WO2012156996A2

WO2012156996A2 - Load detection valve for a motor vehicle

Info

Publication number: WO2012156996A2
Application number: PCT/IN2012/000352
Authority: WO
Inventors: Sundaramahalingam SELVAMANI; Narayanan SREENIVASAN; Arumugham GANESAMOORTHY; Syed Azhar JIFRI
Original assignee: Wabco India Limited
Priority date: 2011-05-18
Filing date: 2012-05-16
Publication date: 2012-11-22
Also published as: BR112013028153A2; WO2012156996A3; BR112013028153B1

Abstract

The invention refers to a load detection valve (2) for a lift axle control system of a motor vehicle, comprising: an air supply port (20) for receiving air, an air delivery port (21) for delivering air with a delivery pressure (p2), a cam (10) for rotating in relationship to an axle load, a slidable piston assembly (14), a valve means (24) being displaceable provided in said piston assembly (14), a follower means (12) for actuating said valve means (24), said follower means (12) being shiftable in dependence of said cam rotation, a graduating spring (16) for loading said piston assembly (14), a conduit (30) connected to said air delivery port (21), said delivery pressure in said conduit (30) acting on said piston assembly (14) against said graduating spring (16) in order to output said delivery pressure (p2) in dependence of said graduating spring (16).

Description

Load detection valve for a motor vehicle Background of the invention

The invention relates to a load detection valve to be used in a lift axle control system of a commercial vehicle, further to a lift axle control system comprising such a load detection valve, and a vehicle, in particular a commercial vehicle, comprising such a lift axle control system.

A lift axle system is used in a commercial vehicle 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 system of a commercial vehicle comprises in general a pair of suspension bellows (like the other axles) for damping and for adjusting the distribution of the axle load between the axles of the vehicle and the distance between the axle and the chassis, and additionally a pair of 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 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, a relay 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 1.5 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.

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.

It is therefore an object of the invention to provide a load detection valve, which provides a high reliability at relatively low costs. Further objects of the invention are to provide a lift axle control system comprising such a lift axle control valve and a vehicle with such a pneumatic system.

Summary of the invention

The load detection valve according to the invention is defined in claim 1. Further a lift axle control system comprising the load detection valve, and a vehicle comprising this lift axle control system are provided.

The load detection valve integrates the functions of a pressure reduction valve and a load sensing valve and replaces both these valves in the lift axle control system. The valve is preferably mounted on the chassis of the vehicle and is connected mechanically directly to the tandem axle of the vehicle or indirectly, e.g. to a link connecting the tandem axles in case of more than one tandem axles, wherein this connection is preferably provided by means of a lever and flexible bush mechanism.

When the vehicle is loaded the distance between the chassis and the tandem axle of the vehicle is reduced due to the deflection of the suspension spring. This results in the upward movement (rotation) of the lever.

According to a preferred embodiment the lever is preferably rigidly connected to a cam, the radius of which varies with the angle of lever rotation. A roller follower is always in contact with the cam. The follower actuates a bonded valve which is part of a spring graduating system that controls the delivery pressure depending on the follower lift. The maximum delivery pressure of the valve during laden condition of the vehicle is adjusted to preferably 5 bar using e.g. a screw adjusting arrangement, thereby eliminating the necessity of a separate pressure reduction valve. One advantage of the invention is that a pressure reduction valve and an additional plumbing between this pressure reduction valve and the subsequent load sensing valve can be avoided. The need for a separate pressure reduction valve can preferably avoided by using a spring graduating system with pressure adjusting facility, where the delivery pressure is independent of the supply pressure.

A further advantage of the invention is that the design with a spring graduating system is compact in construction with a low number of parts, in particular in comparison with prior art systems involving stationary and moving fin profiles sliding inside one another.

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 lift axle control system according to the prior art;

Fig. 2 shows a load sensing valve of the prior art;

Fig. 3 shows a cross section of the load sensing valve of Fig. 2,

Fig. 4 shows a cross section of the pressure reduction valve of the prior art;

Fig. 5 shows a load detection valve according to an embodiment of the invention;

Fig. 6 shows a cross sectional view of the load detection valve of Fig. 5; and

Fig. 7 is an electro-pneumatic diagram of a lift axle control system according to an embodiment of the invention.

Description of the embodiments Referring to figure 1 , a lift axle control system according to the prior art is shown. The lift axle control valve assembly 101 comprises a spool valve 104, actuated via. a solenoid 103, a damping reservoir 105 and a double throw pressure switch 106. The solenoid 103 is actuated through electrical signals, which may be output from a device 108, e.g. on basis of a relay which gets electrical input from a double throw pressure switch 106. The deliveries from lift axle control valve 101 feed to a signal port of two external relay valves

110 and 112. The delivery of relay valve 110 feeds to the suspension bellow 14 and the delivery of relay valve 112 feeds to the lift bellow 116.

A reservoir 122 is provided storing a system pressure pO for pressure supply; the system pressure pO may in general vary, since the reservoir is only periodically filled with pressurized air from a compressor not shown in these drawings. The reservoir 122 supplies the system pressure pO via a piping 11 to a pressure reduction valve 120 for pressure supply which delivers a constant reference pressure p1 of 5 bar to an Automatic load sensing valve 118.

The Automatic load sensing valve 118 outputs a delivery pressure p2 as a pressure signal which is modulated in dependence of an axle load to the lift axle control valve 101 , e.g. via a piping 111. Thus the Automatic load sensing valve 118 senses the axle load or gravitational force of the vehicle structure acting on the axle, and outputs the delivery pressure p2 as an analog signal, e.g. with a pressure value between 1.5 bar in case of an unladen vehicle and 5 bar in case of a maximum load. This construction enables a lift axle application during load change.

Figure 2 shows a hardware embodiment of the Automatic load sensing valve 118 of Fig.1 , comprising a supply port 130 to be connected to the pressure ' reduction valve 120, one or two delivery ports 132 to be connected to the lift axle control valve 101 , and an exhaust port 134. A lever 136 is connected to a flexible link 138 which in turn connects to the axle through a linkage 140.

Figure 3 shows the cross section of the automatic Load Sensing Valve 118 which works on differential area balancing mechanism. Here the lever 136 is rigidly fixed with a cam 142 which maintains contact with a follower 144. The follower 144 operates a bonded valve 146. The modulation of delivered delivery pressure p2 with respect to vehicle load is achieved by varying the reaction area on a diaphragm 148 on which the delivery pressure p2 acts. The reaction area of the diaphragm 148 is varied by the mating profiles present on a stationary fin 150 and a moving fin 152.

Figure 4 shows the cross section of prior art pressure reduction valve 120 which delivers a set delivery pressure as the reference pressure p1 at its delivery port 154, D irrespective of the supplied system pressure pO at its supply port 156. The delivery pressure setting can be varied using an adjusting screw 158. Further an exhaust port 160 of the Pressure Reduction Valve 120 is provided.

In the following the embodiments of the invention are explained in detail.

Figure 5 and 6 show an embodiment of a load detection valve 2 according to the invention. The load detection valve 2 comprises a body with a top part 2a and a bottom part 2b, sealed and fixed together. The body 2a, 2b is to be mounted to a (only roughly depicted) structure, preferably a chassis 8, of the vehicle. A lever 4 is connected with one end via a flexible member 5, in particular a flexible bush member 5, to a linkage 6 which in turn is connected to the tandem axle of the vehicle (not shown in figure); the other end of the lever 4 is fixed (rigidly connected) to a cam 10 pivoted inside the bottom part 2b of the body 2a, 2b; the cam is rotatable around a rotation axis B. The radius of the cam 10 varies with the angle of lever rotation a. Thus the cam 10 is rotated in dependence of the load acting onto the axle.

A follower 12 comprising a roller 13 is provided inside the bottom part 2b of the body 2a, 2b and movable along a longitudinal axis A. The longitudinal axis A is orthogonal to the rotation axis B. The roller 13 contacts the cam 10 and thus the follower 12 is shifted in dependence of the cam rotation. When the vehicle is loaded the cam 10 rotates in the anti-clockwise direction pushing the follower 2 upwards

A split piston assembly 14, which consists of an upper split piston 14a and a lower split piston 14b that are fastened together, is movable inside the bottom body 2b. A graduating spring 16 is positioned between a spring guide 17 and the split piston assembly 14. The spring guide 17 can be displaced by an adjustment screw 18 screwed in an internal thread 19 of the top part 2a. Thus the spring force of the graduating spring 16 can be adjusted via the adjustment screw 18.

A supply port 20 of the load detection valve 2 is connected to an internal space 22 of the split piston assembly 14; therefore the internal space 22 is filled with an input pressure pO, which is the system pressure pO.

A bonded valve 24 is inserted in the internal space 22 of the split piston assembly 14 and loaded by a valve return spring 25. The bonded valve 24 comprises a metallic plunger 24a with a rubber pad 24b attached to the bottom. The bonded valve 24 is pressed against an exhaust valve seat 32 which is formed on the follower 12, thereby sealing the internal space 22 against a first cavity 31 , which is connected to the atmosphere through the exhaust port 40. Air in the internal space 22 passes to a second cavity 26 formed between the bottom body 2b and the split piston assembly 14, through the gap between the lower split piston 14b and the bonded valve 24. The second cavity 26 is connected to the delivery port 21 through a conduit 30 formed in the bottom body 2b. This results in the building up of delivery pressure p2 in the delivery port 21 and the second cavity 26.

The delivery pressure p2 acts at the bottom face of the split piston assembly 14 and therefore against the spring force (load) of the graduating spring 16. When the pressure force (load) of the delivery pressure p2 acting below the split piston assembly 14 equals the spring force (load) of the graduating spring 16, the inlet valve seat 28 formed on the lower split piston 14b is pressed against the bonded valve 24; thereby sealing the internal space 22 from the second cavity 26. This prevents the further rise of delivery pressure p2. Then the bonded valve 24 is in balanced condition (that is both the inlet valve seat 28 and exhaust valve seat 32 are sealed), providing the required delivery pressure p2.

When the vehicle is loaded the cam 10 rotates in the anti-clockwise direction pushing the follower 12 upwards. The follower 12 thus opens the bonded valve 24 which causes the further flow of air from the supply port 20 through the internal space 22 of the split piston assembly 14 to the second cavity 26 which is connected to the delivery port 21 through the conduit 30. This causes further compression of the graduating spring 16 resulting in an increase in spring load. Then a higher delivery pressure p2 is required to equalize the spring load and thereby bring the bonded valve 24 to balanced condition. Thus a higher pressure p2 is delivered at the port 21 when the vehicle is in laden condition compared to the unladen condition.

According to this design the delivery pressure is only based on the vehicle load (axle load) and the resulting rotation of the cam which loads the graduat- ing spring 16. The exhaust port 40 of the load detection valve 2 is positioned on its bottom area.

Claims

Patent claims

1. Load detection valve (2) for a lift axle control system of a motor vehicle, comprising:

an air supply port (20) for receiving air,

an air delivery port (21) for delivering air with a delivery pressure (p2), a cam (10) for rotating in relationship to an axle load,

a slidable piston assembly (14),

a valve means (24) being displaceable provided in said piston assembly (14),

a follower means (12) for actuating said valve means (24), said follower means (12) being shiftable in dependence of said cam rotation, a graduating spring (16) for loading said piston assembly (14), a conduit (30) connected to said delivery port (21),

said delivery pressure (p2) in said conduit (30) acting on said valve means (24) against said graduating spring (16) in order to output said delivery pressure (p2) in dependence of said graduating spring (16).

2. Load detection valve (2) according to claim 1 , wherein said delivery pressure (p2) is independent of an input pressure (pO) of said supply port (20).

3. Load detection valve (2) according to claim 1 or 2,

wherein said piston assembly (14) comprises a valve return spring (25) being supported in said piston assembly (14) and loading said valve means (24) against an inlet valve seat (28) formed in said piston assembly (14).

4. Load detection valve (2) according to one of the preceding claims, wherein an internal space (22) of said piston assembly (14) is connected to said air supply port (20).

5. Load detection valve (2) according to claim 4, wherein said piston assembly (14) is a split piston assembly (14) comprising a first part (14a) and a second part (14b), said first part (14a) and second part (14b) being fixed together and defining said internal space (22).

6. Load detection valve (2) according to claim 4 or 5, wherein said valve means (24) is a bonded valve (24) comprising a plunger (24a) and a rubber pad (24b) attached to said plunger (24a),

wherein said rubber pad (24b) is pressed against an exhaust valve seat (32) thereby sealing said internal space (22) against a first cavity (31), which is connected to an exhaust port (40) for exhausting air to the atmosphere.

7. Load detection valve (2) according to claim 6, wherein said exhaust valve seat (32) is formed on said follower means (12) and said first cavity (31) is formed in said follower means (12).

8. Load detection valve (2) according to one of the preceding claims, wherein said follower means (12) is in contact with said cam (10) and abiits said valve means (24) in order to push said valve means (24) against said valve return spring (25).

9. Load detection valve (2) according to one of the preceding claims, wherein a spring load of said graduating spring (16) is adjustable by an adjusting means, in particular an adjusting screw (19).

10. Load detection valve (2) according to one of the preceding claims, further comprising a body (2a, 2b),

Wherein said cam (10) is pivoted in said body (2a, 2b) and said piston assembly (14) is slidably provided in said body (2a, 2b).

11. Load detection valve (2) according to claim 10, wherein said body (2a, 2b) is comprised of a top part (2a) and a bottom part (2b) fixed together.

12. Load detection valve (2) according to claim 10 or 11 , wherein a second cavity (26) is formed between said body (2a. 2b) and said piston assembly (14) and connected via said conduit (30) to said delivery port (21),

wherein said second cavity (26) is connectable to an internal space (22) of said piston assembly (14) by a gap to be opened between said piston assembly (14) and said valve means (24).

13. Load detection valve (2) according to claim 12,

wherein said delivery pressure (p2) acts at a bottom face of said assembly (14) and therefore against a spring force of said graduating spring (16),

wherein in the case that a pressure force of said delivery pressure (p2) acting below said piston assembly (14) equals said spring force of said graduating spring (16), an inlet valve seat (28) formed in said piston assembly (14) is pressed against said valve means (24) thereby sealing said internal space (22) from said second cavity (26).

14. Lift axle control system (50) for a commercial vehicle, comprising at least:

a load detection valve (2) according to one of the preceding claims, a lift axle control valve assembly (101) connected to said delivery port (21) of said load detection valve (2),

lift bellows (116), and

suspension bellows (114).

15. Vehicle comprising at least:

a structure (8), in particular a chassis,

a lift axle, and

a lift axle control system (50) according to claim 14 for lifting or lowering said lift axle in dependence of the vehicle load,

wherein said load detection valve (2) of said lift axle control system (50) is connected to said structure (8) and said axle.