Customer Magazine Articles
Two articles on automobile braking systems written for Delphi Chassis
Systems' customer magazine "Thinking Ahead" by Richard Stewart
Electro-Hydraulic Brake-By-Wire is Here
Lift the hood on a vehicle equipped with a Galileo(TM)
Intelligent Brake Control System from Delphi Chassis and
you immediately notice that something is missing. It's the
vacuum booster. That large, round, difficult-to-package
component that provides power assist to the brakes is gone.
It isn't needed. With electrically applied hydraulic wheel brakes
on the front and a fully electric rear braking system, Galileo
employs true brake-by-wire technology.
But underhood packaging flexibility is just one benefit of
this new family of electro-hydraulic brake apply systems,
according to Greg Kochendorfer, Delphi Chassis Global
Planning Team Leader for Intelligent Brake Control. He cites
reduced mass for improved fuel efficiency, less complexity
for easier assembly by vehicle manufacturers, improved
braking performance, and tunable pedal feel as other
advantages offered by this modular system.
Galileo is the first brake-by-wire system to reach market
on a production vehicle, the GM EV-1 electric coupe. And
while Galileo is ideal for electric vehicles, since no engine
vacuum is available for power brake assist, the system is
equally adaptable to any other platform, Kochendorfer notes.
Last winter a Galileo system was demonstrated on a
Mercedes-Benz E-Series sedan during a press event in Sweden.
"Galileo allows us to offer advanced braking features such
as four-channel ABS, traction control and our vehicle stability
enhancement system, TRAXXAR™, in a single, integrated unit
without adding any incremental hardware," he observes. "That
gives our customers cost-savings, mass reduction and packaging
How It Works
When the driver presses on the brake pedal, sensors in the
master cylinder measure pedal travel, force and rate of apply.
Normally open solenoid valves close, isolating the brake pedal
from directly supplying pressure to the brake fluid as in a
conventional hydraulic brake system.
An electronic controller commands an electro-hydraulic
apply actuator to generate boosted pressure proportional to the
pedal force. And a tunable pedal-feel emulator pushes back
against the driver's foot, providing the feel of conventional brakes.
In the case of a loss of electrical power, the isolation solenoids
stay open, allowing hydraulic "push through" to apply the brakes.
Pedal feel remains consistent, regardless of vehicle loading
or system wear, according to Greg Bartley, product marketing
leader and a member of the Intelligent Brake Control Global
"Even if the brake pads are worn or the brakes are hot from
a steep descent, the electro-hydraulic system will continue to
apply pressure at a greater level of energy—in full ABS control
—until it slows the vehicle at the rate the driver commands," he
explains. "It senses for information and makes decisions using
Future enhancements to the Galileo Intelligent Brake Control
System family include assisted boost for surer and safer "panic"
stops and hill holding capability to keep the brakes applied after
a stop until the accelerator is depressed.
Says Kochendorfer, "It's a good feeling knowing that while
we're working on our next generation of brake-by-wire products,
our competitors are still working on their first."
Delphi's Newest Brake Controls:
INTRODUCING DBC 7
A new Delphi family of high-performance, solenoid-based ABS
and ABS/TCS intelligent brake control is being readied for '99
model year introduction. Known as Delphi Brake Control DBC 7,
the system builds on the success of Delphi's award-winning and
highly acclaimed ABS-VI, reports Greg Kochendorfer, who heads
the Delphi Chassis Intelligent Brake Control Systems Global
Planning Team. Developed jointly by Delphi Chassis and Delco
Electronics, DBC 7 systems will be available for passenger cars,
light trucks and sport utility vehicles.
"The DBC 7 family represents a broadening of our ABS
product line, and it is a key part of our intelligent brake control
strategy for the future," says Kochendorfer, noting that the
system is designed to be flexible and upgradeable. "We'll offer a
baseline unit at a very competitive price, which will mean a
significant cost savings for automobile manufacturers. Plus, the
system will be easily adaptable to the next generation of ABS
through electronics," he adds. The system can be upgraded to
accommodate traction control, dynamic rear proportioning, tire
inflation monitoring and variable effort steering.
Other Benefits for Customers
According to Kochendorfer, the new DBC 7 system represents
optimal design and delivers superior performance. It incorporates
tried and proven features that manufacturers can appreciate:
• Precision Pumps & Solenoids — with two solenoids per
channel for optimized wheel control, closed hydraulic
recirculation for fail-safe operation, and magnetically
coupled valves for ease of serviceability.
• Integrated Electronic Controls — featuring integrated
relays for underhood space-savings and reduced harness
costs, a single-point ECU connector for fast installation
and improved reliability, plus enhanced diagnostics and
separately serviceable hydraulic modulator and ECU for
• Ease of Vehicle Assembly — a single brake pipe and
bracket mounting for ABS and ABS/TCS minimizes
installation costs and assembly, top-load installation
saves time and effort, and ample spacing between brake
connector ports permits use of automatic torque wrenches.
The small size (100 x 104 x 133 mm) and low mass (as low as
2.7 kg.) are additional benefits of DBC 7 that can contribute to
efficient underhood packaging and weight savings for added fuel
economy, Kochendorfer points out. In addition, production of
the units incorporates "clean-room" manufacturing technology to
avoid contamination of sensitive components during assembly.
"We've designed a high-quality, very robust system," he adds.
"There's no external wiring and minimal electronic components.
And it's a fully sealed, submersion-proof package designed to
withstand the harsh underhood environment."
Testing To The Max
DBC 7 systems have been subjected to extensive laboratory and
real-world testing and validated to the highest levels of mechanical,
electrical and environmental stresses, according to Delphi Chassis
lead hydraulics engineer Dave Reuter, supervisor of Engineering
& ABS/TCS Brake Controls.
"We've been fine-tuning our testing and validation processes
since the mid-'80s, starting with our Powermaster III program and
carrying through with our ABS VI program," he recounts. Delphi
Chassis lab testing of DBC 7 systems includes prolonged exposure
to a wide range of temperatures, voltages and pressures, plus
simulated underhood environmental conditions, such as splash,
gravel bombardment and salt-spray, among others. Computer
analysis and simulation also play an important role, too, particularly
in performing complex flow analyses on pumps and solenoids, notes
Delphi Chassis also uses what's called a "step-over stress test"
as an additional safety measure for validation. "After a certain
amount of testing under simulated conditions," he says, "we start
to escalate the stress levels beyond what we would actually see in
the field. We take pressures, temperatures and voltages higher
than those normally encountered, purposely looking for a point of
failure. It's this particular test method that has enabled us to be so
successful in the field with ABS VI," he says. "We've produced
over 7.5 million units and we have one of the best ABS warranty
records in the industry. The same kind of validation philosophy
and techniques have been carried over to DBC 7."
Such a rigorous validation program ultimately means minimized
risk for the manufacturer who installs the new Delphi ABS system
on his vehicles. The result is a brake control system with excellent
performance that is not expected to require service during the life
of the vehicle, according to Reuter.
"This kind of validation is part of being a major player in the
industry. We test our products like crazy — in the laboratory and
on vehicles prior to production — so the platforms can have a high
level of confidence that they won't have a problem in the field.
That is the essence of our validation."
Delphi Chassis plans to market DBC 7 worldwide and to
manufacture the system at various facilities around the globe. "We
feel the fundamental design and features of DBC 7 will become
the springboard for future Delphi Chassis product offerings," says
Reuter. "It's part of our total brake system package that represents
a wealth of efficiencies and benefits for automobile manufacturers,
at a cost that will allow them to expand the availability of anti-lock
braking in their product lines."