Abstract:
A control interface for drivetrain braking provided by a regenerative brake and a non-regenerative brake is implemented using a combination of switches and graphic interface elements. The control interface comprises a control system for allocating drivetrain braking effort between the regenerative brake and the non-regenerative brake, a first operator actuated control for enabling operation of the drivetrain braking, and a second operator actuated control for selecting a target braking effort for drivetrain braking. A graphic display displays to an operator the selected target braking effort and can be used to further display actual braking effort achieved by drivetrain braking.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The technical field relates generally to hybrid motor vehicles and, more particularly, to an operator interface for control over braking response of a hybrid vehicle equipped for regeneration braking and compression braking. 
         [0003]    2. Description of the Technical Field 
         [0004]    The application of parallel hybrid internal combustion/electric drivetrains to commercial or heavy duty vehicles raises operator issues not present in private automobiles. One issue relates to blending braking response derived from the drivetrain braking system where it supports a compression release engine brake function (commonly referred to as a Jake brake or a compression brake) in addition to regenerative braking. Addressing this issue raises other issues relating to operator control over drivetrain braking power. 
         [0005]    An internal combustion (IC) engine functioning as a compression brake operates as an air pump which retards the (normally forward) motion of a vehicle. A compression brake is implemented on a diesel cycle IC engine by altering operation of the engine intake and exhaust valves and cutting off fuel flow to the engine. The operation can be described with reference to a single cylinder with both intake and exhaust valves closed, the piston nearing the top of its travel in the cylinder (termed “top dead center”) and a charge of compressed air in the cylinder. As the piston reaches the top of its travel the exhaust valve(s) open and compressed air is discharged to the exhaust manifold. The exhaust valve(s) then close and the piston moves toward the bottom of its travel in the cylinder pulling against an increasing vacuum in the cylinder. At the bottom of the piston&#39;s travel the intake valve(s) open and air is drawn into the cylinder. The intake valve then closes and the piston travels upwardly compressing the air for another cycle. Energy to force movement of the piston comes from the vehicle&#39;s forward motion. The IC engine remains mechanically coupled to the vehicle&#39;s drive wheels so the vehicle&#39;s momentum provides the energy to back drive the engine to force the cycle. In a typical non-hybrid vehicle equipped with an IC engine modified to operate as a compression brake, an operator can select whether the system is operational and the number of cylinders of the IC engine to be used for braking (e.g., 2, 4 or 6 cylinders) by operation of switches mounted in-side the cab. Thus compression braking is not the default braking mode for a vehicle but is engaged by the driver/operator. When engaged it typically activates upon the driver removing pressure from the vehicle accelerator pedal and does not require depression of the brake pedal. Depression of the brake pedal continues to engage the vehicle&#39;s service brakes. 
         [0006]    Contemporary hybrid vehicles equipped with a parallel hybrid electric drivetrain use an electrical machine having two modes of operation. One mode is the traction mode where the electrical machine operates as a traction motor drawing power from a storage (traction) battery to provide traction (motive) power for the vehicle. In the other mode the electrical machine functions as an electrical generator which may be back driven from the vehicle&#39;s drive wheels to generate electricity, or which may be driven by the IC engine to generate electricity. Power generated by the electrical machine is stored in the vehicle&#39;s fraction battery where it can be drawn upon the supply power to the electrical machine in its traction mode. Using the electrical machine as a back driven generator slows the vehicle while recapturing energy which would otherwise be lost as heat. Like the engine compression brake the regenerative braking system provides braking through the vehicle&#39;s drive train. While it is known for regenerative braking to be built so that it engages upon release of the accelerator pedal (first mode), regenerative braking usually engages only upon depression of the brake pedal (second mode). 
         [0007]    It might appear that regenerative braking could readily displace engine compression braking by provision of operator controls allowing selection of whether regenerative braking is engaged upon release of the accelerator pedal or upon depression of the brake pedal. While it is true that regenerative braking can usually partially displace use of the compression brake it frequently cannot fully replace it. This is due to limitations frequency inherent to a regenerative braking system. For example, regenerative braking generally does not supply as much braking torque as compression braking so compression braking remains a useful supplemental braking source which spares the use of the service brakes. In addition, regenerative braking may not be available if the vehicle&#39;s traction battery is fully charged and there is nowhere to store the power. Still, using regenerative braking is given priority since energy absorbed by the compression brake is wasted. Cooperative operation of the elements of the drivetrain braking system is dynamic, varying considerably with conditions. 
         [0008]    Issues can arise relating to both modes of hybrid regeneration on a vehicle equipped for compression braking in that either mode can coincide with operation of the compression brake and with operation of the vehicle&#39;s service brakes. The potential exists for the loss of kinetic energy that could have been applied to generating electrical power if braking is provided by the compression brake or the service brakes. Driver input mitigates some of these issues. 
       SUMMARY 
       [0009]    On a parallel hybrid electric vehicle, a control interface for implementing operator control over drivetrain braking where drivetrain braking is provided by a regenerative brake and a non-regenerative brake. The control interface comprises a control system for allocating drivetrain braking effort between the regenerative brake and the non-regenerative brake, a first operator actuated control for enabling operation of the drivetrain braking, and a second operator actuated control for selecting a target braking effort for drivetrain braking. A graphic display displays to an operator the selected target braking effort and can be used to further display actual braking effort achieved by drivetrain braking. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a side elevation of a vehicle which may be equipped with a parallel hybrid electric drivetrain and a compression brake. 
           [0011]      FIG. 2  is a high level block diagram of a control system for the vehicle of  FIG. 1 . 
           [0012]      FIG. 3  is a more detailed view of a portion of the control system for the vehicle of  FIG. 1 . 
           [0013]      FIG. 4  is a flow chart illustrating operation of the user control interface. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    In the following detailed description, like reference numerals and characters may be used to designate identical, corresponding, or similar components in differing drawing figures. Furthermore, example sizes/models/values/ranges may be given with respect to specific embodiments but are not to be considered generally limiting. In circuit diagrams well-known power and ground connections, and similar well-known elements, may be omitted for the sake of simplicity of illustration. 
         [0015]    Referring now to the figures and in particular to  FIG. 1 , a truck  11  with cab  13  is shown. Truck  11  rides on wheels including non-drive wheels  15  and drive wheels  26 . Drive wheels  26  are part of a vehicle drivetrain as described below. Drive wheels  26  are the prime movers for drivetrain braking system components. 
         [0016]      FIGS. 2 and 3  are, respectively, a high level schematic of a control system representative of systems used for a parallel hybrid electric drivetrain  20  and a more detailed illustration of particular components of an electronic control system  22 , including operator controls  56 . A display  76  related to particularized control over braking functionality of the drivetrain  20  for truck  11  is optional. 
         [0017]    The vehicle drivetrain for truck  11  is a type of parallel hybrid electric drivetrain  20  (hereafter “drivetrain  20 ”) which comprises an internal combustion (IC) engine  28 , typically a diesel cycle engine, an autoclutch  30 , an electrical machine  32  which can operate in a traction motor mode or in a generator mode for regenerative braking, a transmission  38  and drive wheels  26 . Either the IC engine  28  or the electrical machine  32  can provide direct motive (traction) power to the drive wheels and may operate in conjunction with one another to supply traction power. The IC engine  28  can also be used to drive the electrical machine  32  to generate electrical power, possibly while concurrently providing traction power to the drive wheels  26 . An autoclutch  30  allows selective coupling and decoupling of the electrical machine  32  from the IC engine  28  to allow operation of the electrical machine, either as a traction motor or a generator, in conjunction with or isolation from the IC engine. 
         [0018]    When the electrical machine  32  provides traction power it draws power from traction battery  34  through hybrid inverter  36 . Hybrid inverter  36  supplies 3 phase 340 volt rms power. Traction battery  34  is referred to as a traction battery to distinguish it from a secondary 12 volt lead acid battery  60  which may be present to supply power to various low voltage vehicle systems. Alternating current electrical power generated by the electrical machine  32  during regenerative braking is applied to a hybrid inverter  32  which in turn applies direct current power to the traction batteries  34  to maintain their charge. The hybrid inverter  36  may also be used to monitor the traction battery  34  state of charge (SOC), or at least operational variables relating to the traction battery  34  SOC. The operational variables, or the state of charge, depending upon availability, are reported to a hybrid controller  48 . Some electrical power may be diverted from hybrid inverter  36  to maintain the charge of a conventional 12-volt DC chassis battery  60 , if present, through a voltage step down DC/DC inverter  62 . 
         [0019]    IC engine  28  is typically a diesel cycle engine. A valve controller  52  is provided for enabling operation of IC engine  28  as a compression brake for retarding forward motion of truck  11 . 
         [0020]    Electrical machine  32  has two operational modes, a traction motor mode where it operates either alone or in conjunction with the IC engine  28  as the vehicle&#39;s prime mover and a generation mode. In its generator mode the electrical machine  32  can absorb torque from the drive wheels  26  through transmission  38  in order to slow a vehicle. The electrical machine  32  can also absorb torque from the IC engine  28  with the drive wheels either coupled or uncoupled by the transmission  38 . 
         [0021]    Torque sourced from either the electrical machine  32  or from the IC engine  28  is transmitted to the drive wheels  26  through transmission  38 . Torque can also be absorbed from the drive wheels  26  by either the electrical machine  32  or the IC engine  28  through a transmission  38 . When torque is absorbed by the electrical machine  32  when it operates as a generator and by the IC engine  28  when operating as a compression brake. These operations can occur concurrently. 
         [0022]    The vehicle also provides conventional service brakes  40  which operate on the drive wheels  26  (and on non-drive wheels  15 ) for stopping or slowing the vehicle. Under normal operation, upon the occurrence of braking demand received on a brake input to an electrical system controller (ESC)  24 , braking torque is allocated among the vehicle&#39;s braking systems including the service brakes  40  and to the electrical machine  32  operating in generation mode (regenerative braking). Upon actuation of the “e-Jake brake” braking demand can also be allocated to the IC engine  28  operating as a compression brake. 
         [0023]    The braking elements of drivetrain  20  can be operated to recapture or dissipate energy from the vehicle&#39;s inertial momentum during braking or slowing. When energy is recaptured it is called regenerative braking. During regenerative braking transmission  38  allows the electrical machine  32  to be back driven as a generator by the vehicle&#39;s forward momentum. Auto-clutch  30  may or may not be disconnected to isolate the IC engine  28  from the electrical machine  32  during this operation depending upon whether compression braking is supplementing or replacing regenerative braking. 
         [0024]    When drivetrain braking includes contributions from both the regenerative braking provided by electrical machine  32  and compression braking provided by IC engine  28  allocation of the braking load can become a complex process. The particulars of that process will be reviewed only in brief here. Essentially drivetrain  20  braking contribution is allocated to regenerative braking up its capacity limit, which varies dynamically, then to compression braking. Both the operation of and interaction between drivetrain  20  components are handled by a control system  22 , which is described in some detail here. 
         [0025]    Control system  22  is based on programmable controllers most of which are dedicated to particular major vehicle systems such as the transmission  38  or IC engine  28 . Communications between controllers occurs over communication buses or “datalinks” which may be elements of a controller area network (CAN). The datalinks may conform to the Society of Automotive Engineers J1939 standard. Two such CAN datalinks are used in control system  22 , a public datalink  18  and a proprietary datalink  68 . Proprietary datalinks conform in all aspects to the SAE standard but may use non-standard codes. In addition an SAE J1708 datalink  64  is provided. The SAE J1939 standard provides for twisted wire pairs with terminating resistors  90 . 
         [0026]    The controllers generally relate to major vehicle systems and include a transmission controller  42  which controls the transmission  38 , a hybrid controller  48  which controls the electrical machine  32 , the hybrid inverter  36  and the autoclutch  30 , an engine controller which controls the IC engine  28 , a valve controller which controls the valves of IC engine  28  and provides for implementing operation of the IC engine as a compression brake, and an antilock brake system (ABS) controller  50  which controls the vehicle&#39;s service brakes  40 . There are also a gauge controller  58  and a display  76  with an incorporated controller. In addition to controllers which closely relate to particular drivetrain  20  systems there are two higher level controllers. One of these is a hybrid supervisor  44  which coordinates drivetrain  20  braking functions implemented directly by the engine controller  46 , the hybrid controller  48  and the valve controller  52 . Another is an electronic system controller (ESC)  24  which has supervisory functions and which receives a number of switch and rheostat like inputs including brake pedal position, ignition position (IGN), accelerator pedal position and switch and controller inputs relating to control over the drivetrain  20  braking functions from over an SAE J1708 datalink  64  from an in-cab switch pack  56 . 
         [0027]    As suggested by the presence of a pair of SAE J1939 datalinks  18 ,  68 , communications occur over two paths depending upon the character of the data. ESC  24  operates as a portals and/or translation devices between the public datalink  18  and all other vehicle datalinks  68 ,  64 . The transmission controller  42 , hybrid controller  48  and engine controller  46  all communicate directly with either of the SAE J1939 datalinks  18 ,  68 . Display  76  receives data over SAE J1939 datalink  68  as can an audio device  78  if used for audio haptic feedback. The valve controller  52 , gauge cluster  58  and ABS controller  50  communicate directly with the public SAE J1939 datalink  18 . 
         [0028]    ABS controller  50  controls application of service brakes  40  in response to a braking command from ESC  24 . ABS controller  50  may be used to measure vehicle speed from wheel speed sensors (not shown) used to implement an anti-skid algorithm. Vehicle speed also may be measured using a transmission tachometer (not shown) or other means. In any case the relevant controller reports vehicle speed in a CAN formatted signal. The significance of the ABS controller  50  is that indication of wheel skidding indications can result in the ABS controller  50  overriding operation of drivetrain  20  braking and engaging controlled service brake  40  operation, if the brake pedal is depressed. 
         [0029]    The transitions between positive and negative traction motor mode contribution by the electrical machine  32  are detected and managed by a hybrid controller  48 . Hybrid controller  48  looks at the ABS controller  50  datalink traffic to determine if regenerative kinetic braking would increase or enhance a wheel slippage condition if regenerative braking were initiated. Transmission controller  42  detects related data traffic on datalink  18  and translates these data as control signals for application to hybrid controller  48  over datalink  68 . 
         [0030]    Operator control over drivetrain  20  braking functions emulates conventional control over a compression brake but invokes both the compression brake function of the IC engine  28  and the backdriven generator function of the electrical machine  32  to produce and electrical “Jake brake” effect. Using a pair of switches  86 ,  88  from an in-cab switch-pack  56  the operator of a vehicle can enable the system through one center panel mounted switch  86  and choose the desired amount of “e-Jake brake” effort/effect using a second toggle or multi-position switch  88 . Switches  86 ,  88  communicate via datalink  64  to a CAN module such as the ESC  24 . ESC  24  then broadcasts the desired amount of “e-Jake braking” effort/effect as requested by the vehicle&#39;s operator over the proprietary SAE J1939 datalink  68 . The signals are acted upon by the hybrid supervisory control module  44 . The hybrid supervisory control module  44  then executes its supervisory role by determining the braking contribution to be made by the regenerative braking and compression braking respectively. The allocation determined the appropriate requests are formulated and broadcast over datalinks  18 ,  68  for operation upon by other nodes which exercise control over drivetrain  20  components involved in braking including particularly the engine controller  46 , the valve controller  52  and the hybrid controller  48 . 
         [0031]    The amount and type of desired “e-Jake brake” effort/effect is reconfigurable through software programming—making available various levels and scales of braking effort/effect to the operator of the hybrid electric vehicle. In the case where the vehicle is configured with a graphic display  76 , the operator control interface switch actuator  88  can be configured as a momentary (3-position, mono-stable) switch actuator. The momentary operator control interface switch actuator  88  can be manipulated by the operator through its various “e-Jake brake” request states while simultaneously a graphic display  76  provides the amount of “e-Jake brake” effort/effect being requested by the operator via the ESC  24  to the hybrid supervisory control module  44 , for example, percent of brake effort/effect, Ft-lbs of torque, etc., as verification. In addition, the hybrid supervisory control module  44  can broadcast the actual amount of “e-Jake brake” effort/effect being performed by the electrical machine  32  or the IC engine  28  operating as a compression brake device and display it in the form of graphic dynamic feedback through the graphic display  76 . 
         [0032]    A momentary operator control interface switch actuator  88  also provides the operator with the ability to incrementally increase or decrease the amount of requested “e-Jake-brake” effort/effect by momentarily maintaining the switch actuator  88  in either of its non-stable active states and releasing it (i.e. “bumping” the switch actuator up or down). If the switch actuator  88  is maintained and “sustained” for an interval of time, the level of “e-Jake-brake” requested effort/effect will increase or decrease automatically such that the operators does not have to repeatedly “bump” the switch actuator  88  to navigate though the full range of available “e-Jake-brake effort/effects. Additionally, the longer the operator sustains the switch actuator  88  in either of its active states the faster the “e-Jake-brake requested effort/effect will increment. This option gives the operator the ability to navigate through the full range of available “e-Jake-brake effort/effect requests at an increasing and, or decreasing rate while the actuator is being maintained and sustained in either of its active states (up or down). 
         [0033]    If the vehicle is not configured with a graphic display device  76  it could be difficult for the operator to know or keep track of the amount of variable ‘e-Jake brake” effort/effect as request by the momentary operator control interface switch actuator device  88 . In the case where a such a hybrid vehicle is not configured with a graphic display device  76  the vehicle&#39;s software can be reconfigured to support a 3-position latched (3-position, tri-stable) or other suitable type operator control interface switch actuator  88  designed to mimic the switch operation of a conventional non-hybrid vehicle thermal mechanical engine compression brake device. In this scenario the latching operator control interface switch actuator  88  will serve as the visual feedback mechanism relating the amount of requested “e-Jake brake” effort/effect (e/g., 2, 4, or 6-cylinders) being sent to the hybrid supervisory control module  44  by the vehicle&#39;s electric system controller  24 . 
         [0034]    The foregoing steps are illustrated as a flow chart in  FIG. 4  where Start (step  100 ) represents activation of the system upon sensing a position change of switch  86 . Step  88  determines if a graph display  76  is available. If not execution advances along the NO step to step  104  where the position of a three position switch  88  is determined to set the effective operational level of drivetrain  20  braking (step  106 ). This will equal 2, 4 or 6 cylinders. Given the availability of regenerative braking it is possible to provide “ 6  cylinder” braking capacity on a vehicle equipped with a 4 cylinder IC engine. 
         [0035]    If graphics are available more flexible control over drivetrain  20  braking may be implemented along the YES branch from step  102 . Initially the operational level of drivetrain braking is set to a default level (step  108 ) which may be zero. Next, (step  110 ) switch  88  position is scanned and if neutral the default (current) operational level is displayed at step  112 . If the switch  88  position is not at neutral than it is determined if the switch is set to increase drivetrain braking (step  114 ). If YES the operational level is increased (step  116 ). If NO the operational level is decreased (step  118 ). After either step  116  or  118  the display  76  is updated and the program loops back to step  110 . 
         [0036]    Alternative modes exist for providing feedback where the vehicle audio entertainment system or internal loudspeakers  78  are accessible over either the proprietary J1939 datalink  68  or the public J1939 datalink  18 . Loudspeakers  78  may be used to reproduce within the vehicle&#39;s cab  13  the full sound associated with operation of a conventional compression brake adjusted for engine RPM&#39;s (sourced from the engine controller  46 ), the selected braking level (2, 4 or 6 “cylinders”) of effective braking force while accounting for the proportion of drivetrain braking being contributed by regenerative braking. In addition, haptic feedback can take into account whether the windows are up or down (as determined by ESC  24  from a window position (WIND) input). Such feedback may be provided even where a graphic display  76  is present as confirmation to the operator that the system is working or just for the sake of the operator&#39;s enjoyment. Additional haptic feedback can be considered such as adding vibration to the operator&#39;s seat when regenerative braking is occurring to simulate the effects of compression braking. 
         [0037]    The hybrid supervisory control module  44  has control over valve controller  52  to implement the IC engine  28  compression break operation, and exercises related limited control over the hybrid controller  48  and the engine controller  46 . The hybrid supervisory control module  44  integrates operator requests passed from the ESC  24  and coordinates the blending of the breaking effects/efforts of the electrical machine  32  followed by the IC engine  38  compression brake. Once the electric machine  32  has reached it maximum breaking effect/effort (due the high voltage battery state of charge (SOC), temperature, traction motor/generator maximum electrical output and the like), the balance of any remaining requested breaking effort/effect (as requested by the operator interface control device actuator  88 ) can be satisfied by compression braking using the IC engine  28 . If the breaking effect/effort created by the electrical machine  32  is adequate for meeting or exceeding the operators requested drivetrain  20  braking effort/effect, then compression braking is not be employed. 
         [0038]    This system provides the operator of a parallel hybrid electric vehicle equipped with at least one electrical machine  32  and at least one IC engine  28  configured for compression braking with the means of controlling the vehicle&#39;s drivetrain  20  breaking effects through a series, ratiometric control methodology initiated through an in-cab mounted operator interface control  86 ,  88  and system performance feedback device  76 ,  78 . 
         [0039]    The reconfigurable software and an electrical hardware architecture of the system can be used to control both compression braking of an IC engine  28  and the hybrid electric traction motor/generator to produce an “e-Jake brake” effect from switch-pack mounted, operator control interface switch devices located inside the cab of a vehicle. Disengagement of the “e-Jake brake” simply restores normal vehicle braking response to depression of the brake pedal where braking effort is allocated between the regenerative brake mode of the electrical machine  32  and the service brakes  40 . With disengagement of the “e-Jake brake” the compression brake function of the IC engine  28  is not used. 
         [0040]    This system provides the operator of a hybrid electric vehicle equipped with at least one electric traction motor/generator and at least one thermal mechanical engine device configured with a compression brake device with the means of controlling the vehicle&#39;s drivetrain breaking effects/efforts through a series, ratiometric control methodology initiated through an in-cab mounted operator interface control and system performance feedback device. Lower cost since this system uses the existing vehicle architecture. Enhanced system robustness is achieved by using the datalink and controller environment. 
         [0041]    Existing vehicle data link environment is exploited to implement the system taught here to control the operation of the existing chassis and hybrid electric vehicle components, systems and subsystems such as: the thermal mechanical engine device, a thermal mechanical engine device integrated compression break, in-cab operator controls and a in-cab mounted operator system performance display.