Vacuum-boosting device

Abstract

 A vacuum-boosting device for motor vehicles fitted with vacuum-operated load systems, the vacuum being provided by the engine air induction in the case of a petrol engine or by a suitable vacuum pump (34) in a Diesel engine. The device acts to increase the rate of evacuation of the load system (15) when the vacuum of the engine is weaker than a predetermined value, by increasing the idling revolutions of a petrol engine, or acting on a throttle valve (19) in the air inlet (18) of a Diesel engine so as to create a vacuum in the induction manifold to assist the vacuum pump (34) in evacuating the load circuit.

Description

[0001] The present invention relates to a device for rapidly boosting the vacuum produced at idling by an engine for motor vehicles provided with vacuum-operated load systems, the vacuum being provided by the induction of the engine in the case of a petrol engine, or by a suitable vacuum pump in the case of a diesel engine, of the type comprising a vacuum actuator acting upon a throttle valve in the induction duct system of the engine and, in the case of a petrol engine, comprising the throttle valve of the carburettor or of the injection system.

[0002] Modern motor vehicles there are often fitted with load systems of various types, such as servo-brakes, power steering, and various controls for air conditioners and for door locking etc., which are operated by the vacuum furnished by the engine.

[0003] In the case of petrol engines, the vacuum is generally created in the induction manifold of the engine; a non-return valve is positioned in a connecting duct between the induction manifold and a load system in such a way that, at full engine power, when the manifold vacuum is noticeably weakened, or when the engine is stopped, the vacuum is maintained in the load system.

[0004] In diesel engines, in which vacuum in the induction ducts is practically non-existent under all the operating conditions, a volumetric vacuum pump is provided to generate the vacuum necessary for the load systems, various types of such pump being known in the prior art. This pump is driven by the engine and therefore functions continuously,drawing air from the load system with a flow rate which is susbtantially proportional to the number of revolutions (r.p.m.) of the engine.

[0005] In certain circumstances it can happen that the flow rate of air evacuated from the load system is insufficient. For example, for a vehicle having a petrol engine equipped with vacuum power steering, in a parking manoeuvre carried out with an idling engine, the flow rate of air evacuated by the engine may be too low to maintain a sufficient vacuum in the power steering circuit, and the servo-assisted effect becomes inadequate. The same occurs in a vehicle with a diesel engine: at idling, the vacuum pump gives a flow rate which is too low for a sufficient vacuum to be formed in the circuit of a power steering system. Similarly the power available in a servo-braking system may become critically low if the brake is applied repeatedly at short intervals with the engine idling. The petrol engine does not present this problem in a servo-braking system because the air flow rate which it provides, for a given swept volume, is much greater than that of a vacuum pump of a diesel engine. In a diesel engine, so as to resolve the problems described it would be necessary to use a vacuum pump of a size and flow rate that are significantly greater than those normally employed, with obvious penalties with regard to costs, weight and power dissipation.

[0006] The object of the present invention is that of resolving the problems described above without incurring the consequent penalties aforementioned.

[0007] According to the present invention there is provided a vacuum-boosting device of the type referred to, characterised in that the vacuum actuator is actuated by the vacuum existing in the pneumatic circuit of the load system and controls the throttle valve in such a way that, when said vacuum is.weaker than a given predetermined value, the actuator, in the case of a petrol engine, opens the throttle valve slightly for the purpose of slightly increasing the engine idling revolutions, or in the case of a diesel engine, the actuator ensures that the valve throttles the air flow in the supply system in order to create in the said supply system a vacuum that assists the vacuum pump to exhaust air from the load system , the actuator returning the engine, be this a petrol engine or a diesel engine, to its normal operating condition once the vacuum in the load system has reached the said predetermined value.

[0008] The device of the invention allows the times of evacuation of a load system to be significantly reduced, with negligible increase in cost compared with the cost of the load system itself.

[0009] The invention will be described, by way of example, with reference to the appended drawings, in which:

Figure 1 is a diagram of a "high idling" device for a petrol engine; according to one embodiment of the invention;

Figure 2 is a diagram of a throttle device in the induction system of a diesel engine according to another embodiment of the invention, and

Figure 3 is a cross-sectional view of part of the . device, taken on line III-III in Figure 2.

[0010] In the drawings the same reference numerals are used to designate the same or corresponding components of the different embodiments.

[0011] In Figure 1 reference numeral 2 indicates a lever for controlling the carburettor throttle of a petrol engine, fixed to a spindle 1 on which the said throttle, not shown, is mounted. The lever 2 is provided with a tab 3 having a threaded hole in which is engaged an idling adjustment screw 4, locked by a safety lock nut 5.

[0012] On the same carburettor, or on another engine element near the carburettor, a vacuum actuator capsule 16 is mounted by means of a bracket llb. The actuator capsule 16 comprises two half-casings 10 and 11, and a piston formed by two caps 7 and 8, a diaphragm 9 sandwiched between the caps and a small rod 6 attached to the caps 7 and 8. A preloaded helical spring 12 bears against the cap 7, urging the piston to the left as viewed in Figure 1.

[0013] The half-casing 10 is equipped with a connector spigot 10b on which a pipe 14 is fitted. The pipe 14 connects a chamber 10a defined between the piston 7,8 and the half-casing 10 to a load circuit, for example a servo-braking system identified 15 in the drawings.

[0014] The carburettor/accelerator control system is provided with a resilient biassing system, not shown in the drawings, which tends to bias the throttle to an idling position and, therefore, to bias the lever 2 to the position indicated by a continuous line in Figure 1. Under such conditions the idling adjustment screw 4, which abuts the small rod 6, is adjusted so as to ensure the desired normal idling engine revolutions.

[0015] The spring 12 exerts a load greater than the thrust exerted by the screw 4 against the rod 6, and consequently, in the absence of any vacuum in the chamber 10a the spring 12 displaces the piston and the rod 6 fully towards the left and the lever 2 into the position indicated by a dotted line. Under these conditions, the engine is slightly accelerated to a "high idling" condition at a higher number of revolutions per minute, (r.p.m.) than "normal idling" r.p.m.

[0016] The difference in r.p.m. between the high idling and normal idling depends on the throttle opening imposed by the rod 6. When the vacuum in the load circuit and in the chamber 10a strengthens and exceeds the value at which the thrust on the piston of the actuator capsule 16 resulting from the vacuum is greater than the difference between the load of the spring 12 and the thrust of the adjusting screw 4 against the rod 6, the piston, together with the lever 2, is displaced towards the right and normal idling is resumed.

[0017] If, by virtue of an excessive loss of air in the load system 15 the vacuum therein weakens and falls belowthe value mentioned above, the spring 12 returns the lever 2 to the high idling position. The vacuum level at which the device intervenes is easily controlled by regulating the load of the spring 12 and the dimensions of the piston capsule 16.

[0018] If it were useful, in order to counteract possible surging of the engine in the idling state, a restricted air passage may be provided in the half-casing 11, for example by means of a small hole lla of suitable 3iameter.

[0019] Figure 2 shows a device for choking the air flow into the induction manifold of a diesel engine. By way of example, it is supposed that the device is mounted on an air filter 17 upstream of the induction manifold. Within the air inlet pipe 18 of the filter 17 there is positioned a butterfly throttle valve 19 carried upon a shaft 20 rotatably supported by two bushes 21, 21a, fixed to the walls of the pipe 18, as shown in Figure 3. On one end of the shaft 20 there is fixed a lever 22 which is connected by means of a rod 23 to a piston 24 of a vacuum actuator capsule 25.

[0020] The capsule 25 is made up of two half-casings 26 and 27 and a diaphragm 30 sandwiched between two caps 28, 29 which together constitute the piston 24. Within a cap 28 there is housed a spring 31 which biases the piston 24, downwardly as viewed, tending to rotate the throttle valve 19 towards the "high idling" position indicated in Figure 2 by a dotted line. The capsule 25 is fixed to the pipe 18 by means of a bracket 32.

[0021] In Figure 2 the pneumatic connections of the system are shown diagrammatically. The load system 15 is connected to a vacuum pump 34 driven by the engine and to the said air filter 17, downstream of the throttle valve 19. In the duct between the filter 17 and the load system 15 there is interposed a non-return valve 33 which prevents the pump 34 from drawing air from the filter 17.

[0022] The operation of the device Figures 2 and 3 is as follows. When the vacuum in the load system 15 exceeds a predetermined value, the thrust on the piston 24 overcomes the load of the spring 31 and maintains the throttle valve 19 in the position indicated in the Figure by a continuous line, so that air flows freely into the pipe 18, without creating a vacuum in the filter 17 and in the induction manifold downstream of the filter 17. Under these conditions, the load system 15 is evacuated only by the vacuum pump 34. If, because of a high leakage of air from the load system 15 the vacuum weakens below the predetermined value the spring 31 causes the throttle valve 19 to rotate, thus bringing it into the position indicated in broken outline in the drawing, and therefore closing the air passage. Under such conditions, the engine is constrained to draw air from the load system 15, and does so at a very high flow rate. The vacuum in the load system 15 then strengthens rapidly until it reaches the preset value of the capsule 25 when the latter re-opens the throttle valve 19, restoring the normal conditions of supply of the engine.

[0023] Instead of being inserted in the inlet pipe of the filter 17, the device may obviously be inserted in the inlet of the induction manifold or at any other point where the flow of air into the manifold is restricted.

[0024] If in a diesel engine, it were desired to increase further the boosting effect for the vacuum pump at idling it would be possible to apply thereto, in addition to the throttling device hitherto described, the high idling device of the type schematically illustrated in Figure 1. It is evident that in this case the vacuum actuator capsule should act on the regulating member of the fuel injection system, instead of on the throttle valve of the carburettor, while continuing, however, to operate in the same way.

Claims

1. A device for rapidly boosting the vacuum produced at idling by an engine for motor vehicles provided with vacuum-operated load systems (15), the vacuum being provided by the induction of the engine in the case of a petrol engine,or by a suitable vacuum pump (34) in the case of a diesel engine, of the type including a vacuum actuator (16; 25) acting upon a throttle valve (19) in the induction duct system (18) of the engine and, in the case of a petrol engine, comprising the throttle valve of the carburettor or of the injection system,
characterised in that:

the vacuum actuator (16; 25) is actuated by the vacuum existing in the pneumatic circuit of the load system (15) and controls the throttle valve (19) in such a way that, when said vacuum is weaker than a given predetermined value, the actuator (16; 25) in the case of a petrol engine, opens the throttle valve slightly for the purpose of slightly increasing the engine idling revolutions, or in the case of a diesel engine, the actuator (16; 25) ensures that the valve throttles the air flow in the supply system in order to create in the said supply system a vacuum that assists the vacuum pump (34) to exhaust air from the load system (15), the actuator (16; 25) returning the engine, be this a petrol engine or a diesel engine, to its normal operating condition once the vacuum in the load system (15) has reached the said predetermined value.

2. A device for rapidly boosting the vacuum produced by an idling engine according to Claim 1, in particular for a petrol engine in which the vacuum is provided by the induction manifold,
characterised in that the device includes a vacuum actuator (16) which acts upon an idling stop (4) for the throttle valve of the carburettor - or of the injection system - in such a way as to increase the engine idling revolutions when the vacuum weakens and falls below the predetermined value, the actuator (16) being connected to the circuit of the load system (15) so that the force exerted by the actuator on the throttle valve stop (4) depends on the vacuum in the said circuit, and elastic means (12) for biassing the throttle valve stop (4) to a high idling position, the vacuum actuator (16) returning the stop into a normal idling position when the vacuum in the load system (15) reaches the predetermined value.

3. A device for rapidly boosting the vacuum produced by an idling engine according to Claim 1, in particular for a diesel engine, in which the vacuum is provided by a vacuum pump (34) driven by the engine characterised in that
a throttle valve (19) preferably of the butterfly type, is provided in the induction duct system (18) and is controlled by the vacuum actuator (25), said actuator (25) being biassed by suitable elastic means (31) to a position in which the valve (19) allows the free passage of air, and the actuator acting so as to bring the valve into an air flow restricting position when the vacuum in the load system (15) is lower than the predetermined value.

4. A device for rapidly boosting the vacuum produced by an idling engine according to Claims 1 and 3, only for diesel engines,
characterised in that
in addition to the throttle valve (19) the subject-of Claim 3, there is also used the high idling device according to Claim 2, said high idling device acting upon the injection system of the engine.

Drawing