gvcormack@watdaisy.UUCP (Gordon V. Cormack) (01/08/85)
It has been suggested that the valves in an engine be operated electrically rather than by a cam. There is no doubt that such operation could give more nearly optimal valve operation than a fixed cam. The above scheme has been implemented for the purposes of engine testing (I can't remember the reference, it was either PM or C&D or R&T in the last 10 years). The trouble is that the solenoids to operate the valves are tremendously inefficient and consume a significant fraction of the overall output from the engine. On a test bench, this is not a problem. In addition, the electronics must switch a tremendous amount of current to operate the solenoids quickly. Such switches are not cheap. The alternator, battery, etc. on existing cars would also be totally inadequate. If someone could invent an efficient mechanism to control the valves like this, he would indeed have a better mousetrap. I suggest the following compromise: (perhaps it has been investigated, too) use a twin-cam engine where the valve is open if either of the cam lobes is up (the valve operation is the OR of the two cams). Statically, both cams are the same. At increased engine speed, one of the cams is advanced and the other retarded as necessary to get the desired overlap. The device to advance and retard the cams should be feasible as it operates at a much lower speed than that described above. It could be implemented in much the same way as existing hydraulic timing chain tensioners. It is not clear that the extra mechanical complexity is justified, but such a device would give a factor of 2 in adjustment of the valve durations.
jlw@ariel.UUCP (J.WOOD) (01/09/85)
A much better approach would be to use an engine type that doesn't require poppet valves. I would suggest that rotary valves could be used. Still better than this would be to use an engine type that does not require valves at all, the rotary. On Mazda street engines the primary intake is through the side plates of rotor housings. Like a two cycle engine the 'valve' timing is determined by the shape, size, and placement of this hole. Going to a wilder cam in these engines is the mere (:-)) matter of a few minutes with a hand grinder. Some kind of sliding plate over a larger orafice could do the trick for dynamic timing, and it doesn't have to operate at engine speed. The rotary is a true four-stroke cycle engine, not a two stroke. Joseph L. Wood, III AT&T Information Systems Laboratories, Holmdel (201) 834-3759 ariel!jlw
david@tekig.UUCP (David Hayes) (01/10/85)
Recently I've seen an advertisement for a slightly modified hydraulic lifter that enables the use of a higher performance camshaft and still retain some decent low end manners. These lifters had a small groove machined down the side of the inner sleeve. Its purpose was to keep the lifter from pumping up fully until a higher rpm. This keeps the overall valve lift and duration down a little until there is sufficient rpm to keep the lifter full and at maximum lift. Claims include smoother low end running while maintaining high end performance of "hot" cams. Anyone ever try any of these?? I think a set was $89. tektronix!tekig!david
jackh@zehntel.UUCP (jack hagerty) (01/11/85)
> It has been suggested that the valves in an engine be operated > electrically rather than by a cam. There is no doubt that such > operation could give more nearly optimal valve operation than > a fixed cam. > > The above scheme has been implemented for the purposes of engine > testing (I can't remember the reference, it was either PM or C&D or > R&T in the last 10 years). The trouble is that the solenoids to > operate the valves are tremendously inefficient and consume a > significant fraction of the overall output from the engine. > > If someone could invent an efficient mechanism to control the valves > like this, he would indeed have a better mousetrap. This article, and the one suggesting the use of solenoids to operate springless, desmodronic valves, miss the point. What you have to do is separate the energy required to open the valves from the control of that energy. Assuming that we stay with valves opened by engine-driven cams and closed by springs, how can we vary the lift and overlap of the valve timing? Well, as it turns out, the elements of a system to do that have already been marketed although one beat a hasty retreat. For five years now, Alfa Romeo has had dynamic valve timing on their 4 cylinder, twin cam engines. The intake cam can rotate several degrees relative to its drive sprocket. It is set to be fully retarded at low speed to give a smooth idle and good low end torque. It advances to produce a good degree of overlap at high speeds for top end power. Orignally the cam timing was controlled by a govenor but now that they've gone to the new Bosch FI, it's controlled by the same module that controls the spark timing. Cadillac's ill fated "modulated displacement" 4-6-8 engine (marketing wouldn't allow "variable displacement" because of the acronym) had an ingeniously simple method of shutting off the unused cylinders. A solenoid was positioned above the pivot of each rocker arm. If the cylinder was to be "on", the solenoid was extended forcing the rocker onto its pivot and the valve worked normally. If the cylider was to be "off", then the solenoid retracted allowing the rocker arm to "float" with the tip of the arm pivoting on the valve stem. Of course, this represents the "bang-bang" approach to valve lift control: full lift or no lift at all. It seems that a variation on this idea could produce the infinitely variable lift desired. I realize that this postulates a twin cam engine with rocker arms, a rather odious thought to those of us that admire the simplicity of the classic twin cam design. But at least that's much more in the realm of accepted engine design than solenoid-actuated desmodronic valve trains! Jack Hagerty, Zehntel Automation Systems ...!ihnp4!zehntel!jackh
rickb@tekig1.UUCP (Rick Bensene) (01/11/85)
> > > Recently I've seen an advertisement for a slightly > modified hydraulic lifter that enables the use of a > higher performance camshaft and still retain some decent > low end manners. These lifters had a small groove machined down > the side of the inner sleeve. Its purpose was to keep the > lifter from pumping up fully until a higher rpm. This keeps the > overall valve lift and duration down a little until there > is sufficient rpm to keep the lifter full and at maximum lift. > > Claims include smoother low end running while maintaining high > end performance of "hot" cams. Anyone ever try any of these?? > I think a set was $89. > > > tektronix!tekig!david The lifters mentioned in he above article are available from Rhoads. Rhoads has been manufacturing these lifters for quite a few years, and many hot rodders have found them to the best thing since Nitrous Oxide! The Rhoads lifters take a radical cam grind, and transform it into an economical, smooth running, high-bottom end torque grind at low RPM ranges. However, once the RPM's climb, the lifters begin to pump up, and the radical grind of the camshaft becomes apparent in increased top end power. A friend had a 1969 Camaro with a heavily modified LS-6 454. The cam had a very wild grind. It would not idle at anything below around 2000 RPM, and even then, the "idle" would shake the car. This made the car very difficult for street driving (mind you, this was NOT a racecar). After getting tired of either turning over the tires at every light to get away because of the high idle, or having to literally slip the clutch to death to make a "smooth" start, he decided to try a set of Rhoads lifters. I believe the set cost him around $90 or so. The difference was very impressive. The engine would idle fairly smoothly at around 1100 RPM. There was still a little lope, and the engine still sounded real healthy, but it's low-end manners were drastically improved. Bottom-end torque increased dramatically, and the top end suffered little, if at all. Rhoads lifters are *hydraulic* lifters... if your cam is ground for solid lifters, it would probably not work too well if you put Rhoads lifters in in place of the solids. If you've got a hot hydraulic grind cam, Rhoads lifters are the way to go. If you're looking for Rhoads lifters, I believe that they are sold DIRECT from Rhoads. You can find ads for them in the back of any good hot-rod type magazine, such as HOT ROD, CAR CRAFT, SUPER CHEVY, or the like. Rick Bensene ..tektronix!tekig1!rickb Phone: Weekdays: (503) 627-3559 BBS (24 hours): (503) 254-0458 USnail: Rick Bensene/Tektronix, Inc./Mail Stop 39-170/P.O. Box 500/Beaverton, Oregon/97077 Baseball, Hot-Dogs, Apple Pie, and CHEVROLET!
gvcormack@watdaisy.UUCP (Gordon V. Cormack) (01/12/85)
> > It has been suggested that the valves in an engine be operated > > electrically rather than by a cam. There is no doubt that such > > operation could give more nearly optimal valve operation than > > a fixed cam. > > > > The above scheme has been implemented for the purposes of engine > > testing (I can't remember the reference, it was either PM or C&D or > > R&T in the last 10 years). The trouble is that the solenoids to > > operate the valves are tremendously inefficient and consume a > > significant fraction of the overall output from the engine. > > > > If someone could invent an efficient mechanism to control the valves > > like this, he would indeed have a better mousetrap. > > This article, and the one suggesting the use of solenoids to operate > springless, desmodronic valves, miss the point. What you have to do > is separate the energy required to open the valves from the control > of that energy. > > Assuming that we stay with valves opened by engine-driven cams and > closed by springs, how can we vary the lift and overlap of the valve > timing? > > Well, as it turns out, the elements of a system to do that have already > been marketed although one beat a hasty retreat. For five years now, > Alfa Romeo has had dynamic valve timing on their 4 cylinder, twin cam > engines. The intake cam can rotate several degrees relative to its drive > sprocket. It is set to be fully retarded at low speed to give a smooth > idle and good low end torque. It advances to produce a good degree of > overlap at high speeds for top end power. Orignally the cam timing was > controlled by a govenor but now that they've gone to the new Bosch > FI, it's controlled by the same module that controls the spark timing. > > Cadillac's ill fated "modulated displacement" 4-6-8 engine (marketing > wouldn't allow "variable displacement" because of the acronym) had > an ingeniously simple method of shutting off the unused cylinders. > A solenoid was positioned above the pivot of each rocker arm. If the > cylinder was to be "on", the solenoid was extended forcing the rocker > onto its pivot and the valve worked normally. If the cylider was to > be "off", then the solenoid retracted allowing the rocker arm to "float" > with the tip of the arm pivoting on the valve stem. > > Of course, this represents the "bang-bang" approach to valve lift > control: full lift or no lift at all. It seems that a variation on > this idea could produce the infinitely variable lift desired. > > I realize that this postulates a twin cam engine with rocker arms, a > rather odious thought to those of us that admire the simplicity of > the classic twin cam design. But at least that's much more in the realm > of accepted engine design than solenoid-actuated desmodronic valve trains! > > Jack Hagerty, Zehntel Automation Systems > ...!ihnp4!zehntel!jackh It is not I who missed the point. First, the thing that is difficult to vary with a cam is the duration of the valve opening. It is not clear that varying the timing is all that desirable without extending the duration. Second, I did suggest a cam-operated scheme that was able to achieve this. It looks like many of the components from the Alfa system you describe would be applicable. Third, I never suggested that valve lift should be modulated. I think it is more reasonable to consider the Cadillac system as bang-bang control over valve duration. If the intake valve duration could be controlled precisely, the intake valve could be closed when there was enough air/fuel in the cylinder for the desired power. Such a scheme could eliminate throttling and its inherent losses. I would like to make a couple of semantic points. First, I don't know what "desmodronic" means, and neither does my OED. Second, I have long been on a campaign to stamp out the use of the phrase "infinitely variable" for "continuously variable". In this context I am not really complaining, but the term first started to irk me when manufactures of electric ranges began to tout them as having "infinite heat" controls. To get back to the point at hand, I believe there are many interesting things one might do with a different mechanism to control the valves (whether with or without a cam). And I do not believe that this newsgroup is a forum only for "accepted engine design". Gordon V. Cormack, University of Waterloo gvcormack@watdaisy.uucp gvcormack%watdaisy@waterloo.csnet
phil@amdcad.UUCP (Phil Ngai) (01/12/85)
I would appreciate it if people who follow up to articles edit the included text. It makes a big difference at 1200 baud. > I would like to make a couple of semantic points. First, I don't > know what "desmodronic" means, and neither does my OED. Second, desmodronic simply means instead of a spring and a cam/rocker arm, the valve is pushed in both directions, in and out. This would seem more efficient for direct solenoid operation, although as Jack points out, there are many other ways to operate valves. I was actually thinking about using a rotating sphere with a cylinderical hole perpendicular to the axis of rotation as a valve. I can see problems with lubrication, however. Any comments on this? -- AMD assumes no responsibility for anything I may say here. Phil Ngai (408) 749-5790 UUCP: {ucbvax,decwrl,ihnp4,allegra}!amdcad!phil ARPA: amdcad!phil@decwrl.ARPA
jackh@zehntel.UUCP (jack hagerty) (01/15/85)
> > I realize that this postulates a twin cam engine with rocker arms, a > > rather odious thought to those of us that admire the simplicity of > > the classic twin cam design. But at least that's much more in the realm > > of accepted engine design than solenoid-actuated desmodronic valve trains! > > > > Jack Hagerty, Zehntel Automation Systems > > ...!ihnp4!zehntel!jackh > > > I would like to make a couple of semantic points. First, I don't > know what "desmodronic" means, and neither does my OED. Second, > I have long been on a campaign to stamp out the use of the phrase > "infinitely variable" for "continuously variable". In this context > I am not really complaining, but the term first started to irk me > when manufactures of electric ranges began to tout them as having > "infinite heat" controls. > > To get back to the point at hand, I believe there are many interesting > things one might do with a different mechanism to control the valves > (whether with or without a cam). And I do not believe that this > newsgroup is a forum only for "accepted engine design". > > Gordon V. Cormack, University of Waterloo > > gvcormack@watdaisy.uucp gvcormack%watdaisy@waterloo.csnet Well my goodness, I didn't mean to step on anyone's toes! I just wanted to make the point that solenoid-actuated valves seem unworkable while solenoid *controlled* valves have already made it to production, albiet briefly. I guess we're even because I don't know what OED means. Desmodronic (the spelling may be off) refers to a valve system where the cam (or other acuator) closes the valve as well as opening it. Valve float is impossible since the valves are forced closed. Mercedes used such a system on the 300 SLR. I don't know if it was used on the production cars. I agree with your semantic objections so I'll just consider this a literary slap on the wrist. Finally, I don't want to restrict anyone's freedom to post new and/or unusual ideas. It's just that, as we all know, if you want an idea to get anywhere near production, it can't stray too far from established practice. Even then, and the Cadillac engine is again a good example, there's no guarentee that it will last for long. Pity. - Jack Hagerty, Zehntel Automation Systems ...!ihnp4!zehntel!jackh
jackh@zehntel.UUCP (jack hagerty) (01/15/85)
> I was > actually thinking about using a rotating sphere with a cylinderical > hole perpendicular to the axis of rotation as a valve. I can see > problems with lubrication, however. Any comments on this? > -- > > Phil Ngai (408) 749-5790 > UUCP: {ucbvax,decwrl,ihnp4,allegra}!amdcad!phil > ARPA: amdcad!phil@decwrl.ARPA This sounds like a variation on the sleeve valve. This is an arrangement where the intake and exhaust ports are not in the cylinder head, but rather are holes near the top of the cylinder wall. A slowly rotating sleeve with matching holes surrounds each cylinder, hence the name. As the sleeve rotates, the holes are alternately covered and uncovered providing the valving action. This, as someone has already pointed out, is very similar to the way the valving on a rotary (Wankle) works. Advantages of this design are quiet operation (no valve clatter), low valve actuation energy (no recipricating masses and, since the sleeve can have many holes, it can rotate at only a fraction of engine speed) and fewer moving parts. Disadvantages are uneven cooling (water jackets can go only part way up the cylinder), poor sealing between the cylinder/valve sleeve/intake- exhaust ports causing a high amount of blow by and lubrication problems. The design was used by several high powered aircraft engines during WWII. The only automobile of any significance to use it was the Knight in the teens and twentys. Due to its quiet operation, the engine was called, I kid you not, the Silent Knight. -- Jack Hagerty, Zehntel Automation Systems ...!ihnp4!zehntel!jackh
rs55611@ihuxk.UUCP (Robert E. Schleicher) (01/18/85)
For people who've been wondering what the term "desmodromic" (sp?) means, it's a term that's been used in Road and Track articles (in particular, one describing the engine used in 1930's Mercedes-Benz Grand Prix cars) in which there are no valve springs to return the valves to a closed position. Instead, some form of positive return action is used. In one variant, a separate cam lobe is used to close the valve. This implies two cam lobes per valve, perhaps on separate shafts. In another theoretically possible variant, the cam lobe has a slot in it through which the end of the valve stem "travels" as the cam shaft rotates. Thus, the valve is both "pushed" and "pulled" by the cam lobe, rather than being pushed by the cam lobe and pushed back by a spring. In theory, desmodromic valve operation should allow higher RPM operation without valve float, although there is a complexity penalty. Bob Schleicher ihuxk!rs55611
davew@shark.UUCP (Dave Williams) (01/21/85)
The famous 300SL gullwing coupe built in the mid 50's by Mercedes-Benz had a 3 liter 6 cylinder engine with desdromic valve gear. As I recall, it had a cam lobe to open the valve and another one to close it. I also recall it had a very light weight valve spring to help seal the valve in its seat. The whole engine was laid over about 30 degrees so it would fit under the low hood. It also had timed fuel injection.
lrd@drusd.UUCP (DuBroffLR) (01/24/85)
Ducati motorcycles have been using desmodromic valves for years (although this is not a camless operation). Their claim to fame among sporting riders, and road racers is NOT engine power, but outstanding handling.