System for reducing powertrain reaction torque

A system is provided for controlling the inertia of a vehicle's powertrain during sudden braking events. Torque generated by rapid deceleration of the vehicle's drive wheels during braking is prevented from being transmitted through the vehicle's driveline by a clutch which disengages the drive wheels from high effective inertia components in the driveline. The clutch is actuated by a signal produced by any of several sensors on the vehicle which sense a sudden braking event. Driveline speed is adjusted to match drive wheel speed before the clutch is deactivated to reengage driveline with the drive wheels.

FIELD OF THE INVENTION

This invention generally relates to vehicle powertrains, and deals more particularly with a system for controlling powertrains having high inertias and reaction torques.

BACKGROUND OF THE INVENTION

Environmental concerns and the need for fuel conservation has spurred the development of new hybrid propulsion systems for vehicles. Hybrid electric vehicle (HEV) powertrains for example, typically include electric traction motors, high voltage electric energy storage systems, and modified transmissions. Electric energy storage systems include batteries and ultra capacitors. Primary power units for these systems may include spark ignition engines, compression ignition direct injection (e.g., diesel) engines, gas turbines and fuel cells.

HEV powertrains are typically arranged in series, parallel or parallel-series configurations. With parallel-series arrangements, multiple motors operating in multiple operating modes sometimes require the use of several gear sets to effectively transmit power to the traction wheels. As a result, HEV powertrains often possess considerable effective inertia at the wheels compared to conventional ICE powertrains. This is due in part to the potentially large inertia of the hybrid motor devices, as well as the significant gearing from motor to wheels that is often employed.

Powertrains possessing relatively high effective inertias such as those of HEVs, result in certain problems that require solutions. For example, the application of braking force to the vehicle's traction wheels during a sudden braking event, may result in a very rapid angular momentum change in the powertrain. Specifically, a rapid deceleration of the traction wheels during braking results in a counter-torque being transmitted from the traction wheels back through the driveline. Because many of the components connected in the driveline have relatively large effective inertias at the wheels, the counter-torque produced by the braking event can produce relatively high reactive torque levels in the powertrain. This reaction torque is transmitted through the gearing mechanisms to the transmission housing, and can have deleterious effects on powertrain and driveline components, particularly under sudden conditions, such as when the vehicle's ABS system is activated.

Accordingly, a need exists in the art for a system of reducing or controlling powertrain inertia during operating conditions that impose high inertial forces on drive train components. The present invention is intended to satisfy this need.

SUMMARY OF THE INVENTION

A system is provided for controlling inertial forces within a vehicle powertrain during certain operating conditions, such as sudden braking events. The control system reduces these inertial forces through the use of relatively simple powertrain components such as clutches and existing vehicle sensors. A further advantage of the present system resides in its compatibility with a wide range of HEV configurations and powertrain geometries.

In accordance with a first, non-limiting embodiment of the invention, a method is provided for controlling a vehicle powertrain during a braking event, which includes at least partially disengaging the powertrain from a set of traction wheels when the onset of the braking event is sensed. The braking event is sensed using a variety of methods, including monitoring the vehicle's existing ABS (Antilock Braking System), or measuring the rotational speed of the traction wheels. In one embodiment, a planetary gear in the transmission is controlled in a manner to disconnect the driveline from the traction wheels. In another embodiment, an automatically actuated clutch is used to disconnect the powertrain from the wheels. In still another embodiment, a slip clutch is used to partially disconnect the powertrain from the traction wheels, thereby reducing the counter-torque applied to the driveline by the traction wheels.

According to another non-limiting aspect of the invention, a hybrid vehicle drive system is provided that includes an internal combustion engine, an electric motor, a pair of vehicle traction wheels and a driveline connecting the traction wheels with the combination of the internal combustion engine and the electric drive motor. The system also includes a vehicle braking system for applying brake force to the traction wheels during a braking event, and an inertial control system for controlling the effective powertrain inertia at the wheels during a vehicle braking event. The inertial control system is automatically activated by control signals produced during a braking event. The system includes one or more devices which partially or fully disengage the driveline from the wheels vehicle before undesirable counter-torque produced by the rapidly decelerating wheels is transferred back through the driveline.

These and other features and advantages of the present invention may be better understood by considering the following details of a description of a preferred embodiment of the invention, which should be considered as illustrative and non-limiting. In the course of this description, reference will frequently be made to the attached drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 4shows a generic architecture for a hybrid vehicle system134, to which the present invention may be applied. The system134includes a primary power source114, such as a gasoline, diesel or other gas fuel supply, coupled to a primary power generating system116, such as an internal combustion engine. The primary power generating system116generates a primary drive torque that is transmitted to the vehicle's driveline132via power transmission assembly118. The power transmission assembly118can be a conventional manual, automatic or continuously variable automotive transmission, or other equivalent gearing mechanism for transmitting mechanical power produced by the primary power generating system116. The system134further includes a secondary power source120, such as a battery, ultracapacitor, hydraulic accumulator or other energy storage device, and secondary power generating system122, such as one or more electric machines or other torque generating devices, for supplementing the drive torque delivered by the primary power generating system116. The system may further include an auxiliary power source126coupled to an auxiliary power generating system128, such as a fuel cell system or Auxiliary Power Unit (APU) for providing additional drive torque.

The primary power generating system116may, for example, be a gasoline, natural gas, hydrogen or other gaseous, fuel-burning internal combustion engine. Power transmission assembly118transmits the output of both the internal combustion engine116and the secondary power generating system122to the vehicle driveline132. The power transmission assembly118may be a converter-less automatic transmission constructed and arranged with the secondary power generating system122, such as an integrated high voltage electric motor/generator. The power transmission assembly118and secondary generating system120can be packaged into a single modular hybrid transmission unit124

FIGS. 5A through 5Cshow exemplary hybrid powertrain system configurations that may be used to implement the present invention. The systems shown inFIGS. 5A-5Care shown by way of example and not limitation.

FIG. 5Adepicts a so-called “series” hybrid configuration136having an internal combustion engine142coupled to a modular hybrid transmission unit144. Modular hybrid transmission unit144includes an electric generator154that produces electrical energy for powering the vehicle drive wheels150via an electric motor156and gear set158. Electrical storage device152stores electrical energy via the generator154when the internal combustion engine produces more power than required, and supplements engine power via the electric motor when power demand exceeds the engine power output.FIG. 5Bshow a so-called “parallel” hybrid configuration138wherein modular hybrid transmission unit46delivers driveline torque via a first power path having the internal combustion engine142, a coupling device160and a gear set162. The coupling devices160, can be any suitable devices, for example a gear set or clutch, for transmitting mechanical energy to the vehicle driveline160. The coupling devices160,166can be the same device.FIG. 5Cshows a so-called “parallel-series” configuration140wherein a modular hybrid transmission unit148includes motor/generators172,174electrically and/or mechanically coupled, for example via planetary gearset, to deliver power to a gearset170and driveline150.

Referring now toFIG. 1, a high effective inertia powertrain74for driving a vehicle is depicted. In the illustrated embodiment, the powertrain74is suitable for use in an HEV utilizing one or more fuel and/or motor drives. As shown, the powertrain74includes an internal combustion engine (ICE)10and a DC electric motor54, each connected through a later-described driveline to drive a pair of traction wheels68, sometimes also referred to as drive wheels. The engine10has a crankshaft12rotating in the direction of arrow14, which is connected to the driveline by a damper coupling16. The rotating friction of the engine10is schematically indicated by the damper40. Torque is transmitted by the damper coupling16through a rigid or compliant shaft20to a planetary gear set22. A damper18between the damper coupling16and the shaft20functions to isolate torsional fluctuations transmitted from the engine10to the transmission line. The planetary gear set22includes a carrier gear24and sun gear26driving a ring gear28. A one-way clutch30connected between the carrier gear24and a transaxle housing42functions to prevent the engine10from rotating in a reverse direction. The transaxle housing42encases transmission and differential components. The mechanical mounting or connection of these various components is schematically represented by the various broken lines92connecting these components to transaxle housing and engine block42. The sun gear26is connected through an output shaft32of an electric motor generator36whose speed is controlled by a torque control signal delivered to its control input38.

Although not specifically shown, it should be noted that the motor54and generator36are connected with one or more suitable energy storage systems. The speed of the carrier gear24and the engine10is a function of the speeds of the ring gear28and the sun gear26. Thus, generator36is used to control the speed of the engine10by changing the speed of the sun gear26. The use of the generator36to control the speed of the engine10may be used in an intelligent control system to control engine speed independent of driveline speed. A clutch34operated by a control signal at its input52functions to selectively lock the generator36against rotation. Locking the generator36prevents the sun gear26from rotating, the result of which is the planetary gear22directly connects the engine10to the traction wheels68.

Ring gear28is connected through counter shaft48and gear assemblies50,64to a torque splitting device in the form of a differential66. A parking brake44actuated by control signal at its input46is connected to and selectively locks the countershaft48against rotation. Gear assemblies50,64possess inertia represented by the numeral62. The differential66splits the driveline torque and delivers it through a pair of half shafts88,90respectively to the traction wheels68.

A second power source for driving traction wheels68is provided by the DC electric motor54whose speed is determined by a torque control signal received at its input56. Motor54provides the dual function of driving the traction wheels68and acting as a regenerative braking generator. During vehicle braking, the motor54functions as an electrical generator using kinetic energy of the vehicle to generate electricity that is stored in a battery (not shown) for later use. The motor54delivers torque at its output shaft58through a gear set60to the differential66, which in turn transmits the torque to the traction wheels68. The motor54possesses a relatively high effective inertia at the wheels, compared to an conventional ICE powered vehicle, due in part to its own inertia as well as that of the gear assemblies60and64.

The powertrain74described above possesses a relatively high amount of effective rotating inertia at the wheels, compared to the powertrain of a conventional ICE powered vehicle. This relatively high amount of effective rotating inertia is partially due to the use of multiple drive motors, motor controls and gear sets that are necessary to manage the delivery of power to the traction wheels68. A major portion of this inertia is attributable to the electric motor54and the gear sets60and64that mechanically connect it to the traction wheels68. The gear sets22and50also materially contribute to the effective powertrain inertia, as does the ICE10and the generator36. The various component parts of the powertrain74are mechanically connected either directly or indirectly to a transaxle housing and ICE engine block42. The transaxle housing and engine block42are in turn carried on corresponding transaxle and engine block mounts70that are secured to the vehicle's chassis108. Thus, numerous components, including gear assemblies transmit torque to mountings on the transaxle housing and engine block42, which in turn transfer this torque to the mounts70.

In the event of a sudden braking event, as occurs during a sudden where the vehicle's ABS system is actuated, the braking force applied to the traction wheels68causes rapid deceleration of these wheels, in turn resulting in a rapid deceleration of the powertrain that is mechanically connected to the wheels68. This rapid deceleration of the powertrain, which has a large effective inertia, produces a commensurately large counter-torque which is transferred back through the driveline and powertrain74. This counter-torque is transmitted to each of the powertrain components where it is applied to the transaxle housing and engine block42, and their mounts70. The reactive forces on the transaxle housing and engine block42, as well as their chassis mounts70are particularly high because of the large effective rotating inertia of the powertrain74. As a result, the reactive forces applied to the transaxle housing and block42, and the mounts70may be sufficient to damage these components under certain sudden braking conditions. Even under normal braking conditions the relatively high powertrain inertia and torque levels can produce undesirable noise, vibration and harshness (NVH). Furthermore, large fluctuating torques in the powertrain can affect the performance of the ABS system.

In accordance with the present invention rapid changes in powertrain angular momentum stemming from sudden braking is controlled by limiting or substantially eliminating the amount of reactive torque transmitted between the traction wheels68and the powertrain components upstream from the wheels, particularly those contributing higher effective rotational inertias. As will be described below, this inertial control can be carried out by either completely disconnecting high inertia powertrain components from the wheels68, in response to a braking event, or by reducing the amount of reactive torque transmitted through the driveline during a braking. The inertial control of the present invention may be implemented using one or more clutches72for selectively disengaging high inertial components of the powertrain74. For example, a clutch72may be interposed between gear sets60and64to disengage the electric motor54from the differential66. Alternatively, a clutch72may be interposed between gear sets50and64to disengage both the electric motor54and engine10. In order to effect even greater control over powertrain inertia, one or two clutches72may be installed between the differential66and the traction wheels68, thereby allowing disengagement of the entire powertrain74from the traction wheels68.

Referring now also toFIG. 2, the construction of the clutch72will depend on the particular application and available packaging geometries, however a number of conventional mechanisms can be employed to provide the clutch function. For example, a conventional clutch disc assembly may be employed in which a number of friction disc plates are brought into engagement with each other to connect an input shaft with an output shaft. In one approach, the clutch discs are normally biased into engagement with each other to connect the input shaft with the output shaft, and a control signal is used to actuate a hydraulic or electrical actuator which forces the discs apart in the event of a braking event. Alternatively, hydraulic pressure may be employed to normally force the clutch plates together which are spring biased to separate when hydraulic pressure is removed in response to a braking signal.

A number of other clutch and similar technologies may be employed such as an integrated wheel end, a magnetorheological or electroheological device. In any event, the clutch72is automatically actuated by a signal generated by a controller76which may be a dedicated, programmed device, or an existing controller on the vehicle which is used to manage the inertial control system as an auxiliary function. Essentially, the control signal received by the clutch72is indicative of an braking event in which the level of brake force applied to the traction wheels68is sufficient to create undesired levels of counter-torque in the powertrain74. The controller76actuates the clutch72in response to any of a variety of signals or vehicle conditions that indicate an aggressive or sudden braking event. Examples of such signals are those produced by the vehicle's existing ABS sensors78, brake pedal brake travel sensors80or various event prediction sensors82used to predict events or conditions suggesting that sudden braking may be required or imminent. In addition, the inertial control system may rely on its own dedicated event sensors84which might comprise by way of example, inertial sensors or body deflection sensors which senses events suggesting that sudden braking is eminent or has commenced. Similarly, torque sensors86mounted on the transaxle housing or engine block42, or their mounts70could be used to sense when an unusually high reactive torque is present in the powertrain74which requires activation of a clutch72to disengage the powertrain74from the wheels68. In any event, it is important that the various sensors or other signal generators used to activate the clutch72have a particularly rapid response time so that the powertrain is disengaged before significant reactive torque can be transmitted.

Although a clutch72has been described and illustrated as a suitable means of disengaging the power train, other equivalent devices are suitable for effecting powertrain disengagement and reactive torque control. For example, a device can be provided for locking the ring gear28against rotation in response to a braking event. Such a device would, in effect, function very similar to the parking brake34, preventing the reactive torque in the powertrain74from reaching the engine10. Alternatively, any one of the gear sets50,60,64could be replaced by a planetary gear assembly that would nominally have one port (ring, sun or carrier) locked against the transmission housing. When the powertrain is to be disconnected, the locked port would be released and allowed to spin freely, thereby disconnecting the powertrain from the wheels.

In many cases, it may be desirable to reconnect the driveline and powertrain74with the wheels immediately following a braking/powertrain disconnect sequence. For example, when a vehicle passes over a series of ice patches, the vehicle's ABS system may be successively activated for brief periods, resulting, each time in the powertrain being disconnected from the wheels. If however, during the period of disconnection, the driveline speed falls substantially below that of the wheels, the reconnection process may produce substantial NVH, and in some cases, possibly damage the driveline components. Therefore, in accordance with the present invention, the driveline speed is synchronized with that of the wheels before they are reconnected. This is achieved by sensing both the driveline and wheel speeds using corresponding sensors110,112, and determining the speed difference using the controller76. Based on the determined speed difference, the controller transmits a control signal to any of the motor54, generator36or the engine10to increase driveline speed until it is within a preselected range of the wheel speed, at which time the controller76deactuates the clutch72thereby effecting re-engagement.

Attention is now also directed toFIG. 3which shows the basic steps employed in carrying out the control method of the invention. Brake and other systems on the vehicle are monitored at step94to determine whether an aggressive or sudden braking event has occurred, is about to commence, or could potentially occur in the immediate future. As previously discussed, this monitoring function can be performed by any a variety of sensors on the vehicle which feed information to a controller76. At step96, the controller76determines whether an aggressive or sudden braking event has occurred, based on the information developed by the event sensors. If it is determined that a sudden braking event is occurring, the controller76actuates the clutch72to disengage the powertrain74, as indicated at step98. In order to assure smooth reengagement of the powertrain74with the wheels68at the end of the braking event, the controller continues to monitor the information provided by the event sensors to determine when the sudden braking event has ended, as shown at step100. When it is determined that the braking event has ended, the powertrain speed is adjusted at step102, so that the powertrain speed is close to the speed of the wheels68. Next, at step104, a determination is made of whether the powertrain speed is within certain limits that assure smooth re-engagement. If the powertrain speed is within these limits, then at step106, the clutch is actuated to re-engage the powertrain74with the wheels68

It is to be understood that the specific methods and techniques which have been described are merely illustrative of one application of the principle of the invention. Numerous modifications may be made to the method as described without departing from the true spirit and scope of the invention.