DE1605907C - Axle lifting device for an axle of a double axle assembly of a motor vehicle - Google Patents

Description

The invention relates to an axle lifting device for an axle of a double axle assembly of a motor vehicle with a pressure medium-controlled servomotor to which the pressure medium is supplied by a an electric motor-driven pump is supplied via a pressure line.

Such axle lifting devices are used to lift the wheels of one wheel axle when it is unloaded or to protect only a lightly loaded vehicle and at the same time reduce the rolling resistance of the vehicle to hold than would be the case if all the wheels of the tandem axle unit rolled off. This serves in the known axle lifting device (USA.-Patent 2777529) for controlling the through the Pressure line feedable pressure medium a manually controllable control valve, which the pressure medium either through the pressure line to the servomotor in the sense of raising the impeller axle or connects the pressure line to a container that is only subjected to atmospheric pressure, from which the pump sucks the pressure medium, which is usually made of oil.

It is still disadvantageous that it is difficult to assess when loading the motor vehicle concerned is whether the load on the vehicle has already reached the value at which all wheels of the Double axle assembly must be used to support the vehicle on the roadway. Apart from that that weighing devices for the currently existing axle pressure of a loaded vehicle, as they do in individual cases, for example on the departure ramps of gravel works to determine the the amount of gravel supplied are generally not available, it would also be too cumbersome to such stationary weighing devices for checking the axle load of the loaded vehicle

to look for stuff first. It must therefore still be the assessment of the driver of the motor vehicle It is left up to whether it is with the raised or lowered second wheel axle of the tandem axle assembly moves. If the wheel axle has been lowered unnecessarily, this results in unnecessary rolling resistance and unnecessary wear and tear of the lowered wheels while the second is raised Wheel axle and overloaded other wheel axle the risk of damage to the vehicle and a there is excessive wear and tear on the road surface.

It can also happen that the usually drivable wheels of the non-liftable axis of the Double axle unit suddenly larger when the second wheel axle is raised while driving Are exposed to shock loads, e.g. B. when driving over railway tracks, frost breakouts, stones or other bumps in the road, in which case the associated congestion of the Drive axle can damage the axle assembly or other parts of the motor vehicle.

The invention is based on the object of perfecting the axle lifting device mentioned at the outset in such a way that that the driver of the vehicle during or after its loading with the vehicle no special Need to visit weighing device more and still depending on the load on the vehicle can keep the raised or lowered position of the liftable wheel axle correctly at any time.

This object is achieved according to the invention in that the electric motor of the aforementioned Axle lifting device via one connected on the one hand to its circuit and on the other hand to the pressure line Pressure guard can be switched off when a certain wheel load is reached.

Because of the fact that in the affected axle lifting devices in the pressure line leading to the servomotor If the pressure is proportional to the total load on the axle assembly, it does the aforementioned Measure possible in a simple manner, the axle lifting device itself to a weighing device to perfect, by which a lifting of the liftable wheel axle is excluded automatically is when the maximum permissible load on the other axle of the tandem axle assembly is through loading of the vehicle should be exceeded. It is only necessary to ensure that in front of a When loading the vehicle, the liftable wheel axle is initially in its lowered position. After loading the vehicle, the driver makes an attempt by switching on the electric motor Raising the liftable wheel axle, then the weighing device simply decides whether lifting of the wheel axle can be permitted.

According to one embodiment of the invention, the pressure line is followed by a relief line via a pressure relief valve, which is set to the in the pressure line at the maximum permissible total load of the axle assembly is set to the pressure that occurs when the impeller axle is raised. One such Pressure relief valve is advantageous, for example, when the already partially loaded vehicle is raised The impeller axle is to be additionally loaded. It can then, of its own accord, lower the Raised impeller axle cause when the maximum permissible total load on the axle assembly should be exceeded when the wheel axle is raised. It should be noted, however, that such a simple Overpressure valve might not be able to counteract the effect of the aforementioned pressure watch to replace. Of course, such a spring-loaded pressure relief valve offers a certain flow resistance and usually only has a limited flow cross-section. It could hardly be dimensioned in such a way that a Lifting of the liftable wheel axle with the electric motor switched on and correspondingly rotating Pump could be prevented if, for example, there is only a small overload should be. The pressure relief valve also offers the other advantage that a lowering of the raised impeller axle can also take place automatically, for example, if the set maximum permissible pressure due to repeated impact loads on the other wheel axle, for example on especially bad roads, should be exceeded.

According to a preferred structural embodiment of the invention, the pressure guard consists of a piston-cylinder unit, which is connected to the pressure line via a branch line and with a circuit breaker in the circuit interacts. Such a construction of the Druckwache is simple and yet very reliably effective.

According to a further embodiment of the invention, the servomotor is also in the sense of a lowering movement the impeller axle can be driven, including according to an associated structural embodiment of the invention in the pressure line leading from the pump to one side of the servomotor and in that of the the other side of the servomotor to an oil tank that is also connected to the suction side of the pump leading further line a solenoid-controlled four-way valve which crosses both lines together it is provided that, when one of two associated actuating magnets is excited, one raises or lowering of the impeller axis, while it is without the influence of the magnet assumes a starting position that isolates the servomotor from the pump It is natural of great advantage if a rapid lowering of the previously raised wheel axle is already ahead a load on the vehicle quickly brought about without the cooperation of the aforementioned pressure relief valve can be.

According to another embodiment of the invention, there is also one of the impeller axle in the circuit Her controllable breaker switch provided in all positions that are not completely lowered the impeller axle is switched on, while it is here according to a further embodiment of the invention It is preferred that the electromagnets of the four-way valve can be selected via a selector switch m the circuit in series with the circuit breaker and the circuit breaker can be switched on. If the selector switch and the solenoid-controlled four-way valve are used, a lowering is achieved the previously raised wheel axle is selected, for example, when the vehicle is unloaded, with the Circuit breaker is in its closed position, then the additional breaker causes an automatic shutdown of the electric motor and the pump when the liftable impeller axle reached their lowest position.

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According to yet another embodiment of the pressure guard bil invention explained in more detail below If the pressure relief valve is part of a piston-cylinder unit 23 opens between the areas emanating from the servomotor. On the other hand, the lines 21 and 20 connect

Chen the pressure line and the further line upstream of the four-way valve 18 in the direction of the pressure line seen double-acting shock valve, 5 21 a delivery line emanating from the pump 16 that between the two ends of the servo motor 24 and in the direction of the line 20 one in an oil defrost Interruption of the pressure medium circuit, an emptying line 25 opening into the container 26. Pressure lowering or raising the impeller axis. The bottom of the oil reservoir 26 is via a feeder flow enables such a double action 27 connected to the suction side of the pump 16 Shock valve gives a dampening 10 sen.

Resilience of the liftable wheel axle at The solenoid-controlled four-way valve 18 has the

occurring shock loads in both directions. 'Shape of a transverse to the lines 20 and 21 running other Embodiments of the invention relate to fenden slide, which is shown in Fig. 1 from its further structural details of the created middle starting position by an object according to the invention Axle lifting device and in particular electromagnet 28 in a lower end position special from their selector switch. and by a lower electromagnet 29 in a

In the drawing, the invention is, for example, the upper end position can be moved. As illustrated It clearly shows that the mean shown in Fig. 1 corresponds to ^ · 1 shows a schematic illustration of the axle lifting device for blocking lines 20 and 21 direction in connection with a circuit diagram for 20 on the four-way valve 18, while the delivery line 24 the servomotor drive is connected to the emptying line 25 when the impeller axle is lowered. Provided, corresponding to a journey with a fully loaded vehicle - one of the additional trains described below, possibilities of influencing via valve block 1? FIG. 2 initially disregards the circuit diagram according to FIG. 1, the piston of the servomotor Setting in which the servomotor controls the liftable 25 11 and thus also the liftable wheel axle 12 Impeller axis corresponding to only a slight travel due to the load in the servo motor 11 and the Leitunzeug load can just lift, gene 20 and 21 located oil in the respective in-Fig. 3 the same circuit diagram is retained in the same position, while the pump 16 ment, with the weighing device, however, in the event of the electric motor 17 being switched on If the permissible total load has just been exceeded, the oil is only short-circuited into the oil container 26 stung ensures that the previously at least partially pumps. In its upper area, the four-way is raised Been running wheel axis again lowered valve 18 of two parallel to each other can be penetrated and channels, which in the lower valve stem Fig.4 the same circuit diagram in one setting, on the one hand, for a connection of the line 20 ment, in which the previously raised impeller axis 35 with the drain line 25 and on the other hand for a despite not or only slightly loaded vehicle by connecting the delivery line 24 to the pressure sore Servomotor is lowered, provision 21. In its lower part is that The axle lifting device shown has a four-way valve 18 with two cross servo motors 11 with a piston, the KoI- zenden channels connected to the upper end rod 13 at its lower end at the lifting position of the valve ensure that the pressure body wheel axle 12 of a double axle unit tion 21 with the discharge line 25 and the Föreines Motor vehicle attacks. The impeller axle 12 of the line 24 is connected to the line 20, is at one end of a double-armed Waagebai- The valve block 19 has three valves 30, 31 and kens 14 stored, which in its central area in not 32, of which the first two mentioned between especially shown, the usual way on the chassis 45 of the two lines 20 and 21 arranged, respectively one of the tandem axle unit having a force opening in the opposite direction of flow vehicles is stored The other, according to which check valves are off. They imagine together management example drivable wheel axle of the double double-acting shock valve, which in the Axis unit is fixed to a spring assembly 15, if a sudden shock load gives way sets that on the one hand at the other free end of the Waa- 50 of the impeller axis 12 up or down enabling bar 14 and on the other hand also in the usual, light, so that the piston of the servo motor U to Not specifically shown on the chassis of the avoidance of overloading of the Mate vehicle The servomotor 11 can yield one or the other of the two valves from a pump 16 from, which in turn can 55 from an electric motor 17, even if the two lines 20 and 21 can be driven, be supplied with pressure oil. Between the starting position shown in FIG See the pump 16 and the servomotor 11 located four-way valve 18 at their ends there a further described below are curious. The opening magnet-controlled according to FIG. 1 upwards Four-way valve 18 and a leveling valve 31 of the valve block 19 is, moreover, if valve 60 described in more detail below is set in its closing force so that it at the same time block 19, which from one of the upper end of the forms a pressure relief valve, which is then through seme Servomotor 11 outgoing line 20 and opening a lowering of the piston of the servomotor from one of the lower end of the servo motor 11 11 and thus the impeller axis 12 allows when the outgoing pressure line 21 according to the four-way maximum permissible total load of the double axle valve 18 is penetrated to between the 65 gregates with the impeller axle 12 raised via a servo motor 11 and the valve block 19 should be located. A short part is then created the pressure line 21 closes a branch line closing circuit of the oil from the lower part of the servo, which is in the cylinder of a component of a motor 11 via the pressure line 21, the overpressure

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valve 31 and the line 20 to the upper part of a contact there from a line 40 to the servo motor 11, whereby the piston solenoid 29 of the four-way valve 18 leads, can lower. A reverse flow of the oil, from further contacts located directly next to the aforementioned but instead of through the pressure relief valve 31 through the contacts also pass valve 30, occurs when the driven wheels 5 merge into a line 41 branch lines of the tandem axle unit due to uneven ground that are suddenly connected to the motor 17 with one terminal contact of the electric and in particular potholes. Even those who should avoid the Leiunten. Apart from the deviation 3 £ and 40 remote ends of the two elec- tromagnets of the overpressure valve 31 when loading, solenoids 28 and 29 are axially admissible for a non-specific vehicle beyond the line shown with the impeller lifted on this line 41 this causes double-closing. The other connection contact of the electrical shock load valve 30, 31, a protection motor 17, is connected via a further line 42 to the loaded parts of the axle lifting device at the breaker switch 33, in which unavoidable shock loads from the driving power source 45 are located. That gave way. 15 closed circuit can in practice via the

The third check valve 32 of the valve block line 42 to a conventional motor vehicle battery.

19 is to be closed to a for example by the oil container 26.

formed oil well connected and opens in the on the arc of motion of the Kontaktseg line 20 in. This valve is used to that in Mentes of the selector lever 38 can both sides to the the cylinder of the piston-cylinder unit 23 with 20 of the aforementioned contacts still another contact Exceeding the total permissible load of the connected, of which the erne, according to Doppelachsaggregates with raised wheel axle Fig. 1 via a line 43, and the other, via 12 with a correspondingly descending impeller axis a line 44 penetrating the aforementioned line 42 oil is closed above the piston of the servo motor. The arrangement is such that 11 to replace. Without the check valve 32, the selector lever 38 would be swung out for the first time In this case there is a risk that in the oiling to the left with its contact segment only circuit at any leaks air in - a contact to the lines 39 and 41 and at is sucked. his first swing to the right only one

As can also be seen from FIG. 1, the contact with the two lines 40 and 41 is closed in accordance with the aforementioned maximum permissible 30. Only through a further swiveling of the total load set upward spring force of the selector lever 38 can a contact to the piston rod line 36 with an overload switch 34 or to the line 44 be closed via its closed contacts for the two preloaded pistons of the pressure switch.
The axle lifting device described works and is in the circuit of the electric motor 17 of 35 as follows and can be set as follows who-the axle lifting device is The overload switch:

34 interrupts the circuit as soon as it is assumed that the wheel axle Piston of the pressure switch moved downwards 12 was raised and the selector switch 35 the in that should. In series connection with the above Fig. 1 position shown, the load switch can 34 is located in said circuit 40 device in a subsequent, given a breaker switch 33 which is normally included in the event of further loading of the vehicle is and are switched, for example by the piston, that the selector lever 38 in the in rod 13 is opened only when the position shown in Figure 2 is pivoted. Da impeller axle 12 in their according to FIG. 1 is completely cut off when switches 33 are initially closed lowered position. 45 and 34 of the electric motor 17 and thus also the

In that switched on from the circuit breaker 34 to the electric pump 16 and the piston of the servo motor 17 leading branch of the circuit is located motor in the direction of the arrow of Fig.2 upwards a selector switch 35 with a selector lever 38 loaded with pressurized oil. However, if the load is the which exceed the maximum permissible value at the overload switch 34 via a line 37, at which connected. The selector lever 38 is located 50 with the wheel axle 12 raised according to Fig. 1 in its neutral starting position, may, then by the correspondingly increased oil the one located at its outer end pressure in the pressure line 21 and in the two-wire contact segment cannot make a contact, the piston of the piston-cylinder unit 23 ration 22 that, in this position, the electric motor 17 is also shifted downwards according to FIG. 3 and the switch is switched over remains even if the switches 33 and 34 55 load switch 34 open. This has the consequence that the should be closed. Both sides of the Kontaktseg- circuit to the electric motor 17 and to the upper Mentes are located along the circle of motion electromagnet 28 of the four-way valve 18 underneath however, contact points with adjoining labia and thus also beforehand become appropriate lines, whereby with a corresponding pivot Fig.2 located in its lower end position movement of the selector lever 38 according to FIG. 1 in the 6 <j four-way valve 18 into its central position according to FIG clockwise a lifting or when pivoting Fig. 1 returns, in which the oil circuit on the of the lever clockwise a lowering of the running point of the four-way valve 18 is interrupted, wheel axle 12 can be selected. This corresponds to that in the piston-cylinder unit 23 Purpose leads from an oil volume penetrating at the upper half of the toe, here the KoI-des The arc of movement of the contact segment moves 65 ben of the servomotor 11, with oil at the same time Sensitive contact from a line 39 to the electrical via the check valve 32 (Fig. 1) in the line magnets 28, while from the left flows in symmetrically and a possible formation of a Vaeenüberlieeende Point of the arc of motion kuums prevented In addition, a corresponding

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accordingly the increased oil pressure is pushed under the piston of the, in which the oil lines 20 and 21 in

Servomotor 11 at the same time the pressure relief valve 31- in the manner shown in Figure 4 crosswise to the

Direction of the in Fig. 3 at the other point of the valve block delivery line 24 of the pump 16 or the EnÜee-

kes 19 arrow shown, whereby the piston approximately line 25 are connected. As a result

of the servo motor 11 and thus also the impeller 5 reaches the pressure oil from the delivery line 24 via the

axis 12 steadily in the direction of the arrow on the piston line 20 on the top of the piston of the servo

of the servo motor 11 can lower. Heard the over-motor 11 and also presses via the piston rod 13

last before a complete lowering of the wheel axle 12 to the ground support of the

The impeller axle 12 is about to open again, then the impellers can go down, with that under the piston

Circuit by reclosing the over- io existing oil through line 21 and the

Load switch 34 is switched on again by itself and the drain line 25 drains into the oil container 26

the wheel axle 12 can again via the servomotor 11.

be raised. Should the impeller axle 12 ever be completely lowered at the last moment of the lowering movement and thus the sub-impeller axle 12 is opened in the manner already described, breaker switch 33 must be opened beforehand, then the 15 of the breaker switch 33 must first be opened and the current selector lever 38 according to the in Fig. 2, the circuit of the electric motor 17 shown is interrupted, whereby the four-way valve 18 is also pivoted again in the counterclockwise position to such an extent that all three left-hand contacts of the returns to its starting position according to FIG. Selector switch 35 can also be connected to the return of the selector lever 38 in its Ausment of the selector lever 38 together with the Kontaktseg. In the starting position according to FIG. 1, any setting can then be made to the running wheel axle 12 manually or automatically, whereby all bridging of the two switches 33 and 34 on each part of the axle lifting device is raised again as in FIG. 1. Should this for any reason take the position shown,
It can also be desirable to have the load on the running gear, so the selector wheel axle 12 can be raised for any reason, at 38 then back to the position shown in FIG The only position shown in Abund3 is swiveled back. In occurs. In this case, the selector lever 38 is out of range

Has the impeller axle 12 when the gear position is set according to FIG. 1 in the counterclockwise direction Selector lever 38 according to FIG. 2 because of an existing something over the one shown in FIGS. 2 and 3 nen overload reaches the lower end position, then swiveled out the lifting position until its contact seg- | the interrupter switch 33 and the electrode not only open the contacts to the lines 39! motor 17 is stopped. Although this also and 41, but also the contact to line j the electromagnet 28 is switched off and the four-way 35 43 closes. valve 18 again in its circuit shown in Fig. 1 of the electric motor 17 and the upper ι is brought to the neutral center position, the result is the electromagnet 28 shown in FIG by switching off the electric motor 17, it is closed in this way, although the overload switch 34 at the same time a notable reduction in the oil pressure as a result of the overload assumed above in the branch line 22, whereby the KoI- 4 ° dimension Fig. 3 is open. So that such a normal heir the piston-cylinder unit 23 again shifted upwardly inadmissible lifting operation in general and the circuit breaker 34 remains closed closed, it is moreover preferred that will. the selector lever 38 only with respect to a yielding one;

Furthermore, it is also possible to move so far counterclockwise by means of the usual, non-special restoring force.

ders shown means ensure that 45 can be pivoted that the contact with the j

the selector lever 38 is also closed either after the line 43 has ended. If the driver then '

Lifting process or after the lowering process has been completed after the lifting process described last, the |

the impeller axle 12 releases itself again from its in selector lever 38, then this returns from i

Fig. 2 in the lifting position shown in Fig. 1 itself again in its position shown in Fig. 3!

shown starting position is returned. 50 back, whereby the impeller axis of the in the er!

If it is known from the outset that the vehicle is "overloaded" in the manner described above, then the vehicle is to be reloaded into its lowering position, its maximum load by itself according to FIG the previously raised impeller axle It could also happen that the piston! wants to lower the servomotor U after an I already described in spite of only a slight load on the vehicle, then the driver swings the selector-lowering movement according to FIG. at 38 from its starting position in a clockwise direction already supported on the roadway wheels Weiin the position shown in Fig. 4, in which its terhin should remain preloaded downwards. So that the contact segment closes both the contact to the line 40 in this case through the interrupter relay and the contact to the branch line there, which is interrupted to the line 41 60 switch 33. Since the vehicle can remain closed, the selector lever is only lightly loaded and the running wheels raised 38 in the clockwise direction still above the ones shown in FIG. Contact segment via the contacts to the lines The electric motor 17 is switched on and the contact to the line 44 also closes due to the thus completely closed current 65 40 and also to the branch line to the line 41
It should also be mentioned that the four-way valve 18 moves into its upper end position in its upper end position on the running wheels or in the event of sudden lowering movements.

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conditions of the drive axle as a result of unevenness in the floor can also occur that this is over the piston rod 13 the breaker switch 33 is opened. Since the selector lever 38 while driving but the vehicle is usually in its starting position according to FIG. 1 and the circuit of the electric motor 17 is interrupted anyway, this is irrelevant. Even if such an upward movement of the piston rod 13 despite the aforementioned hydraulic pressing down of the piston of the servomotor U should occur, the resulting opening of the circuit breaker remains 33 has no effect because in this case the circuit is closed via line 44 and selector lever 38 remains

It must also be taken into account that the Impeller axis 12 and thus the piston of the servo motor 11 starts fluttering, d. H. after an upward movement as described above, it also returns downwards with greater force, when the pressure created under the piston is so great that the pressure relief valve 31 opens and the oil through the pressure line 21 and this valve via line 20 to the Can reach the top of the piston of the servo motor 11. Is that the piston of the servo motor 11 again downward pulling force, however, smaller than it corresponds to the setting of the pressure relief valve 31, then the piston and thus also the impeller axle 12 remains in the case of a previously switched off according to FIG. 1 Position of the axle lifting device in the more or less raised position caused by the road bumps Standing position. However, the driver has it in hand by swiveling the Selector lever 38 closes the wheel axle 12, for example according to FIG. 4, back into its lowered position shift.

To ensure that the previously raised wheel axle 12 is in a starting position while driving of the selector lever 38 according to FIG. 1 can not drop anyway, between the Lines 20 and 21 in the area between the four-way valve 18 and the valve block 19 are still a common one hydraulic lock may be provided. It is also advantageous if a precaution is taken for this is that the breaker switch 33 can also be closed if desired, when the wheel axle 12 is in its fully lowered position.

1 sheet of drawings

Claims (11)

Patent claims: 1. Axle lifting device for an axle of a Double axle assembly of a motor vehicle with a pressure medium-controlled servo motor, the the pressure medium from a pump driven by an "electric motor" via a pressure line is supplied, characterized in that the electric motor (17) is connected on the one hand to its circuit (37, 41, 42), and, on the other hand, a pressure monitor (23, 34, 36) connected to the pressure line (21) when it is reached a certain wheel load can be switched off. ' 2. Apparatus according to claim 1, characterized in that indicates that a relief line (line 20) is connected to the pressure line (21) via a pressure relief valve (31) is connected to that in the pressure line at the maximum permissible total load of the axle assembly when the impeller axle (12) is raised. 3. Apparatus according to claim 1 or 2, characterized in that the pressure guard from one. The piston-cylinder unit (23) is connected to the pressure line via a branch line (22) (21) is connected and interacts with a circuit breaker (34). 4. Device according to one of the preceding claims, characterized in that the Servomotor (11) can also be driven in the sense of a lowering movement of the impeller axle (12). 5. Apparatus according to claim 4, characterized in that in the of the pump (16) to one side of the servomotor (11) leading pressure line (21, 24) and in that of the other Side of the servomotor to an oil tank that is also connected to the suction side of the pump (26) leading further line (20, 25) a two lines (21, 24 and 20, 25) together crossing solenoid-controlled four-way valve (18) is provided, which when energized by one of two associated actuating magnets (28, 29), one raising or lowering the impeller axle (12) assumes the effecting position, while it is a.den servomotor without the influence of the magnet assumes the starting position locking off the pump. 6. Device according to one of the preceding claims, characterized in that im Circuit still a from the impeller axis (12) controllable interrupter switch (33) is provided is switched on in all not completely lowered positions of the impeller axle (12) is. 7. Device according to claims 5 and 6, characterized in that the electromagnets (28 and 29) of the four-way valve (18) via a selector switch (35) optionally in the power circuit in series with the overload switch (34) and the circuit breaker (33) can be switched on. 8. Device according to one of claims 5 to 7, characterized in that the pressure relief valve (31) Part of a region between the servomotor (11) Pressure line (21) and the further line (20) provided double-acting shock load valve (30, 31) is that between the two ends of the servo motor despite the interruption of the Pressure medium circuit a pressure medium flow that lowers or raises the impeller axis (12) enabled .; . 9. Device according to one of claims 5 to 8, characterized in that of the line (20) between the servo motor (11) and the four-way valve (18), possibly the Shock valve (30, 31) still leads to a branch leading to a pressure medium source, in which a check valve (325 opening towards the pressure medium circuit) is arranged. 10. Device according to one of claims 6 to 9, characterized in that the circuit also has a switching on of the drive motor (17) and switching of the four-way valve (18) when the overload switch (34) and / or breaker switch (33) enabling short circuit. 11. The device according to claim 10, characterized in that the short-circuit circuit Can be switched on via the selector switch (35) for each selected magnetic excitation of the four-way valve (18) is.