Cam Follower Maths

[Charles P]

Does anyone have a mathematical approach to calculating the lift impact of different radius cam followers?
I can probably interpolate something from measurements that I've made but was wondering if someone smarter than me has a proper solution.

Charles

[Bob Culver]

Hi Charles

Dunno what your level of knowldge is but...I have an ancient textbook which is far far smarter than me;

You can compare  stresses one form to another, assuming eveything is rigid! on the lift flank

accel= w sqd (rbase+rfollower) (1+2tansqdA)/cosA  where w is angular vel in radians, A is angle turned past tangent opening point.
With a flat follower theoretical accel is infinite......

When I was supposed to be digesting this stuff eons ago, if they had related it to Sevens i might have absorbed some of it at the time and not just 55 years later!

Too late in the day here to sort out proper symbols.

The critcal point is intial lift where accel just wsqd(rb +rf)

(for others, all else equal, loading is proportional to accel)

[geoffharrison]

Charles , will PM you later today with the info I have from Keith Dixon on the Worden engine camshaft/followers .
All still relevant without computers !
Geoff

[Charles P]

Bob

I have velocity and its derivatives worked out already but thanks anyway

Geoff

Sounds very useful - thanks.
Your car went well at Loton (especially with Greg driving!)

Best wishes

Charles

[geoffharrison]

Thanks Charles , yes it always goes well with Greg driving , permanently seconds ahead ! Must be an age thing.
Will probably take NV316 the de Villiers car , to VSCC Prescott long for an airing.
Geoff .

[Steve Jones]

Like Geoff's car, mine went well at Loton too. Also, like Geoff, it goes best when the younger generation's driving it!! However, in my case, my younger generation won't be at long Prescott as he's had a better offer at Spa so I can guarantee he won't beat me for once.

Sorry for the thread drift, Charles.

Steve

[Charles P]

Like Geoff's car, mine went well at Loton too. Also, like Geoff, it goes best when the younger generation's driving it!! However, in my case, my younger generation won't be at long Prescott as he's had a better offer at Spa so I can guarantee he won't beat me for once.

Sorry for the thread drift, Charles.

Steve

Both sadly and fortunately neither of my sons are interested in cars so at least I can't be embarrassed by them. I have to do it myself. 

C

[Special Bits]

Does anyone have a mathematical approach to calculating the lift impact of different radius cam followers?
I can probably interpolate something from measurements that I've made but was wondering if someone smarter than me has a proper solution.

Charles

Hi Charles

Funnily enough I had been pondering this myself, but haven't got beyond the going to sleep thinking about it stage yet. 
My thought, entirely untested by any means, is that the flatter the follower the earlier and later the valve will open. I'm wondering about using that to create scatter cam timing on the inlet valves to mitigate charge robbing. I'm also wondering if it would be possible to grind the follower asymmetrically. As I say this is just idle moment, mind wander at the moment.

Stuart Palmer

[Charles P]

You can't change the actual opening times with different radius followers but you can alter the rate of opening, and therefore the volume of charge that can flow at low angular movements, albeit at the cost of higher valve train acceleration and therefore loading. Assymetic followers do exist and are really a way of compensating for the limitations of regrinding a cam onto a pre-existing profile.

Charles

[Special Bits]

You can't change the actual opening times with different radius followers but you can alter the rate of opening, and therefore the volume of charge that can flow at low angular movements, albeit at the cost of higher valve train acceleration and therefore loading.  Assymetic followers do exist and are really a way of compensating for the limitations of regrinding a cam onto a pre-existing profile.

Charles

Right, thanks Charles, my idle mind wanderings are often flawed!

---

You can't change the actual opening times with different radius followers but you can alter the rate of opening, and therefore the volume of charge that can flow at low angular movements, albeit at the cost of higher valve train acceleration and therefore loading.  Assymetic followers do exist and are really a way of compensating for the limitations of regrinding a cam onto a pre-existing profile.

Charles

Yes, just reimagining what's going on, you could potentially have the cam applying all of the lift in very few degrees indeed. The loads would be horrendous! I can see why the advice was always to maintain a radius. Maybe a flatter side could be used to shut the valve quickly, but then you need to keep it on its seat! Oh dear, I must stop pondering things that have already been pondered for 80 years! ha ha