GB2051416A - Hydraulic servo-controlled amplifier for internal combustion engines - Google Patents

Abstract

The amplifier includes a double- acting follow-up piston 13 and a control spool 15 disposed coaxially thereof, and its adjusting movement is controlled by a valve device which comprises two control edges (31, 32), Fig. 3 (not shown), on the control spool 15 which enable pressure medium to flow out of a selected one of the pressure chambers 18, 19, and a hydraulically actuable change-over valve 24 which operates as a logic valve and is in the form of a three-port, two-position valve interposed between a pressure medium supply line 23 and two branch conduits 21, 22 leading to the pressure chambers. The valve 24 automatically controls the supply of pressure medium to one of the pressure chambers 18 or 19 when the other of the pressure chambers is relieved of pressure, whereby the piston 13 and governor rod 11 move to a new position. The amplifier with its compact construction and simplified control is particularly suitable for rapid actuation of the adjusting member of a fuel metering device. <IMAGE>

Description

SPECIFICATION Improvements in or relating to hydraulic servo-controlled amplifiers for internal combustion engines The present invention relates to hydraulic servo-controlled amplifiers for-internal combustion engines.

One form of a hydraulic servo-controlled amplifier as disclosed in German Patent Specification No. 564,019 has a double-acting piston which actuates a hollow camshaft, provided with tapered cams, of a fuel injection pump for the purpose of varying the quantity of fuel delivered, a control spool of the fuel injection pump being actuated by a centrifugal governor. The control spool is provided with four control edges and is disposed in a follow-up piston and controls five control passages disposed in the follow-up piston, one of which control passages serves to feed pressure medium, two serve to establish communication with two pressure chambers in the follow-up piston, and two serve to discharge the pressure medium.Since the control passages serving to feed and discharge the pressure medium have to communicate with corresponding lines disposed in the housing during the entire stroke of the piston, and these lines have always to be sealed relative to the adjacent pressure chambers, this requires the follow-up piston to be of very great overall length and, disadvantageously, four adjacent chambers of differing pressure which have to be sealed relative to one another by sealing fits around the the periphery of the follow-up piston. The long overall length of the followup piston, together with the large number of complicated control passages, results in a servo-controlled amplifier of very expensive construction. The large mass of the follow-up piston is also disadvantageous with respect to rapid control and regulating movements.This disadvantage arises particularly when a low working pressure is to be used, such as the prefeed pump pressure of a fuel injection pump, and the effective suface areas of the piston have to be correspondingly enlarged.

According to the present invention there is provided a hydraulic servo-controlled amplifier for internal combustion engines having a double-acting follow-up piston which serves as a movable wall to separate two pressure chambers in the amplifier housing, a control spool disposed coaxially in the follow-up piston, a pressure medium supply line, and a valve arrangement for controlling the inflow and outflow of pressure medium to and from the pressure chambers and formed by a valve device comprising two control edges on the control spool for controlling the outflow of pressure medium from the pressure chambers and a hydraulically actuable change-over valve which operates as a logic valve and which is disposed in a connection between the pressure medium supply line and two branch conduits leading to the pressure chambers.

A hydraulic servo-controlled amplifier embodying the present invention can have the advantage that, by virtue of using the hydraulically operable change-over valve operating as a logic valve, only two control edges controlling the outflow from the pressure chambers are required on the control spool, which leads to a very simple piston arrangement of short construction. Since the follow-up piston only has to seal the two chambers relative to one another, a simple piston seal is sufficient. The very short overall length of the piston thus rendered possible facilitates adjustment of the cylinder fit and results in a relatively small mass of the follow-up piston, which is advantageous with respect to rapid actuating movements.A servo-controlled amplifier embodying the present invention can operate with an adequately large working capacity with a relatively low pressure of the pressure medium since, owing to the very slender piston which it is possible to provide, any necessary increase in the diameter of the piston only leads to a slight increase in the size of the moved masses.

Preferably the change-over valve is movable by the pressure drop effected in one of the pressure chambers by one of the control edges on the control spool and by the unchanged pressure in the other of the pressure chambers, into a switching position in which for actuation of the follow-up piston, the supply line is only connected to the pressure chamber which is still pressurised and, when the control spool is in a neutral position, the change-over valve is also held by valve springs in neutral position in which the supply line communicate with the two pressure chambers, so that the change-over valve can be of very simple construction.

Preferably the two control edges located on the control spool are formed by an annular groove which communicates with a return conduit for the outflow of pressure medium and one control edge co-operates with a control point which is disposed in the follow-up piston and which is formed by at least one control port and leads away from one pressure chamber, and the other control edge co-operates with that end face of the follow-up piston which faces the other pressure chamber and which serves as the second control point with this arrangement only a single control bore is required in the follow-up piston.

In a hydraulic servo-controlled amplifier when arranged to actuate or limit the adjusting travel of a fuel delivery quantity regulating element of a fuel injection pump, the so-called "roll start cut-out" required in modern vehicles can be realised by utilizing the initial position of the follow-up piston to determine the stop position of the delivery apparatus regulating member.

Preferably the control spool is connected to an armature of an actuating solenoid disposed coaxially of the follow-up piston and the control spool whereby to provide an electro-hydraulic servo-controlled amplifier in the form of a compact structural unit and which can be used in a particularly advantageous manner for remote control or as an adjusting member in fuel injection pumps, in electro-hydraulically actuated and electronically controlled injection timers, and for the actuation of stops, particularly in large pumps. With relatively small electro-magnetic control forces, the amplification factor can be adapted to the intended use in a simple manner by adaptation of the pressures of the pressure medium and the surfaces of the follow-up piston which are subjected to pressure.Furthermore, by using a proportional solenoid with a return spring biasing the armature towards one limit position it is possible to ensure that the servocontrolled amplifier operates towards a preferred stop direction upon failure of the control current proportional to the adjusting travel, whereby safety requirements can be taken into account. Preferably the return spring has a restoring force which increases progressively towards the end of the stroke of the armature or is assisted towards the end of the stroke by an additional buffer spring: in this way it is possible to ensure that an excess starting quantity can be introduced only in the case of corresponding excess current and never during normal operation under load.

The invention will be further described by way of example with reference to the accompanying drawings, in which: Figure 1 is a fragmentary longitudinal section through a hydraulic servo-controlled amplifier according to one embodiment of the invention, Figure 2 shows a portion of Fig. 1 comprising a change-over valve, drawn to a larger scale, and Figure 3 shows a portion of Fig. 1, also drawn to a larger scale, and illustrates control edges on a control spool.

A hydraulic servo-controlled booster illustrated in Fig. 1 serves to actuate a governor rod 11, acting as a delivery quantity regulating member, of a known fuel injection pump (not further illustrated) It will be appreciated, that alternatively, instead of actuating the governor rod 11, the servo-controlled booster 10 can actuate an actuation linkage for a butterfly valve, or an injection timer, or an adjusting lever or a correction stop of a speed governor.

The servo-controlled booster 10 comprises, in a common housing 12, a double-acting follow-up piston 13 which is actuable by a hydraulic pressure medium and which has a control spool 1 5 disposed coaxially in a longitudinal bore 14, and an actuating soleniod 1 6 in the form of a proportional solenoid whose armature 1 7 is secured to the control spool 15.

A front portion of the housing 1 2 presented to the governor rod 11 is designated "booster housing 12at' and incorporates two pressure chambers 1 8 and 1 9 which are separated by the follow-up piston 1 3 serving as a movable wall and which are alternately supplied by way of respective branch conduits 21 and 22 with pressure medium fed from a source of pressure medium (not illustrated) by way of a pressure medium supply line 23. a hydraulically actuated change-over valve 24, operating as a logic valve and in the form of a threeport, two-position valve, is fitted in the connection between the pressure medium supply line 23 and two branch conduits 21 and 22, the valve 24 being shown more clearly, and drawn to a larger scale, in Fig. 2.

As is shown in Fig. 2, the change-over valve 24 has a valve member in the form of valve ball 26 arranged between two valve springs 25, and the mutually oppositely located spring chambers 27 and 28 accommodating the valve springs 25 at the same time serve as portions of the branch conduits 21 and 22. The valve ball 26 is held in its illustrated neutral position by the two valve springs 25 either when the two pressure chambers 1 8 and 1 9 and the pressure medium supply line 23 are pressureless, or when the two pressure chambers 1 8 and 1 9 are subjected to the same pressure of the pressure medium when the control spool 1 5 is in its neutral position.

The control spool 1 5 is provided with an annular groove 29 whose boundary edges form two control edges 31 and 32. The two control edges 31 and 32, together with the change-over valve 24, form part of a valve arrangement for actuation of the follow-up piston 1 3. The annular groove 29 communicates by way of a return conduit 33, formed by a transverse bore and a longitudinal bore, with a transverse bore 34 which is disposed in a piston rod 13a, in the form of a hollow piston, of the follow-up piston 1 3 and which serves for the outflow of pressure medium to a pressureless chamber (not further illustrated).

The governor rod 11 and the control spool 15 are respectively secured and slidingly guided in the longitudinal bore 14 in the piston rod 1 3a and the follow-up piston 1 3. One control edge 31 (see Fig. 3) of the control spool 1 5 controls a plurality of control ports 35 which are incorporated in the piston rod 1 3a and distributed around the periphery thereof. The control ports 35 serve as a first control port and, when the control spool 1 5 is displaced to the left as seen in Figs. 1 and 3 relatively to the piston 13, allow the pressure medium to flow from the pressure chamber 1 8 to the pressureless chamber by way of the return conduit 33.When the control spool 1 5 is correspondingly displaced to the right relatively to the piston 13, the other control edge 23 controls the outflow of pressure medium from the pressure chamber 1 9. In the present instance, an end face 1 3b, facing the pressure chamber 19, of the follow-up piston 1 3 serves as a second control point co-operating with the control edge 32, thus resulting in a saving on control ports which are otherwise customarily provided in the piston 1 3. Alternatively, the control ports 35 could be connected by a known annular groove (not illustrated) serving as a first control point, although, in the chosen arrangement, they have, in addition to the advantage of inexpensive manufacture, the additional advantage that the opening cross section, determined by their form and number, controls an initially throttled outflow of pressure medium from the pressure chamber 18, and thus a damped adjusting movement of the follow-up piston 1 3.

The mode of operation of the valve arrarigement comprising the change-over valve 24 and the control edges 31 and 32 is as follows: When, for example, the control spool 1 5 is displaced to the left from its illustrated position by the armature 1 7 of the actuating solenoid 16, the pressure chamber 1 8 is relieved of pressure by way of the annular groove 29, the return conduit 33 and the transverse bore 34; by way of the branch conduit 21, this pressure drop also takes effect in the spring chamber 27 of the change-over valve 24 whose spring chamber 28 continues to be subjected, by way of the branch conduit 33, to the pressure of the pressure medium located in the pressure chamber 1 9. As a result of this pressure difference in the two pressure chambers 1 8 and 1 9 and in the spring chambers 27 and 28 communicating therewith, the valve ball 26 of the change-over valve 24 is urged to the left onto a valve seat 36 and thus shuts off the supply of pressure medium of the pressure chamber 1 8 and at the same time enlarges the flow-through cross section of a pressure medium inlet which is formed between the valve ball 26 and a second valve seat 37 and which leads from the pressure medium supply line 23 to the pressure chamber 1 9 by way of the spring chamber 28 and the branch conduit 22.When the control spool 1 5 is displaced to the right from its neutral position, the pressure drop in the pressure chamber 1 9 moves the valve ball 26 to the right onto the valve seat 37, and the pressure remaining in the pressure chamber 1 8 moves the follow-up piston 1 3 to the right until the latter shuts off the communication established between the pressure chamber 1 9 and the pressureless chamber by the control edge 32. When the outlet is closed, the two pressure chambers 1 8 and 1 9 are subjected to equal pressure by the pressure medium in the operating position assumed at any given time, and the valve ball 26 returns to its neutral position shown in Fig. 2.

A return spring 39 is accommodated in the pressure chamber 1 8 and abuts at one end against the follow-up piston 1 3 and at the other end against a cover 38 sealing the pressure chamber 18. The spring 39 urges the follow-up piston 1 3 into one limit or initial position which is shown in Fig. 1 and which, in a preferred manner, determines the stop position of the governor rod 11. The follow-up piston 1 3 assumes its illustrated initial position either when the control spool 1 5 is also in its one limit position as illustrated or when the two pressure chambers 1 8 and 1 9 are non-pressurised in the absence of pressure supplied by the pressure medium.

Thus, the return spring 39 always ensures that, as a safety requirement, the piston 1 3 is returned to its initial position of the pressure of the pressure medium fails, since the two valve springs 25 return the valve member 26 of the change-over valve 24 to its illustrated neutral position in which the two pressure chambers 1 8 and 1 9 are connected to one another. A return spring 41 acting on the armature 1 7 of the actuating solenoid 1 6 also serves as a safety cut-out.Advantageously, the return spring 39 can be designed such that the action of its force substantially compensates for the difference between the effective pressure surfaces on the follow-up piston 1 3 which are subjected to the pressure of the pressure medium in the pressure chambers 1 8 and 1 9. It will be appreciated that it is also possible for the return spring 39 to act in the opposite direction and then effect an automatic movement of the governor rod 11 into its starting position when the engine is not running and the pressure medium is nonpressurised.

That end of the control spool 1 5 which is remote from the governor rod 11 is connected, in line with the follow-up piston 1 3 and the armature 1 7 of the actuating solenoid 16, to an actuating pin 42 which is guided out of the housing 1 2b of the actuating solenoid 1 6 and which, as indicated by an arrow 43, can be acted upon by governor elements of a mechanical governor or some other adjusting means, so that influencing of the position of the control spool 15, superimposed on the adjusting movement of the armature 7, or alternative influencing of the position of the control spool, is possible and, if required, emergency operation can be maintained in the event of failure of the actuating solenoid 1 6. Furthermore, a position sensor 45, such as an inductive position sensor, for measuring the position of the control spool 1 5 is connected to the actuating pin 42 by way of a transverse connecting link 44, the position sensor always being required when the adjusting movement of the actuating solenoid 1 6 has to be fed back to a control or regulating circuit for signal processing. When used in variable-speed governors which serve to govern a set speed with the use of a speedmeasuring member, the position sensor can be omitted.

Pressure medium located in the pressure chamber 1 9 is prevented from flowing into the interior of the solenoid housing 1 2b by means of a leakage collecting groove 46 and a leakage conduit 47 connected thereto.

With a given external diameter and pressure of the pressure medium, the follow-up piston 1 3 operating as a double-acting piston has a relatively large working capacity and, owing to the absence of passages within the piston 1 3, is very slender and operates with a relatively low pressure of the pressure medium. Therefore, in a preferred manner, the fuel fed to the fuel injection pump can serve as the pressure medium, and the pressure medium supply line 23 can be connected to the fuel injection pump pressure system subjected to a pre-feed pump pressure of approximately 1 to 2.5 bar.

The actuating solenoid can be constructed with various forms of poles. The proportional solenoid 1 6 illustrated in a preferred embodiment.

With the appropriate configuration of the armature 1 7 and of the solenoid housing 12b, the proportional solenoid 1 6 produces, in a known manner, an adjusting force which is proportional to the excitation current and, with a constant excitation current, an adjusting force which is as constant as possible over the stroke irrespective of the position of the armature 1 7. Thus, in conjunction with the return spring 41, defined positions of the armature 1 7 are obtained in dependence upon the value of the excitation current.

In a further embodiment of the return spring 41 having a characteristic which rises progressively only towards the end of the stroke and which can be obtained by, for example, unequal spacing of the last turns of the spring, or by an additional buffer spring 48 (indicated by dash-dot lines) which becomes effective only towards the end of the stroke, an arrangement can be obtained whereby the proportional solenoid 16 first has to receive an excess current before the followup piston 1 3 assumes its end position determining the starting position of the governor rod 11.

It can thereby be ensured that there is a sufficient margin of safety to prevent the starting position of the governor rod 11 from being assumed with normal operating currents. This measure is particularly recommended when the position sensor can be omitted.

Alternatively, any other known mechanical, electrical or pressure medium controlled adjusting member can be used instead of the actuating solenoid 6 for actuation of the control spool 1 5.

Claims (11)

1. A hydraulic servo-controlled amplifier for internal combustion engines, having a double-acting follow-up piston which serves as a movable wall to separate two pressure chambers in the amplifier housing, a control spool disposed coaxially in the follow-up piston, a pressure medium supply line, and a valve arrangement for controlling the inflow and outflow of pressure medium to and from the pressure chambers and formed by a valve device comprising two control edges on the control spool for controlling the outflow of pressure medium from the pressure chambers and a hydraulically actuable change-over valve which operates as a logic valve and which is disposed in a connection between the pressure medium supply line and two branch conduits leading to the pressure chambers.

2. A hydraulic servo-controlled amplifier as claimed in claim 1, in which the changeover valve is movable by the pressure drop effected in one of the pressure chambers by one of the control edges on the control spool and by the unchanged pressure in the other of the pressure chambers into a switching position in which, for actuation of the follow-up piston, the supply line is only connected to the pressure chamber which is still pressurised, and when the control spool is in a neutral position, the change-over valve is also held by valve springs in a neutral position in which the supply line communicates with the two pressure chambers.

3. A hydraulic servo-controlled amplifier as claimed in claim 2, in which the two control edges located on the control spool are formed by an annular groove which communicates with a return conduit for the outflow of the pressure medium, and one control edge co-operates with a control point which is disposed in the follow-up piston and which is formed by at least one control port and leads away from one pressure chamber, and the other control edge co-operates with that and face of the follow-up piston which faces the other pressure chamber and which serves as the second control point.

4. A hydraulic servo-controlled amplifier as claimed in any of claims 1 to 3, in which the change-over is in the form of a hydraulically actuated three-port, two position valve and has a valve member in the form of a valve ball disposed between two valve springs, and mutually oppositely located spring chambers accommodating the valve springs at the same time serve as portions of the branch conduits.

5. A hydraulic servo-controlled amplifier as claimed in any of claims 2 to 4 in which the follow-up piston is urged by a return spring into its initial position or one limit position when the pressure medium is non pressurised and when the change-over valve is in its neutral position.

6. A hydraulic servo-controlled amplifier as claimed in claim 5, when arranged to actuate or limit the adjusting travel of a delivery quantity regulating member of a fuel injection pump, in which the initial position of the follow-up piston determines the stop position of the delivery quantity regulating member.

7. A hydraulic servo-controlled amplifier as claimed in any of claims 1 to 6, in which the control spool is connected to an armature of an actuating solenoid which is disposed coaxially of the follow-up piston and the control spool and which is assembled to form a structural unit with an amplifier housing accommodating the pressure chambers and the follow-up piston.

8. A hydraulic servo-controlled amplifier as claimed in claim 7, in which the actuating solenoid is in the form of a proportional solenoid which is provided with a return spring biassing the armature towards one limit position.

9. A hydraulic servo-controlled amplifier as claimed in claim 8, in which the return spring is provided with a restoring force which increases progressively towards the end of the stroke of the armature, or is assisted towards the end of its stroke by an additional buffer spring.

1 0. A hydraulic servo-controlled amplifier as claimed in any of claims 7 to 9, in which the follow-up piston the control spool and the actuating solenoid are accommodated in a common housing.

11. A hydraulic servo-controlled amplifier as claimed in any of claims 7 to 10, in which the control spool is disposed in line with the follow-up piston and'the armature and is connected to an actuating pin guided out of the housing of the actuating solenoid.

1 2. A hydraulic servo-controlled amplifier as claimed in any of claims 6 to 11, in which fuel is used as the pressure medium.

1 3. A hydraulic servo-controlled amplifier as claimed in claim 12, in which the pressure medium supply line is connected to the fuel injection pump pressure system subjected to the pressure of the pre-feed pump.

1 4. An electrohydraulic servo-controlled amplifier having a valve device constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in the accompanying drawings.