Active Accessory Drive Control System

Abstract

A method for operating an accessory drive system of a motor vehicle, wherein the accessory drive system includes: one or more accessory components; a motor-generator of the motor vehicle; and a flexible drive element configured to transfer torque loads between the one or more accessory components and the motor-generator, wherein the operating method includes: determining a maximum allowable flexible drive element torque threshold; detecting an increase in torque demand on the flexible drive element; determining when the torque demand on the flexible drive element will exceed the flexible drive element torque threshold; and reducing the torque demand on one or more of the accessory components so that the flexible drive element torque threshold is not exceeded.

Description

Technical Field

[0001] The present invention relates to an accessory drive system having improved performance and, in particular, but not exclusively, to an accessory drive system for a hybrid motor vehicle. Background Art

[0002] Traditional hybrid vehicles use a combination of an internal combustion engine and an electric motor. The electric motor can also act as a generator and provide regenerative braking, recovering the vehicle's kinetic energy as it slows down. With a mild hybrid configuration, the electric motor can be placed in the front-end accessory drive (FEAD) and connected to the internal combustion engine via a drive belt. This arrangement is known as a belt-integrated starter-generator (B-ISG) system. In such a system, the electric motor provides torque assistance and regenerative energy recovery via the FEAD. For optimal hybrid performance, the B-ISG must operate at maximum charge potential to recover or harvest as much kinetic energy as possible during a recuperation event. By providing torque assistance to the engine's crankshaft, the B-ISG can offset or supplement engine torque.

[0003] A key limitation of the FEAD system is the maximum torque that can be transmitted through the drive belt. Maximum drive belt torque is a limit to the torque that can be transmitted through the drive belt before the drive belt experiences parasitic losses (e.g., drive belt slippage), and torque transfer is reduced. This limitation reduces the potential benefits of the hybrid system, for example, by preventing optimal performance during regenerative recovery. This limitation can reduce the efficiency of belt-driven components and, consequently, degrade overall hybrid performance during regular use. Therefore, it is desirable to reduce FEAD parasitic losses to prevent drive belt damage, extend drive belt service life, and prevent loss of torque transfer through the drive belt.

[0004] Reference Figure 1 The passive front-end accessory drive system 100 includes a generator pulley 102 , a drive pulley 104 , an accessory component pulley 106 (e.g., an air conditioning compressor pulley), a first idler pulley 108 , a second idler pulley 110 , an idler pulley connector 120 , and a drive belt 112 , which includes a first drive belt portion 114 , a second drive belt portion 116 , and a third drive belt portion 118 . Figure 1 The arrows on each pulley indicate the direction of rotation of each pulley.

[0005] In the passive front-end accessory drive system 100, as Figure 1As shown, the generator pulley 102, the drive pulley 104, and the air conditioner compressor pulley 106 are arranged in a triangle, wherein a drive belt 112 is wrapped around the outer circumference of each pulley, thereby connecting the pulleys and dividing the drive belt 112 into three sections. A first drive belt section 114 connects the drive pulley 104 and the air conditioner compressor pulley 106, a second drive belt section 116 connects the air conditioner compressor pulley 106 and the generator pulley 102, and a third drive belt section connects the drive pulley 104 and the generator pulley 102.

[0006] Idler pulley connector 120 is mounted generally centrally relative to drive pulley 104, generator pulley 102, and air conditioner compressor pulley 106. First idler pulley 108 and second idler pulley 110 are connected to idler pulley connector 120 and are biased toward each other by a biasing element associated with idler pulley connector 120, such as a tension spring (not shown).

[0007] First idler pulley 108 is disposed between generator pulley 102 and air conditioner compressor pulley 106 and is biased toward second idler pulley 110 by an idler pulley biasing element, thereby deflecting second drive belt portion 116 toward the second idler pulley and tightening drive belt 112. Second idler pulley 110 is disposed between generator pulley 102 and drive pulley 104 and, under the action of a biasing element of a center idler pulley connector 120, deflects third drive belt portion 118 toward the first idler pulley.

[0008] First idler pulley 108 and second idler pulley 110 are used to increase friction between drive belt 112 and the pulleys, thereby minimizing belt slip. The idler pulleys increase friction by increasing tension in the drive belt and increasing the wrap angle of drive belt 112 relative to generator pulley 102, drive pulley 104, and air conditioner compressor pulley 106. Drive belt tension is increased by the idler pulleys pulling second drive belt portion 116 and third drive belt portion 118 toward each other. As the idler pulleys, under the action of a biasing element, pull second drive belt portion 116 and third drive belt portion 118 toward each other, an increased portion of the drive belt contacts the circumference of the pulleys, thereby increasing the wrap angle.

[0009] When a pulley (e.g., drive pulley 104) is driven to rotate, a rotational force is generated on the rotating pulley. This force is transferred as a torque load to drive belt 112, and drive belt 112 accordingly transfers torque between each pulley. The idler pulley provides a passive device that is used to increase the maximum torque load that can be transmitted by drive belt 112 by increasing the friction between the drive belt 112 and the pulleys through increased drive belt tension and increased pulley wrap angle.

[0010] Reference Figure 2 , active front end accessory drive system 122 and Figure 1 The passive front end accessory drive system 100 differs in that the idler pulley connector 120 is replaced by a first idler pulley connector 124 connected to a first idler pulley 128 and a second idler pulley connector 126 connected to a second idler pulley 130 .

[0011] The first idler pulley connector 124 can be provided with a first actuator, such as an electric, hydraulic, or pneumatic drive unit operable to pivot the first idler pulley 128 a variable amount into the path of the second drive belt portion 116, and the second idler pulley connector 126 can be provided with a second actuator, such as an electric, hydraulic, or pneumatic drive unit operable to pivot the second idler pulley 130 a variable amount into the path of the third drive belt portion 118. In an alternative arrangement, only one of the first and second idler pulleys can be moved by the actuator to tension the drive belt. By pivoting the idler pulley toward or away from the drive belt 112 a variable amount, the idler pulley connector of the active front accessory drive system 122 provides a means for varying the drive belt tension and the pulley wrap angle of the drive belt 112. Thus, the active front accessory drive system 122 provides a means for adjusting the tension in the drive belt 112 to accommodate the momentary demands of the vehicle and minimize belt slip.

[0012] Referring to Table 1 below, typical torque limits for the passive front end accessory drive system 100 and the active front end accessory drive system 122 are provided. Table 1 illustrates that a typical passive front end accessory drive system 100 will lose 2 to 6 kW of regenerative charging opportunities based on limitations of the passive front end accessory drive system 100 (e.g., drive belt slippage or drive belt damage).

[0013]

[0014] Table 1

[0015] As can be seen from Table 1, the active front end accessory drive system 122 has a higher torque limit than the passive front end accessory drive system 100. However, the introduction of active control increases the cost and control complexity of the system.

[0016] exist Figure 3 A graph 132 of an optimal machine dwell 134 during the New European Driving Cycle (NEDC) is provided in FIG. The graph 132 includes the optimal machine dwell 134 , passive front end accessory drive system limits 136 , potential regenerative charging opportunities 138 , motor torque limits 140 , and generator torque limits 142 .

[0017] The potential regenerative charging opportunity 138 illustrates the intersection between the generator torque limit 142 and the optimal machine dwell 134 below the passive front end accessory drive system limit 136. Thus, the potential regenerative charging opportunity 138 indicates that a significant regenerative charging opportunity is lost in the present passive front end accessory drive system 100.

[0018] Figure 4 A torque loaded front end accessory drive system 144 is shown where the drive belt 112 drives the accessory component pulley 148 and the generator pulley 150 from the drive pulley 152. The drag from the driven pulleys 148, 150 causes instantaneous belt deflection and stretching, as Figure 4 As shown by line 146 in FIG.

[0019] The maximum torque limit of a torque-loaded front-end accessory drive system 144 is limited by the degree of drive belt slip or stretch, as well as the need to operate one or more accessory components (e.g., the air conditioning compressor, power steering pump, and water pump, all of which may typically be contained on the same front-end accessory drive loop). The need to accelerate or decelerate pulleys (particularly accessory component pulley 148 and generator pulley 150) in response to changing engine speed can further limit the maximum torque. These issues are magnified when the generator is replaced by a motor-generator in the B-ISG, as hybrid systems require steady-state torque to be transferred between the B-ISG and the engine for torque assist or regenerative recovery.

[0020] exist Figure 4 In a torque-loaded front end accessory drive system 144 , the drive belt wrap around the drive pulley 152 is insufficient to provide the torque required to overcome the resistance of the accessory component pulley 148 and the generator pulley 150 when both are operating at maximum effort.

[0021] One object of the present invention is to modify already controllable elements of the passive front-end accessory drive system 100 in order to maximize hybrid functionality. Summary of the Invention

[0022] According to a first aspect of the invention, there is provided a method of operating an accessory drive system of a motor vehicle.

[0023] The flexible drive element may for example comprise a chain, a toothed belt or a V-belt. In the arrangement described below, the flexible drive element comprises a drive belt.

[0024] The step of predicting when the drive belt torque threshold is approached may include using at least one of an algorithm and a lookup table.

[0025] The increase in torque demand on the belt may be caused by a recuperation event, where the motor-generator operates as a generator and converts the vehicle's kinetic energy into electrical energy, thereby decelerating the vehicle.

[0026] The method may further include reducing a torque demand of one or more of the accessory components during a time period of the recovery event.

[0027] The method may further include reconfiguring the front end accessory drive system upon completion of the recovery event. Thus, even during recovery, the maximum torque demand remains below the drive belt load threshold, but the accessory components can still operate at full efficiency for the maximum possible time.

[0028] If the accessory component with reduced torque demand during the recovery event is an air conditioning compressor, the vehicle air conditioning capacity will be temporarily reduced, but because the recovery event is typically short in duration and full torque of the compressor will be restored as soon as the recovery event is over, the vehicle occupants are unlikely to perceive a significant change in cabin temperature.

[0029] The method may further include reducing the torque load to below the drive belt torque threshold by reducing the torque at one or more accessory pulleys. For example, if a clutch is installed between the accessory component and the accessory pulley, the clutch may be disengaged. If the torque reduction at the one or more accessory pulleys is proportional to the torque increase at the generator pulley, the maximum torque load on the belt will remain constant. Thus, at a constant drive shaft torque, as the motor-generator torque demand increases, the accessory drive system torque demand can be controlled to decrease proportionally.

[0030] The step of reducing the torque demand of one or more of the accessory components may include at least partially reducing the load on the accessory component. For example, where the accessory component is an air conditioning compressor, the air conditioning output may be reduced, or the air conditioning may be turned off completely.

[0031] The method may further include increasing the drive belt torque threshold by increasing drive belt tension. The drive belt tension may be adjusted by adjusting a position of an accessory pulley or accessory component relative to the engine (e.g., by pivoting the accessory component or accessory pulley away from the engine to thereby tighten the drive belt).

[0032] The method may further comprise increasing the drive belt torque threshold by increasing the wrap angle of one or more accessory pulleys and / or the drive pulley. The wrap angle of the accessory pulley may be increased by adjusting the position of an idler pulley engaging the belt.

[0033] The method may further comprise adjusting the drive belt torque threshold based on the measured belt slip.

[0034] The method may further include adjusting the drive belt torque threshold based on an age of the drive belt.

[0035] The method may further include adjusting the drive belt torque threshold based on a condition of the drive belt.

[0036] The step of determining the condition of the drive belt may include determining the age of the drive belt and inferring the condition of the drive pulley based on its age. As the belt ages, the maximum allowable drive belt torque threshold is generally reduced, but in some cases, the maximum allowable drive belt torque threshold may be incrementally increased over a predetermined period as the belt "breaks in" from its new state and its frictional properties increase, and then gradually reduced as the drive belt degrades with age. In other applications, the maximum allowable drive belt torque threshold may be gradually or stepwise reduced from the outset or from a predetermined age to reflect possible drive belt degradation.

[0037] The method may further comprise the following steps:

[0038] measuring one or more drive belt parameters;

[0039] determining a condition of the drive belt based on the measured value of the or each belt parameter; and

[0040] The drive belt torque threshold is adjusted based on the determined condition of the belt. Thus, the maximum allowable drive belt torque threshold can be reduced to a safe level as the drive belt degrades in service.

[0041] The method may include using at least one of an algorithm and a lookup table that correlates a given measured drive belt parameter to a corresponding condition of the drive belt or a corresponding drive belt maximum torque threshold.

[0042] The one or more drive belt parameters may include at least one of drive belt slippage, drive belt stretch, drive belt friction characteristics, drive belt cracking, drive belt pilling, drive belt wear, drive belt abrasion, and drive belt rib separation.

[0043] According to the arrangement of the present invention, improved availability of hybrid functionality through the passive front end accessory drive system 100 may be provided without introducing the losses associated with excessive belt tension and without the complexity and cost of an active front end accessory drive system 122 .

[0044] According to the present invention, there is provided a method for operating an accessory drive system of a motor vehicle, wherein the accessory drive system comprises:

[0045] one or more accessory components;

[0046] Motor generators for motor vehicles;

[0047] A flexible drive element configured to transmit torque loads between one or more accessory components and a motor-generator, wherein a method of operating comprises:

[0048] Determining a maximum allowable flexible drive element torque threshold;

[0049] detecting an increase in torque demand on a flexible drive element;

[0050] determining when a torque demand on the flexible drive element will exceed a flexible drive element torque threshold; and

[0051] reducing the torque demand of one or more of the accessory components so that the flexible drive element torque threshold is not exceeded,

[0052] Wherein the step of determining when the torque demand on the flexible drive element will exceed the flexible drive element torque threshold comprises comparing a most recently calculated maximum torque load on the flexible drive element to a rate of change of the maximum torque load and predicting when the flexible drive element torque threshold is approached.

[0053] According to one embodiment of the present invention, the increase in torque demand on the flexible drive element is caused by a recovery event, and the torque demand of one or more of the accessory components is reduced during the time period of the recovery event.

[0054] According to one embodiment of the present invention, the accessory drive system is reconfigured at the end of the time period of the recovery event.

[0055] According to one embodiment of the present invention, reconfiguring the front end accessory drive system includes restoring torque demand of one or more accessory components upon completion of the restoration event.

[0056] According to one embodiment of the present invention, during a recuperation event, a decrease in torque at one or more accessory components is equal to an increase in torque at the motor-generator.

[0057] According to one embodiment of the present invention, the step of reducing the torque demand of one or more of the accessory components comprises opening a clutch between the accessory component and a pulley of the accessory component.

[0058] According to an embodiment of the invention, the step of reducing the torque demand of one or more of the accessory components comprises at least partially reducing the load on the accessory components.

[0059] According to one embodiment of the present invention, the method further comprises the step of increasing the torque threshold of the flexible driving element by increasing the tension of the flexible driving element.

[0060] According to one embodiment of the present invention, the tension of the flexible drive element is increased by adjusting the position of a pulley engaging the flexible drive element.

[0061] According to one embodiment of the present invention, the method further comprises the step of increasing the flexible drive element torque threshold by increasing a wrap angle of at least one of the accessory component pulley, the motor generator pulley, and the drive pulley.

[0062] According to one embodiment of the present invention, the wrap angle is increased by adjusting the position of a pulley engaging the flexible drive element.

[0063] According to one embodiment of the present invention, the method further comprises the step of adjusting the flexible driving element torque threshold according to the age of the flexible driving element.

[0064] According to one embodiment of the present invention, the method further comprises the step of adjusting a torque threshold of the flexible driving element according to a state of the flexible driving element.

[0065] According to one embodiment of the present invention, the method further comprises the following steps:

[0066] measuring one or more flexible drive element parameters;

[0067] determining a state of the flexible drive element based on a measured value of the or each flexible drive element parameter; and

[0068] The flexible drive element torque threshold is adjusted based on the determined state of the flexible drive element.

[0069] In order to avoid unnecessary duplication of effort and repetition of text in the specification, certain features are described only with respect to one or more aspects or arrangements of the present invention. However, it should be understood that, where technically feasible, features described with respect to any aspect or arrangement of the present invention may also be used together with any other aspect or arrangement of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] For a better understanding of the present invention, and in order to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

[0071] Figure 1 is a schematic diagram of a passive front-end accessory drive system;

[0072] Figure 2 is a schematic diagram of an active front-end accessory drive system;

[0073] Figure 3 is a graph of optimal machine residency during the New European Driving Cycle (NEDC);

[0074] Figure 4 is a schematic diagram of a torque-loaded front-end accessory drive system;

[0075] Figure 5 is a schematic diagram of a torque-loaded front-end accessory drive system according to a first arrangement of the present invention;

[0076] Figure 6 is a schematic diagram of a front-end accessory drive system with reduced torque loading according to a first arrangement of the present invention;

[0077] Figure 7 is another schematic diagram of a torque-loaded front-end accessory drive system according to a first arrangement of the present invention;

[0078] Figure 8 is another schematic diagram of a front-end accessory drive system with reduced torque loading according to a first arrangement of the present invention;

[0079] Figure 9 is a schematic diagram of a torque loaded front end accessory drive system according to a second arrangement of the present invention; and

[0080] Figure 10 is a schematic diagram of a front-end accessory drive system with reduced torque loading according to a second arrangement of the present disclosure. DETAILED DESCRIPTION

[0081] Reference Figure 5 , the front end accessory drive system 200 includes an accessory pulley 202 , a drive pulley 204 , a generator pulley 206 , a drive belt 208 , a pair of idler pulleys 210 , and a torque load 212 transmitted through the drive belt 208 .

[0082] Torque load 212 is transmitted through drive belt 208 by means of the rotational forces applied to drive belt 208 by accessory pulley 202, drive pulley 204, and generator pulley 206. If this torque load 212 is allowed to increase excessively, drive belt 208 may slip and may become stretched, worn, or damaged.

[0083] For example, the torque load is determined by measuring the torque applied to the drive belt 208 by each pulley in the front end accessory drive system 200 and adding together each measured torque. The resulting calculation represents the torque load transmitted by the drive belt 208.

[0084] To improve the ability of the drive belt 208 to transfer torque between the pulleys, the torque applied by the accessory pulley 202 is modified. By managing the torque applied to the drive belt 208 from the accessory pulley 202 attached to, for example, the air conditioning compressor, the function of the front end accessory drive system 200 is optimized.

[0085] Specifically, the modification of the torque applied by the air conditioning compressor through accessory pulley 202 involves reducing the torque below a predetermined maximum allowable drive belt torque threshold to accommodate a battery charging or recuperation event. For example, a recuperation or recharge event is a period of time during which the motor-generator generates electricity to power electrical components of the vehicle, such as the vehicle's headlights or windshield wipers, or during a deceleration period during which the motor-generator converts kinetic energy into electrical energy to decelerate the vehicle. If the air conditioning compressor also applies high torque to the belt during a recharge or recuperation event, the torque load on the belt may be excessive.

[0086] Because typical regeneration events can be very short, according to the present invention, the torque applied by the air conditioner compressor to drive belt 208 can be reduced until the recovery event ends. Alternatively, the reduction in applied torque can be reduced over a predetermined period, after which the air conditioner compressor is determined to be too severely damaged. After the recovery event ends or the predetermined period has expired, the air conditioner compressor returns to operation.

[0087] The predetermined allowable drive belt torque threshold defines the maximum torque load that can be transmitted through the drive belt before parasitic losses are introduced into the front end accessory drive system 200. The predetermined allowable drive belt torque threshold may be determined empirically through experimentation or theoretically through calculation.

[0088] Figure 6 A reduced torque load 214 is shown transmitted through drive belt 208 due to the modified torque of the air conditioner compressor.

[0089] Techniques for reducing the torque applied by the air conditioner compressor to drive belt 208 include using a compressor with an externally variable displacement or using a compressor with an externally variable suction pressure set point.

[0090] Reference Figure 7 The front end accessory drive system 216 includes an accessory pulley 220 , a drive pulley 222 , a generator pulley 224 , a drive belt 226 , a pair of idler pulleys 228 , and a torque load 218 transmitted through the drive belt 226 .

[0091] Figure 7 and Figure 8 A situation is shown where the engine is accelerating rapidly (e.g., during a hard first gear acceleration or at the end of a closed pedal downshift for better engine braking). In this situation, the total force transmitted by drive belt 226 is increased by the need to accelerate the rotational inertia of generator pulley 224 and accessory pulley 220 or each accessory pulley 220.

[0092] exist Figure 7 In front-end accessory drive system 216, the torque load 218 transmitted through drive belt 226 is managed to accommodate rapid changes in engine speed. That is, the torque load on the air conditioning compressor's accessory pulley 220 and / or the motor-generator's generator pulley 224 is limited only when the system is subjected to strong engine speed transients. By managing the torque applied to drive belt 226 by accessory pulley 220 and / or generator pulley 224 during engine acceleration, the inertial torque transmitted through drive belt 226 is offset when drive belt 226 is forced to change speed, resulting in a reduced risk of belt slip. This arrangement reduces or increases the potential for regenerative torque during engine speed changes while ensuring that the torque available to operate front-end accessory drive system 216 is maximized during engine speed changes.

[0093] exist Figure 8 In the front-end accessory drive system 216 , the inertia and static torque of the accessory pulley 220 are reduced by opening a clutch (e.g., an electromagnetic air conditioner compressor clutch), thereby disconnecting the air conditioner compressor from the accessory pulley 220 . Since the air conditioner compressor is disconnected from the front-end accessory drive system 216 , a reduced torque load 230 is transmitted through the drive belt 226 , thereby reducing parasitic losses in the front-end accessory drive system 216 .

[0094] Inertial torque is further managed by actively controlling the motor generator and the air conditioner compressor. By actively controlling the torque applied to the drive belt 226, the regenerative drag torque of the generator pulley 224 can be temporarily reduced during regeneration events, and the inertial torque applied by the accessory pulley 220 can be temporarily reduced during use of the air conditioner compressor, thereby ensuring that the torque load 218 transmitted by the drive belt 226 remains within the limits of the maximum allowable drive belt torque threshold.

[0095] The technique for controlling the motor generator and air conditioner compressor involves measuring the torque applied to the drive belt 226 via the pulleys in real time and increasing or decreasing the torque demand of the motor generator and / or air conditioner compressor to ensure that the total torque transmitted through the drive belt 226 does not exceed the maximum allowable drive belt torque threshold.

[0096] Another drive belt 226 torque management technique involves utilizing energy supplied from the motor-generator to compensate for the inertial torque applied to the drive belt 226 by, for example, an air conditioning compressor. This technique provides a means for the air conditioning compressor to extract the required torque from the drive belt 226 by adding energy from the motor-generator to the front-end accessory drive system 216. In this technique, the inertial torque applied to the front-end accessory drive system 216 is compensated by the motor-generator via the generator pulley 224, leaving the drive belt 226 to handle only the static torque load applied by the air conditioning compressor via the accessory pulley 220.

[0097] Figure 9 and 10 2 shows how the inertial torque applied to the drive belt 226 by the accessory pulley 220 is offset by the energy added to the front end accessory drive system 216 by the generator pulley 224. Specifically, compared to Figure 9 Torque load 232, Figure 10 The torque load 234 is significantly reduced.

[0098] Another technique for extending the useful life of the drive belt 226 of the front end accessory drive system 216 includes monitoring the condition of the drive belt 226 during the life of the front end accessory drive system 216 and proactively managing the maximum allowable drive belt torque threshold accordingly. In this technique, the maximum allowable drive belt torque threshold is reduced over the life of the front end accessory drive system 216 to reflect expected belt degradation. Drive belt degradation is determined based on drive belt performance characteristics, including, for example, drive belt slippage, drive belt stretch, friction characteristics, drive belt cracking, drive belt pilling, drive belt wear, drive belt age, and drive belt rib separation.

[0099] The maximum allowable drive belt torque threshold is determined by measuring each of one or more drive belt performance characteristics at a predetermined frequency during the life of the front end accessory drive system 216. The measured drive belt performance characteristics are then used to calculate a drive belt status value. The drive belt status value is compared to a database of drive belt status values ​​versus drive belt adjustment values, and the amount by which the maximum allowable drive belt torque threshold should be adjusted is selected as the drive belt adjustment value that is closest to the calculated drive belt status value.

[0100] Techniques for actively managing the maximum allowable drive belt torque threshold may be used in conjunction with any of the techniques discussed above for managing the torque load applied to the drive belt 226. By combining these techniques, the level of intervention required (e.g., disconnecting the accessory compressor by releasing the clutch) will increase over the life of the vehicle as the drive belt 226 degrades through normal aging.

[0101] In all of the techniques discussed above, control of accessory component torque (i.e., air conditioning compressor) or motor generator torque can be achieved by an electronic control module in the motor vehicle, such as a powertrain control module (PCM). The PCM estimates the torque applied to the drive belt at each pulley and calculates the maximum allowable drive belt torque load. The torque requirements of the components connected to the front-end accessory drive system are adjusted accordingly to avoid drive belt slip at any pulley on the drive belt. In certain embodiments, only one or more selected driven components will be subject to torque limiting. For example, in a typical front-end accessory drive system, the drive pulley can always take priority so that the total required torque at the drive pulley is always allowed, while the calculated limit is applied to other components.

[0102] The predetermined limit pulley and corresponding component are determined based on, for example, the criticality of the operation of the remaining components or the balance between hybrid operation, use of motor generators, air conditioning compressor operation, and power-assisted steering operation. Furthermore, when limiting the torque applied by other controllable components, the torque load applied to the front-end accessory drive system from accessory pulleys of components that cannot be controlled or are critical to safe vehicle operation (e.g., hydraulic power steering or water pump) should be considered.

[0103] Although the above embodiments are described with respect to a passive front end accessory drive system, the present invention may also be applied to an active front end accessory drive system to extend the operating range in the passive state or to reduce the maximum drive belt tension required in the active state.

[0104] It will be appreciated by those skilled in the art that although the invention has been described by way of example with reference to one or more exemplary embodiments, the invention is not limited to the disclosed examples and that alternative examples may be constructed without departing from the scope of the invention as defined by the appended claims.

Claims

1. A method for operating an accessory drive system of a motor vehicle, wherein the accessory drive system comprises: one or more accessory components; a motor generator of said motor vehicle; a flexible drive element configured to transmit torque loads between the one or more accessory components and the motor-generator, wherein the operating method comprises: Determining a maximum allowable flexible drive element torque threshold; detecting an increase in torque demand on the flexible drive element; detecting a rate of change of a maximum torque load on the flexible drive element; comparing a most recently calculated maximum torque load on the flexible drive element to a rate of change of the maximum torque load and predicting when the flexible drive element torque threshold is approached to determine when the torque demand on the flexible drive element will exceed the flexible drive element torque threshold; and The torque demand of one or more of the accessory components is reduced such that the flexible drive element torque threshold is not exceeded.

2. The method of operating an accessory drive system of a motor vehicle according to claim 1 , wherein the increase in the torque demand on the flexible drive element is caused by a recuperation event, and the torque demand of one or more of the accessory components decreases during a time period of the recuperation event. 3 . The method of operating an accessory drive system of a motor vehicle according to claim 2 , wherein the accessory drive system is reconfigured at the end of the time period of the restoration event. 4 . The method of operating an accessory drive system of a motor vehicle according to claim 3 , wherein reconfiguring the accessory drive system comprises restoring the torque demand of the one or more accessory components upon completion of the restoration event. 5 . The method of operating an accessory drive system of a motor vehicle according to claim 2 , wherein during the recovery event, a decrease in torque at the one or more accessory components is equal to an increase in torque at the motor-generator.

6. The method of operating an accessory drive system of a motor vehicle according to claim 1, wherein the step of reducing the torque demand of one or more of the accessory components comprises opening a clutch between the accessory component and a pulley of the accessory component. 7 . The method of operating an accessory drive system of a motor vehicle according to claim 1 , wherein the step of reducing the torque demand of one or more of the accessory components comprises at least partially reducing a load on the accessory components. 8 . The method of operating an accessory drive system of a motor vehicle according to claim 1 , further comprising the step of increasing the flexible drive element torque threshold by increasing tension in the flexible drive element.

9. The method of operating an accessory drive system of a motor vehicle according to claim 8, wherein the tension in the flexible drive element is increased by adjusting the position of a pulley engaging the flexible drive element.

10. The method of operating an accessory drive system of a motor vehicle according to claim 1, further comprising the step of increasing the flexible drive element torque threshold by increasing a wrap angle of at least one of an accessory component pulley, a motor generator pulley, and a drive pulley.

11. The method of operating an accessory drive system of a motor vehicle according to claim 10, wherein the wrap angle is increased by adjusting a position of a pulley engaging the flexible drive element.

12. The method of claim 1, further comprising the step of adjusting the flexible drive element torque threshold based on an age of the flexible drive element. 13 . The method of claim 1 , further comprising the step of adjusting the flexible drive element torque threshold according to a state of the flexible drive element.

14. The method for operating an accessory drive system of a motor vehicle according to claim 13, further comprising the steps of: measuring one or more flexible drive element parameters; determining the state of the flexible drive element based on a measurement of the or each flexible drive element parameter; and The flexible drive element torque threshold is adjusted based on the determined state of the flexible drive element.

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