GB2078319A - Device for transmitting pressure from the suction side of an internal combustion engine to an automatic change-speed gear - Google Patents

Abstract

The invention relates to a device (1) for transmitting pressure from the suction side of an internal combustion engine to an automatic change-speed gear. The device has a chamber (2) sealed by a membrane (4) and connected to the suction side of the engine whereby the movement of the membrane (4) caused by the change in pressure in the chamber (2) is transmitted to a gear shift member (18). To prevent changes in atmospheric pressure from changing the operation point of the gear change a force generator (22) of bellows construction is provided within the device to act against gear shift member displacement in response to changes in atmospheric pressure, the exterior of the generator being in communication with the atmosphere via a bore (25). <IMAGE>

Description

SPECIFICATION Device for transmitting pressure from the suction side of an internal combustion engine to an automatic change-over gear The invention relates to a device for transmitting pressure from the suction side of an internal combustion engine to an automatic change-over gear between the engine and a device driven by the engine, the transmitting device having a chamber sealed by a membrane and being connected to the suction side of the engine whereby the movement of the membrane caused by the change in pressure in the chamber is transmitted to a gear shift lever cooperating with the change-over gear, the upward or downward change of gear being dependent upon the position of the gear shift lever.

In a known device of this kind which, from the suction side of the internal combustion engine effects the change of change-over gear in response to a vacuum, the change-over point changes with a change in atmospheric pressure, particularly in a motor vehicle which drives up or down hills. This can result in a displcement of the operating speed of the engine into an unfavourable range.

It is an object of the present invention to provide a device of the aforementioned type which works essentially independently of changes in atmospheric pressure.

According to the invention this is achieved by providing the device with a force generator whose force is dependent upon the atmospheric pressure and which acts against the gear shift lever displacement in response to a change in atmospheric pressure.

The gear shift lever thus retains its position determined by the vacuum on the suction side of the internal combustion engine practically independent of the changes in atmospheric pressure, thus also rendering independent from atmospheric pressure the respective change-over point of the change-over gear.

Preferably the force generator on one side is supported from the chamber and on the other side is supported by the membrane. In this way the force generator acts in an undiminshed way against a movement of the membrane during a change in pressure in the chamber as a result of changes in atmospheric pressure, thereby correspondingly compensating for a displacement of the flexible membrane in response to atmospheric pressure changes.

The space between the force generator and the membrane can be varied by an adjusting screw.

Since one side of the force generator is supported from the chamber and is thus fixed to the housing, a change in the adjusting screw results in a change in the pre-tension of the force generator so that its transmission characteristic can be simply adapted to the transmission characteristic of the chamber.

Attached to the chamber can be a support against which rests one side of the force generator, while the other side of the force generator is connected with the membrane and when the atmospheric pressure rises the force generator becomes shorter in the direction of transmission. This causes one side of the force generator to be raised from the support when the atmospheric pressure exceeds a predetermined value, preferably normal pressure. The value may alternatively be chosen to correspond to the maximum possible atmospheric pressure. In this way the adjusting range of the force generator can be used to the fullest.

Futhermore, the shift lever can be rigidly connected with the membrane through a member which surrounds the force generator without making contact with it. This results in a transmission device which is compact and short in the direction of transmission and which has a transmission characteristic which is substantially independent of variations in temperature. A pressure capsule makes a particularly simple force generator.

When the pressure generator comprises at least one bellows, the self-adjusted pre-tension can be effected by the spring elasticity of the bellows itself, thus removing the need for special pre-tensioning springs. When the force generator comprises several bellows, a defect in one of them does not immediately result in the complete breakdown of the force generator.

The pressure capsule may contain a vacuum or may be evacuated and its spring force may act against the vacuum. The vacuum has the advantage that because of the lack of air the humidity content in the capsule is very small and therefore the temperature response of the pressure capsule characteristic because of th e the temperature-responsive evaporating humidity is negligably small.

Also, a change in position of the membrane as a result of a reduction in pressure in the chamber can be impeded by an adjustable spring force. This adjustable spring force additionally influences the transmission characteristic of the transmission device for adapting to the respective application.

One example of a transmission device according to the invention will now be described with reference to the accompany drawing with is a cross-section of the device.

The transmission device has a housing 1 with an upper part 2 and a lower part 3. The upper part 2 forms a cylindrical chamber, sealed from the lower part 3 by a membrane 4 stretched between the upper part 2 and lower part 3, and is connected with the suction side of an internal combustion engine (an internal combustion power engine) of a motor vehicle through a pipe 5.

In the chamber 2 there are mounted for axial displacement a spring disc 6, a membrane disc 7 contacting the membrane 4, as well as a pressure spring 8 in the form of a helical spring arranged in between the discs 6 and 7.

In a small recess in the top of the chamber 2, opposite the membrane 4, there is a hole 9 which, in operation, is hermetically sealed by a cap 10. In order to adjust the force of the pressure spring 8, the cap 10 is removed and the spring disc 6 is displaced by means of a pressure plunger (not shown) until the desired spring force is attained. In this position of the spring disc 6 there is pressed into the side wall of the chamber 2 from outside a clip 11 against which the spring disc 6 can be supported. The cap 10 is then reinserted.

The lower part of the housing 3 contains a member in the form of a bracket 12 having a cylindrical part 13 and axial wall extensions 14.

Furthermore the bracket 12 contains a transverse wall 15 which is axially secured to the side wall of the lower part3 and has perforations 15a in the edge region through which the wall extensions 14 pass.

The free ends of the wall extensions 14 are secured, e.g. soldered, to a transverse member 16, which, all round its periphery, is spaced at a distance from the inside of the side wall of the lower part 3. To the transverse member 16 there is fixed a receiving member 17 for holding a gear shift lever 18 which in turn is secured in a drilling of the receiving member 17. The top end of the cylindrical part 13 of the bracket 12 rests against the membrane 4. Aflat headed rivet 19 extends through concentric holes in the membrane disc 7, membrane 4 and bracket 12 and holds these parts together and hermetically sealed.

The flat headed rivet 19 has a threaded hole going through its centre into which is screwed an adjusting screw 20 containing a hexagonal recess arranged opposite a concentric hole 21 in the spring disc 6.

After adjusting the adjusting screw 20 this can be secured in its position and hermetically sealed in the threaded hole by applying a liquid seal. The other end of the adjusting screw 20 is secured to a force generator 22, in the form of a pressure capsule comprising several bellows sections 23 connected in series, for example being hermetically soldered into a hole on the front face of the uppermost bellows 23, as shown. The bellows 23 are connected together while the lowermost bellows 23 loosely rest against the transverse wall 15.All bellows 23 are evacuated and have corrugated upper and lower sides (not shown in the schematic representation) which act as pressure springs and which against the vacuum in the inner chamber or the higher external pressure acting on the outside of the pressure capsule 22 in contact with the atmosphere are designed to expand the pressure capsule in the axial direction. The transverse wall 15 and the lower part 3 hereby act as a support for the pressure capsule 22.

Through the cap 10 the adjusting screw 20 is reached through holes 9 and 21 and by means of a hexagonal key the screw 20 is adjusted under normal atmospheric pressure so that the pressure capsule 22 under pressure rests against the transverse wall 15 and the receiving member 17 rests evenly against the connecting member 24.

The connecting member 24 is secured to the lower side of the bottom part 3 in an opening of the bottom part 3 in an opening of the bottom part 3 and connects this with an opening in the housing of an automatic change-over gear which, depending on the position of the gear shift lever 18, effects an up or downward movement or gear change of the changeover gear.

The inner chamber of the bottom part-of the housing 3 is connected with the atmosphere through drilling 25 and the change-over gear.

When the engine is switched off, the inside chamber 2 and the interior of the bottom part 3 of the housing are at atmospheric pressure (approx. 1000 mb). The pressure capsule 22 or its lowermost bellows 23 is then pressed against the transverse wall 15, while the receiving member 17 rests against the connecting member 24 under the effect of the preloaded spring 8.

When the engine is switched on, as a result of the suction effect of the engine, the pressure on the suction side and accordingly the pressure in chamber 2 diminishes. Since in the bottom part 3 normal pressure remains, i.e. higher pressure than in the chamber 2, the membrane 4 is displaced upwards into the interior of chamber 2 against the action of spring 8. As a result of the rigid connection of the membrane 4 through the bracket 12, the plate 16 and the receiving member 17 with the gear shift lever 18, the lever 18 is displaced upwards by the same amount as the membrane 4. In a pre-determined position of the gear shift lever 18 ih the change-over gear there then takes place a change to the next highest driving stage (lower number of engine revolutions). During this displacement, the pressure capsule 22 is released from the force of the spring 8, thereby expanded axially.If, however, there is a drop in atmospheric pressure, for example because the vehicle is going uphill, the pressure in the chamber 2 does not decrease by the same amount as in the bottom part 3, because between the connecting point of the pipe 5 on the suction side of the engine and the atmosphere there is if necessary provided a throttle, while the connection of the inner chamber of the bottom pa rt 3 with the atmosphere practically has no throttle. Without the pressure capsule 22, because of the decrease in atmospheric pressure, the membrane 4would not be displaced as far towards the inside of the chamber 2 and the gear shift lever 18 would not be delayed in reaching the change-over position. The engine would therefore be changed to the lower revolutions too late, i.e. it would run at excessive speed.

The interposed pressure capsule 22 makes this good, because as the atmospheric pressure in the bottom part 3 of the housing decreases, lower air pressure is exerted from outside onto the pressure capsule 22, the spring tension of the pressure capsule acting outwards thereby effecting a stronger axial expansion of the pressure capsule 22 supported against the transverse wall 15 so that the membrane 4 and thus the gear shift lever 18 is displaced more effectively by the additionally reieased force of the pressure capsule in the direction towards the interior of the chamber 2 while the gear change-over is still effected at the proper place. An increase in atmospheric pressure sees a reversal of the relationships provided the atmospheric pressure does not exceed normal pressure. Above normal pressure the pressure capsule could contract and lift up from the transverse wall 15 thereby having no more influence upong the membrane 4 or the gear shift lever 18. However, relatively uncritical is the situation when the atmospheric pressure rises above normal when compared with air pressure variations such as experienced in up and downhill travel in mountaineous regions. At atmospheric pressure when the pressure capsule lifts off from the transverse wall 15 the atmospheric pressure can of course be adjusted to a higher value by means of an adjusting screw 20 and/or the spring disc 6 so that the pressure capsule 22 and thus also its compensating effect is effective at all prevailing atmospheric pressures.

In supercharged internal combustion engines the expression "suction side" in this context means that of the supercharger.

Claims (9)

1. A device for transmitting pressure from the suction side of an internal combustion engine to an automatic change-over gear between the engine and a device driven by the engine, the transmitting device including a chamber connected to the suction side of the engine and, sealed by a membrane whereby the movement of the membrane caused by a change in the pressure in the chamber is transmitted to a gear shift lever cooperating with the change-over gear, the upward or downward change of gear being dependent upon the position of the gear shift lever, and a force generator whose force is dependent upon atmospheric pressure and which acts against the gear shift lever displacement in response to a change in atmospheric pressure.

2. A device according to claim 1, in which the force generator is supported on one side from the chamber and on the other side is supported by the membrane.

3. A device according to claim 2, in which the space between the force generator and the membrane can be varied by an adjusting screw.

4. A device according to claim 2 or 3, in which the chamber has fixed to it a support which is contacted by one side of the force generator, the other side of the force generator being connected with the membrane, the force generator being arranged to shorten in length in the direction of transmission when the atmospheric pressure rises.

5. A device accoding to claim 4, in which the gear shift lever is rigidly connected with the membrane by means of a member which surrounds the force generator without making contact with it.

6. A device according to any of claims 1 to 5, in which the force generator has a pressure capsule.

7. A device according to any of claims 1 to 6, in which the force generator has at least one bellows.

8. A device according to claim 6 or claim 7, in which the pressure capsule is evacuated and its spring action acts against the vacuum.

9. A device according to claim 1, substantially as described with reference to the accompanying drawing.