Pedal emulator for a motor vehicle

A pedal emulator (20, 100) is provided. The pedal emulator includes an emulator piston (28, 102) coupled to a damper (46, D1) that is contained within a housing (22, 104). The damper is surrounded by first (34, S1) and second (38, S2) springs that are carried by a lower spring seat (114), the lower spring seat being upwardly biased by a third spring (S3), for example a wave spring. The first and second springs and the third spring cooperate to provide a counter-force that is tailored to the desired feel of the pedal. First and second sensors measure travel (72, 74) and force in response to downward compression of the emulator piston, and the damper provides hysteresis upon return travel of the emulator piston. A method comprising: providing a brake pedal emulator (100) including an emulator piston (102), the emulator piston (102) being operatively coupled to a brake pedal, wherein the brake pedal emulator (100) is adapted to provide a first force response during a first portion of travel of the emulator piston (102) and a second force response during a second portion of travel of the emulator piston (102); detecting a sequence of actuations of the brake pedal using the brake pedal emulator (100) for conversion into a selected driver input command; and providing vibratory feedback to the brake pedal using a haptic actuator, the vibratory feedback being in response to the selection of a driver input command.

FIELD OF THE INVENTION

The present invention relates to pedal emulators for motor vehicles, and in particular, pedal emulators for providing a counter-force to a pedal of a brake-by-wire system and other applications, including accelerator pedals and clutch pedals.

BACKGROUND OF THE INVENTION

Motor vehicles can include brake-by-wire systems, in which a braking demand is determined electronically at the brake pedal. Brake-by-wire systems offer a number of advantages over conventional brake systems, including weight advantages and reduction of vehicle packaging space, and can be readily integrated into anti-lock braking systems and regenerative braking systems.

Some brake-by-wire systems provide a brake pedal feel that differs from the brake pedal feel found in conventional brake systems. For example, conventional brake systems provide a counter-force that typically varies as the brake pedal is depressed due to a non-linear reaction force in the brake master cylinder, among other factors.

Accordingly, brake pedal emulators have been developed for brake-by-wire systems to simulate a desired counter-force and replicate the feel of a conventional braking system. Existing brake pedal emulators typically include a spring piston and/or a hydraulic piston that gradually opposes depression of the brake pedal. Despite the advantages of existing brake pedal emulators, there remains a continued need for an improved pedal emulator for brake pedals, accelerator pedals, and clutch pedals. In particular, there remains a continued need for an improved pedal emulator that provides a desired counter-force and hysteresis in response to depression of a pedal, optionally with efficiencies in mass and packaging over existing systems.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the invention, a pedal emulator for a motor vehicle is provided. The pedal emulator includes an outer housing for mounting the pedal emulator to a footwell, a control rod for mounting the pedal emulator to a pedal, and a parallel circuit therebetween, the parallel circuit including a first spring in series with a second spring as a first series circuit, the parallel circuit further including a damper connected in parallel with the first series circuit and including a hysteresis generating system. The pedal emulator is adaptable for use with different types of pedals of a motor vehicle without changes in its basic structure. For example, the very different haptic feedback of conventional brake pedals, accelerator pedals, and clutch pedals can be simulated in their respective complexity using the pedal emulator of the current embodiments. Using the damper of the pedal emulator, a speed dependency of the simulated haptic feedback is realized, since the damper acts as a function of the actuation speed of a pedal equipped with the pedal emulator of the current embodiments.

In one embodiment, the parallel circuit includes a second series circuit of at least two springs. In this way, the adjustment of the pedal emulator and the imitation of complex haptic feedback is further improved. In addition, by the parallel connection of a first series circuit and a second series circuit, redundancy is generated, which ensures, for example, in a malfunction in one of the series circuits, that a pedal equipped with the pedal emulator in case of non-actuation by a user is moved in the direction of the rest position.

The springs of the first series circuit and the second series circuit include a type, spring constant, dimension, material, and arrangement that are freely selectable within wide appropriate limits. The springs of the first series circuit and the second series circuit expediently bias the control rod apart from the base of the outer housing in a rest position of the pedal emulator. As a result, any undesired slip in the operation of the pedal emulator according to the embodiment is effectively prevented in a structurally simple manner.

Further, the springs of the first series circuit and the second series circuit at least partially have a linear spring characteristic and/or a progressive spring characteristic. Springs with the aforementioned spring characteristics are particularly well suited to simulate the complex haptic feedback of conventional pedals of a motor vehicle. Each spring is disposed between two mutually corresponding bearing parts and is arranged with a limited amount of travel. The two bearing parts are formed as two pistons or as a piston and a housing part. The bearing parts are also referred to herein as “spring seats,” which carry the ends of the springs.

The present embodiment can provide a spring with a progressive spring characteristic arranged between mutually corresponding bearing parts. In this way, transitions from one portion of travel of the control rod (relative to the base of the outer housing) to a subsequent portion of travel of the control rod can be made more uniform.

The hysteresis generation system is freely selectable in terms of type, material, dimension and arrangement, within suitable limits. In the current embodiment, the hysteresis generating system is a friction system. The friction system includes at least two friction partners with mutually corresponding friction surfaces sliding over each other. Frictional hysteresis is manifested for example in the slowed return of the control rod. Friction systems are structurally easy to implement and easily adjustable to the particular requirements of the individual case.

In the current embodiments, the friction system is biased by the first series circuit, the second series circuit, or the first and second series circuits, such that the mutually corresponding friction surfaces are pressed against one another. This ensures that the friction partners of the friction system generate in each position of the pedal emulator a defined, predetermined friction. In addition, the mutually corresponding friction surfaces are arranged parallel to the direction of the spring force of the first series circuit and/or the second series circuit, wherein the spring force is deflected radially outward by 90°. In this way, a compact construction of the pedal emulator according to the current embodiment is made possible.

The pedal emulator according to one embodiment includes at least one displacement sensor for detecting the relative movement between the outer housing and the control rod. As a result, the pedal emulator is simultaneously designed as a displacement sensor for detecting the pedal travel of the pedal equipped with the control rod. Additional components and thus additional installation space for the sensor system can thus be saved.

The pedal emulator according to one embodiment includes at least one force sensor to detect the force applied to the control rod. In this way, the pedal emulator is simultaneously a force sensor for detecting the force exerted on the pedal equipped with the pedal emulator of this embodiment. Thus, a further saving of components and space is feasible.

The displacement sensor and/or force sensor is freely selectable according to type, dimension, material, and arrangement, within suitable limits. Advantageously, the force sensor has at least one sensor spring, wherein the sensor spring is arranged in series with the parallel circuit. As a result, an additional adjustment of the pedal emulator according to an embodiment of the invention is created in order to mimic each different complex haptic feedback

In accordance with another embodiment of the invention, a brake pedal emulator for a brake-by-wire system is provided. The brake pedal emulator includes an emulator piston coupled to an internal damper. The internal damper is surrounded by first and second springs that are carried by a lower spring seat, the lower spring seat being upwardly biased by a third spring, for example a wave spring. The first, second, and third springs cooperate to provide a counter-force to the emulator piston. The counter-force includes multiple stages that allow for tailoring to a desired feel of the brake pedal. Further embodiments can optionally include a fourth spring, for example a resilient bumper. The internal damper provides a desired elastic hysteresis during return travel of the emulator piston, and first and second non-contact sensors measure position and force through a full range of motion of the emulator piston.

In another embodiment, a method for providing vibratory feedback to the brake pedal is provided. The vibratory feedback can relate to a vehicle operating state. For example, a haptic actuator can provide vibratory feedback in response to activation of the motor, for example an electric motor. The haptic actuator is incorporated into the brake pedal emulator in some embodiments, while in other embodiments the haptic actuator is external to the brake pedal emulator. In addition, the brake pedal emulator can be used to receive information from the driver, separate and apart from a desired braking demand. For example, multiple actuations of the brake pedal during a vehicle non-operating state can be converted into an engine/motor start command, or to a transmission shift command. Acknowledgment of these commands can be confirmed with a haptic vibration of the brake pedal.

These and other features and advantages of the present invention will become apparent from the following description of the current embodiments, when viewed in accordance with the accompanying drawings and appended claims.

DETAILED DESCRIPTION OF THE CURRENT EMBODIMENTS

Referring toFIGS. 1-5, a pedal emulator in accordance with one embodiment is illustrated and generally designated20. The pedal emulator20includes an outer housing22for mounting the pedal emulator20to a footwell panel and includes a control rod24with a ball head26for mounting the pedal emulator20to a pedal. The control rod24is attached to a first piston28. The first piston28engages with a first bearing part30functioning as a friction element. Between the first bearing part30and a second piston32that serves as a bearing member, is disposed a first spring34, and between the first bearing part30and a third piston36is disposed a second spring38. The first spring34and the second spring38are arranged in parallel.

Between the second piston32and the closed end of the inner housing40is disposed a third spring42, and between the third piston36and the closed end of the inner housing40is disposed a fourth spring44. The springs34,38,42,44are formed as coil springs. The pedal emulator20also includes a damper46connected to the control rod24and the inner housing40. The inner housing40is nested within the outer housing22as shown inFIG. 2. The outer housing22and the inner housing40are both cup shaped. The assembly of the outer housing22and the inner housing40is sealed with a cover48. The cover48has an opening50through which the rod24protrudes. Between a bottom52of the inner housing40and a fourth piston54serving as a bearing member is a cup spring56serving as a fifth spring of the pedal emulator20. Between the fourth piston54and a bottom58of the outer housing22is a plate spring60serving as a sixth spring of the pedal emulator20. The springs34,38,42,44,56,60each have a linear spring characteristic. A seventh spring62comprises a rubber part with a progressive spring characteristic disposed between the first piston28and the damper46.

A surface64of the friction element30establishes a frictional contact with an inner annular side surface66of the inner housing40to function as a hysteresis generation system. The hysteresis generating system generates frictional hysteresis in the current embodiment. This system includes two friction partners, namely, the friction element30and the inner housing40, wherein the inner annular side surface66of the inner housing40and the outer annular side surface64of the friction element30slide over each other.

As shown inFIG. 2, the springs34and42and the springs38and44are each connected in series, with a first series circuit comprising the springs34and42and a second series circuit comprising the springs38and44. The first and the second series circuit together form a parallel circuit with each other and with the damper46and with the friction-based hysteresis generating system. The springs56and60are connected in series both to each other and to the aforementioned parallel circuit.

By means of the friction-based hysteresis generating system of the present embodiment, there a dependency of the simulated haptic feedback achieved by the pedal emulator20upon the speed at which the control rod24is moved. Moreover, since two series of springs are used in the pedal emulator20as depicted inFIGS. 1-5, an advantageous functional redundancy is created ensuring that, for example, during a malfunction in one of the two series circuits of springs, the pedal will nevertheless still be moved in the direction of a rest position, which is shown inFIG. 2.

More specifically, the control rod24is biased in the rest position shown inFIG. 2by means of the springs34,38,42,44,56,60. To generate a force required for the friction interaction to take place between the friction surfaces64,66of the friction system, the first piston28and the friction element30have mutually corresponding bevels68,70so that the total spring force is at least partially deflected by about 90°. As shown inFIG. 2, the first piston28includes a sloped bevel68with a surface that flares outwardly at approximately 45° as measured from the longitudinal axis of the pedal emulator20. Similarly, the friction element30includes a sloped bevel70with a surface that flares outwardly at approximately 45° as measured from the longitudinal axis of the pedal emulator20. Consequently, the bevels68,70meet at a sloped interface of approximately 45°. The spring circuits urge the friction element30against sloped interface, which results in the friction surface64of the friction element30being biased radially outward against the friction surface66of the inner housing40. In the rest position, the friction surfaces64,66are pressed against each other and are in frictional engagement with one another.

For detecting the relative displacement of the control rod24with respect to the outer housing22, the pedal emulator20includes a displacement sensor taking the form of an inductive sensor. The displacement sensor comprises a cursor72in combination with an electrical circuit board74and excitation and sensor coils (not shown). The cursor72is on the first piston28and the circuit board74is disposed on the outer housing22. The pedal emulator20further includes a Hall Effect sensor comprising a magnet76disposed on the inside housing40and the circuit board74with an electrical circuit (not shown). The Hall Effect sensor is also a displacement sensor and detects the relative movement between the inner housing40and the outer housing22and determines therefrom a force transmitted from the control rod24to the base part58. To facilitate better resolution of the force determined by means of the Hall Effect sensor, the fifth spring56has a smaller spring constant compared to the sixth spring60and thus a softer spring characteristic. Accordingly, the spring travel of the fifth spring56is greater relative to the travel of the sixth spring60in response to the same force. The displacement of the fifth spring56is limited by the inner housing40and the fourth piston54and the displacement of the sixth spring60is limited by the fourth piston54and the outer base part58of the outer housing22.

In the following paragraphs, the pedal emulator20according to the first embodiment is explained in more detail with reference toFIGS. 2-6.

FIG. 2shows the pedal emulator20in its rest position; that is, the position in which the pedal emulator20is mechanically connected to the footwell and the brake pedal but a user (a driver) has not depressed (actuated) the brake pedal. Due to the bias of the control rod24relative to the base part58of the pedal emulator20, the user must first overcome an initial bias force A to actuate the brake pedal. This initial force, which corresponds to a displacement of the control rod24, is depicted as the section marked “V” inFIG. 6.FIG. 6shows the relative displacement of the control rod24with respect to the base part58on the X-axis and the operating force necessary to achieve a given displacement is shown on the Y-axis. The pedal displacement is measured by the inductive displacement sensor and the actuating force is measured by the Hall Effect force sensor.FIG. 6additionally shows the force-displacement profile corresponding to both control rod24actuation (upper curve) and to the return of the control rod24from an actuated position back to the rest position (lower curve). In what follows, reference is made only to the upper curve ofFIG. 6, and thus to the forces associated with actuation of the control rod24by the user.

If, after overcoming the bias force, the user continues to exert more force on the brake pedal, the control rod24will continue to move in the direction of the base part58. At this point in the displacement of the control rod24, essentially only the first spring34and the second spring38are being compressed. “Essentially” because the other springs42,44,56,60are also compressed to a certain extent, which is also the case for the processes described below. By continuing to compress the first spring34and the second spring38, the first piston28approaches the second piston32and the friction element30is moved relative to the inner housing40resulting in friction between the two friction partners64,66. The forces and displacement corresponding to the compression of the first spring34and the second spring38correspond to “A” inFIG. 6. The compression of the first spring34is terminated when the friction element30contacts the second piston32, as shown inFIG. 3. As an alternative, which is described below, the first piston28could be designed to serve as a bearing part for the first spring34and the second spring38rather than the friction element30.

If the user continues to actuate the brake pedal, the control rod24will continue to be displaced in the direction of the base part58, essentially compressing the second spring38and the third spring42. See the corresponding section “B” inFIG. 6. Compression of the second spring38is completed when the second piston32contacts the third piston36, as shown inFIG. 4. Upon further actuation of the brake pedal, thus further displacing the control rod24in the direction of the base part58, the third spring42and the fourth spring44are essentially compressed. See the corresponding section “C” inFIG. 6. The compression of the third spring42and the fourth spring44is terminated when the third piston36is prevented by the inner housing40to move further in the direction of the base part58, as shown inFIG. 5.

During the displacement described above of the control rod24in the direction of the base part58, corresponding to the sections “V”, “A”, “B”, and “C” inFIG. 6, the friction surfaces64,66of the friction pair comprising the friction element30and the inner housing40engage each other. In addition, the aforementioned displacement of the control rod24takes place against a force exerted by the damper46. Moreover, once the section “C” ofFIG. 6has been passed, the springs34,38,42,44are not further compressed due to the above described limitations imposed on spring travel, and the damping path of the damper46is substantially traversed. However, further displacement of the brake pedal, corresponding to section “D” inFIG. 6, is possible through compression of the seventh spring62comprising a rubber part (seeFIG. 5) that is disposed between the damper46and the first piston28. The spring travel of the sensor springs54,56is not considered inFIG. 6because the spring travel of the sensor springs54,56is approximately 2 mm, which is negligible compared to the total travel of the control rod24, amounting to approximately 80 mm.

Referring now toFIG. 7, a brake pedal emulator in accordance with a second embodiment is illustrated and generally designated80. The brake pedal emulator80is functionally and structurally similar to the brake pedal emulator20ofFIGS. 1-5, except that the friction element30is positioned at the bottom of the inner housing40.

More specifically, the hysteresis generating system of the brake pedal emulator80comprises a friction element30functioning as a bearing member and disposed adjacent to the bottom52of the inner housing40. The friction system according to this embodiment has an advantage over that of the first embodiment of a larger effective friction surface. This is because a friction surface82of the first piston28frictionally engages with a friction surface64of the friction element30. This frictional engagement further takes place in cooperation with the frictional engagement of a friction surface82of the first piston28(the outer annular surface of the piston82) frictionally engaging a friction surface66of the inner housing40(the surface of the interior of the inner housing40). For generating the normal force required to frictionally engage the individual friction surfaces with one another, the friction element30and the bottom52of the inner housing40have mutually corresponding beveled surfaces84,86. The first piston28functions as the first bearing part in the present embodiment of the brake pedal emulator80.

Referring now toFIG. 8, a brake pedal emulator in accordance with a third embodiment is illustrated and generally designated90. The brake pedal emulator90is functionally and structurally similar to the brake pedal emulator ofFIG. 7, except that disposed between the contact surfaces of the first piston28and the second piston32is an eighth spring92taking the form of a rubber part with a progressive spring characteristic. As can be seen fromFIG. 8, this spring92has the effect that the transition from the portion “A” to the portion “B,” in a representation analogous toFIG. 6, is made softer. The dashed line94inFIG. 9illustrates the influence of the eighth spring92on the force-displacement curve of the control rod44of the brake pedal emulator90in comparison to a solid line representing a force-displacement curve of a control rod44of a brake pedal emulator lacking the eighth spring92. Analogously, the other transitions between “V” and “A”, “B” and “C”, and “C” and “D” shown inFIG. 6could be made softer by corresponding additional springs between the respective contact surfaces of the individual pistons32,36, the friction element30, and the inner housing40.

A fourth exemplary embodiment of a pedal emulator is described herein merely with reference to an exemplary force-displacement curve shown inFIG. 10since it largely corresponds to the embodiment ofFIGS. 1-6. As in the case ofFIGS. 6 and 9, the relative displacement of the control rod44with respect to the base part58is plotted on the X-axis and the actuating force corresponding to each displacement position is plotted on the Y-axis. The pedal emulator according to the fourth embodiment differs from the second embodiment in that the fourth embodiment does not have a seventh spring62. The section “D” ofFIG. 7, which is based essentially on the action of the seventh spring62of the pedal emulator according to the first embodiment, is thus not found inFIG. 10. As mentioned above with respect toFIG. 6, the spring travel of the sensor springs54,56is not taken into account inFIG. 10since the spring travel of the sensor springs54,56is only approximately 2 mm, which is negligible compared to the total travel of the control rod24amounting to approximately 80 mm. Similarly, the second and third embodiments of the pedal emulator80,90can be modified so as not to include a seventh spring62.

Referring toFIGS. 11-16, a brake pedal emulator in accordance with a fifth embodiment is illustrated and generally designated100. The brake pedal emulator100includes a body having an emulator piston102extending through an opening in an emulator housing104. The emulator housing104includes two halves106,108that are secured together to define an internal chamber. In other embodiments, the emulator housing104includes a unitary construction. An input rod110is fixedly attached to the emulator piston102, such that downward travel of the input rod100—typically in response to depression of a brake pedal—results in downward travel of the emulator piston102into the internal chamber. As generally set forth below, downward travel of the emulator piston102is measured by one or more sensors and is opposed by counter-force.

Referring now toFIG. 12, the brake pedal emulator10includes a damper D1, a first spring S1, a second spring S2, a third spring S3, a fourth spring S4, an intermediate spring seat112, and a lower spring seat114. The damper D1includes a damper shaft116that is moveable in relation to a damper body118. The damper body118is fixedly attached to the lower spring seat114and provides hysteresis during return travel of the input rod110. The first spring S1is a coil spring in the illustrated embodiment, but can be a wave spring in other embodiments. The coil spring or the wave spring can be linear or progressive, and optionally a dual-rate coil spring, and further optionally a progressive coil spring. Similarly, the second spring S2is a coil spring in the illustrated embodiment, but can be a wave spring. The first and second coil springs S1, S2are concentrically arranged about the damper D1and bear against the lower spring seat114. The fourth spring S4is an elastomeric bumper in the illustrated embodiment but can be a coil spring or a wave spring in other embodiments. The fourth spring S4provides a further counter-force to the emulator piston102, intermediate spring seat112, and lower spring seat114, and consequently the input rod110, depending on the amount of travel as discussed below.

Referring again toFIG. 12, the first coil spring S1is carried between an annular channel120of the emulator piston102and an inner annular channel122of the lower spring seat114. Similarly, the second coil spring S2is carried between an annular channel121of an intermediate spring seat112and an outer annular channel124of the lower spring seat114. The emulator piston102further includes an annular flange126adapted to bear against an intermediate spring seat112. Downward travel of the emulator piston102causes the annular flange126to engage the intermediate spring seat112, which causes the second spring S2to contribute to the counter-force of the brake pedal emulator100as set forth in greater detail below.

As noted above, the brake pedal emulator100includes one or more sensors to measure the position of the emulator piston102, and consequently the brake pedal travel. The brake pedal emulator100is electrically connected to an external voltage source and ground in the current embodiment, while in other embodiments the brake pedal emulator100is powered by a power supply contained within the emulator housing104. In the current embodiment, the brake pedal emulator100includes a non-contact inductive position sensor, for example a CIPOS® by Hella GmbH & Co. KGaA. The non-contact inductive position sensor includes an excitation coil disposed on a PCB128contained within the emulator housing104and includes a cursor target affixed to the emulator piston102, and in particular the annular flange126. The non-contact inductive position sensor provides an output, for example an analog output, a pulse-width-modulated output, or a SENT protocol output, which is based on the position of the cursor target relative to the excitation coil. This output is provided to a brake-by-wire electronic control unit (ECU) for conversion into a braking demand. The brake pedal emulator100additionally includes a non-contact force sensor, for example a Hall Effect sensor, affixed to the lower spring seat114. Movement of the lower spring seat114relative to the PCB128is detected by the Hall Effect sensor and converted into a force value for output to the brake-by-wire ECU. In this respect, the brake pedal emulator100provides displacement and force outputs for a brake-by-wire ECU for conversion into a braking demand. Though two sensors are described in the current embodiment, greater or fewer sensors can be implemented in other embodiments as desired.

The brake pedal emulator100provides a counter-force when actuated by a brake pedal during a braking event. The counter-force varies with respect to travel of the input rod110, such that the counter-force mimics that of a conventional brake pedal. In particular, the counter-force according to the current embodiment exhibits two inflection points, such that the rate of change of the counter-force varies non-linearly through full compression of the emulator piston102, followed by damper hysteresis to slow the return of the emulator piston102. This counter-force generally includes three stages: a first force response, a second force response, and a third force response. As used herein, the term “force response” means the cumulative counter-force applied to the emulator piston102through a given amount of travel, which is also the work applied to the emulator piston102to achieve that amount of travel. The first stage force response is provided by the first spring S1in parallel with the damper D1, which are in series with the third spring S3. The second stage force response is provided by the first spring S1in parallel with the second spring S2in parallel with the damper D1, which are in series with the third spring S3. The third stage force response is provided by the first spring S1in parallel with the second spring S2in parallel with the damper D1, which are in series with the third spring S3in parallel with the fourth spring S4.

Each stage is discussed below in connection withFIGS. 13 through 16, in which a force input is depicted, the force input being equal to the counter-force. Travel-force curves are also depicted, in which the downward travel of the emulator piston102is plotted against the force input (or the counter-force). In particular,FIG. 13illustrates a state of rest, in which no force input is applied to the input rod110, and consequently no counter-force is provided.FIG. 14illustrates a first stage force response curve,FIG. 15illustrates a second stage force response curve, andFIG. 16illustrates a third stage counter-force curve, each being in response to a gradually increasing force input on the input rod110. In addition, distance x1is the distance separating the annular flange126of the emulator piston102and the intermediate spring seat112, distance x2is the distance separating the intermediate spring seat112from the lower spring seat114, and distance x3is the distance separating the lower spring seat114from the elastomeric bumper S4.

Referring now toFIG. 13, no force input is applied, and the brake pedal emulator100is at a state of rest. The emulator piston102is upwardly biased by the first spring S1in series with the third spring S3, and each of distance x1, x2, and x3are at their maximum.

Referring now toFIG. 14, a force input results in a first stage counter-force. The first stage counter-force increases with the downward travel of the emulator piston102. This downward travel is opposed by the first spring S1in series with the wave spring S3. In addition, the damper D1contributes a resistive force upon the emulator piston102, the damper D1operating in parallel with the first coil spring S1. Once distance x1reaches zero (i.e., once the emulator piston102contacts the intermediate spring seat112), the counter-force reaches a first inflection point, at which point the second coil spring S2is engaged. The first stage counter-force is therefore dependent upon the position of the emulator piston102and is dependent upon the spring constants of the respective springs S1and S3and damper D1.

Referring now toFIG. 15, a continued force input results in a second stage counter-force. The second stage counter-force increases with the downward travel of the emulator piston102, but at a faster force rate (force per unit travel) than with the first stage counter-force. This downward travel is opposed by the first spring S1in parallel with the second spring S2and in series with the third spring S3. In addition, the damper D1again contributes a resistive force upon the emulator piston102, the damper D1operating in parallel with the first spring S1and second spring S2. The counter-force is therefore dependent upon the spring constants of the respective springs S1, S2and S3and dependent upon the damper D1. Once distance x2reaches zero (i.e., once the intermediate spring seat112contacts the lower spring seat114) and distance x3reaches zero (i.e., once the lower spring seat114contacts the fourth spring S4), the counter-force reaches a second inflection point, at which point the fourth spring S4is engaged.

Referring now toFIG. 16, a continued force input results in a third stage counter-force. During this third stage, a continued force input results in only marginal downward travel of the emulator piston102. The first spring S1, the second spring S2, and the damper D1are at their maximum compression, and downward travel is opposed by the third spring S3in parallel with the fourth spring S4. Consequently, the final force/travel rate is a function of the third spring S3in parallel with the fourth spring S4.

When the force input is reduced, the emulator piston102travels upwardly until the counter-force equals the reduced force input, at which point the system is again in equilibrium. If the force input is reduced to zero, for example if the driver releases the brake pedal, the emulator piston102travels upwardly until the counter-force is zero, i.e., the emulator piston102is fully extended to an “at rest” position. During this return, the damper D1provides hysteresis in response to relative movement of the damper shaft116with respect to damper body118. The damper D1is provided with a compact size in order to meet packaging requirements in some embodiments, while also being sufficiently robust to provide the desired hysteresis.

In use, the emulator housing104is mounted to a vehicle panel, for example a footwell panel, and the input rod110is mounted to a pedal arm. A brake pedal pad is joined to the pedal arm, such that downward deflection of the brake pedal pad causes a corresponding downward deflection of the emulator piston102(via input rod110). Downward deflection of the emulator piston102is measured by the brake emulator100in the manner set forth above and converted into a braking demand by the brake-by-wire ECU.

In some embodiments, a haptic actuator provides vibratory feedback to the brake pedal pad. The haptic actuator can be incorporated into the brake pedal emulator100or can be external to the brake pedal emulator100. For example, the haptic actuator can be mounted to the brake pedal arm or mounted to the underside of the brake pedal pad. Haptic information is provided to the driver in the form of one or more vibrations or pulses, the haptic information relating to a vehicle operating state. For example, the haptic actuator can impart a first vibration or pulse on the brake pedal arm or brake pedal pad in response to activation of an electric motor to simulate the starting of an internal combustion engine. Further by example, the haptic actuator can impart a second vibration or pulse (different from the first vibration or pulse) on the brake pedal arm or brake pedal pad to simulate engagement of vehicle anti-lock brakes.

The foregoing examples of haptic information relating to a vehicle operating state are not exhaustive, and further haptic information can be provided in other embodiments as desired. In addition, the brake pedal emulator100can be used to receive information from the driver, separate and apart from the desired braking demand. For example, a first number of actuations of the brake pedal pad by the driver during a vehicle non-operating state can be converted into an engine/motor start command by the brake pedal emulator100or by the brake-by-wire ECU. Further by example, a second number of actuations of the brake pedal by the driver during a vehicle non-operating state can be converted by the brake pedal emulator100or by the brake-by-wire ECU into a transmission shift command (e.g., shift from park to neutral). Acknowledgment of these commands can be confirmed with a haptic vibration of the pedal arm or brake pedal pad. For example, the haptic actuator can provide a first series of pulses in response to the engine/motor start command and can provide a second series of pulses in response to the transmission shift command, the first series of pulses being different from the second series of pulses. Also by example, the haptic actuator can provide a first vibration in response to the engine/motor start command and can provide a second vibration in response to the transmission shift command, the first vibration being different from the vibration, for example, having a different frequency, intensity, duration, or combinations thereof.

As noted above, the one or more sensors are powered by a power supply contained within the emulator housing104. The power supply can additionally provide electrical power to the haptic actuator. The power supply is rechargeable in the current embodiment, optionally drawing power from the vehicle electrical system. Further optionally, the power supply draws power from a regenerative power supply, for example a regenerative power supply that generates electrical power with each compression of the emulator piston102. In other embodiments the brake pedal emulator100draws power directly from the vehicle electrical system.

Accordingly, a method for operating a vehicle using a pedal emulator100is provided. The method includes providing a brake pedal emulator100including an emulator piston102, the emulator piston102being operatively coupled to a brake pedal. The brake pedal emulator100is adapted to provide a first force response during a first portion of travel of the emulator piston, a second force response during a second portion of travel of the emulator piston, and a third force response during a third portion of travel of the emulator piston. The method further includes detecting a series of actuations of the brake pedal using the pedal emulator100and detecting a vehicle operating state, e.g., the vehicle engine and/or motor is off, the vehicle engine and/or motor is off and the vehicle is in park, or the vehicle engine and/or motor is on and the vehicle is in park. The series of actuations can include a plurality of actuations of the brake pedal (or other pedal) in quick succession. The method then includes correlating the detected series of actuations, and the vehicle operating state, into a driver input command, for example a transmission shift command, an engine start command, or a motor start command. The method further optionally includes providing vibratory feedback to the brake pedal using a haptic actuator, the vibratory feedback being in response to the detected series of actuations of the emulator piston102during a given vehicle operating state, for example the number of actuations within a predetermined time period (e.g., three actuations within five seconds) when the vehicle is in park. The vibratory feedback varies in accordance with the driver input command. For example, the vibratory feedback can include a first frequency or intensity to provide confirmation of a first driver input command and a second frequency or intensity to provide confirmation of a second driver input command. The method can further include converting kinetic energy from the actuations of the emulator piston into electrical power, stored to a battery, for operation of the haptic actuator and/or the brake pedal emulator100.

To reiterate, the present embodiment includes an improved brake pedal emulator100for a brake-by-wire system. The brake pedal emulator100includes a damper D1surrounded by first and second springs S1, S2that are carried by a lower spring seat114, the lower spring seat114being upwardly biased by a third spring S3and a fourth spring S4. The first, second, third, and fourth springs S1, S2, S3, S4provide a counter-force to the emulator piston102, the counter-force including multiple stages. The internal damper D1provides a desired hysteresis during return travel of the emulator piston102, and non-contact sensors measure position and force through a full range of motion of the emulator piston102. The brake pedal emulator100is operable to detect the position of the brake pedal for conversion into a braking demand. Haptic feedback is also provided, and the brake pedal emulator100includes an on-board power supply such that the brake pedal emulator100can receive driver commands, e.g., vehicle start, before the vehicle is operating.

The above description is that of current embodiments of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention. This disclosure is presented for illustrative purposes and should not be interpreted as an exhaustive description of all embodiments of the invention or to limit the scope of the claims to the specific elements illustrated or described in connection with these embodiments. Any reference to elements in the singular, for example, using the articles “a,” “an,” “the,” or “said,” is not to be construed as limiting the element to the singular.