GB2072265A

GB2072265A - An Exhaust Brake Valve Assembly

Info

Publication number: GB2072265A
Application number: GB8107015A
Authority: GB
Original assignee: Exhaust Brake Sales & Services
Current assignee: Exhaust Brake Sales & Services
Priority date: 1980-03-14
Filing date: 1981-03-05
Publication date: 1981-09-30

Abstract

An exhaust brake valve assembly for connecting into the exhaust system of an internal combustion engine, comprises an actuator for operating the valve, the actuator including a cylinder in which are fitted (a first piston 13 and a second piston 14. There is also provided first biasing means 7 which is located between said first and second piston 5 to bias said first piston 13 away from said second piston 14 and second biasing means 6 which biases said second piston 14 in the same direction as said first piston 13. An inlet 28 is provided on the opposite side of said first and second piston 5 to said biasing means for applying pressure to said first piston. The applied pressure initially causes the first piston 13 to move towards said second piston 14 and subsequently said first and second pistons to move together from a first connecting rod 12 interconnects said first piston with an exhaust brake valve slider. <IMAGE>

Description

SPECIFICATION An Exhaust Brake Valve Assembly This invention relates to an exhaust brake valve assembly, that is to say a valve assembly adapted to be positioned in the exhaust system of an internal combustion engine so that upon closure of the valve, back pressure to the engine is created, thus providing or enhancing engine braking and hence braking of a road vehicle.

Various designs for such exhaust brake valve assemblies have been proposed in the past, one such valve being that disclosed and claimed in our British Patent No. 1,501,631. The exhaust brake valve assembly of British Patent 1,501,631 was designed to allow the exhaust brake to be serviced without dismantling the exhaust system, particularly the complex exhaust systems of modern engines where the exhaust brake valve is disposed between the exhaust parts of the engine and a turbo-charger. Furthermore, the engine compartment of such vehicles having these complex exhaust systems is extremely cramped and the exhaust brake valve assembly of British Patent 1,501,631 is suited for dismantling in such cramped conditions.

Applicant's earlier exhaust brake uses a spring return air operated piston cylinder device, the length of which cylinder is determined by the length of the spring when compressed, without being coil bound, plus the length of movement required by the piston rod. Furthermore, in exhaust brake applications the force required to move an exhaust valve closure member is sufficiently great as to require a very strong and therefore large return spring for the piston in the cylinder. Consequently, it has been found that in order to obtain a 7.6cm (3 inch) movement of the piston rod it is necessary to provide a cylinder which is approximately 12.7cm (5 inches) in length.

Attempts to overcome this problem have been made by using a double acting cylinder in which compressed air is supplied to one side of the piston to move the piston rod in one direction and then the air pressure is released and air pressure is applied to the other side of the piston in order to return the piston rod in the opposite direction.

Such a construction has the advantage of reducing the length of the cylinder required for a given movement of the piston rod. However, where the piston rod passes out of the cylinder it is necessary to provide a nose gland seal so that the cylinder can work efficiently and no air leaks occur between the piston rod and cylinder.

Furthermore, it must be remembered that exhaust brakes are subject to very high temperatures of exhaust gases and also to carbon deposits which adhere to the piston rod. The combination of heat and carbon deposits on the piston rod cause premature failure of the nose gland seal and therefore such cylinder construction has been found to be unsuitable for use with exhaust brakes.

Furthermore, the double acting type cylinder also has the inherent disadvantage that when the driver of a vehicle applies his brakes when he has finished a journey and the vehicle is left overnight for example, any leaks in the system will reduce the air pressure and when a driver attempts to remove the brakes for the next journey there is no air pressure to disengage the brakes. In addition, if the exhaust brake was mounted vertically and there was an air leak, the exhaust brake closure member could drop to close the exhaust outlet and it would not be possible to start the vehicle.

It is an object of the present invention to overcome the above disadvantages by providing a fluid operable piston cylinder device which will provide a given movement of the piston rod from a cylinder of reduced length relative to known type fluid cylinders providing such a given movement.

According to the present invention there is provided an exhaust brake valve assembly, including a cylinder, first and second pistons located in the cylinder, the first piston being biased away from the second piston with the second piston being biased the same direction, and a piston connecting rod arranged to interconnect an exhaust brake valve slider with the first piston, whereby upon the application of fluid pressure to move the first and second pistons from a first to a second position, the first piston initially moves against its bias towards the second piston and then moves with the second piston towards the second position.

In a preferred embodiment of the invention the first and second pistons comprise inner and outer pistons, respectively, in which the piston rod is connected to the inner piston which is movable with the piston rod within the outer piston. The outer piston is closed at one end with an aperture in the closed end through which the piston rod passes. The end of the outer piston opposite to the closed end is open and has a radially outwardly extending flange including a seal to effect sealing between the outer piston and the internal peripheral surface of the cylinder of said assembly.

Preferably, the bias for the first and second pistons comprises first and second coil springs.

The first coil spring is preferably of a frustoconical compression spring which when compressed has an axial length equal to the thickness of one of the turns of the spring. The second coil spring is of a cylindrical configuration.

Preferably, the cylinder is closed at one end by a closure disc which is recessed to receive the second piston. the cylinder is closed at its opposite end by a wall integrally formed therewith and has a fluid inlet passage therein extending radially relative to the longitudinal axis of the cylinder of the assambly.

The main portion of the inlet passage extends radially of the longitudinal axis of the cylinder so that a fluid supply is coupled at the side of the cylinder. This helps to reduce the overall length of the exhaust brake which would otherwise be increased by the necessary coupling between the cylinder and supply. Ideally, the radially extending passage is provided with an enlarged threaded portion into which the fluid supply can be conveniently coupled.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a side elevational view of one exhaust brake valve assembly of the present invention, and Figure 2 is a part sectional side elevational view of an air cylinder device forming part of the exhaust brake valve assembly of Figure 1.

Referring now particularly to Figures 1 and 2 of the drawings there is shown an exhaust brake valve assembly having a valve housing 1 and an air operated piston cylinder device 2. The housing 1 has an exhaust passage 1 a therethrough and is connectible into an exhaust system of an internal combustion engine by screws (not shown) engaging holes 1 b on the housing.

Air cylinder device 2 is provided with a cylindrical housing 3, a piston rod 4, a piston operating assembly generally indicated by the reference numeral 5 and return springs 6 and 7.

The cylindrical housing 3 is closed at one end by an end portion 8 integral with the housing 3 and at the other end by a cylinder closure disc 9.

At the end of the housing in which the disc 9 is located there is provided a flange 10 in which there are holes 11 for fixing the cylinder device to the valve housing 1.

The piston rod 4 passes freely through a bore 12 in the disc 9 and is coupled at its free end with a valve closure member (not shown) of the exhaust brake. At its opposite end the piston rod supports in a fixed manner a first piston 13 of the piston assembly 5. A second piston 14 of the assembly 5 is of a cylindrical form with its lower end, in Figure 2, closed but having an aperture 15 therein through which the piston rod 4 passes. At the open end of the second piston 14 there is provided an outwardly extending annular flange 1 8 in which a silicone seal 1 9 is located to provide a fluid seal between the flange 1 8 and the inner peripheral surface of the cylinder housing 3.

The second piston 14 of the piston assembly is maintained, in the absence of air pressure, at the closed end of the air cylinder by the return spring 6 which is located between the disc 9 and an undersurface 21 of the annular flange 18.

When compressed to its fullest extent, without being coil bound and with the second piston 14 located in recess 20 in the disc 9, the spring 6 has a length which is sufficient to fit easily into the annular space defined between undersurface 21 of flange 18, annular surface 22 of disc 9 and outer surface 23 of piston 14.

The first piston 13 of the piston assembly 5 is also provided with a silicone seal 24 which sealingly engages inner wall 25 of the piston 14.

The spring 7 which is a frustoconical compression spring, is located between undersurface 26 of the piston 1 3 and the inner surface of the closed end of the piston 14. The spring 7 is so arranged that when compressed the turns of the spring will lie one inside the other so that when piston portion 1 3 moves with the piston rod to its furthest extremity within the piston 14, the coil spring 7 will lay flat. In other words when flat the axial length of the spring 7 is equal to the outside diameter of the material defining the coils of the spring.

The closed end 8 of the air cylinder is provided with passage 27 having an enlarged diameter portion 28 which is screw threaded to receive a coupling member from a source of compressed air. Therefore, the overall length of the valve assembly is kept to a miminum.

When the exhaust brake valve assembly is fitted into an exhaust system the air cylinder device operates by the application of compressed air through the air passage 27. This initially moves the piston 1 3 against its spring 7 downwardly within piston 14. Before piston 13 moves to its fullest extent within piston 14, piston 14 also begins to move downwardly against its return spring 6. When the second piston 14 reaches the opposite end of the air cylinder its closed end engages in the recess 20 in the closure disc 9.Furthermore, with the piston rod at the fullest extent of its movement the spring 7 lays flat against the closed end of piston 14, being held in this position by air pressure upon piston 1 3. In this latter condition the closure member of the exhaust brake would be in a position in which the exhaust passage 1 a is closed and the exhaust brake is therefore applied. Under working conditions the manifold pressure may be 689.4 Kilopascals (100 psi) and therefore for a 10.16cm (4 inch) diameter closure member the force required to move the exhaust brake towards an off position is approximately 1677 Newtons (377 Ibs force).This figure can be obtained from the following formula where D is the diameter of the exhaust manifold, P is the inlet manifold pressure, C is the coefficient of friction between the closure member and the exhaust brake housing and F is the force required to initially remove the closure member towards its open position.

DxrxPxC=F Therefore, when the diameter D is 10.16 cm (4 inches), the inlet manifold pressure P is 689.4 Kilopascals (100 psi.) and the coefficient of friction is 0.3, the force required to move the closure member of the exhaust brake is approximately 1677 Newtons (377 Ibsforce).

Accordingly, very strong and thick springs have to be used to overcome this initial force and it is for this reason, in addition to the need to avoid coil binding, that air cylinders on exhaust brakes are much longer that the actual movement required of the piston rod.

Although the exhaust brake valve unit of the present invention will operate with inlet manifold pressures which are normally of the order of 552 Kilopascals (80 psi) but which can rise to a maximum of 827 Kilopascals (120 psi), the exhaust brake is designed to withstand inlet manifold pressures of 1 379 Kilopascals (200 psi).

Upon removal of air pressure from the air cylinder the return spring 6 initially moves the piston assemble inwardly of the air cylinder away from the closure disc 9. Simultaneously, the reduction of air pressure allows the spring 7 to move piston portion 13 towards the open end of the piston portion 14.

As the inlet manifold pressure reduces with the opening of the exhaust passage the piston assembly will move more easily under spring pressure back towards the opposite end of the air cylinder and the springs 6 and 7 will finally move the piston rod to the position shown in the drawings.

Therefore, there has been disclosed above an exhaust brake valve assembly having an air cylinder in which the movement of the piston rod is substantially equal to the internal axial length of the air cylinder. Consequently, for a given movement of the exhaust brake closure member, for example 7.6 cm (3 inches), an exhaust brake valve assembly of the present invention will have an air cylinder in which the internal axial length is approximately 7.6 cm (3 inches).

In the prior art exhaust brake valve assemblies mentioned above such a 7.6 cm (3 inch) movement would also require a 7.6 cm (3 inch) movement of the piston rod. However, in order to accommodate the compressed length of the return coil spring the cylinder device must be of an additional 3.8 to 5.1 cm (1.5 to 2 inches) in internal axial length resulting in an internal axial length of an air cylinder of 10.16 two 12.7 cm (4.5 to 5 inches).

The exhaust brake valve assembly of the present invention is therefore much smaller in overall length than any known exhaust brake of this type designed to withstand the same loading and heat parameters. Accordingiy, an exhaust brake assembly of the present invention is even more ideally suited for use in the cramped conditions within the engine compartment of a commercial vehicle, thereby advantageously resulting in much easier servicing, shorter servicing time and consequently lower servicing costs. Furthermore, applicants exhaust brake can be inserted into engine compartments which are so restricted in space that even applicants exhaust brake described and claimed in British Patent No.

1,501,631 could not be used for the same load parameters, and yet all the same advantages as regards space and ease of servicing are to be found in the exhaust brake assembly of the present invention.

In order to withstand the effects brought about by changes in temperature on the materials from which the exhaust brake is made, the piston rod 4 is preferably made of mild steel whilst the springs 6 and 7 are preferably made of silicone chrome.

The housing 3, however, is made of aluminium although mild steel may be used.

Claims

1. An exhaust brake valve assembly, including a cylinder, first and second pistons located in the cylinder, the first piston being biased away from the second piston with the second piston being biased in the same direction, and a piston connecting rod arranged to interconnect an exhaust brake valve slider with the first piston, whereby upon the application of fluid pressure to move the first and second pistons from a first to a second position, the first piston initially moves against its bias towards the second piston and then moves with the second piston towards the second position.

2. An assembly as claimed in claim 1 , wherein the first and second pistons comprise inner and outer pistons, respectively, in which the piston rod is connected to the inner piston which is movable with the piston rod within the outer piston.

3. A assembly as claimed in claim 2, wherein the outer piston is cylindrical and is closed at one end with an aperture in the closed end through which the piston rod passes.

4. An assembly as claimed in claim 3, wherein the end of the outer piston opposite to the closed end is open and has a radially outwardly extending flange including a seal to effect sealing between the outer piston and the internal peripheral surface of the cylinder of said assembly.

5. An assembly as claimed in any one of the preceding claims, wherein the bias for the first and second pistons comprises first and second coil springs, respectively.

6. An assembly as claimed in claim 5, wherein the first coil spring is a frustoconical compression spring which when compressed has an axial length equal to the thickness of one turn of the coil spring.

7. An assembly as claimed in claim 5 or 6, wherein the second coil spring is of a cylindrical configuration.

8. An assembly as claimed in any one of the preceding claims, wherein the cylinder is closed at one end by a closure disc which is recessed to receive the other second piston.

9. An assembly as claimed in claim 8, wherein the cylinder is closed at its opposite end by a wall integrally formed therewith and has a fluid inlet passage therein, which extends radially relative to the longitudinal axis of the cylinder.

10. An exhaust brake valve assembly substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.