U.S. patent application number 09/168032 was filed with the patent office on 2001-06-14 for method of braking an electrically driven vehicle.
This patent application is currently assigned to HAYES SOLOWAY HENNESSEY GROSSMAN & HAGE. Invention is credited to VALFRIDSSON, GORAN, VIKMAN, LEIF.
Application Number | 20010003401 09/168032 |
Document ID | / |
Family ID | 20408533 |
Filed Date | 2001-06-14 |
United States Patent
Application |
20010003401 |
Kind Code |
A1 |
VIKMAN, LEIF ; et
al. |
June 14, 2001 |
METHOD OF BRAKING AN ELECTRICALLY DRIVEN VEHICLE
Abstract
Method of braking a vehicle driven by an electric motor, in
particular industrial truck, where the rotational speed of the
motor is reduced according to a predetermined deceleration
characteristic (a-d) when braking is activated. Preferably the
deceleration characteristic is chosen in dependency of the length
of depression of a brake pedal.
Inventors: |
VIKMAN, LEIF; (MIOLBY,
SE) ; VALFRIDSSON, GORAN; (MIOLBY, SE) |
Correspondence
Address: |
HAYES SOLOWAY HENNESSEY
GROSSMAN & HAGE
175 CANAL STREET
MANCHESTER
NH
031012335
|
Assignee: |
HAYES SOLOWAY HENNESSEY GROSSMAN
& HAGE
|
Family ID: |
20408533 |
Appl. No.: |
09/168032 |
Filed: |
October 7, 1998 |
Current U.S.
Class: |
303/20 |
Current CPC
Class: |
B60L 7/26 20130101; B60L
50/51 20190201; Y02T 10/70 20130101; Y02T 10/64 20130101; Y02T
10/72 20130101 |
Class at
Publication: |
303/20 |
International
Class: |
B60T 013/66 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 7, 1997 |
SE |
9703652 |
Claims
1. Method of braking a vehicle driven by an electric motor, where
the vehicle drive wheel (10) rotational speed is proportional to
the rotational speed of the electric motor (6), characterized in
that a vehicle driver activates a maneuvering means (14, 16, 18) at
which an electronic control unit sends signals to a control unit
(28) of the electric motor to reduce the rotational speed of the
motor according to a predetermined deceleration characteristic
(a-d).
2. Method according to claim 1 where the maneuvering means (16) can
be activated to a number of different activation positions,
preferably, in the form of a brake pedal, characterized in the
rotational speed of the electric motor (6) being reduced during the
time the maneuvering means (16) is activated according to one of a
number of available predetermined deceleration characteristics
(a-d) where the characteristic (a-d) is chosen in dependency of the
activation position of the maneuvering means (16 ) so that the
rotational speed is reduced more rapidly the further the
maneuvering means (16) is brought from its initial position.
3. Method according to claim 1 or 2 where the maneuvering means 16
can be activated to a number of different activation positions,
characterized in that when the driver activates the maneuvering
means (16) past a first position a supplementary brake device (36)
is activated that influence one or more vehicle wheels (12) .with a
braking torque, the control unit (28) of the electric motor feeding
the motor the current/torque that is required for the motor
rotational speed to correspond the deceleration characteristic (ad)
in question.
4. Method according to claim 3, characterized in that a number of
supplementary brake devices (36, 30) are activated when the
maneuvering means (16) pass a for respective brake device
corresponding position, the electric motor control unit (28)
feeding the motor (6) the current required for the rotational speed
of the motor to correspond to the current deceleration
characteristic (a-d).
5. Method according to any of the preceding claims , characterized
in the method being used on an industrial truck with an
asynchronous motor (6) where the maneuvering means (16) is
constituted by a brake pedal.
6. Method according to claim 5, characterized in that when the
maneuvering means (16) pass a first position an electromagnetic
brake (36) is activated working on support wheels (12) arranged in
support arms (13) of the truck, and when the maneuvering means (16)
pass a second position close to its mechanical end position an
electromagnetic brake (30) is activated working directly or
indirectly on the driving wheel (10).
7. Method according to claim 1, characterized: in the driver
activating a travel direction switch (18), in particular in an
industrial truck.
8. Method according to claim 7, characterized in that the
rotational speed of the electric motor (6) is reduced according to
one of a number of available predetermined deceleration
characteristics (a-d), where the characteristic (a-d) is chosen in
dependency of the activation position of an accelerator (14) so
that the rotational speed is reduced quicker farther the pedal is
from its initial position.
9. Method according to claim 1, characterized in that the driver
activates an accelerator (14), in particular an industrial truck,
by release towards an initial position.
10. Method according to any of the preceding claims, characterized
in that one or several available predetermined deceleration
characteristics (a-d) can be varied by adjustment of a parameter
influencing the electronic control unit (24).
Description
[0001] This invention concerns a method of braking a vehicle driven
by an electric motor in accordance with the preamble of claim
1.
STATE OF THE ART
[0002] The industrial trucks of today that are used indoors are
usually provided with an electric motor in the form of a DC-motor
driving a drive wheel via a gearbox. The truck is further provided
with a number of pivot wheels and/or support wheels.
[0003] The truck is among other things maneuvered by means of a
throttle pedal or accelerator that dependent on its position sends
signals to an electronic control unit that furthers signals to the
control unit of the motor regarding suitable rotational speed for
the driving of the truck with the chosen travel speed.
[0004] The truck is further maneuvered with a brake pedal that
influence hydraulically controlled mechanical brakes that can
influence support wheels as well as drive wheel with suitable
torque in dependency of the position of the brake pedal.
[0005] The truck can also be braked by the driver changing a travel
direction switch to opposed travel direction, alternatively just
releases the accelerator, so called auto-braking, at which the
electronic control unit delivers a signal to the motor control unit
to brake the engine with a suitable torque.
[0006] These solutions leads to a variation of the brake distance,
depending on how heavily loaded the truck is since a heavier load
requires greater breaking torque to retain a given break
distance.
[0007] Further there is the risk that such a high braking torque is
applied that the wheels lock which in addition to longer braking
distance also leads to increased wear on wheel as well as gearbox.
The wheel also risk becoming locked where the friction is
insufficient, e.g. at an oil spot, where it thus will be locked
when sufficient friction again exists which can give the mentioned
damages. Furthermore this can lead to technical control problems
since the control system can get the impression of the truck
standing still when the wheel no longer rotates and therefore
interrupts the braking which then can lead to serious
accidents.
[0008] Regenerative return of braking energy to the battery can
only take place at "motor braking" using travel direction switch or
released accelerator.
OBJECT OF THE INVENTION
[0009] The object of the invention is to provide a method to brake
an industrial truck where the brake distance is relatively
independent of the load of the truck, where maximum brake torque
can be limited in order to prevent overloading of tie gearbox, and
where the risk of wheel locking is minimized.
BRIEF STATEMENT OF THE INVENTION
[0010] The object of the invention is achieved with a method in
accordance with the characterizing part of claim 1. By controlling
the motor so that its rotational speed is reduced according to a
predetermined function of the time the deceleration of the motor is
thus controlled and therewith also the deceleration of the driving
wheel and the track according to a predetermined characteristic.
Accordingly a constant brake distance is obtained independent of
load since the control unit controls the motor with the braking
torque required to give the desired deceleration, where thus the
braking torque varies with the load.
[0011] By choosing a suitable characteristic a deceleration can be
obtained that at permitted loads gives a braking torque that do not
cause damage to the gearbox and minimizes the risk of the wheel
becoming locked since it has a rotation speed proportional to that
of the motor.
[0012] Regenerative feedback of brake energy to the battery can
take place in some known way.
[0013] By using a method according to claim 2 different
deceleration characteristics can be used dependent on the activated
position of the maneuvering means. Thus the truck can be triggered
to a faster braking (greater deceleration) the more the brake pedal
is depressed.
[0014] By using a method according to the claims 3 and 4
supplementary brake systems can be triggered when the brake pedal
is depressed further than a predetermined position. Hence the motor
need only to be fed with the braking current /torque that is
required in addition to the braking torque of the supplementary
system/systems and a relatively powerful deceleration can be
achieved,
[0015] The claims 5 and 6 defines further specified preferred
embodiments when applied to industrial trucks, while the claims 7-9
defines embodiments where accelerator and travel direction switch
are used as maneuvering means.
[0016] By using a method according to claim 10 the desired vehicle
deceleration can be adapted dependent on type of vehicle and
driving conditions.
[0017] Further features and advantages of the invention are
apparent from the below described preferred embodiment with
reference to the enclosed figures.
LIST OF FIGURES
[0018] FIG. 1 shows a schematic view of a truck.
[0019] FIG. 2 shows schematically the components of the brake
system of the truck.
[0020] FIG. 3 shows a more detailed picture of the control unit of
the motor according to FIG. 2.
[0021] FIG. 4 shows a diagram of the motor rotational speed n as a
function of the time t dependant of the brake pedal depression.
[0022] FIG. 5 shows a diagram of the brake force F as a function of
the brake pedal depression x.
DESCRIPTION OF AN EMBODIMENT
[0023] The industrial truck 1 shown in FIG. I is preferably used
indoors and includes as essential parts a chassis 2 to which a mast
assembly 4 for the handling of goods is arranged. The truck is
driven via an asynchronous motor 6 transferring power to a driving
wheel 10 via a gearbox 8. The truck is further provided with
support wheels 12 in the front end of the support arms 13. The
support wheels 12 and the drive wheel 10 can be braked with
electromagnetic brakes (not shown in FIG. 1).
[0024] The truck is maneuvered in the usual way with among other
things an accelerator 14 and a break pedal 16 whose starting
position is define as fully released position. Further there is a
travel direction switch 18 and a steering wheel 20. The components
for goods handling are maneuvered in some known manner that does
not influence the invention and are therefor not described
here.
[0025] At use the driver gives signals to the truck regarding
desired travel speed in the usual way by means of the accelerator
14. When the driver depresses the accelerator 14 a signal is
delivered to an electronic control unit 24 that in turn delivers a
signal to a motor control unit 28 that control the motor 6. The
signal that is transmitted to the electronic control unit varies
dependent on how far the accelerator 14 is depressed and the
electronic control unit 24 then delivers a signal to the motor
control unit 28 to run the motor with a rotational speed
corresponding to the accelerator position.
[0026] More specific this is achieved by the electronic control
unit 24 delivering a signal of desired rotational speed to a
rotational speed controller 38 in the electronic control unit
delivering a signal to a torque controller 40 that via a power
controller 42 delivers a current to the motor 6 with an amperage
corresponding to suitable torque for the desired rotational speed.
The signals are controlled in usual manner by means of feedback 44,
46 of actual values to the rotational speed controller 38 and the
torque controller 40.
[0027] The braking method according to the invention according to
the invention is now described below with reference to the FIGS.
2-5.
[0028] Principally one can say that the driver can brake the track
in three different ways by means of different maneuvering means;
with the brake pedal 16, by changing travel direction by means of
the travel direction switch 20, or by releasing the accelerator and
letting the truck motor brake. The method for maneuvering with the
brake pedal is now described below.
[0029] When the driver depresses the brake pedal 16 a signal is
delivered to the motor 6 via is the electronic control unit 24 and
the motor control unit 28 to reduce the rotational speed of the
motor according to a characteristic with a predetermined
deceleration. The deceleration characteristic is preferably
constituted of the rotational speed as a function of the time. The
controlling is done in a way that corresponds to the above method
at accelerating The signal transmitted to the electronic control
unit 24 varies dependent of how far the pedal 16 is depressed with
more depression giving a steeper characteristic, which thus gives a
greater deceleration and thus a more powerful braking. This Is
apparent from FIG. 4 where the characteristics a-d show different
decelerations dependant of how far the pedal is depressed, where
characteristic d shows the greatest deceleration, that is the most
powerful braking.
[0030] Since the driving wheel 10 is connected to the motor 6 via a
fixed gear 8 its rotational speed is directly proportional to the
motor rotational sped and its brake distance is therefor the same
independent of load since the control system will provide the motor
with the braking torque that is required.
[0031] By choosing these characteristics in suitable manner it is
possible to avoid so powerful torques that the wheel locks at
normal friction. In this way the additional damages that otherwise
may occur are avoided.
[0032] Since the wheel the entire time rotates with a given speed
the properties at temporary slippery places are improved, as for
instance small oil spots, Here the wheel of course risks to slip on
the ground reducing the deceleration of the truck, but the wheel is
not locked entirely but will rotate according to the given
characteristic and when sufficient friction exist again the truck
continues to decelerate.
[0033] Regeneration of brake energy to the battery 32 of the truck
can be achieved in some known manner.
[0034] Cases may occur, in particular with a heavily loaded truck
and high initial speed, where only braking through controlling the
motor torque as: described above can not provide sufficient brake
power to brake the truck according to the desired characteristic.
This is of course not desirable from the point of safety since this
leads to a longer braking distance.
[0035] This problem is by the invention solved by the following
further developed embodiment.
[0036] When the brake pedal is depressed past a first predetermined
position, for instance 50% of maximum depression, a supplementary
brake system is activated. I n this case it is an electromagnetic
brake 36 working on the support wheels 12 when an incoming signal
is received from the electronic control unit 24.
[0037] This brake 36 is analogous so that the braking torque
increase with increased pedal depression past the mentioned
position. The electronic control unit however continue to deliver a
signal to the motor control unit 28 to follow the default
characteristic a-d, possibly a steeper characteristic is chosen
since the pedal depression increases. This results in the
rotational speed of the motor following the characteristic
according to FIG. 4 and the deceleration and wheel speed follow
this independent of the activation of the support wheel brake. The
resulting difference is that the motor control unit 28 will adjust
to give the motor 6 the braking torque (motor brake) that is
required in addition to the torque from the support wheel brake 36.
In FIG. 5 the braking force F as a function of the brake pedal
depression x. From this it is apparent that the contribution M from
the motor brake cease to increase at 50% depression of the pedal 16
and that the support wheel brake contribute with the remaining part
of the required brake torque S. Depending on the type of operation
percentage distribution of the contributions may vary some. Thus in
some cases the contribution of the motor brake may decrease
somewhat when the support wheel brake is activated.
[0038] It is desirable to dimension the controlling so that the
motor brake take as large a pan as possible of the brake energy
since only this contribution can be used for regenerative feedback,
and to reduce the wear of the supplementary support wheel
brake.
[0039] Furthermore additional supplementary brake systems can be
activated as the pedal depression continues. According to the
preferred embodiment shown here a final digital one step brake 30
is activated just before the pedal 16 reaches its bottom position
This brake subjects the driving wheel to a predetermined braking
torque. Owing to this the motor brake only have to contribute with
the torque that is required addition to the torques of the one step
brake 30 and the support wheel brake 36. The one step brake is
preferably constituted of the same electromagnetic brake that is
used as parking brake and its brake contribution is in FIG. 5
denoted with P.
[0040] In this way the truck braked according to a predetermined
deceleration dependent of the degree of pedal depression, but where
the electronic control system activates supplementary brake devices
in differing degree depending on type of operation so that the
predetermined deceleration progress is followed independent of type
of operation. The support wheel brake and parking brake are
activated first after a predetermine pedal movement so that the
motor brake can contribute with as big a part as possible and
without the driver actually having to observe that different brake
systems are activated. An even and secure brake progress is
obtained.
[0041] The brake progress can in the normal way be disrupted before
the truck bas stopped entirely by the driver releasing the pedal to
its initial position.
[0042] According to a further development of the invention the
inclinations of the characteristics ad can be set differently
depending or type of truck or actual driving conditions. This is
preferably achieved by adjustment of a parameter that influence the
electronic control unit 24, the parameter can preferably be changed
by a service engineer.
[0043] Braking by means of the travel directions switch 18 is done
in principally the same way when the driver signals changed travel
direction tie motor is braked in the same way by the electronic
control unit delivering signals concerning desired deceleration.
Also here a number of deceleration characteristics ad corresponding
to FIG. 4 can exist. These are chosen depending the position of the
accelerator 14 where a more depressed pedal gives a more powerful
deceleration. Adjustment of the parameter 22 is possible here also.
At this type of braking however tic supplementary brakes 36, 30 are
never activated.
[0044] The same principal method is also used at so called auto
braking where the truck is braked when the driver ease up the
accelerator. Here also the parameter 22 can be changed in order to
enable different choice of characteristics Corresponding to FIG. 4.
In this case the maneuvering means is constituted by the
accelerator 14 that activates the braking at release towards
inactivated position.
[0045] This further means that auto braking occurs after braking
with the brake pedal 16 where this is disrupted by release of the
pedal.
[0046] The invention can within the scope of the Patent claims be
executed according to other embodiments than those above described.
It may for instance be used On other types of trucks where
analogous conditions and problems exist. Furthermore the
asynchronous motor can be replaced by some other type of electric
motor used at trucks. Furthermore the brake pedal can be replaced
by some other maneuvering means, as travel direction switch or
accelerator according to the second and third brake method above,
or some other type of known maneuvering means even if the mentioned
ones are to be preferred since they are well tested and safe
designs.
[0047] According to the embodiment the predetermined deceleration
characteristics have the rotation speed of the motor as a function
of time, which is suitable choice. It may also be possible to
control according to other parameters that give a deceleration
controlled braking, as vehicle speed or distance.
* * * * *