TURBO COMPOUND ENGINE

Abstract: A turbo compound engine comprising an engine (1) having an output shaft (15) and an exhaust line (4b), a power recovering turbine (12) disposed at the exhaust line (4b), a gear train (100) connecting the power recovering turbine (12) with the output shaft (15) of the engine (1), and a power reversing mechansim (40) including a hydraulic cluthc (51, 51a, 56) provided with the gear train (100), so that energy consumed by the power turbine (12) may serve as braking effort against the vehicle upon swithcing of the power revrersing mechanism (40), and large load may not be applied to the gear train (100) at one occasion by allowing the hydraulic clutch (51, 51a, 56) to slip during a certain period from the switchcing of the power reversing mechanism (40), thereby protecting the drive power transmission system of the vehicle and improving the driveability.

Description: The present invention relates to a turbo compound engine. Such engine is capable of recovering the energy of the exhaust gas as expansion work of a power turbine and of transmitting the recovered energy to a drive shaft of the engine via a gear train, so as to rotate the power turbine in a reverse sense upon deceleration of the vehicle in order to obtain a braking action. In particular, the invention relates to a turbo compound engine provided with a gear train having a clutch to absorb a large load produced when the power turbine is rotated in reverse sense. Recently, turbo compound engines have been developed, which recover their exhaust gas energy as supercharging energy of a turbocharger and exhaust gas energy from the turbocharger as diabatic expansion energy of a power turbine. In such turbo compound engines, the power output performance, the fuel consumption rate, and the gain of the engine are improved by raising the expansion ratios of the turbocharger and of the power turbine. On the other hand, however, it remains a problem to secure an adequate braking action (for example, by means of an exhaust brake) to counterbalance the increased power output of the engine. In other words, the braking action against the engine decreases with an increase of turbocharged pressure so that a main brake (i.e. foot brake) should be manipulated in order to offset the relative decrease of the entire braking action. Guarantee of a sufficient braking action is important not only for the maneuverability and safety of the vehicle (engine brake force of more than approximately 60 % of the rated output power is required), but also for utilizing the turbo compound engine more effectively. In EP-A-272 680 and EP-A-0 297 287 (this document falls under Article 54, paragraph 3, EPC), turbo compound engines are mentioned in which, as shown in Fig 3 of the accompanying drawings, a power turbine a for recovering the exhaust gas energy is disposed in an exhaust passage b1 of a vehicle, and a fluid passage c3 is connected to an exhaust passage b2 upstream of the power turbine a so as to bypass the power turbine 1. Fluid passage switching means e is provided at the junction of the exhaust passage b1 upstream of the fluid passage c opening the fluid passage c when the vehicle is in deceleration mode and the driving power is transmitted from the crank shaft d to the power turbine a. This construction makes it possible that the power turbine recovers the exhaust gas energy from the engine so as to utilize the recovered energy as driving energy of the engine during the normal driving. During exhaust braking and when the clutch of the vehicle is in connection mode, the fluid passage switching means e closes the exhaust passage b1 upstream of the fluid passage c while connecting the passage b2 to the passage c with the junction of the two passages being throttled. At the same time, the rotation of the crank shaft d is transmitted via one of the gear trains to the power turbine a, with the rotation reversed by the gear train. Accordingly, the power turbine a, which is originally designed for energy recovery, performs pumping work i.e., the power turbine compresses the air from the exhaust passage b2 into the fluid passage c. Therefore, it is possible to obtain a large braking action including motor friction of the engine, negative work upon pumping work by the power turbine, and the exhaust braking force during exhaust braking. However, the power turbine rotates at a revolution speed ranging from 80,000 to 100,000 r.p.m. during normal driving of the vehicle, and the rotation energy at such a revolution speed is equivalent to the moment of the inertia (polar moment of inertia of area) of the flywheel of the normal engine. Hence, when the rotation of the power turbine is switched from normal rotation to reverse rotation, a considerable amount of energy has to be consumed somewhere between the crank shaft and the power turbine. Experiments have shown that said energy reaches its maximum if it takes a relatively short time (2-3 seconds) from the beginning of the reversing till the power turbine reaches its maximum speed in reverse direction. Thus, there is a need for a turbo compound engine which can absorb said energy by certain means disposed between the crank shaft and the power turbine. When the rotation of the power turbine is reversed, the following shortcomings appear unless said energy is absorbed (in a case where elements between the power turbine and the crank shaft are sufficient in strength). (1) the vehicle skids momentarily (2) An anti-driving force upon skidding exerts an extremely large load on the driving system of the vehicle. (3) An abnormal abrasion of tyres and brake pads or shoes occurs. (4) The riding comfort is deteriorated. One object of this invention is to provide a turbo compound engine including two gear trains for connection of a power recovering turbine, disposed in the exhaust line of the engine, with the output shaft of the engine so that the transmission direction of the driving power may be reversed, and a temporarily rapidly increasing large load may not be produced upon switching of the gear trains for reverse mode, whereby the useful life of the drive power transmitting system and driveability of the vehicle are improved. A turbo compound engine of the present invention includes power reversing means in the gear train which connects the output shaft of the engine with the power turbine, the power reversing means having a hydraulic clutch which slips upon connection of the hydraulic clutch so that the large energy, produced when the power turbine is rotated in reverse sense, is consumed at the hydraulic clutch. In order to accomplish the above object, according to the present invention, there is provided a turbo compound engine having the features of claim 1. Further developments of this engine are described in the respective subclaims. During deceleration of the vehicle, when the hydraulic clutch is in connection mode, the power turbine is rotated in reverse sense by the planetary gears. While the power turbine is between normal rotation and reverse rotation, a slip occurs in the hydraulic clutch, whereby energy produced between the crank shaft and the power turbine is absorbed. Figure 1 is a system diagram of a preferred embodiment of a turbo compound engine according to the present invention. Figure 2 is a flow chart for the turbo compound engine of Figure 1. Figure 3 is a schematic view showing related art. A preferred embodiment of the turbo compound engine of the present invention will be described with reference to the accompanying drawings. In Figure 1, reference numeral 1 indicates an engine of a vehicle (not shown), 2 the intake manifold of the engine 1, and 3 the exhaust manifold of the engine 1. As depicted in Figure 1, an exhaust gas passage 4a is connected to the exhaust manifold 3, and to the intake manifold 2 there is connected an intake-air passage 5. A turbine 10a of the turbocharger 10 is disposed at an intermediate point in the exhaust passage 4a while the compressor 10b of the turbocharger 10 is disposed in the intake passage 5. In an exhaust passage 4b downstream of the turbocharger 10, a power turbine 12 is disposed for recovering the exhaust gas energy. A fluid passage 25 branches from the exhaust gas passage 4b between the power turbine 12 and the turbine 10a of the turbocharger 10, and is connected to the passage 4c downstream of the power turbine 12. At the junction of the passage 4b and the fluid passage 25 upstream of the power turbine 12, there is provided a passage switching means 30 for closing the fluid passage 25 while throttling the passage 4b to a predetermined degree. The switching means 30 is constructed to have at least two switching positions. An external atmosphere conduit 7 is connected to the exhaust passage 4c connecting the fluid passage 25 to the outlet port 6 of the power turbine 12. At the intersection of the passages 7 and 4c, there is disposed a switching means 31 which opens the external atmosphere conduit 7 upon closing of the exhaust gas passage 4c. Moreover, an exhaust brake valve 32 is provided in the passage 4b between the switching valve 30 and the turbine 10a. In the following, gear trains for connecting the power turbine 12 to the crank shaft 15 will be explained. As shown in Figure 1, an output gear 16 is disposed at the end 13a of the shaft 13 of the power turbine 12, and planetary gears 17a and 17b are engaged therewith. The planetary gears 17a and 17b are engaged with a ring gear 18 rotating together with an input pump wheel 21b of a fluid coupling 21 provided with a lock up mechanism 21a. In other words, the output gear 16 is connected to the fluid coupling 21 via the planetary gear mechanism 19 including the planetary gears 17a and 17b, so that the rotation of the power turbine 12 is transmitted to an output pump wheel 21c of the fluid coupling 21. The epicyclic gear 19 is employed for having a large moderating ratio and a high transmission efficiency To the output pump 21c there is fixed a gear 20 which rotates with the pump 21c, and to the crank shaft 15 there is fixed a crank shaft gear 23. Another epicyclic gear 40 for connecting the crank shaft 23 with the gear 20 and for rotating the power turbine 12 in both normal and reverse senses will be explained. The epicylic gear 40 comprises a sun gear 41, a sun gear shaft 42, a ring gear 44 engaged with planetary gears 43, at intervals in the circumferential direction thereof, and circumferentially surrounding the sun gear 41, and a carrier 45 for maintaining constant the relative positional relationship of the planetary gear 43 and the sun gear 41 while the planetary gear 43 rotates autorotationally and revolutionally around the sun gear 41. The epicyclic gear 40 will be explained in detail below. The sun gear shaft 42 is provided with a first transmission gear 46 engaged with the crank shaft gear 23 at one end thereof, and supports said carrier 45 by a bearing 47 near the other and thereof. On the other hand, the ring gear 44 is provided with a second transmission gear 48 engaged with the gear 20. The second transmission gear 48 includes a hollow shaft 49 housing a part of the sun gear shaft 42 between the first and second transmission gears 46 and 48. The hollow shaft 49 rotates about the shaft 42 and is provided with a one way clutch 50. The one way clutch connects the first transmission gear 46 with the shaft 49 only if drive power is transmitted from the gear 46 to the crank shaft 15. The carrier 45 includes a clutch element 51 extending outwardly in a radial direction The direction of rotation of the epicyclic gear 40 is controlled by hydraulic clutch means 55. In this embodiment, the hydraulic clutch means 55 includes a hydraulic clutch 56 which can be connected to said clutch element 51 so as to stop the carrier 45 during the connection mode, a pump 56 supplying oil to the hydraulic clutch 56, a valve 59 disposed in an oil conduit 58 connecting the pump 57 with the hydraulic clutch 56, and a controller 60 controlling a valve 59. An ON-OFF signal from a clutch switch 62 of the engine 1, an ON-OFF signal from an accelerator switch 63, a rotating speed signal from a rotating speed sensor 61 of the engine 1, and a brake control signal from a brake control switch 64 are input into the controller 60 while control signals are output from the controller 60 to the switching valves 30 and 31, the exhaust brake valve 32, the epicyclic gear 19, and the partition valve 59. The brake control switch 64 of the illustrated embodiment has an OFF position, a position 1, and a position 2. At position 1, the controller 60 outputs a command signal to fully close the exhaust brake valve 31 only, whereas at position 2, same outputs a command signal to close the exhaust passage 4c and to open the air inlet passage 7, a command signal to actuate the switching valve 30 of the fluid passage 25 to a predetermined extent for throttling, a command signal to fully close the partition valve 59 of the hydraulic clutch 56, and a command signal to cancel locking-up of the locking-up mechanism 21a. When the brake control switch 64 supplies an instruction to the controller 60 for OFF position, the controller 60 supplies command signals to the switching valve 30 for full closing of the fluid passage 25, to the switching valve 31 for full closing of the external atmosphere duct 7, to the locking-up mechanism 21a for locking-up, and to the valve 59 for full closing so as to allow the hydraulic clutch 56 to be free from the clutch element 51. In the following, a control effected by the controller 60 during deceleration of the vehicle will be described with reference to Figure 2. In the controller 60 during normal driving, it will be judged whether the accelerator switch 63 is OFF at step 70, whether the clutch switch 62 is ON at step 71, and whether the engine revolution speed is equal to or higher than 700 r.p.m. at step 72. When the answers at steps 70, 71 and 72 are all YES, the controller 60 detects that the vehicle is decelerated, and the following steps are executed. First, the exhaust brake valve 32 is fully closed at step 73 so as to increase the exhaust gas pressure, then it is judged whether the brake control switch 74 is in position 2 or not. If the answer at step 74 is NO, the program returns to step 70, and repeats the above-mentioned procedures. If one of the answers during steps 70 through 72 is NO, i.e. the brake control switch 64 is turned off, the program jumps to step 82. If the answer at step 74 is YES, the controller 60 sends a command signal to the locking-up mechanism 21a of the fluid clutch 21 for eliminating the locking-up as stated in the box labelled 75. Then, the controller sends a command signal to the valve 30 at step 76 so that the fluid passage 25 may be throttled to a predetermined extent while sending a signal at step 77 to the valve 31 so as to close the exhaust passage 4c and open the external atmosphere duct 7. The partition valve 59 is closed by a command signal at step 78. Referring to Figure 1, as the partition valve 59 is closed, the clutch element 51 and the hydraulic clutch 56 are connected to one another. Thereupon, the drive power of the crank shaft 15 is transmitted from the crank shaft gear 23 via the first transmission gear 23 and the planetary gear 43 to the sun gear 41 with the rotation being reversed. After that, the drive power is transmitted from the sun gear 41 to the gear 20 while reversing the rotation again. Then the power is transmitted to the epicyclic gear 19 via the fluid coupling 21. The rotation is reversed at the epicyclic gear 19 and the rotative power is transmitted to the power turbine 12, so that the power turbine 12 is rotated in a direction opposite to its own direction during normal driving of the vehicle, whereby air is sucked through the duct 7 and the power turbine 12 assumes the function of an air compressor. In addition to the normal exhaust brake, energy consumed by compressing the air by the power turbine serves as braking action against the engine 1. Therefore a large braking effort can be applied to the engine 1. At the same time, it is possible to absorb the energy produced when reversing the power turbine by constructing the clutch element 51 and the hydraulic clutch 56 in such a way that sufficient slip may occur between the clutch element 51 and the hydraulic clutch 56. Referring again to Figure 2, it is checked whether the connection of the hydraulic clutch 56 has lasted three minutes at step 79. When the answer is NO, steps 75 and 78 are repeated, so that the heat generation in the hydraulic clutch 56 is limited to a predetermined extent and no unduly large braking action is applied to the engine 1. When the answer at step 79 is YES, the lock-up mechanism 21a starts working. Then, if the brake control switch 64 is still ON at step 81, i.e., if the control switch 64 is either in position 1 or 2, the above-described control for deceleration is repeated. This repetition of deceleration control makes it possible to gradually reduce the engine speed while suppressing load against the hydraulic clutch 56. When the answer at step 81 is YES, the control for normal driving is performed. More specifically, the controller 60 outputs command signals to the valves 30, 31, and 59, so as to turn off the hydraulic clutch 56 and close the fluid line 25 and the air duct 7. Thereupon, the power turbine 12 starts rotating in normal sense effected by the exhaust gas, so as to recover the energy of the exhaust gas, and the rotative power of normal direction is transmitted to the crank shaft 15 via the planetary gear 29, and the other gears 20, 48, 46, and 23.

Claims: A turbo compound engine comprising an engine (1) having an output shaft (15), an exhaust gas line (4a, 4b, 4c), a gear train connecting the output shaft (15) of the engine (1) to a power recovering turbine (12) disposed in the exhaust gas line (4b) of the engine (1), and a power reversing mechanism located in the gear train, whereby the power reversing mechanism includes a planetary gear set (40) and whereby a hydraulic slip clutch means (55) is provided in the planetary gear set (40) in a manner such that the hydraulic slip clutch means (55) slippingly connects the output shaft (15) of the engine (1) to the power recovering turbine (12) upon rotational reversal of the power recovering turbine (12) thereby absorbing energy produced upon the rotational reversal of the power recovering turbine (12). A turbo compound engine of claim 1, characterized in that said exhaust gas line (4b) has a bypass line (25) bypassing said power recovering turbine (12), an exhaust brake valve (32) is disposed upstream of the bypass line (25), a switch valve (30) is disposed at an intersection of the bypass line (25) and the exhaust gas line (4b) so as to close the exhaust gas line (4b) while opening the bypass line (25) during deceleration of the vehicle, an external atmosphere duct (7) is connected to a part of the exhaust gas line (4c) between the bypass line (25) and the outlet port (6) of the power recovering turbine (12), and a switching valve (31) disposed at said part of the exhaust gas line (4c) so as to close said part of the exhaust gas line (4c) while opening the external atmosphere duct (7). A turbo compound engine of claim 1 or 2 characterized in that said power reversing means comprises a sun gear (41), a planetary gear (43) engaged with the sun gear (41), a ring gear (44) having an internal gear (44a) engaged with the planetary gear (43) and an external gear (48) engaged with a gear (20) connected to the power recovering turbine (12), the hydraulic slip clutch means (55) limiting revolution of the planetary gear (43), a transmission gear (46) supported by a hollow shaft (49) rotating with the ring gear (44) via a one way clutch (50) so as to engage with a gear (23) of said output shaft (15) and to rotate with a shaft (42) of the sun gear (41) extending through the hollow shaft (49). A turbo compound engine of one of claims 1 through 3, characterized in that said hydraulic clutch means (55) includes a clutch plate (51) attached to a carrier (45) of the planetary gear (43), a further clutch plate coupled with said clutch plate (51), and an actuator (56) coupling and decoupling said two clutch plates with each other based on oil pressure supplied thereto. A turbo compound engine according to any one of the foregoing claims, characterized in that the power recovering turbine (12) is disposed in the exhaust gas line (46) downstream of a turbine (10a) of a turbocharger (10) so as to recover energy from the exhaust gas, and that a controller (60) is provided for actuating the exhaust brake valve (32) and the switching valve (31) and for causing the hydraulic slip clutch means (55) to slippingly connect the output shaft (15) with the power recovering turbine (12) upon the rotational reversal of the power recovering turbine (12). A turbo compound engine of claim 5, characterized in that said controller (60) is constructed in such fashion that it produces command signals to close the exhaust brake valve (32), to actuate the switching valve (30) disposed in the bypass line (25) and the switching valve (31) disposed downstream of the power recovering turbine (12), and to actuate said hydraulic slip clutch means (55) for coupling. A turbo compound engine according to any one of the foregoing claims, characterized in that the hydraulic slip clutch means (55) does not slip for more than three minutes from the connection of the hydraulic slip clutch means (55).

Inventors: OKADA, MASAKI KAWASAKI FACTORY OF ISUZU MOTORS LTD
Applicants: ISUZU MOTORS LIMITED
Application year: 1988
Main classification: F02B41
IPC codes: F02B41