Demand from customers for convenience features and the
drive to improve safety have made vehicles bigger and heavier. But
turning the steering wheel hasn’t become any more of a struggle, and
that is owing to hydraulic power steering, developed more than 80 years
ago by Francis W Davis.
The American engineer was well
aware of the problems drivers faced in the early 20th century. Cars were
difficult to drive, and weight was the key factor: “There has been a
trend toward larger automobiles equipped with an increasing number of
accessories adding still further to the weight,” he said in his 1927
patent continuation. The introduction of pneumatic tyres increased
steering resistance yet further.
Many engineers
attempted to reduce friction in the steering mechanisms. While this
slightly eased the problem, according to Davis it created new
challenges: “It gave rise to a greater evil, that is the tendency on the
part of the steering wheels to vibrate excessively.” Vacuum,
mechanical, electrical and hydraulic power-steering systems were all
designed, but all failed. Problems of durability, packaging and cost
hindered the development of a solution. Davis was convinced that a
hydraulic system was the answer.
Davis had graduated
from Harvard University in 1906 after studying mechanical engineering.
He worked for Pierce-Arrow after graduating, which gave him an insight
into how hydraulic technology worked – the OEM’s press tools were all
hydraulically operated. When he left the company in 1922 to become a
consulting engineer he began to research the technology more closely.
The
challenge for Davis was to make the technology scaleable – hydraulic
systems used in industrial presses needed huge storage tanks of
pressurised oil, pumps, unloader valves, accumulators and hose lines.
After a myriad of failures because of pressure losses, leaks and
unworkable packaging, Davis changed direction. Rather than use a
pressurised closed valve, he developed an open-valve system that allowed
oil to flow continuously, but when power-steering assistance was needed
it was closed and pressure built up.
Demand from customers for convenience features and the
drive to improve safety have made vehicles bigger and heavier. But
turning the steering wheel hasn’t become any more of a struggle, and
that is owing to hydraulic power steering, developed more than 80 years
ago by Francis W Davis.
The American engineer was well
aware of the problems drivers faced in the early 20th century. Cars were
difficult to drive, and weight was the key factor: “There has been a
trend toward larger automobiles equipped with an increasing number of
accessories adding still further to the weight,” he said in his 1927
patent continuation. The introduction of pneumatic tyres increased
steering resistance yet further.
Many engineers
attempted to reduce friction in the steering mechanisms. While this
slightly eased the problem, according to Davis it created new
challenges: “It gave rise to a greater evil, that is the tendency on the
part of the steering wheels to vibrate excessively.” Vacuum,
mechanical, electrical and hydraulic power-steering systems were all
designed, but all failed. Problems of durability, packaging and cost
hindered the development of a solution. Davis was convinced that a
hydraulic system was the answer.
Davis had graduated
from Harvard University in 1906 after studying mechanical engineering.
He worked for Pierce-Arrow after graduating, which gave him an insight
into how hydraulic technology worked – the OEM’s press tools were all
hydraulically operated. When he left the company in 1922 to become a
consulting engineer he began to research the technology more closely.
The
challenge for Davis was to make the technology scaleable – hydraulic
systems used in industrial presses needed huge storage tanks of
pressurised oil, pumps, unloader valves, accumulators and hose lines.
After a myriad of failures because of pressure losses, leaks and
unworkable packaging, Davis changed direction. Rather than use a
pressurised closed valve, he developed an open-valve system that allowed
oil to flow continuously, but when power-steering assistance was needed
it was closed and pressure built up.
Davis described
the system in his 1926 patent: “I supply the gear, particularly suitable
for automobiles, which is adapted for direct hand steering where the
steering resistance is slight, which instantly and automatically
augments the manual steering efforts of the operator by the application
of power from fluid pressure when the steering resistance exceeds a
predeterminable value.”
Davis was so sure of the system
that he installed it in his Pierce-Arrow Roadster in 1925, proving that
it not only made the car easier to drive but also removed vibrations
through the steering wheel.
Just as modern
power-steering systems cause debate about driver feedback, so Davis was
also aware of the issues surrounding driveability.
Steering
reversibility, as Davis described it – when the car hits an obstacle
and the force is transmitted to the steering wheel – can cause the wheel
to be wrenched from the driver’s hands. But removing reversibility
completely can cause a loss of feeling between the driver, steering
inputs and movement of the car. Davis solved this by making his system
tuneable, so it could be constructed with a degree of reversibility,
where the maximum torque that could be impressed on the steering wheel
by road shocks was limited to a predetermined value.
As
ingenious as Davis’s design was, the depression of the 1930s meant that
few car manufacturers were interested. But military applications opened
up, helping Davis to develop the system. When the car market picked up
after the Second World War, Chrysler was the first OEM to introduce a
hydraulic power-steering system on its Imperial sedan. That was in 1951
and the system was based on design principles that Davis had patented,
but by this time his patents had expired. Davis signed an agreement with
GM to license his system to the OEM.
By 1956, more
than two million vehicles had been sold with power steering in the US.
Thanks to Davis’s persistence, the technology is an intrinsic part of
today’s vehicles.
Davis described
the system in his 1926 patent: “I supply the gear, particularly suitable
for automobiles, which is adapted for direct hand steering where the
steering resistance is slight, which instantly and automatically
augments the manual steering efforts of the operator by the application
of power from fluid pressure when the steering resistance exceeds a
predeterminable value.”
Davis was so sure of the system
that he installed it in his Pierce-Arrow Roadster in 1925, proving that
it not only made the car easier to drive but also removed vibrations
through the steering wheel.
Just as modern
power-steering systems cause debate about driver feedback, so Davis was
also aware of the issues surrounding driveability.
Steering
reversibility, as Davis described it – when the car hits an obstacle
and the force is transmitted to the steering wheel – can cause the wheel
to be wrenched from the driver’s hands. But removing reversibility
completely can cause a loss of feeling between the driver, steering
inputs and movement of the car. Davis solved this by making his system
tuneable, so it could be constructed with a degree of reversibility,
where the maximum torque that could be impressed on the steering wheel
by road shocks was limited to a predetermined value.
As
ingenious as Davis’s design was, the depression of the 1930s meant that
few car manufacturers were interested. But military applications opened
up, helping Davis to develop the system. When the car market picked up
after the Second World War, Chrysler was the first OEM to introduce a
hydraulic power-steering system on its Imperial sedan. That was in 1951
and the system was based on design principles that Davis had patented,
but by this time his patents had expired. Davis signed an agreement with
GM to license his system to the OEM.
By 1956, more
than two million vehicles had been sold with power steering in the US.
Thanks to Davis’s persistence, the technology is an intrinsic part of
today’s vehicles.
