If steering feel is one of the most important parameters while choosing a car, you probably own one which is hydraulically assisted.
Don't get it wrong. Electric power assisted steering (EPS/EPAS) can have great feel, it depends on the calibration but one thing where it lacks completely is feedback. This is because the motor of EPAS is either rack or column mounted. This effectively acts as a dampener and one can not feel the things hitting the tires translating to the steering wheels, which is both a good and bad thing. But to us enthusiasts, we see that they are numb as hell.
Some cars with so called feel some EPAS steering has lower assistance and less dead zone, but they just can't match the hydraulics, can they? Other than this one con, EPAS has the following advantages:
1. Reduced Power consumption: Because hydraulic systems are driven by the motor, the motor becomes a bit lethargic than it actually is. The hydraulic pump is driven at all times, even at idle versus EPAS where the motor is working only when assisting.
2. Increased fuel efficiency: Due the reason stated above, EPAS will return marginally higher fuel efficiency. The increase is noticeable.
3. Ease of tuning: Manufacturers buy EPAS units from suppliers and tune it according to them. Its level of assistance is determined by the computer which receives the position and torque of the steering column. Often many cars can have units from the same supplier.
4. Packaging: Since there is no belt driving from the engine, a lot of space is freed up under the hood. Hydraulic systems also have a couple of complex systems like pipes, master cylinder, pump, etc vs a motor in EPAS which is column or rack mounted.
5. Cheaper to build and maintain: Since they are less complex systems, they are simpler to build.
6. Less Noise: Ever heard the high pitch noise coming from a car with hydraulic steering? I've heard it from my friend's Duster. Yeah its the hydraulic power steering pump noise and not the turbo spooling! No surprises from EPAS here.
7. Reduced fire risk: Since most power steering oils are light petroleum based oils, there is a risk of fire during collision.
8. Speed dependent assist: The level of assist can be varied. Realize your EPAS unit gets noticeably heavier at triple digits speeds while people owning hydraulically assisted cars don't know what I'm talking about.This happens because, the level of assistance in an EPAS unit is tuned to give less assistance at higher speeds.
9. Anti-Kickback compensation: It has already been talked about. It's both good and bad.
10. Driving modes and other modern features: EPAS systems can have driving modes and other advanced features such as:
a. Autonomous driving
b. Lane Keep Assist
c. Nibble filtration- A system and method for actively cancelling steering nibble and/or brake judder in an electric power steering system using a controller and an electric motor by converting a selected wheel speed to a frequency, selecting a nibble order, determine nibble enable frequencies for cancellation, selecting a damping factor based on changes in vehicle velocity, calculating filter coefficients based on the selected damping factor, the selected nibble order and the wheel frequency, applying a gain scheduler to a steering column torque signal for the nibble enable frequencies, applying a tuned resonator filter to an output of the gain scheduler and using the filter coefficients to produce a nibble signal, calculating an active nibble cancelling torque signal from the nibble signal and applying the active nibble cancelling torque signal to the electric motor to cancel steering wheel nibble vibration.
d. Auto park: Though more of a gimmick but now more and more mainstream cars are getting it. Anyone with a specked out Ford Endeavour?
e. Side wind compensation- when crosswind compensation is carried out firstly the need of judging whether vehicle is keeping straight on, the present invention is in addition to application steering angle and steering angular velocity relevant information, the lateral displacement information of the azimuth information and opposite lane between road ahead curvature information and track is obtained at the imaging sensor that accessory system is also kept from track, and judges whether vehicle keeps straight on according to above- mentioned information.After whether the vehicle that accurately forms a prompt judgement in this way keeps straight on, crosswind compensation is carried out.
f. Road crown compensation: in other words, one will suffer less steering pull caused by road crown.
11. I know the list is endless. I request the members with the expertise to correct me if I am wrong anywhere and keep adding to the list. Just to let you know, even after writing this, if I have in a hypothetical situation a chance to pick a car with all other parameters remaining same, I'll probably ditch the EPAS!