Home / Car care / The difference matters between hydraulic and electric steering
The difference matters between hydraulic and electric steering
By Jack Biddle • 04/04/2015
FORGET ABOUT THOSE ‘GOOD OLD DAYS’. THEY WEREN’T
A Far North reader asks about the difference between hydraulic and electric power steering, and just what “drive-by-wire technology” is. The writer asks about maintenance and whether these components cost more to service.
We can’t actually say these innovations are part of modern technology anymore. Electric power steering (EPS) and drive-by-wire (DbW) technology have been part of motor vehicle manufacture for some time now although EPS has been a little slower to find its way into mainstream vehicles.
Why have manufacturers headed down this track? There are several reasons: both are fuel-savers, there are safety advantages and long-term savings for the manufacturers.
Electric power steering
The traditional hydraulic power-steer system uses a number of components including a pump, driven by a belt which is connected to the engine crankshaft pulley much like an alternator or air-conditioning belt. Added to that are hoses and pipes which feed high-pressure fluid to the internals of the steering rack, so it all adds unwanted weight and potential ongoing wear and tear.
Some other downsides of the hydraulic system include:
■Oil leaks in the internal steering rack as vehicles age
■Cost of repairs
■It takes energy from the engine to drive the pump so fuel consumption is affected
■The pump is continually turning when the engine is running and the vehicle is stationary
■There are limited options to offer some sort of variable assistance to the driver
■Some garages recommend draining and flushing the system as part of a routine service (don’t get me started on that subject)
An EPS system does away with any mechanical engine-to-pump connection, hydraulic fluids or reservoirs. Steering assistance is controlled directly by an electronic module which allows an electric motor to vary assistance according to inputs such as road speed and steering effort.
It can also, in some systems, work with Electronic Stability Control (ESC) to help overcome loss of vehicle control by automatically changing the steering characteristics. Without EPS, there would be no self-parking cars, another feature becoming more common. From an additional safety point of view, any electronic-related faults in the EPS system are highlighted by a dash warning light.
It’s fair to say in the pioneering days some of the EPS systems were downright awful in terms of driver feedback and feel, but they have been fine-tuned and are becoming more and more accepted and intuitive.
In the days of the old-fashioned throttle cable — the link between accelerator and the under-bonnet throttle body — the driver had sole control of the power they felt required for a given situation.
If you thought that was still the case for vehicles fitted with drive-by-wire technology (no throttle cable), then think again. DbW allows the driver to “believe” they are in total control but an on-board Engine Management Control (EMC) system has the ability to overrule and automatically alter the amount of throttle opening it feels appropriate for a given situation.
■Improvement in fuel economy and tailpipe emissions
■Works with some ESC systems to help overcome loss of vehicle control
■Is an integral part of an adaptive cruise control system
■Fewer moving parts, so less throttle-related wear
■Smoother accelerator operation and less throttle lag
■Engine can synchronise better with electronically controlled automatic transmission
Some would argue motor vehicles are becoming far too complicated these days but with the introduction of and improvements in systems like EPS and DbW, vehicles need less service as they age. Electronic components do not suffer from the deterioration, stress and wear inflicted on items such as pumps, belts, seals, cables and linkages.
And while we may well argue about the benefits of charging owners for replacing the power steering fluid on older vehicles, no such discussions should be required in the future.
Add the potential fuel savings and safety benefits, and then ask yourself if you really want to go back those so-called good old days. I’m sure you wouldn’t.