GB1573306A - Motor vehicle with hydrodynamic torque converter - Google Patents

Description

(54) MOTOR VEHICLE WITH HYDRODYNAMIC TORQUE CONVERTER (71) We, BL CARS LIMITED, formerly known as BRITISH LEYLAND UK LIMITED, a British Company of Leyland House, 174 Marylebone Road, London, NW1 5AA, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement. This invention relates to a motor vehicle. According to the present invention a motor road vehicle with drivable wheels has a transmission system comprising, in sequence, a prime mover, a reducing ratio coupling, a hydrodynamic torque converter, a gearbox and the drivable wheels, in which the reducing ratio coupling consists of one of the following: (i) a pair of meshing gears (ii) a pair of chain wheels linked by a chain; (iii) a pair of wheels linked by a belt.

In a preferred form of the invention the gearbox has a single forward gear ratio and a single reverse gear ratio and means to select one or other ratio.

An embodiment of the invention will now be described with reference to the accompanying drawing which is a part-sectioned view of an engine and transmission unit of a passenger road vehicle.

Engine 11 contains four in-line cylinders 12 in which pistons reciprocate to drive crankshaft 13 in a known way. The crankshaft has secured to one end chain wheel 14 coupled by chain 15 to chain wheel 16. The chain wheel 14 is of smaller diameter than wheel 16 to provide a reduction ratio between crankshaft 13 and shaft 17.

Shaft 17 carries impeller 18 of torque converter 19 within housing 20. Turbine 21 of the torque converter is secured to input shaft 22 of gearbox 23.

Output shaft 24 of gearbox 23 is coupled by propeller shaft 25 to a differential unit driving the rear wheels of the vehicle.

Input shaft 22 has a splined centre section on which dog clutch member 27 can be axially displaced, while driven by the shaft 22, by a lever operable by the vehicle driver. Forward gears 28, 30 and reverse gears 29, 31 are in permanent mesh, in the case of 29, 31 by way of an idler gear (not shown). Gears 28, 29 are integral with, respectively, sleeves 32, 33 rotatable on shaft 22. The sleeves 32, 33 incorporate, respectively, dog clutch members 34, 35.

To select a forward or reverse direction of travel the driver operates the lever to displace dog clutch member 27 into engagement with the appropriate dog-clutch member 34, 35.

The input shaft 22 has at one end a transmission disc brake 36. With the engine operating at idling speed the transmission brake 36 enables the input shaft to be braked against rotation by driven member 21 of the torque converter 19 and so prevent "creep" of the vehicle arising from low speed rotation of propeller shaft 25.

Our copending application 53409/72 specification number 1454262 discloses a combined torque converter and gearbox of the type described in the embodiment. However the copending application makes use of a power unit of relatively large capacity that develops maximum torque near the lower end of its speed range while having a low specific output near the upper end of its speed range. In the embodiment this torque/speed range characteristic is achieved by using a small capacity engine 11 and a reduction ratio (chain, wheel and drive between crankshaft 13 and shaft 17) between engine and torque converter.

The following table shows the effect of utilising two different reduction gear ratios on a 1275 cc engine as against a direct drive 1500 cc engine (that is to say one with no reduction gear between engine and torque converter).

The input torque to the impeller is taken with engine brake mean effective pressure of 140 pounds per square inch.

Reduction Input Tor- Final Overall MPH Vehicle Speed Capacity Ratio que to Drive Ratio at Impeller 1000 80 mph 90 mph RPM BHP RPM BHP RPM 1500 Nil 84 lb ft 3:1 3:1 18 42 4444 58 5000 1275 1.2 84 lb ft 3:1 3.6:1 15 42 5333 58 6000 1275 1.4 100lb ft 2.58:1 3.6:1 15 42 5333 58 6000 It will be apparent that the provision of a relatively high torque figure to the torque converter impeller gives a reduced rotor speed on the converter while allowing a high final drive ratio to be used. This reduces the ratio of output speed to input speed across the converter to give higher torque multiplication relative to vehicle speed. In our copending application the high torque input is achieved by the use of a relatively large capacity engine.

The present embodiment enables the same characteristics to be achieved using a small capacity engine and a reduction ratio between the engine and the torque converter. This increases the torque input to the impeller and, with the same final drive ratio as the larger engine, the same torque multiplication takes place. The embodiment makes use of a chain with chainwheels linking crankshaft and torque converter input shaft. Gears or belts could be used as alternative couplings.

Claims (4)

WHAT WE CLAIM IS:

1. A motor road vehicle with driveable wheels has a transmission system comprising, in sequence, a prime mover, a reducing ratio coupling, a hydrodynamic torque converter, a gearbox and the drivable wheels, in which the reducing ratio coupling consists of one of the following: (i) a pair of meshing gears (ii) a pair of chain wheels linked by a chain; (iii) a pair of wheels linked by a belt.

2. A motor vehicle as claimed in claim 1 in which the gearbox has a single forward gear ratio and a single reverse gear ratio and means to select one or other ratio.

3. A motor vehicle as claimed in claim 2 in which the gearbox includes a transmission brake to prevent rotation of the wheels with the prime mover idling.

4. A passenger road vehicle equipped with an engine and transmission unit as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.