LIFT AXLE CONTROL MODULE FOR A MOTOR VEHICLE

Background of the invention

The invention refers to a lift axle control module to be used in a lift axle suspension system of a commercial vehicle, further to a lift axle suspension system comprising such a lift axle control module, and a vehicle, in particular a commercial vehicle, comprising such a lift axle suspension system.

A lift axle system is used to minimize the wear of tyres and to increase the traction of driving wheels when the vehicle is in unladen condition. In a multi axle vehicle all the wheels need not touch the road when the vehicle is in unladen condition. In this condition one of the axles is lifted from the road, thereby preventing unnecessary wear of tyres and providing improved traction due to higher load acting on the driving axle.

A lift axle suspension system of a commercial vehicle comprises in general suspension bellows (like the other axles) for damping and for adjusting the distribution of the axle load between the axles of the vehicle, and additionally one or more lift bellows capable for lifting the axle in order to detach the wheels of the lift axle from ground; further, pneumatic valves for controlling these bellows are provided.

A lift axle suspension system in a commercial vehicle enables the following functions:

Automatically raising or lowering the lift axle depending on vehicle load condition,

Override to raise the lift axle when the vehicle is fully loaded for better traction and maneuverability of the vehicle. This override can be initialized manually or automatically by the device based on the chassis deflection input.

Preferably a damping delay is provided for maintaining the axle position during road undulations. Further it is often preferred to keep the lift axle during an ignition off condition in its lowered position in order to avoid theft of wheels.

Valve assemblies often comprise solenoid valves for receiving electrical signals and relay valves to enlarge the volume flow.

Raising or lowering the axle is achieved through pneumatically actuated valves, which in turn receive appropriate pneumatic and/or electrical signals.

A conventional lift axle control system consists of the following components:

a pressure reduction valve or a manual pressure regulator, a load sensing valve, a lift axle control valve, two external relay valves or one quick release valve or a relay valve and a quick release valve, a pair of lift actuators and a pair of suspension bellows. The pressure reduction valve or the manual pressure regulator is connected to an auxiliary reservoir that contains system pressure which can vary from e.g. 6 bar to 8.5 bar. The pressure reduction valve delivers a constant pressure of e.g. 5 bar to the load sensing valve. In some cases a manual pressure regulator is also used instead of the pressure reduction valve. The load sensing valve delivers a pressure proportional to the load on the axle. When the vehicle is fully laden, the load sensing valve delivers full supply pressure of 5 bar to the lift axle control valve. When the vehicle is in unladen condition, the delivery of the load sensing valve drops to around 2.5 bar. The delivery of the load sensing valve serves as an input to the lift axle control valve. The lift axle control valve in turn has two deliveries, one of which is connected to the lift actuators and the other to the suspension bellows of the lift axle.

One disadvantage of those prior art lift axle control systems are the high costs of manufacture due to separate brackets and sealing for the individual valves and piping to join them together. A further disadvantage of the known art lift axle control valve can be seen in the fact that load sensing is performed through a double throw pressure switch. This results in more inconsistency of pressure sensing and it affects the reliability of the system. A still further disadvantage of the known art is that a lowering of the lift axle during ignition off condition has to be achieved through an external electrical relay. This affects the reliability of the system.

The prior art load sensing valve uses a variable area ratio controlling mechanism wherein the modulation of delivery pressure according to the laden condition of the vehicle is controlled by varying the area ratio on which the delivery and supply pressures act.

The major disadvantage of the prior art load sensing valve is that the delivery pressure is dependent on the supply pressure and varies proportionally with supply pressure. Thus the above mentioned pressure reducing valve or a pressure regulator is provided upstream of the load sensing valve to maintain a constant supply pressure of 5 bar. This necessitates additional plumbing in the system to connect the pressure reduction valve to the load sensing valve.

Another disadvantage of the prior art load sensing valve is the complicated design of the valve involving stationary and moving fin profiles sliding inside one another, which requires close control on tolerances to achieve differential area ratio control.

The W02012140672A2 discloses a lift axle control valve assembly comprising a stack arrangement of layers including several pneumatic valves to be connected to a reservoir and to lift bellows and suspension bellows. Also W02012156996A2 discloses a load detection valve assembly comprising of a pressure reduction valve and load sensing valve connected to a reservoir and to the lift axle control valve.

Disadvantages of this system are still the complexity in its design and the costs of manufacturing, besides the piping to joining the separate valves.

It is therefore an object of the invention to provide a lift axle control module, which provides a high reliability at relatively lower costs and piping.

Further objects of the invention are to provide a lift axle suspension control system comprising such a lift axle control valve and load detection valve and a vehicle with such a pneumatic system.

Summary of the invention

The lift axle control module according to the invention is defined in claim 1.

Further a lift axle suspension system for a commercial vehicle comprising this lift axle control module and air bellows is provided.

The present invention enables an integration of the following functions in a modular way:

Automatically raising or lowering the lift axles depending on vehicle load condition,

Lifting of the lift axle with preferably manual override function on fully loaded vehicle for better traction and maneuverability,

Preferably lifting of the lift axle during reverse gear on fully loaded vehicle for better maneuverability,

Damping delay for maintaining the axle position during road undulations

Lowering of the lift axle during the vehicle ignition OFF condition irrespective of the vehicle load.

Most valve elements except the load sensing valve are integrated in a layer stack arrangement, i.e. a multi-layer modular construction comprising a sidewall. The load sensing valve is preferably fixed or attached to the sidewall of the a layer stack arrangement.

Thus according to a preferred embodiment the function of both lift axle control valve and load detection valve are achieved by a single control module. So the pneumatic, piping and vehicle assembly can be provided in only one single unit, which can be handled as one part.

The lift axle control module assembly enables a reduced plumbing on the vehicle. Separate pneumatic supply for individual devices is eliminated and plumbing between the units is reduced.

According to a preferred embodiment one of the air connections of the load detection valve is directly connected to the layer stack arrangement, i.e. without an additional piping; a connection with only a sealing is possible. This air connection is in particular the air inlet of the load detection valve. Thus only one air connection of the load detection valve has to be connected to the layer stack arrangement. Such a system is reliable and does not need much space for packaging. It can be manufactured as a unit to be handled and provided inside the vehicle.

The load detection valve can be comprised of two valve bodies housing a mechanical arrangement which senses the axle load and modifies the air outlet as a pressure signal.

The lift axle control module is preferably provided with three pressure settings, for laden, unladen and lever broken conditions, which ensures the vehicle stability at structural failures of the linkage or lever arrangement in the system.

The preferred multilayer construction permits flexibility in connecting the air passages between the functional groups of components, said layers being preferably flat bodies with cavities and passages, which results in simplified manufacture and hence reduced costs.

The invention is explained in more detail below by means of preferred embodiments shown in the drawings, wherein

Fig. 1 is an electro-pneumatic diagram of a suspension system according to the prior art;

Fig. 2 is an electro-pneumatic diagram of a suspension system according to the yet another prior art;

Fig. 3 s an electro-pneumatic diagram of a suspension system according to an embodiment of the invention;

Fig.4 is a first sectional view of a lift axle control module according to an embodiment of the invention,

Fig. 5 is a second sectional view of a lift axle control module according to an embodiment of the invention,

Description of a preferred embodiment

Referring to figure 1, lift axle control system of the prior art comprises of five devices, a lift axle control valve 101, two relay valves 110 and 112, pressure reduction valve 120 and a load sensing valve 118. The pressure reduction valve 120 reduces the system pressure to the required pressure setting of the suspension bellows 114. The output of the pressure reduction valve 120 is fed to load sensing valve 118 which gives a delivery pressure corresponds to the vehicle load to lift axle control valve 101. The lift axle control valve 101 having Spool valve 104, Damping reservoir 105, Solenoid valve 103, and Double throw pressure switch 106, The solenoid valve 103 and double throw pressure switch 106 is actuated through electrical signals and relay 108.

The deliveries from lift axle control valve 101 feeding to signal port of two external relay valves 110 and 112.The delivery of relay valve 110 feeds to Suspension bellow 114 and delivery of relay valve 112 feeds to Lift bellow 116. This construction gives the lift axle application during load change, manual override and ignition conditions.

Referring to Figure 2, yet another lift axle control system 1101 of the prior art comprises two devices, both shown in dashed lines: a lift axle control valve 1102 and a load detection valve 1103. Further a pressurized air reservoir 1111, suspension bellows 14 and lift bellows 16 are provided. The lift axle control valve 1102 comprises a spool valve 1105, a differential pressure valve 1106, a first solenoid valve 1107 for receiving an ignition signal IG, a second solenoid valve 1108 for receiving an electric override signal TA and for enabling a manual override, a relay valve 1109, a damping reservoir 1110 and a small orifice (throttle) 1112.

The delivery pressure 1700 of said load detection valve 1103 is given as control input 1550 to the lift axle control valve 1102. The control input 1550 is then given to damping reservoir 1110 through said small orifice 1112. The control pressure from damping reservoir 1110 is given to pressure differential valve 1106 through first solenoid valve 1107 and second solenoid valve 1108 for load detection. The damping reservoir 1110 and orifice 1112 are used to reduce the air consumption by avoiding frequent air exhaust in bump road conditions. The first solenoid valve 1107 is getting the signal from dashboard. The second solenoid valve 1108 is used for traction assistance to manual override the axle irrespective of load condition.

The pressure differential valve 1106 is actuating the spool valve 1105 to charge the lift bellow 16 by delivery port 1800 and suspension bellow 14 by another delivery port 1900. The supply pressure from reservoir 1111 is supplied to supply ports 1600 for the load detection valve 1103 and to port 1500 for the lift axle control valve 1102.

Once the relay valve 1109 gets activated through the spool valve 1105, then the delivery air of relay valve 1109 feeds to suspension bellows 14 connected to delivery port 1900. When the second solenoid 1108 gets the signal TA from dashboard, it switches from the position shown in Fig.l to the other position. This switches the pressure differential valve 1106 into its other position and actuates the spool valve 1105 to the other, second position. The lift bellow 16 is charged from the supply pressure at 1800 from reservoir 1111. The supply air at port 1500 from auxiliary reservoir 1111 is passing through first solenoid valve 1107 as shown in Fig 1 and through second solenoid valve 1108 as shown in Figl to activate the pressure differential valve 1106 and subsequently spool valve 1105 and to charge the suspension bellow 14 through relay valve 1109 corresponding to the control pressure 1550 received from load detection valve 1103 for achieving the axle in lowered position during ignition off condition. The lift bellow 16 can be discharged through the common exhaust 1130.

Figure 3 discloses an embodiment of an inventive lift axle suspension system 3 of a vehicle 80 comprising a lift axle control module 2, suspension bellows 14, lift axle bellows 16 and a reservoir (pressure tank) 22. The lift axle control module 2 visualized by dotted lines includes the functions of the lift axle control valve 102 and the load detection 103 of Fig. 2, but integrated into one single device. The vehicle 80 is in particular a commercial vehicle.

The lift axle control module 2 comprises a first supply port (air inlet, system pressure supply port) 24 connected to the reservoir 22, a first delivery port (air outlet) 26 connected to the suspension bellows 14 and a second delivery port (air outlet) 27 connected to the lift bellow 16. The lift axle control module 2 comprises further a first electric signal input 28 for receiving an ignition function and signal SI and a second electric signal input 29 for receiving a lift control signal S2. These signals may be output from a control unit 23 symbolized by dashed lines; however such a control unit 23 is not necessary and this embodiment may in particular be realized by using signals SI and S2 available in the vehicle 80 via a data bus or by separate electric lines. The ignition function signal SI may be fed from a relevant terminal which provides a voltage if the ignition of the vehicle 80 is in its "on" position and the lift control signal S2 may be input by the driver (e.g. via a switch or lever) in order to raise the lift axle.

The lift axle control module 2 comprises the following relevant elements disclosed in Fig. 3:

A load detection valve 18, a 5/2 spool valve 4, a first 3/2 solenoid valve (electro pneumatic valve) 7 for receiving the ignition function signal SI, a second 3/2 solenoid valve (electro pneumatic valve) 8 for receiving the lift control signal S2, a 3/2 pressure differential valve 9 to be pneumatically controlled by a series connection of the solenoid valves 7 and 8 and for controlling the spool valve 4, a damping reservoir 5, a throttle 6 which may be realized by a small orifice hole, and a relay valve 10. Air passages 11a, l ib, 11c, l id, l ie, l lf, l lg, l lh, I lk, 11m (air passages, air conduits) are provided internally in the lift axle control module 2 for an air flow between these elements 4 to 10, i.e. damping reservoir 5, throttle 6, solenoid valves 7 and 8, pressure differential valve 9 and relay valve 10.

A layer stack arrangement 100 is depicted by a dotted block and comprises most elements of the lift axle control module 2 but the load detection valve 18 and a piping 33. The layer stack arrangement 100 is depicted in detail in Fig. 6. The load detection valve 18 is provided externally of the layer stack arrangement 100 and fixed to a sidewall 100a of the stack arrangement, which sidewall 100a runs parallel to a stack direction. A piping 33 connects an outlet 18a of the load detection valve 18 to an block air inlet 25 of the block 100.

The reservoir 22 (auxiliary reservoir) outputs system pressure pO to the first supply port 24; the system pressure pO is fed to the load detection valve 18 and a signal pressure pi delivered by the load detection valve 18 corresponds to the load in the vehicle 80 which is sensed by a lever arrangement in a device connected to the load detection valve 18. The signal pressure pi is fed inside the piping 33 to the block air inlet 25, in which it is then smoothened by the damping orifice 6 and the damping reservoir 5 and afterwards fed as smoothed signal pressure pla to the solenoid valve 7 and the spool valve 4.

The supply port 24 of the lift axle control module 2 is realized in the layer stack arrangement 100; the air passage 11m inside the layer stack arrangement 100 feeds the system pressure pO to the input 18a of the load detection valve 18, the output 18b of the load detection valve 18 is connected to the piping 18.

The spool valve 4 can be switched into two positions. In the first position shown in fig 3, it connects the damping reservoir 5 to the control input of the relay valve 10; thus the relay valve is connected between the supply port 24 and delivery port 26 i.e. between the reservoir 22 and the suspension bellows 14. In this position a charging of the suspension bellows 14 is possible in dependence of the axle load acting on the automatic load detection valve 18. In its second position, the spool valve 4 connects the first supply port 24 to the delivery port 27, i.e. provides pressure from the reservoir 22 to the lift bellow 16 for lifting the lift axle and holding the lift axle in its lifted (upper) position. The lift axle can be lowered again by switching the spool valve 4 back into its first position. The spool valve 4 is controlled by the pressure differential valve 9 which connects the control input 4a of the spool valve 4 to the first supply port 24 in dependence of a series connection of the solenoid valves 7 and 8.

The first solenoid valve 7 receives the ignition function signal SI and transmits either the system pressure pO of the first supply port 24 or the load dependent smoothed signal pressure pla via the air passage 1 lb to the second solenoid valve 8. The first solenoid valve 7 receives the load dependent signal pressure pi via the damping reservoir 5 and an air passage 11a as the smoothed signal pressure pla. The second valve 8 is either open (transmitting) or shut, in dependence of the lift control signal S2 input by the driver. If S2 is not activated and ignition function signal SI is off. i.e. S1=0 and S2=0, then the basic constellation of Fig 2 is realized in which the lift bellow is discharged via the spool valve 4 in order to lower the lift axle. Thus the lift axle remains in its lower position and the wheels of the axle cannot be removed.

The spool valve 4 remains in its first position even when the ignition function signal S 1 switches to ON, as long as the lift control signal S2 remains OFF there by holding the second solenoid valve 8 and the pressure differential valve 9 in the position of Fig. 2, in which the pressure differential valve 9 is blocking.

The suspension bellows 14 are supplied with system pressure in dependence of the automatic load detection valve 18; however this load dependent pressure supplied to the second supply port is first damped (filtered) by the damping reservoir 5 and the throttle 6 and afterwards supplied to the relay valve 10 via the air passage 1 If, the spool valve 4 and the air passage l lg. The damping reservoir 5 and the throttle 6 together serve as a low pass filter; thus unnecessary variations of the suspension bellows 26 due to the road undulations can be prevented. Thus a damping delay is

realized which helps to avoid frequent exhaust of air from suspension bellow when the vehicle 80 is passing through bump road condition, which results in reduction of air consumption.

When the driver inputs the lift control signal S2, i.e. S2 = 1, the second solenoid valve 8 is switched and closed, i.e. blocking the air passage to the control input of the pressure differential valve 9, thereby enabling the pressure differential valve 9 to switch back, thereby switching the spool valve 4 into its activated second position for supplying air to the lift bellow 16. Thus the lift axle is lifted and remains in its lifted position as long as S2=l.

Fig. 4 is a sectional view of the lift axle control module 2 which is realized as a multilayer construction constituting one single body 100, with first, second, third, fourth layer 41, 42, 43, 44 and first, second, third valve levels 51, 52, 53.

The load detection valve 18 with the function as described with respect to Fig. 3 is comprised of load detection valve bodies 2a and 2b which are fixed together; this unit is then fixed to the sidewall 100a of the stack arrangement 100. Inside the fastened load detection valve bodies 2a and 2b there is a cam and lever arrangement B which provides a linear movement for a follower 31. The supply air from supply port 24 is taken by an air passage 1 lm provided in the valve level 53; this air passage 1 lm ends at the sidewall 100a of the layer stack arrangement 100. An air inlet 11a of the load detection valve 18 is connected to the end of the air passage 11m at the sidewall 100a; this air connection is sealed by a sealing 30, in particular to a cartridge subassembly 39 in the load detection valve 18 as supply and based on the follower 31, a delivery pressure is delivered as the pressure signal through the piping 33 to the block air inlet 25. The pressure setting of the load detection valve can be adjusted with a setting screw 19 to the desired level to suit the application. The signal pressure pi will be exhausted through a separate exhaust 40 in the load detection

valve 18 in case of state changes or delivery pressure variations due to lever fluctuations.

At the top of Fig. 4, the first layer 41 is provided comprising the block air inlet 25, followed by a second layer 42. Beneath the second layer 42 the first valve level 51 is provided, in which the first and second solenoid valves 7 and 8 and the damping reservoir 5 are positioned, the damping reservoir 5 being formed in a central area between the first and second solenoid valves 7 and 8. The throttle 6 can be realized by a small orifice hole in the second layer 42 (or the first layer 41). The passages between the damping reservoir 5 and the first solenoid valve 7 and between the solenoid valves 7 and 8 are realized as air passages 11a, l ib (air conduits) in the second layer 42 and or in the subsequent third layer 43 made of plastic material.

As can be seen in Fig.4, the air passages l id and 1 If are realized in the third layer 43, and the air passages 1 lg are realized in the fourth layer 44.

Fig. 5 is the sectional view at the line V - V in Fig. 4, i.e. at the spool valve 4 and the pressure differential valve 9 which are positioned in the subsequent second valve level 52 beneath the third layer 43. They can be integrated, positioned in parallel next to each other, with a common valve casing 61 separating and covering them, as can be seen in Fig. 5, in which the spool valves 4 and pressure differential valve 9 are symbolized by dashed lines, respectively.

A fourth layer 44 is provided between the second valve level 52 of the valve casing 61 of the spool valve 4 and pressure differential valve 9 and the third valve level 53 with the relay valve 10, which fourth layer 44 provides the air passage l ie between these valves 4 and 9. The supply port 24 for system pressure and the first delivery port 26 for the suspension bellow 14 are realized at the sides of the valve level 53 of the relay valve 10. A silencer 63 for the exhaust can be provided at the bottom part. Further a relay valve piston 10a is shown.

As can be seen in Fig. 4, the supply port 24, the block air inlet 25 and first and second delivery ports 26, 27 can be realized at the top or sides of the multilayer construction. The first, second, third and fourth layer 41, 42, 43, 44 and the first, second, third valve level 51, 52, 53 are fixed together by vertically extending bolts 70 penetrating the first, second, third, fourth layer 41, 42, 43, 44 and first, second, third level 51, 52, 53, i.e. a bolt and nut arrangement. Thus an integration with a platform concept with first, second, third, fourth layers 41, 42, 43, 44 (or further layers) permits flexibility in interconnecting the air passages 11a, l ib, 11c, l id, l ie, 1 If, l lg, l lh between the spool valve 4, solenoid valve 7, 8 and relay valve 10. This construction gives the automatic lift axle application during load change, manual override and ignition OFF conditions. In addition this construction simplifies the manufacturing of the layers without cross holes and without steel balls used for blocking the cross drilled holes normally used for connecting the passages in the lift axle control module known to the prior art. It will be appreciated that various other embodiments are possible without departing from the scope and ambit of this invention.
We Claim

1. Lift axle control valve module (2) for a lift axle suspension system (3) of a vehicle (80), said lift axle control valve module (2) comprising:

a pneumatic spool valve (4) for adjusting the air volume of at least a suspension bellow (14) and a lift bellow (16),

a pressure differential valve (9) for controlling said spool valve (4), an electrically actuated pneumatic valve device (7, 8) for receiving at least one electric control signal (SI, S2) and for controlling said pressure differential valve (9), and

a relay valve (10) controlled by said pneumatic spool valve (4),

a load sensing valve (18) for delivering a signal pressure (pi) in dependence of an axle weight in order to control the pneumatic valve device (7, 8) and/or the pressure differential valve (9),

wherein said lift axle control valve module (2) comprises a layer stack arrangement (100) with at least two valve levels (51, 52, 53) and at least two layers (41, 42, 43, 44) comprising air passages (11a, l ib, 11c, 1 Id, 1 le 1 If, 1 lg, l lh, I lk, 11m) for conducting air, wherein the spool valve (4), the pressure differential valve (9), the electrically actuated pneumatic valve device (7, 8) and the relay valve (10) are integrated in the layer stack arrangement (100) and the load sensing valve (18) is fixed to the layer stack arrangement (100) and connected to the air passages (1 lm, 1 lk) of the layer stack arrangement (100).

2. Lift axle control valve module (2) according to claim 1 , wherein the load sensing valve (18) is fixed to a sidewall (100a) of the stack arrangement (100).

3. Lift axle control valve module (2) according to claim 1 or 2, wherein an valve inlet (18b) of the load sensing valve (18) is connected to a passage end (30a) of an air passage (1 lm) of the stack arrangement (100), which passage end (30a) is provided in the sidewall (100a).

4. Lift axle control valve module (2) according to claim 3, wherein the valve inlet (18b) of the load sensing valve (18) is directly connected to passage end (30a) of the supply air passage (1 lm) and sealed by a sealing (30).

5. Lift axle control valve module (2) according to claim 3 or 4, wherein the air passage (1 lm) extends directly and/or linear from the air inlet (24) to its passage end (30a).

6. Lift axle control valve module (2) according to one of the preceding claims, wherein an valve outlet (18a) of the load sensing valve (18) is connected to a block air inlet (25) of the layer stack arrangement (100) by a piping (33).

7. Lift axle control valve module (2) according to one of the preceding claims, wherein the load detection valve (18) comprises at least two load detection valve bodies (2a, 2b) fixed together and housing a mechanical arrangement (B) to be actuated in dependence of an axle load.

8. Lift axle control valve module (2) according to claim 7, wherein the mechanical arrangement (B) comprises a cam and lever arrangement (B) which provides a linear movement for a follower (31) in dependence of the axle load in order to modify an air outlet (18a).

9. Lift axle control valve module (2) according to one of the preceding claims wherein said valve levels (51, 52, 53) are separated by at least two layers (43, 44) of said layers (41, 42, 43, 44),

wherein said pneumatic spool valve (4), said pressure differential valve (9), said electrically actuated pneumatic valve device (7, 8) and said relay valve (10) are positioned in said valve levels (51, 52, 53) an connected with each other by said air passages (11a, l ib, 11c, l id, l ie l lf, l lg, l lh, 1 lk) of said layers (41, 42, 43, 44).

10. Lift axle control valve module (2) according to one of the preceding claims, comprising:

a first electric signal input (28),

a second electric signal input (29),

a first supply port (24) for air supply connected to said spool valve (4) and to be connected to an external reservoir (22),

a block air inlet (25) for air supply to be connected to the load sensing valve (18),

a first delivery port (26) connected to said relay valve (10) and to be connected to at least one suspension bellow (14),

a second delivery port (27) connected to said spool valve (4) and to be connected to at least one lift bellow (16).

11. Lift axle control valve module (2) according to claim 10, further comprising a damping reservoir (5) being connected to said block air inlet (25) and being

further connected to said electrically actuated pneumatic valve device (7, 8) and/or to said spool valve (4).

12. Lift axle control valve module (2) according to claim 10 or 11, wherein said electrically actuated pneumatic valve device (7, 8) comprises a first electrically

- actuated pneumatic valve (7) connected to said first electric signal input (28) for receiving a first electric control signal (SI) and a second electrically actuated pneumatic valve (8) connected to said second electric signal input (29) for receiving a second electric control signal (S2),

13. Lift axle control valve module (2) according to claim 12, wherein said first electric control signal (SI) is an ignition function signal and/or said second electric control signal (SI) is a lifting control signal for lifting the lift axle.

14. Lift axle control valve module (2) according to one of the preceding claims, wherein said layer stack arrangement (100) comprises

a first layer (41) defining an end part of said multilayer construction and comprising an supply port (25),

a second layer (42) connected to said first layer (41) and a subsequent first valve level (51) comprising said electrically actuated pneumatic valve device (7, 8),

a third layer (43) positioned between said first valve level (51) and a second valve level (52) of said spool valve (4),

a fourth layer (44) positioned between said second valve level (52) and a third valve level (53) of said relay valve (10).

15. Lift axle control valve module (2) according to claim 14, wherein a supply port (24) and a delivery port (26) to be connected externally are positioned in said third valve level (53) of said relay valve (10).

16. Lift axle control Valve module (2) according to claim 14 or 15, wherein said layers (41, 42, 43, 44) and said valve levels (51, 52, 53) of said multilayer construction are fixed together by one or more bolts (70) extending trough all layers (41, 42, 43, 44) and valve levels (51, 52, 53).

17. Lift axle control valve module (2) according to one of claims 14 to 16, wherein said first layer (41) is made of a metal material and at least one of said second, third and fourth layer (42, 43, 44) is made of a plastic material, in particular as casted, die casted or injection molded parts comprising said air passages (11a, 1 lb, 1 lc, 1 Id, 1 le 1 If, 1 lg, 1 lh, 1 lk) and bolt holes (47).

18. Lift axle suspension system (3) for a vehicle (80), comprising: a lift axle control valve module (2) according to one of the preceding claims, at least one suspension bellow (14) connected to said Lift axle control valve module (2), and at least one lift bellow (16) connected to said Lift axle control valve module (2).

19. Vehicle (80) comprising a lift axle suspension system (3) according to claim 18.