to the tank, while the proportional connections A of the valves are connected to the gear elements First, Reverse, Second and Fourth.

The last transmission element (THIRD) of the transmission area 42 can be operated electrically via a second one Pressure reducing valve 70 is controlled so that the connection of the transmission elements Fourth and Third of the transmission area 42 corresponds to the connection of the transmission elements HIGH and LOW of the transmission area 40.

It can be seen from FIG. 4 that, in the safety circuit according to the invention, each transmission area with n transmission elements, n being greater than 1, is assigned a proportional valve according to the invention to the first to (nl) th transmission elements, while the nth Gear element only has to be assigned a commercially available pressure reducing valve. This means that the safety circuit essentially contains two basic valves, through the corresponding variation of which any number of gear elements can be controlled.

In the starting position of the safety circuit shown, third gear (third) is actuated in the transmission area 42, the proportional valves 62 to 68 being flowed through by the hydraulic fluid 44 in its switching position (c). To control the third gear, the second DRE 70 must of course also be actuated via its proportional magnet in order to ensure passage of the hydraulic fluid to the third gear element. In the event that the second pressure reducing valve 70 is not activated accordingly, none of the transmission elements of the second transmission area 42 is activated.

At this point it should be mentioned again that the proportional magnets of the pressure reducing valves 60, 70 and 54 and of the proportional valves 56, 62, 64, 66 and 68 according to the invention are connected to a common control unit, so that a coordinated control of the individual hydraulic components is guaranteed. As soon as one of the proportional valves 62 to 68 of the second gear area 42 is moved into its central position (b) or into the proportional area, the connection to the adjoining proportional valves is interrupted, so that their gear elements are connected to the tank T, while the gear element which is assigned to the proportional valve located in the proportional area is supplied with hydraulic fluid via the pump 46 and the pressure line 44. However, this supply is only possible if the upstream proportional valves are biased into the basic position shown, in which flow through from port P to port B is made possible.

In this way it is ensured that at most one of the gear elements of a gear area can be supplied with hydraulic fluid, while the other gear elements are connected to the tank and are therefore not controllable.

An inadvertent connection of two gear elements of a gear range is therefore excluded.

From the above, it is clear that the safety circuit according to the invention can be combined in a simple manner in a total valve, essentially only two valve types (proportional valve according to the invention and DRE) having to be used. The simplified structure of the safety circuit enables a simple channel construction of the entire overall valve housing. Furthermore, due to the reduced number of valves compared to the prior art, the installation space is reduced and the costs of the entire valve arrangement are minimized. Since the modulation takes place primarily via the common control unit, no hydraulic tuning of the modulation is necessary, so that the development effort for the hydraulic part is comparatively low. Furthermore, the modulation can be more easily adapted to different operating states via the central control unit.

In the first test tests of the safety circuit according to the invention, it has been shown that the safety level which is the same as that of the known circuits described at the outset can be achieved with considerably reduced circuit complexity.

Of course, the use is not limited to the type of complex gearshift system shown in FIG. 4, but the proportional valve according to the invention in accordance with FIG. 2 can also be used, for example, in a PTO gearshift system of a tractor, for example a brake cylinder being connected to the switching connection B while the proportional port A is connected to the clutch cylinder of a single implement connected to the PTO.

Instead of the control pressure lines 38 to the spring side of the control slide 32, the pressure limiting function can also be carried out electrically by evaluating the output signal of a pressure sensor and correspondingly controlling the permanent magnet. The same applies to the control of the DRE 60, 70.

What is disclosed is a safety circuit for alternately controlling consumers, for example transmission elements of a powershift transmission, and a proportional valve for such a safety circuit, where the proportional valve is preferably designed to be electrically adjustable. The proportional valve has a switching output to which one of the consumers is connected, while a proportional output of the proportional valve leads to another consumer. By correspondingly controlling the proportional magnet, a smooth switchover from one consumer to another consumer can be effected without the need for a separate hydraulic device for modulating the changeover process.

Claims

Expectations

1. Safety circuit for alternately controlling n consumers (HIGH, LOW, First, Reverse, Second, Fourth, Third) (n> 1), each consumer having a valve arrangement (56, 62, 64, 66, 68; 60 , 70), via which a pressure fluid can either be supplied to the assigned consumer or to the next consumer or the valve arrangement (60, 64, 66, 68, 70) assigned to it, characterized in that the 1st to (nl) -th consumer each associated valve arrangement is a proportional valve (56, 62 to 68), with a pressure connection (P), a tank connection (T), a first working connection (A) and a second working connection (B) , a control slide (32) being suitably activated from a central position (b), in which a pressure connection (P) is blocked and work connections (A) and (B) are connected to the tank connection (T), into an end position ( a) is movable, so that the connection between Chen the pressure connection (P) and the first working connection (A) can be opened proportionally and the next consumer or the valve arrangement assigned to it can be supplied with pressurized fluid while the assigned consumer is connected to a tank, the control slide (32) Switching function is assigned, so that in a switching position (c) of the control slide (32) the pressure connection (P) with the associated consumer and the tank connection (P) with the next consumer or the valve arrangement (60, 64, 66, 68, 70) can be connected.

2. Safety circuit according to claim 1, marked by a proportional magnet (34) via which the switching position (c), the middle position (b) and the end position are changed one after the other by changing the current strength (a) of the control slide (32) of the proportional valve can be driven through.

3. Safety circuit according to one of the preceding patent claims, characterized in that the control slide (32) of the proportional valve is biased into its switching position (c) via a valve spring (36).

4. Safety circuit according to claim 2, characterized in that the proportional magnet (34) against one

Control pressure acts, which is tapped via a control pressure line (38) from the first port (A).

5. Safety circuit according to one of the preceding patent claims, characterized in that after switching the control slide (32) of a proportional valve from its switching position (c) to the central position (b), a predetermined adjustment range (X) is first passed through that must be done before the proportional control of the next consumer takes place.

6. Safety circuit according to one of the preceding claims, characterized in that the n-th consumer (LOW, third) is assigned a pressure reducing valve (60, 70), at the output of which the n-th consumer (LOW, third) connected.

7. Safety circuit according to claim 6, characterized in that the pressure reducing valve (60, 70) and the proportional valves (54, 62 to 68) can be actuated electromagnetically and are connected to a common control unit.

8. Safety circuit according to one of the preceding patent claims, characterized in that the switching output (B) of the proportional valves (56, 62 to 68) with the Pressure connection (P) of the following valve arrangement is connected.

9. Proportional valve, in particular for a safety circuit according to one of the preceding claims, with a pressure connection (P), a tank connection (T), a first working connection (A) and a second working connection (B), a control slide (32 ) can be moved into an end position (a) by suitable control from a middle position (b), in which the pressure connection (P) is blocked and the work connections (A) and (B) are connected to the tank connection (T), so that the connection between the pressure connection (P) and the first working connection (A) can be opened proportionally and a first consumer can be supplied with pressurized fluid while a second consumer is connected to a tank, with the control slide (32) being assigned a switching function net, so that in a switching position (c) of the control slide (32) the pressure connection (P) can be connected to the second consumer and the tank connection (P) to the first consumer and after switching the control slide (32) from its switching position (c) to the middle position (b), a predetermined adjustment range (X) must first be passed through before the proportional control of the second consumer takes place.