[joekitch]

Making this thread to either be a monument to my failure or a how-to on my success

Hydroboost is a system which uses hydraulic pressure from the power steering system, as the pressure to press the brake master cylinder, instead of vacuum or electrics

I'm doing this instead of electric power steering + electric brake booster because this will give significantly better breaking and steering feedback and feel, also this has much higher packaging efficiency, and comes with a lot less fabrication requirements for bolting stuff to the firewall. It's also way cheaper and uses stuff the car came with.

The pump is a volvo electric power steering pump, from an 04-13 volvo,
04-13 Volvo Electric Power Steering Pump S40 V50 OEM Bracket/Pigtails Included | eBay
it uses up to 80 amps at peak when the steering is at lock, has a beefy main power input plug and a little canbus input plug as well.

it'll be paired with a hydratech brake booster and a flaming river steering rack
Hydratech Braking Systems :: 1968-1982 C3 Corvette Hydraulic Brake Assist System Listings
1967-82 Corvette Power Rack & Pinion Cradle Kit - No Column
in a 1971 corvette

big unknowns as of now:

• unclear if backpressure is a problem, most hydroboost systems have two separate return lines because the brake booster HATES backpressure. the volvo pump has only a single return inlet...
• unclear if the "failsafe mode" of the pump, which runs it at 50% speed, is sufficient to drive the system, getting good steering assist and good brake pressure, but not overboosted steering
• unclear if adding variable speed to the pump, using a control board like this: Universal PSC/NMS-PSC – NMStec , will cause the braking force to be significantly reduced at low pump RPM. the idea being that outside of a parking lot, you don't need that much steering assist so why not turn it down pretty low
• unclear what is a good way to silence the pump, since its pretty loud and annoying at low speeds, i'll need to put it into some kind of sound-resistant box, and still keep it somewhat cool in there (possibly running the PS hose around the motor a few times, and putting the fluid through a little heat exchanger somewhere)

I'm about to purchase the pump, here goes nothing

some videos on the pump from gas car builds

here's how it sounds when running, very forklift esque

 

[Nmstec]

If you use my controller (above you linked to), I can add brake switch provision to increase assist. You can as well just install a pressure sensor and my controller can compensate for it. A similar style system is used using a volvo pump on a schooner (some fancy boat). They attached pressure sensor to my controller that whenever low pressure side sees a difference in pressures, pump increases to assist to the high pressure side.

 

[joekitch]

Dynamically speeding the pump up with brake force is an interesting idea, although that may feel extremely weird if I'm decelerating while turning, with the wheel getting lighter as I brake harder into the turn

 

[Nmstec]

Personally I don't think this is the right way to do this, and would instead recommend an iBooster as a seperate system, or perhaps dual hydro pumps (even then double the noise).

 

[remy_martian]

I doubt the pump can react fast enough to brake pedal force input.

It's designed to work with a PS pump, so no need to go beyond what a belt-driven (or hydroboost) pump does.

 

[remy_martian]

I seem to recall some trucks having a dedicated hydroboost electric pump....

Too busy to do an extensive search: BENDIX BOSCH HYDROMAX ELECTRIC PUMP MOTOR 2771544

 

[brian_]

My motorhome has a Hydro-Max system (apparently from Bosch), which is hydraulically boosted braking with a backup electric pump mounted on the booster assembly to provide boost if the engine-driven pump is not providing flow (as indicated by a flow switch)... which happens if the driver pushes on the brake pedal before starting the engine, and is really loud. Fortunately, the GM system to be used apparently doesn't have that feature.

I note in online remarks about the Hydro-Max system that in at least some cases the booster does not tolerate any back pressure, and apparently separate pumps are used for steering and braking... although I have not confirmed that on my motorhome. So it's just a heads-up: you might need two pumps, as already mentioned. But you might not, because apparently some systems (both no-backup Hydro-Boost and Hydro-Max) does tolerate routing the flow from one pump in series through two loads (steering and brakes).

Power steering hydraulics are weird: the pump is controlled as a pressure source; instead, the pump speed determines volumetric flow rate, and the control valve (at the steering rack of box) controls a bypass to determine effective pressure. Having both steering and braking assists working in parallel should work (since both systems tolerate widely varying flow rate due to engine speed changes), but the interactions could be a challenge.

The backup pump on the Hydro-Max system might initially seem tempting to use full-time, instead of a separate pump. Unfortunately the backup only produces a fraction of the full assist force... and it is so loud that the first time I heard it I was seriously concerned about what might be broken.

 

[brian_]

I seem to recall some trucks having a dedicated hydroboost electric pump....

Too busy to do an extensive search: BENDIX BOSCH HYDROMAX ELECTRIC PUMP MOTOR 2771544

That is labelled as "HYDROMAX BOOSTER EMERGENCY PUMP MOTOR ASSY." in the description, and is presumably the backup pump which mounted to the bottom of the Hydro-Max booster (#29 in the following illustration from a Bosch manual), rather than a regular service pump dedicated to the brakes.

 

[joekitch]

the hydroboost system in my car has a basic belt fed power steering pump, the only distinction begin two separate return lines, i dont think a two loop system is necessary, more like just characterizing what happens to my brake feel at lower flow rates. from elsewhere it sounds like lower flow will mean less assist on brakes so my brakes become "more manual" in a sense, which might not be that big of a deal? unsure.

i'm trying to call up the tech support line for a company called Tuff Stuff performance which deals a lot in hydroboost in passenger cars

 

[joekitch]

called up hydratech this morning and got a tech on the line, i took some notes:

• they haven't heard of anyone successfully using an electric pump with their system, they always say it just "didnt work"
• ideal flow range is 2.2 to 2.6 gpm
• over 2.6 causes churn and aerates the system, cause erraticness, pump noise
  • however this is specific to the pump, if the pump doesn't aerate at higher flow rates, it doesn't matter
• can go down to 2gph since the foxbody rack needs that
• pressure doesn't control control quickness on steering, flow flow rate does
• pump reservoir should be vented, otherwise it can build up pressure, which heats the fluid
• avoid overheating the fluid since it causes the fluid to expand and lose braking pressure
• recommend synthetic fluid
• 2psi of backpressure will self-apply the brakes, if there's a T-line on the return it must be within 3" of the brakes
• using a PS cooler is a bad idea without two return lines, coolers can cause some backpressure which is BAD
• to add another return line to the reservoir, use bulkhead adapters, and then attach using socketless AN-6 fitting
• needs to return to the primary resevoir, not T off the secondary reservoir

according to this random thread Volvo EPAS Conversion , this volvo pump can do up to 1700psi at 4.4gpm flow rate, which is way beyond what they're used to apparently, and at this point im a little concerned this thing could blow the steering rack apart?

time to call flaming river and ask how much psi their rack can take

 

[remy_martian]

Which is why you PWM the Volvo pump speed...

Good writeup - thnks for sharing. May be useful to someone some day.

 

[joekitch]

Considering I plan to hook the pump up to my current rack and hydraboost soon, hopefully it'll be useful to me someday

The back pressure and heat situation has me a little worried though. Tapping a new return line is probably for the best but that may be really hard because it's a rounded reservoir....I feel like putting a T on the little vertical tube to the above secondary reservoir is the play since the brake booster return only squirts out a tablespoon whenever you lift off the brakes apparently

 

[remy_martian]

You can always run a dedicated EPS pump for each system, i.e. two Volvos or whatever ones you pick.

 

[joekitch]

I forgot to mention my pump arrived, paid about $160 on eBay for it, and it came with the data end power harnesses plus the big mounting cage, which is nice.

 

[Nmstec]

called up hydratech this morning and got a tech on the line, i took some notes:

• they haven't heard of anyone successfully using an electric pump with their system, they always say it just "didnt work"
• ideal flow range is 2.2 to 2.6 gpm
• over 2.6 causes churn and aerates the system, cause erraticness, pump noise
  • however this is specific to the pump, if the pump doesn't aerate at higher flow rates, it doesn't matter
• can go down to 2gph since the foxbody rack needs that
• pressure doesn't control control quickness on steering, flow flow rate does
• pump reservoir should be vented, otherwise it can build up pressure, which heats the fluid
• avoid overheating the fluid since it causes the fluid to expand and lose braking pressure
• recommend synthetic fluid
• 2psi of backpressure will self-apply the brakes, if there's a T-line on the return it must be within 3" of the brakes
• using a PS cooler is a bad idea without two return lines, coolers can cause some backpressure which is BAD
• to add another return line to the reservoir, use bulkhead adapters, and then attach using socketless AN-6 fitting
• needs to return to the primary resevoir, not T off the secondary reservoir

according to this random thread Volvo EPAS Conversion , this volvo pump can do up to 1700psi at 4.4gpm flow rate, which is way beyond what they're used to apparently, and at this point im a little concerned this thing could blow the steering rack apart?

time to call flaming river and ask how much psi their rack can take

I will have to call this out as wrong. Any Ford variant pump (Mazda and volvo) has a 1200psi internal bypass to my knowledge.

On the other hand, the pump itself isn't the part that creates the pressure, only the flow.

 

[brian_]

... On the other hand, the pump itself isn't the part that creates the pressure, only the flow.

The pump obviously is the part which creates the pressure - that's what pumps do. The pump does not control the pressure - it is controlled on a flow basis, and the pressure that it must produce to push that flow is determined by the valve in the powered device (steering rack or brake booster).

Higher-than-required pressure capability of the pump isn't a problem by itself. That high pressure will only occur if the steering rack or brake booster excessively restricts flow.

 

[brian_]

called up hydratech this morning and got a tech on the line, i took some notes:

• ...
• pressure doesn't control control quickness on steering, flow flow rate does
• ...

It's not entirely clear to me what they mean by "quickness" here.

• If they mean that maximum rate that the rack can be moved while maintaining assistance, then yes, that's limited by the flow rate (since obviously the assist cylinder displaces fluid).
• If they mean level of assistance, then that assistance is the result of pressure output from the control valve in the rack, and that is determined by torque applied by the steering wheel and flow rate of the fluid, limited at the extreme by the pressure that the pump can deliver.

 

[Nmstec]

The pump obviously is the part which creates the pressure - that's what pumps do. The pump does not control the pressure - it is controlled on a flow basis, and the pressure that it must produce to push that flow is determined by the valve in the powered device (steering rack or brake booster).

Higher-than-required pressure capability of the pump isn't a problem by itself. That high pressure will only occur if the steering rack or brake booster excessively restricts flow.

Semantics, but yes, restriction is what dictates pressure was my point.

 

[joekitch]

It's not entirely clear to me what they mean by "quickness" here.

From the way the guy said it, too high gpm results in the rack being over boosted and very little steering input resulting in a lot of steering "sneeze and you fly off the highway", etc. This is from experimenting with foxbody racks

 

[brian_]

The odd way that these assist systems work, in which flow rate is determined by pump speed and pressure (and thus assistance force) is determined by control valves which bypass flow, will make the steering and brakes interact if connected to the same pump.
If they are plumbed in series (flow through one then the other) they'll get the same flow - like electrical devices wired in series getting the same current - then both will have suitable flow but they may be messed up by pressure to ambient (analogous to voltage to ground) being affected by the resistance of the other device. This is the "backpressure" which has been mentioned as a potential issue.
If they are plumbed in parallel (flow splits then re-combines at the return to the pump) they'll get the same inlet pressure - like electrical devices wired in parallel getting the same voltage - then the flow rate through each will be affected by the resistance of the other device.