POWER DRIVE SYSTEM FOR ROAD VEHICLES

Abstract: A power drive system for road vehicles comprises, in series relationship, at least a prime motor (1), at least a hyd­ raulic pump (2,4) driven by the prime motor and at least one hydraulic motor (10,11) connected to the hydraulic pump (2,4) and driving a differential gear (12,13) interposed between the hydraulic motor (10,11) and a respective pair of driving wheels (14,15).

Description: This invention relates to a drive system for road vehicles, in particular public transportation and semitrailer vehicles. Several hydrodynaimic or oil-operated drive systems are currently known and marketed, all such systems being referred to hereinafter as "hydraulic drive systems", as known are advantages afforded thereby. For transmitting motive power on transportation vehicles, such hydraulic drive systems have gained acceptance mainly on account of their inherent ability to provide a continuously variable drive ratio and independent control of the speed and torque delivered to each driving wheel. To accomplish the former goal, hydraulically operated units have been developed for installation in lieu of the clutch/transmission assembly employed in traditional drives. The latter goal is instead achieved by providing a pump to feed a number of hydraulic motors, each motor being coupled to one wheel of the vehicle. While the former system is mainly directed to making the driving of the vehicle more convenient, as an alternative to fully automated transmissions, the latter has substantial advantages from the standpoint of engineering and economy, and is generally preferred for industrial vehicles. Moreover, the latter system affords the additional advantage of eliminating the need for differential gears and driveshafts, such that, at least in principle, it may be reduced to but one pump and two or four hydraulic motors. However, traditional power drive systems have been definitely improved through the years, especially as relates to automatic transmissions . and differential gears. Thus, the technical problem arises of investïgating whether novel and particularly advantageous combinations may be found of hydraulic drive units and mechanical drive units. invention sets out to solve the aforesaid technical problem by providing a novel hydraulic and mechanical drive system for road vehicles, which at least in specific conditions can be more advantageous than conventional drive systems. More specifically, the invention is directed to providing a drive system which is particularly suitable for application to public transportation vehicles, especially vehicles of the semitrailer type. According to one aspect of the present invention, there is provided a power drive system for road vehicles of the type having a differential gear for the driving wheels and which comprises, serially arranged to one another, at least one prime motor, at least one hydraulic pump driven by said prime motor, and at least one hydraulic motor connecked to said hydraulic pump through conduit means, and is characterized in that it comprises transmission means drivingly connecting said at least one hydraulic motor with said differential gear. The features and advantages of the invention will be detailed hereinafter through a description of a presently preferred embodiment thereof, with reference to the accompanying drawing, where: Figure 1 is a hydraulic diagram of the drive system according to the invention; Figure 2 shows a drive system, as illustrated diagramatically in Figure 1, as installed on the frame of a public transportation vehicle of the semitrailer type, of which vehicle frame only the rear portion and part of the front portion are shown; and Figure 3 is a function and hydraulic diagram of the inventive system. With particular reference to Figure 1, the drive system according to the invention provides in essence, and particularly for a vehicle having two drive axles, a prime motor 1, such as an internal combustion engine, driving a hydraulic pump 2.. In parallel therewith, there is provided an electric primary motor 3, preferably of the constant speed type, which drives, in turn, a hydraulic pump 4 of its own, identical to the pump 2.. The two pumps, 2 and 4, are respectively connected, through dual, delivery and return, first lines or ducts 5 and second lines or ducts 6, to a dis tributorvalve anit 7 feeding in parallel,throagh third lines 8 and fourth lines 9, also of the dual type, respectively the two hydraulic motors 10 and 11. Such hydraulic motors are each mounted on a differential gear 12 and 13, respectively, which rotatively drive pairs of driving wheel sets, 14 and 15, through axle shafts 16 and 17.. Figure 2 illustrates, in a topographic and schematic manner, the arrangement and location of a hydraulic drive system, in accordance with the layout diagram fo Figure 1, across the frame of a public transportation vehicle of the semitrailer type which has two driving axles and includes an internal combustion engine type of prime motor, e.g.. a diesel engine, for self-propulsion, and a primary electric motor for operation as a trolleybus or tramcar. Corresponding parts in Figures 1 and 2 are designated with the same reference numerals. The semitrailer vehicle of Figure 2 is generally indicated at 20., Reference has been made, for illustrative purposes only, to a three-axle type of semitrailer vehicle, of which only the two rear axles are shown in the figure. There may be seen a load bearing or main frame 2.1 comprising two sections articulated to each other by a rotary ring or plate or "fifth wheel" 22,known per set, e.g. as maufactured and sold by CHEEK of Stuttgart, West Germany. The rear section or portion mounts the prime motor 1 and primary motor 3: in particular, a latticework structure 21a accommodates an internal combustion engine constituting the prime motor 1, whilst between the fifth wheel 22 and the driving wheel sets 14 there is accommodated the electric primary motor 3. The front portion of the frame, mounting the steering wheels, is not shown in the drawing and may be set up in a manner known per se. The motors 1 and 3, hydraulic pumps and hydraulic motors, are all located between two parallel side spars 23 and 24, which extend from the fifth wheel 22 both towards the front section and rear semi-trailer, wherefor they form the supporting framing, in-a quite conventional manner. The passenger-carrying coach is positioned on both frame sections or portions. The hydraulic motors 10 and 11 are mounted directly over the differential gears 1,2 and 13, and are swingable therewith. As shown in Figure 2, connectIons 25 are led to the valve unit 7, as well as to the prime motor 1 and primary motor 3, which interconnect these elements with the throttle and brake controls at the driver's station. The unit 7 controls the liquid flow being circulated, both for starting and braking purposes, by acting on the hydraulic pumps 2,4, and on the hydraulic motors 10,11.. Moreover, the unit 7 includes a change-over device, known per Se, which is operative to prevent the simultaneous actuaton of the motors 1 and 3. More specifically, the unit 7 is only ideally, for convenience of illustration, a unitary construction. In actual practice, the various elements which concur to the functions of the unit 7 may be scattered throughout the vehicle structure, while remaining operatively interconnected. in essence, besides the cited change over device, such elements may be divided into: electric control devices 7a, solenoid valves 7b, and electric control devices 7c. The electric control devices 7a may be, for example, sensors adapted for detecting the vehicle travel condition parameters (e.g.. the wheel rpm's, the rpm' s of the prime motor when in operation, the road gradient, the oiltpressure and temperature, etc., in the various crcuts). The solenoid valves 7b, known per se, are arranged along the oil lines wherethrough the hydraulic oil or fluid is circulated by the hydraulic pumps 2 and 4, and are provided with a plurality of operative positions. Thus it becomes possible, ina manner known per se and by operating said solenoid valves, to sh#toffeithertheinoperative pump 2 or 4 and perform other operations relating to the controlof the vehicle rm For example, the flow of oil or the like fluid to the hydraulic motors 10 or 11 can be shut off, or the oil be caused to flow through closed circuits located either at the hydraulic motors 10 and 11, and hydraulic pumps 2 or 4. Thus, the vehicle can be rapidly braked or the drive system set to neutral. In normal running conditions, said solenoid valves direct the oil or the like fluid from one of the hydraulic pumps 2 or 4 to the hydraulic motors 10 and 11. The electric control devices 7c receive signals from both said electric control devices 7a, and the controls (actually, the throttle and brake pedal controls) located at the driver's station, The signals are processed, e.g by means of electrolac cards, and so converted as to control both the positions of the solenoid valves 7b and the flow rates of the hydraulic pumps 2 or 4 and hydraulic motors 10 and 11. In fact, the system according to this invention may include advantageously hydraulic motors 10 and 11 and hydraulic pumps 2 or 4 of the variable volume type, that is wherein the rpm's and flow rate (at constant rpm's) can be changed independently. The net result is that, whereas the rpmss of the pumps 2 or 4 and motors 10 and 11 are respectively dictated by the rpmls of the prime motor1 ? and primary motor 3, which are directly controlled by the driver and the amount of oil being circulated through the lines 8 and 9, the flow rate or volume of said pumps and motors is controlled by the electric control devices, both in accordance with the driver's own decisions and of the running conditions detected by the electric control devices 7a. Figure 3 illustrates the operation of the drive system as described hereinabove, the unit 7 being subdivided into said portions 7a, 7b, 7c, there being shown in addition to the hydraulic diagram already shown in Figure 1, also mutual interactions, as indicated in dotted lines, between the various members. In practice, the road vehicle is jointly placed under control by the driver, who will control the prime motor 1 and primary motor 3 directly, and by the unit 7 which will control the power delivered to the differentials 12 and 13 in accordance with the running conditions of the vehicle and the driver's decisions. By way of example, and in order to show how' the invention can be implemented by utilizing readily available means, the internal combustion engine prime motor 1 maybe a Xagir¯ eatz V-8 diesel engine of 256 KP, while the primary electric motor 3 may be a Marelli motor developing 190 KW at 2600 rpm'# and the hydraulic pumps 2 or 4 may be of the Linde EPV 100 motel type, while the hydraulic motors 10 or 11 may be of the Linde BMV 105 model type, the vehicle frame may be a Fiat 470 main frame, and the differentials 12 or 13 may be a Fiat differential gear with a 1:12 gear' ratio. The advantages afforded by this drive system may be summarized as follows. The fact should be considered first that the problems inherent to the drive train ending with the drive axles are effectively solved without involving any alteration of readily available and proven assemblies. This is particularly important for semitrailer vehicles, where the driveshafts pose serious installation and operation problems, owing to the long distances, sharp bends, and likelihood of vibration involved. Another advantage Is that in the drive system of this invention, it is easy to optimize the distribution of the torque to the axles, the differences among such torques being relatively small. The torque distribution between the inside and outside wheels in a bend is instead practically accomplished through the differential gear, where the rpms are dictated by the steering radius rather than by the torque, which instead adjusts itself to the demand. Therefore, the invention achieves a maximum in economy optimization, while leaving unaffected the behavi'or of the vehicle in a bend. Finally, with the electric motor operating at a constant speed, no pick up power need be applied at each start in the case of the trolleybus application. Accordingly, the power requirements on the mains can be reduced' drastically. By way of example, a single embodiment has been described, but the invention is not limited thereto, neither as relates to the type of vehicle, nor to the number of the axles involved or provided. For instance, a two-axle vehicle may be contemplated, wherein a single, either Diesel or electric, prime motor is preferable, each hydrauli'c motor being then connected to its related differential gear through a conventional drive shaft set up in a similar manner to conventional road vehicle shafts.

Claims: CLAIMS 1. A power drive system for road vehicles of the type having a differential gear for the driving wheels, comprising, serially s#ren¯5Sed to one another, at least one prime motor, at least one hydraulic pump driven by said prime motor, and at least one hydraulic motor connected to said hydraulic pump through conduit means, characterized in that it comprises transmission means (10a,IIa) drivingly connecting said at least one hydraulic motor (10,11) with saiddifferential gear (12,13). 2. A power drive system according to Claim 1, characterized in that said at least one hydraulic motor (10,11) is mounted directly on the housing of said respective differential gear (12,13) and is swingabi # therewith. 3. A power drive system according to Claim 1, characterized in that said at least one hydraulic motor (10,11) is connected to said respective differ- ential gear (12,13) through a cardan shaft. 4. A power drive system according to Claim 1 characterized in that on said conduit means (5,6,8,9) connecting said at least one hydraulic motor (10,11) to said at least one hydraulic pump (2,4) there is inserted a controlling unit (7) adapted for controlling, through electrically operated valves, said at least one hydraulic pump (2,4) and said at least one hydraulic motor (10,11) by varying the flow rate and pressure delivered thereto. 5. A power drive system according to Claim 4, characterized in that said unit (7) is operatively interlocked with the vehicle throttle and brake controls. 60 A power drive system according to Claim 5, characterized in that it comprises an electric control line (25) operated by the vehicle brake control effective to control said unit (7) such as to shut off the power supply to said at least one hydraulic motor (10,11) as the brakes are operated. 7. A power drive system comprising an internal combustion engine type of prime motor (1) and a primary electric motor (3), according to Claim 4, characterized in that said controlling unit (7) includes an automatic device adapted for switching over the power supply and related adjusting control on said conduit means (5,6) of that one of said prime motor (i) and primary electric motor (3) which happens to be at the time active drive-wise.

Inventors: MAURI, AMBROGIO
Applicants: MAURI E C. DI MAURI AMBROGIO E ZORLONI COSTANZA E C. -S.A.S.
Application year: 1980
Main classification: B60K17
IPC codes: B62D47, B60K17