Electronic pedal assembly and method for providing a tuneable hystersis force

Abstract

An electronic throttle control pedal pivotally couples a lever arm to a pedal beam and biases the beam for resisting an applying force to the pedal beam and for biasing sliding surfaces together in frictional contact. A compression spring carried between a mounting bracket and the lever arm biases the pedal beam toward an idle position while at the same time causing a frictional force between the frictional surfaces, such that displacing the pedal beam with an applying force compresses the spring which increases a frictional force between the friction surfaces with an increasing displacement of the pedal beam distal end, and reducing the displacement through a retracting force on the pedal beam distal end expands the compression spring and returns the pedal beam to the idle position through a hysteresis force response for the pedal beam displacement. The hysteresis may be tuned by modifying element dimensions of the pedal.

Description

FIELD OF THE INVENTION

The present invention relates to pedal assemblies in particular to a pedal for vehicle engines employing electronic throttle control systems, wherein the pedal provides a hysteresis force to simulate a mechanical feel to the pedal during operation by a driver of the vehicle.

BACKGROUND OF THE INVENTION

Electronic controls and computers are well known in the art of automotive manufacturing. It is not unusual for a late model automobile to have a computer for monitoring and controlling many of its operating systems. Typically an input stage may include data collection by sensors. The collected data is input to a processing stage where an electronic control module interprets the data and calculates appropriate output for delivery to an output stage. Actuators within the output stage convert the appropriate output to a desired physical movement. One such operating system includes the electronic throttle control (ETC). In the ETC system, often referred to as a “drive-by-wire” system, the accelerator pedal is not connected to the throttle body by a cable, as in earlier model vehicles, but rather by an electrical connection between the pedal and a throttle controller, as described by way of example in U.S. Pat. Nos. 5,524,589 and 6,073,610. As described by way of example with reference to U.S. Pat. No. 6,098,971, a potentiometer typically replaces the cable that normally runs to the throttle body and electrical wires send pedal position information to a computer. As a result, the pedal must now have its own springs. However, it is desirable to simulate the mechanical feel of a conventional pedal. With each spring having its own feel and no hysteresis effect as does a cable in a sheath, a spring and mechanical hysteresis device is desirable for operation with the pedal for simulating the mechanical feel. A hysteresis force is a controlled frictional force which simulates the friction created in a conventional pedal as the linkage cable is pushed and pulled through a cable sheath. The hysteresis forces have the beneficial effect to a driver, by way of example, of preventing fatigue, as the force needed to maintain a fixed position of the pedal is less than the force to move the pedal to the fixed position. In addition, the hysteresis force helps enable the vehicle operator to maintain a fixed pedal position over bumpy roads. A pedal position sensor provides an electrical voltage output responsive to pedal angular position. The pedal position sensor typically includes a resistive potentiometer that replaces the cable that normally runs to the throttle body of the vehicle engine. As described in U.S. Pat. No. 6,098,971 to Stege et al., and as is well known in the industry, problems inherent with drive-by-wire systems include the need for the pedal to have its own spring, and with its own spring, the feel of the pedal can change from pedal to pedal and manufacturer to manufacturer. To provide a desirable feel, pedals used with electronic controls have included hysteresis devices that provide varying friction during depressing and releasing of the pedal. Typically, and as further described in U.S. Pat. No. 6,098,971, a pedal module for use with ETC systems includes return springs operable with hysteresis elements that provide a varying force against the pedal when being operated between an idle position and an accelerating control position, by way of example.

Various measures of hysteresis force are defined in vehicle manufacturer's specifications for ETC accelerator pedals. In some cases a constant hysteresis force is specified, but in others a hysteresis force which increases with applied pedal force is preferred. Also, the amount of hysteresis force as a percentage of applied force has generally increased as the specifications have become more refined. The need to provide a mechanism which produces a controllable, and “tuneable,” hysteresis force of significant magnitude presents a challenge to the pedal designer.

With no hysteresis force, the force from the return spring balances the applied pedal force. The hysteresis force is a form of friction force that subtracts from the applied force as the pedal is being depressed and subtracts from the spring force as the pedal is being returned toward its idle position. Such friction force depends on a normal force being generated at a frictional surface. A number of arrangements of springs and friction pads, or washers are known. However, there remains a need for a low cost pedal that is simple to fabricate using plastic molding technology and can be tuned to a broad range of customer requirements.

SUMMARY OF THE INVENTION

In view of the foregoing background, the present invention provides a pedal operable with an electronic throttle controller that may be easily and effectively modified to meet varying hysteresis requirements. A reliable yet inexpensive hysteresis effect for a pedal results.

Advantages and features of the present invention are provided by a pedal having a base and a pedal beam rotatably connected to the base. An arm member is pivotally coupled to the pedal beam and includes a friction surface that slidably engages a surface of the base for movement on the surface during rotation of the pedal beam. In one preferred embodiment, a compression spring provides means for biasing the pedal beam and arm member toward a preselected position through a biasing force on the arm member, while simultaneously biasing the friction surface of the arm member against the surface of the base, wherein rotating the pedal beam with an applying force to a free end thereof results in a frictional force between the arm member and the base with an increasing displacement of a pedal free end. Further, reducing the displacement through a retracting force returns the pedal to the preselected position through a hysteresis force response for the pedal beam displacement, wherein the retracting force is less than the applying force by a predetermined amount for a preselected displacement.

A method aspect of the invention provides a preselected hysteresis force response during displacement of a pedal. The pedal includes the pedal beam pivotally connected to the base for rotation about a shaft carried by the base. The method includes pivotally coupling an arm member to the pedal beam. The arm member has a friction surface positioned for engaging a surface of the base for slidable movement thereon. The pedal beam is biased toward a preselected position through a biasing force on the arm member, while simultaneously biasing the friction surface of the arm member against the surface of the base. As a result, rotating the pedal beam with an applying force to a free end of the pedal beam creates a frictional force between the arm member and the base with an increasing displacement of a pedal free end. In addition, reducing the displacement through a retracting force returns the pedal to the preselected position through a hysteresis force response for the pedal beam displacement, wherein the retracting force is less than the applying force by a predetermined amount for a preselected displacement.

By providing the arm member with first and second arm portions of a preselected length dimensions, a preselected biasing of the friction surface of the arm member against the surface of the base can be achieved. In addition, with a longitudinal axis of the arm member extending through a pivot point thereof, and with the friction surface engaging the surface of the base along a friction plane axis oriented at a non-zero angle to the longitudinal axis of the arm member, orienting the friction plane axis at a preselected orientation provides an alternate method of providing desired frictional forces and thus a desired hysteresis. Yet another method includes modifying friction surface materials so as to change their coefficients of friction.

A method further includes sensing rotation of the pedal beam for providing an electrical signal representative of pedal rotation about the rotation axis and thus pedal pad displacement.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention, as well as alternate embodiments are described by way of example with reference to the accompanying drawings in which:

FIGS. 1 and 2 are perspective views of alternate embodiments of the present invention illustrating accelerator pedals operable with an electronic throttle control system;

FIGS. 3 and 4 are exploded perspective views of the pedals of FIGS. 1 and 2, respectively;

FIG. 5 is a partial cross-section view of the pedal of FIG. 1, taken through lines 5—5;

FIG. 6 is a graph of load on a pedal of FIG. 1 versus displacement of the pedal illustrating a desirable hysteresis effect;

FIG. 7 is a geometric diagram, not to scale, illustrating forces acting on elements of a hysteresis device; and

FIG. 8 is an alternate illustration of FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

With reference initially to FIGS. 1-5, and as herein described by way of example, an embodiment of the present invention includes a pedal 10 useful for operation with a motor vehicle having an electronic throttle control system. The pedal 10 comprises a mounting bracket 12 forming a base for mounting the pedal to a vehicle wall. A shaft 14 is carried by the bracket 12 with a pedal beam 16 having a proximal end 18 rotatably connected to the shaft and a distal end 20 operable by a user for applying a force to displace the pedal beam distal end and rotate the pedal beam about a rotation axis 22. As illustrated, by way of example, with reference again to FIGS. 1-4, the pedal beam distal end 20 may have a pedal pad 24 fixed to the distal end, alternatively, a pivotal pad 26 connected via a pivot pin 28 and coil spring 30, or yet other connection, without departing from the intent and teachings of the present invention.

With continued reference to FIGS. 3 and 4, and to FIG. 5, a friction block 32 carried by the mounting bracket 12 includes a first friction surface 34 which is slidable with a second friction surface 36 on an a lever arm 38. Preferably, but not required, the first and second friction surfaces include arcuate surfaces, and in particular concave and convex, respectively. The lever arm 38 is pivotally coupled to the pedal beam 16 at a medial portion 40, with opposing first and second arm members 42, 44 pivotal about the medial portion. By way of example for one coupling arrangement, a boss 46 extends outwardly from an underside surface 47 of the pedal beam 16 and is pivotal within a depression 48 within the medial portion 40 for pivotally coupling the lever arm 38 to the pedal beam 16. The first arm member 42, as herein described by way of example with reference to FIG. 5, includes the second friction surface 36 that slidably engages the first friction surface 34 of the friction block 32.

With continued reference to FIGS. 3-5, a compression spring 50 provides a biasing of the pedal beam 16 away from the mounting bracket 12 by biasing the second arm member 44 away from the mounting bracket, which biasing causes the lever arm 38 to pivot about the boss 46 and cause the second friction surface 36 of the first arm member 42 to be biased against the first friction surface 34 on the friction block 32. A tab 52 carried on the proximal end 18 of the pedal beam 16 is driven against a stop 54 extending from the mounting bracket 12. The stop 54 is positioned for providing an idle pedal position 56 through a biasing spring force 58 on the lever arm 38. Further, a biasing normal force 60 is provided from the second friction surface 36 against the first friction surface 34.

With reference again to FIG. 5, by way of example, and to FIG. 6, displacing the pedal beam distal end 20 by applying an applying force 62 thereto compresses the compression spring 50 which increases the normal force 60, and thus a frictional force 64 between the first and second friction surfaces 34, 36 with an increasing displacement 66 of the pedal beam distal end. Further, reducing the displacement through a retracting force 68 on the pedal pad 24 expands the compression spring 50 and returns the pedal beam 12 to the idle position 56 through a hysteresis force response 70 for the pedal beam displacement 66. The retracting force 68 is desirably less than the applying force 62 for a given displacement.

With reference again to FIG. 5, one preferred embodiment of the present invention includes the first arm member 42 generally orthogonal to the second arm member 44. With such an arrangement, the medial portion 40 pivots with the pedal beam 16, the second arm member is operable with the compression spring 50 for rotating the first arm member about the medial portion and for biasing the second friction surface 36 against the first friction surface 34, without the first arm member contacting the underside 37 of the pedal beam 16. As illustrated with reference again to FIGS. 3-5, the compression spring 50 may include an inner compression spring 72 and an outer compression spring 74 as redundant biasing means or for enhancing the compression required to compress the spring, as desired. Alternatively, resilient material such as plastic or rubber may be used in place of the compression spring. By way of further example, a torsion spring may be used with a pinned pivot point without departing from the teaching of the present invention.

With reference again to FIGS. 5 and 7, and as earlier described, the first friction surface 34 comprises a concave surface and the second friction surface 36 comprises a convex surface. One embodiment of the present invention includes each of the convex and concave surfaces 34, 36 to be defined by a radius of curvature centered about the rotation axis 22 of the pedal beam 12. Further, with a longitudinal axis 76 of the first arm member 42 extending through a pivot point 78 thereof, and the second friction surface 36 engaging the first friction surface 34 along a friction plane axis 80 defining an orientation of the first and second friction surfaces at an angle 82 to the longitudinal axis as illustrated with referenced to FIG. 7 for a flat surface, changing the angle will affect the hysteresis response 70 and can be tuned, or modified as desired, as will be described in greater detail later in this section. By way of further example, the lengths of the first and second arm members 42, 44 can be modified for providing a preselected biasing of the first friction surface to the second friction surface. With reference to the preferred arcuate friction surface of FIG. 5, it should be noted that wear is reduced as a result of the increase in surface contact between the friction surfaces as the pedal is displaced and the normal force increases with the displacement.

With reference again to FIGS. 1-5, a position sensor 84 responsive to rotation of the pedal beam 12 about the shaft 14 provides an electrical signal representative of the rotation and thus the displacement 66 of the pedal.

By way of further example, the pedal 10 described earlier with reference to FIG. 5, by way of example, is shown in schematic form with reference to FIG. 8. Referring to such a schematic and including reference numerals as earlier presented, the pedal beam 16 rotates about the rotation axis 22 with the bracket 12 supporting the pedal beam. The compression spring 50 biases against the lever arm 38 and applies a force to the pedal beam through the lever arm such that the force is applied at the controlled pivot point. Such pivot point may be a pinned joint, or it may be a cylindrical rib interfacing with a mating feature in the pedal beam. As the pedal is depressed, the lever arm interferes with the pedal bracket at the friction surfaces. The normal force 60 is created by the spring operating through the geometry of the lever arm 38. The hysteresis force response 70, as earlier described with reference to FIG. 6, can be altered by the geometry of the lever arm and by the frictional characteristics of the materials that form the friction surfaces. This device uses only one pair of frictional surfaces, for both the down and up displacements of the pedal, to create the hysteresis force. The spring force 58 is the result of the enforced displacement of the spring due to the motion of the pedal beam as well as the motion of the friction link of the friction surfaces.

By way of example, it can be shown by analysis that the applied force 62 to the pedal beam by the hysteresis link can be expressed by: $F_{1y}=F_s+F_s\frac{x_3}{y_1}\left[\frac{\sin \theta +\mu \cos \theta }{\cos \theta -\mu \sin \theta }\right]$for the case in which the pedal is traveling downward.

To simplify, letting Θ=0, Θ being angle 82, the force applied to the pedal beam is $F_{1y}=F_s+F_s\mu \frac{x_3}{y_1}$

The hysteresis force contribution to the force applied to the pedal beam is $F_s\mu \frac{x_3}{y_1}$

The hysteresis force can thus be tailored by the ratio x₃/y₁.

For the case in which the pedal travels upward, or moves in a direction so as to return to the idle position, the direction of the friction force changes so that the force applied to the pedal beam by the hysteresis link is $F_{1y}=F_s+F_s\frac{x_3}{y_1}\left[\frac{\sin \theta -\mu \cos \theta }{\cos \theta +\mu \sin \theta }\right]$

FIG. 8 shows an alternate embodiment of the concept. In this case the friction surface is located at a distance x₄ from the hysteresis pivot point. As before, the frictional surfaces of the hysteresis lever and pedal bracket can be contoured in order to maintain a controlled contact area as the pedal is depressed. For each configuration, the y-component of the normal force contributes to the composite vertical force F_1y transmitted to the pedal beam. For the configuration in FIG. 7, the y-component of the normal force impedes downward pedal motion and aids upward motion. For the configuration of FIG. 8, the y-component of the normal force tends to impede motion in the upward direction.

For the configuration of FIG. 8, it can be shown that the force applied to the pedal beam by the hysteresis link, for the downward pedal travel direction, can be expressed by: $F_{1y}=F_s+\frac{F_s{X}_3\left(\sin \theta +\mu \cos \theta \right)}{y_1\left(\mu \sin \theta -\cos \theta \right)-x_4\left(\mu \cos \theta +\sin \theta \right)}$

The magnitude of the hysteresis force relative to the spring force can be tailored by the values of the hysteresis link parameters x₃, x₄, and y₁.

For the case of upward pedal travel, the force applied to the pedal beam by the hysteresis link can be expressed as: $F_{1y}=F_s+\frac{F_s{X}_3\left(\sin \theta +\mu \cos \theta \right)}{x_4\left(\mu \cos \theta -\sin \theta \right)-y_1\left(\cos \theta +\mu \sin \theta \right)}$

Yet alternate configurations will come to the mind of those skilled in the art as a result of the teachings of the present invention. Regardless of the exact arrangement, knowing the moment arms and forces, a relationship can be developed for elements of interest when determining a desired value for the hysteresis response of displacement versus force for a selected spring constant and element dimensions.

It is to be understood that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

Claims

1. A pedal comprising: a base having a surface thereon; a pedal beam rotatably connected to the base; an arm member having a medial portion pivotally coupled to the pedal beam, the arm member having a friction surface on a first arm portion for slidably engaging the surface of the base and a second arm portion opposing the first arm portion and pivotal about the medial portion; and biasing means operable with the second arm portion for biasing the pedal beam toward a preselected position while simultaneously biasing the friction surface against the surface of the base, wherein rotating the pedal beam with an applying force to a free end thereof results in a frictional force between the arm member and the base with an increasing displacement of the pedal beam free end, and wherein reducing the displacement through a retracting force returns the pedal toward the preselected position through a hysteresis force response for the pedal beam displacement.