Abstract:
A vehicle control system is programmed to stop the vehicle&#39;s internal combustion engine upon certain conditions including the vehicle being stopped and engine temperature having reached a minimum operating level. On vehicles equipped with air brakes and having an engine driven air compressor, engine restarts are provided by an air pressure supported hydraulic motor once triggered by operator actions such as releasing the brake and/or depressing the vehicle&#39;s accelerator indicative of the driver&#39;s intention to move the vehicle.

Description:
BACKGROUND 
     1. Technical Field 
     The technical field relates to vehicle starter systems and more particularly to a vehicle starter system allowing use of the vehicle engine for regenerative braking and supporting operation of vehicle accessories when the vehicle&#39;s thermal or internal combustion engine is off. 
     2. Description of the Problem 
     Medium duty trucks employed for daytime small package deliveries are subject to relatively frequent stops and extended total idle time due to the urban traffic environment they are often used in and the many stops made for pick-ups and deliveries. Having drivers shut down the internal combustion engine of their vehicle when the vehicle is stopped to avoid engine idling is recognized by firms engaged in this business as effective in reducing fuel consumption and air pollution. However, increasing the frequency of shut downs also increases the frequency of engine restarts and this, in turn, increases wear on the vehicles&#39; starter systems. Package delivery companies have found it economically viable to equip their vehicles with heavy duty starter systems built for durability to handle frequent restarts, notwithstanding the added expense of such systems. 
     However, even heavy duty electric starter motors accelerate relatively slowly under a cranking load. In addition, due to the step down gear ratios used with such motors, they usually crank the engine at lower RPMs than the engine idles at. Even with the use of a high capacity electric starter motor there can be a delay of a two or three seconds before an engine restarts during cranking. Thus it has been impractical to turn the engine off for many traffic stops due to the delay in following traffic. 
     Shutting off the engine also cuts power from vehicle accessories which are conventionally mechanically coupled to the engine for power, for example: power steering pumps; and air conditioning system compressors. In addition, some of these accessories are automatically shed when cranking using a starter motor. Engine shut downs done for traffic stops are not seamless operation for the driver due to loss of cab cooling and power steering. 
     SUMMARY 
     A vehicle control system is programmed to stop the vehicle&#39;s engine upon certain conditions potentially including any stop of the vehicle. Engine quick stops are usually restricted until the engine has reached a normal operating temperature. Engine restart after a quick stop is triggered by operator actions, such as releasing the brake and/or depressing the vehicle&#39;s accelerator. On vehicles equipped with air brakes and having an engine driven air-compressor, engine restart is done with an air pressure driven hydraulic motor. Power boost for vehicle accessories such as steering can also be maintained using available air pressure. Load monitoring and selective load shedding extend the period for which the engine can be off and reduce the load for cranking without loss of seamless operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cutaway view of a medium duty delivery truck showing the driver position. 
         FIG. 2  is a high level schematic diagram on an engine cranking system for a rapid stop/start system. 
         FIG. 3  is a schematic of a control system for implementing load shedding features of the engine cranking system of  FIG. 2 . 
         FIG. 4  is a state machine for a rapid stop/start system. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a medium duty delivery vehicle  10  is shown having a driver station  15  including a steering wheel  12  and other driver controls. Vehicle  10  is entered using a doorway  17  sometimes located along the non-driver side of the vehicle. A cargo area  16  may be accessed by an interior door  18  or a sliding rear gate  20 . Vehicle  10  is equipped with various lights including tail lights  22  on the back of the vehicle. Vehicle  10  may be equipped with conventional climate control features, including heat and air conditioning (HVAC). Vehicle  10  may be equipped with power steering and power brakes. Typically vehicle  10  will have a compressed air system for air brakes. 
     Referring to  FIG. 2 , a combined schematic for a hydraulic starter system  99  and power boost system  199  is shown. An air pump  72  compresses atmospheric gas and supplies the compressed air/gas for the vehicle&#39;s air brake system and to operate a hydraulic engine starter system  99 . Internal combustion engine  70  is coupled, typically using a mechanical linkage, to drive air pump  72  which in turn supplies compressed air to a primary air tank  74 . Primary air tank  74  is connected by an air distribution subsystem  79  to an engine start air tank  78  and a brake air tank  76 . A check valve  80  blocks the return of air from start tank  78  to brake tank  76 . A solenoid controlled return valve  82  may be located between the engine start air tank to the brake tank  76  which allows air to be supplied from the start tank  78  to the brake tank in case air pressure in the brake tank is lower than a preselected minimum. Pressure in the engine start tank  78  and the brake tank  76  may be monitored using pressure transducers, such as pressure transducer  84  for the engine start tank  78 , and reported to an engine controller or body computer. 
     The air pressurization system for the vehicle air brake system or a separate air compression system may be used to pressurize the hydraulic starter system. An alternative air supply system is described in U.S. Pat. No. 6,922,997 to Larson et al. and is incorporated herein by reference. The &#39;997 patent describes a vehicle high air pressure system utilizing a pressure amplifying pump driven by air exhausted into or pumped through the exhaust manifold of an internal combustion engine by the engine. Use of such a system here would allow use of a smaller air tank or air pressure accumulator since the system could operate at a higher pressure than conventional truck air brake systems. 
     The vehicle is equipped with a conventional direct current electric starter motor  89  and the hydraulic starter system  99 . For the hydraulic starter system  99  compressed air is supplied from the engine start air tank  78  under the control of a body computer or engine controller/ECU (described below). The hydraulic starter system  99  is normally used after the engine  70  has been operated long enough for engine to be in a normal operating temperature range, although hydraulic starting could be used when the engine is cold. For engine  70  cranking air is delivered from the engine start air tank  78  to a hydraulic pressure vessel  88  by a solenoid controlled start control valve  64 . At the same time, a pawl  92  is used to engage hydraulic motor  90  to a drive gear  94  which is mechanically coupled to the crankshaft of engine  70 . Upon application of air pressure to the hydraulic pressure vessel  88  hydraulic fluid is forced from the vessel the hydraulic motor  90  to provide power to a drive gear  94  for cranking engine  70 . Once the engine begins to run, the body computer disengages the pawl  92  to decouple drive gear  94  from motor  90 . 
     Fluid from hydraulic pressure vessel  88  passing through hydraulic motor  90  is discharged through hydraulic motor  90  to a reservoir  96 . A fluid return pump  98  returns hydraulic fluid discharged by the motor  90  into a reservoir  96  via a check valve  100  to the pressure reservoir  88 . The fluid return pump  98  may be operated by an electric motor which engages after solenoid valve  64  closes and when engine  70  is running and alternator power is available. Hydraulic motor  90  should have sufficient power to crank engine  70  at the engine&#39;s idle speeds, and to accelerate the engine relatively quickly to those speeds. 
     An automatic shut down of engine  70  for a traffic stop may be made operationally transparent to the driver if there is no loss of power steering and power brake boost assist remains present. In other words, even though the engine  70  is off, power steering and power brakes are still available. Compressed air from the engine start tank  78 , or other pressurized air source, can be used to provide bridging power to the power steering system while the engine  70  off. 
     A power assist system  199  is applicable to a power steering system, or other engine driven accessory or power take-off system (PTO), and allows the use of compressed air as an alternative prime mover for either steering or another accessory when the vehicle engine  70  is off. Power assist boost system  199  is supplied with compressed air from engine start tank  78  (or other pressurized air source) by a pressure regulator  102  and a body computer controlled solenoid valve  43  when the engine is off. When the engine  70  is on, the power assist boost system  199  is driven by a mechanical connection (typically a front engine accessory drive (FEAD)) belt between engine  70  and pump  116 . Steering, or another accessory or power take-off application, receives a power boost (or is driven by) from the power assist motor  118 . Hydraulic fluid can be supplied to the power assist motor  118  or other pressure utilizing system from check valve  114  or check valve  112 . Working fluid is supplied through check valve  112  when under pressure in pressure vessel  108 . It is supplied through check valve  114  when power assist pump  116  is driven by engine  70 . Power assist pump  116  supplies hydraulic fluid to the motor  118  from reserve tank  106 . Hydraulic fluid is returned to reserve tank  106  from motor  118  regardless of its immediate source. Solenoid valve  43  is to be opened when engine  70  is not running and closed when the engine is running. 
     Whether engine  70  or air pressure actuated, power assist boost system  199  uses the same working fluid. When power assist boost system  199  is engine  70  powered, the working fluid is pressurized using a power assist pump  116  in sub-circuit  199 A (power assist pump  116  and check valve  114 ). Power assist pump  116  is driven by engine  70 . When power assist boost system  199  is actuated by compressed air, the working fluid is pressurized in fluid reserve pressure vessel  108  which is part of a hydraulic sub-circuit  199 B (check valve  110 , fluid reserve pressure vessel  108  and check valve  112 ). A power assist motor  118  (if present for a power steering application, accessory or other power take-off application) and a fluid reserve tank  106  are common to both sub-circuits  199 A and  199 B. The fluid reserve tank  106  supplies each of the sub-circuits  199 A and  199 B with working fluid. 
     Fluid reserve tank  106  is connected by a conduit to the power assist pump  116  and by a check valve  110  to the fluid reserve pressure vessel  108 . During engine  70  operation pump  116  draws hydraulic fluid from the fluid reserve tank  106 . Fluid reserve tank  106  can supply fluid reserve pressure vessel  108  with working fluid through a check valve  110  by gravity feed until the fluid reserve pressure vessel  108  is full. Upon an engine  70  shut down, with a consequent discontinuance of pumping by pump  116 , and opening of valve  43 , air pressure from the engine start air tank  78  is applied through valve  43  to the fluid reserve tank  108  which causes working fluid to circulate from the fluid reserve tank  108  via check valve  112  to the power assist motor  118 . The outlet from valve  43  is also connected by a capillary to fluid reserve tank  106  to balance the pressure in the reserve tank  106  and vessel  108  so fluid may continue to drain from the tank  106  to the vessel  108 . A check valve  110  prevents working fluid, or air, from escaping the pressure vessel  108  back to the reserve tank  106 . 
     With engine  70  running, power steering and air brake functionality is conventional. With the engine off, and armed for quick restart, the check valves function to direct pressurized fluid to the assist motor  118  bypassing the power assist pump  116  to provide full power steering. The air brake system operates conventionally. 
       FIG. 3  is a schematic illustrating one possible arrangement for integrating control of the starter system with an existing vehicle control system. Vehicle control systems may incorporate a body computer or electrical system controller  30 . Such body computers  30  communicate with more specialized controllers such as an engine control unit (ECU)  140 , a transmission control unit  160  and a gauge controller (EGC)  40 . Communication is implemented over a controller area network (CAN) implemented by CAN communication modules  162 ,  152 ,  143  and  133  and a network bus. A twisted wire pair conforming to the SAE J1939 standard (J1939 data link  60 ) is a suitable network bus. 
     Load control/shedding can be implemented from the body computer  30  communicating with other controllers over the J1939 data link  60  to disconnect engine driven loads to reduce the loads on the hydraulic starter system  99  applied to the starter system through engine  70  and ease fast cranking of engine  70 . 
     Body computer  30  comprises a microprocessor  31  which can access a memory  143 . Memory  143  includes volatile and non-volatile sections and can be used to store programs for execution by microprocessor  31  in order to implement computer control of the quick start system. Body computer  30  is equipped with a plurality of field effect transistor (FET) switches  51 ,  52 ,  53 ,  54 ,  55 ,  56 ,  57  and  58  which in turn control application of power to a number of devices. For the sake of simplicity, arrangements for staged control of some functions are omitted. FET  51  represents control over a blower motor  36  used with the vehicle&#39;s cab climate control system. Park Light FET  52  is connected to control illumination of various park and identification lights  37 ,  38 . FETs  53  and  54  are connected to control illumination of the vehicle&#39;s low and high beam headlights  61 ,  48 . FET  55  is connected to control the state of solenoid  43 A which in turn opens and closes valve  43  for the power steering system. FET  56  is shown connected to deliver power to solenoid coil  64 A associated with the hydraulic starter system  99 . FETs  57  and  58  are shown connected to supply power to an A/C valve  201  and a coolant motor  203 , respectively. These represent possible additions to the control arrangements for the quick start system. Control of coolant motor may be located with the ECU  140  rather than the body computer  30 . 
     Body computer  30  implements the control regime in response to various inputs, including user actuation of the rapid stop/start system switch input  138 . Switch input  138  may be applied directly to the body computer  30  as shown, or as a switch input to EGC  40 . Restart signals will typically involve the brakes, and brake status is communicated to the body computer through switch inputs  140 ,  136  to the microprocessor  31 . In addition, rapid restart is armed only when the ignition is on. Ignition status is supplied by EGC  40  to body computer  30  based on the status of the IGN switch input to microprocessor  41  in EGC  40 . 
     Rapid stop/start is armed when the engine operating temperature meets a minimum level. Engine temperature is illustrated as monitored by temperature sensor  146  connected as an input to a microprocessor  240  in ECU  140 . ECU  140  also provides for monitoring the air pressure sensor  84 , reporting engine  70  rpms from a tachometer  144  and for reporting electrical voltage on the vehicle power bus  150  from a voltage sensor  148 . Engine speed should not exceed idle levels before engine  70  is shut off. Engine shut off may be accomplished by cutting operation of the fuel injectors  187 . To accommodate some power take-off applications (PTO) it may be provided that PTO actuation cancels arming of the rapid stop/start, or the higher engine speeds initiated in response to an actual PTO operation initiate an engine restart on PTO equipped vehicles. Alternatively, a PTO vocation powered by a power assist system  119  may be accommodated without the introduction of such interlocks. 
     Vehicle speed is monitored as a condition of turning the engine  70  off Vehicle speed may be determined from a transmission tachometer  166  coupled to the output shaft of the vehicle transmission  168 . These data are supplied to the body computer  30  from a transmission controller  160  and its microprocessor  164 . 
     Differing control regimens may be implemented depending upon the control features available. In one version quick or rapid stop/start is enabled after engine temperatures considerations are met. An air conditioning expansion valve is activated (by operation of solenoid  201 ) regardless of heating, ventilation, air conditioning (HVAC) system settings. At minimum or zero vehicle speed, with the service brake applied, the engine is turned off Electrical power available on bus  150  is then monitored. If bus/battery voltage falls below 11.5 volts DC all loads with the exception of flashers  38  and marker lamps  37  will be shut down. If the headlamps  61 ,  48  are on they revert to their daytime running light state. If battery/bus voltage exceeds 11.5 volts DC accessory and lamp functions are maintained in the status they were at before the engine was shut down. Blower motor  36  will move to its low setting and the HVAC system will otherwise continue to operate at operator selected settings. 
     Load control may be modified as a function of ambient temperature. At cold temperatures, an electric coolant pump (driven by coolant motor  203  which may be an electric motor or another iteration of power assist system  119 ) may be provided to maintain circulation of engine coolant to the HVAC system when the engine is shut down. In hot temperatures, the blower fan for the evaporator may be operated for temporary cooling while the compressor is off Alternatively, a eutectic package (with an integral expansion valve) may be added to the refrigeration loop. This provides a heat sink to be collocated with the evaporator for use when the engine is shut down to extend the cooling period that can be obtained. 
       FIG. 4  is a representative, high level state machine  400  illustrating possible operation of the rapid stop/start system by the control system of  FIG. 3 . The state machine  400  assumes manual control over arming of the rapid stop/start system through operator selection. State  402  represents the system armed with the engine  70  running. Power steering and power brakes are operative, and various electrical and cab climate loads are assumed to have been selected by the operator/driver. With brakes applied, vehicle speed below a maximum allowed value, engine temperature reasonably close to its operating norm and minimum air pressure levels available the state shifts to an engine off state  404 , armed for a rapid restart of the engine  70 . Initially the climate and electrical loads already active are carried. Air pressure to operate power assist for the brakes and steering is supplied to continue operation of those accessories using air pressure as an alternative prime mover for as long as the engine is off In other words, were the driver stopped for traffic, he or she would not feel a loss of steering boost nor would the air brakes discontinue operation. 
     Deterioration in the voltage state, or loss of air pressure would represent a load condition violation and the state would change depending upon the character of the violation. A deteriorating electrical state could be dealt with by shedding the electrical loads, as represented by state  406 . State  406  represents various electrical loads having been shed, possibly as the result of a progressive series of transitions feeding back on state  406 . Alternatively, a load condition violation, if it persists or exceeds other thresholds, may be dealt with by cranking the engine for a restart, either hydraulically (state  410 ) for an electrical load condition violation or electrically (state  408 ) for a pressure condition violation. It is possible that the load condition violation could be removed by connection of the vehicle to an external air or power source, or operation of an auxiliary power unit, if available. Accordingly a transition from state  406  back to state  404  is shown. Electrical and cab climate control related loads may be shed during cranking states though power steering and power brakes normally would not lose boost. 
     Restart conditions may be selected. An example might involve loss of one of the shut off conditions, or combination of such a loss with another operator action, such as depressing the gas pedal or deactivation of the rapid stop/start system. From either state  404  or state  406  there is a transition to an engine cranking state, either using the conventional starter (state  408 ) if air pressure is inadequate, or to cranking with the hydraulic motor (state  410 ), if available. Start of the engine effects a transition from state  408  or  410  to state  402 , with the engine running and any shed loads being restored to operation. Failure of cranking after a time out period results in transition to a fail state  412 . This may provide for operator election of alternative cranking. 
     The present system provides for some regenerative power capture by loading the engine with the air compressor  72  during braking. A clutch mechanism may be introduced to the engine  70  to air compressor  72  power transmission mechanism to restrict compression of air for engine restarts to instances of braking. Such an arrangement might be used on a vehicle not equipped with air brakes. The engine  70  itself might be used as air pump for the start air tank  78  by modification of a Jepson engine brake to direct compressed air to the start air tank. An engine brake application would work with the pressure amplifier taught in U.S. Pat. No. 6,922,997.