VALVE ARRANGEMENT

Abstract: A method and device for taking up valve clearance in the valve mechanism (1) of an internal combustion engine, which mechanism includes rocker arms (4) arranged on at least one rocker arm shaft (5). The take-up occurs by means of an actively adjustable, hydraulically operated take-up means (6) operable between two positions, i.e. a withdrawn position and an extended position, which take-up means (6) is arranged at the operating end of the valves rocker arms whose valve clearance is to be taken-up. The hydraulic pressure for operating the take-up means is achieved by a somewhat increased lubrication pressure in the rocker arm shaft (5) for this type of engine, which pressure for said extension of the take-up means (6) is increased by wholly or partially blocking the oil's normal drainage.

Description: Title: Valve arrangement Technical field: The present invention relates both to a method to take up valve clearance in the valve mechanism of an internal combustion engine, which mechanism includes rocker arms arranged on at least one rocker arm shaft, by means of an actively adjustable, hydraulically operated take-up means operable between two positions, i.e. a withdrawn position and extended position, and by means of a control arrange¬ ment with which the take-up means is switched between its respective positions, and to a device for controlling the take-up of valve clearance which, since a take-up means is arranged at the operating end of each rocker arm which is operated by a hydraulic unit included in the engine, permits an active take-up of the clearance in the mechanism. Background and problem: Known methods and devices for valve clearance take-up have up until now above all been used specially for this purpose, that is the take-up of clearance both so as to achieve a quieter running of the engine and to reduce the stresses therein. The ever growing demands over the last few years for more effective auxiliary braking systems on commercial vehicles has led to ever more advanced solutions to satisfy the demands. One of these is described in Swedish patent application 8900517-7. According to this document the camshaft of the engine's valve system is used to obtain negative work from the engine instead of positive work which it is normally intended to achieve. This is achieved with the aid of extra lobes on the camshaft which open a connection between the engine's combustion chambers and its exhaust system during the latter portion of the inlet stroke (four-stroke motor) and by closing this connection at the first portion of the corresponding compression stroke. In this way, a large portion of the compression work is lost as braking. The said additional lobes on the camshaft are so small that in terms of size they fall into the category which can be called normal clearance in an engine of this type. Known methods and devices for actively adjustable valve clearance take-up include separate systems for the activation and de-activation, controlled either by electrical systems or by separate hydraulic systems. No matter which type is chosen, a relatively high grade of complexity is required, particularly with the implementation of a separate hydraulic system. In addition to the fact that this means almost a doubling of the number of hydraulic components in the valve system, a result thereof is the reduced reliability and a larger production cost per unit. Solution: A principal object of the present invention is to provide a method and a device whereby the engine's existing pressurized oil system is used in order to guarantee the above mentioned function with minimal modification using essentially already existing components. At the same time it is an object to facilitate a compara¬ tively lower production cost per unit with maintained or improved reliability of the function by means of said optimisation of the use of the engine's existing components. Advantages: Practical trials have shown that, with the invention described by way of introduction, exceedingly good operation in all respects is achieved. The method according to the invention is characterized in that the control arrangement operates by selectively at least partially hindering drainage of the lubricant which is fed to the valve mechanism via its rocker arm shaft, whereby the pressure of the lubricant in its feed conduit to the rocker arm's operating end where the take-up means is arranged is increased to such a level that the take-up means is expanded to its extended position. The device according to the invention is characterized in that the drainage of the oil fed to the rocker arm shaft and thence to the rocker arms and respective take-up means is arranged such that only a small quantity of the oil, i.e. that which is necessary for the bearing surfaces of the rocker arms, is drained via normal leakage flow between the rocker arms and their shafts, whilst the rest is drained via a specially arranged conduit from the rocker arm shaft back to the engine oil reservoir, which conduit's outlet orifice is blockable by means of a pneumatically operable piston cylinder unit which is arranged close to the outlet orifice, such that the pressure in the rocker arm shaft and associated rocker arms is increasable so that the take-up means can be extended. An advantage with the invention is that additional machine- ing or assembling of oil conduits can, in the main, be avoided on a so called base engine with which at the start of production it is not yet known whether the engine will definitely be equipped with actively controlled valve clearance or not. Brief description of the drawings: The invention will be described in the following in more detail with reference to a preferred embodiment and attached drawings in which Fig. 1 shows an internal combustion engine's valve mechanism with a device for valve clearance take-up according to the invention. Fig. 2 shows a rocker arm according to figure 1 seen in partial cross-section as it is mounted in an engine, seen from above. In figure 1 a valve mechanism 1 for a (not shown) internal combustion engine is schematically shown. The mechanism 1 includes a camshaft 2 which, via a cylindrical roller 3, transmits its rotational movement to a rocker arm 4. The rocker arm 4 is arranged on a hollow rocker arm shaft 5 which is intended to be mounted to a cylinder head (not shown) by means of bolts (not shown). The rotational movement is imparted to the camshaft by conventional means via a transmission from the engine's crank shaft (not shown). From the figures it can be seen that the rocker arm 4, via means 6 and a hemispherical guide 7 thereon, acts directly on a yoke 8 which is moveable up and down on a guide S in the cylinder head. The yoke 8 acts in turn on two valve stems 9 on whose ends, in a conventional way, valve heads (not shown) are arranged. Each rocker arm 4 accordingly operates two valves which simultaneously move up and down. In order for this to be possible, each valve stem 9 is surrounded by a valve spring 10, which, in a conventional manner with the aid of a locking means and a washer (not shown) on each one, is held in a controlled position against the valve's closed position. In addition to both the valve springs 10, there is a spring 11 which is arranged beneath the yoke 8. The purpose of this spring is to maintain the yoke 8 in such a position that the clearance which always arises in a valve mechanism of this type occurs between the respective valve stems 9 and the underside of the yoke 8. The spring 11 has a further purpose which will be referred to in more detail below. The described valve mechanism is pressure lubricated by oil which is supplied via conduits in the cylinder block and cylinder head of the engine to the hollow interior of the rocker arm shaft 5. The plain bearings of the rocker arms 4 are lubricated by a certain leakage flow between the shaft 5 and the bearings. Under normal circumstances this is, however, not large and a drainage of a portion of the lubricant also occurs via a special conduit 13. According to the invention, a pneumatically, or alternatively mechanically, operated piston-cylinder device 14 is introduced into the return conduit 13, which device during normal operation maintains the oil pressure at a pre¬ determined low value by means of the resiliency of a spring 14 which facilitates the drainage of the oil to the lubricant reservoir via an outlet 13a and which, when activated, prevents the pressure oil from being drained via the outlet 13a. The only remaining outlet for the oil after activation is hereby between the shaft 5 and the plain bearings (according to the above), whereby a considerable pressure increase is achieved to a pressure in the oil approaching the engine's feed pressure. Since the oil is also fed to the working end of the rocker arm 4 via a conduit 15 and to the means 6 arranged there, the following occurs; the means 6 which in principle is of piston cylinder type is activated and as soon as the pressure in the means 6 climbs to such a level that it overcomes the force of the spring 11 it will act as a clearance take-up means. The force from the means 6 is however never so large that it can affect any of the valve stems 9. For the sake of safety, as can be seen in figure 1, the means 6 also has a ball valve 17 influenced by a spring 16. This valve assures that the oil pressure can never become too high in the cavity at the means 6 so that various components in the valve system become damaged. In the event that the valve 17 opens, the oil is drained back to the motor via one or more conduits 21 via normal drainage in the engine back to the engine's lubrication reservoir. In figure 2 the rocker arm 4 is shown in partial section, as mentioned earlier. In addition, it can be seen that the oil in the oil conduit 15 must pass through a check valve arrangement 18 before it reaches the means 6. The purpose of this arrangement is that, during operation of the engine without valve clearance according to the earlier descrip¬ tion, "pumping" is prevented, which means that the pressure from the springs and other valve forces should give a return pressure in the conduit 15. The check valve is of the spring/ball type 22 resp. 23 and solves the pumping problem. The check valve arrangement 18 does however prevent the overriding of the operation of the valve take- up means 6 when so desired. In order for this to be able to occur, a piston 19 is arranged in a cylinder right behind the ball bearing 23 of the check valve arrangement 18, which piston has a plunger-shaped prong 24 at its end towards the ball bearing which, at low cf pressure, presses the ball bearing from its seat under tl • _ influence of a spring 20. The plunger-shaped prong 24 extends in a tubular conduit 25 which, despite the prong 24, permits a flow of oil in both directions. At high pressure, the piston's 19 effect on the ball bearing is overcome since the spring 20 cannot overcome the oil pressure on the end of the piston 19 provided with the prong. With the accordingly described device, a method as described in the introduction can be attained which solves the stated problems. Naturally the invention is not restricted to the above described embodiment, and changes can be made within the scope of the appended claims. By way of example, the piston-cylinder arrangement 14 can be dimensioned such that during operation it gives a temporarily increased back pressure in the drainage conduit whereby a faster clearance take-up is achieved.

Claims: Claims: 1. A method to take up valve clearance in the valve mechanism (1) of an internal combustion engine, which mechanism includes rocker arms (4) arranged on at least one rocker arm shaft (5), by means of an actively adjustable, hydraulically operated take-up means (6) operable between two positions, i.e. a withdrawn position and an extended position, and by means of a control arrangement with which the take-up means is switched between its respective positions, c h a r a c t e r i z e d i n that the control arrangement operates by selectively at least partially hindering drainage of the lubricant which is fed to the valve mechanism (1) via its rocker arm shaft (5), whereby the pressure of the lubricant in its feed conduit (15) to the rocker arm's (4) operating end where the take- up means (6) is arranged is increased to such a level that the take-up means (6) is expanded to its extended position. 2. Method according to claim 1, c h a r a c t e r i z ¬ e i n that the drainage is hindered by causing a pneumatically operated piston-cylinder unit (14) to seal a drainage hole (13a) along a drainage conduit (13) which runs from the rocker arm shaft (5) to the engine's oil reservoir. 3. Method according to claim 2, c h a r a c t e r i z ¬ e d i n that the pneumatic operation of the piston- cylinder unit (14) is achieved via the utilization of an existing pneumatic system connected to the engine. 4. Method according to claim 3, c h a r a c t e r i z ¬ e i n that the piston-cylinder unit's (14) dimensions are chosen such that operation of the unit means that a pressure impulse is created in the drainage conduit (13), by means of which a quicker pressure increase response is achieved. 5. Device for controlling the take-up of valve clearance in the valve mechanism of an internal combustion engine, comprising, on the one hand, a rocker arm system (4, 5) with at least one typically hollow-formed rocker arm shaft (5) and, on the other hand, a hydraulically operated take- up means (6) arranged in connection with the operating end of those valves whose valve clearance is to be taken up, whereby each valve's rocker arm has a conduit (15) for the supply of oil to the take-up means (6), c h a r a c - t e r i z e d i n that the drainage of the oil fed to the rocker arm shaft (5) and thence to the rocker arms (4) and respective take-up means (6) is arranged such that only a small quantity of the oil, i.e. that which is necessary for the bearing surfaces of the rocker arms (4), is drained via normal leakage flow between the rocker arms (4) and their shaft (5), whilst a quantity is drained via a specially arranged conduit (13) from the rocker arm shaft back to the engine oil reservoir, which conduit's (13) outlet orifice (13a) is blockable by means of a pneumatically operable piston-cylinder unit (14) which is arranged close to the outlet orifice (13a), whereby the pressure in the rocker arm shaft (5) and associated rocker arms (4) is increasable so that the take-up means can be extended. 6. Device according to claim 5, c h a r a c t e r i z ¬ e d i n that it has an operating plunger/check valve arrangement (18) which is arranged so that at low pressure in the conduit (15) return flow of oil from the take-up means is permitted and at high pressure in the conduit said return flow is prevented. 7. Device according to claim 6, c h a r a c t e r i z ¬ e d i n that the operating plunger/check valve arrangement has two components, each acted upon by a spring (20, 22 resp.), a plunger piston (19) and a ball bearing (23), which parts' force components are opposed so that when no oil pressure forces act on the arrangement, the spring (20) of the plunger (19) can cancel the action of the ball bearing's (23). 8. Device according to claim 7, c h a r a c t e r i z ¬ e d i n that the plunger piston (19) is substantially cylindrical except for its end region facing the ball bearing (23) which is formed into a thin plunger-shaped prong (24) connected to the cylinder body in the direction of its sleeve. 9. Device according to claim 8, c h a r a c t e r i z ¬ e i n that the action between the plunger piston (19) and the ball bearing occurs via a narrow tubular conduit which, in addition to said plunger prong, also permits a flow of oil in both directions. 10. Device according to claim 9, c h a r a c t e r i z ¬ e d i n that the tubular conduit's one end is shaped as a sealing valve-seat for the ball bearing (23).

Inventors: HAAKANSSON OLOF, HAAKANSSON, OLOF
Applicants: VOLVO AB, AB VOLVO
Application year: 1990
Main classification: F01L1
IPC codes: F01L1, F01L13, F01M1, F01M9