Car electronics question for boffins!!!!
Discussion
A question from my lad and waaaay above me!!
I quote
" I need help with my electronics assignment because I don't understand it.
What are the reasons behind electronic control of wipers, and how do two - speed wiper and intermittent wiper systems operate. Not how they work mechanically, but how they operate electronically. With all the circuits and stuff"
Thanks in advance chaps!
I quote
" I need help with my electronics assignment because I don't understand it.
What are the reasons behind electronic control of wipers, and how do two - speed wiper and intermittent wiper systems operate. Not how they work mechanically, but how they operate electronically. With all the circuits and stuff"
Thanks in advance chaps!
Try googling Intermittent wiper circuit and a bunch of diagrams and explanations come up.
I would have thought the previous link given (CAN bus) is not quite what they are looking for (even if it is how they might be controlled on more modern cars).
https://www.google.co.uk/search?q=intermittent+wip...
I would expect any of the first few image results are about right.
Either a 555 timer controlled one or an analogue one depending on which bit of course they are currently studying.
Bit surprised your lad hasn't stumbled across google yet
Bob
I would have thought the previous link given (CAN bus) is not quite what they are looking for (even if it is how they might be controlled on more modern cars).
https://www.google.co.uk/search?q=intermittent+wip...
I would expect any of the first few image results are about right.
Either a 555 timer controlled one or an analogue one depending on which bit of course they are currently studying.
Bit surprised your lad hasn't stumbled across google yet
Bob
Funnily enough, windscreen wipers are pretty much one of the few electromechanical systems in your car that are still pretty basic and non-smart!
Mechanically, they pass the rotation of permanent magnet, mechanically commutated, motor through a high reduction ratio worm gear, to drive a crank, that converts that rotary motion into reciprocating motion. That linear motion is then passed, usually via stiff tubular rods, to a pair of cranks, that convert it back to a rotary sweeping motion, that pushes the wiper blades through the arc of their travel.
The motor and linkages are a welded/ crimped one peice assembly that bolts into place below the windscreen scuttle panel:
The clever bit is the stopping of the blades / motor in the right place:
Basic systems use a multi contact mechanical switch, that runs on contacts molded into the output crank of the motor:
This is set up so that as the wipers pass through their park position, and if they have been switched off, those switches short the motor across itself, resulting a a strong braking effect, and that causes the motor to stop rapidly and in the right place. If you just turn off the power, the wipers slow down slowly, due to the mechanical inertia of the system, and hence do no stop in the right place (and in fact, where they stop becomes dependent on the frictional conditions between wiper and screen, which changes massively with environmental conditions ie rain!). Outside of the park position a second set of contacts acts in parallel with the wiper switch, to ensure the motor has power provided to it even if the wiper switch is turned off, so ensuring the motor can always reach it's park position and then be stopped at that point.
These old motors used a pair of parallel windings on the rotor to provide the two speed settings. The 'High speed' windings has roughly half as many turns on it as the 'low speed' one, meaning for the same input voltage the motor runs twice as fast. Those windings were selected as appropriate by the position of the wiper switch, that was hardwired to the motor terminals.
Today, increasingly, the direct mechanical contact switching is replaced by solid state electronics, using a pulse width modulated 'Half Bridge' output driver like this: InfineonBTN8962 to control the motor supply voltage and hence its speed.
This also allows for things like motor blocking detection for frozen wiper detection (old systems would just blow the fuse if your wipers were turned on when frozen to the screen). Motors now use a solid state hall effect sensor, reading a magnet embedded in the motor output crank, to tell the power electronics when the wipers have reached their park position, and the control pulse width to the output driver is modulated to provide the necessary motor torque to stop the wiper exactly in the correct place. This can now include different rates of acceleration on starting and stopping to minimise wiper noise and judder (old systems would often clank and judder as they suddenly started or stopped)
Some cars, which have their wipers housed in the A Pilars now have individual wiper motors, connected directly to a single blade, and these are phased to ensure the blades miss each other as they travel through their intersecting arcs. The controller delays starting each motor by just the right amount to phase the motion correctly, and can use a position feed back sensor (toothed wheel) to measure where the wipers are in real time, meaning changes in system friction (water, snow, ice, hto sun wet) don't cause phasing errors and result in the blades crashing together and jamming!
On top of the basic wiping functionality, there now are of course a multitude of higher level control strategies, for time delay (intermittent) and fully automatic wiper control etc. Intermittent wipers started off a very basic time delay relays, that use the charging rate of a large capacitor to provide a fixed delay between triggering a blade sweep. Smarter systems provided control of that delay via a small switch or wheel on the wiper stalk, which effectively was a potentiometer wired to control the flow of current into the delay capacitor. More current meant quicker charging, and a shorter time before the threshold voltage was reached to trigger the relay and a blade sweep event.
Today fully automatic systems use an infrared reflectometer mounted above the interior mirror, within the wiped zone to determine how dirty the windscreen is, and if the wiper should carry out a sweep. They use an small LED (Light Emitting Diode) to shine a beam of infrared light onto the inside on the glass. if the outside of the glass is clean / dry, it acts as a good mirror, and most of the IR light gets reflected back to a LDR (light dependant resistor) sensor. However, if the glass is dirty or wet, it's refractive index changes and a lot of that light is now able to exit the far side of the glass, is scattered away, and hence not reflected back to the sensor. In this way, the cleanliness of the glass can be mapped against the voltage signal returned from the sensor. When the system estimates the screen is too dirty or wet, the system triggers a blade sweep. You'll notice that every time you turn on the autowipers, the system wipes once, no matter what. This is deliberate, and is used to calibrate the thresholds. By wiping the scree, it is ensured it is clean (even if it was clean to start with) and the system them uses the returned light intensity as its 'clean' baseline. If it didn't do this, the system would struggle to cope with changes between individual screens, aging of the glass, and different system tollerances (such as the exact mounting angle of the sensors etc) By doing this 'localisation sweep' the system is self calibrating.
Going forward, the big changes for Wiping systems are:
1) continued cost reduction
2) Reduction in noise during operation (especially for EV's which have very quiet cabins!)
3) System mass and package volume reduction, particularly for reduced aero drag and aesthetic reasons
4) Optimised linkage design, to optimise blade contact, especially on high curvature screen profiles
5) Additional interlinked control logic, with other control modules, including smart lighting systems, GPS, and chassis and powertrain system controllers. Auto systems now use things like vehicle speed, lighting settings and even chassis / vehicle modes to modify how and when they decide to wipe
There you go, and you though windscreen wipers were simple eh!! ;-)
Mechanically, they pass the rotation of permanent magnet, mechanically commutated, motor through a high reduction ratio worm gear, to drive a crank, that converts that rotary motion into reciprocating motion. That linear motion is then passed, usually via stiff tubular rods, to a pair of cranks, that convert it back to a rotary sweeping motion, that pushes the wiper blades through the arc of their travel.
The motor and linkages are a welded/ crimped one peice assembly that bolts into place below the windscreen scuttle panel:
The clever bit is the stopping of the blades / motor in the right place:
Basic systems use a multi contact mechanical switch, that runs on contacts molded into the output crank of the motor:
This is set up so that as the wipers pass through their park position, and if they have been switched off, those switches short the motor across itself, resulting a a strong braking effect, and that causes the motor to stop rapidly and in the right place. If you just turn off the power, the wipers slow down slowly, due to the mechanical inertia of the system, and hence do no stop in the right place (and in fact, where they stop becomes dependent on the frictional conditions between wiper and screen, which changes massively with environmental conditions ie rain!). Outside of the park position a second set of contacts acts in parallel with the wiper switch, to ensure the motor has power provided to it even if the wiper switch is turned off, so ensuring the motor can always reach it's park position and then be stopped at that point.
These old motors used a pair of parallel windings on the rotor to provide the two speed settings. The 'High speed' windings has roughly half as many turns on it as the 'low speed' one, meaning for the same input voltage the motor runs twice as fast. Those windings were selected as appropriate by the position of the wiper switch, that was hardwired to the motor terminals.
Today, increasingly, the direct mechanical contact switching is replaced by solid state electronics, using a pulse width modulated 'Half Bridge' output driver like this: InfineonBTN8962 to control the motor supply voltage and hence its speed.
This also allows for things like motor blocking detection for frozen wiper detection (old systems would just blow the fuse if your wipers were turned on when frozen to the screen). Motors now use a solid state hall effect sensor, reading a magnet embedded in the motor output crank, to tell the power electronics when the wipers have reached their park position, and the control pulse width to the output driver is modulated to provide the necessary motor torque to stop the wiper exactly in the correct place. This can now include different rates of acceleration on starting and stopping to minimise wiper noise and judder (old systems would often clank and judder as they suddenly started or stopped)
Some cars, which have their wipers housed in the A Pilars now have individual wiper motors, connected directly to a single blade, and these are phased to ensure the blades miss each other as they travel through their intersecting arcs. The controller delays starting each motor by just the right amount to phase the motion correctly, and can use a position feed back sensor (toothed wheel) to measure where the wipers are in real time, meaning changes in system friction (water, snow, ice, hto sun wet) don't cause phasing errors and result in the blades crashing together and jamming!
On top of the basic wiping functionality, there now are of course a multitude of higher level control strategies, for time delay (intermittent) and fully automatic wiper control etc. Intermittent wipers started off a very basic time delay relays, that use the charging rate of a large capacitor to provide a fixed delay between triggering a blade sweep. Smarter systems provided control of that delay via a small switch or wheel on the wiper stalk, which effectively was a potentiometer wired to control the flow of current into the delay capacitor. More current meant quicker charging, and a shorter time before the threshold voltage was reached to trigger the relay and a blade sweep event.
Today fully automatic systems use an infrared reflectometer mounted above the interior mirror, within the wiped zone to determine how dirty the windscreen is, and if the wiper should carry out a sweep. They use an small LED (Light Emitting Diode) to shine a beam of infrared light onto the inside on the glass. if the outside of the glass is clean / dry, it acts as a good mirror, and most of the IR light gets reflected back to a LDR (light dependant resistor) sensor. However, if the glass is dirty or wet, it's refractive index changes and a lot of that light is now able to exit the far side of the glass, is scattered away, and hence not reflected back to the sensor. In this way, the cleanliness of the glass can be mapped against the voltage signal returned from the sensor. When the system estimates the screen is too dirty or wet, the system triggers a blade sweep. You'll notice that every time you turn on the autowipers, the system wipes once, no matter what. This is deliberate, and is used to calibrate the thresholds. By wiping the scree, it is ensured it is clean (even if it was clean to start with) and the system them uses the returned light intensity as its 'clean' baseline. If it didn't do this, the system would struggle to cope with changes between individual screens, aging of the glass, and different system tollerances (such as the exact mounting angle of the sensors etc) By doing this 'localisation sweep' the system is self calibrating.
Going forward, the big changes for Wiping systems are:
1) continued cost reduction
2) Reduction in noise during operation (especially for EV's which have very quiet cabins!)
3) System mass and package volume reduction, particularly for reduced aero drag and aesthetic reasons
4) Optimised linkage design, to optimise blade contact, especially on high curvature screen profiles
5) Additional interlinked control logic, with other control modules, including smart lighting systems, GPS, and chassis and powertrain system controllers. Auto systems now use things like vehicle speed, lighting settings and even chassis / vehicle modes to modify how and when they decide to wipe
There you go, and you though windscreen wipers were simple eh!! ;-)
Edited by anonymous-user on Friday 3rd March 16:46
I should have added, on basic mechanically switched motor systems, the wiping speed depends on supply voltage and the level of friction between blade and screen. To ensure wiping speed was as constant as possible, the motors were very under rated in terms of maximum torque output. In effect they were wound to be constant speed motors, with a very low series resistance. Because of that, changes in the dynamic load, and hence motor torque don't result in large changes in in speed (google 'electric motor back EMF' for more on how motors work)
Modern, single winding, pulse width modulated and hence voltage controlled wiper motors are generally closed loop controlled in real time, where the controller uses a position feedback sensor in the motor to measure it's speed, and hence apply precisely the right amount of output voltage to keep the motor at a constant speed through out it's arc (except fo course where specific velocity profiling is used to gradually and smoothly start and stop the blades)
Like most things car related, increasingly mechanical complexity and tuning is being replaced by software optmisation, allowing the same basic hardware to be used in different platforms without being changed, hence allowing for increased economies of scale. Back in the day, each model had it's own motor and linkage design, today the 'one size fits all' approach is king!
Modern, single winding, pulse width modulated and hence voltage controlled wiper motors are generally closed loop controlled in real time, where the controller uses a position feedback sensor in the motor to measure it's speed, and hence apply precisely the right amount of output voltage to keep the motor at a constant speed through out it's arc (except fo course where specific velocity profiling is used to gradually and smoothly start and stop the blades)
Like most things car related, increasingly mechanical complexity and tuning is being replaced by software optmisation, allowing the same basic hardware to be used in different platforms without being changed, hence allowing for increased economies of scale. Back in the day, each model had it's own motor and linkage design, today the 'one size fits all' approach is king!
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