Modifying Real Time 4wd

[frehau]

After reading a test of the 2007 CR-V's ability to get up a snowy hill, I was not too impressed. It was the only vehicle not able to overcome the test hill, and was standing still with only one wheel spinning. Other cars in the test were: Toyota Rav4, Suzuki Grand Vitara, Chevrolet Captiva, Hyundai Santa Fe and BMW X3.

So having red up on the real time 4wd system, it seems to me that it should be possible to modify it so that you can have a switch to activate on the dash when you want the rear wheels engaged.

The question is, has anyone done this?

[OSX2000]

RealTime 4WD is a purely mechanical system, no electronics involved. So, short answer, no.

[tsmithvt]

After reading a test of the 2007 CR-V's ability to get up a snowy hill, I was not too impressed. It was the only vehicle not able to overcome the test hill, and was standing still with only one wheel spinning. Other cars in the test were: Toyota Rav4, Suzuki Grand Vitara, Chevrolet Captiva, Hyundai Santa Fe and BMW X3.

So having red up on the real time 4wd system, it seems to me that it should be possible to modify it so that you can have a switch to activate on the dash when you want the rear wheels engaged.

The question is, has anyone done this?

It is not possible to have one wheel spinning unless something broke or it was a FWD CR-V. I'm going to assume that nothing was broken and that the testers were not using a 2WD machine. If the RT4WD system was working properly, a minimum of two wheels were spinning. A wheel, probably on the other side of the CR-V, was spinning where you could not see it. Now it comes down to locking differentials and tires. The CR-V is not offered with LSDs or lockers. They cost extra money and are not something that the typical CR-V buyer would opt for. Not sure but I'm betting that price wise, the CR-V is at the bottom end of vehicles tested, particularly the BMW. The tires supplied with the CR-V (primarily Bridgestone) are not known for their winter prowess and we hear that frequently in this forum. Tires, however, are something CR-V owners can easily do something about. With decent winter rubber the CR-V becomes as sure footed as any cross-over on the market and we hear that all the time in this forum also.

Your real question was about mods to the RT4WD system to manually engage it. If you have seen the hydraulic schematic, you understand that the system is not as simple as two pumps, and using the differential pressure generated during wheel slip to engage a clutch pack. Actually making the system work reliably, smoothly and in a variety of situations is akin to making an automatic transmission work reliably, smoothly and in a variety of situations. It takes balance circuits, a modulating circuit, a relief valve and carefully sized orifices. Bottom line is: Of course it could be done but if it were easy or cheep, the after-market or Honda would probably be offering it. It does not seem to be a "Do-It-Yourself" mod unless you have a great deal of time and money.

[Davecr-v]

Again I see it as a fault with the CR-V the vehicles ambition was to get rid of all the confusing drivetrain slections i.e. 4H 4L Honda wanted to make an urban practical SUV with nothing to worry about. 4WD that kicked in when you needed it seems great, however, there are time I would like to have a 4WD lock button that made the 4 wheels have power at all times it would be very helpful in deep snow and starting out of ruts without having to burn up the front tires. The Problem with most 4wd are they are 2 wheel drive most of the time, however, they are commonly rearwheel drive which is fine in everyting but bad weather, but if you turn and leave on the 4HI you cack the transfer case, the benefit of the Honda system is it is a Front Wheel Drive system allowing good traction in poor conditons without VSC, or TSC and it still saves fuel.

[2RedV's]

That "test" is a joke. They did not want the CR-V to make it. Many people have posted comments on this in multiple forums on the net. If they wanted the CR-V to make it up the hill, they would have kept their foot on the throttle, not let off. The system kicks in when the fronts are slipping, even ever so slightly. If you let off on the throttle, that means that the rears don't get torque. I got stuck once last year in snow. It was a blizzard and I was trying to get home in 50+mph winds. This was in "middle of nowhere" country. I went 2 miles thru drifted hard packed snow that between 6 and 24 inches deep at spots. I got stuck when the V finally high-centered about 100 yards into a section that was 3+ feet deep. Two 4x4 trucks were afraid to come anywhere near me to pull me out. Both drivers kept asking me how I made it that far. I eventually got pulled out by a County road grader with a V snow plow. He said the same thing. "How did you ever make it this far?"

How did I? I kept my foot on the gas big time to keep the rears engaged as much as possible. i also kept the tranny in 1st gear.

[frehau]

The Rav 4 and Suzuki Grand Vitara are cheaper than the Cr-v, the rest are more expensive. The test was done with a 4wd V, you can't get the 2wd in Norway. I don't think the test was a joke, as the magazine is a pretty serious one ("Motor" a Norwegian one). However, how they got it to spin on one wheel only is a mystery to me, and it coud offcourse be a matter of crappy tires that made it flunk the test. Anyway, it's reasuring to hear some of your experiences, and I can't wait to pick up my new CR-V 2,2 CDTi exec. on Tuesday. I can promise you that it will be tested exstensively when the snow starts falling!

Another Q: If you are going down a steep slippery road/hill with a manual tranny in a low gear to use the engine to control your speed, will it just bite on the front wheels? If you know what I mean?

[tsmithvt]

The Rav 4 and Suzuki Grand Vitara are cheaper than the Cr-v, the rest are more expensive. The test was done with a 4wd V, you can't get the 2wd in Norway. I don't think the test was a joke, as the magazine is a pretty serious one ("Motor" a Norwegian one). However, how they got it to spin on one wheel only is a mystery to me, and it coud offcourse be a matter of crappy tires that made it flunk the test. Anyway, it's reasuring to hear some of your experiences, and I can't wait to pick up my new CR-V 2,2 CDTi exec. on Tuesday. I can promise you that it will be tested exstensively when the snow starts falling!

Another Q: If you are going down a steep slippery road/hill with a manual tranny in a low gear to use the engine to control your speed, will it just bite on the front wheels? If you know what I mean?

Not real sure what you mean but..... Weight transfer will always concentrate the braking load on the front wheels assuming you are going forward. This is a fact of life and physics. The RT4WD System will not react to front wheel slippage as it does under acceleration. The system is hydraulically biased to not engage when braking while going forward. This allows the ABS to do its thing. 4WD is not much of an advantage going down hill anyway. The biggest influence will be your skill and common sense. It sounds like you have a handle on that one ("tranny in low gear to use the engine to control your speed"). Short answer: No it won't "just bite on the front wheels" but it sure will concentrate the braking load there.

[2RedV's]

Here are a couple of youtube videos of CR-V's in snow.

http://www.youtube.com/watch?v=AtOs_SeKEyc&mode=related&search=

http://www.youtube.com/watch?v=FOWvb-skBU0&NR=1

http://www.youtube.com/watch?v=q6qxbyUlRz4&NR=1

Note how the V in the 3rd video is a manual tranny and the owner is bouncing it off the rpm limiter with no issues.

[frehau]

Not real sure what you mean but..... Weight transfer will always concentrate the braking load on the front wheels assuming you are going forward. This is a fact of life and physics. The RT4WD System will not react to front wheel slippage as it does under acceleration. The system is hydraulically biased to not engage when braking while going forward. This allows the ABS to do its thing. 4WD is not much of an advantage going down hill anyway. The biggest influence will be your skill and common sense. It sounds like you have a handle on that one ("tranny in low gear to use the engine to control your speed"). Short answer: No it won't "just bite on the front wheels" but it sure will concentrate the braking load there.

Yeah, you're right. I wasn't thinking straight. You see, I'm used to my old 4x4's (Jeep cherokee, Toyota Hilux) with rear wheel/ 4wd and they have no ABS so I'm used to not using the brakes while decending, only using the gearbox and rpm's to control my speed. And with those cars 4wd is a must while going downhill. I guess I can use the brakes a bit more now with the ABS keeping the wheels from locking up.

OSX2000: Even though it's a hydraulic/mecanical system does not mean that it can't me modified. We landed on the moon quite a few years ago (well, to be fair, you did... ha ha) so modifying is a matter of money.:)

Davecr-v: I agree, it would be handy to have that possibility in some cases, thats why I started this thread. And not to confuse people they could have made it an option.

[OSX2000]

OSX2000: Even though it's a hydraulic/mecanical system does not mean that it can't me modified. We landed on the moon quite a few years ago (well, to be fair, you did... ha ha) so modifying is a matter of money.:)
That's why I prefaced my answer of no with "short answer". With enough money, and enough know-how, absolutely anything can be accomplished. But it has been widely discussed before, and the general consensus is that it just wouldn't be worth all the effort.

[cwalti]

Q: If you are going down a steep slippery road/hill with a manual tranny in a low gear to use the engine to control your speed, will it just bite on the front wheels? If you know what I mean?

I know exactly what you mean... Any speed differential between the front and the rear axle will cause the double pump system to cause a pressure differential that in turn will engage the clutch plates. With the earlier single pump it would not but the double pump will engage the rear wheels when the front wheels lock up. However there is a provision, read in the owners manual, where the system will NOT cause a locked up set of front wheels to be powered ahead, or overpowering the brakes. If I recall right I saw a solenoid in the hydro diagram where the over-pressure and over-heat relief valve is, - it may be opening in certain such conditions...

[cwalti]

Yeah, you're right. I wasn't thinking straight. You see, I'm used to my old 4x4's (Jeep cherokee, Toyota Hilux) with rear wheel/ 4wd and they have no ABS so I'm used to not using the brakes while decending, only using the gearbox and rpm's to control my speed. And with those cars 4wd is a must while going downhill. I guess I can use the brakes a bit more now with the ABS keeping the wheels from locking up.

OSX2000: Even though it's a hydraulic/mecanical system does not mean that it can't me modified. We landed on the moon quite a few years ago (well, to be fair, you did... ha ha) so modifying is a matter of money.:)

Davecr-v: I agree, it would be handy to have that possibility in some cases, thats why I started this thread. And not to confuse people they could have made it an option.

I have not taken a look at the actual hardware BUT if a portion of the one pump's oil wer to be diverted and NOT sent into the second pump as is the case under normal operation one would fool the system into 'thinking' that there is wheel spin / slip and the resulting pressure differential would compress the clutch pack. If there is a way to tap into one pump circuit a solenoid could drain a portion of that oil right back into the sump...

[Davecr-v]

I have not taken a look at the actual hardware BUT if a portion of the one pump's oil wer to be diverted and NOT sent into the second pump as is the case under normal operation one would fool the system into 'thinking' that there is wheel spin / slip and the resulting pressure differential would compress the clutch pack. If there is a way to tap into one pump circuit a solenoid could drain a portion of that oil right back into the sump...

Maybe you have a point there, however, you have the fact that this car isn't built to have Permanent AWD so maybe you get the same cracking the transfer case issue my advice buy a truck where you have a selective AWD format much better than trying to fit it on a car already designed.

[tsmithvt]

As I said in my first response in this thread, this mod might be more complex than it appears on the surface. The RT4WD System is an evolved and carefully thought out system. To get it to operate smoothly and as desired in different situations has required more than two pumps and a clutch pack.

The RT4WD System operates in six distinctly different modes: 1) Accelerating forward - 2) Normal (2WD) operation, forward - 3) Decelerating (braking), forward - 4) Accelerating in reverse - 5) Normal (2WD) operation in reverse and 6) Deceleration (braking) in reverse. No two modes are the same. The flow paths and circuit pressures are different for each mode. One might expect Modes 2 and 5 to be the same but they are not because the pumps are turning in the opposite direction and the flow reverses. A flow reversal creates a different reaction because of where the valve body/cluster is placed in the overall circuit. This valve body/cluster is in the "return" side of the circuit when the system is operating forward. (There is no real "return" side because it's a reversing system. It's titled "return side" because it has to be named something.)

The simplest mode is #1. When accelerating forward the system operates as most car magazines describe it. Front wheels slip - front pump turns faster than rear pump - surplus flow (volume) generated by front pump is diverted to clutch pack engaging it - torque flows to rear wheels. Mode #2 is also as most articles explain it. Front and rear pumps turn at the same speed - no surplus flow is generated - no clutch engagement - 2WD. Mode #3 is where it gets interesting. When decelerating forward under normal conditions, the deceleration is not sufficient to generate large amounts of wheel slip (slip rate under ~10%). The RT4WD System will generate small amounts of clutch engagement but not much. When decelerating under extreme conditions (conditions that might generate a wheel lockup/heavy braking) the two pumps are essentially short circuited. The RT4WD System does NOT engage the rear wheels. This allows the ABS to do its job.

Mode #4 operation is very much like Mode #1 except the flow is reversed and different check valves are used (flow path is different). Mode #5 operation (2WD in reverse) is different as described above. Mode #6 operation does allow the engagement of the rear wheels. How this effects or interferes with the ABS is unknown to me.

In addition to the pump control valve body/cluster, flow to the clutch pack is regulated by two orifices and a pressure relief valve. This helps to prevent sudden engagement (jerky). The thermal relief uses the same relief valve. The thermostat uses the same type of metallic slug as a cooling system thermostat. When the slug expands more than normal (over heat), it pushes the relief valve off its valve seat and relieves system pressure back to reservoir. This effectively takes the RT4WD System off line.

There is more to it than what I have posted. To go deeper, however, would definitely require a circuit diagram and I'm guessing that this post is already too long.

The bottom line is that any modification to the system, while I'm sure possible, would require a great deal of thought and would probably be very complex.:cool:

[cwalti]

The bottom line is that any modification to the system, while I'm sure possible, would require a great deal of thought and would probably be very complex.:cool:

Agreed 100%+

I would NEVER engage the 4WD even on a flat and level road. The only compensatory feature is a small orifice to compensate for tight corners and worn tires beyond the 2% pump volume differential. Imagine what that would do going 80 mph... If you want offroad competence you need to look at the Pilot and the Ridgeline, the E will NEVER be a rock crawler...!!!