Actuation and control of a differential lock

Abstract

Differential lock actuating device, comprising: a housing, a lead screw (180) rotatably mounted in the housing, a lead screw nut (190) which cooperates with the lead screw (180), an actuator pin (235) which cooperates with the lead screw nut (190), an elastic coupling between the lead screw nut (190) and the actuator pin (235), and an electronic control unit (300) comprising a first lead screw nut sensor (330.1) for detecting a first position of the lead screw nut (190) and a first actuator pin sensor (340.1) for detecting a first position of the actuator pin (235).

Description

CLAIM TO PRIORITY AND REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to and the benefit of, under all applicable laws, agreements, and regulations, U.S. Provisional Application Serial No. 62 / 468,777, filed March 8, 2017, and entitled "Electrical Actuator for Differential Locking System." The subject matter of this document is incorporated herein by reference in its entirety. BACKGROUND 1. Technical field

[0002] The invention relates generally to actuators, and more particularly to actuators suitable for providing a motive force for locking elements on differential gears. The invention further relates to systems for controlling actuators. 2. State of the art

[0003] Vehicles commonly use differential gears to control the speed and torque of each pair of driven axles under different driving conditions. When a vehicle is moving in a straight line, the wheels rotate at approximately the same speed, and torque is divided equally between the two wheels. When the vehicle is cornering, the outer wheel must travel a greater distance than the inner wheel. Differential gears, or "differentials," provide torque and speed control for each wheel so that the inner wheel can travel at a lower speed than the outer wheel when the vehicle is cornering.

[0004] Under some driving conditions, such as slippery road conditions, vehicle control may be affected by the operation of the differential, which may tend to transfer the majority of torque to a spinning or slipping wheel and leave the non-spinning wheel without power, preventing the vehicle from moving forward.

[0005] Limited-slip differentials were developed to overcome the above-mentioned problem. Limited-slip differentials can be selectively configured from an "unlocked" mode of operation, in which the differential functions normally and the wheels can rotate at different speeds relative to each other, to a "locked" mode, in which both wheels rotate, albeit on a common shaft. "Locked" can also be defined here as a condition in which different—not necessarily equal—amounts of drive torque are applied to each corresponding wheel. Limited-slip differentials improve the vehicle's driving power in slippery road conditions by allowing some torque to be applied to a non-slipping wheel when another of the wheels is slipping on a surface. Differential locking mechanisms typically use an actuator to engage the locking mechanism.These actuators can be controlled manually or automatically by a vehicle control system.

[0006] However, the state-of-the-art solutions suffer from several drawbacks. For example, the state-of-the-art actuators incorporate hydraulic systems that significantly increase the physical size of the actuator itself, as well as the overall cost of the vehicle and the weight of the hydraulic components. Furthermore, the state-of-the-art actuators do not feature very compact configurations if they are to provide robust capabilities and safety.

[0007] Furthermore, prior art actuators have rather rudimentary actuator status sensing capabilities, usually being limited to sensing two states (i.e., an engaged and a disengaged state) of the actuator, and therefore the control and safety provided by such actuators are limited. For example, during a locking operation, a differential may experience a tooth-to-tooth condition in which the power-transmitting components do not mesh properly. If a force is applied to the locking mechanism under these circumstances, its components may be damaged or unsafe conditions may result. Thus, prior art actuators and the control systems using them are limited in terms of controlling the differential lock and preventing damage or unsafe conditions.

[0008] State-of-the-art actuators typically lack the capability to integrate with existing onboard communication and control capabilities of vehicles. Today's vehicles utilize a data bus, such as a CAN bus or a LIN bus, to enable communication with and control of onboard subsystems. Such systems do not require separate and independent sets of wires and control infrastructure for each component. In contrast, state-of-the-art differential lock actuators typically require their own controls, such as relay systems. It would be advantageous to provide differential lock actuators that integrate with vehicle onboard systems and do not require additional or separate control components, yet still provide more robust control.

[0009] There is therefore a need for actuators and control systems that eliminate the above-mentioned deficiencies, etc., of the state of the art.

[0010] Further relevant prior art is disclosed in the following documents: DD 2 47 493 A1, DE 11 2017 002 133 T5, US 2015 / 0 053 027 A1 and US 4 425 814 A. SUMMARY

[0011] According to one aspect of the invention, an exemplary differential lock actuator may have a compact configuration that utilizes electromechanical components including an electric motor and a lead screw drive assembly for driving an actuator pin configured to engage the differential lock.

[0012] To solve the aforementioned problem, a differential lock actuating device having the features of claim 1 is provided. Furthermore, a method for operating a differential lock actuating device having the features of claim 10 is specified.

[0013] Further advantageous embodiments are defined in the subclaims.

[0014] According to one aspect of the invention, the actuator pin may be elastically coupled to the lead screw to prevent excessive force from being applied to the actuator pin under otherwise harmful conditions such as a tooth-to-tooth condition of the differential.

[0015] According to another aspect, an electromechanical actuator may include sensors for sensing the position of a lead screw nut and sensors for sensing the position of an actuator pin. The sensors may provide improved control by sensing multiple states of the actuator, including a state in which a tooth-to-tooth condition exists in the differential.

[0016] According to a further aspect of the invention, electromechanical actuators may be provided with manual or automatic fail-safe features for releasing and unlocking the differential lock in the event of a loss of power. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other advantages and features of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which like reference numerals are used to indicate corresponding elements throughout. It should be understood that the embodiments described herein are exemplary and do not limit the scope of the invention defined by the appended claims. The following figures illustrate exemplary aspects of the invention. Fig. 1 is an exploded top perspective view of an exemplary actuator. Fig. 2 is an exploded perspective view from below of the exemplary actuator of Fig. 1. Fig. 3 is a cross-sectional view of the assembled exemplary actuator of Fig. 1 and Fig. 2 along a vertical plane through an axis of the lead screw. Fig. Figure 4 is a detailed perspective view of an exemplary lead screw and an exemplary actuator pin mounting configuration. Fig. Figure 5 is a cross-sectional view of the assembled lead screw and drive pin mounting configuration of Fig. 4. Fig. 6 is a block diagram of an exemplary electronic control unit. Fig. Figure 7 is a schematic view of an example detection configuration. Fig. Figure 8 is a block diagram showing an example control system. Fig. Figure 9 is a block diagram showing input and output commands to and from an example engine control unit. Fig. Figure 10 is a perspective view of an exemplary automatic and fail-safe mechanism. Fig. Figure 11 shows an exemplary automatic and fail-safe feature. Fig.Figure 12 shows another exemplary automatic and fail-safe feature. DETAILED DESCRIPTION

[0018] An exemplary actuator according to aspects of the invention is described below with reference to Fig. 1-3 described. Fig. 1 and Fig. 2 show exploded views, and Fig.Figure 3 shows a cross-sectional view of the assembled state of an exemplary actuator. The components may be contained within a housing, which may include a housing base 20 and a housing cover 40 secured together by threaded fasteners and defining an interior space. Sealing elements, such as a gasket 42 and a sleeve 50, may seal the housing interior from contamination. A number of subassemblies, such as a lead screw drive assembly 100, an actuator pin assembly 200, and an electronic control unit (ECU) 300, may be housed within the interior space. Each of these assemblies is discussed below.

[0019] The lead screw drive assembly 100 may include an electric motor 110 attached to a motor mounting portion 120 and including a motor shaft coupled to power transmission elements in a drive train or transmission 140. A transmission cover 130 may seal and retain the power transmission elements 140. Gear ratios may be selected to achieve a desired reduction in speed and increase in torque in a manner known in the art. A first lead screw mounting portion 160 may be attached to the motor mounting portion 120, including a journal or bore 162 for supporting one end of the lead screw 180 for rotational movement. An opposite end of the lead screw 180 may be supported for rotational movement in a second lead screw mounting portion 170 and having a bore 172. A bearing and lubricating elements may be provided in a manner known in the art.The lead screw 180 may include a threaded portion 182 that engages a lead screw nut 190 such that rotation of the lead screw 180 results in lateral displacement of the lead screw nut 190. The lead screw 180 may include one or more bearing washers 184 that act as thrust bearings to counteract axial forces on the lead screw 180.

[0020] As continued in Fig. 4 and Fig.5, the lead screw nut 190 may be resiliently coupled to an actuator pin body 230, which may be mounted for sliding movement on the lead screw 180 through a laterally extending bore 231 that may receive a collar 232. The actuator pin body 230 is positioned on the lead screw and in a nut guide 250. A first biasing element, which may be a spring 210, is positioned in the nut guide 250 between a first end wall 251 of the nut guide 250 and a shoulder 234 of the actuator pin body 230. The nut guide 250 may have a second end wall 253, and each end wall of the nut guide 250 may have a nut guide end wall bore. When the lead screw nut 190 rotates in a locking direction (right in Fig. 1-5), the spring 210 sees a preload force in the same direction (to the right in Fig.1-5) and a resilient coupling between the nut guide 250 and the actuator pin body 230. For additional resilient coupling, a damper element 191, which may be formed of an elastomeric material, may be positioned adjacent the nut 190 to provide a resilient coupling between the nut 190 and the first end wall 251 of the nut guide 250. In this manner, the actuator pin body 230 is indirectly coupled to the nut guide and the lead screw nut 190 such that, in a tooth-to-tooth condition, the actuator pin body 230 may resist movement in the locking direction as the lead screw 180 continues to rotate and the lead screw nut 190 and the nut guide 250 continue to move, compressing the spring 210 until the tooth-to-tooth condition no longer exists.The collar 232 may be a friction reduction element that may be secured in the bore 231 to provide stable and smooth movement of the actuator pin body 230. Additional friction reduction elements, such as bushings 233, may be provided in the end wall bores of the nut guide 250 to provide stable sliding movement of the nut guide 250 on the non-threaded portion of the lead screw 180. As best shown in FIG. Fig.5, an end 237 of the actuator pin body 230 can engage and abut against an inner surface of the second end wall 253 of the nut guide 250. A second biasing element, which can be a spring 220, can engage a shoulder 256 on an outer surface of the second end wall 253 of the nut guide 250. The spring 220 thus exerts a biasing force on the nut guide 250 and the actuator pin body 230 in a direction opposite to the locking direction and the force of the biasing element 210. The housing base 20 can have a slot 22 ( Fig. 2) which provides for movement of an actuator pin 235 extending from the actuator housing to engage a cooperating element on the differential (not shown) for locking and unlocking the same. Acquisition and control configurations

[0021] Fig.6 is a block diagram showing exemplary components of an ECU 300 according to aspects of the invention. The ECU may be built around a microcontroller 310 that includes a memory 320 for storing data for commands and numerical data / control parameters. A number of lead screw nut position sensors 330 may communicate electronically with the microcontroller 310 via a data bus or other communication links known in the art. A number of actuator pin position sensors 340 may also communicate with the microcontroller 310 in a similar manner. A communication module 350 may be a Local Interconnect Network (LIN BUS) interface to the onboard communication system for a vehicle. The ECU 300 may include an engine control module 360 ​​for controlling the engine 110 ( Fig. 1-5) in the manner described below.

[0022] According to one aspect of the invention, the actuator may be a sensing configuration for sensing a number of different states of the actuator and associated states of the differential unit. Fig. Figure 7 schematically shows an exemplary sensing configuration for sensing four different states of the actuator. Sensors 330.1, 330.2, 340.1, and 340.2 may be reed switches, contact sensors, inductive sensors, or other suitable sensors known in the art that are provided in the actuator to sense the positions of the lead screw nut 190 and the actuator pin 235. Sensors 330.1 and 330.2 may sense the position of the lead screw nut 190, and sensors 340.1 and 340.2 may sense the position of the actuator pin body 230. As further shown in Fig.5, sensors 330.1 and 330.2 may be mounted on the underside of the ECU and positioned to inductively or otherwise detect a magnetic element 193 on the lead screw nut 190. Similarly, sensors 340.1 and 340.2 may be mounted on the underside of the ECU and positioned to inductively or otherwise detect a magnetic element 239 on the actuator pin body 230. Using the exemplary configuration of Fig.7, multiple actuator states can be determined. Sensor 330.1 can be located at an unlocked position of the lead screw nut 190. Sensor 330.2 can be located at a locked position of the lead screw nut 190. For example, the "locked" position can correspond to a position of the lead screw nut 190 when the actuator pin 235 is displaced to a locked position in normal differential lock operation. Similarly, the "unlocked" position can correspond to a position of the lead screw nut 190 when the actuator pin 235 is in a fully retracted position and the differential is unlocked. Additional sensors 340.1 and 340.2 can be positioned to simultaneously detect unlocked and locked positions of the actuator pin 235.

[0023] Multiple states of the actuator may be detected using the example logic of Table A, where "closed" indicates the state of detecting the presence of the monitored element, as in the case of a closed switch-type sensor, and where "open" indicates the state of not detecting the presence of the monitored element, as in the case of an open switch-type sensor. TABLE A Sensor states Actuator state 330.1 330.2 340.1 340.2 Unlocked closed open closed open Ready-to-lock (tooth-to-tooth) open closed open open Blocked open closed open closed Ready-to-Unlock closed open open closed

[0024] Using the control logic described above, multiple actuator states may be determined and communicated to the onboard communication and control systems via the ECU 300. These states may include a ready-to-lock (tooth-to-tooth) state, in which modifications to the actuation control algorithms may be made to prevent excessive forces from being applied to the actuator when the differential gear is not yet properly engaged. For example, if the determined state is ready-to-lock (tooth-to-tooth), a motive force applied by the motor 110 to the lead screw 180 may be adjusted by changing the current and / or voltage applied to the motor 110 to reduce rotation of the lead screw 180. Engine control

[0025] Fig.Figure 8 is a block diagram showing an exemplary motor control system. A LIN bus transceiver 802 can receive control information from a data link monitor (DLM) 801 and communicate control information to an actuator motor control unit (MCU) 804. Sensors 1330, which correspond to sensors 330.1 and 330.2 described above ( Fig. 7), detect the position of the lead screw nut 1190. The sensors 1340 correspondingly detect the position of the actuator pin 1230. The MCU 804 can transmit information and / or signals to an H-bridge 810, which supplies voltage to the motor 110, and can change polarity to accomplish changes in direction. Fig. Figure 8 also shows physical, mechanical connections between the gear 160, the lead screw 180, the lead screw nut 190, the biasing element or spring 210, and the actuator pin 230 according to aspects of the invention.

[0026] Fig.Figure 9 is a block diagram showing input and output commands to an example motor control unit. The lock / unlock commands may be received via a LIN bus transceiver. The actuator states may be determined based on the states of sensors 330.1, 330.2, 340.1, and 340.2 as input to the MCU and according to the logic of Table A. The sensor states, as well as the current, voltage, and temperature information, may be input to the MCU, and signals and / or information may be sent to the H-bridge 810 to control the motor 110 accordingly. Status information regarding the current, voltage, temperature, actuator status, and fault conditions may be communicated from the MCU to vehicle systems via the LIN bus transceiver 802. Fail-safe configurations

[0027] According to aspects of the invention, features are provided to ensure fail-safe operation of the differential lock actuators. These fail-safe features provide for release of the differential lock in the event of a loss of power to the actuator.

[0028] Fig. Figure 10 shows a fail-safe feature for automatically releasing the actuator in the event of a loss of power. When the actuator moves to a locked / engaged position during operation, a motor spring (a clock spring) 400 is wound synchronously with the lead screw 180 as the lead screw 180 is rotated to place the locked / engaged position to store energy that can later be used in the event of a loss of power to return the actuator (and thus the differential gear) to an unlocked / released position. The motor spring 400 can be connected to the lead screw 180 ( Fig.1-5) and a friction disk 420. Once the motor spring 400 has been wound, an electromagnet 410 may be energized (under the control of the ECU 300) to cause the friction disk 420 to engage, essentially providing a braking force against discharge of the motor spring 400 while power is supplied to the unit in the locked / engaged state. If a loss of power occurs, the electromagnet is de-energized and releases the friction disk 420, allowing the motor spring to exert a rotational force on the lead screw and cause the lead screw to move to a released / unlocked position. If there is no loss of power, the motor spring force is used during actuator unlocking / release to move the lead screw and return the lead screw nut to an unlocked position.

[0029] In addition to aspects of the invention, features for fail-safe operation may require user intervention, such as manual actuation to release the actuator from a locked position. Fig. Figure 11 shows a screw member 500 that extends into the interior of the housing and can be removed or retracted to allow the actuator pin to return to a released position. Fig. Figure 12 shows another fail-safe feature in which a rotary knob 600 is accessible on the outside of the housing and is directly coupled to the lead screw or a center gear to allow manual rotation of the lead screw and return of the lead screw nut to a loosened position.

[0030] The embodiment of the invention described in detail herein is to be considered exemplary and not restrictive. Numerous changes may be made to the illustrated embodiments without departing from the scope of the invention. Furthermore, various modifications may be made within the scope of the invention as long as the general principles of the invention are followed.

Claims

[1] Differential lock actuating device, comprising: a housing, a lead screw (180) rotatably mounted in the housing, a lead screw nut (190) which cooperates with the lead screw (180), an actuator pin (235) which cooperates with the lead screw nut (190), an elastic coupling between the lead screw nut (190) and the actuator pin (235), and an electronic control unit (300) comprising a first lead screw nut sensor (330.1) for detecting a first position of the lead screw nut (190) and a first actuator pin sensor (340.1) for detecting a first position of the actuator pin (235). [2] The apparatus of claim 1, further comprising an actuator pin body (230) having a bore (231), the actuator pin (230) extending from the actuator pin body and the lead screw extending through the bore (231) of the actuator pin body (230). [3] The apparatus of claim 1, further comprising a nut guide (250) having opposed nut guide end walls (251, 253), each nut guide end wall having a nut guide wall bore, the lead screw extending through each of the nut guide wall bores. [4] The device of claim 1, wherein the elastic coupling comprises a spring (210). [5] The device of claim 1, further comprising: an actuator pin body (230) having a bore (231), wherein the actuator pin (235) extends from the actuator pin body and wherein the lead screw (180) extends through the bore (231) of the actuator pin body (230), a nut guide (250) having opposite nut guide end walls (251, 253), each nut guide end wall (251, 253) having a nut guide wall bore (231), the lead screw (180) extending through each of the nut guide wall bores (231), and wherein the elastic coupling comprises a spring (210) disposed between one of the nut guide end walls and the actuator pin body. [6] Device according to claim 5, wherein the spring (210) is arranged concentrically with the lead screw (180). [7] The apparatus of claim 5, wherein the elastic coupling further comprises an elastomeric member (191) disposed between the lead screw nut (190) and one of the nut guide end walls (251, 253). [8] The apparatus of claim 1, further comprising a second lead screw nut sensor (330.2) for detecting a second position of the lead screw nut (190) and a second actuator pin sensor (340.2) for detecting a second position of the actuator pin (235). [9] The apparatus of claim 1, wherein the electronic control unit (300) includes a microcontroller for receiving information from the first lead screw nut sensor (330.1) and the first actuator pin sensor (340.1) and determining a tooth-to-tooth condition of the differential based on the received information. [10] A method of operating a differential lock actuating device, the differential lock actuating device comprising: a housing; a lead screw (180) rotatably mounted in the housing; a lead screw nut (190) cooperating with the lead screw (180); an actuator pin (235) cooperating with the lead screw nut (190); a resilient coupling between the lead screw nut (190) and the actuator pin (235); and an electronic control unit (300) including a first lead screw nut sensor (330.1) for detecting a first position of the lead screw nut and a first actuator pin sensor (340.1) for detecting a first position of the actuating pin, the method comprising: Turning the lead screw to cause the lead nut (190) to move in a locking direction, Transmitting a force from the lead screw nut to the actuator pin (235) via the elastic coupling, Detecting the position of the lead screw nut (190), Detecting the position of the actuator pin (235), and Determining a state of the actuator based on the detected positions of the lead screw nut (190) and the actuator pin (235). [11] The method of claim 10, wherein the step of determining a condition of the actuator comprises determining that the actuator has experienced a tooth-to-tooth condition of a differential. [12] The method of claim 10, wherein the step of determining a state of the actuator comprises determining that the actuator is in a locked state corresponding to a locked condition of a differential. [13] The method of claim 10, wherein the step of determining a state of the actuator comprises determining that the actuator is in an unlocked state. [14] The method of claim 10, further comprising a step of adjusting a moving force applied to the lead screw (180) based on the determined state of the actuator.

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