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Vehicle Speed Sensitive Steering VS Engine Speed Sensitive Steering

Hello guys, I’m new here, but I have my first question. I’ve been reading a lot of articles on Google about speed sensitive steering, and I would like to know the differences between engine speed sensitive power steering and Vehicle Speed Sensitive Steering. I would also like to know where the Vehicle Speed Sensitive Steering system get’s it’s speed readings (from the Vehicle Speed Sensors or from the Wheel Speed Sensors). Thanks if anyone can help!

That’s not a thing. It would be dangerous. It isn’t done that way from anything I’ve ever read, seen or driven.

That is a thing. The amount of assist is based on vehicle speed. The speed comes from the vehicle speed sensor mounted in the transmission. It could be controlled from the ECU or a dedicated steering system controller. If the car has electric power assist steering, the program would be run in the steering controller but the speed signal would still com from the ECU.

Why do you want to know?

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Ok, thank you for helping. By the way, engine speed sensitive power steering does exist, its fairly old and used in some modern models (for instance, a brand new Lexus LX has it) but I think it goes off of RPM, like, at lower RPM its easy to turn and then at higher RPM there is less assist. Here is a forum post from 2002 talking about a Nissan having the ESSPS: https://www.nissanclub.com/threads/engine-speed-sensitive-power-steering.53761/. And as far as why I wanted to know, I sort of like gathering knowledge when I’m bored. Sorry if it’s bothersome xd

I rarely open links in posts so I don’t know what to think of the OP’s but I too am unaware of an engine speed variable assist steering. And it doesn’t sound like there would be any reason for it. Of course electric power steering that would operate with the engine off(zero RPM) but the vehicle moving would sound logical.

From your link, it appears as though the posters made a mistake. It is vehicle speed sensitive, not engine speed sensitive. Same for the Lexus LX. Vehicle speed, not engine.

Steering engineers go to great lengths to eliminate engine speed sensitivity. It makes the car’s assist inconsistent and thus dangerous. My 1992 Saturn had speed sensitive steering, so its been around a long time but it is vehicle, not engine, speed variable.

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I read the post on the link. The poster asked a question about engine speed sensitive steering. All the replies ignored the engine part of his post because as others have said: it is not a thing.

Below is some information on the Lexus LX 570 engine speed sensing steering system;

General

(a) A rack and pinion type steering gear with an engine revolution sensing type power steering is used.

(b) A variable gear ratio type steering rack is used.

© A Variable Flow Control (VFC) power steering system is used.

(d) A Variable Gear Ratio Steering (VGRS) system, which variably controls the steering angle in accordance with the vehicle speed, is used.

Variable Flow Control Power Steering;

General

(a) The VFC power steering is provided with a solenoid valve in the vane pump assembly, which is controlled by the power steering ECU assembly. The solenoid valve controls the discharge flow rate of the power steering fluid in accordance with the operating conditions of the steering wheel, vehicle speed, and engine speed. Thus, it reduces the load on the engine applied by the actuation of the vane pump, and improves fuel economy.

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In other words, it compensates for the variable engine speed’s effect on the steering boost.

Wouldn’t an older car with hydraulic power steering be considered “engine speed sensitive” steering? The power steering pump rotates faster as the engine RPMs increase. It doesn’t know how fast the car is moving, or which gear the transmission is in.

The Lexus system seems to be sort of like going to a sports stadium and counting all the fingers, and noses going in and dividing by 11 to find out how many people went in.

I am guessing they were only a few hundredth of a mile a gallon away from being able to claim a 1 mpg gain.

Not gonna lie, the engine speed sensing idea does seem a bit… dangerous, but I do believe it exists. By the way, the Lexus’ LX 570 actually has a REALLY unique steering box (for instance, it has VGRS but also has a engine speed sensing power steering system, considering its hydraulic), but I have heard that a engine speed sensing system is a LOT cheaper than a vehicle speed sensing system.

Some Lexus models use the power steering pump pressure to turn the radiator cooling fan so apparently there is a module just to regulate pump pressure and demand. But then I imagine that I could buy a reliable, economical, well maintained basic model used car a decade or so old at a price cheaper than the cost of the modules on a similar aged Lexus. But would I face being shunned at the Country Club in my old Blazer?

Actually, I think you’re right, but I believe the new Lexus models (past 2005) have electric fans. And yes, Lexus parts are fairly expensive

No. The pumps produce so much flow that is just circulated through the steering gear so that power assist is available when needed. Known as an “open center” hydraulic system. Lots of flow with little pressure until power assist is needed. Then the pressure rises in proportion to the need for assist.

Think about it a minute:

Power steering is most needed when stopped, engine idling, driver turning the wheel. The pump output needs to be enough to provide full boost at that condition.

That very same pump is producing a ton of flow when the engine is running down the highway at high RPM but there is next to no power assist needed. The flow is just wasted at that point and the power assist is really more that you’d like. That’s where the variable assist part comes in. A solenoid valve is added to restrict the max pressure and limit the power assist.

That is how power steering systems are designed and why the hydraulic types are so very inefficient.

As for the LX, there’s a lot more going on there than just speed variable power assist. Variable ratio adds a great deal of complexity and the solenoid valve is being mapped to vehicle and engine speed to prevent loss of assist at low RPM and better fuel efficiency at higher RPM.

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I agree 100%, electric power steering types are probably easier to work on and maybe even more reliable, not to mention they are efficient. To me, VGRS is sort of… too complex, since it would cost a fortune to build and a fortune to fix, when you could have normal EPS with the vehicle speed sensing function that is a whole lot more simple, maybe even more reliable than a VRGS system. To me, VGRS is sort of unnecessary in a vehicle, as it adds so much complexity to an already complex vehicle. I like my non-VRGS vehicle-speed sensing power steering :stuck_out_tongue:

No, not as far as anyone here knows. Why do you say this?

Electric power steering has its own complexities. Hydraulic systems can be very small but still provide a lot of power. Electric systems need to be quite a bit bigger, especially with only 12 volts to work with.

Consider a big electric motor attached to the steering system. It has to be big to provide enough assist - that old parking lot problem - but a big motor has a lot of inertia. That inertia makes the steering feel very heavy and unresponsive. “Steering feel” as it is termed, suffers greatly. Makes emergency steering movements overly heavy.

To overcome that, the electronics supplying the power need to sense the force from your hands and add power when it isn’t needed just to take away that heavy feeling. It takes time to build a magnetic field in the motor to add power PLUS reverse the direction when you turn the other way. It was a huge challenge to overcome. It is why you saw electric power steering only on smaller cars first.

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I’m here and I find it very dangerous. Imagine a automatic transmission downshift in the middle of a turn. The engine speed jumps up and changes the power steering assist mid-turn. The driver will drive right off the corner.

If vehicle speed is considered as well, that solves the problem. But then now it would be a speed sensitive steering system and not an engine speed sensitive system.

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In sports cars, the speed-sensing EPS systems tend to change the amount of assist based on driving mode (normal would be easier to turn while sport/sport+ mode would give less assist for more steering feel). Like, in sport+ mode, when parking, the steering would feel decently more heavy than in normal mode. I genuinely believe that having stiffer steering is more beneficial because you get more steering feel. Nowadays, modern cars generally have great response time when emergency steering, they can take only a few hundredths of a second to engage the motor. Back in the early 2000’s, computers were a decent amount slower, and therefore the motor’s assist was a lot slower of a response time compared to modern systems. Now I think I understand why ‘steering feel’ in increased when the assist level is turned down some.