ENGINE BRAKING SYSTEM

Abstract: An engine braking system including an axial flow com­ pressor (3) connected to an output shaft (5) of an engine (1) so as to be driven by said output shaft (5) and to discharge air or exhaust gas supplied there­ to, so that the compression and discharging work by axial flow compressor (3) serves as a braking effort during engine braking.

Description: The present invention relates to an engine braking system according to the generic clause of claim 1. In general, a large bus or a track in which the heat-exchange upon friction braking is large, is equipped with an auxiliary braking device in addition to a main braking device. Heretobefore, according to said brake, the engine or a rotative resistor is driven by wheels of the vehicle so as to produce resistance loss which serves as a braking force. Among those which include the rotative resistor, fluid retarder and electric retarder are known and utilized. The fluid retarder is disposed within a driving force transmitting shaft that connects the engine to the wheels of the vehicle, and eddy is generated in fluid (for example, water or oil) between a rotor fixed to the side of output and a stator fixed to the side of input so that energy absorbed therein is transformed into heat. Said fluid is cooled by an heat-exchanger disposed in a fluid tank, and recirculated. Braking effort is adjusted by changing the flow rate by means of valve. On the other hand, the electric retarder disperses in the form of ohmic heat the eddy current (Foucault current) generated when the rotor of the same kind as said fluid retarder rotates in the magnetic field between electromagnets. In above retarders, the torque of output side is finally changed to heat energy and the thusly transformed energy becomes braking energy. Thus, in order to raise braking efficiency, a device for cooling the working medium is necessary. Disposition of such a device is troublesome in terms of spacing and cost. An engine braking system according to the generic clause of claim 1 is known from GB-A-746 681. This braking system is provided with a supercharging compressor and a braking compressor, both being operatively connected to the output shafts of the engine-driven distributing mechanism. The known arrangement further comprises a throttling device adapted to regulate the output of the braking compressor by throttling the air inlet. Said throttling device is operatively connected with the brake pedal and controls the throughput of the braking compressor. In the DE-C-1,807,070 there is disclosed an engine braking system comprising an axial flow compressor connected to an output shaft of an engine to be driven by said engine to discharge air in an intake passage of said engine. Between the axial flow compressor and the engine there is disposed a throttling means for adjusting the amount of the intake air. It is an object of the invention to form an engine braking system as mentioned in the generic clause of claim 1 with better adjusting properties. The above object is achieved by an engine braking system including the characterising features of claim 1. Further embodiments of the invention are mentioned in the subclaims. The invention will be further described with reference to the accompanying drawings. Figure 1 is an enlarged view, showing throttling means. Figure 2 is a system diagram, showing a second embodiment of the present invention equipped with the throttling means of Figure 4. Figure 3 and 4 are enlarged views, showing another throttling means and gas passage switching means. Figure 5 is a flow sheet, showing control of a controller. Figure 6 is a system diagram, illustrating a conventional example. First a conventional example will be described with reference to Figure 6. As shown in Figure 6, the fluid retarder 201 is disposed within a driving force transmitting shaft 204 that connects the engine 202 to the wheels 203 of the vehicle, and eddy is generated in fluid (for example water or oil) between a rotor 205 fixed to the output side and a stator 206 fixed to the input side so that energy absorbed therein is transformed into heat. Said fluid is cooled by an heat-exchanger 208 disposed in a fluid tank 207, and recirculated. Braking effort is adjusted by changing the flow rate by means of valve 209. On the other hand, the electric retarder disperses in the form of ohmic heat the eddy current (Foucault current) generated when the rotor of the same kind as said fluid retarder rotates in the magnetic field between electromagnets. In above retarders, the torque of output side is finally changed to heat energy and the thusly transformed energy becomes braking energy. Thus, in order to raise braking efficiency, a device for cooling the working medium is necessary. Disposition of such a device is troublesome in terms of spacing and cost. Now a preferred embodiment of the engine braking system of the present invention will be described with reference to the accompanying drawings. In Figure 2 of the accompanying drawings, 101 indicates an engine, 102 an intake air port, and 103 an exhaust port. As depicted in Figure 2, an exhaust passage consists of 104a, 104b, 104c, 104d, and 104e. The upstream part thereof 104a is connected to the exhaust port 103, and an intake passage 105 is connected to the intake port 102. A turbine 110a of a turbocharger 110 is disposed in the exhaust passage 104a, and a compressor 110b of the turbocharger 110 is in the intake passage 105. In the exhaust passage 110b downstream of the turbocharger 110, there is disposed a power turbine 112 for recovering the exhaust gas energy. One objective of the turbo compound engine of this embodiment is to ensure an engine braking effort which is adequate for the output performance of the engine 101. In order to increase the engine braking effort, it is considered to be effective to impose a resistance force against the rotation of the crankshaft 115 directly or indirectly so that the crankshaft 115 performs a large negative work. In the turbo compound engine of this embodiment, the power turbine 112 is rotated in reverse sense during exhaust braking so that the power turbine 112 performs a large negative work. To the exhaust passage 104b between the power turbine 112 and the turbine 110a of the turbocharger 110, as depicted in Figure 2, a fluid passage 125 is connected at one end, and the other end thereof is connected to the exhaust passage 104c downstream of the power turbine 112. A passage switching means 130 is disposed at one junction of the fluid passage 125 upstream of the power turbine 112. In this illustrated embodiment, the passage switching means 130, as shown in Figures 2-4, comprises a rotary valve 131 as a switching valve, which is provided at said junction, and an actuation means 132 for the rotary valve 131. The rotary valve 131, as depicted in Figures 3 and 4, houses rotatably a rotor 131b in a casing 131a. Two ports, namely a first port P1 and a second port P2, are formed in the rotor 131. The diameter of first port P1, d1 is equal to the diameter of the exhaust passage 104b, d0, while the diameter of the second port P2, d2 is smaller than the diameter of the fluid passage 125, d3. In the casing 131a, on the other hand, an opening 131c is formed as a part of the exhaust passage 104b. The first port P1 and the second port P2 are formed in a manner such that the exhaust passage 104b is disconnected to the fluid passage 125 when the exhaust passage 104b is connected to the first port P1. A drive mechanism or means 132 for switching-control of the rotary valve 131 is constructed as below. As shown in Figures 2 and 3, a lever member 135 is connected to the rotor 131b at one end, and the other end thereof, which extends outward in the radial direction of the exhaust passage 104b, is connected to a rod 133 of an actuator 134. Referring to Figure 2, 136 indicates a fluid feeding apparatus. This feeding apparatus 136 and the actuation chamber 137 of said actuator 134 are connected to each other by a fluid feeding passage 139. At an intermediate point of the fluid feeding passage 139, there is disposed an electromagnetic valve 140 that connects said actuation chamber 137 to the fluid feeding passage 139 when an electric current is supplied thereto. The electromagnetic valve 140 is turned ON only when a neutrality sensing switch 141 of the engine 101, a clutch actuation switch 142, and an exhaust brake switch 143 are all turned ON. 145 indicates a DC electric source such as a battery. 147 indicates an electromagnetic clutch switch for reverse mode, and it is an open contact (A contact point). Now, a gear train for connecting the power turbine 112 to the crankshaft 115 will be explained. As illustrated in Figure 2, an output gear 116 is integrally disposed at an output end 113a of the turbine shaft 113 of the power turbine 112. The output gear 116 is engaged with planetary gears 117a and 117b. These gears 117a and 117b are engaged with a ring gear 118 which rotates with an input pump wheel 121a of a fluid coupling 121. In other words, the output gear 116 is connected to the fluid coupling 121 via planetary gearing 119 consisting of the planetary gears 117a and 117b, and the ring gear 118, so that the rotative power of the power turbine 112 is transmitted to the output pump wheel 121b of the fluid coupling 121. The planetary gearing 119 is employed because of its large reduction ratio and high transmission efficiency. An input-output gear 120 is fixed to the output pump wheel 121b so as to rotate together. The crankshaft 115 has a first crankshaft gear 123 which can be disconnected by the electromagnetic clutch 122 and a second crankshaft gear 124. The second crankshaft gear 124 is engaged with a second intermediate gear 127 equipped with a one-way clutch 126. The second intermediate gear 127 is connected to said input-output gear 129 via a first intermediate gear 128 having a mutual axis with the gear 127. The first intermediate gear 128 and the first crankshaft gear 123 are connected to each other by a reverse idle gear 129. When the electromagnetic clutch 122 is ON, that is to say, when said electromagnetic clutch switch 147 is ON, the first crankshaft gear 123 is connected to the first intermediate gear 128 so that the rotative power is transmitted from the crankshaft 115 to said input-output gear 120. In this case, the rotative power is not transmitted between the second intermediate gear 127 and the second crankshaft gear 124 because of the one-way clutch 126, with the one-way clutch 126 rotating freely. A gear ratio of each gear namely the first crankshaft gear 123, the idle gear 129, the first intermediate gear 128, and the input-output gear 120, is determined in a manner such that the gear ratio between the first crankshaft gear 123 and the input-output gear 120 is small compared with that between the input-output gear 120 and the second crankshaft gear 124. This is because it prevents the power turbine 112 from overrunning when the rotative power is transmitted from the crankshaft 115 to the power turbine 112 at the engine rated speed. In this embodiment, the gear ratio between the first crankshaft gear 123 and the first intermediate gear 128 is set smaller than that between the second crankshaft gear 124 and the second intermediate gear 127. Here, the second crankshaft gear 124, the one-way clutch 126, the first intermediate gear 128, and the input-output gear 120 are comprised in a gear train 156 that transmitts the rotation from the power turbine 112 to the crankshaft 115 while the first crankshaft gear 123, the idle gear 129, the first intermediate gear 128, and the input-output gear 120 are comprised in another gear train 157 that transmitts the rotation from the crankshaft 115 to the power turbine 112. Referring to Figure 1, drive means 200 is provided to the power turbine 112. The drive means 200 is, more precisely, provided to the casing 150 of the power turbine 112 so that each movable nozzle vane 152 is adjusted in accordance with running conditions of the engine. Each nozzle vane 152 changes a throat area 151 of the power turbine 112 so that it serves as a throttling means for adjusting workload of the power turbine 112 in accordance with velocity of fluid supplied thereto. Next, the construction of the movable nozzle vane 152 will be described. As depicted in Figure 1, within the inner wall 150a of the casing 150 of the power turbine 112, the movable nozzle vanes 152 are spacedly disposed along the circumference of said inner wall, with each nozzle vane 152 being movable in the radial direction as well as in the circumferential direction of said housing. In the illustrated embodiment, the nozzle vane of wing type is employed. Each nozzle vane 152 is pivotably supported by a rotative shaft 153 penetrating the casing 150 in the direction of power turbine's shaft so that the angle of the nozzle vane can be changed. The drive mechanism 200 now will be described. At that end of each rotative shaft 153 which penetrates the casing 150, lever member 154 is integrally attached at one end, respectively. The other end of each lever member 154 is engaged with an engaging portion 156 of a control ring 55. It is a matter of course that the control ring 55 and the movable nozzle vane 152 are constructed in a manner such that the nozzle throat areas 151 (called "throttling" hereinafter) formed by the power turbine 112 and nozzle vanes 152 are equal to each other. The control ring 55 is prevented from moving in the axial direction relative to the casing 150, and the end of the lever member 154 is also prevented from moving in the axial direction relative to the control ring 55. To one of the rotative shafts 153, there is fixed a control lever 197 at one end, which is a point of application, via the lever member 154 so as to actuate the control ring 55. Thus, when the control lever 197 is rotated, the control ring 55 is rotated accompanying the nozzle vanes 152. The control lever 197 is connected via a linkage 161 to a step motor 160 moved by a controller 162 which will be described later. The step motor 160 is employed as an actuation means for the control lever 197 in this particular embodiment though, another device is satisfactory as long as it can adjust the stroke of the linkage 161 by the controller 162. The construction of the controller 162 and the control thereby will be explained. As shown in Figure 1, vehicle velocity, engine rotating speed, loadage, and time are fed as input signals to the input of the controller 162. Said time is time passed since the step motor 160 has driven the nozzle vanes 152 to a certain optimum position. Besides the above signals, a ON-OFF signal of the exhaust brake switch 143, an ON-OFF signal of the electromagnetic clutch switch 142, an ON-OFF signal of the accel switch (not shown), and an ON-OFF signal of the electromagnetic valve 140 are supplied to the input of the controller 162. The output of the controller 162 is connected to the controller of the step motor 160. The controller 162, as shown in Figure 5, has already stored various data obtained by experiments in maps 163, 164, 165, 166, and 167. The stored data in the maps 163-167 are compared with the input data in the controller 162, and said step motor 160 is controlled based on the data resulting from the above comparison. Referring to Figure 5, the control by the controller 162 now will be described. First, the control during normal driving will be explained. The program proceeds to the step 206 for normal driving when the exhaust brake switch 143 is OFF at the step 168, the clutch switch 142 is OFF at the step 169, or the accel switch is OFF at the step 170. Namely, in the above case, as shown in Figures 2 and 3, when the exhaust brake switch 143 is OFF, the electromagnetic valve 140 is OFF. Thus, the exhaust passage 104d just upstream of the power turbine 112 and the exhaust passage 104b upstream of the rotary valve 131 are connected to each other via the first port P1. Therefore, the energy of the exhaust gas transferred from the engine through the exhaust port 103 and the exhaust passage 104a is recovered by the turbine 110a of the turbocharger 110. Since the turbine 110a drives the compressor 110b disposed on the same axis as the turbine 110a, the compressed air is supplied into the cylinders of the engine 101. The exhaust gas from the turbine 110a gives a rotative power to the power turbine 112. This means that the remaining energy of the exhaust gas is recovered by the power turbine 112. In this case, the electromagnetic clutch 122 is OFF so that the exhaust gas energy recovered by the power turbine 112 is transmitted to the crankshaft 115 via the planetary gearing 119, the gear 120, the second intermediate gear 127, and the second crankshaft gear 124, with its rotating speed being reduced at the planetary gearing 119. Here, it is possible to adjust the degree of opening by the nozzle vane 152 in a range that prevents the power turbine 112 from overrunning so as to effectively recover the exhaust gas energy. The control in this case is performed, for example, by the controller 162 based on the map storing the engine running condition. Now, the control during exhaust braking will be explained. When all the answers at the steps 168, 169, and 170 are YES, the control for exhaust braking is performed. During exhaust braking, the neutrality sensing switch 141, the clutch switch 143, the accel switch, and the exhaust brake switch 143 are all ON. Thus, the electromagnetic switch 147 is turned ON at the step 172, turning the electromagnetic valve 140 ON. Then, the working fluid is supplied to the actuation chamber 137 of the actuator 134 from the fluid feeding apparatus 136. In other words, the step 171 is executed so that the rod 133 moves the rotary valve 131 via the lever member 135, closing the exhaust passage 104b and connecting the exhaust passage 104d downstream of the rotary valve 131 to the fluid passage 125 via the second port P2. After that in the controller 162, the step 173 is executed, adjusting the step motor 160 to the minimum throttling, i.e., the nozzle throat area is maximum. Then at the step 174 the vehicle velocity is detected. Therefore, while the rotative power is not supplied to the power turbine 112, the rotative power of the crankshaft 115 is transmitted to the input-output gear 120 and the fluid coupling 121 via the first crankshaft gear 123 and the first intermediate gear 128. The power turbine 112, as depicted in Figure 4, is rotated in reverse sense, so that it serves as a compressor of low efficiency which feeds the gas from the exhaust passage 104c downstream of the power turbine 112 to the junction of the fluid passage 125. The gas fed to the fluid passage 125 is throttled and accelerated through the second port P2. The gas agitating work and compressing work by the power turbine 112 let the crankshaft 115 perform a large negative work. Hence, during exhaust braking, an optimum engine braking effort including the above-mentioned negative work in addition to another negative work by the exhaust brake and a normal engine brake. This engine braking effort is adjusted so that it does not exert a duly resistance against the driving system of the vehicle. The exhaust braking effort is produced by actuating an exhaust brake valve (not shown) disposed downstream of the exhaust port 103. As the exhaust resistance, that is to say pumping work, increases upon fully closing the exhaust brake valve, an engine braking effort by the exhaust brake system is imposed on the engine. Here, the diameter of the second port P2, d2 is determined with regard to the configuration of the power turbine 112 so as to prevent the power turbine 112 from overrunning (see Figures 3 and 4). After detecting the vehicle velocity at the step 174 in the controller 162, the program proceeds to the step 175 at which the detected vehicle velocity is compared with the data stored in the map 163. There is determined an optimum throttling DO. At the step 176 a loadage of the vehicle is detected, and another optimum throttling DT is obtained at the step 177. The thusly obtained DO and DT are compared with each other in order to choose one of them at the step 178. Specifically, if DT<DO, DT is chosen as the optimum throttling. If DT≧DO, DO is chosen. In a word, smaller one is picked up. The controller 162 detects the engine rotating speed at the step 179, and at the step 180 an optimum throttling DE relative to the detected engine rotating speed is obtained from the map 165. After that, it is determined which has priority, DE or Do at the step 181. If DE<DO, the value of DE is chosen and assigned to that of DO as the optimum value while if DE≧DO, Do is chosen as the optimum throttling. The controller 162 checks time T1 passed since the step motor 160 has been activated at the step 182. At the step 183, an optimum throttling DM and time T2 to maintain the optimum throttling DM are determined from the map 166 based on said time T1. Then, it is determined which has to be chosen, DO or DM at the step 184. If DM<DO, the value of DM is assigned to DO, while if DM≧DO, the value of DO comes out from the step 184. The thusly obtained DO is the final optimum throttling, and the movement of the step motor 160 relative to DO, namely the moving angle (step angle) of the step motor 160 is determined at the step 185. And at the step 186, the step motor 160 is activated according to the thusly determined moving angle. Here, at the steps 178, 181, and 184, the minimum and optimum throttling Do is determined by judging the priority, with respect to parameters, i.e., the vehicle velocity, loadage, the engine rotating speed, and the time, so that a large exhaust brake force is not applied to the driving systems of the engine and the vehicle at one time. If the circumstance still demands the exhaust brake, the judgement is performed at the step 187. And, if the answer is YES, the program returns to the step 174 and repeats the above described procedure until step 186, whereby the optimum and minimum exhaust brake force is cyclically applied to based on the driving condition of the vehicle. Hence, during exhaust braking, a large driving power is not applied to the driving system of the vehicle, the skidding and the abnormal wear of the brake pads and shoes are prevented, and the shock to the vehicle driver is reduced. In this embodiment, it is acceptable to dispose a three-way valve 155 (Figure 2) in the exhaust passage 104c near the junction 104e of the exhaust passage 104c downstream of the power turbine 112 and the fluid passage 125. This construction makes it possible during exhaust braking to close the exhaust passage 104c and directly introduce the external atmosphere which is cleaner than the exhaust gas. In the illustrated embodiment, the switching between the exhaust passage 104 and the fluid passage 125 is executed by the rotary valve 131. However, it is not limited to the rotary valve. For instance, when the driving rotation of reverse sense is transmitted from the crankshaft 115 to the power turbine 112 during exhaust braking, it is permittable to provide an opening-closing valve and a throttling valve in a manner such that the opening-closing valve opens the exhaust passage 104b upstream of the fluid passage 125 and the throttling valve converges the fluid passage 125. It is also satisfactory to form a converging portion in the fluid passage 125 to a certain degree beforehand, and to open/close the exhaust passage 104b upstream of the fluid passage 125. In employing the rotary valve 131, the diameter of the port P2, d2 is determined in a manner such that the power turbine 112 will not go into overrun condition even when the nozzle vanes 152 are moved minimizing the throat area. According to this embodiment, since the suitable exhaust braking effort is applied depending on the running conditions of the vehicle during exhaust braking, the resistance force that may damage the vehicle driving system, and skidding of tires will not occur. Thus, reliability and durability of the braking system and the vehicle are ameliorated.

Claims: An engine braking system for a vehicle comprising: a turbine (112) rotatably disposed in an exhaust passage (104a-d) of an engine (101); driving force transmitting means (157) for connecting an output shaft (115) of the engine (101) to the turbine (112) during engine braking so as to allow the turbine (112) to consume energy of the engine (101); and controlled throttling means (152) in use adjusting an amount of the exhaust gas flowing to said turbine (112); characterized by a controller (162) in use adjusting the throttling means (152) in accordance with speed of the vehicle, weight of the vehicle and engine revolution speed. An engine braking system of claim 1, characterized in that said turbine (112) is provided in an involute casing (150), in that said controlled throttling means (152) includes a plurality of movable nozzle vanes (152) of wing type disposed around said turbine (112) and in said casing (150) such that the nozzle vanes (152) define a plurality of nozzle throat areas (151) around said turbine (112), the nozzle vanes (152) being pivotable about their respective shafts (153) and being spacedly disposed in the circumferential direction of said casing (150) such that said nozzle vanes (152) can change said nozzle throat areas (151). An engine braking system of claim 1 or 2, characterized in that said controller (162) determines a first degree (DO) of throttling of the throttling means (152) using the vehicle speed, a second degree (DT) of throttling using the weight of the vehicle and a third degree (DE) of throttling using the engine revolution speed, and then adjusts the throttling means (152) using the smallest degree among these three degrees (DO, DT, DE). An engine braking system of one of claims 1 to 3, characterized in that a fluid passage (125) is connected to the exhaust passage (104b, 104d) between said engine (101) and said turbine (112), in that passage switching means (130) is provided at a position at which the fluid passage (125) is connected to the exhaust passage (104b, 104d), for stopping the exhaust gas from the engine (101) when engine brake is operated, and in that an air passage is connected to the exhaust passage (104c) downstream of the turbine (112) for introducing external air to the turbine (112) when the passage switching means (130) stops the exhaust gas from the engine (101), said turbine (112) sucking the external air and discharging it into the fluid passage (125).

Inventors: OKADA, MASAKI C/O KAWASAKI FACTORY OF ISUZU, SEKIYAMA, SHIGEO C/O KAWASAKI FACTORY OF ISUZU
Applicants: ISUZU MOTORS LIMITED
Application year: 1988
Main classification: F02D29
IPC codes: F02D9, B60T1