Accelerator pedal for a vehicle

A pedal assembly that provides a hysteresis in pedal force-response upon actuation is provided. The pedal assembly includes a housing and a pedal arm that has an end. The end has a rotatable drum that defines a braking surface. The pedal arm is rotatably mounted to the housing. A lever extends from the second end. A brake pad is retained by the housing and has a contact surface that is substantially complementary to the braking surface. The brake pad is adapted to be engaged with the braking surface. A bias spring device is situated between the lever and the brake pad for urging the contact surface of the brake pad into frictional engagement with the braking surface of the drum. A sensor is coupled to the pedal arm to sense the position of the pedal arm.

FIELD OF THE INVENTION

This invention relates to a pedal mechanism. In particular, the pedal may be an accelerator pedal in a vehicle.

BACKGROUND OF THE INVENTION

Automobile accelerator pedals have conventionally been linked to engine fuel subsystems by a cable, generally referred to as a Bowden cable. While accelerator pedal designs vary, the typical return spring and cable friction together create a common and accepted tactile response for automobile drivers. For example, friction between the Bowden cable and its protective sheath otherwise reduce the foot pressure required from the driver to hold a given throttle position. Likewise, friction prevents road bumps felt by the driver from immediately affecting throttle position.

Efforts are underway to replace the mechanical cable-driven throttle systems with a more fully electronic, sensor-driven approach. With the fully electronic approach, the position of the accelerator pedal is read with a position sensor and a corresponding position signal is made available for throttle control. A sensor-based approach is especially compatible with electronic control systems in which accelerator pedal position is one of several variables used for engine control.

Although such drive-by-wire configurations are technically practical, drivers generally prefer the feel, i.e., the tactile response, of conventional cable-driven throttle systems. Designers have therefore attempted to address this preference with mechanisms for emulating the tactile response of cable-driven accelerator pedals. For example, U.S. Pat. No. 6,360,631 Wortmann et al. is directed to an accelerator pedal with a plunger subassembly for providing a hysteresis effect.

In this regard, prior art systems are either too costly or inadequately emulate the tactile response of conventional accelerator pedals. Thus, there continues to be a need for a cost-effective, electronic accelerator pedal assembly having the feel of cable-based systems.

SUMMARY

In one embodiment, the present invention provides a pedal assembly. The pedal assembly includes a housing and a pedal arm that has an end. The end has a rotatable drum that defines a braking surface. The pedal arm is rotatably mounted to the housing. A lever extends from the second end. A brake pad is retained by the housing and has a contact surface that is substantially complementary to the braking surface. The brake pad is adapted to be engaged with the braking surface. A bias spring device is situated between the lever and the brake pad for urging the contact surface of the brake pad into frictional engagement with the braking surface of the drum. A sensor is coupled to the pedal arm to sense the position of the pedal arm.

These and other objects, features and advantages will become more apparent in light of the text, drawings and claims.

DETAILED DESCRIPTION

While this invention is susceptible to embodiment in many different forms, this specification and the accompanying drawings disclose several forms as examples of the invention. The invention is not intended to be limited to the embodiments so described, however. The scope of the invention is identified in the appended claims.

Referring toFIGS. 1-4, a non-contacting accelerator pedal assembly20according to the present invention includes a housing32, a pedal arm22rotatably mounted to housing32, a brake pad44and a bias spring device46. The labels “pedal beam” or “pedal lever” also apply to pedal arm22. Likewise, brake pad44may be referred to as a “body” or “braking lever.” Pedal arm22has ends22A and22B. A footpad27is located toward end22A. Pedal arm end22B has a drum portion29that presents a curved, W-shaped braking (or drag) surface42(best seen inFIGS. 5 and 6). Drum portion29also has a raised center ridge43. A lever210extends from pedal arm end22B adjacent to drum portion29.

Housing32has a sensor section82and a friction mechanism section37. A sensor80is mounted in sensor section82and a friction generating mechanism270is mounted in friction mechanism section37.

Pedal arm22has a forward side28nearer the front of the car and a rearward side30nearer the driver and rear of the car. Footpad27may be integral with the pedal lever22or articulating and rotating at its connection point to pedal lever22. Pedal arm22has an aperture40. Braking surface42of accelerator arm22includes braking surfaces42A,42B,42C and42D that are define a W-shape. In alternate embodiments, surface42can have other shapes.

Pedal arm22pivots from housing32via an axle connection through drum29such that drum29and its contact surface42rotate as pedal arm22is moved. Spring device46biases pedal arm22towards the idle position. Brake pad44is positioned to receive spring device46at one end and contact drum29at the other end. Brake pad44is pivotally mounted to housing32such that a contact surface70is urged against braking surface42as pedal arm22is depressed.

Pedal arm22is coupled to a sensor assembly80in sensor section82for creating a signal representative of pedal displacement. Sensor assembly80can be a contacting variable resistance position sensor. Other sensors could also be used such as optical, mechanical, electrical, magnetic and chemical means.

In an embodiment as illustrated, housing32also serves as a base for the mounted end22B of pedal arm22and for sensor80. Proximal end22B of pedal arm22is pivotally secured to housing32with an axle34. More specifically, drum portion29of pedal arm22includes an opening40for receiving axle34, while housing32has a friction generating cavity or section37with corresponding openings39A and39B also for receiving axle34. Axle34may be press fit into opening40. Axle34is narrowed at its ends where it is collared and supported by a bearing journals19that are mounted in openings39A and39B. A cover220is mounted to housing32and covers one end of axle34and bearing19.

Turning now toFIGS. 8 and 9, in addition to contact surface70, the other features of brake pad44include a top230, a bottom231a button232, a ridge110and ends233and234.

Contact surface70is W-shaped and is located at end234. Contact surface70includes contact surfaces70A,70B,70C and70D that define a W-shape. In alternate embodiments, contact surface70can have other shapes. Contact surfaces70A-D mate with braking surfaces42A-D to form a friction generating mechanism270.

Brake pad44also has opposed trunnions60A and60B (also called outriggers or flanges) to define a primary pivot axis238positioned between spring device46and contact surface70. Contact surface70of brake pad44is situated on one side of this pivot axis and a donut-shaped socket104for receiving one end of bias spring46is provided on the other side.

Brake pad44has stepped flanges240,241and242located toward end233. An aperture233passes through flange242. Bias spring device46includes bias springs46A and46B. Spring46A is larger in diameter than spring46B. Springs46A and46B are co-axial with spring46B being located inside spring46A. Springs46A and46B provide redundancy in case one of the springs fail, another is able to operate. One end of spring46A goes over flange241and rests on flange240. One end of spring46B goes over flange242and rests on flange241.

Contact surface70is substantially complementary to braking surface42. In one embodiment, contact surface70is curved and w-shaped with a substantially constant radius of curvature. In alternate embodiments, braking surface has a varying radius of curvature and other shapes. The frictional engagement between contact surface70and braking surface42may tend to wear either surface. The shape of contact surface42may be adapted to reduce or accommodate wear.

Pedal arm22includes a lever210that extends from pedal arm end22B. Lever210includes a bottom211, a flat base portion260, a rounded flange262and another rounded flange264. One end of spring46A rests on base portion260and one end of spring46B rests on flange262. Therefore, bias spring device46is situated between lever210and brake pad44. Spring device46includes two, redundant coil springs46A and46B in a concentric orientation, one spring nestled within the other. This redundancy is provided for improved reliability, allowing one spring to fail or flag without disrupting the biasing function. It is useful to have redundant springs and for each spring to be capable—on its own—of returning the pedal lever22to its idle position.

As pedal arm22is moved in a first direction72(accelerate) or the other direction74(decelerate), the force FSwithin compression spring46increases or decreases, respectively. Brake pad44is moveable in response to the spring force FS.

As pedal arm22moves towards the idle/decelerate position (direction74), the resulting drag between braking surface42and contact surface70urges brake pad44towards a position in which trunnions60A and60B move slightly outward in slots66and67. This change in position of brake pad44may not be visibly detectable. As pedal arm22is depressed (direction72), the drag between braking surface42and contact surface70draws brake pad44further into cavity portion37and causes trunnions60A and60B to move slightly inward in slots66and67. The sliding motion of brake pad44is gradual and can be described as a “wedging” effect that either increases or decreases the force urging contact surface70into braking surface42. This directionally dependent hysteresis is desirable in that it approximates the feel of a conventional mechanically-linked accelerator pedal.

When pedal force on arm22is increased, brake pad44is urged inwardly on slots66and67by the frictional force created on contact surface70as braking surface42rotates forward (direction120inFIG. 7). This urging forward of brake pad44likewise urges trunnions60A and60B into slots66and67, such that the normal, contact force of contact surface70into braking surface42is relatively reduced.

It is noted that the W-shape of braking surface42and contact surface70provides a larger area to generate increased friction over than just a simple straight surface.

When pedal force on arm22is reduced, the opposite effect is present: the frictional, drag force between44and braking surface42urges brake pad44outward from slots60A and60B (direction121inFIG. 7). This urging backward of brake pad44urges trunnions60A and60B outward from slots60A and60B such that the normal-direction, contact force between braking surface42and contact surface70is relatively increased. The relatively higher contact force present as the pedal force on arm22decreases allows a driver to hold a given throttle position with less pedal force than is required to move the pedal arm for acceleration.

Also for improved reliability, brake pad44is provided with redundant pivoting (or rocking) structures. In addition to the primary pivot axis238defined by trunnions60A and60B, brake pad44defines a ridge110, which forms a secondary pivot axis250.

When assembled, ridge110is juxtaposed to portion248and may form a secondary pivot axis250on which brake pad44may pivot or rock. The secondary pivot axis provided by ridge110and portion248is a feature of accelerator pedals according to the present invention to allow for failure of the structural elements that provide the primary pivot axis, namely trunnions60A and60B and slots66and67. Should the structure of these features be compromised, the pivoting action of brake pad44can occur at ridge110.

With reference toFIGS. 10-13, pedal arm22has predetermined rotational limits in the form of an idle, return position stop500and a depressed, open-throttle position stop520. Open throttle position stop520comprises pedal arm posts525that extend out from each side of pedal arm22and stop walls530on housing32. When pedal arm22is fully depressed, pedal arm posts525come to rest against stop walls530, thereby limiting forward movement of pedal arm22. Stops500and520may be elastomeric or rigid.

Idle position stop500comprises pedal arm wall505and housing wall510. When pedal arm22is released, pedal arm wall505comes to rest against housing wall510and can not move any further in direction74(FIG. 7).

Turning back toFIGS. 1-7, housing32is securable to a vehicle wall via fasteners through mounting holes38. Pedal assemblies according to the present invention are suitable for both firewall mounting or pedal rack mounting by means of an adjustable or non-adjustable position pedal box rack via a bracket or clip602(FIGS. 1 and 2) and a pin610(FIGS. 1,3,4,11, and13). Clip602projects outwardly from the side or wall32A of housing32. In the embodiment as shown inFIG. 3, clip602is in the form of an L-shaped arm or hook604which includes a first portion605which protrudes outwardly from the wall32A of housing32, an elbow607at the end of the first portion605, and a second portion609projecting from the elbow607in a relationship generally normal to the first portion605and spaced from the side or wall32A of housing32and includes a round pin606(FIG. 2) which protrudes outwardly from a distal end of the exterior surface of the second portion609of the arm604and faces the connector shroud320. The pin610projects outwardly from a side32B of housing32and extends in the direction of cover381.

Housing32also has a sensor section or cavity82. Sensor assembly80can be mounted in sensor section82. Sensor assembly80can include a Kapton flexible film371that has resistor tracks372and conductor tracks374. Film371is located in sensor cavity82and rests against wall375. One end of film371is located in slot377. Terminals383are insert molded into housing32. The terminals would extend into connector shroud320and can be connected with a wire harness. A metal pressure wedge380is pressure fit into slot377to make electrical connections between conductor tracks374and terminals383. A rotor376is pressure fit over shaft34. Rotor376has contactors or wipers378attached to one end of the rotor. A sensor cover381is ultrasonically welded to housing32to seal sensor cavity82. In operation rotor376moves as shaft34does. Shaft34is connected to pedal arm22. Movement of pedal arm22causes rotor376and contactors378to move along resistor tracks372and conductor tracks374. As the contactors378move, a voltage applied to the terminals will change magnitude. This is called an electrical output signal and is indicative of the position of pedal arm22. Additional details on the operation and construction of sensor assembly80are detailed in U.S. Pat. Nos. 5,416,295 and 6,474,191, the contents of which are specifically herein incorporated by reference in their entirety.

When a vehicle operator presses on pedal arm22, shaft326rotates. As shaft326rotates, rotor376turns which causes the wipers378to move along the resistor tracks372and conductor tracks374which causes the electrical output signal to change as a function of the pedal position.

A wire harness (not shown) would be mounted to connector shroud320and connect with terminals383. The wire harness typically connects with an engine control computer. The engine control computer controls an electric motor attached to a throttle plate mounted on the intake of the engine. In this manner, the pedal assembly is able to control the throttle setting on the engine electronically or through a wire. Systems of this type are called drive by wire systems.

Housing32can further have a kickdown clip opening or cavity402located on the side of housing32. A kickdown clip400can be mounted inside of and be retained by cavity402. Kickdown clip400can include a projecting button404. Pedal arm22may also include a kickdown lever422that has a flat wall portion422. Kickdown lever422extends from lever210along one side of spring46.

Additional details on the operation and construction of kickdown clip400are detailed in U.S. Pat. No. 6,418,813, entitled, “Kickdown Mechanism for a Pedal”,the contents of which are specifically herein incorporated by reference in their entirety.

When the pedal arm22is near a point of maximum depression, flat wall portion422presses on and engages button404of kickdown clip400. Extra force is then required to be applied to pedal arm22to cause button404to move inwardly into kickdown clip400. The kickdown clip provides a tactile feedback to the pedal operator that the pedal is at a maximum point of depression. The maximum point of pedal depression can correspond to a wide open engine throttle position or can be used to indicate a downshift point for an automatic transmission.

When a pedal operator lifts his foot from footpad27, the loaded bias spring device46causes pedal arm22to rotate about axle34back to the original starting position. This position corresponds to an idle engine throttle position.

When footpad27is depressed, an increasing normal force FNis exerted by the contact surface70against braking surface42. A friction force Ffbetween the surface70and surface42is defined by the coefficient of dynamic friction multiplied by normal force FN. As the normal force FNincreases with increasing applied force Faat footpad27, the friction force Ffaccordingly increases. The driver feels this increase in his/her foot at footpad27. Friction force Ff runs in one of two directions along face70depending on whether the pedal lever is pushed forward72or rearward74. The friction force Ffopposes the applied force Faas the pedal is being depressed and subtracts from the spring force FSas the pedal is being returned toward its idle position.

The pedal assembly20of the present invention can have a directionally dependent actuation-force hysteresis. Initially are larger amount of force may be required to start movement of pedal arm22. A smaller amount of force may then be needed to keep moving pedal arm22.

Pedal assembly20may further have a no-movement zone that allows the driver to reduce foot pedal force while still holding the same accelerator pedal position.

FIG. 14shows a graph of force versus pedal arm travel demonstrating the directionally dependent actuation-force hysteresis provided by accelerator pedal assembly20of the present invention. In an embodiment, pedal force can be reduced 40 to 50 percent before pedal arm22begins to move towards an idle position.

Numerous variations and modifications of the embodiments described above may be effected without departing from the spirit and scope of the novel features of the invention. It is to be understood that no limitations with respect to the specific system illustrated herein are intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.