Controlling A Hydraulic Solenoid valve With PWM

[oldnslo]

Npalen,
Canemek site shows a D03 style valve so depending on its coil and armature construction it might respond to PWM signal like a low end non feedback proportional valve. These valves use the PWM to keep the spool dithering slightly so that it will respond quicker to signal. I.e. a body in motion tends to stay in motion concept. I suspect this system will move the valve in pulses of flow by rapidly opening and closing the valve Vs finer metering of a true proportional valve. Depending on cylinder size, flow rate, pulse time and valve response time this system could provide a reasonable level of control for the average person trying to get something close to grade.


I believe the original Spectra Physics systems from 20 or more years ago that were used on large scrapers being pulled by 4 wheel drive tractors used poppet valves and they just cycled them on and off to get the cylinders into position. They claimed accuracy of quarter inch in 1000 feet.

 

[npalen]

Npalen,
Canemek site shows a D03 style valve so depending on its coil and armature construction it might respond to PWM signal like a low end non feedback proportional valve. These valves use the PWM to keep the spool dithering slightly so that it will respond quicker to signal. I.e. a body in motion tends to stay in motion concept. I suspect this system will move the valve in pulses of flow by rapidly opening and closing the valve Vs finer metering of a true proportional valve. Depending on cylinder size, flow rate, pulse time and valve response time this system could provide a reasonable level of control for the average person trying to get something close to grade.


I believe the original Spectra Physics systems from 20 or more years ago that were used on large scrapers being pulled by 4 wheel drive tractors used poppet valves and they just cycled them on and off to get the cylinders into position. They claimed accuracy of quarter inch in 1000 feet.

It appears to be an off-the-shelf 12 VDC open center with A and B ports blocked when spool is centered. I'm trying to get information from Canamek regarding how the valve is controlled. I do know that their control allows for adjustment of the flow rate. It would seem that rapid switching on/off would cause premature spool wear. Hope to find out more from them.

Thanks for your info!

 

[oldnslo]

D03 and proportional valves operate for years on industrial equipment so I would not be to concerned about premature spool wear in this system provided the oil is kept clean.


I suspect the system has flow controls to adjust speed of movement depending on cylinder size.

Curious if Canemek will provide anymore information.

 

[mrmikey]

I've worked with a Rexroth/Bosch system to control plow trucks a few years back. Some functions such as plow, wing, dump body are on/off solenoids they don't use any type of feedback as it's not needed. Other functions such as salt rate and spinner control are proportional as they use a feedback enabled hydraulic motor. In their system which is closed loop, the solenoids use a PWM control and the solenoid is used to control pilot pressure going to each valve section, pilot pressure being around 3-400psi. The solenoids don't directly control the main spools as they don't have enough power, they, solenoids, control the low pressure pilot which in turn is applied to either end of the main spool/s.
So the main spool isn't always 'feathering' for lack of a better word, the only actual feathering is taking place in the solenoid which controls a lower volume of oil.
The reason I was told years ago that the solenoid controls the pilot (other than effort needed) is that a solenoid is either on or off, there's no such thing as an actual proportional solenoid, it may seem that way but by using PWM you're switching it off so many times a second...the frequency escapes me at the moment. By using a feedback loop, you're also compensating for any differences in the solenoid stickion........Mike

 

[npalen]

I've worked with a Rexroth/Bosch system to control plow trucks a few years back. Some functions such as plow, wing, dump body are on/off solenoids they don't use any type of feedback as it's not needed. Other functions such as salt rate and spinner control are proportional as they use a feedback enabled hydraulic motor. In their system which is closed loop, the solenoids use a PWM control and the solenoid is used to control pilot pressure going to each valve section, pilot pressure being around 3-400psi. The solenoids don't directly control the main spools as they don't have enough power, they, solenoids, control the low pressure pilot which in turn is applied to either end of the main spool/s.
So the main spool isn't always 'feathering' for lack of a better word, the only actual feathering is taking place in the solenoid which controls a lower volume of oil.
The reason I was told years ago that the solenoid controls the pilot (other than effort needed) is that a solenoid is either on or off, there's no such thing as an actual proportional solenoid, it may seem that way but by using PWM you're switching it off so many times a second...the frequency escapes me at the moment. By using a feedback loop, you're also compensating for any differences in the solenoid stickion........Mike

That's interesting! I see that spreader controllers are available with ground speed control via GPS. Looks like there would be some salt savings.
Why should I consider Ground Speed Control? | HillTip

Here is a really interesting video on electronic (PWM) solenoid control with a cutaway to show the movement of the spool which has notches in the lands for precise control. It's rather long but can skip ahead as needed:
Proportional Directional Valves: Fun With Electro-Hydraulics - YouTube

 

[mrmikey]

I see that spreader controllers are available with ground speed control via GPS.

Yup although ours are road speed using either an extra pickup off the transmission or tapping into the actual truck circuit. The setup we use, uses a feed back circuit so the gate opening is calculated to get the correct spread rate and the spreader chain speed is adjusted appropriately.

Looks like there would be some salt savings.

Definitely is when you consider we used to use the ole manual hydraulic clock valve:

Problem with that valve is when the truck stops, the spreader keeps going unless the operator stops it, which didn't happen. Also meant you had hydraulic plumbing in the cab which was a real pia to run as there were 2 #12 and 2 #10 lines. Not to mention when you burst a hose it flooded the floor of the truck which was good for preventing rust but not so much for the poor SOB that had to run a new line......Mike

 

[Texasmark]

I'd get some user inputs on reliability of the digital system before I'd jump into it. I don't see a problem with the electronics part of the setup, it would be the solenoid actuator itself and the mechanical aptitude of the actual flow valve mechanics. Having had experience with non "feathered" hydraulic valves in typical high flow/high pressure situations, I can understand that things can go wary if not properly designed and built.

 

[npalen]

Below is the reply I received from Canamek when asking about how the system controls the solenoid valve:

Yes Nelson,
it is called PWM you can adjust number of pulses and the ratio of open/close times to make movements smooth.

It may make the life of the valve a little shorter depending on your hydraulic and your application but we have thousands of users around the world are using it without any negative report on valve please consider some users do land levelling 20 hrs a day in work season with 2 drivers.

you can put the valve speed on maximum and so you will have a simple on/off not PWM.

 

[oldnslo]

Sounds like they allowing adjustments to configure valve open time vs flow rate adjustment to provide an incremental height adjustment similar to operator shaking a joystick handle very rapidly to adjust height

Sounds similar in concept to the old spectra physics systems they just didn稚 use PWM

 

[npalen]

Do you think they are actually controlling the position of the spool "open" to some extent or just varying the timing and duration of full on/off? The reason I ask is that it seems a simple relay could be pulsed at timed intervals and duration to provide controlled on/off. I suppose that the durability of solid state PWM would be better than a relay.