Patent Description:
Electric driven vehicles have been known for many years. A conventional drive design comprises an electric motor and some type of transmission dedicated to, and located at or immediately adjacent to, each driven wheel. These drive arrangements are known in the art as wheel-adjacent motor configurations. Examples of such designs are disclosed by, for example, <CIT>; <CIT>; <CIT>; and <CIT>. Designs of this type add complexity, weight and cost to a vehicle and while such designs may be suitable for some heavy trucks, they are generally unsuitable for application in today's electric passenger vehicles (e.g. cars, light trucks, etc.).

Compact electric vehicles (e.g. cars, light trucks, etc.) require a cost effective and compact solution for the location of the electric motor and the transmission. Even small electric vehicles require a transmission if the maximal possible motor efficiency has to be available in the majority of drive conditions.

As an example, the torque and efficiency optimal RPM of an <NUM> KW electric motor for a compact vehicle is between <NUM> and <NUM> RPM. If the nominal driving speed is <NUM>/h and the optimal motor speed is <NUM>,000RPM, the optimal ratio between motor and wheels (using a wheel diameter of <NUM>) is 1x9. <NUM>: <MAT> Where:.

A variety of electric drive (i.e. eDrive) concepts have been developed. One example is shown in <FIG> wherein the motor and transmission are arranged between the front wheels with the motor axis being parallel to the axis of the wheels and where only one motor is used for driving both wheels. The design, known as an "inline design", is very compact but presents some major obstacles which include:.

The large "width between the wheels" (i.e. required width of the motor and transmission between the wheels) results in short drive shafts. Each of the drive shafts has two constant-velocity joints (i.e. CV-joints) which wear fast in the case of short drive shafts due to the steering inclination and control arm swings. This will also result in a reduced efficiency and front axle noise.

The asymmetric weight distribution has to be offset with other asymmetric vehicle components such as the battery. However, there will still be a negative influence on the dynamic behavior of the vehicle.

The permanent heat radiation of the electric motor in <FIG> may increase the temperature of the adjacent tire by <NUM> to <NUM>. Temperature insulation and an additional cooling fan can reduce the temperature of the hot tire and the electric motor (i.e. e-motor) but the consumption of electrical energy for the evacuation of motor heat is not something electric vehicle (i.e. EV or e-vehicle) manufacturers like to see.

<CIT> discloses for a transmission including a ring gear and a hypoid pinion gear the possibility to achieve gear ratios below the typical <NUM>:<NUM> ratio reaching values up to a <NUM>:<NUM> ratio, by utilizing negative pinion offset configuration where the pinion gear has a smaller spiral angle than the spiral angle of the ring gear. This document shows the features of the preamble of claim <NUM>.

<CIT> discloses a transmission comprising a bevel gear pair which is directly connected to the wheel.

<CIT> and <CIT> each disclose configurations in which a ring gear axis of rotation is parallel to the common axis on which wheels are located spaced apart. <CIT> shows a hypoid gearing with a pinion having <NUM> teeth.

The invention is directed to a vehicle being movable by power provided by at least one electric motor with the features of claim <NUM>. The vehicle comprising a power train comprising the electric motor having the drive shaft wherein the drive shaft is oriented preferably perpendicular to the common axis of the wheels which the power train is intended to drive (i.e. rotate). The drive shaft of the electric motor is mechanically connected to the axes of the wheels, which are aligned with the common axis, via a transmission comprising at least one pair of mating gears, one of the pair of mating gears being an offset pinion, and having the reduction ratio of the transmission and the tooth number of the pinion according to the values given in claim <NUM>.

For the subsequent further description with reference to the drawings, it is to be noted that the various shown configurations are, for better graphical representation shown with offset pinion tooth number higher than those within the range <NUM> to <NUM> according to the invention. Thus, the examples are meant for the purpose of explanation for configurations in general but itself as explicitly shown would not form part of the invention, since the invention requires said offset pinion to comprise <NUM> to <NUM> teeth.

Furthermore, this specification does not seek to describe or limit the subject matter covered by any claims in any particular part, paragraph, statement or drawing of the application. Also, it is understood that the phraseology and terminology used herein is for the purposes of description and should not be regarded as limiting.

The details of the invention will now be discussed with reference to the accompanying drawings which illustrate the invention by way of example only. In the drawings, similar features or components will be referred to by like reference numbers.

The use of "including", "having" and "comprising" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Although references may be made below to directions such as upper, lower, upward, downward, rearward, bottom, top, front, rear, etc., in describing the drawings, these references are made relative to the drawings (as normally viewed) for convenience.

In one embodiment of the invention, an electric motor of a vehicle is reoriented from the conventional in-line orientation of <FIG>, preferably by ninety degrees, which enables the establishment of a symmetric electric drive unit capable of providing an operative ratio between electric motor and wheels solely by a single stage reduction. For example, the gearset shown in <FIG> is a bevel gearset <NUM> comprising a bevel ring gear <NUM> and a mating hypoid pinion <NUM>. In this example, the ring gear has <NUM> teeth and the pinion has <NUM> teeth thereby providing a gear tooth ratio (ZG/ZP) for the gearset of <NUM>/<NUM> or <NUM>. In a bevel hypoid gearset, the ring gear and pinion operate on non-parallel and non-intersecting axes, AG and AP respectively, (<FIG>) wherein the distance, h, between parallel planes, one containing the ring gear axis, AG, and the other containing the pinion axis, AP, is usually referred to as the offset, pinion offset or hypoid offset.

<FIG> illustrates a transmission having a single stage reduction <NUM>, comprising a bevel ring gear <NUM> and mating hypoid pinion <NUM>. The transmission comprises at least one input and at least one, preferably at least two, outputs. Input power is provided by an electric motor <NUM>. A transmission housing and differential (located at <NUM>) are not shown for reasons of viewing clarity. The electric motor <NUM> is oriented such that the axis of rotation Am of the drive shaft of the electric motor <NUM> is preferably coincident with the axis AP of hypoid pinion <NUM> and is preferably substantially perpendicular to the transmission output axis AT about which the ring gear <NUM> rotates in the transmission.

Compact and low priced electric vehicles require a simple, compact and cost effective transmission between electric motor and front or rear wheel or wheels. Small compact vehicles with electric drive mostly do not require top speeds above <NUM>/h. Their major application is inner city driving for commuting or shopping. All important objectives for such a vehicle can be fulfilled with one electric motor and one single stage hypoid transmission positioned, preferably mid-way, between a pair of wheels, as shown in <FIG> for example.

<FIG> illustrates a transmission comprising a single stage reduction <NUM> (bevel ring gear <NUM> and mating hypoid pinion <NUM>) and an electric motor <NUM> wherein the motor <NUM> is oriented such that the axis of rotation Am of the drive shaft of the electric motor <NUM> is preferably coincident with the axis AP of hypoid pinion <NUM> and is oriented preferably substantially perpendicular to the axis AT about which the ring gear <NUM> rotates. Axis Aw is a common axis about which the wheels <NUM> rotate. Axis AW preferably extends in a widthwise direction of a vehicle and is preferably parallel to and aligned with, preferably coincident with, wheel axles <NUM> and <NUM> and ring gear axis AT.

The small width of the transmission allows for a reduced width between the wheels of <FIG> making for a compact vehicle solution which allows optimal packaging and an ideal vehicle weight distribution. The gearset ratio need not be larger than 1x15, although the ratio may be larger. A second gearset, which can serve to adjust the vehicle speed more optimally to the electric rotor RPM, is not required but may be included. The single stage transmission of <FIG> has a ratio of <NUM> (7x55) and a back driving coefficient of about <NUM>, which is acceptable for energy recuperation during coast operation.

Electric drive reductions require high efficiency as well as a good back driving ability. Back driving ability is the degree of ease of which a motor can be driven by its attached load when power is removed from the motor. The back driving is important in two ways. The first reason is the regeneration of electrical energy in case the vehicle driver takes a foot off the accelerator pedal. The electric motor is switched to generator operation and the kinetic energy of the vehicle is used to re-charge the battery, rather than being wasted by simply using the brakes. The second reason for the back driving ability is to avoid wheel locking in case of an abrupt release of the accelerator pedal. The gearset in <FIG> fulfills both requirements very well. Preferably the ring gear is phosphatized, or equivalently coated, in order to increase the efficiency of the gearset before break-in and avoid costly polishing. As the phosphor layer breaks down, the break-in of the gearset is finished and the initial efficiency will be maintained. Preferably both members of the gearset have been heat treated and ground after heat treatment.

The electric drive unit in <FIG> has a high degree of symmetry and moves the heat radiating electric motor away from the tire that was exposed to the heat from the motor as is the case with the inline design of <FIG>. The distance between the drive shaft flanges <NUM> presents a very small "width between wheels, of the motor which allows for rather long drive shafts. With the possibility to face the motor either towards the front or towards the back of a vehicle (i.e. in the lengthwise direction of the vehicle), the ideal weight distribution and optimal packaging for a particular vehicle can be achieved. This very compact design with only two gears and two shafts can be manufactured very cost effective and presents a very good electric drive solution for a small compact electric vehicle.

The invention also contemplates even higher ratios with a single stage hypoid gearset, such as by utilizing pinions having five or fewer teeth (<NUM>, <NUM>, <NUM> or <NUM> teeth for example), as well as the combination of a hypoid gearset and a cylindrical reduction gearset while still preserving the basic advantages mentioned above.

An aspect that one may consider is the maximal sliding velocity between the tooth flanks in mesh, generated by the hypoid offset of the pinion. Conventional hypoid gearsets (e.g. 1x3 ratio) with a typical offset as used in automotive and truck applications (e.g. <NUM> - <NUM>) have about <NUM>/min relative sliding velocity when the vehicle is driving at a speed of <NUM>/h. An electric drive with hypoid gearset ratio of 1x9. <NUM> and a motor speed of <NUM>,<NUM> RPM, for example, generates a relative sliding velocity of <NUM>/min. This is more than twice the relative surface sliding of the conventional hypoid gearset mentioned above. Under such conditions, it is preferable to use high pressure synthetic hypoid oil as well as tooth surface coatings, as previously discussed, in order to achieve the necessary gear life with respect to tooth surface damage.

While the number of teeth of the pinion may be an indicator of back driving ability, it is not the only indicator of the back driving ability of a hypoid gearset. The spiral angle of the pinion must also be considered. Generally speaking, the larger the spiral angle, the lower the back driving ability becomes. The following categories of spiral angles may be defined:.

Two examples, one with a large spiral angle and one with a very large spiral angle are shown in <FIG>. A certain number of teeth on a small diameter results in a lower spiral angle than the same number of teeth on a large diameter. In order to take the opposing effects into account, the back driving ability may be determined by considering the correct geometry and an assumed coefficient of friction of <NUM>. The fraction Tbr/Tdr, (back driving opposing force Tbr / back driving force Tdr) is called the Back Driving Coefficient CBD. A value of CBD = <NUM> and above indicates a self-locking condition. A value of CBD = <NUM> cannot be achieved. In the Table below, the results of CBD for five different hypoid gearsets are shown.

While a <NUM>-tooth automotive hypoid pinion has a CBD of <NUM> which is excellent, the <NUM>-tooth pinion example is self-locking with a CBD of <NUM>. The <NUM>- to <NUM>-tooth pinions have very similar coefficients, with the unexpected low coefficient of the <NUM> tooth pinion, which is lower than the <NUM>-tooth pinion. Additionally, optimization of certain ring gear and/or pinion parameters, such as tooth depth, pinion diameter and face angles may further enhance back driving ability.

For example, if an ideal ratio for an electric drive hypoid reduction is in the range of <NUM>, then one example is to select <NUM> pinion teeth and <NUM> ring gear teeth (preferably <NUM> or <NUM> because of hunting tooth advantage, i.e. no common factor in the numbers of teeth in ring gear and mating pinion). Such a gearset should preferably be optimized with the goal to achieve a back driving coefficient CBD = <NUM>.

Another embodiment of an electric drive transmission is shown in <FIG>. This is a dual stage reduction with a first cylindrical reduction <NUM>, <NUM> of <NUM> (21x49) and a second hypoid reduction <NUM>, <NUM> of <NUM> (11x51) which results in an overall ratio of <NUM>. The driving efficiency of the dual stage transmission will be higher than the transmission in <FIG> because of the lower ratio in the hypoid stage and the back driving coefficient of about <NUM> which is also better than the transmission in <FIG>.

Another embodiment of an electric drive transmission is shown in <FIG> wherein a dual reduction cylindrical-hypoid transmission is shown. Midsize or premium electric vehicles may benefit from a transmission of this type. A clutch unit (e.g. electromagnetically or hydraulically actuated) can activate either a cylindrical ratio <NUM>, <NUM> of <NUM> (26x38) or a cylindrical ratio <NUM>, <NUM> of <NUM> (16x48). The hypoid reduction <NUM>, <NUM> has a ratio of <NUM> (13x50). In forward driving with lower speeds (e.g. up to <NUM>/h) the overall ratio can be switched to <NUM> • <NUM> = <NUM>. As the speed increases above <NUM>/h, the electric motor will operate with less efficiency and the second cylindrical gear pair <NUM>, <NUM> can be activated. The overall ratio changes to <NUM> • <NUM> = <NUM> which enables the motor to reduce its RPM to a more efficient operation.

The transmission in <FIG> is of particular interest in a coast operation, when the motor is switched to generator mode to utilize the kinetic energy of the vehicle to recharge the battery. If the speed is, for example, <NUM>/h (transmission ratio = <NUM>) the transmission will switch the higher ratio of <NUM> in order to give the generator (motor) more RPM for a more efficient electricity generation. This embodiment provides flexibility while maintaining advantages such as packaging, good weight distribution as well as heat radiation away from one of the wheels as discussed above with respect to the single-stage and dual-stage transmissions.

Another embodiment comprising a planetary-hypoid reduction transmission is shown in <FIG>. The planetary gear system <NUM> comprises an internal ring gear <NUM>, one or more planet gears <NUM>, a sun gear <NUM> and a cage or carrier <NUM>. The motor shaft <NUM> is connected to the sun gear <NUM> and the hypoid pinion <NUM> is connected to, or integral with, the cage <NUM> as planetary output. Ring gear <NUM> rotates about axis AW which is the axis of rotation of the wheels being driven (see <FIG>).

In a planetary gear system, the sun gear may have a different number of teeth than the planet gears. However, in the following example, the planet gears each have the same number of teeth (e.g. <NUM>) as the sun gear (<NUM>) and the internal ring gear has three times the number of teeth (e.g. <NUM>) as the sun gear. Regardless of whether the sun gear has the same number teeth or a different number of teeth than the planet gears, two ratios are possible with a planetary system. The planetary-hypoid transmission requires a clutch which can connect the internal ring gear <NUM> to either of (a) the sun gear (ratio <NUM>), wherein the ring gear rotates with the planet gears and sun gear at the same speed, or (b) the stationary transmission housing (not shown) (ratio <NUM>) wherein the ring gear does not rotate. Because one of the two possible ratios is always <NUM>, the flexibility of the planetary transmission is lower than the dual reduction cylindrical-hypoid version. The planetary-hypoid transmission would require the highest possible hypoid reduction ratio which, as discussed earlier, delivers a lower back driving ability. In <FIG>, the hypoid ratio is <NUM> (11x57). The overall ratio in <NUM>st gear is <NUM> * <NUM> = <NUM> and in <NUM>nd gear is <NUM> * <NUM> = <NUM>.

In the case of a single speed transmission (<FIG>), the relationship between motor RPM and vehicle speed is of course proportional as shown in <FIG>. This applies if the electrical prime mover is in motor mode or in generator mode. The efficiency optimal operating RPM of a motor which is rated for <NUM>,<NUM> RPM maximum is in the vicinity of <NUM>,<NUM> to <NUM>,<NUM> RPM. This is the speed range with high efficiency in the case of average load. If the load is small, then the efficiency optimal RPM is lower and vice versa if the load is higher. The ratio of a single stage transmission is preferably defined such that the majority of the driving falls into the optimal motor efficiency range. <FIG> also indicates that the increasing speed graph is only for a short period within the optimal motor efficiency range. When the operator takes a foot of the accelerator pedal, the motor-generator control can take the leads off the motor (i.e. no power going into or coming out of the motor) and the vehicle coasts down naturally. If the brake pedal is applied lightly, the control can switch the motor to generator mode while the disk brakes are not yet engaged. Only when the brake pedal is pressed hard do the disk brakes kick in and support the electric generator brake.

In case of a dual speed transmission, the vehicle's electronic control module can decide which of the two ratios with respect to the load would provide a better motor efficiency. <FIG> shows a typical speed diagram with the first ratio larger than a second ratio. The first gear is active until the maximal motor RPM is reached. Then the clutch switches to the second gear which stays active until the maximal motor speed is reached again. The speed graph in <FIG> has two sections which pass the optimal motor efficiency range. Depending on the duty cycle of the vehicle, the two speed transmission can double the operating time within the optimum efficiency speed range and significantly reduce the energy consumption of the vehicle.

Depending on gentle coasting to a full stop (leads off motor) or breaking light or hard, the vehicle's electronic control module can regulate the downshift in order to optimize the brake force and maximize the battery re-charging. The flexible downshift is shown in <FIG> as dashed lines. The following breaking conditions may be considered:.

Some electric vehicles, even larger premium models, realize breaking by releasing the accelerator pedal. This technology reduces the driving comfort, is counterintuitive and can lead to unsafe driving conditions. It requires a steady and unnatural foot positions which fatigues the accelerator foot as well as the driver.

As previously mentioned, a hypoid reduction enables placement of the electric motor in the center of the front or rear axle between the wheels. The images of a small size compact sedan in <FIG> show the electric motor in front of the front axle. With a battery location below the passenger cabin floor (between front and rear wheels), the motor orientation as shown in <FIG> presents a good weight distribution and could become part of the passive passenger impact safety concept. It is possible to reverse the direction of the hypoid offset (motor higher or lower) and find a packaging optimal motor orientation angle as shown in <FIG>.

While it is preferred that the electric motor be oriented such that the drive shaft rotational axis is horizontal or parallel to the ground (e.g. parallel to a plane containing the front wheel axis and rear wheel axis of a vehicle standing on a flat level surface) as shown in <FIG>, the invention is not limited thereto. The orientation of the electric motor may be angular such that the drive shaft rotational axis does not extend horizontal or parallel to the ground (not parallel to a plane containing the front wheel axis and rear wheel axis of a vehicle standing on a flat level surface) but at an angle thereto as is shown in <FIG>.

In case of an all-wheel drive passenger car, the same transmission unit which is propelling the front wheels can be used to propel the rear wheels as well. <FIG> show a front wheel drive with the motor body pointing to the rear (<FIG>) and an all-wheel drive arrangement with body of both motors pointing backwards (<FIG>).

The arrangements shown in <FIG> exemplify how compact the hypoid electric vehicle transmission (i.e. e-transmission) is and how well it can adjust to the given packaging constrains in a given overall vehicle concept. Other electric transmission orientations are possible which accomplished tailored solutions for all already existing electric vehicle designs.

The electric motor, or motors, of a vehicle may be located such that the rotational axis of the motor drive shaft extends in the lengthwise (longitudinal) direction of a vehicle with the motor drive shaft facing either toward the front or rear of the vehicle. Furthermore, while it is preferred that the ring gear of the transmission be located midway (i.e. center location in the widthwise direction of a vehicle) between the wheels it is intended to drive (see <FIG> for example), the invention is not limited thereto. The ring gear of the transmission may be located at any location along the wheel axis within a distance "d", in either direction, from the center location between a pair of wheels. The distance "d" is preferably not greater than <NUM> percent of the distance from the center location to each individual wheel. <FIG> shows an example of the distance "d".

The inventive hypoid reduction brings a variety of advantages. Symmetric weight distribution and reduced heat radiation exposure of the wheels and battery can be accomplished very well. The speed drop which is possible with the hypoid reduction is a multiple of what is conventionally realized for cylindrical gearsets (ratios between <NUM> and <NUM> have been realized for the present inventive electric drive developments). This makes it possible for small size compact vehicles to limit the transmission to one fixed but large ratio. The result is a simple and low cost transmission with a motor shaft also being a pinion shaft and with only one additional shaft for the ring gear. Of course, just like in all axle drives with hypoid gears, the differential cage fits conveniently inside of the pinion-ring gear silhouette (see <NUM> in <FIG>) without additional space consumption.

Although the invention has been discussed with reference to bevel gearsets comprising a ring gear and hypoid pinion, the invention is not limited thereto. Other gearsets such as a worm and worm wheel or a face gear and offset cylindrical pinion are also contemplated. Spiral bevel and straight bevel gearsets may also be utilized particularly in combination with a dual-stage or planetary reduction as shown in <FIG>, <FIG> and <FIG> for example.

While it is preferred that the drive shaft rotational axis of the electric motor, Am, and the axis of the wheels, Aw, be perpendicular as shown in <FIG>, for example, the invention is not limited thereto. The motor drive shaft axis, Am, may be oriented by up to as much as plus/minus (±) <NUM> degrees from the perpendicular orientation (e.g. <FIG>) of drive shaft rotational axis Am with respect to the wheel axis, Aw. In other words, the drive shaft axis, Am, of the electric motor may be oriented at any angle within the range of <NUM> degrees to <NUM> degrees with respect to the wheel axis AW. An appropriate cone angle change of the ring gear and pinion would accompany such a change in drive shaft axis orientation.

Compared to a conventional vehicle driveline comprising a motor, transmission or gearbox, differential, axles and wheels, the invention essentially eliminates the need for separate transmission (or gearbox) and differential components. In general, the inventive transmission effectively combines transmission and differential components into a single component which is particularly beneficial for electric vehicles as it provides freedom for motor placement and orientation. This is possible due to the utilization of a hypoid pinion having a low number of teeth and a high gearset ratio particularly for the inventive transmission having a single stage reduction.

While the preferred utility of the inventive transmission is to receive input power from an electric motor such as for driving a car or truck, for example, the transmission is also contemplated for use in vehicles where the prime mover is of a type other than electric or solely electric, such as hybrid vehicles or fuel cell driven vehicles.

Claim 1:
A vehicle being moveable by power provided by at least one electric motor having a drive shaft, said vehicle having a pair of rotatable wheels being rotatable via power provided by said at least one electric motor, said pair of rotatable wheels being located spaced apart in a widthwise direction of said vehicle along a common axis (AW), said vehicle further comprising a transmission, said transmission providing electric drive reduction with defined back driving ability and comprising an input having an input axis of rotation and at least one pair of mating gears with one of the pair of mating gears being an offset pinion having an axis or rotation (AP) defining said input axis of rotation, said transmission being located centered between the pair of wheels or at a distance (d) from the centered location, said distance (d) being equal to or lower than <NUM> percent of the distance from the centered location to each individual wheel of the pair and said transmission further comprising at least one output with said at least one output having an output axis of rotation and being rotatably connected to each of the pair of wheels by a respective axle, characterized in that said transmission has a reduction ratio in the range of <NUM> to <NUM>, and in that the back driving ability, expressed as Back Driving Coefficient CBD being the ratio of back driving opposing force to back driving force, is given by CBD being lower than <NUM> while said offset pinion comprises only <NUM> to <NUM> teeth.