GB2288219A

GB2288219A - Piston valve for an engine brake device

Info

Publication number: GB2288219A
Application number: GB9506649A
Authority: GB
Inventors: Erwin Schmidt; Siegfried Lamsbach
Original assignee: Daimler Benz AG; Mercedes Benz AG
Current assignee: Daimler Benz AG
Priority date: 1994-04-09
Filing date: 1995-03-31
Publication date: 1995-10-11
Anticipated expiration: 2015-03-31
Also published as: ITRM950137A1; DE4412298A1; IT1277312B1; GB9506649D0; DE4412298C2; ITRM950137A0; GB2288219B

Description

2288219 1 Piston valve for an engine brake device The invention relates to

a piston valve for an engine brake device on an internal combustion engine, in which the piston valve for opening and closing an additional outlet valve provided for an associated engine cylinder is arranged so as to be longitudinally displaceable in a corresponding receiver.

A piston valve of this type has been disclosed in the Offenlegungsschrift DE 3,428,626 Al. The piston valve is part of an adjusting device which is actuated by an auxiliary force and by means of which the respective additional outlet valve is opened and closed in dependence on the position of a brake pedal, a plunger f ace of the piston valve striking against the end of a valve rod of the additional outlet valve and subsequently pressing the valve rod away in the longitudinal direction out of the closed position against the pressure of the air compressed in the engine cylinder to open the valve. In the previous design, the piston valve consists of a steel body and a seal which is inserted separately in an annular groove on the external circumference of the steel body and is formed in two parts by a plastic O-ring core and a sealing ring which surrounds the latter and is made of polytetrafluoroethylene bronze.

The high opening and closing speed of the additional outlet valve during operation signifies a correspondingly highly accelerated movement of the piston valve in its receiving bore, f or which reason a low piston-valve mass and a low frictional resistance between the outer wall of the piston valve and the inner wall of the receiving bore are desirable. Such a low frictional resistance additionally reduces the risk of the piston valve becoming jammed in the receiver.

It is known f rom Of f enlegungsschrift EP 0, 515,771 Al to produce a ram for the valve drive of an internal combustion engine with a housing which consists at least in part of polymer material in order to reduce the weight of 2 the ram and thus the loads occurring and to reduce the wear. For this purpose, provision is made for the housing to be of cup-shaped design, the bottom consisting likewise of polymer material in an integral housing design. Alternatively, a housing bottom of metallic or ceramic material can be fitted in the form of a bottom plate onto an axial end side of a housing ring of polymer material, the bottom plate being in contact with the polymer body of the housing ring only at one end face and partially around the circumference.

As the technical problem, the invention is based on the provision of a piston valve of the type mentioned at the beginning of comparatively low dead weight, which can be produced in a simple manner and makes it possible during operation to minimize the frictional resistance between it and the receiving wall surrounding it.

According to the present invention there is provided a piston valve adapted for use in an engine brake device on an internal combustion engine, in which the piston valve, for opening and closing an additional outlet valve provided for an associated engine cylinder, is arranged so as to be longitudinally displaceable in an associated receiver, wherein the piston valve is made with a body of a dimensionally stable, heatresistant plastics material, and the body contains a base of the plastics material, into which a plunger made of steel, which has a contact face for interaction with an actuating rod of the additional outlet valve and at least one radially projecting disc face, is cast in such a way that the contact f ace is exposed and the plunger is supported with its radially projecting disc f ace or f aces against the surrounding plastics material of the base in both axial directions on at least one disc face..

The design of the piston-valve body of a plastics material signifies a noticeable weight reduction compared to the known steel design, such that the piston valve can be operated at lower actuating f orces and/or with a shorter 4 3 response time. At the same time, the use of a plastics material minimizes the frictional resistance between the piston valve and its receiver. The plastics used withstands the temperatures prevailing in the region of the engine cylinder head due to its heat-resistance. By making the piston- valve body out of plastics, seizing-up of the piston valve in the case of insufficient lubrication or tilted position is additionally prevented. In order to protect the plastics material from excessive wear due to directly striking against the valve rod of the additional outlet valve, a steel plunger which provides a stop face for the valve rod is cast centrally into the piston-valve body. The casting of the plunger takes place in a favourable manner during the manufacture of the piston-valve body so that no additional assembly step is required to mount it. Since this steel plunger takes up only a small part of the volume of the piston valve, the advantage of a noticeable weight reduction remains intact compared to the known piston-valve design made completely of steel. In this case, the steel plunger is cast in such a way that it is supported against the surrounding plastics material of the bottom axially in both directions by means of one or more radially projecting disc faces, thus allowing a favourable transmission of forces from the steel plunger to the plastics body in both axial directions..

As the plastics for the piston-valve body, a polypropylene PP, polyacetal, i.e. polyoxymethylene POM or polytetrafluoroethylene PTFE material is preferably used.

Moreover, it is advantageously possible to provide sealing ring, cast into an annular groove on the external circumference of the piston-valve body made of plastics. In this case, too, the casting preferably takes place at the same time as the manufacture of the piston- valve body so that, in contrast to the known piston valve, no additional assembly step is required to mount the sealing ring on the finished piston-valve body. Preferred materials for the sealing ring are of PTFE plastics with embedded graphite 4 particles as sliding particles, alternatively made of graphite or a fluorine-containing elastomer. Like the materials preferably used for the piston-valve body, these materials are resistant to oil and fuel and also in part to smoke gases and are heat-resistant to an extent which is sufficient for the application on the engine cylinder.

Preferred embodiments of the invention are illustrated in the drawings and will be described below, by way of example. In the drawing:- Figure 1 shows a longitudinal section of a piston valve with a dumbbell- shaped plunger of steel and Figure 2 shows an extract in longitudinal section of a piston valve with a plunger of a different shape from that in Figure 1.

The piston valve 1 shown in Figure 1 can be used for an engine brake device not shown on an internal combustion engine, it being inserted so as to be longitudinally displaceable in an associated receiving bore on the engine cylinder, in the conventional manner described at the beginning, as disclosed in DE 3,428,626 Al, in order to actuate an additional outlet valve located there, by means of the opening of which an engine braking effect is achieved. It is of a rotationally symmetrical design about its longitudinal axis 3 and contains a cylindrical pistonvalve body 2 which consists of PTFE plastics, alternatively of PP or POM plastics. Formed on the external circumference of the piston-valve body 2 is an annular groove 9 in which there is located a cast-in sealing ring of PTFE plastics with embedded graphite particles as sliding particles, alternatively made of graphite or a fluorine-containing elastomer, such as, for example, the elastomers marketed under the brand names Viton and Teflon. On its end face located at the bottom in Figure 1 and facing the additional outlet valve after installation of the piston valve 1 in the associated receiver on the engine cylinder, the piston-valve body 2 is provided with an annular groove 4 which, together with a corresponding face in the receiving bore not shown 11 serves to limit the movement of the piston valve. Whereas the piston- valve body 2 on this end face is open to introduce the valve rod of the additional outlet valve, on the opposite end f ace it is closed by a bottom in which there is located a plunger 6 made of steel C45 or a similar type of steel. The plunger 6 is of dumbbell-shaped design and passes through the bottom of the piston-valve body 2 through the longitudinal centre with the dumbbell axis lying in the longitudinal axis 3 of the piston valve, said plunger terminating on the outside f lush with the bottom of the piston-valve body 2 whereas a contact face 7 is provided on the opposite side, which contact f ace interacts with the valve rod of the additional outlet valve after installation of the piston valve 1.

During operation, the piston valve 1, which is supported after installation resiliently against the bottom of its receiver, is pressurized by a compression force, e.g. by means of compressed air, f rom the outer side of the piston bottom in dependence on the position of the brake pedal, after which it is accelerated in the direction of the valve until the contact f ace 7 of the plunger 6 strikes against the valve rod and subsequently carries the latter along in the longitudinal movement for opening the additional outlet valve. The plunger 6 thus serves as a pressure piece for actuating the valve so that the plastics material of the piston-valve body 2 is not loaded by constantly striking against the valve rod. By means of this measure, the wear of the piston valve 1 remains low. The plastics material f or the piston-valve body 2 is selected such that it has sufficient strength and dimensional stability in order to be able to transmit the occurring forces from and to the plunger 6 and, at the same time, in conjunction with the sealing ring 5 to maintain a permanent seal between the valve chamber on one side and the compressed-liquid chamber on the other side.

The plunger 6, like the sealing ring 5, is cast into or onto the pistonvalve body 2 during the manufacture 6 thereof, i.e. the plunger 6 and the sealing ring 5 are placed in the associated casting mould before casting of the piston-valve body 2 and are then encased by the plastics casting compound of the piston-valve body 2. This guarantees a secure fit of the sealing ring 5 and the plunger 6 in the piston-valve body 2 so that, on the one hand, the forces acting in each case on the plunger 6, in particular when the latter impacts on the valve rod, are reliably transmitted to the piston-valve body 2 and can be absorbed by the latter and, on the other hand, the sealing ring 5 remains securely in its receiving groove 9 while sliding along the wall of the receiving bore.

The selection of materials described above for the piston-valve body 2, the plunger 6 and the sealing ring 5 signifies that the piston valve 1 is resistant to the effect of oil and fuel and to the greatest extent also to smoke gases, such that it has a long service life although it is subjected to these substances due to the respective opening of the additional outlet valve and the thus obtaining connection to the engine cylinder chamber. Additionally, the materials used are heat-resistant to an extent which is sufficient for this application on the engine cylinder.

The implementation of the piston-valve body 2 of plastics instead of the known implementation of steel prevents not only any seizing-up of the piston valve in the case of insufficient lubrication or a tilted position thereof, but moreover reduces the response duration upon actuation since the piston valve 1 formed in this way has a considerably lower weight compared to a design made completely of steel and is therefore accelerated more quickly under the same actuation force. This results additionally compared to the known design in dispensing with an additional assembly step to mount the sealing ring 5 which is now also cast in during the manufacture of the piston-valve body 2 and does not have to be attached subsequently.

In Figure 2, a piston valve 10 is illustrated as an t 7 extract, which piston valve corresponds fully, in terms of the application, form and materials used, to that of Figure 1 apart from the shape of the plunger 61 and the bottom of the piston-valve body 2.' which is of slightly thinner construction. The plunger 61 used here, which likewise consists of steel, has a disc-shaped plate 8 onto whose one side a narrow pin attachment is moulded while a disc-shaped contact plate of smaller radius adjoins on the other side, which contact plate provides the contact face 71 for striking against the valve rod. For this purpose, the plunger 61 protrudes with this contact-face side out of the bottom of the piston-valve body 21 on the valve side whereas the disc plate 8 having the larger diameter and the pin moulded onto it are cast completely into the bottom of the piston-valve body 21. Of course, in this case, too, the plunger 6', like the sealing ring not shown here, is cast in at the same time as the manufacture of the piston-valve body 21 without an additional subsequent assembly step.

For the piston valve according to Figure 2. the same advantages result compared to the known piston valve, as already described above with reference to the piston valve of Figure 1, in particular preventing wear of the pistonvalve body 21 of plastics by mounting the steel plunger 61, saving assembly by casting in the sealing ring during the production of the piston-valve body 21, high resistance and thus long service life due to the material selection undertaken, reliable functioning due to relatively low frictional resistance of the piston-valve body 21 on the metal wall of the receiving bore and avoiding seizing-up of the piston valve 11 in the case of insufficient lubrication or a tilted position and higher response speed due to the weight reduction by designing the pistonvalve body 21 in plastics. In particular, It should be noted as an advantage in relation to this variant that, in this case, the plunger 61 is of comparatively small construction and is thus of relatively low weight, which has a further positive effect on the response speed of the piston valve 11, care being 8 taken due to the specific design of the plunger 61 that it is held securely in the piston-valve body 20 and a reliable transmission or absorption of forces is guaranteed between the plunger 61 and the piston- valve body V.

1 :K 9

Claims

1. A piston valve adapted f or use in an engine brake device on an internal combustion engine, in which the piston valve, f or opening and closing an additional outlet valve provided for an associated engine cylinder, is arranged so as to be longitudinally displaceable in an -associated receiver, wherein - the piston valve is made with a body of a dimensionally stable, heat- resistant plastics material, and the body contains a base of the plastics material, into which a plunger made of steel, which has a contact face for interaction with an actuating rod of the additional outlet valve and at least one radially projecting disc f ace, is cast in such a way that the contact f ace is exposed and the plunger is supported with its radially projecting disc f ace or f aces against the surrounding plastics material of the base in both axial directions on at least one disc face.

2. A piston valve according to Claim 1, wherein the piston-valve body consists of polypropylene, polyacetal or polytetrafluoroethylene.

3. A piston valve according to Claim 1 or 2, wherein a sealing ring, which consists of a plastics material, is cast into an annular groove on the external circumference of the piston-valve body.

4. A piston valve according to claim 3, wherein the sealing ring consists of polytetrafluoroethylene with embedded sliding particles, graphite or a fluorine containing elastomer.

5. A piston valve adapted for use in an engine brake device on an internal combustion engine, substantially as described herein with reference to and as illustrated in the accompanying drawing.