Abstract:
A system and a method for supplying electrical energy to high-power vehicle braking resistors to generate heat for supplemental heating. Supplemental heat is transferred from the braking resistors to a desired use by means of circulating liquid or air, and heat exchangers at the desired location. The supplemental heat can be supplied external to the vehicle by circulating liquid or air and using appropriate external heat exchangers.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The field of the invention relates, in general, to the heating systems for a heavy-duty vehicle, and, in particular, to the heating systems for a hybrid-electric heavy-duty vehicle.  
         [0003]     2. Background of the Invention  
         [0004]     Most vehicles use a liquid coolant-to-air heat exchanging radiator to extract heat from engine coolant for heating the interior of the vehicle in cold temperature environments. In extreme cold weather conditions a diesel fired supplemental coolant heater may be added to transit buses and heavy-duty trucks. This type of heater is used to supply additional heating for the interior of the bus or truck and to help warm the engine prior to starting. It is also used for the overnight heating of over-the-road truck sleeper cabs without idling the engine. Pro Heat is a company that develops and sells diesel fired supplemental heaters and a typical heater provides 13 kW of heat.  
         [0005]     Plug-in electric engine block and engine oil heaters are also common in cold climates as an aid to starting the engine during extreme cold air temperatures. Quickly bringing engine coolant up to temperature results in lower exhaust emissions because typical engines operate in an open loop mode when coolant temperature is below a low temperature threshold. Open loop operation during low engine temperatures generates excessive hydrocarbons from unburned fuel.  
       SUMMARY OF THE INVENTION  
       [0006]     An aspect of the present invention involves a method for supplying supplemental heating from high-power braking resistors. High-power braking resistors dissipate excess electric energy produced from electromagnetic drag on a moving vehicle drive line during deceleration. An electric generator is connected to a wheel axle shaft or differential gear driveshaft. During electromagnetic braking the generator is connected to the braking resistor and the resulting power generation puts a torque load on the driving shaft while the electric power is dissipated as heat in the braking resistor. With braking resistors, electromagnetic braking can also be used on conventional vehicles similar to the use of retarders in some transmissions. A generator-braking resistor combination may replace or supplement friction brakes as a way of providing more braking capacity and/or reducing brake wear. In all-electric or hybrid-electric vehicles with a generator—braking resistor combination an electric motor propels the vehicle during acceleration and helps decelerate the vehicle during braking (electric motor is switched into a generator configuration to help decelerate the vehicle during braking). When electric power produced by braking is either transmitted back into the power grid or into on-board energy storage, the operation is typically referred to as “braking regeneration”. Adding a braking resistor to a braking regeneration system provides additional power dissipation capacity to protect the energy storage and to reduce friction brake wear.  
         [0007]     In an aspect of the present invention, a switch is closed to connect the braking resistor(s) to the high-power electric bus on the electric or hybrid-electric vehicle whenever supplemental heat is desired for the vehicle. In this way the braking resistor(s) become heating resistor(s). Although the present invention will be described in conjunction with liquid cooled braking resistors, in an alternative embodiment, air cooled resistors may be used. The heating resistors can be used for various applications at multiple locations on or off-board the vehicle wherever heated air, water, or fluid is desired.  
         [0008]     In another aspect of the invention a hybrid-electric bus drive system has a gasoline engine that powers a 140 kW permanent magnet generator and the system includes two 70 kW braking resistors used to provide resistive braking in the event that the energy storage system is full during regenerative braking. Power is sent directly from a high voltage bus, supplied by the generator, motor (operating in braking regeneration mode), or energy storage system, into the braking resistors. An engine and/or accessory coolant pump circulates engine coolant thru the braking resistors whereby heat generated by the resistors is dissipated thru an engine radiator. A standard heater core type heat exchanger is included in a cooling loop and the heated air is circulated into the vehicle interior for space heating. With generator and/or stored energy power available to heat the braking resistors, a supplemental heater is unnecessary for maintaining a comfortable vehicle interior temperature in the coldest climates.  
         [0009]     In a further aspect of the invention a liquid-to-liquid heat exchanger is added to the braking resistor cooling loop where the secondary liquid is water. The hot water produced may be potable, for human bathing and cooking, or the water may be for more industrial or commercial uses. The water source may be from a reservoir tank inside the vehicle and/or provided from a connection to an off-board water supply. The water may be used either on-board the vehicle and/or off-board the vehicle.  
         [0010]     Another aspect of the invention involves a method of supplying supplemental heating from one or more braking resistors of a vehicle to a separate location. The method includes supplying electrical energy to the one or more braking resistors so as to cause heat energy to be generated there from; transferring the heat energy of the one or more braking resistors by a circulating fluid medium to the separate location; and extracting the transferred heat energy in the circulating fluid medium for use at the separate location.  
         [0011]     A further aspect of the invention involves a system for supplying supplemental heating from braking resistors of a vehicle to a separate location. The system includes means for supplying electrical energy to one or more braking resistor heating elements, the electrical energy converted to heat energy by the one or more braking resistor heating elements; means for transferring the heat energy of the one or more braking resistor heating elements by a circulating fluid medium to a separate location; and means for extracting the transferred heat energy in the circulating fluid medium for use at the separate location  
         [0012]     Other aspects, advantages, and novel features of the invention, will become apparent from the following Detailed Description of Preferred Embodiments, when considered in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of this invention.  
         [0014]      FIG. 1A  is a block diagram illustrating an embodiment of a vehicle engine cooling loop with braking resistors and an auxiliary heat exchanger for interior heating.  
         [0015]      FIG. 1B  is a block diagram illustrating an embodiment of a braking resistor cooling loop with an auxiliary heat exchanger for interior heating, but without an engine.  
         [0016]      FIG. 2A  is a block diagram illustrating an embodiment of mechanical and electrical energy flow in a series hybrid-electric drive system with braking resistors.  
         [0017]      FIG. 2B  is a block diagram illustrating an embodiment of mechanical and electrical energy flow in a series hybrid-electric drive system with braking resistors where a fuel cell and DC-DC converter is an alternative to an internal combustion engine-generator.  
         [0018]      FIG. 3  is a block diagram illustrating an embodiment of mechanical and electrical energy flow in a parallel hybrid-electric drive system with braking resistors.  
         [0019]      FIG. 4  is a block diagram illustrating an embodiment of an electromagnetic brake system with axle generators and braking resistors.  
         [0020]      FIG. 5  is a block diagram illustrating an embodiment of an electromagnetic brake system with a drive line generator and braking resistors. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]     With reference to  FIGS. 1A and 1B , embodiments of cooling loops  200 A,  200 B and methods for supplemental heating from braking resistors in a heavy-duty all-electric or hybrid-electric vehicle with a generator-braking resistor combination will be described. As used herein, a heavy-duty vehicle is a vehicle with a gross weight of over 10,000 pounds. Although the invention will be described in conjunction with a heavy-duty vehicle, the invention may be used with other types of vehicles have a generator-braking resistor combination. Although the loops  200 A,  200 B are described as “cooling” loops, the loops  200 A,  200 B will be described herein in conjunction with heating applications. The loops  200 A,  200 B may also be used for cooling applications.  
         [0022]     The cooling loops  200 A,  200 B include vehicle coolant flows  250  with a braking resistor(s)  230  in the cooling loops  200 A,  200 B.  FIG. 1A  shows the braking resistor(s)  230  incorporated into the engine coolant loop  200 A, while  FIG. 1B  shows a braking resistor cooling loop  200 B independent of an engine cooling loop. As the name implies a braking resistor  230  is a high-power electrical resistance heating element used to dissipate generator power from electromagnetic braking. The braking resistor  230  heats the circulating fluid medium in coolant flow  250 , which carries the heat energy to the radiator heat exchangers (interior heater radiator  210 , engine radiator  220 , braking resistor radiator  260 ) in the loop where the excess heat is dissipated into the exchange medium, typically air or a separate fluid. Various control valves, coolant bypass connections, pumps, temperature sensors, fluid reservoir tanks, or other components may be added to the cooling loops  200 A,  200 B in accordance with the desired application.  
         [0023]     With reference to  FIGS. 2A and 2B , embodiments of systems  300 A,  300 B and methods for supplemental heating from braking resistors in a heavy-duty series hybrid-electric drive system will be described. With reference initially to  FIG. 2A , an internal combustion engine  310  includes a rotating output shaft  315  connected to a generator  320  that supplies electrical power and energy through a controller  330  to a high-voltage DC bus  355 . The energy storage  350 , propulsion motor controller  360 , and a braking resistor switch  365  is also connected to the same high-voltage DC bus  355 .  
         [0024]     During vehicle acceleration, a combination of power from the generator  320  and power from the energy storage  350  is supplied to the DC bus  355  and power from the DC bus  355  is supplied to the propulsion motor(s)  380  through the motor controller(s)  360 . The shaft output of the electric motor(s)  380  may be connected to a speed reduction gear box  385  to match the propulsion motor(s) rpm range to the desired rpm range of a differential axle drive  395 . A drive shaft  390  completes the connection between the reduction gear box  385  and the differential axle drive  395 .  
         [0025]     During vehicle deceleration, the motor controller  360  operates the propulsion motor  380  as a generator to put a drag on the drive shaft  390  and store the generated energy into the energy storage  350  through braking regeneration. If the energy storage  350  is full or if the braking regeneration power exceeds the energy storage input capacity the power is switched into the braking resistors  370  rather than generate heat and wear in the standard friction brakes on each wheel. In this way the braking resistor(s)  370  add heat to the cooling loops  200 A,  200 B of  FIGS. 1A, 1B . In the embodiment shown in  FIGS. 2A and 2B  the switching occurs in the IGBT switch controller  365 . In an alternate embodiment the switching is part of the motor inverter/controller  360 . An Insulated Gate Bipolar Transistor (IGBT) is a solid state switching device typically used for repetitive high power switching applications.  
         [0026]     Similarly, the system  300 B of  FIG. 2B  uses a fuel cell  340  and, if required, a DC-DC converter  345  in place of the engine generator system  310 ,  315 ,  320  of the system  300 A in  FIG. 2A , to supply power to the high-voltage bus  355 .  
         [0027]     During acceleration, the fuel cell  340  and energy storage  350  supply power to the high-voltage bus  355  for use by the motor controller  360 , propulsion motor  380 , reduction gear box  385  (if required), drive shaft  390 , and the differential axle drive unit  395 . During deceleration and braking regeneration the operation proceeds exactly as described above for the system  300 A.  
         [0028]     In both systems  300 A,  300 B, the braking resistors  370  are connected into the cooling loops  200 A,  200 B along with a radiator  210  for heating the vehicle interior as described above and shown in  FIGS. 1A and 1B .  
         [0029]     During the braking regeneration operation of systems  300 A and  300 B, as described above, excess braking regeneration power heats the braking resistor cooling loop  200 A,  200 B. However, the braking resistors  370  may be heated at any time from the high-voltage bus  355  by power supplied form any combination of energy storage  350  and either engine generator  310 ,  315 ,  320 , or fuel cell  340  and DC-DC converter  345 . Because of the 140 kW high power of the braking resistors  370  rapid heating of the cooling loop  250  occurs, thus, providing immediately available extra heat for the interior of the vehicle through heater radiator  210 .  
         [0030]     With reference back to cooling loop  200 A of  FIG. 1A , the braking resistor  230  and the engine  240  are on the same cooling loop  250 . Therefore, the braking resistor  230  can rapidly heat the engine coolant to bring the engine  240  up to a desired operating temperature, even under the most extreme low-temperature conditions. This startup heating can occur from the energy storage  350  such as batteries, if the energy is available, or from an off-board power source through an external connection to the vehicle. Once the engine  240 ,  310  is started, the generator  320  can supply power to the braking resistors  230 ,  370  and heat the coolant faster than waiting for the waste heat of the engine  240 ,  310  to heat the coolant.  
         [0031]     In an alternative embodiment of  FIG. 2A  the energy storage  350  is an ultracapacitor pack that drains over night and is precharged in the morning. The braking resistors  370  act as a high-power current limiter to quickly precharge the ultracapacitor pack from the generator  320  while at the same time rapidly heating the engine coolant up to the desired operating temperature.  
         [0032]     With reference to  FIG. 3 , another embodiment of system  400  and method for supplemental heating from braking resistors in a heavy-duty parallel hybrid-electric drive system will be described. As in a conventional drive system an engine  410  with output crankshaft  415  drives the transmission  430 , the driveshaft  490 , and the differential axle assembly  495 . However, an electric motor/generator  420  connects between the crankshaft  415  and an input shaft of the transmission  430 . In an alternate embodiment the electric motor/generator  420  connects between the output shaft of the transmission  430  and the drive shaft  490 . Clutches and torque converters may be part of the driveline design.  
         [0033]     During vehicle acceleration, the electric motor  420  assists the engine crankshaft  415  to drive the transmission  430 . During vehicle deceleration, the motor  420  and a motor controller  460  switch into a braking regeneration mode to store energy into an energy storage  450  and dissipate excess energy in braking resistors  470  as controlled by a switch  465 . The energy storage  450  can also receive energy from the motor/generator  420  when the engine  410  has excess power available beyond what is required to propel the vehicle. Similar to systems  300 A and  300 B in  FIGS. 2A and 2B , the braking resistors  470  may draw power from the energy storage  450  and/or the electric motor/generator  420  whenever additional heat is desired.  
         [0034]     With reference to  FIG. 4 , a further embodiment of system  500  and method for supplemental heating from braking resistors in a heavy-duty vehicle will be described. In the embodiment of the system  500 , electromagnetic braking supplies energy to braking resistors  570  for additional vehicle heating. Input shafts of electric generators  530  are driven by two axles of a differential axle drive assembly  595 . When the generators  530  are activated by the brake controller  580 , the resulting drag on the axles decelerates the vehicle and supplies power to the braking resistors  570  and/or to an optional energy storage  550 . The system  500  would be an alternate form of a parallel hybrid-electric drive if the electric generators  530  were also motors and the energy storage  550  was included. Furthermore, an engine  510 , a crankshaft  515 , a transmission  520 , a driveshaft  590 , and differential unit are not required for this invention because the braking resistors  570  may be heated by any electromagnetic braking generators  530  on the wheels/axles applied to any type of vehicle, with or without a differential, such as, but not limited to, a conventional engine transmission drive, a hybrid-electric drive, an all-electric drive, and a downhill coasting vehicle.  
         [0035]     With reference to  FIG. 5 , a further embodiment of system  600  and method for supplemental heating from braking resistors in a heavy-duty vehicle will be described. In the embodiment of the system  600 , the electromagnetic braking generator  630  is positioned in vehicle drive line  615 ,  620 ,  630 ,  690 ,  695  rather than the wheels or wheel axles as shown in  FIG. 4 . When a brake controller  680  activates a generator  630 , the resulting drag on the drive line helps decelerate the vehicle and/or pull excess power from an engine  610  to heat braking resistors  670  and/or store energy in an optional energy storage  650 . Similar to the hybrid-electric drive configurations shown in  FIGS. 2, 3 , and  4  auxiliary heating from the braking resistors  670  may be powered by the engine/generator  610 ,  615 ,  630 ; braking regeneration  630 ,  680 ; or optional energy storage  650 .  
         [0036]     While embodiments and implementations of the invention have been shown and described, it should be apparent that many more embodiments and implementations are within the scope of the invention. Accordingly, the invention is not to be restricted, except in light of the claims and their equivalents.