EP0446577B1 - Engine brake for air compressing engine - Google Patents

Abstract

The invention relates to an engine brake for air compressing engines. To increase the braking power, the exhaust valve (1) is raised slightly even during the compression stroke, allowing additional braking work to be performed by the piston by virtue of the restricting effect of the exhaust valve. A hydraulic linkage (4) is inserted between the cam (2) and the exhaust valve (1) for the purpose of raising the exhaust valve. According to the invention, this linkage is activated in the braking mode by the closure, during the compression stroke, of a solenoid valve (12) connected in parallel with the linkage. The solenoid valve is controlled via sensors (20, 21) with the interposition of a control unit (19), the sensors interacting with the flywheel (23). By means of the closed position of the solenoid valve in braking mode, the exhaust valve can be raised by a second lobe of the cam in the compression stroke as well. By virtue of this measure, braking work is performed not only during the exhaust stroke but also during the compression stroke. <IMAGE>

Description

The invention relates to an engine brake according to the preamble of the claim.

From US-PS3786 792 it is known to provide a hydraulic linkage for power transmission between a camshaft and an exhaust valve of an air-compressing internal combustion engine. The hydraulic linkage has a control device and a hydraulic valve lash adjuster, as well as leak oil compensation. The control device consists of a fast solenoid valve which can be controlled by a contact, the contact being closed by actuating the brake pedal. When the brake pedal is operated, the contact closes and a solenoid of the solenoid valve causes it to close. By closing the solenoid valve, a cylinder chamber of the hydraulic linkage is shut off, which means that the linkage behaves like a rigid push rod. The hydraulic linkage can be raised in braking operation by a brake cam provided on the camshaft towards the end of a compression cycle, so that the compressed air is blown off and the braking work stored in it is thus destroyed. The solenoid valve is permanently closed while the engine brake is actuated, while it is permanently open during engine operation. Due to the permanent closing of the solenoid valve in engine braking mode the movement of the exhaust valve is determined solely by the shape of the brake cam. An adjustment of the control time during braking operation to a variable braking characteristic is therefore impossible.

According to DE-OS 33 00 763 it is proposed to connect the cylinder space of the piston cooperating with the camshaft via a line to a controllable valve, so that the transmission of the movement of the piston to a valve piston can be interrupted as desired. To supplement leakage oil losses, the hydraulic linkage can in turn be connected to the lubricating oil circuit via a check valve. A hydraulic linkage of this type takes up a larger construction volume, since the cylinders and pistons do not form such a compact unit. In the absence of this unit, a connecting line, albeit a short one, is necessary between the cylinder spaces, which gives rise to greater inertia.

DE-A-39 39 934 proposes switching on a hydraulic linkage between a camshaft and an exhaust valve, the camshaft each having two elevations. A first survey serves in the usual way to open the outlet valve in the push-out phase. A second elevation can also raise the exhaust valve in the compression phase in order to perform braking work by throttling. The switchover from normal operation to braking operation takes place by activating a solenoid valve which branches off from a connecting line of the pistons of the hydraulic linkage. During the time interval in which the solenoid valve is closed, the second elevation of the cam can transmit its movement to the outlet valve, so that the latter can also be slightly raised during the compression phase and braking work is performed by pushing out. Leakage oil losses are supplemented by a check valve from the lubricating oil circuit. Thereby, that the piston actuated by the cam and the piston of the exhaust valve are separated and connected to one another via a longer line, this valve actuation is structurally relatively complex. The long connecting line makes the valve train sluggish, which limits its use in high-speed engines.

Starting from an engine brake according to the generic term, the invention is based on the object of optimizing the engine braking power by means of variable control times of the exhaust valve and adapting it to the necessary boundary conditions when operating commercial vehicles.

This object is achieved by the characterizing features of patent claim 1.

A particular advantage of the engine brake according to the invention compared to the prior art is that the hydraulic pump unit required there, driven by the camshaft, to achieve the additional elevation of the exhaust valves in the compression cycle is dispensed with. The additional survey in the engine brake according to the invention, which is approximately the same in terms of survey characteristics and opening times, is represented by a modified outlet cam shape and electronic control by means of "fast" solenoid valves, each of which is assigned to each outlet tappet.

The electronic control according to the invention is therefore used to advantage over that by a hydraulic pump unit, since fast magnetic valves are now inexpensive to manufacture and work reliably because of the widespread use of electronics in engine construction. To display the control current impulses, the control units and power current distributors which are anyway required for the fully electronic diesel control, which is planned as standard, can be adapted accordingly, so that for this purpose there are no significant additional costs. Compared to the control by means of a hydraulic pump unit, further advantages include simplification due to the reduced number of moving parts, the possibility of dispensing with external high-pressure lines, and greater flexibility with regard to the design of the outlet control times during the additional survey.

An advantageous development of the invention can be found in claim 2.

The hydraulic valve clearance compensation ensures that the exact exhaust valve control times are retained unchanged even when the exhaust valve is seated or the valve drive wears out, so that the function is guaranteed in normal or engine braking mode, regardless of the state of wear. Due to the lack of valve clearance, the usual cam ramps at the beginning and end of the cam stroke are not required to overcome the valve clearance area. This makes it possible to make the angles 2 and 6 correspondingly large in order to have sufficient time for emptying and filling the cylinder space 10.

An advantageous control for the solenoid valves is characterized by the features of claim 3.

By acting on the solenoid valves by means of an electronically operating control device, a flexible and inertia-free variation of the control times of the exhaust valve is achieved.

A further advantageous embodiment can be found in subclaim 4.

Figur 1

einen Schnitt durch ein hydraulisches Gestänge mit parallel geschaltetem Magnetventil

Figur 2

einen Nocken mit einer zweiten Erhebung zur Betätigung eines Auslaßventils im Motor-Bremsbetrieb

Figur 3

ein Steuerdiagramm eines Ein- und Auslaßventils im Motor-Bremsbetrieb, wobei die Ventilwege als Funktion über dem Drehwinkel einer Kurbelwelle aufgetragen sind.

An embodiment of the invention is shown in drawings. It shows:

Figure 1

a section through a hydraulic linkage with a solenoid valve connected in parallel

Figure 2

a cam with a second elevation for actuating an exhaust valve in engine braking mode

Figure 3

a control diagram of an intake and exhaust valve in engine braking, the valve paths are plotted as a function of the angle of rotation of a crankshaft.

For controllable actuation of an exhaust valve 1, a hydraulic linkage 4 is switched on according to FIG. 1 between a cam 2 and a push rod 3. This hydraulic linkage 4 consists of the valve tappet 5, which at the same time takes over the function of a cylinder and a piston 6 which is movable in the axial direction, but its movement can be limited by first and second stops 7a and 7b. In the piston 6, in turn, a compensating piston 8 is arranged, which transmits the movement of the piston 6 to the push rod 3. Between the piston 6 and the valve tappet 5, a compression spring 9 is switched on, which holds the piston 6 in the starting position. The cylinder space 10 enclosed by the valve tappet 5 and the piston 6 is connected to a solenoid valve 12 via a short-held connecting line 11, the connecting line 11 again being in communication with an engine lubricating oil circuit 13 when the solenoid valve 12 is open.

To compensate for the unavoidable wear, the compensating piston 8 can be provided in the valve train as a hydraulic valve lash adjuster, which has a bore 14 which allows a cylinder space 15 between the piston 6 and the compensating piston 8 to be connected to the engine lubricating oil circuit 13 by means of a compensating line 16. By means of a spring 17 loaded valve 18, which can be designed as a ball, the bore 14 is closed, or oil can be sucked in via the compensating line 16.

To control the exhaust valve 1, the cam 2 is provided with a first and a second elevation 2a and 2b, the first elevation 2a bringing about the normal opening of the exhaust valve 1 during the push-out phase and the second elevation 2b opening the exhaust valve 1 in the compression phase with the engine - Brake operation is reserved.

The control of the solenoid valve 12 is carried out by a control device 19, which operates electronically and which receives its signals to be processed from at least one transmitter, which is designed as a sensor 20, and works on an inductive basis. Of course, as shown in FIG. 1, two or more sensors 20 and 21 can also be provided, which are arranged offset by a certain angle on the periphery of a flywheel 23 provided with ring gear 22. Instead of the flywheel 23, a camshaft gear can also be provided. The voltage pulses coming from the sensors 20 and 21 are processed in the control device 19 in such a way that the position of the cam 2 and its second elevation 2b are recognized and the angular ranges α 1 to α 6 described below in FIG. 2 are determined. The pulses processed in the control unit 19 are fed to a solenoid 24 of the solenoid valve.

In a multi-cylinder internal combustion engine, a fast solenoid valve 12 is assigned to each exhaust valve 1. The control unit 19 is able to determine the position of all the cams via the sensors 20 or 21.

To initiate engine braking, the control unit 19 is activated by a switch 25, which switch 25 can be one or two stages, so that the Motor brake is actuated in stages. In the first stage, only a throttle, not shown here, is closed in an exhaust pipe; in the second stage, when there is a greater need for braking power, the solenoid valve 12 is also actuated in order to open the exhaust valve 1 even during the compression phase to such an extent that push-out work is carried out in order to reduce the braking power to increase. The order of the graduated engine brake can of course also be reversed in adaptation to the desired braking power.

The mode of action will be discussed in more detail below.

When the engine is running, the solenoid valve 12 is permanently open, and the electronic control is thus completely inactive. During the extension phase, the first elevation 2a of the cam 2 lifts the valve lifter 5. Since the solenoid valve 12 is open, no pressure can be built up in the cylinder space 10. Only when the first stop 7a in the valve tappet 5 hits the piston 6 is the movement of the valve tappet 5 transferred to the piston 6 and, via the second stop 7b, to the push rod 3, which opens the outlet valve 1. With further rotation of the cam 2, the exhaust valve 1 closes again. The run-up of the valve tappet 5 on the second elevation 2b of the cam 2 has no effect, since no pressure can build up in the piston chamber 10 because of the open solenoid valve 12 and the stroke h of the tappet as a result of the second elevation 2b is equal to the free path length s between the is the first stop 7a of the valve lifter 5 and the piston 6. The exhaust valve 1 thus only opens through the first elevation 2a to the exhaust stroke.

If you want to switch to engine braking mode, you actuate the switch 25 and thus activate via the control unit 19 the solenoid valve 12, which is closed during the lifting of the tappet 5 by the second elevation 2b, so that the movement of the valve tappet 5 hydraulically on the piston 6 is transmitted, the outlet valve 1 with the interposition of Push rod 3 opens slightly during the compression phase, so that additional braking work can be performed by destroying the compression work due to the throttling action of the exhaust valve 1. In the area of an angle 5 (FIG. 2) of the second elevation 2b, the solenoid valve 12 opens again, so that the hydraulic connection between the valve tappet 5 and the piston 6 is interrupted and the outlet valve 1 closes, only to open again in area 1. The switch 25 can also be carried out in two stages, so that in a first stage only the normal exhaust brake is actuated and in a second stage the hydropneumatic brake or vice versa. The braking power can thus be graded.

FIG. 2 shows a cam according to the invention with a second elevation. Cam 2 is divided into sectors with angles α 1 to α 6. With its first elevation 2a, a sector with angle α 1 serves to open the valve in the push-out phase. A sector with angle α 2 fulfills the task. Fill up the cylinder space 10. A sector with angles .alpha.3 gives the solenoid valve 12 (FIG. 1) time to close in engine braking mode. The second elevation 2b begins in a sector with an angle α 4. During the angle α 4, the solenoid valve 12 (FIG. 1) is closed and the outlet valve 1 opens in the compression phase, so that braking work can be carried out in addition to the extension phase. A sector with angle α 5 gives the solenoid valve time to open. A subsequent sector with angle α 6 serves to push the oil out of the cylinder space 10.

In Figure 3, piston and valve travel are shown plotted against the crank angle. The valve opening curve of the exhaust valve is labeled A. In normal engine operation, the exhaust valve opens between bottom dead center UT and a gas exchange GOT. When the exhaust engine brake is actuated, push-out work is carried out in this phase against a throttle in the exhaust line.

When the solenoid valve 12 (FIG. 1) is additionally activated, the second elevation 2b of the cam 2 also opens the outlet valve 1 between the bottom dead center UT and an ignition ZOT, so that in this phase the throttle effect of the outlet valve 1, which is only slightly opened further push-out work is done and compression work is destroyed, and the braking power is increased in addition to the braking power of the known exhaust brake.

Claims (4)

1. An engine brake for air-compression internal combustion engines, consisting of a hydraulic rod linkage (4) arranged between a cam (2) and an outlet valve (1), wherein the hydraulic rod linkage is connected via a connection line (11) to an external regulating device in the form of a high-speed solenoid valve (12) and to an oil-leakage replenisher from a lubricating-oil circuit (13) of the engine, and wherein the internal combustion engine has a throttle valve in the exhaust pipe, which throttle valve partially blocks the exhaust manifold on actuation of the engine brake, and/or wherein the solenoid valve (12) is activated simultaneously on actuation of the engine brake, characterised in that the solenoid valve (12) can be triggered to activate at least one sensor (20), the signals from this sensor (20) being passed to the solenoid (24) of the solenoid valve (12) via a control device (19), in such a manner that the solenoid valve (12) is closed in the compression phase of the engine when a valve tappet (5) is lifted by a second elevation (2b) of the cam (2) on actuation of the engine brake during a given interval, the signals from the sensor (20) derived from the cam position and the rotational speed of the camshaft being processed in the control device (19) in order to establish this interval, and in that the cam (2) is divided into several sectors in such a manner that a sector with an angle α 2 serves to fill a cylinder space (10) within the valve tappet (5), the control device (19) actuates the solenoid valve (12) so that its closure is initiated in a sector α 3 of the cam (2), a sector with an angle α 4 has the actual elevation (2b), whilst the solenoid valve (12) is opened again in a sector with an angle α 5, and a cylinder space (10) in the valve tappet (5) is emptied in a sector with an angle α 6.
2. An engine brake according to Claim 1, characterised in that the hydraulic rod linkage has a hydraulically acting valve clearance compensator formed from a compensating piston (8) arranged coaxially in the piston (6) of the hydraulic rod linkage (4), the compensating piston (8) being inserted between the piston (6) and the tappet push rod (3), in that a cylinder space (15) located between the piston (6) and the compensating piston (8) is connectable to the engine lubrication system via a borehole (14), and in that this borehole (14) is closable via a spring-loaded valve (18).
3. An engine brake according to Claim 1, characterised in that the sensor (20) is arranged at the periphery of a toothed ring of a flywheel (23) or opposite a camshaft gearwheel, the sensor (20) being constructed on an inductively acting basis and its voltage pulses being supplied to a control device (19) for reprocessing, and in that the control device (19) operates the solenoid valves (12).
4. An engine brake according to Claim 1, characterised in that a second solenoid valve is provided for the successive connection of the exhaust brake.

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