I'm currently playing about with some wiper system designs, and there's a type of wiper that I don't have any information about - wrap-over wiper systems.
These are the wipers which have spindles at the lower corners of the screen, and the wipers move from being parked nearly horizontally to being almost vertical at the screen edges. The area in the middle of the screen is wiped four times per cycle, twice by each wiper, while outside this "overlap" zone, only the twice as per a usual wiper.
The numbers I'm after are the distances;
1) between the 2 main spindles or pivots
2) between each main pivot and the wiper attachment point to the arm
3) the wiper length
and the model of car.
I'm not sure which cars have this type of wiper, and for a whole number of reasons, I'd rather not lurk around in public car parks with my tape measure! - if any backroomers have a car with this type of system, and are kind enough to post the numbers, they would be very helpful to me.
Many thanks,
Number_Cruncher
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I can only help with the model. Pretty sure the Zafira (and a few other people carriers, Ford Galaxy for example?) have this type of design.
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>>...For a whole number of reasons, I'd rather not lurk around in public car parks with my tape measure! -
A quick wander by might identify the vehicles with such wipers and then you could concentrate on such models elsewhere.
An alternative might be a non franchised car lot.
All that remains is to convince a spotty salesman that " I am researching windscreen wipers" ;-)
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I have just remembered that these type of wipers are often called "clap hands".
Try a Google search with "windscreen wipers" and "clap hands"
The results will at least short circuit some of the identification process.
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Sorry I can't help with the dimensions, NC, as I no longer have a car with clap-hands wipers. But if you're designing a set-up, you could make a great contribution by ensuring that they can be adapted to both RHD and LHD with mimimum expense.
Citroen can manage it with the Xsara Pcasso, but my late, unlamented Mercedes B-class not only had the passenger's wiper on top in the park position, thus enabling it to wipe nearer to the A-pillar than the driver's wiper; it was also longer and swept a greater area than the driver's. A disgrace in a car costing over £20,000.
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Toyota Previa has this design - i'll get the tape measure out tonight.
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Thanks all. (Norm - I'm still interested in the dimensions, if you can take the measurements, it would be helpful to me)
To clarify, the system I'm asking about looks like that on this Smart Car.
www.flickr.com/photos/nickythecap/219983951/
To put my work into context, I'm not designing a wiper system for a car company, actually, I'm playing around with writing some basic code to do linkage design and stressing for another (much lower volume!) application.
Short of the amazing Mercedes single wiper systems as fitted to W124s, the wrap-over wipers are among the most complex in terms of their linkage design. For the sake of my own curiosity (and potentially to see if my work can be re-used in another technical field) I want to see if my software will enable me to design and analyse a wrap-over system that's not too far removed from a real system, hence my plea for some basic real life dimensions.
Number_Cruncher
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I thought this linkage stuff was obsolete.
The new S-Max & Galaxy have a motor per spindle.
The bad news is that you cannot change just one motor plus a lot more complex servicing procedure.
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I thought this linkage stuff was obsolete. The new S-Max & Galaxy have a motor per spindle.
You are 100% correct:
www.bosch.co.uk/content/language2/html/3492_4530.h...m
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1) between the 2 main spindles or pivots
1470mm - difficult to measure because the air intake grille is in the way.
2) between each main pivot and the wiper attachment point to the arm
750mm
3) the wiper length
650mm
and the model of car.
Citroen C8
Hawkeye
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Stranger in a strange land
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1) - 1330mm
2) - 600mm RHS 550 LHS
3) - 710mm
1990 Toyota Previa (UK 2.4cc petrol spec not an import)
nb the LHS wiper on this model has an additional 'brace' which is 500mm long on a 60mm pivot arm each end above the main arm, later models do not have this addition.
there is only one motor with linkages.
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Spindles are 1258mm between centres
Pivot/Wiper attachment distance is 650mm
Wiper length 810mm for the top wiper and 760mm for the bottom
This is for a Citroen C4
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Doh!
Citroen C4 Grand Picasso which has the wall of glass windscreen
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Many thanks all.
I'll plug the numbers in, and see if my sums work!
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Two wiper motors! Under electronic control for phasing! What profligacy! It's hardly an 'elegant' engineering solution.
Number_Cruncher
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Presumably you're using stepper motors to avoid complicated linkages, if you had bell-cranks on each end of the spindles and on one motor this would work?
Each wiper travels through an approximate 90 degree arc and back so roughly a quarter of a turn each way at the motor
I just know I've over-simplified this but I'm now intrigued?
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There is surely nothing new or very clever about these wipers. I wish I could remember which were the cars I remember as a child in the 50s that had wipers like this - could it have been a Ford Consul or a Standard Vanguard? I used to watch the wipers very carefully, convinced that they were going to clash, but miraculously, each time, they didn't.
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Got it - Mercedes 220 fintail wipers have about a foot of overlap when parked flat, tucked down at the foot of the windscreen.
The early Vauxhall Crestas and Wyverns also sweep inwards, but only overlap by a few inches, so are not so exiting.
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Cliff, Malcolm,
Yes, at first sight, these wrap over wipers are simple.
Wipers like on split screen Morris Minors were laid out like this, but there was no overlap area - it is the overlap that provide the complication.
But, once there's some overlap, the timing is very important to avoid a clash. If they simply set off at the same speed, they will clash.
So, taking the timings relative to the upper arm, initially, the lower arm must move more slowly, to avoid a clash. When the upper arm has moved far enough to make a clash impossible, the lower arm must then accelerate, and move quicker than the upper arm if they are both to be at the top of the screen at the same time. When they come back down, a similar phasing is needed.
This can be done mechanically, using an extra four bar linkage, and this is the system I'm playing about with. My code currently has the ability to analyse two inter-linked four bar linkages, I just need to mess about with it a bit to deal with this geometry - a job for the weekend I think!
Number_Cruncher
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Yes, I see the problem, and I am not sure how those early examples achieved it - presumably by the mechanism you describe. Photos I have found of the Mercedes show the two wipers folded down flat on top of each other, so obviously the mechanism must as you say ensure that the upper blade immediately starts off fast than the lower. Especially so, in fact, because the point of contact of the fast-moving tip of the lower blade would contact the slower-moving mid-point of the upper one.
Couldn't this be achieved by means of eccentric drives on each spindle, or alternately by cranks starting at different points in their rotational cycle? Looking at the way it works on my Volvo, the motor rotates at constant speed turning a crank, but the other end of the link turns a larger crank so its motion is only backwards and forwards. But its rate of sweep is not constant because the motor crank when at 90 degrees to the link makes a greater movement than it does at the end of its stroke (TDC).
I don't know why it needs to do this on the Volvo because the wipers move in the ordinary way. The second wiper merely reproduces that of the first. But if it had a separate crank set up in reverse, and suitably staggered in its cycle, perhaps with a different length crank, wouldn't it be a simpler way of achieving the desired effect of a staggered start but catching up, then lagging again, in the full cycle?
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On further reflection, it needs a single crank on the motor, but with two rods, one going to similar but longer cranks on each wiper spindle. One of these is "underslung" so that it moves in the opposite sense.
If the crank on the upper parked blade has its crank at 90 degrees to its rod, but the lower one say at 45 degrees to its own rod, then the upper wiper will initially move much faster then the lower. The other will however catch up as its crank in turn approaches 90 degrees, but then slow down earlier on the return stroke in order to let the lower blade streak ahead.
The degree of "advance" could obviously be fine-tuned in order to achieve the desired degree of clearance between the blades.
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I've not got as far as finishing the wrap-over wipers, but here's a screenshot of my code's simulation of a pantograph wiper as fitted to a train.
web2k.co.uk/fullsize.php?im=1193003229
Number_Cruncher
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