Process and device for actuating a braking system during the starting of a motor vehicle

A process and device for starting a motor vehicle having a braking system in which a brake force is at least partially supplied by at least brake energy storage devices. Prior to starting a motor vehicle, the vehicle is initially switched into a non-drivable state in which the vehicle is disabled from movement. A charging state of each brake energy storage device may be checked to ensure an adequate charging state. If the charging state of at least one of the brake energy storage devices is greater than or equal to a predetermined minimum charging state, the vehicle may be switched into a drivable state and, thus, operable by the driver.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention may be directed to a process for starting a motor 
vehicle having a braking system that obtains brake actuation energy at 
least partially from brake energy storage devices. A charging state for 
each brake energy storage device may be checked when the motor vehicle is 
started. The invention may also be directed to a motor vehicle having a 
braking system that obtains brake actuation energy at least partially from 
brake energy storage devices, and having a testing device for checking the 
charging state of the brake energy storage devices. 
2. Discussion of Background Information 
Braking systems, particularly those utilized in passenger motor vehicles, 
have been developed which are of the brake-by-wire type. In braking 
systems of this kind, an amount of braking desired by the driver is 
translated from a foot force exerted on a brake pedal, and the exerted 
foot force is detected by a sensor and converted into an electrical 
signal. The signal is transmitted to brake actuators associated with a 
particular wheel of the motor vehicle, and each brake actuator exerts a 
braking force on the vehicle wheel with the assistance of an electromotor. 
Thus, the brake actuation energy required for performing a braking 
procedure is not mechanically supplied, as in conventional brake systems, 
but is electrically supplied. Accordingly, electrical brake energy storage 
devices must be supplied to enable the supply of electrical energy to the 
braking system to perform the desired braking procedure. In this regard, 
part of the energy supplied to the braking system can come from the normal 
wiring system of the vehicle and another part of the supplied energy, 
which would overload the normal wiring system, comes from separate brake 
energy storage devices. A brake system substantially similar to the 
above-described system is described in the Applicants' German Patent 
Application No. 195 40 265.0, the disclosure of which is incorporated by 
reference. Alternatively, the electrical energy required for the brake 
system may be exclusively supplied by a separate brake energy storage 
device. Thus, a sufficient charging state of the separate brake energy 
storage devices is particularly important to the safety of the braking 
system. For this reason, the charging state of the brake energy storage 
devices has to be continuously checked, particular when the vehicle is 
started. 
A brake system with electrically controllable brake devices has been 
disclosed in DE 35 02 100 A1. The system includes a first energy storage 
device for normal operation and a second energy storage device for 
emergency operation. Both brake energy storage devices are associated with 
a voltage monitoring device to continuously check the charging state of 
the brake energy storage devices. If an insufficient charging state level 
(amount) is detected in the first energy storage device to perform normal 
operation, then a change-over device switches the system over to the 
second energy storage device for emergency operation. The first energy 
storage device is switched over to be charged by a generator. The 
changeover to emergency operation is optically or acoustically indicated 
to the driver of the vehicle with a signal transmitter. 
The charging state of the first energy storage device is also checked when 
the vehicle is started. When the charging state is found insufficient, the 
above-mentioned signal transmitter indicates this state to the driver and 
the braking system is then switched over to the second energy storage 
device to utilize its energy supply. If the second energy storage device 
has an insufficient charging state, then the signal transmitter indicates 
this state to the driver. 
According to DE 35 02 100 A1, an additional safety is produced by checking 
the charging state of the brake energy storage device of the braking 
system and by providing a second energy storage device. The process for 
starting a vehicle disclosed in the above-noted document relates to a 
passive process, since the charging state of the energy storage device for 
normal operation or the charging state of the energy storage device for 
emergency operation is only optically or acoustically indicated to the 
driver. The safety of the vehicle, therefore, is not actively increased by 
this starting process. 
SUMMARY OF THE INVENTION 
An object of the present invention is to create a process for starting a 
motor vehicle having a braking system that obtains brake actuation energy 
at least partially from brake energy storage devices which actively 
increases the safety of the vehicle over the above-noted drawbacks of the 
prior art. It is also an object of the present invention to produce a 
motor vehicle with a braking system that obtains brake actuation energy at 
least partially from brake energy storage devices to carry out the 
process. 
In accordance with the present invention, the process for starting a motor 
vehicle may include automatically transferring the vehicle into a 
non-drivable state prior to checking a charging state level or amount of 
each brake energy storage device, checking the charging state of the brake 
energy storage devices, and transferring the vehicle into a drivable state 
if a measured charging state of at least one of the brake energy storage 
devices is greater than or equal to a predetermined minimum charging 
state. 
In accordance with the present invention, the motor vehicle may include a 
switch that automatically switches the motor vehicle into a non-drivable 
state, a control device, which includes a charging state measuring device, 
compares a charging state of each brake energy storage device with a 
predetermined minimum charging state, and a switchover device that 
switches the vehicle into a drivable state when the measured charging 
state of at least one of the brake energy storage devices is greater than 
or equal to the predetermined minimum charging state. 
In the present disclosure, the term "non-drivable" may be understood to 
mean a state in which a motor vehicle is technically in order but in which 
a component required for driving the vehicle is purposefully disengaged, 
e.g. the transmission, or in which the vehicle is purposefully blocked 
from being drivable, e.g. by setting the parking brake. 
In accordance with the present invention, the non-drivable state of a motor 
vehicle may be achieved (or set) prior to checking the charging state. As 
a result, the active safety of the motor vehicle during starting is 
distinctly increased. For example, a "consequence" (result) of a positive 
check of the charging state is the switchover of the motor vehicle into a 
drivable state. If, however, this "consequence" is suppressed for any 
reason, then the vehicle remains in the non-drivable state and is, 
therefore, safe. The increase in active safety through the process of the 
present invention is particularly pronounced when the process is compared 
to a process in which a negative check of a charging state transfers the 
vehicle from a drivable state into a non-drivable state. Thus, if this 
negative result is suppressed for any reason, then the vehicle remains in 
a drivable state despite the negative check indicative of brakes that 
cannot be used or that can only be used to a limited degree. 
A particular advantage of the process according to the invention for 
starting the vehicle is that it may be performed automatically and cannot 
be influenced by actions of the driver. That is, the process may be 
non-overridable, i.e., the process cannot be "overridden" by the driver to 
transfer the vehicle into a drivable state despite the fact that the 
brakes cannot be used or can only be used to a limited degree. A 
switchover of the vehicle into the non-drivable state may preferably take 
place automatically when the vehicle is turned off. 
According to the process of the present invention, a recharging of the 
brake energy storage devices may occur when a check detects an 
insufficient charging state and the vehicle may be transferred into a 
drivable state if, after recharging, at least one of the brake energy 
storage devices has attained a predetermined minimum charging state. This 
recharging of the brake energy storage devices can be performed by an 
external energy source or by a generator of the vehicle. 
To recharge the brake energy storage device via a generator of the vehicle, 
the motor of the vehicle should preferably be running. A recharging of the 
brake energy storage devices via an internal generator of the vehicle has 
the added advantage that, when the brake energy storage devices have an 
insufficient charging state, the recharging may be performed without 
needing service personnel. 
According to another feature of the process of the present invention, the 
vehicle may be switched over into a non-drivable state by switching an 
immobilizer into a currentless (non-current carrying) state and the 
vehicle may be switched over into the drivable state by switching the 
immobilizer into a current carrying state. The switchover of the vehicle 
into the non-drivable state may occur automatically before checking the 
charging state of the brake energy storage devices and preferably when the 
vehicle is turned off. 
According to another feature of the process of the present invention, the 
immobilizer may be an electrical parking brake that is automatically 
transferred into a currentless state when the vehicle is turned off, thus, 
immobilizing the vehicle. This feature achieves the further advantage that 
immobilizer, used to produce the non-drivable state, may be already be a 
component of the vehicle. Additionally, this feature may prevent unwanted 
rolling of the vehicle during starting. 
According to another feature of the present invention, the immobilizer may 
be a transmission lock that may be automatically transferred into a 
currentless state when the vehicle is shut off. Transmission locks 
generally known in the prior art may be utilized as an immobilizer. If 
automatic transmissions are shifted, for example, into position "P" for 
park, a mechanical ratchet lock is engaged which blocks the transmission. 
This mechanically actuated transmission lock may be embodied as an 
electrically actuated device in which a currentless state may create a 
locked state of the transmission. 
The present invention may be directed to a method for disabling a brake 
lock in a motor vehicle upon starting of the motor vehicle. The brake lock 
may be actuated prior to starting of the motor vehicle and the motor 
vehicle may include at least one brake energy storage device and a control 
device. The method may include measuring a charging state level of each 
brake energy storage device; comparing each measured charging state level 
to a predetermined minimum charging state level; and disabling the brake 
lock when at least one of the measured charging state levels is at least 
equal to the predetermined minimum charging state level. 
In accordance with another feature of the present invention, when the 
measured charging state level of each of the at least one brake energy 
storage devices is less than the predetermined minimum charging state 
level, the method may further include recharging each brake energy storage 
device; measuring each recharged charging state level; comparing each 
recharged charging state level to the predetermined minimum charging state 
level; and disabling the brake lock when at least one of the recharged 
charging state levels is at least equal to the predetermined minimum 
charging state level. 
In accordance with still another feature of the present invention, the 
method may also include disabling the brake lock when each measured 
charging state level is at least equal to the predetermined minimum 
charging state level. Further, the disabling may include applying a 
predetermined voltage to the brake lock; reducing a friction force applied 
to a brake actuator; and releasing a brake disk. 
In accordance with yet another feature of the present invention, the brake 
lock may include an electromagnetic friction slip coupling device having a 
friction head and the reducing the friction force may include withdrawing 
the friction head from a spindle nut. 
In accordance with a further feature of the present invention, once 
disabled, the brake lock may remain disabled until the motor vehicle is 
turned off. 
In accordance with a still further feature of the present invention, the 
method may also include initially actuating the brake lock by turning off 
the motor vehicle. 
The present invention may be directed to a motor vehicle having a braking 
system that includes a brake lock that is enabled upon starting the motor 
vehicle, and the motor vehicle may be locked until the brake lock is 
disabled. The vehicle may include a switching device coupled to the brake 
lock that enables and disables the brake lock; at least one brake battery; 
a charging state measuring device for measuring a charging state of each 
brake battery; a control device that compares the measured charging state 
level to a predetermined minimum charging state level; and a control 
device coupled to the switching device for transmitting a control signal 
to the switching device to one of enable and disable the brake lock. 
In accordance with a further feature of the present invention, the control 
device may include a comparator and the switching device may include an 
electromagnetic friction slip coupling device having a coil. 
In accordance with a still further feature of the present invention, the 
switching device may be disabled by a current applied to the coil. 
In accordance with another feature of the present invention, the vehicle 
may further include a recharging device that recharges brake batteries 
having a charging state level below the predetermined minimum charging 
level. 
In accordance with yet another feature of the present invention, the brake 
lock may include an electromagnetic device having friction head and a 
spindle nut. During enabling of the brake lock, the friction head may be 
spring biased against a surface of the spindle nut to restrict movement 
thereof. During disabling of the brake lock, the friction head may be 
biased toward the electromagnetic device to allow unrestricted movement of 
the spindle nut. 
Other exemplary embodiments and advantages of the present invention may be 
ascertained by reviewing the present disclosure and the accompanying 
drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The particulars shown herein are by way of example and for purposes of 
illustrative discussion of the preferred embodiments of the present 
invention only and are presented in the cause of providing what is 
believed to be the most useful and readily understood description of the 
principles and conceptual aspects of the invention. In this regard, no 
attempt is made to show structural details of the invention in more detail 
than is necessary for the fundamental understanding of the invention, the 
description taken with the drawings making apparent to those skilled in 
the art how the invention may be embodied in practice. 
FIG. 1 illustrates a schematic representation of a braking system for a 
motor vehicle in which energy, e.g., electrical energy, utilized for 
performing a braking procedure may be supplied from brake energy storage 
devices. A vehicle driver determines an amount of desired braking by 
exerting a foot force on a brake pedal 2. 
A sensor 24 may be positioned to detect the path covered by brake pedal 2 
upon the application of foot force. Sensor 24 may convert the detected 
path into an electrical signal corresponding to the driver's amount of 
desired braking. Sensor 24 may transmit a signal to control units 6 
through respective lines 4. A respective control unit 6 may be associated 
with each of the front and rear axles of the vehicle to convert the sensor 
signal into a control signal to control the braking procedure. Control 
units 6 may transmit control signals to respective brake actuators 12 
through lines 26. 
Each brake actuator 12 may exert a brake application force, in accordance 
with the control signal from control unit 6, on a respective brake disk 
14. The brake application force may be applied through an electrically 
driven brake application device, discussed below, which may produce a 
braking action at each of the wheels 16. Each brake actuator 12 may 
receive all, or at least a portion, of the electrical energy necessary to 
perform a braking operation from brake energy storage devices 8, e.g., 
brake batteries. Each axle of the vehicle may have a brake energy storage 
device 8 associated therewith to supply the brake actuator 12. Brake 
storage device 8 may be coupled to either or both brake actuators 12 
associated with the respective axle of the vehicle. That is, brake energy 
storage device 8 may communicate directly with control units 6 through 
electrical lines 28 and, through lines 26 from control unit 6, to brake 
actuators 12. When only a portion of the electrical energy is supplied via 
the brake energy storage devices 8, the remaining portion may be supplied 
from the vehicle's wiring system 10, which may communicate with brake 
actuators 12 in a similar manner to the brake energy storage device 8. 
Whether or not the braking energy for a braking operation is fully or 
partially supplied from brake energy storage devices 8, safe braking of 
the vehicle may only be possible when brake energy storage devices 8 are 
included. Accordingly, at least one of the brake energy storage devices 8 
should have a sufficient minimum charging state to properly actuate brake 
actuators 12. Particularly, when starting the vehicle, the brake energy 
storage devices 8 should be tested to ensure that a sufficient charging 
state exists. That is, when the vehicle has not been run or operated for 
an extended period of time, partial discharging of the brake energy 
storage devices 8 may occur, resulting in an improper charging level for 
actuating brake actuators 12. Brake energy storage devices 8 may be 
coupled to charge state sensors 18, for checking the charging state. 
Charge state sensors 18 may transmit a result of charging state detection 
(or check) to a control device 20 via lines 30. Control device 20 may 
assess whether the charging state of at least one of the brake energy 
stores 8 has a sufficient magnitude or level to safely operate the braking 
system of the vehicle. If a sufficient level is detected, an immobilizer 
22, activated by a signal from control device 20 prior to checking the 
charging state to switch the vehicle into a non-drivable state, may be 
"released" via another signal from control device 20. The vehicle is now 
in a drivable state and operable by the driver. Conversely, if an 
insufficient level is detected, control device 20 will not send a second 
signal to immobilizer 22 to release the vehicle. Thus, if the charging 
state is inadequate, then the vehicle will remain in the non-drivable 
state and, thus, be inoperable by the driver. 
FIG. 2 illustrates an exemplary flow diagram of the process for starting a 
motor vehicle in accordance with the present invention. At step 201, the 
vehicle may be automatically switched into a non-drivable state, e.g., via 
actuation of an immobilizer. In accordance with the present invention, the 
actuation of the immobilizer may be automatically effected prior to the 
starting process, e.g., when the vehicle was previously turned off. 
After it is determined that the vehicle is in a non-drivable state, a 
measurement of the charging state of the brake energy storage devices 8 
may occur through the charge state sensors 18 at step 202. The result of 
the charging state measurement may be transmitted to control device 20. At 
step 203, the process, via control device 20, determines whether the 
measured charging state is greater than or equal to a predetermined 
minimum charging state that may be stored within a memory storage device 
in control device 20. Further, control device 20 may include a comparator 
device to carry out a comparison of the measured charging state to the 
predetermined value. When a positive result is found, i.e., at least one 
of the brake energy storage devices 8 is greater than or equal to the 
predetermined minimum charging state, the vehicle may be safely switched 
over to the drivable state. Accordingly, control device 20, at step 204, 
may transmit a signal to the immobilizer to effectuate a release. The 
process for safely starting the vehicle can be further enhanced by 
alternatively adjusting the process to include an additional step of 
transferring the vehicle into the drivable state only if each brake energy 
storage device 8 is found to meet or exceed the predetermined minimum 
charging state. 
Conversely, when a negative result is found, i.e., the measured charging 
state of each brake energy storage device 8 is found to be lower than the 
predetermined minimum charging state, the brake energy storage devices 8 
may be recharged at step 205. The recharging process can be carried out by 
either a vehicle-based generator or an external recharging device. The 
recharged charging state of the brake energy storage devices 8 may be 
measured at step 202. The result of the charging state measurement may be 
transmitted to control device 20 for comparison with the predetermined 
minimum charging state at step 203. A loop including steps 202, 203, and 
205 may be repeated as necessary until the measured charging state of at 
least one brake energy storage device 8 enables a positive result from 
control device 20. Upon transmission of the positive result to immobilizer 
22, the immobilizer may be released, thus, switching the vehicle into its 
drivable state. 
FIGS. 3a and 3b illustrate an exemplary diagram of a drivable and 
non-drivable state, respectively. Immobilizer 22, e.g., an electrical 
parking brake, may be constructed to actuate the non-drivable state when 
in a non-current carrying state and to effectuate a release of the vehicle 
(into the drivable state) when in a current carrying state. FIG. 3 shows 
schematic representations of only the components sufficient for the 
purposes of explanation. The electrical parking brake may be integrated 
into brake actuator 12. Brake actuator 12 may also include an electromotor 
32 for imparting rotational movement on a spindle nut 34 and for imparting 
axial movement on a spindle rod 58 engaged with spindle nut 34. 
Rotational movement of spindle nut 34 may produce axial movement of spindle 
rod 58 to force brake piston 36 in a direction toward or away from brake 
disk 14. As a result, during a braking operation, brake linings 38, which 
may be operatively connected to piston 36, may likewise be imparted with 
axial movement in a direction toward or away from brake disk 14 through 
brake linings 38. In a brake actuation, i.e., towards brake disk 14, after 
traversing an air gap 52, brake linings 38 may abuttingly rest against 
brake disk 14 to produce a predetermined braking force. After the braking 
operation, brake linings 38, brake piston 36, the spindle rod 58 may be 
substantially returned to their initial positions by restoring forces. 
In addition to the above-described components of the vehicle braking 
system, brake actuator 12 may also include an electrical parking brake 
(brake lock) 40 that may selectively lock disk brake 14. Electrical 
parking brake 45 may include, e.g., an electromagnetic friction slip 
coupling. Electromagnetic friction slip coupling may include, e.g., an 
electromagnet comprising a conductive coil 42 wound around a metal core 54 
and may be located within a housing 44 of electrical parking brake 40. 
Electrical parking brake 40 may also include a metal pin 48, having a 
friction head 56, that may be supported to axially move within housing 44. 
Further, a compression spring 46 may be disposed between metal core 54 and 
metal pin 48 to bias metal core 54 and metal pin 48 away from each other. 
FIG. 3a shows brake actuator 12 as a "released" parking brake, i.e., 
immobilizer 22 is disposed in its "released" (current carrying) state. The 
"released" state of electrical parking brake 40 may be effected by 
applying an electric voltage across conductive coil 42 to provide a 
current therethrough. In operation, if at least one of brake energy 
storage devices 8 has been shown, e.g., through the exemplary procedure 
shown in FIG. 2, to have a sufficient charging state when the vehicle is 
started, control device 20 may effectuate the application of electric 
voltage to brake actuators 12 to actuate the electromagnet. 
When the electromagnet is actuated via current flow through conductive coil 
42, metal pin 48 may be attracted toward the electromagnet and pulled into 
housing 44. The magnetic attraction of the conductive coil 42 to metal pin 
48 is sufficient to overcome the spring force of spring 46. In the 
"released" state, electrical parking brake 40 does not hinder the 
rotational movement of spindle nut 34, thus, enabling the actuation or 
resetting of brake linings 38 and brake pistons 36. 
FIG. 3b shows brake actuator 12 located in a locked state, i.e., the 
immobilizer 22 is in its active state. Preferably, the active state of 
immobilizer 22 may be automatically enabled when the vehicle is turned 
off. 
In the "released" electrical parking brake, brake actuator 12 may be 
actuated until brake linings 38 abuttingly rest against brake disk 14. As 
discussed above, the actuation of brake actuator 12 may be carried out, 
for example, by control device 20 when the vehicle is shut off. While 
maintaining this state, electrical parking brake 40 may be switched over 
from the current carrying "released" state into the non-current carrying 
"locked" or "set" state. The braking system may also be located in the 
locked state by actuation of by control device 20 when the vehicle is shut 
off, i.e., while brake linings 38 are abuttingly resting against brake 
disk 14. The action of the electromagnet may then cancelled by control 
device 20, i.e., the voltage may be removed from conductive coil 42. Upon 
the cessation of the magnetic attraction between conductive coil 42 and 
metal pin 48, compression spring 46 may bias metal pin 48 (and friction 
head 56 ) outward, i.e., toward spindle nut 34. The outward biased force 
exerted on metal pin 48 against spindle nut 34 may produce a friction 
force that is greater than the restoring force of brake linings 38 or the 
spindle rod 58. Thus, the braking system will remain in the locked 
position until an outside force, e.g., via control device 20, releases the 
brakes. 
Thus, brake linings 38 may be locked in their position even when 
electromotor 32 is not being driven and, consequently, brake linings 38 
may also immobilize brake disks 14. 
It is noted that the foregoing examples have been provided merely for the 
purpose of explanation and are in no way to be construed as limiting of 
the present invention. While the invention has been described with 
reference to a preferred embodiment, it is understood that the words which 
have been used herein are words of description and illustration, rather 
than words of limitation. Changes may be made, within the purview of the 
appended claims, as presently stated and as amended, without departing 
from the scope and spirit of the invention in its aspects. Although the 
invention has been described herein with reference to particular means, 
materials and embodiments, the invention is not intended to be limited to 
the particulars disclosed herein; rather, the invention extends to all 
functionally equivalent structures, methods and uses, such as are within 
the scope of the appended claims. For example, the present invention may 
utilize a higher or lower number of press gaps depending on the specific 
need. 
Reference Numeral List 
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2 brake pedal 
4 lines 
6 control unit for brake actuators 
8 brake energy storage device (battery) 
10 wiring system 
12 brake actuators 
14 brake disk 
16 wheel 
18 charge state sensor 
20 control device 
22 immobilizer 
24 sensor 
26 lines 
28 lines 
30 lines 
32 electromotor 
34 spindle nut 
36 brake piston 
38 brake lining 
40 electrical parking brake, e.g., an electrical metal 
friction slip coupling 
42 conductive coil 
44 housing of friction slip coupling 
46 compression spring 
48 metal pin 
52 air gap 
54 metal core 
56 friction head 
58 spindle rod 
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