REGENERATIVE braking is a core technology for increasing
the fuel efficiency of the electric vehicle
(x-EV) equipped with energy storage units, such as a battery
and an ultracapacitor [1]. Toyota reported that the greatest
factor for an improved fuel efficiency hybrid electric vehicle
Manuscript received August 8, 2013; revised December 24, 2013 and
March 18, 2014; accepted May 9, 2014. Date of publication May 21, 2014;
date of current version February 9, 2015. This work was supported in part by
the Ministry of Trade Industry and Energy and in part by the Korea Institute for
Advancement of Technology.
J. Ko, S. Ko, H. Son, and H. Kim are with the School of Mechanical Engineering,
Sungkyunkwan University, Suwon 440-746, Korea (e-mail: rapkjw@
nate.com; blacksure@naver.com; hanho1014@naver.com; hskim@me.skku.
ac.kr).
B. Yoo is with the Hyundai-Kia R&D Center, Hwasung 445-706, Korea
(e-mail: a7ybs1@hyundai.com).
J. Cheon is with the Hyundai Mobis R&D Center, Youngin 446-912, Korea
(e-mail: jaeseungcheon@mobis.co.kr).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TVT.2014.2325056
(HEV) is regenerative braking, which accounts for about 35%
of the total energy efficiency improvement, as evident in the
Toyota Prius. Studies showed that HEVs have remarkably improved
their fuel efficiencies by 30%–40% through regenerative
braking [2]–[4].
However, the braking force required by a driver cannot be
guaranteed through regenerative braking alone, due to various
limitations, such as battery state of charge, and vehicle speed.
Therefore, separate friction braking, which enables active cooperative
control in response to regenerative braking, according
to the braking demand of the driver and the driving state, is
needed [5].
A brake-by-wire system, such as the electronic hydraulic
brake (EHB) or an electric actuator, has been used in the
friction brake system for regenerative braking cooperative control.
For an EHB, an electronically controlled brake system,
and electronic stability control, the use of an oil pump and a
hydraulic control unit has been developed [6], [7]. Furthermore,
a system using an electronic hydraulic servo, as well as a smart
booster using an electrical booster, has been proposed [8], [9].
Electronic brakes for cooperative control, which use the x-bywire
technology, include the screw-type electronic mechanical
brake (EMB) and the electronic wedge-type brake (EWB). The
EMB pushes the brake pad against the brake disk using a piston,
which is connected to the screw, to produce a clamping force.
The EWB uses a self-reinforcing effect using a wedge, which
is connected to the screw, to produce a clamping force.
The EMB and EWB are new brake types that use a motor,
instead of hydraulic pressure, to generate the braking force.
Thus, they respond faster and can be operated under active
electronic control, which can be used to independently control
the braking force of each wheel [10]–[14]. In addition, a pedal
simulator is required to provide the same braking feeling as that
in conventional vehicles [15], and a separate fail-safe device is
required, because there is no physical connection between the
driver and the brake system.
The regenerative braking cooperative control algorithm is determined
by the structure of the friction brake system. Research
done on the regenerative braking cooperative control algorithm
include a study based on the method of increasing the energy
recovery by considering the efficiencies of both the front- and
rear-wheel motors for four-wheel drive (4WD) HEVs [6]; a
study based on an algorithm that focuses the braking force on