Electric brake actuator for vehicles

An electric brake actuator includes first and second electric motors and an actuator output, a first cycloidal speed reducer having a first reducer input rotatable about a first reducer axis and operatively connected to the first motor output gear to receive a first driving force, and a first reducer output rotatable about the first reducer axis and operatively connected to the actuator output to transfer the first driving force to the actuator output, and a second cycloidal speed reducer having a second reducer input rotatable about a second reducer axis and operatively connected to the second motor output gear to receive a second driving force and a second reducer output rotatable about the second reducer axis and operatively connected to the actuator output to transfer the second driving force to the actuator output.

TECHNOLOGICAL FIELD

The disclosure here generally pertains to vehicle brakes including parking brakes and service brakes. More specifically, the disclosure involves an electric brake actuator for actuating vehicle brakes through motor-operation.

BACKGROUND DISCUSSION

Automotive vehicles commonly include a parking brake which is operable to switch between an engaged state and a disengaged state. Somewhat recently, vehicles have been outfitted with electric parking brakes in which the parking brake is switched between the engaged and non-engaged states through operation of a motor.FIG. 1schematically illustrates a known electric parking brake arrangement in which a single motor M is used in combination with one or more torque multiplication devices P1, P2. . . Pnto achieve the desired output for operating the parking brake. The torque multiplication devices are typically in the form of belts, pulleys or a series of gears. The torque multiplication devices increase the torque produced by the motor output, but also reduce the speed.

FIG. 2illustrates an example of a motor-operated parking brake, sometimes referred to as a motor-on-caliper parking brake. An actuator12, which includes a motor, is operatively coupled to the brake10. The caliper portion of the motor-on-caliper converts the rotational motion of the actuator into linear motion.FIG. 2Bschematically illustrates a way in which this is accomplished. The actuator12, under the operation of the motor, rotates a screw (lead screw)16which causes linear movement of a nut18. The nut18pushes the caliper piston20. A thrust bearing exists between the caliper and the screw, and allows the screw to rotate even though a relatively large load is being transmitted from the screw into the caliper. In a known manner, the movement of the piston linearly moves a brake pad toward and into contact with the brake rotor. Another brake pad opposes the one brake pad and contacts the opposite side of the brake rotor. The operation of the actuator12, including the motor, thus produces a clamping force applied to the brake rotor.

Many known parking brakes utilize a single electric motor to effect operation of the parking brake. This motor must be relatively large to provide the power necessary to achieve the required brake performance. Motors of the size typically used exhibit a relatively low power density compared to smaller motors.

United States Application Publication No. 2003/0205437 proposes an electric brake assembly involving the use of two motors.FIG. 3schematically illustrates the disclosed arrangement involving the use of spur gear trains P1, P2, P3to produce an output. The drive shaft of one motor M1engages and rotates the spur gear P1, while the drive shaft of the other motor M2engages and rotates the spur gear P2. The two spur gears P1, P2engage and rotate the third spur gear P3. The patent application publication states that the disclosed electric brake assembly permits a more compact design and allows two smaller-diameter motors, which exhibit lower inertia, to be used in place of the a larger-diameter single motor. The gear trains have only one input and one output, and so the speeds of the two motors are forced to be a constant ratio of one another.

SUMMARY

One aspect of the disclosure here involves an electric brake actuator operatively connectable to a vehicle brake to operate the vehicle brake. The electric brake actuator includes a first electric motor having a first motor output shaft rotated by operation of the first electric motor to produce a first driving force and a first motor output gear fixed to the first motor output shaft, a second electric motor having a second motor output shaft rotated by operation of the second electric motor to produce a second driving force and a second motor output gear fixed to the second motor output shaft, an actuator output rotatable about an output axis and operatively connectable to the vehicle brake to operate the vehicle brake, and a differential operatively connected to both the first motor output gear and the second motor output gear and the actuator output to transfer the first and second driving forces to the actuator output by way of the differential. An effective gear ratio between the first motor output gear and the actuator output is different from an effective gear ratio between the second motor output gear and the actuator output.

According to another aspect, an electric brake actuator operatively connectable to a vehicle brake to operate the vehicle brake includes: a first electric motor having a first motor output shaft rotated by operation of the first electric motor to produce a first driving force and a first motor output gear fixed to the first motor output shaft, an actuator output rotatable about an output axis and operatively connectable to the vehicle brake to operate the vehicle brake; and a first cycloidal speed reducer having a first reducer input rotatable about a first reducer axis and operatively connected to the first motor output gear to receive the first driving force, and a first reducer output rotatable about the first reducer axis and operatively connected to the actuator output to transfer the first driving force to the actuator output. The first reducer axis is non-coaxial with both the first motor output shaft and the output axis.

A further aspect of the disclosure here involves an electric brake actuator comprising a first electric motor having a first motor output shaft rotated by operation of the first electric motor to produce a first driving force and a first motor output gear fixed to the first motor output shaft, a second electric motor having a second motor output shaft rotated by operation of the second electric motor to produce a second driving force and a second motor output gear fixed to the second motor output shaft, an actuator output rotatable about an output axis and operatively connectable to the vehicle brake to operate the vehicle brake, and a first cycloidal speed reducer having a first reducer input rotatable about a first reducer axis and operatively connected to the first motor output gear to receive the first driving force and a first reducer output rotatable about the first reducer axis and operatively connected to the actuator output to transfer the first driving force to the actuator output, and a second cycloidal speed reducer having a second reducer input rotatable about a second reducer axis and operatively connected to the second motor output gear to receive the second driving force and a second reducer output rotatable about the second reducer axis and operatively connected to the actuator output to transfer the second driving force to the actuator output.

DETAILED DESCRIPTION

Set forth below is a detailed description the electric brake actuator disclosed here. The electric brake actuator is described and illustrated in terms of several embodiments disclosed as examples of the electric brake actuator. The description which follows describes the actuator used to actuate or operate a parking brake such as the parking brake generally illustrated inFIG. 2, though it is to be understood that the electric brake actuator can also be used to operate or actuate parking brakes of a different type or construction, and can also be used to operate or actuate vehicle service brakes (i.e., the brakes used during normal vehicle driving).

FIG. 4is a schematic illustration of the electric brake actuator disclosed here. Generally speaking, the electric brake actuator includes a plurality of motors M1, M2, Mn−1, Mnin combination with a plurality of torque multiplication devices R1, R2, Rn−1, Rnand a plurality of differentials D1, Dn−2, Dn−1, which can also serve as power combining devices. The torque output by each of the respective motors M1, M2, Mn−1, Mnis increased by the torque multiplication devices R1, R2, Rn−1, Rn, and the increased torque is then combined at the differentials D1, Dn−2, Dn−1. The resulting combined torque can be subjected to further torque multiplication by the torque multiplication device Rn+1to produce an output that is used to operate the parking brake.

FIGS. 5-7illustrate an example of one possible arrangement for the electric brake actuator disclosed here and generally illustrated inFIG. 4. Referring toFIGS. 5-7, this embodiment of the electric brake actuator30disclosed by way of example includes a housing (not shown) having an interior in which is positioned the illustrated features of the electric brake actuator, except for the actuator output, and is operatively connected to a vehicle brake to operate the vehicle brake.

The electric brake actuator30includes a first electric motor36and a second electric motor38positioned in the housing interior. The first electric motor36has a first motor output shaft40rotated by operation of the first electric motor36to produce a first driving force and a first motor output gear44fixed to the first motor output shaft. The second electric motor38has a second motor output shaft42rotated by operation of the second electric motor38to produce a second driving force and a second motor output gear46fixed to the second motor output shaft42.

The first motor output gear44is operatively connected to a input of a first cycloidal speed reducer100to transfer the first driving force thereto, and the second motor output gear46is connected to an input of a second cycloidal speed reducer200to transfer the second driving force thereto. An output of the first cycloidal speed reducer100is operatively connected to a first intermediate gear50to transfer the first driving force to the first intermediate gear50, and an output of the second cycloidal speed reducer200is operatively connected to a second intermediate gear52to transfer the second driving force to the second intermediate gear52. The first and second cycloidal speed reducers100,200will be discussed in further detail below.

The electric actuator also includes a differential formed, by way of example, by a planetary gear set having a plurality of planet gears68rotatably mounted to a common carrier70by way of respective mounting pins72. In the embodiment, the mounting pins72are integral with the common carrier70. As will be discussed in further detail below, the differential is operatively connected to the first motor output gear44by way of the first cycloidal speed reducer100such that the first driving force is transferred from the first motor output gear44to the differential by way of the first cycloidal speed reducer100, and is operatively connected to the second motor output gear46by way of the second cycloidal speed reducer200such that the second driving force is transferred from the second motor output gear46to the differential by way of the second cycloidal speed reducer200.

In the embodiment, a differential output gear74serves as the differential output and is fixed to the common carrier70so that rotation of the common carrier70results in rotation of the differential output gear74. By way of example, a shaft58which is integral with the differential output gear74is fixed, such as press fit, into an opening in the common carrier70. A bearing60is press fit into the second intermediate gear52and supports the shaft58so the shaft58can rotate relative to the second intermediate gear52.

In the embodiment, the differential output gear74is operatively connected to an actuator output80, by way of example, by a reduction gear78, to thereby transfer the first and second driving forces to the actuator output80by way of the differential. The actuator output80is operatively connectable to the vehicle brake to operate the vehicle brake, by way of example, by engaging the screw16(lead screw assembly) shown inFIG. 2to effect operation of the parking brake. The reduction gear78, which can be configured to provide further gear reduction and torque multiplication, is fixed to the actuator output80so that the rotation transferred to the reduction gear78results in rotation of the actuator output80about an output axis.

In the embodiment, the differential also includes a sun gear56meshed with the plurality of planet gears68and a ring gear66meshed with the plurality of planet gears68. The first intermediate gear50is fixed to the sun gear56so that the first intermediate gear50and the sun gear56rotate together as a unit, and the second intermediate gear52is fixed to the ring gear66so that the second intermediate gear52and the ring gear66rotate together as a unit. The first motor output gear44is thus operatively connected to the sun gear56by way of the first cycloidal speed reducer100and the first intermediate gear50to transfer the first driving force to the sun gear56, and the second motor output gear46is thus operatively connected to the ring gear66by way of the second cycloidal speed reducer200and the second intermediate gear52to transfer the second driving force to the ring gear66. Additionally, a fixing pin76is fitted through concentric openings in the shaft58/differential output gear74, spacer bearing60, a washer62provided on the side of the common carrier70facing the planet gears68, and first intermediate gear50/sun gear56, to hold together the planetary gear set.

In the embodiment, three planet gears68mesh with the sun gear56and the ring gear66. During operation, the first driving force is transferred to the sun gear56while the second driving force is transferred to the ring gear66. The combined rotation of the sun gear56and the ring gear66is transferred to the planetary gear unit formed by the planet gears68mounted on the common carrier70. This in turn results in rotation of the differential output gear74which in turn drives the actuator output80by way of the reduction gear78. The planetary gear set formed by the sun gear56, the ring gear66and the planet gears68mounted on the common carrier70thus operate as a differential operatively connected to the differential output gear74and to both the first motor output shaft40of the first electric motor36and the second motor output shaft42of the second electric motor38to transfer the driving forces or torque produced by each motor to the differential output gear74by way of the differential. The differential allows the motors36,38to operate at speeds which are independent of one another.

The first cycloidal speed reducer100is illustrated in more detail inFIGS. 8 and 9. In the first cycloidal speed reducer100, a first reducer input gear102is fixed to a first eccentric104so that the first reducer input gear102and the first eccentric104rotate together as a unit about a first reducer axis. The first electric motor36and the first cycloidal speed reducer100are relatively positioned such that the first motor output gear44meshes with the first reducer input gear102. The first reducer input gear102and the first eccentric104therefore serve as a first reducer input operatively connected to the first motor output gear44to receive the first driving force.

The first cycloidal speed reducer100further includes a first input disc106configured to be driven by the first eccentric104in a cycloidal motion within a first reducer housing108. In particular, the first input disc106includes an opening within which the first eccentric104rotates, and plurality of protrusions which mesh with a plurality of recesses in the first reducer housing108. The number of recesses in the first reducer housing108is greater than the number of protrusions in the first input disc106. The combination of the eccentric motion of the first input disc106caused by the rotation of the first eccentric104and the meshing of the protrusions on the first input disc106with the greater number of recesses in the first reducer housing108causes a cycloid rotation to be imparted to the first input disk106when the first reducer input gear102, and thus the first eccentric104, are caused to rotate by rotation of the first motor output gear44.

The first cycloidal speed reducer100further includes a first output disc110. The cycloid motion of the first input disc106causes the first output disc110to rotate by mutual engagement of a plurality of pins within a plurality of holes which are larger than the plurality of pins. The pins and holes are each arranged in a circular pattern, and are sized such that the pins and holes will move in loops relative to each other in a manner which causes the first output disc110to rotate about the first reducer axis in steady, non-cycloidal rotation. In the embodiment, the plurality of pins are provided on the first output disc110and the plurality of holes are provided on the first input disc106. However, the plurality of holes could also be provided on the first output disc110, with the plurality of pins being provided on the first input disc106.

The first output disc110is fixed to a first reducer output gear112such that they rotate together as a unit about the first reducer axis. The differential and the first cycloidal speed reducer100are relatively positioned such that the first reducer output gear112meshes with the first intermediate gear50. The first output disc110and the first reducer output gear112therefore serve as a first reducer output rotatable about the first reducer axis and operatively connected to the first intermediate gear50and thus to the sun gear56fixed to the first intermediate gear50and, by way of the differential, the actuator output80, to transfer the first driving force to the first intermediate gear50and thus to the sun gear56fixed to the first intermediate gear50, and, by way of the differential, the actuator output80.

In the embodiment, the first electric motor36is mounted to the first reducer housing108by way of, for example, screws114, to assist in disposing the first electric motor36in the proper position relative to the first cycloidal speed reducer100. As illustrated inFIG. 8, a reducer shaft116fixed to the reducer housing108, a reducer bearing118disposed on the reducer shaft116between the portion of the reducer housing108from which the reducer shaft116protrudes, and a reducer screw120in threaded engagement with the free end of the reducer shaft116serve to hold and position the components of the first cycloidal speed reducer100, and also to define the first reducer axis.

In the embodiment, the second cycloidal speed reducer200is identical to the first cycloidal speed reducer100(by way of example, the second cycloidal speed reducer200includes a second reducer input gear202rotatable within a second reducer housing208about a second reducer axis) and so a detailed description of the rest of its structure is not repeated. The first and second reducer housings108,208are fixed to or integral with the actuator housing.

The second cycloidal speed reducer200is positioned relative to the second electric motor38such that the second motor output gear46meshes with the second reducer input gear202of the second cycloidal speed reducer200. The second cycloidal speed reducer200is positioned relative to the differential such that the second reducer output gear meshes with the second intermediate gear52. The second cycloidal speed reducer thus includes a second reducer output rotatable about the second reducer axis and operatively connected to the second intermediate gear52and thus to the ring gear66fixed to the second intermediate gear52and, by way of the differential, the actuator output80, to transfer the second driving force to the second intermediate gear52, and thus to the ring gear66fixed to the second intermediate gear52, and, by way of the differential, the actuator output80.

The first and second cycloidal speed reducers100and200multiply the torque produced by the first and second electric motors36,38. The increased torque is then combined by way of a power combining device having multiple inputs and a common output. In this embodiment, the planetary gear set including the sun gear56, the ring gear66and the planet gears68mounted on the common carrier70forms the power combining device. In other words, the sun gear56, the ring gear66and the planet gears68combine the torque produced by rotation of the first and second motor output shafts40and42to produce a combined torque which is applied to the differential output gear74to rotate the differential output gear, while at the same time allowing the first and second electric motors36,38to rotate at speeds independent of one another.

In the embodiment, the gear train between and including the first motor output gear44and the first intermediate gear50is equivalent to the gear train between and including the second motor output gear46and the second intermediate gear52. Thus, the effective gear ratio between the first motor output gear44and the first intermediate gear50is equal to the effective gear ratio between the second motor output gear46and the second intermediate gear52. However, because the effective gear ratio though the planetary gear set between the sun gear56to which the first intermediate gear50is fixed and the differential output gear74(and thus the actuator output80) is different from the effective gear ratio though the planetary gear set between the ring gear66to which the second intermediate gear52is fixed and the differential output gear74(and thus the actuator output80), the effective gear ratio between the first motor output gear44and the differential output gear74(and thus the actuator output80) is different from the effective gear ratio between the second motor output gear46and the differential output gear74(and thus the actuator output80).

By providing for the effective gear ratio between the first motor output gear44and the differential output gear74(and thus the actuator output80) to be different from the effective gear ratio between the second motor output gear46and the differential output gear74(and thus the actuator output80), the first and second electric motors36,38themselves effectively function with different gear ratios. This allows the actuator to meet a two part performance specification with less power than would be needed with only one gear ratio. Different effective gear ratios can also be provided in alternative embodiments which use a differential in which the effective gear ratio is the same for both inputs, such as arrangement in which two identical spur gears operatively connected to the respective motors mesh with a spur gear differential. In such an arrangement, the different effective gear ratios can be provided by, for example, using differently sized intermediate gears in each of the gear trains between the respective motors and the respective spur gears.

The cycloidal speed reducer100(and, by extension, the cycloidal speed reducer200) has a much higher efficiency when driven by the first input disc106than the first output disc110. This allows more torque to be applied to the ring gear than the motor with the small gear ratio is able to generate by itself, keeping the motor with the small effective gear ratio from being caused to rotate backwards by the motor with the large gear ratio, which would limit the output torque of the actuator. Instead, the torque from the motor with the smaller gear ratio is supplemented with torque generated by friction in the cycloidal speed reducer to prevent the motor from the smaller gear ratio from rotating backwards and allow the motor with the larger torque ratio to reach its full torque output.

In an electric brake actuator having the configuration discussed above, the rotational axes of the first and second reducers (i.e., the first reducer axis and the second reducer axis discussed above) are non-coaxial with each other, and are also each non-coaxial with the first motor output shaft40, the second motor output shaft42, and the axis of rotation of the actuator output80(i.e., the output axis discussed above). The cycloidal speed reducers100and200generate large radial forces, and by providing for their rotational axes to be unique and not shared with any other component (i.e., the motors36,38and the actuated screw16/nut18/piston20arrangement), the large radial forces are not transmitted to the other components and bearings are not needed to support those components.

FIGS. 10 and 11illustrate an example of another possible arrangement for the electric brake actuator disclosed here and generally illustrated inFIG. 4. Referring toFIGS. 10 and 11, this embodiment of the electric brake actuator1030disclosed by way of example includes a housing (not shown) having an interior in which is positioned the illustrated features of the electric brake actuator, except for the actuator output, and is operatively connected to a vehicle brake to operate the vehicle brake.

The electric brake actuator1030includes a first electric motor1036and a second electric motor1038positioned in the housing interior. As illustrated inFIG. 12, the first electric motor1036has a first motor output shaft1040rotated by operation of the first electric motor1036to produce a first driving force and a first motor output gear1044fixed to the first motor output shaft. The second electric motor1038has a second motor output shaft1042rotated by operation of the second electric motor1038to produce a second driving force and a second motor output gear1046fixed to the second motor output shaft1042. As also illustrated inFIG. 12, in the embodiment, the first and second electric motors1036and1038are mounted side-by-side on a mount1048, with the first and second electric motors1036and1038on a bottom side relative to the mount1048, the first and second motor output shafts1040and1042projecting through openings in the mount1048, and the first and second motor output gears1044and1046on a top side relative to the mount1048. In the embodiment, the mount1048is attached to the actuator housing by screws1049, and the first and second electric motors1036and1038are attached to the mount1048by screws1047, as illustrated inFIGS. 10 and 11.

The first motor output gear1044is operatively connected to a input of a first cycloidal speed reducer1100to transfer the first driving force thereto, and the second motor output gear1046is connected to an input of a second cycloidal speed reducer1200to transfer the second driving force thereto. An output of the first cycloidal speed reducer1100is operatively connected to a first intermediate gear1050to transfer the first driving force to the first intermediate gear1050, and an output of the second cycloidal speed reducer1200is operatively connected to a second intermediate gear1052to transfer the second driving force to the second intermediate gear1052. The first and second cycloidal speed reducers1100,1200will be discussed in further detail below.

The electric actuator also includes a differential formed, by way of example, by a planetary gear set illustrated by way of example inFIGS. 14 and 15and having a plurality of planet gears1068rotatably mounted to a common carrier1070by way of respective mounting pins1072. In the embodiment, the mounting pins1072are integral with the common carrier1070. As will be discussed in further detail below, the differential is operatively connected to the first motor output gear1044by way of the first cycloidal speed reducer1100such that the first driving force is transferred from the first motor output gear1044to the differential by way of the first cycloidal speed reducer1100, and is operatively connected to the second motor output gear1046by way of the second cycloidal speed reducer1200such that the second driving force is transferred from the second motor output gear1046to the differential by way of the second cycloidal speed reducer1200.

In the embodiment, a differential output spline1074serves as the differential output and is fixed to the common carrier1070so that rotation of the common carrier1070results in rotation of the differential output spline1074. In the embodiment, a shaft1058which is integral with the differential output spline1074is integral with the common carrier1070, but could be, for example, press fit into an opening in the common carrier1070. In the embodiment, the differential output spline1074serves as an actuator output operatively connectable to the vehicle brake to operate the vehicle brake, by way of example, by engaging the screw16(lead screw assembly) shown inFIG. 2to effect operation of the parking brake.

In the embodiment, the differential also includes a sun gear1056meshed with the plurality of planet gears1068and a ring gear1066meshed with the plurality of planet gears1068. The first intermediate gear1050is fixed to the sun gear1056so that the first intermediate gear1050and the sun gear1056rotate together as a unit, and the second intermediate gear1052is fixed to the ring gear1066so that the second intermediate gear1052and the ring gear1066rotate together as a unit. The first motor output gear1044is thus operatively connected to the sun gear1056by way of the first cycloidal speed reducer1100and the first intermediate gear1050to transfer the first driving force to the sun gear1056, and the second motor output gear1046is thus operatively connected to the ring gear1066by way of the second cycloidal speed reducer1200and the second intermediate gear1052to transfer the second driving force to the ring gear1066. Additionally, a shaft1064which projects from the top side of the first intermediate gear1050along the rotational axis is received in a bearing in an opening in the mount1048, and, a washer1062is provided on the shaft1058on a side of the common carrier1070facing the planet gears1068and first intermediate gear1050/sun gear1056, to separate the sun gear1056from the common carrier1070.

In the embodiment, three planet gears1068mesh with the sun gear1056and the ring gear1066. During operation, the first driving force is transferred to the sun gear1056while the second driving force is transferred to the ring gear1066. The combined rotation of the sun gear1056and the ring gear1066is transferred to the planetary gear unit formed by the planet gears1068mounted on the common carrier1070. This in turn results in rotation of the differential output spline/actuator output1074. The planetary gear set formed by the sun gear1056, the ring gear1066and the planet gears1068mounted on the common carrier1070thus operate as a differential operatively connected to the differential output spline/actuator output1074and to both the first motor output shaft1040of the first electric motor1036and the second motor output shaft1042of the second electric motor1038to transfer the driving forces or torque produced by each motor to the differential output spline/actuator output1074by way of the differential. The differential allows the motors1036,1038to operate at speeds which are independent of one another.

The cycloidal speed reducers1100and1200are illustrated in more detail inFIGS. 12 and 13. In the first cycloidal speed reducer1100, a first reducer input gear1102is fixed to a first eccentric1104so that the first reducer input gear1102and the first eccentric1104rotate together as a unit about a first reducer axis. The first electric motor1036and the first cycloidal speed reducer1100are relatively positioned such that the first motor output gear1044meshes with the first reducer input gear1102. The first reducer input gear1102and the first eccentric1104therefore serve as a first reducer input operatively connected to the first motor output gear1044to receive the first driving force.

Similarly, in the second cycloidal speed reducer1200, a second reducer input gear1202is fixed to a second eccentric1204so that the second reducer input gear1202and the second eccentric1204rotate together as a unit about a second reducer axis. The second electric motor1038and the second cycloidal speed reducer1200are relatively positioned such that the second motor output gear1046meshes with the second reducer input gear1202. The second reducer input gear1202and the second eccentric1204therefore serve as a second reducer input operatively connected to the second motor output gear1046to receive the second driving force.

The first cycloidal speed reducer1100further includes a first input disc1106configured to be driven by the first eccentric1104in a cycloidal motion within a first reducer housing1108. In particular, the first input disc1106includes an opening within which the first eccentric1104rotates, and a plurality of protrusions which mesh with recesses defined by a plurality of cylinders1130press-fit in the first reducer housing1108. The number of recesses in the first reducer housing1108is greater than the number of protrusions in the first input disc1106. The combination of the eccentric motion of the first input disc1106caused by the rotation of the first eccentric1104and the meshing of the protrusions on the first input disc1106with the greater number of recesses in the first reducer housing1108causes a cycloid rotation to be imparted to the first input disk1106when the first reducer input gear1102, and thus the first eccentric1104, are caused to rotate by rotation of the first motor output gear1044. The cycloidal speed reducer1100has a much higher efficiency when driven by the eccentric1104than the first output disc1110.

The first cycloidal speed reducer1100further includes a first output disc1110. The cycloid motion of the first input disc1106causes the first output disc1110to rotate by mutual engagement of a plurality of pins within a plurality of holes which are larger than the plurality of pins. The pins and holes are each arranged in a circular pattern, and are sized such that the pins and holes will move in loops relative to each other in a manner which causes the first output disc1110to rotate about the first reducer axis in steady, non-cycloidal rotation. In the embodiment, the plurality of pins are provided on the first output disc1110and the plurality of holes are provided on the first input disc1106. However, the plurality of holes could also be provided on the first output disc1110, with the plurality of pins being provided on the first input disc1106.

The second cycloidal speed reducer1200further includes a second input disc1206, a second output disc1210, and a second reducer housing1208including recesses defined by a plurality of cylinders1230press-fit therein which, in the embodiment, are identical to the first input disc1106, first output disc1110, first reducer housing1108and plurality of cylinders1130of the first cycloidal speed reducer1100. Additionally, in the embodiment, the first and second reducer housings1108and1208are defined by portions of the mount1048and a mount cover1090which is attached to the mount1048by fasteners. In particular, as illustrated inFIG. 12, portions of the mount1048and mount cover1090, when the mount cover1090is fixed to the mount1048, define two identical annular spaces in which the cylinders1130and1230are fixed and in which the input discs1106and1206are free to rotate in a cycloidal fashion.

The first output disc1110is fixed to a first reducer output gear1112such that they rotate together as a unit about the first reducer axis. The second output disc1210is fixed to a second reducer output gear1212such that they rotate together as a unit about the second reducer axis. A shaft1140which fixes the first output disc to the first reducer output gear1112is shorter than a shaft1240which fixes the second output disc1210to the second reducer output gear1212. The lengths of the shafts1140and1240are selected such that, while the speed reducers1100and1200are at the same height relative to the planetary gear set, the first reducer output gear1112meshes with the first intermediate gear1050while the second reducer output gear1212meshes with the second intermediate gear1052.

The first output disc1110and the first reducer output gear1112therefore serve as a first reducer output rotatable about the first reducer axis and operatively connected to the first intermediate gear1050and thus to the sun gear1056fixed to the first intermediate gear1050and, by way of the differential, the differential output spline/actuator output1074, to transfer the first driving force to the first intermediate gear1050and thus to the sun gear1056fixed to the first intermediate gear1050, and, by way of the differential, the differential output spline/actuator output1074. Similarly, the second output disc1210and the second reducer output gear1212therefore serve as a second reducer output rotatable about the second reducer axis and operatively connected to the second intermediate gear1052and thus to the ring gear1066fixed to the second intermediate gear1052and, by way of the differential, the differential output spline/actuator output1074, to transfer the first driving force to the second intermediate gear1052and thus to the ring gear1066fixed to the first intermediate gear1052, and, by way of the differential, the differential output spline/actuator output1074.

The first and second cycloidal speed reducers1100and1200multiply the torque produced by the first and second electric motors1036,1038. The increased torque is then combined by way of a power combining device having multiple inputs and a common output. In this embodiment, the planetary gear set including the sun gear1056, the ring gear1066and the planet gears1068mounted on the common carrier1070forms the power combining device. In other words, the sun gear1056, the ring gear1066and the planet gears1068combine the torque produced by rotation of the first and second motor output shafts1040and1042to produce a combined torque which is applied to the differential output spline/actuator output1074to rotate the differential output spline, while at the same time allowing the first and second electric motors1036,1038to rotate at speeds independent of one another.

In the embodiment, the gear train between and including the first motor output gear1044and the first intermediate gear1050is equivalent to the gear train between and including the second motor output gear1046and the second intermediate gear1052. Thus, the effective gear ratio between the first motor output gear1044and the first intermediate gear1050is equal to the effective gear ratio between the second motor output gear1046and the second intermediate gear1052. However, because the effective gear ratio though the planetary gear set between the sun gear1056to which the first intermediate gear1050is fixed and the differential output spline/actuator output1074is different from the effective gear ratio though the planetary gear set between the ring gear1066to which the second intermediate gear1052is fixed and the differential output spline/actuator output1074, the effective gear ratio between the first motor output gear1044and the differential output spline/actuator output1074is different from the effective gear ratio between the second motor output gear1046and the differential output spline/actuator output1074.

By providing for the effective gear ratio between the first motor output gear1044and the differential output spline/actuator output1074to be different from the effective gear ratio between the second motor output gear1046and the differential output spline/actuator output1074, the first and second electric motors1036,1038themselves effectively function with different gear ratios. This allows the actuator to meet a two part performance specification with less power than would be needed with only one gear ratio. Different effective gear ratios can also be provided in an alternative embodiment which uses a differential in which the effective gear ratio is the same for both inputs, such as arrangement in which two identical spur gears operatively connected to the respective motors mesh with a spur gear differential. In such an arrangement, the different effective gear ratios can be provided by, for example, using differently sized intermediate gears in each of the gear trains between the respective motors and the respective spur gears.

The first cycloidal speed reducer1100has a much higher efficiency when driven by the first eccentric1104than the first output disc1110, and the second cycloidal speed reducer1200has a much higher efficiency when driven by the second eccentric1204than the second output disc1210. This allows more torque to be applied to the ring gear than the motor with the small gear ratio is able to generate by itself, keeping the motor with the small effective gear ratio from being caused to rotate backwards by the motor with the large gear ratio, which would limit the output torque of the actuator. Instead, the torque from the motor with the smaller gear ratio is supplemented with torque generated by friction in the cycloidal speed reducer to prevent the motor from the smaller gear ratio from rotating backwards and allow the motor with the larger torque ratio to reach its full torque output.

In an electric brake actuator having the configuration discussed above, the rotational axes of the first and second reducers (i.e., the first reducer axis and the second reducer axis discussed above) are non-coaxial with each other, and are also each non-coaxial with the first motor output shaft1040and the second motor output shaft1042. The cycloidal speed reducers1100and1200generate large radial forces, and by providing for their rotational axes to be unique and not shared with any other component (i.e., the motors1036,1038and the actuated screw16/nut18/piston20arrangement), the large radial forces are not transmitted to the other components and bearings are not needed to support those components.

FIGS. 16 and 17illustrate an alternative cycloidal speed reducer design which can be used in the electric brake actuator illustrated inFIG. 10. Such an electric brake actuator would differ only in the design of the cycloidal speed reducer. The cycloidal speed reducers2100and2200themselves differ in the lengths of the shafts2140,2240fixed to their respective output gears2112,2212but can otherwise be the same, and so only the cycloidal speed reducer2100is described in detail.

In the cycloidal speed reducer2100, an eccentric2104is fixed to a reducer input gear2102so that the reducer input gear2102and the eccentric2104rotate together as a unit about a reducer axis. An input disc2106is configured to be driven by the eccentric2104in a cycloidal motion within a reducer housing2108. In particular, the input disc2106includes an opening within which the eccentric2104rotates, and a set of external teeth which mesh with a set of internal teeth defined by the reducer housing2108. The number of internal teeth defined by the reducer housing2108is one more than the number of external teeth defined by the input disc2106. The combination of the eccentric motion of the input disc2106caused by the rotation of the eccentric2104and the meshing of the external teeth on the input disc2106with the greater number of internal teeth in the reducer housing2108causes a cycloidal motion to be imparted to the input disk2106when the reducer input gear2102, and thus the first eccentric2104, are caused to rotate by the motor2036. Motor2038drives the components of the cycloidal speed reducer2200in similar fashion.

The input disc2106also defines a set of internal teeth which mesh with a set of external teeth defined by an output disc2110. The number of internal teeth defined by the input disc2106is one more than the number of external teeth defined by the output disc2110. The combination of the cycloidal motion of the input disc2106and the meshing of the external teeth on the output disc2110with the greater number of internal teeth on the input disc2106causes the output disc2110to rotate about the reducer axis in steady, non-cycloidal rotation. The output disc2110is fixed to the reducer output gear2112by the shaft2140such that they rotate together as a unit about the reducer axis. The output gears2112and2212of the speed reducers2100and2200are each operatively connected to an input of a differential as discussed in detail above.

The disclosed electric brake actuators exhibit reduced power consumption compared to known actuators, and peak currents are reduced. It is also possible to configure the electric brake actuators so that the motors begin operating at different times. The vehicle will thus not experience the inrush current of both motors simultaneously. This can also help reduce EMI generated by the electric brake actuators.

The detailed description above describes features and aspects of embodiments of an electric brake actuator disclosed by way of example. The invention is not limited, however, to the precise embodiments and variations described. Changes, modifications and equivalents can be employed by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims. It is expressly intended that all such changes, modifications and equivalents which fall within the scope of the claims are embraced by the claims.