I am considering a hydroboost conversion however I have converted to a rack and pinion setup with a GM variable effort steering pump. The pump uses a PWM electronic control valve that returns fluid to the pump (bypassing the hydraulic circuit) at an increasing rate depending on vehicle speed.

So my dilemma is the pumps output is reduced at higher speeds (higher than 0mph). This is the opposite of what is needed by the hydroboost. However, the hydroboost units I have seen seem to have an accumulator on them so it may work. My thinking is that the hydroboost does not really require much flow, only adequate pump pressure. Certainly not the kind of flow rate a rack and pinion needs (I think). Anyone have a cutaway of a hydroboost or know specs like minimum flow rate/pressure?

 

 

Comp, it looks like it's just me and you who are interested in how a hydroboost works. Page two in record time! Got any ideas?

 

Well,its kinda hard to explain but here it goes:
The thing is moved by the crank and moves that other thing up towards the housing.
In the housing it bypasses the thing unless you push on that thing which causes that thing to move and that other thing feels lighter.
This causes that thing to react to that other thing and everything is good in tha hood,wooord.
Any questions?

 

This information may help. There are some GM trucks that have EVO and then some trucks that have EVO variable assist as well as hydraboost. Trucks with just EVO have low flows (at highway speed) of 1.0 gallon per minute. The trucks with EVO and hydraboost have low flows of 1.8 gallons per minute. So from the pump specifications, it seems that the hydraboost does require slightly more flow.

Jim

 

do you have the evo working? if not leave it unpluged and it should default to max flow.

 

never mind that statement that is all my ford training talking. that is fords version of GM variable effort steering. they call it electronic variable output or EVO for short. I thik it should work the same way and unpluged should default to max flow.

 

Mark, I am goint to attempt to make a controller for the EVO in order to increase road feel at speed. I have a Ford Pump w/EVO and I would have used it but the 01 Tahoe pump w/EVO bolted right on. I think the Ford and GM work exactly the same way (PWM control of a pressure releif valve) and may even use the same components.

You wouldn't happen to know the Ford specs on the PWM controller would you? I'll trade you that info for your door trim

 

I can get any specs you need. the ford evo is controlled by the engine control computer. it gets inputs from the speed sensor, steering wheel rotation sensor and the brake signal. it basicly applies a varied voltage to the solenoid to limit fluid flow. you will need some sort of processor and a speed signal input. anyone good with electronics should be able to come up with one. I have seen some controlers for other things that a forum member has designed. I don't remember who but maybe he will see this. let me know the specs you need and I will look them up at work tomorrow.

 

That would be great. I have pics of the Ford and GM EVO taken apart if you would like to see them. They both are configured exactly the same and probably the parts interchange. They both have a DC resistance of 10 ohms. I would like to know pulse width and voltage. If you could find flow rates at speeds that would be good.

I am going to use the VSS from the Tremec for vehicle speed no plans for encoding the steering angle although it seems useful. I thought about a brake feedback that would change the flow rate from the pump but I don't think you want the steering to lighten up when you are hard on the brakes.

Do you know if the Mustang that uses the Hydroboost uses EVO? That's probably closest to what I am doing.

 

The GM EVO valve was designed for a 250Hz PWM signal; modulated between 5% and 95% to get a 12 volt signal.

Most of the GM EVO systems had software that was integrated into the vehicle engine or chassis controller.

I think that the 1996-97 Jeep Grand Cherokee had a EVO controller that was stand-alone. The Jeep controller had another set of inputs besides vehicle speed. It included a handwheel rotation rate sensor that was mounted on the steering column. Without the handwheel sensor hooked up in the controller circuit, I believe that it automatically defaults to high flow.

Since you have converted to rack and pinion steering your system will most likely withstand pressures generated by the pump in the 1400 psi range. Pump pressure is regulated by the linear valve inside the pump behind the discharge fitting.

The standard C2/C3 Corvette steering system was only designed for 1000 psi pressures. The standard Corvette pump had a pressure relief setting of 950 psi. The smaller 1/4 inch ID hoses will not withstand higher pressures. So with a production type C2/C3 steering system, you don't want to exchange a pump linear valve from a GM pickup or SUV truck.

Jim

 

I'm recently retired as a suspension/steering development engineer on Ford's Panther platform. I have worked on both Hydroboost and EVO.

The EVO is controlled by the RAS module that combines rear air suspension and steering into one control. On models that didn't have airsuspenion there is a stand alone module, but I don't recall any of them being combined with the EEC module.

We introduced a steering select swith on the 95 Town Car that allowed the driver to lock out EVO, put it on fully (max assist) or in the middle position it changed with speed like all the others.

In the 2003 model year Panther EVO was replaced by the Ford VAPs system. VAP is much better in that it provides greater effort range, but of course it's more expensive.

Hydroboost was probably used on many models, but I'm only familiar with the 82-83 Continental (not Panther, but developed by Panther group) which used it. It was used for package reasons (power brake booster). There was no effect on steering efforts at highway speed, although I wouldn't see why it couldn't be used with a VAPs steering gear.

The impressive thing with Hydroboost is how quickly and smoothly braking was accomplished. In 2003 our Panther platform started using a panic assist feature that Bosch had which also worked very well.

EVO was standard from 92 to 2002 on all Panther. It was removed from Police units for a couple of years near the end. A stand alone module would be available at a wrecking yard from any othe others unless they have RPO airsuspension or on Town Car which uses the RAS module mentioned. Both are behind the glove box door - at least the later ones.

A steering wheel speed sensor is required as pump "catch up" will be encountered in quick steering movements at low flow of around 1.2 GPM

 

ok he should know a little about this

bbshark I might be able to get you a vaps module from a crown vic if you are interested. for the same price as my mouldings it would be a stand alone module. I have a friend that has many old police cruisers and I can get one from him. I can get you the wirinig diagrams you will just need to wire the inputs.

 

NedP1 another ford person with a C3. I have been with my ford dealership for 30 years. I allways liked the corvette so I bought one. it is the first chevy I ever owned.

 

Sounds like a deal! Thanks Gator.

NedP1, thanks for the information. I have struggled with trying to obtain information about this conversion for a while. If you don't mind I have one more question, I have seen information from Taurus SHO modification sites that the VAPS controls a stepper motor on the rack itself and also controls pump output as discussed here. I assume the Panther platform only regulates the pump. Is this correct?

Whoops, one other question. Is there an encoder on the steering column and do you know if the flow rate correction is proportional to the steering rate?

You and Jim Shea need to get together. He is a retired GM steering systems engineer and has helped me and others on this forum tremendously.

 

Here is some information that might help:

From the previous post by NedP1. The Ford EVO stand alone controller was used on all 1992 thru 2002 Mercury Grand Marquis and Ford Crown Victoria vehicles without optional air suspension. The Ford stand alone controller is in the glovebox and requires input from a handwheel sensor. Also 2000 (roughly) thru 2002 Ford Crown Vic police cars did not have EVO.

EVO on Ford vehicles was used with the Ford Indianapolis power steering pump. The EVO valve that screwed into the Ford pump discharge port will not work properly if you try and attach it to a Corvette P-pump. However, I am very sure that the electronics (coil, pintal, etc) should be the same between the Ford EVO valve and the GM EVO valve. So a Ford stand alone controller should properly control a GM EVO valve on a Saginaw P-pump.

The 1996-97 Jeep Grand Cherokees had a Saginaw pump and EVO valve with a stand alone controller. So that controller should work as well.

The Ford VAPS was a unique variable assist system that was integrated right into the valve on the Ford Indianapolis rack and pinion gear. No chance of it working on any other gear than a Ford.

Jim

 

so a 1992 to 1999 police cruiser should have the module? if not he also has some non police package cars. I think I can fix him up.

 

Jim, As you have observed the Ford EVO component that screws onto the back of the pump seems to be the same as the GM EVO valve. I am using an 01 Tahoe pump with the GM EVO because it fits my serpentine brackets. While researching this I found a 1993 T-bird 5.0L pump with EVO. Whatever controller is driving this does not seem to have any other outputs. I asked the question about the Taurus SHO setup because I believe there is a stepper motor (only on the SHO) that either controls the flow rate at discreet levels based on speed or a combination of the two controls. Could be the push button "sport" suspension option.

I have searched for the Jeep controller for over a year and I cannot tell you how much time I have involved in locating this module. I have called junk yards around the country. For control modules, if you don't have a part number, they can't help. If you go to the dealer and start looking at schematics they want to know the part number. I have looked under Cherokees but, understandably, when tracing the wiring to the module no one will allow me to take their car apart to get the module number. So as appealing as the Jeep controller is, for all practical purposes it does not exist.

The Ford VAPS is the first thing I will be able to get my hands on (with Gators help) and will at least get me started if not get me all the way there.

 

The Ford VAPS system did not have any direct affect on the pump. It actually reroutes fluid right inside the steering gear valve. The stepper motor opened (or closed) a second set of ports inside the gear valve that effectively increased (decreased) the area of the valve and decreased (or increased) its response to steering wheel inputs.

If I remember correctly, the Taurus SHO used a German ZF Servotronic rack and pinion gear. The ZF system also had a solenoid on the gear that somehow changed the steering effort. I just don't remember the specifics on how the ZF system worked.

I was the steering system competitive analysis manager the last 10 years at Saginaw Steering Gear before I retired in 2001. I just hope that my memory holds out on all the different pumps, gears, systems, etc that we used to analyze. We used to spend about $3000 a month just purchasing Ford, Toyota, Honda, BMW, Mercedes, etc parts from dealerships to test and investigate. (That was back when we were part of General Motors and had deep pockets.) I've been afraid to even ask if they have any competitive analysis at Delphi Saginaw now.

Jim

 

The steering wheel speed sensor triggered the system to full flow for a fraction of a second One way to tell if the EVO was operating was to move the steering wheel quickly on center and feel for the effort change.

Jim Shea is absolutely right about the Ford VAPs. I tried to explain it in my post, but he did a better job. We thought of the VAPs as having two steering control valves - one light and one heavy and depending on the calibration and speed flow is shuttled between the two.

I never worked the the Taurus line, but I know VAPs was standard for quite a while. I guess the SHO used the ZF. Putting ZF on a high volume car line was impossible due to labor contracts.

I'm drawing a blank as to the Manufacturer of the EVO valve - it defenitely wasn't Ford. Perhaps Jim Shea knows and they might be willing to help.

Gator, the stand alone controller should be on the 92 through 99 cruiser that we call a CVPI.

Many of these controllers used programable ROM chip, but I couldn't tell you which ones. After things settled down the chip was replaced with a less expensive masked ROM chip or a one time programable as an interim.

We did are steering development with a the programable ROM adjusting slightly for changes in tires or other paramaters during vehicle development. We did the same with VAPS. I think one of my old lap tops still has the program on it.

One other thing - EVO must have clean clean PS fluid. The reservoir should have a good filter in the base. Contaminates can cause the pintal valve to stick - somtimes intermintantly.