Brake pedal for motor vehicle

Information

  • Patent Grant
  • 6186026
  • Patent Number
    6,186,026
  • Date Filed
    Thursday, April 1, 1999
    25 years ago
  • Date Issued
    Tuesday, February 13, 2001
    23 years ago
Abstract
A brake pedal for a motor vehicle brake-by-wire brake system including a pedal lever resiliently flexible in beam bending, a foot pad on the pedal lever, and a mounting for the pedal lever on a body of the motor vehicle which constitutes the pedal lever a variable stiffness cantilever spring. The mounting for the pedal lever includes a socket for an inboard end of the pedal lever, a stationary reaction surface on the body of the motor vehicle, and a pedal lever reaction surface on the pedal lever which faces and diverges from the stationary reaction surface in a release position of the pedal lever. The stationary reaction surface and the pedal lever reaction surface become progressively engaged concurrent with resilient flexure of the pedal lever in cantilever spring bending to vary the stiffness of the cantilever spring. The stationary and pedal lever reaction surfaces are contoured or “tuned” to yield a pedal force which initially increases slowly relative to pedal travel and then increases exponentially relative to pedal travel thereby emulating the relationship between pedal force and pedal travel of a brake pedal in a traditional motor vehicle brake system.
Description




TECHNICAL FIELD




This invention relates to a motor vehicle brake pedal.




BACKGROUND OF THE INVENTION




A traditional motor vehicle brake system includes a plurality of hydraulically actuated wheel brakes, a master cylinder, and a brake pedal. The brake pedal includes a pedal lever on a body of the motor vehicle linked to a piston assembly in the master cylinder. To apply the wheel brakes, an operator pushes on a foot pad on the pedal lever to pivot the pedal lever and linearly stroke the piston assembly in the master cylinder. The linear stroke of the piston assembly is opposed or resisted by a force attributable to fluid pressure in the wheel brakes and in a plurality of hydraulic channels between the wheel brakes and the master cylinder. The “pedal force” with which the operator must push on the foot pad to apply the wheel brakes mirrors the fluid pressure force opposing the stroke of the master cylinder piston assembly and initially increases slowly relative to pivotal movement of the pedal lever, i.e. relative to “pedal travel”, as compliance in the wheel brakes and in the hydraulic channels is taken up. Then, pedal force increases at an increasing rate, i.e. exponentially, relative to pedal travel as the wheel brakes become applied. Motor vehicle operators perceive this relationship between pedal travel and pedal force as the “feel” of the brake system and, because of the widespread use of such traditional brake systems for many years, expect generally the same feel from all motor vehicle brake systems. Accordingly, in a motor vehicle brake system in which fluid pressure to apply a wheel brake is created independently of a brake master cylinder by an electro-hydraulic apparatus such as a pump and an electric motor, i.e. in a “brake-by-wire” brake system, the brake pedal is adapted to artificially mimic or emulate the feel of the brake pedal in a traditional brake system. For example, brake pedals described in U.S. Pat. Nos. 5,729,979 and 5,603,217, issued Mar. 24, 1998 and Feb. 18, 1997, respectively, and assigned to the assignee of the this invention, include elastomeric compliant elements which, when squeezed, mimic the fluid pressure force which opposes pedal travel in a traditional motor vehicle brake system. A brake pedal according to this invention is a novel alternative to prior brake pedals which emulate, in a brake-by-wire brake system, the fluid pressure force which opposes pedal travel in a traditional motor vehicle brake system.




SUMMARY OF THE INVENTION




This invention is a new and improved brake pedal for a motor vehicle brake-by-wire brake system including a pedal lever resiliently flexible in beam bending, a foot pad on the pedal lever, and a mounting for the pedal lever on a body of the motor vehicle which constitutes the pedal lever a variable stiffness cantilever spring. The mounting for the pedal lever includes a socket for an inboard end of the pedal lever, a stationary reaction surface on the body of the motor vehicle, and a pedal lever reaction surface on the pedal lever which faces and diverges from the stationary reaction surface in a release position of the pedal lever. The stationary reaction surface and the pedal lever reaction surface become progressively engaged concurrent with resilient flexure of the pedal lever in cantilever spring bending to vary the stiffness of the cantilever spring. The stationary and pedal lever reaction surfaces are contoured or “tuned” to yield a pedal force which initially increases slowly relative to pedal travel and then increases exponentially relative to pedal travel thereby emulating the relationship between pedal force and pedal travel of a brake pedal in a traditional motor vehicle brake system.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a fragmentary schematic representation of a motor vehicle brake-by-wire brake system including a brake pedal according to this invention;





FIG. 2

is a schematic elevational view of the brake pedal according to this invention; and





FIG. 3

is a graphic representation of the relationship between pedal force and pedal travel for the brake pedal according to this invention.











DESCRIPTION OF THE PREFERRED EMBODIMENT




Referring to

FIG. 1

, a schematically represented motor vehicle brake-by-wire brake system


10


includes a fluid pressure actuated wheel brake


12


connected to an electro-hydraulic fluid pressure apparatus


14


, e.g. a pump driven by an electric motor, through a hydraulic channel


16


. The fluid pressure apparatus


14


is controlled by an electronic control module (“ECM”)


18


on the motor vehicle through a conductor


20


to selectively increase a fluid pressure in the hydraulic channel


16


and in the wheel brake


12


to apply the wheel brake to a brake rotor


22


on a wheel, not shown, of the motor vehicle and to release the rotor from the wheel brake by exhausting the fluid pressure in the hydraulic channel and in the wheel brake.




As seen best in

FIG. 2

, a brake pedal


24


according this invention for the brake-by-wire brake system


10


includes a pedal lever


26


having an inboard end


28


and an outboard end


30


. The pedal lever


26


is a beam which may have any coimon structural shape in cross section, e.g. channel shaped, H-shaped, L-shaped, etc., and is preferably made from a composite material such as fiber reinforced plastic which renders the pedal lever resiliently flexible in beam bending. A foot pad


32


is attached to the pedal lever


26


at the outboard end


30


thereof.




The inboard end


28


of the pedal lever


26


is seated in a socket


34


in a fragmentarily illustrated structural portion


36


of a body


36


, not shown, of the motor vehicle to constitute the brake pedal lever a cantilever spring on the body of the motor vehicle. A side


38


of the socket


34


facing a side


40


of the pedal lever opposite the foot pad


32


is extended beyond the socket and defines a stationary reaction surface


42


on the body of the motor vehicle. The fraction of the side


40


of the pedal lever facing the stationary reaction surface


42


defines a pedal lever reaction surface


44


on the pedal lever between the inboard end


28


thereof and the foot pad


32


. Outboard of the socket


34


, the pedal lever reaction surface


44


and the stationary reaction surface


42


diverge when the pedal lever is in a release position illustrated in solid lines in

FIG. 2

characterized by the absence of flexure of the pedal lever in cantilever spring bending. A schematically represented transducer


46


, e.g. a strain gage, Hall effect sensor, fiber optic device, or the like, on the pedal lever


26


is electronically linked to the ECM


18


through a conductor


48


.




In operation, the pedal lever


26


assumes its release position when the foot of an operator of the motor vehicle is removed from the foot pad


32


. A corresponding the electronic signal from the transducer


46


to the ECM


18


characteristic of instantaneous pedal force and pedal travel or the absence thereof causes the ECM to control the fluid pressure apparatus


14


to exhaust the fluid pressure in the hydraulic channel


16


and in the wheel brake


12


to release the brake rotor


22


from the wheel brake.




To stop or slow the motor vehicle, the operator pushes on the brake pedal


24


by applying a pedal force, schematically represented by a vector force “F”, on the foot pad


32


. The pedal lever


26


resiliently flexes clockwise,

FIG. 2

, in cantilever spring bending in response to application of the pedal force F thereby to mimic the pivotal movement of the pedal lever of a brake pedal in a traditional motor vehicle brake system. At the same time, an electronic signal from the transducer


46


on the pedal lever proportional to the input of the operator with respect to pedal travel and applied force causes the ECM


18


actuate the fluid pressure apparatus


14


to increase the fluid pressure in the hydraulic channel


16


and in the wheel brake


12


to squeeze the wheel brake against the brake rotor


22


.




In its release position, the pedal lever


26


has an effective span S


1


between the socket


34


and the middle of the foot pad


32


. As the pedal lever resiliently flexes clockwise in cantilever spring bending to a full brake apply position


26


′,

FIG. 2

, its effective span progressively decreases to an effective span S


2


as the pedal lever reaction surface


44


progressively engages the stationary reaction surface


42


. As its effective span decreases, the stiffness of the cantilever spring defined by the pedal lever increases. Therefore, in order to stroke the pedal lever from its release position to its full brake apply position, the pedal force F applied by the operator on the foot pad


32


must vary at the rate the stiffness of the cantilever spring varies as dictated by the relative contours of the stationary reaction surface


42


and the pedal lever reaction surface


44


.




The stationary reaction surface


42


, the pedal lever reaction surface


44


, and the structural shape of the pedal lever


26


are all contoured to yield a relationship between pedal force and pedal travel which mimics or emulates the corresponding relationship in a traditional motor vehicle brake system. More particularly, the pedal lever


26


is stiff enough to remain substantially stationary until the pedal force F attains a small minimum magnitude F


1


,

FIG. 3

, when the operator pushes on the foot pad


32


. Then, the relative contours of the pedal lever reaction surface and the stationary reaction surface cause the pedal force F to increase slowly relative to pedal travel to an intermediate magnitude F


2


as the pedal lever flexes resiliently in cantilever spring bending to emulate the interval in the traditional motor vehicle brake system when compliance is eliminated from the hydraulic channels and the wheel brakes. Thereafter, the relative contours of the pedal lever reaction surface and the stationary reaction surface cause the pedal force F to increase at an increasing rate, i.e. exponentially, relative to pedal travel up to a maximum magnitude F


3


in the full apply position


26


′ of the pedal lever to emulate the interval in the traditional motor vehicle brake system during which the wheel brakes become applied.




When the operator releases the foot pad


32


, the cantilever spring defined by the pedal lever


26


resiliently unbends to the release position of the pedal lever. At the same time, the transducer


46


electronically signals the ECM


18


to control the electro-hydraulic apparatus


14


to exhaust the fluid pressure in the hydraulic channel


16


and in the wheel brake


12


to release the brake rotor


22


from the wheel brake.



Claims
  • 1. A motor vehicle brake pedal for a brake-by-wire brake system comprising:a pedal lever resiliently flexible in beam bending having an inboard end and an outboard end, a socket means operative to rigidly connect the pedal lever at the inboard end thereof to a body of the motor vehicle thereby to constitute the pedal lever a cantilever spring on the body of the motor vehicle, a foot pad on the pedal lever at the outboard end thereof whereat a pedal force is applied to effect pedal travel in the form of resilient flexure of the pedal lever in cantilever spring bending from a release position to a brake full apply position, a stationary reaction surface on the vehicle body, and a pedal lever reaction surface on the pedal lever between the inboard end thereof and the foot pad diverging from the stationary reaction surface in the release position of the pedal lever and progressively engaging the stationary reaction surface in response to resilient flexure of the pedal lever in cantilever spring bending from the release position thereof to the brake full apply position thereof, the stationary reaction surface and pedal lever reaction surface being contoured relative to each other to vary the stiffness of the cantilever spring defined by the pedal lever in response to resilient flexure thereof in cantilever spring bending from the release position to the brake full apply position thereby to vary the rate of change of the pedal force relative to the pedal travel of the pedal lever.
  • 2. The motor vehicle brake pedal for a brake-by-wire brake system recited in claim 1 wherein:the stationary reaction surface and the pedal lever reaction surface are contoured relative to each other to yield a first interval in which the pedal force increases at a first rate relative to the pedal travel followed by a second interval in which the pedal force increases at a second rate relative to the pedal travel exceeding the first rate of increase relative to the pedal travel.
  • 3. The motor vehicle brake pedal for a brake-by-wire brake system recited in claim 2 further comprising:a transducer means on the pedal lever operative to provide an electronic signal corresponding to the position of the pedal lever between the release position thereof and the full brake apply position thereof and to the magnitude of the pedal force thereon.
  • 4. The motor vehicle brake pedal for a brake-by-wire brake system recited in claim 3 wherein the transducer means comprises:a device on the pedal lever selected from the group consisting of a strain gage and a Hall Effect sensor and a fiber optic device.
US Referenced Citations (10)
Number Name Date Kind
4958607 Lundberg Sep 1990
5233882 Byram et al. Aug 1993
5385068 White et al. Jan 1995
5415144 Hardin et al. May 1995
5729979 Shaw et al. Mar 1998
5868040 Papenhagen et al. Feb 1999
5887488 Riggle Mar 1999
5937707 Rixon et al. Aug 1999
6003492 Muto et al. Dec 1999
6019016 Takagi et al. Feb 2000
Foreign Referenced Citations (2)
Number Date Country
2833792 A1 Feb 1980 DE
1164637 Feb 1980 FR