TECHNICAL FIELD : The present invention relates to a device for engine breaking of motor ve- hicles comprising an internal combustion engine with at least one cylinder, at least one exhaust valve at said cylinder and a rocker arm for activation of said exhaust valve, which rocker arm is arranged on a hollow rocker arm shaft, and arranged to be effected by ridges on a camshaft. Said device ad- ditionally comprises a control valve for controlling the oil pressure in said rocker arm shaft and means receptive to an increase of oil pressure in said rocker arm shaft being integrated in said rocker arm for absorbing a play between said rocker arm and said exhaust valve in the case of an increased oil pressure, in which case at least one of said ridges then causes the open- ing of the exhaust valve with an engine breaking effect.

The invention also relates to a method for engine breaking of the above- mentioned kind.

BACKGROUND ART: Commercial vehicles such as trucks and buses are normally equipped with an engine breaking function in order to spare the wheel brakes in the vehicle during braking. In this context, it is previously known to provide an engine braking effect in an internal combustion engine by arranging a throttle organ, for example in the form of a valve in the exhaust system of the engine. In this way, a certain portion of the work during the exhaust stroke of the cylinder can be used to increase the braking effect.

Another kind of engine brake is a so-called compression brake, which has the function of one or several of the engine's exhaust valves being controlled so that air which has been compressed during the compressor stroke of the engine in the combustion room is allowed to partially flow out into the exhaust

system. This means that a part of the compression work carried out during the compressor stroke is not utilized during the expansion stroke of the en- gine, which is used to obtained a braking effect on the crank shaft.

In a known kind of compression brake, the exhaust valves are controlled so that the camshaft of the engine is given a profile which is shaped with at least one extra ridge in order to obtain an opening of the exhaust valves with the intention of generating a braking effect. In addition, the valves are shaped with a small play, the size of which is chosen (together with the dimensions of the extra ridge) so that the extra ridge will not effect the valves during normal engine operation. For this purpose, the extra ridge has a lifting height which is very small compared to the ordinary exhaust ridge. In order to make the extra ridge operable during engine braking, i. e. so that the exhaust valves will be able to be open when engine braking, the respective rocker arm is shaped with a device in the shape of a displaceable piston which is effected by oil to be positioned in an expanded position. This causes the valve play to be eliminated, and the lifting height of the extra ridge then becomes sufficient in order to open the exhaust valves.

Apart from utilizing an engine braking device for braking the vehicle as such, i. e. as a complement to the wheel brakes of the engine, there is also a desire to use a compression brake when shifting gears in the gearbox of the vehicle.

It can here be said that commercial vehicles such as trucks and buses are ever more frequently equipped with automatic or semi-automatic gearboxes.

Such boxes can be likened to conventional manual gearboxes, with the dif- ference that the shifting of gears is carried out by means of a control organ instead of manually by the driver. Appended figure 1 shows the principal phases in connection with an up-shift (i. e. to a higher gear) of such a gear- box. Figure 1 shows a comparison between engine torque and engine speed relative to time in a given type of engine.

As is evident from Fig. 1, phase"a"shows a normal operating state before a gear shifting is initiated. Phase"b"shows the removal of engine torque as soon as it has been decided that an up-shift is to take place. Phase"c"shows the release of a claw coupling in order to de-couple the gearbox from the en- gine. Phase"d"shows a release of the engine speed in order to match the engine speed to the gear ratio which is to be chosen. As soon as the engine speed has been reduced sufficiently the new gear can be engaged. Thus, phase"e"shows the engagement of the new claw coupling. Phase"f'shows renewed application of torque, and phase"g"shows a normal operating con- dition after the gear shift has taken place.

In order to reduce loss of driving power of the engine during up-shift, it is an advantage if the engine speed can be matched to the new gear ratio as soon as possible. From document SE-C-502154 it is known to selectively introduce an exhaust brake during an up-shift when certain operating parameters are obtained, in order to achieve a rapid decrease of engine speed during the gear shifting process. In this way, it is alleged that wear on the exhaust brake system is decreased since the introduction of the exhaust brake only takes place during a small part of the total amount of up-shifts.

An auxiliary brake system for commercial vehicles is known from US-A-5 193 497 which shows an internal combustion engine which is equipped with a device for absorbing valve play in the valve mechanism of the engine. The absorption is carried out by means of an actively adjustable, hydraulically driven absorption means, adjustable between two positions, a contracted position, and an expanded position, which absorption means is arranged at the working end of the rocker arms, whose valve play is to be absorbed. In a way which is described in detail in said document, the existing pressurized oil system of the engine is used in order to guarantee the func- tion of the device.

The auxiliary brake system which is described in the above-mentioned

US-A-5 193 497 has enjoyed considerable commercial success. Due to the relatively long time necessary for the absorption means to reach its extended position, the system according to US-A-5 193 497 is, however, not suitable for reducing engine speed at up-shifting.

From the Swedish patent application 9804439-9, an arrangement is previ- ously known for engine braking in an internal combustion engine. This ar- rangement is adapted for engine braking by reduction of the engine speed when gear shifting, and for this purpose comprises a special device which is receptive to a signal which is generated as a reply for a need to obtain a gear shift and for obtaining an absorption of a valve play in a rocker arm.

In connection with engine brake devices which are used when shifting gears, a pressure regulating valve device is utilized for supplying pressurized oil to a device for absorbing valve play in the rocker arm. A previously known control valve device comprises a displaceable valve body which can be effected to be positioned in a first position which corresponds to a pressure reducing function, and a second position which corresponds to a non-pressure reduc- ing function. The oil is supplied to the rocker arm by means of a canal, which is provided with an exhaust in the shape of a very narrow hole through which oil can flow, and in this way be made to effect said valve body to, depending on operation, be positioned in any of said predetermined positions. For this purpose, the control valve is also provided with an adjustable magnet valve arranged for drainage of oil which has been fed through said narrow hole.

Although this previously known device in principle functions satisfactorily, it has some drawbacks. The main one to be mentioned is that it comprises a small and carefully defined hole for the transport of oil, which causes a high sensitivity to clogging and tolerances. In addition, this previously known valve causes a relatively slow coupling and de-coupling, which is particularly no- ticeable in connection with gear shifting. In addition, the design is sensitive to

external disturbances, for example in the form of temperature changes and for pollution such as for example dirt particles or coatings.

SUMMARY OF THE INVENTION : A purpose of the present invention is to provide an improved device for en- gine braking, which in particular is suitable for utilization for a quick decrease of the speed of an engine during gear shifting.

This purpose is obtained according to the present invention by the device of the appended claim 1, in more detail by means of a device of the initially mentioned kind, which is characterised in that said control valve comprises an adjustable valve body and a canal between the valve body and the rocker arm shaft which comprises a controllable exhaust, with the valve body being arranged to be positioned in a first position with a pressure reducing effect, and in a second position without a pressure reducing effect.

It is a further purpose of the invention to obtain a method for rapid decrease of the speed of an engine during gear shifting.

This purpose is obtained according to the present invention by the method of appended claim 12, in more detail by a method of the initially mentioned kind, which is characterized in that it comprises the control of a control valve which comprises a controllable valve body and a canal between the valve body and the rocker arm shaft which comprises a controllable exhaust, with said con- trol comprising the positioning of the valve body in a first position with pres- sure reducing effect and a second position without pressure reducing effect.

By means of the invention, certain advantages are obtained. Most impor- tantly, it can be mentioned that the invention permits a very rapid braking of an engine in connection with gear shifting. The invention also offers a very robust design with a reliable function.

Preferred embodiments of the invention will become evident by the appended dependent claims.

DESCRIPTION OF THE DRAWINGS : The invention will be explained in more detail in the following, with reference to an example of a preferred embodiment and the appended figures in which Fig. 1 shows a graphical representation of the principal phases of an up- shifting in a gearbox, Fig. 2 schematically shows a device for absorbing valve play, Fig. 3 schematically shows the function of the present invention during normal engine operation of an internal combustion engine, and Fig. 4 schematically shows the function of the present invention when braking the engine during gear shifting.

PREFERRED EMBODIMENT : As mentioned previously, Fig. 1 shows principal phases of an up-shift (i. e. to a higher gear) in the kind of gearboxes which change gear while a power in- termission takes place, as is a common occurrence in commercial vehicles.

Fig. 1 shows a comparison between engine torque and engine speed with reference to time. Phase"a"shows a normal operating condition before a gear shift is initiated. Since phase"a"is before the up-shift, the engine speed normally increases during this phase. Phase"b"shows the removal of torque as soon as it has been decided that an up-shift is to take place. A removal of torque necessitates a matching of the rotational speed of the outgoing shaft of the engine and the ingoing shaft of the gearbox, and can be brought about in a number of ways depending on the operational conditions of the vehicle in which the gearbox is situated. Phase"c"shows the release of a (not shown) claw coupling in order to de-couple the gear shift from the engine. In this

phase, the fuel supply to the engine is limited in order to prevent engine speed from increasing. Phase"d"shows the decrease of engine speed in order to match the engine speed to the gear ratio which is to be chosen. It is primarily the time it takes to achieve the desired engine speed which decides how quickly an up-shift can place. As soon as the engine speed has been reduced sufficiently, the new gear can be engaged. Thus, phase"e"shows the engagement of the new claw coupling. Phase"f"shows the renewed ap- plication of torque, and"g"finally shows a normal operating condition after the gear shift has taken place.

According to the present invention, a decrease of the engine speed during phase"d"is obtained (see Fig. 1) by utilizing a special control valve device which will be described in detail below. In this way, a speedy gear shift is made possible.

The invention is in particular intended to be used in connection with gear- boxes which are not synchronized. Furthermore, the invention is intended to be used in connection with a valve mechanism 1, as will become evident from Fig. 2. This valve mechanism is a modified version of the valve play ab- sorbing mechanism shown in US-A-5 193 497, the contents of which are ap- pended as a reference in this application. Fig. 2 thus shows a valve mecha- nism 1 for an internal combustion engine. The mechanism 1 comprises a camshaft 2 which, via a cylindrical roler 3 transfers a rotational movement to a rocker arm 4. The rocker arm 4 is arranged on a hollow rocker arm shaft which is intended to be arranged on a not shown cylinder head in a suitable manner, for example by means of bolts. The camshaft 2 obtains the rota- tional movement in a conventional way, via a transmission from the camshaft of the engine (not shown).

The movement which is transferred from the camshaft 2 to the rocker arm 4 is primarily controlled by a first ridge 2a which is constituted by an exhaust ridge for opening the exhaust valve at a suitable point in time. In addition, the

camshaft 2 is shaped with at least one, according to the embodiment 2, extra ridges 2b, 2c, of which a first extra ridge 2b is constituted by a charging ridge which upon activation of an engine braking function has the purpose of opening the exhaust gas valve at the end of the inlet stroke of the engine, and to keep it open in the beginning of the compression stroke. The second extra ridge 2c is constituted by a decompression ridge which is arranged along the camshaft 2 so that it opens the exhaust valve at the end of the compression stroke. The lifting height of the extra ridges 2b, 2c is very small relative to the lifting height of the first regular ridge 2a.

In principle, the camshaft can be arranged so that it rotates in either direction.

The two extra ridges 2b, 2c are shaped and dimensioned according to the chosen direction of rotation.

The displacement of the rocker arm 4 is transferred via means 6 and a semi- spherically shaped control organ 7 to a yoke 8, which is moveable up and down along a guiding rail S on the cylinder head. In the embodiment shown, the yoke 8 effects two valve pipes 9. Each valve pipe is, in a conventional way, surrounded by a valve spring 10. Apart from these two valve springs 10, there is a spring 11, which is arranged below the yoke 8. The purpose of this spring is to keep the yoke in such a position that the play, which always oc- curs in a valve mechanism of this type, will occur between the respective valve tubes 9 and the underside of the yoke 8.

According to the invention, the above described valve mechanism is supplied with pressurized oil, which is supplied to the cavity in the rocker arm shaft 5 by means of a special control valve device, which will be described below with reference to Figs. 3 and 4. This control valve device is arranged to de- liver oil at a suitable pressure to the rocker arm shaft 5 under the influence of control from a control system (not shown), which in turn can comprise, for example, an engine control unit and a transmission control unit. The control by means of the control system is then arranged to initiate activation of the

control valve device when gear shifting takes place. At such an initiation of a gear shift, oil under pressure will be fed into the rocker arm shaft 5 and fur- ther along in a conduit 13 in the respective rocker arm 4. The oil will then in- fluence the means 6 arranged at the end of the rocker arm above the valve tubes 9. The means 6 is preferably in the shape of a piston which works in two positions, and is moveable between these positions, which are a con- tracted position and an extended position. During normal operational condi- tions, oil is fed to the rocker arm shaft 5 at about 1 bar. During such pressure conditions, the piston 14 is kept in its contracted position by means of the spring 11 which effects the yoke 8.

When additional braking effect is needed, the above-mentioned control sys- tem gives instructions to the control valve device to feed oil to the rocker arm shaft 5 at a higher pressure, for example at 2 bar. In this way, a braking ef- fect is achieved by the piston 14 assuming its extended position at which the valve play will not be absorbed.

In Fig. 3, there is schematically shown a control valve device 15 according to the present invention. This control valve device is utilized for feeding oil to the rocker arm shaft 5, which is schematically indicated in Fig. 3. The control valve device 15 interacts with a throttle valve 16 arranged in connection to the above-mentioned piston 14 in the rocker arm.

Fig. 3 shows the invention in a state which occurs during normal engine op- eration in an internal combustion engine, i. e. when there is no gear shifting and engine braking is thus not needed. The control valve device 15 com- prises an inlet 17 for supplying pressurized oil at a certain inlet pressure pi, which suitably is approximately 1 bar. Oil is then fed from a not shown oil pump device and up to the inlet 17, in the direction indicated by an arrow in Fig. 3. Via the inlet 17, oil is brought to a pressure regulating valve with a valve body 18, which preferably is shaped as a cylinder with a narrow section 19, with a smaller diameter than the rest of the valve body 18. The valve is

displaceable in a holder 20, which comprises an internal tube-shaped recess with an inner diameter which somewhat exceeds the outer diameter of the valve body 18. The oil is brought to flow towards said narrow section 19, with the valve being positioned in a position of equilibrium which is partially de- cided by the oil pressure flowing in at this section 19, but also by the force exerted by a coil element 21 which effects the valve body 18 in a predeter- mined direction (to the left in Fig. 3). In addition the valve body 18 is effected to assume this position of equilibrium by means of the pressure of oil which is present in a chamber 22, and which effects the valve body 18 in the opposite direction compared to the force from the coil element 21 and the pressure from the oil which flows in at the inlet 17.

In the above-mentioned position of equilibrium, the valve body 18 is in a po- sition at which said portion 19 together with the holder 20 defines a relatively narrow slit through which oil is allowed to flow, but however at a reduced pressure. This pressure reduced oil flow flows on through a canal 23 towards the above-mentioned throttle valve 16 which is designed with a ball 24, which is spring loaded via a second spring element 25. By means of the spring element 25, the ball 24 is normally effected in a direction away from a ball seat 26. In this way the ball 24 with its ball seat 26 defines a controllable opening for oil. In the condition shown in Fig. 3-with the oil pressure in the canal 23 being relatively low-the spring element 25 manages to press the ball 24 in a direction away from the ball seat 26, by means of which a con- nection via the throttle valve 16 up to the piston 14 is kept open. In more de- tail, oil is then under relatively low pressure allowed to flow to a space 27 above the piston 14. In this condition which corresponds to normal operation of the vehicle in question, there is no absorption of the valve play, i. e. there is a valve and thus no engine braking effect is obtained.

The control valve device 15 according to the invention furthermore comprises a special solenoid valve 28 which is arranged so that it can either open or block a connection between the canal 23 and the chamber 22. The solenoid

valve 28 can also open or block a connection between the chamber 23 and an outlet 29 for drainage of oil.

With reference to Fig. 2 (which does not show the control valve 15) and Fig.

3, it can be noted that a canal 23 conducts oil up to the rocker arm shaft 5. In addition, the throttle valve 16 is arranged in the rocker arm 4, which cannot be seen in Fig. 2, but which is shown in detail in Figs. 3 and 4.

In Fig. 3 the solenoid valve 28 is shown in a condition which corresponds to normal engine operation, i. e. without any engine braking effect being ob- tained. The solenoid valve 28 comprises a valve element 30 which is shaped as the end of a displaceable valve rod 31. The valve element 30 can be posi- tioned in two positions, so that it is in a sealing position against either an up- per valve seat 32 or a lower valve seat 33.

In the position shown in Fig. 3, the valve element 30 is in an upper position as a result of influence from a spring element 34 comprised in the solenoid valve 28. In this position, the solenoid valve 28 is thus without current and the valve element 30 is in a sealing position against the upper valve seat 33. As explained above, this causes there to be a connection between the canal 23 and the chamber 22.

The solenoid valve 28 is electrically connected to, and controllable by means of, the above-mentioned control system. In more detail, the control system emits a signal for the activation of the solenoid valve 28 when gear shifting is to be initiated. This then causes the valve rod 31 to be pushed out to an ex- tended position (and thus overcomes the force from the spring element 34) by means of an electromagnet 35 in the solenoid valve 28. In this activated position, the valve element 30 is no longer positioned against the upper valve seat 33, but is instead moved into contact with the lower valve seat 33.

The activated state of the control valve device 15 according to the invention is shown in Fig. 4. As is evident from this figure, the connection between the valve 23 and the chamber 22 will then be closed. In this way, it can be said that the controllable outlet 36 which is defined by a connection between the canal 23 and the chamber 22, now with the aid of the solenoid valve 28, has been arranged in a position which makes the canal 23 completely sealed, i. e. without any side flow through the outlet 36. At the same time, a connection is opened between the chamber 22 and an outlet 29, so that oil which has pre- viously been in the chamber 22 is drained. This in turn causes the valve body 18 to be slightly displaced (to the left in Figs. 3 and 4) as a consequence of the spring force which works on the valve body 18 via the spring element 21.

This causes the canal 23 to be opened completely for the supply of pressur- ized oil via the inlet 17 and the valve body 18.

Since the canal 23 now is completely opened, and there is no pressure re- duction of the oil, flow of oil at relatively high pressure is obtained in this acti- vated state, suitably in the order of size of 2-4 bar, through the canal 23 and up to the throttle valves 16. The oil pressure is then adjusted together with the other components in such a way that the oil pressure will overcome the force of the second spring element 25 and will effect the ball 24 into contact with its ball seat 26. For this purpose, the ball is connected to a piston-like element 37 against which the oil pressure works.

When the ball 24 is in contact with the ball seat 26, the oil which is present in the space 27 above the piston 14 will be trapped. The high pressure which is also prevalent will influence the piston 14 to assume its extended position, which means that the valve play in connection with the movement of the ex- hausted gas valves is essentially eliminated, i. e. the valve play is then ab- sorbed. With reference to that which has been described above, this means that an engine braking function is now obtained.

When it is desirable to absorb the valve play, i. e. when further braking effect is desired in connection with gear shifting, the control system gives instruc- tions via signals to the solenoid valve 28 to place the valve rod 31 in its ex- tended position. This causes a movement of the piston 14 to its extended position. In its extended position, the piston 14 uses the valve play in such a way that the rocker arm is effected both by the regular ridge 2a and by the extra ridges 2b, 2c which are formed on the camshaft 2. This means that the corresponding exhaust gas valves can be driven to effect engine braking.

The invention is preferably arranged in such a way that the cross-section area which can be said to be defined by the above-mentioned canal 23 (which for example is constituted by a drilled hole, i. e. a tube-like groove) is in a ratio to the cross-section area which can be said to be defined by the above-mentioned controllable valve 36 in a predetermined manner. In more detail, according to the preferred embodiment the ratio between the cross- section area of the canal 23 and the cross-section area of the controllable outlet 36 is mainly within the interval 1-5. This thus means that these two cross-section areas are of essentially the same order of size. With reference to Figs. 3 and 4, the cross-section area of the controllable outlet 36 can be said to correspond to the area at the opening into the lower inlet of the sole- noid valve 28 (i. e. mainly in connection to the lower valve seat). Due to the design of the canal and the controllable outlet, a very low fall of pressure is obtained and a very short filling time (when filling oil) at the controllable outlet as well.

For a normal application, in which the valve according to the invention is used in connection with an internal combustion engine for a cargo vehicle, in which the stroke volume of a combustion cylinder is in the order of size of 2 litres, the diameter of said canal 23 is preferably in the order of size 5-15 mm, with the diameter of said controllable outlet preferably being in the order of size of 2-10 mm. The invention is however not limited to being shaped with

these dimensions, but can be varied so that adjustment to various applica- tions can be done.

According to one embodiment, the dimensions of said controllable outlet 36 are chosen in such a way that essentially no time delay is obtained during pressurization and depressurization in said controllable outlet 36 in compari- son to a corresponding pressurization and depressurization in said canal 23.

Thus, there is by means of the invention obtained a very rapid pressurization and depressurization, which corresponds to a rapid influence on the piston 14. This in turn allows for a very rapid engine braking, and in a corresponding manner for a very rapid gear shifting.

The invention allows for a particularly advantageous function in that it permits a very quick shifting between engine braking and engine operation (and vice versa) due to the large area of flow for oil in the canal 23. In addition, the so- lenoid valve 28 constitutes a simple and robust device which permits a simple adjustment and a reliable function.

It can thus be concluded that according to the invention there is provided means for controlling the oil pressure in the rocker arm shaft 5, and thus also in the space 27 in connection to the piston 14. These means comprise the above described control valve device 15 and the throttle valve 16, with the control valve device 15 in turn comprising the controllable solenoid valve 28 by means of which the engine braking effect can be engaged and disen- gaged.

In addition, the piston 14 comprises a valve device 38, which in turn com- prises a ball 39 which is effected to be in contact with a ball seat 40 by means of a spring element 41. In addition, the bottom of the piston 14 is shaped with a drainage hole 42. When the pressure of the oil in the space 27 exceeds a certain value, the ball 39 will be pressed out of contact in the ball

seat 40, with oil then being allowed to flow out through the drainage hole 42.

In this way a pressure limiting effect is obtained for the valve device 38.

During normal operation of the vehicle, when the control system sees that up-shifting is needed, and that application of the engine brake is needed to carry through the gear shifting, the control system instructs the solenoid valve 28 to assume the position shown in figure 4. To indicate that gear shifting is to take place, a number of various signals can be utilized (separately or in combination), for example signals referring to the r m p of the engine and its torque, the speed of the vehicle and the current positions of the pedals of the vehicle. The invention is however not limited to being implemented with these signals alone, but can also be used with other signals which give an indica- tion that a gear shifting is necessary and that a braking of the engine is about to take place. As soon as the engine speed has been synchronised with the gear ratio which has been engaged, the solenoid valve 28 is instructed by the control system to reassume the initial position shown in Fig. 3. This corre- sponds to the solenoid valve 28 being without current. This repositioning causes the connection between the canal 23 and the chamber 22 to be es- tablished, in connection with which the valve body 18 is positioned in the above described position, at which it causes a pressure reducing effect. This in turn means that the piston 14 in the rocker arm again will exhibit a valve play which corresponds to engine braking no longer being obtained. In this way, the engine braking stops, and torque can again be applied without un- necessary delay, meaning that the power interruption will be very short.

After engine braking has been performed, the valve element 30 is restored.

This means that the valve body 18 is moved back to the position which gives pressure reduction. In addition, oil is drained under high pressure from the space 27 out through the throttle valve 16. For this purpose, the above- mentioned spring element 25 is used to bring the ball 24 of the throttle valve 16 out of contact with its seat 26. Furthermore, in the throttle valve 16 there is utilized a further lower spring element 43 in order to effect the ball 24 in the

direction of the seat 26. In this way, the throttle valve 16 can be positioned in the correct position depending on the level of the oil pressure.

The invention is not limited to the embodiment described above, but can be varied within the scope of the appended claims. For example, the invention can be utilized in different kinds of vehicles, for example cargo vehicles and cars. In addition, the above described braking effect can in principle be util- ized both when gear shifting and in other situations when engine braking is desirable. Also, the pressurized oil which is fed from the control valve device 15 can be led up to space 27 at the rocker arm 4 in another manner than via a canal in rocker arm shaft 5, for example via special separate oil conduits.