EP0504198A1

EP0504198A1 - Device and method for varying the timing of fuel-injection.

Info

Publication number: EP0504198A1
Application number: EP91900065A
Authority: EP
Inventors: Nils Olof Hakansson
Original assignee: Volvo AB
Current assignee: Volvo AB
Priority date: 1989-11-30
Filing date: 1990-11-28
Publication date: 1992-09-23
Anticipated expiration: 2010-11-28
Also published as: EP0504198B1; WO1991008387A1; SE465134B; SE8904048D0; DE69016457D1; ATE117766T1; DE69016457T2; SE8904048L

Abstract

This invention relates to a device and method for varying the timing of fuel injection for a combustion engine. The device comprises a housing (1) within which two shafts (2, 3) are coaxially arranged and torsionally conjoined by means of splines (6, 7) and a force-transmitting member (5). When the force-transmitting member (5) is displaced, which is partially achieved by means of a hydraulic fluid within the housing, the angular positions of the shafts (2, 3) will be readjusted. Furthermore, the housing (1) contains a revolution sensing device (83, 84) which is movable in a radial direction within a recess (24) which communicate with a pressurized hydraulic fluid. The revolution sensing device (83, 84) controls the flow fhrough the recess (24) in dependence on the number of revolutions. The method deals with the varying of the timing of fuel injection at three different intervals of rotational speed.

Description

Title:

Device and method for varying the timing of fuel-injection.

Technical field:

This invention relates to a method and a device for varying the timing of fuel injection, which device is intended to be connected to the fuel injection pump of an engine and by means of which the timing of the fuel injection is variable as a function of the rotational speed of the engine.

Background and problem:

The timing of fuel injection at different rotational speeds for a diesel engine is the main factor that determines the degree of harmful emissions of exhaust gases from the engine. The largest amount of nitrous oxides are produced at a relatively low rotational speed, when the combustion chamber has a relatively high temperature and the dwell time is quite large at that temperature, whereas the level of unburned hydrocarbons is highest at a high rotational speed, when the temperature in the combustion chamber is relatively low and the dwell time for the combustion is relatively low. By controlling the timing of injection so that it is initiated at a later time within the operational field where the production of nitrous oxides is most intense, and at an earlier time where the production of unburned hydrocarbons is dominant, it is possible to reduce the amount of harmful emissions in the exhaust gases from the engine. This is feasible by means of a device for varying the timing of fuel injection. Devices for varying the timing of fuel injection are previously known. From SE B 439 950 (upon which the pre-characterizing portion of claim 1 has been based) for example, such a device is known. This known device for varying the timing of fuel injection is very complex in its design since it is not only controlled by the rotational speed, but also by the load. Such a complex design implies that the device is expensive. Furthermore, such a design presents the disadvantage that the readjustment of the timing of the fuel injection is made stepwise, with large adjustments in each step, which complicates the control of the engine.

Solutions and advantages:

The main object of this invention is to provide a device for varying the timing of the fuel injection which eliminates existing disadvantages that are known in connection with the use of devices in accordance with the above, known type.

Said main object is achieved by means of a device according to the invention, which is characterized in that said rotational speed sensing device is located within said housing, co- rotating with one of said rotating parts, that said rotational speed sensing means comprises at least one balance member which is, at least radially, movably arranged within a recess, that a channel opens up into said recess, which channel communicates with said pressurized hydraulic fluid, that said recess communicates with a drainage channel and that said balance member comprises means which, dependent on the rotational speed will influence the flow through said channel, in accordance with the following claim 1.

In principle it is known to use systems for varying the timing of fuel injection which only depend on the rotational speed. Generally, however, it can be said that these devices for varying the timing of fuel injection, which are only dependent on the rotational speed, are either too complex or too weak. The weakness is due to the fact that the torque transmitting part of the device also comprise rotational speed sensing means , such as weights and springs (often cam-contolled). This weakness is undesirable since it makes it difficult to control the fuel injection in a precise manner, especially when considering that the development is heading for higher pump pressures which accentuates the latter problem. It is known to avoid the above mentioned weakness, in a device for varying the timing of fuel injection, by interconnecting the input shaft with the output shaft via a displaceable intermediate body having splines which, during displacement, re-adjusts the angular position between the input shaft and the output shaft. The force transmitting part for this known system, however, is separated from the rotational speed sensing device. Accordingly, there is one system for sensing the rotational speed, one system for transmitting a torque from the engine to the fuel injection pump and one control system between the rotational speed sensing device and the torque transmitting device. This is a form of complexity that is undesirable. Furthermore, this latter known system also presents the disadvantage that the readjustment, in general terms, takes place over the whole range of rotational speeds. Hence, it can not be optimized to only take place within a chosen interval.

Moreover, from DE A 1 947 618 it is known per se to arrange the rotational speed sensing means within the housing of the device for varying the timing of fuel injection, in a manner so as to be co-rotating with one of the rotatable parts. This known device however, essentially differs from the invention since the control mechanism is arranged within the housing of the fuel injection pump.

It is a further object of the invention to achieve a device for varying the timing of injection which consists of just one single unit and which enables an optimization of control of the timing of fuel injection which is only dependent on the rotational speed, so that the amount of harmful emissions in the exhaust gases from the engine is kept at a low level by means of a device which is relatively simple and that the proiuctional costs are relatively low.

Brief descriptions of the drawings:

In the following the invention will be described in more detail, by reference to the annexed drawings in which;

Fig. 1 shows a preferred embodiment of the device for varying the timing of fuel injection in accordance with the invention, in a cross sectional view, and Fig. 2 shows a first table representing the torque from an engine in relation to the rotational speed and a second table representing the characteristics of the control mechanism of the device in relation to the rotational speed.

The device for varying the timing of fuel injection which is shown in the figure presents a housing 1 in which an input shaft 3 and an output shaft 2 are rotatably arranged in bearings. The input shaft 3 has an outer connection 31 which via a tooth-wheel (not shown) for which there is a hole 32 for an attachment screw, is intended to be powered by the crank shaft of a turbocharged diesel engine. The output shaft 2 is intended to be connected to the fuel injection pump of the engine for powering it.

The two power-transmitting shafts 2, 3 are non-rotatably interconnected to each other by means of a power-transmitting device 5. This device 5 interacts with each one of the shafts by means of angled splines 6, 7. These angled splines 6, 7 are positioned in counteracting directions, so that an axial displacement of the power transmitting device 5 results in an angular re-positioning α between the shafts 2, 3. This adjustment of the angle α leads to a change of the timing of fuel injection. Furthermore, the angle of the splines is chosen to be so low that it is self braking during power-transmission.

The housing 1 is intended to be fitted on the engine by means of the flange 16. In order to ensure a sealed fitting thereof, there is a circular recess 17 on that side which is intended to face the engine, which recess is intended for an 0-ring (not show ). At one of its ends the housing 1 has inwardly directed flanges and at its other end it has a lid 12 acting as a axial bearing, in order to position the rotating parts therein. Furthermore, the housing 1 presents two input channels 10, 11 and one output channel 15 for input and output of oil respectively. This oil is partly intended to lubricate the contact surface between the inner surface 13 of the housing 1 and the peripheral surfaces of the rotating shafts 2, 3 but also for the axial displacement of the power- ransmitting device 5, which will be explained more in detail below.

One of the channels 10 leads to a peripherally positioned ring channel 33 of the input shaft 3. From this ring channel the oil is delivered further in an axial direction. In one of the directions this stream only provides lubrication and then disappears from the housing and returns to the engine. The oil which moves in the other direction will, amongst others, pass through the junction between the input shaft and the output shaft 2, to be able to move further inwardly in a radial direction towards the common recess which is delimited by the input shaft 2 and the output shaft 3. Said force transmitting device 5 is positioned within this latter recess.

The force transmitting device has an outwardly directed seal 51 which sealingly contacts the inner surface of the output shaft 3. Further, there is a bushing 4, arranged in said recess, which bushing has an axially inwardly directed rear end surface 44 determining one of the extreme positions of the force transmitting device 5. The bushing 4 has a ring element 41 which is the support for a spring 45 which is encapsulated within the force-transmitting device 5. The object of this spring 45 is to act upon the force-transmitting device 5 with a continuous force which is directed to the right hand ε:de of the shown figure. Moreover, the ring element 41 acts as an inner seal (supplementing seal 51) which seals against the oil that passes via the central whole 52. The oil that leaks through via the ring element 41 and via the outer way 34, is drained off through a hole 38 in the input shaft 3 and corresponding hole in the tooth wheel.

In order to limit the movements of the force-transmitting device 5 in its movement to the right, the output shaft 2 has, at its inner axial end, surface distance elements 81. A tie-rod 9 is centrally located, whose function is to axially keep the input and the output shaft 3, 2 together as well as the parts 4, 5 which are positioned therebetween. The rod 9 is attached by means of clamping partly in the central hole 36 of the input shaft and partly in the central hole 27 of the output shaft.

The output shaft 2 has two peripheral ring channels 20 and 28 respectively. The first of these ring channels 20 is directly in connection with one of the channels 11 in the housing 1 and is accordingly directly supplied with oil. From this first ring channel 20 there is a radially extending hole 29 through which the oil can pass into said recess. From this recess it can communicate with the other ring channel 28 via a number of axial holes 21 and a number of radial holes 22 respectively, wherein each radial hole 22 is in communication with one axial hole 21. Furthermore, a certain amount of oil can be supplied by means of axial leakage between the housing 1 and the output shaft 2. A number of similar radial holes 23 are arranged in an offset manner, (45° in the preferred embodiment) in relation to the first mentioned radial holes 22. Within each one of these latter radial holes 23 is a pin 83. The pin 83 is attached to a transversely directed cylindrical body 84. The cylindrical body 84, which supplies an additional load, is positioned in a recess 24 that extends in an axial direction. This latter recess 24 has a diameter which essentially exceeds the diameter of the cylindrical body 84. At the outer end of the pin 83 there are flow channels 82, whose cross sectional surfaces successively increase towards said outer end. The channels are preferably arranged as axially directed grooves, which have their starting point somewhere beyond that place where the cylindrical body is arranged and which grooves then enlarge in a direction towards the outer end of the pin 83. By this arrangement the pin 83 forms a sealing plug within the channel 23 when the cylindrical body 84 is positioned in its most peripheral position, whereas it provides large flow channels when the cylindrical body 84 is positioned in its inner most (most central) position. In the preferred embodiment the number of radial holes is eight (four 22 + four 23). Accordingly, the number of axial holes 21 is four. The figure, on the other hand, does not show this preferred embodiment but shows an output shaft 2 having six radial holes (three 22 + three 23) and three axial holes 21.

Hence, it is possible to freely drain off oil pressure that is supplied to the channel 11 through the output shaft 2 if the pin 83 does not seal the passage between the ring channel 28 and the axial recess 24. The oil is drained off through drainage hole 15 which is located at the end of the housing 1 adjacent the output shaft 2. The cross sectional surface of the this hole 15 has a dimension such that it can drain off the supplied oil. The oil that is drained off via this other drainage hole 15 is returned to the engine via a channel 15a.

The readjustment of the angle between the input shaft and the output shaft is carried out in the following manner. When the engine is off and the oil pressure is zero the force- transmitting device 5 is pushed as far as possible to the right by means of the force from the spring 45. The angular difference between the input shaft 3 and the output shaft 2 is then zero. When the engine is started and oil pressure is built up and via channels 10, 11, is supplied to the housing 1 of the device for varying the timing of fuel injection. The oil will not only lubricate all desired surfaces, but will also pass into the inner recess, via the junction 25/35 and the channel 29. From here the oil can pass through the output shaft 2 in order to leave the housing 1 via the channel 15, by first passing the axial hole 21, and the radial channel 22 in order to reach the ring channel 28, from which it can freely flow through channels 23 into the recesses 24 which are communicating with the drainage hole 15.

When the rotational speed increases, the centrifugal force acting upon the cylindrical body 84 will also increase. The oil pressure, on the other hand, at an early stage reaches a relatively constant maximum pressure, a pressure which at low rotational speeds will depress the cylindrical body and the pin 83 resulting in a flow through the channels 23.

At a certain predetermined rotational speed, which is dependent on the weight of the cylindrical body 84 and the pin 83 as well as the actual oil pressure, the centrifugal force acting on the cylindrical body will start to balance the force which acts on the body due to the oil pressure via the ring channel 23. This results in the cylindrical body 84 with the pin 83 starting to move outwardly, so that the cross sectional surface for the flow via the channels 23 will decrease, which in its turn leads to an increased pressure within the device for varying the timing of the fuel injection.

A successively increased rotational speed now implies a successively increased pressure within the housing 1, approximately proportional to the square of the number of revolutions. When the threashold value to overcome the force from the spring 45 has been reached, the force-transmitting device 5 will successively start to move to the left in the figure. This movement of the piston is feasible, despite small piston areas, thanks to obtaining very short intervals of off loading of the torque (torque) shortly after each occasion of fuel injection. This successive movement of the piston 5 results in, by means of said splines 6, 7, a successive change of the angular position between the shafts 2, 3 whereby a corresponding elastic rotational displacement of the rod 9 arises. Movement of the piston will take place until the piston reaches the second end position, i.e. until it contacts the end surface 44 of the bushing 4. The angular difference between the input shaft 3 and the output shaft 2 is now maximal.

In table 1 there is shown a diagram in which the x-axis relates to the rotational speed of the engine and the y-axis relates to the torque. The plotted graph shows typical torque/rotational speed characteristics for a diesel engine. Underneath said first diagram there is a second diagram where the x-axis also relates to the rotational speed of the engine having the same scale as the first diagram. The Y-axis, on the other hand, describes in this second diagram the angular position between the input shaft 3 and the output shaft 2. The graph which is plotted shows how in a preferred embodiment it has been chosen to dimension the device in order to obtain most favourable emissions possible from an engine having torque/rotational speed characteristics according to diagram 1.

It can be observed that the angular difference between the two shafts is kept at a zero level (a) from starting up of the engine to a rotational speed which slightly exceeds the maximum torque. From this point the successive displacement of the angle between the input shaft and the output shaft will start to take place. This successive increase of the angular difference is proportional to the rotational speed (almost linear) and accordingly it takes place in a continuous manner when the rotational speed increases continuosly, until the maximum angular difference (b) has been reached. In a preferred embodiment this latter transitional point is reached shortly before the rotational speed reaches the point when the engine has its maximum effect.

By means of a device in accordance with the above, it is possible to use relatively simple means to control the fuel injection of a diesel engine so that the environmental load of the emitted gases will be kept at as low a level as possible, which is achieved if the timing of injection at low rotational speeds is late and at high rotational speeds is early. It is obious for the skilled man that the device described above by means of suitable readjustment can be adapted to different kinds of diesel engines. Factors which have an influence as to where the transitional points will be located and the progress there between, is amongst others, the weight of the body 84 and the pin 83, the oil pressure, the flow area within the channel 23, the spring charateristics (e.g. a progressive or linear spring, one or two springs, etc) of the spring 45, the length of the spring, the maximum space for movement of the body 5, etc. The pretensioning of the spring 45 is appropriately varied by having different bushings 4 locating the ring element 41 at different heights. Furthermore, the length of the stroke is appropriately varied by adaption of the thickness of the rear piece (44-42) of the bushing 4 and/or the thickness of the distance element 81.

Nor is the invention limited by what has been described in relation to the preferred embodiment. If it is decided to have a larger effective pressure area on the body 5, a possible change would be to, instead of the ring element 41, have a sealing adjacent the central hole 52. In this latter case it is necessary to drain off at the ring element 41. Moreover, in some cases it is not necessary to have a special hole 29 for the radial inflow of oil, but instead the device can function totally by means of leakage.

The figure shows that the output shaft 2 is arranged with balance means 83, 84. The skilled man, however, will realize that the device can be adapted to have the balance means 83, 84 arranged on the input shaft 3 or on the piston 5.

Another change within the scope of the claims is to form the flow channels 82 in the pins 83 in a different manner. It is essential that the pins are steered by the channels 23 at the same time as at least one of the flow channels has a cross sectional area which is dependent on the position of the pin 83. Accordingly, it is also possible to, for instance, use a centrally placed screw driver slot. Other design aspects of the balance means 83, 84 and the recess 24 as well as the channel

23 can be varied within wide frames, e.g. by letting the recess

24 extend along a part of a circle (the body 84 can then be made larger); to have oval or rectangular cross sectional areas instead of circular; to change the main direction of the channel 23 and the recess 24 respectively, (i.e. to not have them totally radial and axial respectively), etc. For the skilled man it is also evident that the invention is not limited to its use in connection with diesel engines, but could also used together with for instance hesselman engines, etc. Finally, it should be mentioned that the device could also be used the other way around, so that an early injection is obtained at an interval of a rotational speeds that is lower (n_o-ni).

Claims

1. Device for varying the timing of fuel injection for a diesel engine with respect to the rotational speed of the engine, comprising a rotational speed sensing means (83, 84) and a housing (1, 12) incapsulating: an input shaft (3) which at least indirectly is connected to the crank shaft of the engine; an output shaft (2) which at least indirectly is connected to the pump for the fuel injection and a force- transmitting member (5) that is movably positioned between said shafts (2, 3), which force-transmitting member (5) by means of obliquely cut splines (6, 7) and its position determines the angular position between said two shafts (2, 3), whereby the position of the force-transmitting member (5) is at least partly determined by the pressure of a hydraulic fluid within the housing (1) and that said pressure is controlled by said rotational speed sensing device (83, 84) c h a r a c t e r i z e d i n that said rotational speed sensing device (83, 84) is located within said housing, co- rotating with one of said rotating parts (2, 3, 5), that said rotational speed sensing means comprises at least one balance member (83, 84) which is, at least radially, movably arranged within a recess (24), that a channel (23) opens into said recess (24), which channel (23) communicates with said pressurized hydraulic fluid, that said recess (24) communicates with a drainage channel (15) and that said balance member (83, 84) comprises means (82) which dependent on the rotational speed will influence the flow through said channel (23).

2. Device according to claim 1, c h a r a c t e r i z e d in that said member (5) in a first direction is arranged in order to be affected by a resiliently acting means (45) and in a second direction by means of sealings (41, 51) by said pressure.

3. Device according to claim 1, c h a r a c t e r i z e d in that said hydraulic fluid is fed directly to the housing (10, 11) from the lubrication reservoirs of the engine.

4. Device according to claim 1, c h a r a c t e r i z e d in that said channel (23) is made of a substantially radially extending hole within which one end of a radially extending part (83) of said balance means (83, 84) is arranged and that said one end has means (82) which, in a first outer extreme position of said one end, substantially closes the communica_ion between said channel (23) and said recess (24) and which, in a second inner extreme position, allows maximum communication between said channel (23) and said recess (24).

5. Device according to claim 1, c h a r a c t e r i z e d in that said recess is an axially extending, substantially circular, recess and that one part of said balance means (83, 84) is made of a body (84) having a substantially circular cross sectional area which corresponds to said recess (24).

6. Device according to claim 4, c h a r a c t e r i z e d in that said one end is a part of a homogenous body (83), whose cross sectional area substantially corresponds to the cross sectional area of said channel (23) and said means (82) is a recess that extends at least in an axial direction.

7. Method for varying the timing of fuel injection for a diesel engine with relation to the rotational speed of the engine, whereby the timing of the fuel injection is controlled by means of the angular position between two co-axial shafts (2, 3) which are torque transmitting by means of an intermediate transmission member (5), c h a r a c t e r i z e d in that said angular position between the shafts under a first lower interval of rotational speeds (n^n^ is kept at a constant level (a), whereby in a preferred mode, late timing of the fuel injection is obtained, that the angular position between the shafts during a second interval of rotational speeds (n_x-n₂) is varied almost proportionally in relation to the rotational speed, whereby a successive earlier timing and later timing respectively of the fuel injection is obtained, and, that the angular position between the shafts during a third interval of rotational speeds (^-n_^) is kept at a second constant level (b), whereby in a preferred mode an early fuel injection is obtained.